This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kallio, J. Articles by Koulu, M. Search for Related Content PubMed PubMed Citation Articles by Kallio, J. Articles by Koulu, M.

Enhanced Exercise-Induced GH Secretion in Subjects with Pro7 Substitution in the Prepro-NPY

Department of Pharmacology and Clinical Pharmacology (J.K., U.P., M.K.K., Mar.K.), University of Turku, FIN-20520 Turku, Finland; and Department of Biochemistry (Mas.K., H.H., K.K.), National Cardiovascular Center Research Institute, Fujishirodai, Suita, Osaka 565-8565, Japan

Address all correspondence and requests for reprints to: Jaana Kallio, M.D., Ph.D., Department of Pharmacology and Clinical Pharmacology, University of Turku, Kiinamyllynkatu 10, FIN-20520 Turku, Finland. E-mail: jaana.kallio{at}utu.fi

Abstract

The leucine 7 to proline 7 (Leu7Pro) polymorphism in the signal peptide of NPY is associated with high blood lipid concentrations and accelerated rate of atherosclerosis as well as diabetic retinopathy. Also, healthy subjects with this polymorphism have increased NPY secretion during sympathetic stimulation. Because NPY may regulate GH release and ghrelin may regulate NPY formation, we studied the effects of the Leu7/Pro7 genotype on GH, ghrelin, and IGF-I secretion during standardized cycle-ergometer exercise. Furthermore, we studied the effect of the Leu7/Pro7 genotype on diurnal GH secretion in rest in a separate study. The subjects with Leu7/Pro7 genotype had 54% higher maximal increases in the plasma GH concentrations than the controls during exercise. There were no significant differences in the ghrelin or IGF-I concentrations during exercise among the groups. Furthermore, there were no differences in diurnal GH secretion between the genotypes. The results indicate that the prepro-NPY genotype has an influence on GH response during exercise in humans. The clinical significance of this finding is not known, and further studies are needed to evaluate whether the observed change in GH secretion during exercise could play a role in promoting diseases.

NPY IS A WIDELY expressed neurotransmitter and has many important functions in the mammalian central and peripheral nervous systems including control of hormone release (1, 2, 3, 4, 5, 6, 7, 8, 9, 10). In healthy humans, exogenously given NPY has inhibitory effects on hypothalamo-pituitary-adrenocortical axis (11). On the basis of one report (11), exogenously given NPY has no effect on GH secretion in healthy humans, but stimulatory effects of NPY on GH secretion has been observed in prolactinoma and acromegalic patients (12, 13), some of whom also displayed inhibition of GH secretion by NPY (13).

We recently found a leucine 7 to proline 7 (Leu7Pro) polymorphism in the signal peptide of prepro-NPY and reported significant association of this polymorphism with high serum total and low-density lipoprotein cholesterol concentrations (14), with higher serum triglycerides in preschool-aged children (15) and with accelerated atherosclerosis in middle-aged men and type 2 diabetic patients (16) as well as with accelerated progression of diabetic retinopathy in type 2 diabetic patients (16, 17). The carrier frequency for this polymorphism ranges from 6% to 13% in Caucasian populations (14). Baby boys carrying this polymorphism are heavier at birth, but at 5 and 7 yr of age, the polymorphism does not associate with height, weight, or body mass index (BMI) (15).

The mechanisms of how the Pro7 substitution in prepro-NPY could affect the observed blood lipid, vascular intima-media changes, or birth weight are not known but may include increased secretion of NPY from cells to circulation or to local tissues because subjects with the Leu7Pro polymorphism in prepro-NPY (Leu7/Pro7 genotype) have increased NPY concentrations during sympathetic activation, compared with wild-type subjects (Leu7/Leu7 genotype) (18).

Because GH is an important regulator of lipids in serum (19) and has effects on arterial intima-media thickness (20) and NPY may have effects on the GH release (12, 13), the current study was undertaken to compare the GH and IGF-I secretion during standardized strenuous physical exercise between two groups of healthy subjects having either the Leu7/Pro7 or the Leu7/Leu7 genotype. Ghrelin, a recently found GH secretagogues receptor ligand (21), strongly stimulates GH secretion (22, 23) in humans (24) and has been shown to stimulate NPY expression in experimental animals (25). Therefore, ghrelin concentrations in plasma were also measured during exercise simultaneously with GH and IGF-I concentrations in the two study groups. In a separate study, GH secretion was additionally investigated in rest during a 24-h follow-up and compared between healthy volunteers of the two genotypes.

Materials and Methods

Study subjects

Nine subjects (two male and seven female) having the Leu7/Pro7 genotype (aged 22.7 ± 0.6 yr, BMI 22.0 ± 0.8 kg/m², body fat 23.5 ± 2.4%, maximal oxygen consumption [VO_2max] 42.9 ± 2.7 ml/kg per min) and nine pair-matched controls with the Leu7/Leu7 genotype (two male and seven female, aged 22.1 ± 0.7 yr, BMI 22.8 ± 0.9 kg/m², body fat 23.6 ± 2.7%, VO_2max 47.7 ± 2.4 ml/kg per min) were selected for VO_2max determination and the 80% VO_2max cycle-ergometer exercise test (workload 80% of the determined VO_2max workload) based on the former genotyping. At the time of the study, five female subjects in both study groups were taking contraceptive steroids containing ethynylestradiol and progestins.

In a separate session, seven male subjects with the Leu7/Pro7 genotype (age 21.3 ± 0.4 yr, BMI 23.3 ± 0.44 kg/m²) and six pair-matched male subjects with the Leu7/Leu7 genotype (age 22.5 ± 1.0 yr, BMI 23.9 ± 0.45 kg/m²) participated in the diurnal GH secretion study.

To exclude nonhealthy subjects, detailed medical history (including diseases, medication, smoking, trauma, and alcohol consumption) was taken, a physical examination (including electrocardiogram, cardiac and pulmonary auscultation, blood pressure measurement, thyroid palpation, and screening for clinical signs of infection) conducted, and basic laboratory measurements (blood hemoglobin, total cholesterol, low-density lipoprotein cholesterol, glucose, FFA, and alanine amino transferase concentration, leukocyte count, and erythrocyte sedimentation rate) were done before the subjects entered the study. Body fat was determined by skin-fold measurement (26).

The joint Ethics Committee of Turku University and Turku University Central Hospital approved all parts of the study. Written informed consent was obtained from each subject for genotyping and for participation in VO_2max determination and 80% VO_2max cycle-ergometer exercise test as well as for participation in the diurnal GH secretion study.

Genotyping

For genotyping, blood samples (10 ml) were drawn from an antecubital vein. Blood leukocyte DNA was extracted using a DNA isolation kit (Puregene, Gentra Systems, Minneapolis, MN) following the manufacturer’s instructions. The genotype was determined as described earlier (14).

Exercise study protocol

The 18 healthy nonsmoking study subjects were asked to refuse any medication and alcohol-containing drinks for 48 h and any caffeine-containing drinks or food for 12 h before the VO_2max measurement and before the 80% VO_2max cycle-ergometer exercise test. They were asked to eat carbohydrate-rich food and to avoid strenuous physical exercise for 2 d preceding the tests. A standard light meal was offered 2 h before running the tests. VO_2max was determined by using an electronically braked cycle-ergometer (model 800 S, Ergoline, Mijnhart, the Netherlands) with a continuous incremental protocol and direct paramagnetic O₂ and infrared CO₂ analysis of respiratory gases using a personal computer-based automated system (model 202, Medikro, Kuopio, Finland) as previously described (27). The VO_2max was determined and the corresponding power level was considered as 100% VO_2max.

The 80% VO_2max cycle-ergometer exercise test was performed 1–2 months after the VO_2max determination. In the 80% VO_2max exercise study, an iv cannula was inserted into an antecubital vein and the subjects were lying for 35 min thereafter. Before starting to run the cycle-ergometer (at 0 min), they were sitting for 5 min; at 0 min the study subjects started to exercise with minimal (20 W) workload. The workload was increased by 20% VO_2max steps in 2-min intervals and the 80% VO_2max workload was thus reached after four steps in 8 min (Fig. 1). The study subjects then continued to exercise at this 80% VO_2max level for 12 min followed by a 10-min cooling period with 20% VO_2max workload (Fig. 1). The study subjects were monitored (electrocardiogram and blood pressure) by Datex Engstrom AS/3-system (Datex Ohmeda, Oulu, Finland) for 30 min at baseline, during the 30-min exercise, and for 50 min in a sitting position after the exercise. Nine blood samples for the measurement of plasma GH, IGF-I, and ghrelin were collected at -5, 0, 8, 16, 20, 30, 40, 60, and 80 min.

View larger version (16K): [in this window] [in a new window]   Figure 1. Outline of the exercise study protocol. The subjects were lying in the beginning of the study period, and they started to exercise with cycle-ergometer at 0 min. The workload level was gradually increased up to 80% VO2max for 12 min. The exercise ended with a 10-min cooling period at 20% VO2max power level. Thereafter, the subjects were resting at a sitting position.

The 13 healthy nonsmoking male study subjects were asked to refuse any medication and alcohol-containing drinks for 48 h and any food or drink for 10 h before the diurnal GH secretion study. The subjects were followed in a clinical laboratory for 24 h (from 0800 h to 800 h). An iv cannula was inserted into an antecubital vein for blood sampling. Standard meals were offered for breakfast (at 0900 h), lunch (at 1200 h), snack (at 1500 h), dinner (at 1800 h), and evening snack (at 2200 h). The subjects stayed in the laboratory for the whole study period during which they remained recumbent but were allowed to sit and walk occasionally. However, before each blood sampling, the subjects were lying for 15 min. They were encouraged to sleep after 2300 h, at which time all lights were turned off and no activities were allowed. Blood samples for the measurement GH were drawn at 0800, 0900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 0200, 0600, and 0800 h.

Analytical methods

Plasma GH concentrations were determined with a human GH immunoradiometric assay kit (HGH-CTK irma, DiaSorin, Inc., Saluggia, Italy) with the lower limit of detection at 0.2 µg/liter. IGF-I concentrations in plasma were determined using a RIA kit (SM-C RIA-CT, Biosource Technologies, Inc. Europe S.A., Nivelles, Belgium). Plasma ghrelin concentrations were determined with RIA using an antibody against the C terminus of the ghrelin molecule as previously described (28).

Statistical analysis

The normality of distributions of the concentrations at each time was analyzed before further analysis. In the diurnal GH secretion study, GH values were log transformed to normalize their distributions before further analysis. The means of each sequentially measured parameter between the genotypes Leu7/Pro7 and Leu7/Leu7 were compared using repeated-measures ANOVA for mixed models (Table 1). If the ANOVA revealed statistically significant genotype-by-time interaction (overall difference), the Fisher least significant difference multiple comparison procedure was used to test equality of group means at each time point. These tests were carried out as linear contrasts using the same statistical model. If the ANOVA revealed statistically significant time effect, Tukey-Kraemer test was used as a post hoc test to reveal the statistical significant differences in concentrations between the first and any other single time point. For correlation analysis, Pearson’s correlation coefficients were calculated. All data are presented as mean ± SEM. Statistical analysis was performed with SAS software (version 6.12, SAS Institute, Inc., Cary, NC). A two-sided P value of less than 0.05 was considered statistically significant.

During the exercise study, subjects with the Leu7/Pro7 genotype had consistently and markedly higher plasma GH concentrations (Table 1, Fig. 2A) with statistically significant differences at 16-, 20-, and 30-min concentrations (P < 0.05). The mean exercise-induced increase of GH between -5 min and 20 min was 24.1 ± 5.5 µg/liter in the subjects with Pro7 in the prepro-NPY and 11.2 ± 3.1 µg/liter in the subjects without this substitution (P < 0.05, t test). There were no statistically significant differences in the concentrations of ghrelin or IGF-I in plasma (Table 1, Fig. 2, B and C) between the Leu7/Pro7 and Leu7/Leu7 genotypes.

View larger version (14K): [in this window] [in a new window]   Figure 2. The concentrations of GH, ghrelin, and IGF-I in plasma during the exercise study. The mean plasma GH concentrations (A) at 16, 20, and 30 min (*) were significantly higher (P < 0.05) in subjects with the Leu7/Pro7 genotype (open triangles) than in subjects with the Leu7/Leu7 genotype (solid triangles). Similar ghrelin (B) and IGF-I (C) concentrations in plasma were detected in the two study groups. The total exercise-time was 30 min (hatched area).

In the diurnal GH secretion study, there were no statistically significant differences in the GH concentrations between the genotypes (Table 1, Fig. 3). A clear GH peak during sleep was detected in all study subjects.

View larger version (14K): [in this window] [in a new window]   Figure 3. The diurnal GH secretion was similar in the two genotype groups (open triangles; Leu7/Pro7 genotype, solid triangles; Leu7/Leu7 genotype).

Earlier studies have shown that the Leu7Pro polymorphism of prepro-NPY is significantly associated with risk factors and development of atherosclerosis in children and adults (14, 15, 16). This polymorphism is probably changing the intracellular processing of the synthesized prepro-NPY peptide because the substitution causes increased NPY production during sympathetic stimulation in subjects with the Leu7/Pro7 genotype (18). Because NPY is an important cotransmitter with norepinephrine and has effects on hormone secretion in humans (11, 12, 13), the increased NPY concentrations in plasma and tissues are likely to cause several secondary changes in autonomic and hormone balance, including GH-axis. This hypothesis was tested in the present study by using matched healthy volunteers having either the Leu7/Pro7 or the Leu7/Leu7 genotype. In these study subjects, GH secretion was stimulated by well-standardized, high-intense cycle-ergometer exercise; IGF-I and ghrelin concentrations in plasma were also determined. Furthermore, the effect of the prepro-NPY genotype on diurnal GH secretion was studied in a separate session in healthy male volunteers. The results show a 54% higher enhancement of GH secretion during exercise in subjects with the Leu7/Pro7 genotype, compared with controls. However, there was no difference in diurnal GH secretion between the genotypes. The difference in GH secretion during exercise between the genotypes was not reflected in the IGF-I levels and was not owing to increased ghrelin secretion because the levels of IGF-I and ghrelin were similar between the two study groups.

The functional connections between NPY and GH have been largely examined in animals (29, 30, 31), but only a few studies exist on humans. A study on patients with prolactinoma showed stimulatory effects of exogenously given NPY on GH secretion (12). Another study on acromegalic patients reported NPY-induced stimulation of GH release if the patient had a somatotroph-like pituitary adenoma and inhibition of GH secretion by NPY if the patient had a lactotroph-like adenoma (13). However, patients with a pituitary tumor may have disturbed hypothalamic regulation of hormone secretion and/or broken blood brain barrier. Direct stimulation of GH secretion from the pituitary by NPY has been observed in experimental systems (32, 33).

Whether the enhanced GH secretion during exercise in healthy subjects with the Leu7Pro polymorphism is owing to their increased concentration of NPY during exercise (18) is not clear because the underlying mechanisms of exercise-induced GH release are not known. The human anterior pituitary contains NPY receptors (34), where the circulating NPY is able to bind. Therefore, it is possible that NPY in blood could directly stimulate GH secretion. Because low plasma insulin (35, 36) and low FFA levels (37, 38, 39) also stimulate GH secretion in humans, the lower insulin and FFA levels during exercise observed in the subjects with Leu7Pro polymorphism (18) could further facilitate their GH secretion. In addition, it is possible that GHRH or somatostatin secretion from the hypothalamus is changed during exercise in these subjects.

Ghrelin is a recently isolated and cloned endogenous GH secretagogues receptor ligand, which is secreted from the stomach and also expressed in the hypothalamus and many other tissues (21). It strongly stimulates GH secretion in humans, which can also be detected in the peripheral blood (22, 23, 24). There is also evidence in experimental animals that ghrelin regulates NPY expression (25). We therefore determined the plasma concentrations of ghrelin in the study subjects simultaneously with GH and IGF-I during strenuous physical exercise. There were no differences between the genotypes in ghrelin concentrations, which shows that the observed differences in plasma GH concentrations between the genotypes were not determined by ghrelin secretion into plasma. Also, there was no increase in ghrelin concentrations and no association of ghrelin concentrations with GH concentrations during the exercise in either genotype, which suggests that the exercise-induced GH release is not regulated by ghrelin in the peripheral blood.

IGF-I exerts its effects on growth through type 1 IGF receptors, which are found in the skeletal muscle, for example. IGF-I is synthesized mainly in the liver, and the synthesis and secretion of IGF-I are largely regulated by GH (40). Also, insulin regulates the synthesis of IGF-I (35, 36). The lack of difference in the IGF-I concentrations between the genotypes during exercise despite the clear difference in GH levels may be explained by lower insulin levels in subjects with the Leu7/Pro7 genotype (18), which could counteract the effect of GH on IGF-I levels. Furthermore, earlier studies have indicated that the acute increase in IGF-I induced by exercise is independent of the GH response (41).

The clinical significance of the present finding is not known. GH is a significant regulator of lipoproteins in blood (19, 42, 43, 44), and the level of GH during exercise has been related to anabolic adaptations induced by exercise (45). GH has recently been shown to have a role in angiogenesis (46) and retinal vascularization (47, 48). No obvious mechanisms for the association of the Leu7Pro polymorphism with high blood lipids and the accelerated development of atherosclerosis and diabetic retinopathy have been indicated so far, and further studies are needed to evaluate whether the observed change in GH secretion during exercise could play a role in promoting these diseases.

In conclusion, the present study shows that the Leu7Pro polymorphism in prepro-NPY leads to enhanced GH secretion during exercise and provides further evidence that this polymorphism has functional consequences in healthy subjects. This observation is the first evidence that structural variation in the NPY gene has effects on pituitary hormone secretion in humans.

Acknowledgments

We thank Mr. Jukka Kapanen, M.Sc., and the personnel of Paavo Nurmi Center in Turku, for performing the VO_2max determinations. Furthermore, we thank Ms. Ulriikka Jaakkola, Ms. Raija Kaartosalmi, and Ms. Elina Kahra for skillful technical assistance. The volunteers who participated in the study are also acknowledged.

Footnotes

This work was supported by the National Technology Agency of Finland and Turku University Central Hospital.

Abbreviations: BMI, Body mass index; Leu7Pro, leucine 7 to proline 7; VO_2max, maximal oxygen consumption.

Received April 4, 2001.

Accepted August 1, 2001.

References

1. Gerald C, Walker MW, Criscione L, Gustafson EL, Batzl-Hartman C, Smith KE, Vaysse P, Durkin MM, Laz TM, Linemeyer DL, Schaffhauser AO, Whitebread S, Hofbauer KG, Taber RI, Branchek TA, Weinshank RL 1996 A receptor subtype involved in neuropeptide-Y-induced food intake. Nature 382:168–171[CrossRef][Medline]
2. Zukowska-Grojec Z 1995 Neuropeptide Y. A novel sympathetic stress hormone and more. Ann N Y Acad Sci 771:219–233[Medline]
3. Castan I, Valet P, Quideau N, Voisin T, Ambid L, Laburthe M, Lafontan M, Carpene C 1994 Antilipolytic effects of 2-adrenergic agonists, neuropeptide Y, adenosine, and PGE1 in mammal adipocytes. Am J Physiol 266:R1141–R1147
4. Bischoff A, Michel MC 1998 Renal effects of neuropeptide Y. Pflugers Arch 435:443–453[CrossRef][Medline]
5. Morgan DG, Kulkarni RN, Hurley JD, Wang ZL, Wang RM, Ghatei MA, Karlsen AE, Bloom SR, Smith DM 1998 Inhibition of glucose stimulated insulin secretion by neuropeptide Y is mediated via the Y1 receptor and inhibition of adenylyl cyclase in RIN 5AH rat insulinoma cells. Diabetologia 41:1482–1491[CrossRef][Medline]
6. Kalra SP, Sahu A, Kalra PS, Crowley WR 1990 Hypothalamic neuropeptide Y: a circuit in the regulation of gonadotropin secretion and feeding behavior. Ann N Y Acad Sci 611:273–283[Medline]
7. Zukowska-Grojec Z, Karwatowska-Prokopczuk E, Rose W, Rone J, Movafagh S, Ji H, Yeh Y, Chen WT, Kleinman HK, Grouzmann E, Grant DS 1998 Neuropeptide Y: a novel angiogenic factor from the sympathetic nerves and endothelium. Circ Res 83:187–195[Abstract/Free Full Text]
8. Tatemoto K, Carlquist M, Mutt V 1982 Neuropeptide Y—a novel brain peptide with structural similarities to peptide YY and pancreatic polypeptide. Nature 296:659–660[CrossRef][Medline]
9. Edvinsson L, Emson P, McCulloch J, Tatemoto K, Uddman R 1983 Neuropeptide Y: cerebrovascular innervation and vasomotor effects in the cat. Neurosci Lett 43:79–84[CrossRef][Medline]
10. Edvinsson L, Ekblad E, Hakanson R, Wahlestedt C 1984 Neuropeptide Y potentiates the effect of various vasoconstrictor agents on rabbit blood vessels. Br J Pharmacol 83:519–525[Medline]
11. Antonijevic IA, Murck H, Bohlhalter S, Frieboes RM, Holsboer F, Steiger A 2000 Neuropeptide Y promotes sleep and inhibits ACTH and cortisol release in young men. Neuropharmacology 39:1474–1481[CrossRef][Medline]
12. Watanobe H, Tamura T 1996 Stimulation by neuropeptide Y of growth hormone secretion in prolactinoma in vivo. Neuropeptides 30:429–432[CrossRef][Medline]
13. Watanobe H, Tamura T 1997 Stimulatory and inhibitory effects of neuropeptide Y on growth hormone secretion in acromegaly in vivo. Neuropeptides 31:29–34[CrossRef][Medline]
14. Karvonen MK, Pesonen U, Koulu M, Niskanen L, Laakso M, Rissanen A, Dekker JM, ’t,Hart LM, Valve R, Uusitupa, MI 1998 Association of a leucine(7)-to-proline(7) polymorphism in the signal peptide of neuropeptide Y with high serum cholesterol and LDL cholesterol levels. Nat Med 4:1434–1437[CrossRef][Medline]
15. Karvonen MK, Koulu M, Pesonen U, Uusitupa MI, Tammi A, Viikari J, Simell O, Ronnemaa T 2000 Leucine 7 to proline 7 polymorphism in the preproneuropeptide Y is associated with birth weight and serum triglyceride concentration in preschool aged children. J Clin Endocrinol Metab 85:1455–1460[Abstract/Free Full Text]
16. Niskanen L, Karvonen MK, Valve R, Koulu M, Pesonen U, Mercuri M, Rauramaa R, Toyry J, Laakso M, Uusitupa MI 2000 Leucine 7 to proline 7 polymorphism in the neuropeptide Y gene is associated with enhanced carotid atherosclerosis in elderly patients with type 2 diabetes and control subjects. J Clin Endocrinol Metab 85:2266–2269[Abstract/Free Full Text]
17. Niskanen L, Voutilainen-Kaunisto R, Terasvirta M, Karvonen MK, Valve R, Pesonen U, Laakso M, Uusitupa MI, Koulu M 2000 Leucine 7 to proline 7 polymorphism in the neuropeptide Y gene is associated with retinopathy in type 2 diabetes. Exp Clin Endocrinol Diabetes 108:235–236[CrossRef][Medline]
18. Kallio J, Pesonen U, Kaipio K, Karvonen MK, Jaakkola U, Heinonen OJ, Uusitupa MI, Koulu M 2001 Altered intracellular processing and release of neuropeptide Y due to leucine 7 to proline 7 polymorphism in the signal peptide of preproneuropeptide Y in man. FASEB J 15:1242–1244[Abstract/Free Full Text]
19. Vahl N, Klausen I, Christiansen JS, Jorgensen JO 1999 Growth hormone (GH) status is an independent determinant of serum levels of cholesterol and triglycerides in healthy adults. Clin Endocrinol 51:309–316[CrossRef][Medline]
20. Pfeifer M, Verhovec R, Zizek B, Prezelj J, Poredos P, Clayton RN 1999 Growth hormone (GH) treatment reverses early atherosclerotic changes in GH-deficient adults. J Clin Endocrinol Metab 84:453–457[Abstract/Free Full Text]
21. Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K 1999 Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature 402:656–660[CrossRef][Medline]
22. Arvat E, Di Vito L, Broglio F, Muccioli G, Dieguez C, Casanueva FF, Deghenghi R, Camanni F, Ghigo E 2000 Preliminary evidence that ghrelin, the natural GH secretagogue (GHS)-receptor ligand, strongly stimulates GH secretion in humans. J Endocrinol Invest 23:493–495[Medline]
23. Peino R, Baldelli R, Rodriguez-Garcia J, Rodriguez-Segade S, Kojima M, Kangawa K, Arvat E, Ghigo E, Dieguez C, Casanueva FF 2000 Ghrelin-induced growth hormone secretion in humans. Eur J Endocrinol 143: R011–R014
24. Takaya K, Ariyasu H, Kanamoto N, Iwakura H, Yoshimoto A, Harada M, Mori K, Komatsu Y, Usui T, Shimatsu A, Ogawa Y, Hosoda K, Akamizu T, Kojima M, Kangawa K, Nakao K 2000 Ghrelin strongly stimulates growth hormone release in humans. J Clin Endocrinol Metab 85:4908–4911[Abstract/Free Full Text]
25. Nakazato M, Murakami N, Date Y, Kojima M, Matsuo H, Kangawa K, Matsukura S 2001 A role for ghrelin in the central regulation of feeding. Nature 409:194–198[CrossRef][Medline]
26. Durnin JV, Womersley J 1974 Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years. Br J Nutr 32:77–97[CrossRef][Medline]
27. Nuutila P, Knuuti MJ, Heinonen OJ, Ruotsalainen U, Teras M, Bergman J, Solin O, Yki-Jarvinen H, Voipio-Pulkki LM, Wegelius U 1994 Different alterations in the insulin-stimulated glucose uptake in the athlete’s heart and skeletal muscle. J Clin Invest 93:2267–2274
28. Hosoda H, Kojima M, Matsuo H, Kangawa K 2000 Ghrelin and des-acyl ghrelin: two major forms of rat ghrelin peptide in gastrointestinal tissue. Biochem Biophys Res Commun 279:909–913[CrossRef][Medline]
29. Chan YY, Steiner RA, Clifton DK 1996 Regulation of hypothalamic neuropeptide-Y neurons by growth hormone in the rat. Endocrinology 137:1319–1325[Abstract]
30. Kamegai J, Minami S, Sugihara H, Hasegawa O, Higuchi H, Wakabayashi I 1996 Growth hormone receptor gene is expressed in neuropeptide Y neurons in hypothalamic arcuate nucleus of rats. Endocrinology 137:2109–2112[Abstract]
31. Pierroz DD, Catzeflis C, Aebi AC, Rivier JE, Aubert ML 1996 Chronic administration of neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insulin-like growth factor I secretion in intact adult male rats. Endocrinology 137:3–12[Abstract]
32. Peng C, Huang YP, Peter RE 1990 Neuropeptide Y stimulates growth hormone and gonadotropin release from the goldfish pituitary in vitro. Neuroendocrinology 52:28–34[Medline]
33. Peng C, Chang JP, Yu KL, Wong AO, Van Goor F, Peter RE, Rivier JE 1993 Neuropeptide-Y stimulates growth hormone and gonadotropin-II secretion in the goldfish pituitary: involvement of both presynaptic and pituitary cell actions. Endocrinology 132:1820–1829[Abstract/Free Full Text]
34. Gehlert DR, Gackenheimer SL, Millington WR, Manning AB, Chronwall BM 1994 Localization of neuropeptide Y immunoreactivity and [125I]peptide YY binding sites in the human pituitary. Peptides 15:651–656[CrossRef][Medline]
35. Lanes R, Recker B, Fort P, Lifshitz F 1985 Impaired somatomedin generation test in children with insulin-dependent diabetes mellitus. Diabetes 34:156–160[Abstract]
36. Hall K, Johansson BL, Povoa G, Thalme B 1989 Serum levels of insulin-like growth factor (IGF) I, II and IGF binding protein in diabetic adolescents treated with continuous subcutaneous insulin infusion. J Intern Med 225:273–278[Medline]
37. Imaki T, Shibasaki T, Shizume K, Masuda A, Hotta M, Kiyosawa Y, Jibiki K, Demura H, Tsushima T, Ling N 1985 The effect of free fatty acids on growth hormone (GH)-releasing hormone-mediated GH secretion in man. J Clin Endocrinol Metab 60:290–293[Abstract/Free Full Text]
38. Quabbe HJ, Bratzke HJ, Siegers U, Elban K 1972 Studies on the relationship between plasma free fatty acids and growth hormone secretion in man. J Clin Invest 51:2388–2398
39. Blackard WG, Hull EW, Lopez A 1971 Effect of lipids on growth hormone secretion in humans. J Clin Invest 50:1439–1443
40. Schwander JC, Hauri C, Zapf J, Froesch ER 1983 Synthesis and secretion of insulin-like growth factor and its binding protein by the perfused rat liver: dependence on growth hormone status. Endocrinology 113:297–305[Abstract/Free Full Text]
41. Hornum M, Cooper DM, Brasel JA, Bueno A, Sietsema KE 1997 Exercise-induced changes in circulating growth factors with cyclic variation in plasma estradiol in women. J Appl Physiol 82:1946–1951[Abstract/Free Full Text]
42. Christ ER, Wierzbicki AS, Cummings MH, Umpleby AM, Russell-Jones DL 1999 Dynamics of lipoprotein metabolism in adult growth hormone deficiency. J Endocrinol. Invest 22:16–21
43. Hew FL, O’Neal D, Kamarudin N, Alford FP, Best JD 1998 Growth hormone deficiency and cardiovascular risk. Baillieres Clin Endocrinol Metab 12:199–216[Medline]
44. Keller U, Miles JM 1991 Growth hormone and lipids. Horm Res 36 [Suppl 1]:36–40
45. Cuneo RC, Salomon F, Wiles CM, Hesp R, Sonksen PH 1991 Growth hormone treatment in growth hormone-deficient adults. II. Effects on exercise performance. J Appl Physiol 70:695–700[Abstract/Free Full Text]
46. Gould J, Aramburo C, Capdevielle M, Scanes CG 1995 Angiogenic activity of anterior pituitary tissue and growth hormone on the chick embryo chorio-allantoic membrane: a novel action of GH. Life Sci 56:587–594[CrossRef][Medline]
47. Smith LE, Kopchick JJ, Chen W, Knapp J, Kinose F, Daley D, Foley E, Smith RG, Schaeffer JM 1997 Essential role of growth hormone in ischemia-induced retinal neovascularization. Science 276:1706–1709[Abstract/Free Full Text]
48. Hellstrom A, Svensson E, Carlsson B, Niklasson A, Albertsson-Wikland K 1999 Reduced retinal vascularization in children with growth hormone deficiency. J Clin Endocrinol Metab 84:795–798[Abstract/Free Full Text]

This article has been cited by other articles:

				S.-y. Ueda, T. Yoshikawa, Y. Katsura, T. Usui, H. Nakao, and S. Fujimoto Changes in gut hormone levels and negative energy balance during aerobic exercise in obese young males J. Endocrinol., April 1, 2009; 201(1): 151 - 159. [Abstract] [Full Text] [PDF]

				D. R. Broom, R. L. Batterham, J. A. King, and D. J. Stensel Influence of resistance and aerobic exercise on hunger, circulating levels of acylated ghrelin, and peptide YY in healthy males Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2009; 296(1): R29 - R35. [Abstract] [Full Text] [PDF]

				S. T. Ruohonen, U. Pesonen, N. Moritz, K. Kaipio, M. Roytta, M. Koulu, and E. Savontaus Transgenic Mice Overexpressing Neuropeptide Y in Noradrenergic Neurons: A Novel Model of Increased Adiposity and Impaired Glucose Tolerance Diabetes, June 1, 2008; 57(6): 1517 - 1525. [Abstract] [Full Text] [PDF]

				J. Ma, S. Nordman, A. Mollsten, H. Falhammar, K. Brismar, G. Dahlquist, S. Efendic, and H. F Gu Distribution of neuropeptide Y Leu7Pro polymorphism in patients with type 1 diabetes and diabetic nephropathy among Swedish and American populations Eur. J. Endocrinol., November 1, 2007; 157(5): 641 - 645. [Abstract] [Full Text] [PDF]

				J. Jurimae, T. Jurimae, and P. Purge Plasma Ghrelin Is Altered After Maximal Exercise in Elite Male Rowers Experimental Biology and Medicine, July 1, 2007; 232(7): 904 - 909. [Abstract] [Full Text] [PDF]

				D. R. Broom, D. J. Stensel, N. C. Bishop, S. F. Burns, and M. Miyashita Exercise-induced suppression of acylated ghrelin in humans J Appl Physiol, June 1, 2007; 102(6): 2165 - 2171. [Abstract] [Full Text] [PDF]

				R. R. Kraemer and V. D. Castracane Exercise and Humoral Mediators of Peripheral Energy Balance: Ghrelin and Adiponectin Experimental Biology and Medicine, February 1, 2007; 232(2): 184 - 194. [Abstract] [Full Text] [PDF]

				M. K. Karvonen, S. Ruottinen, M. Koulu, U. Pesonen, H. Niinikoski, L. Rask-Nissila, O. Simell, and T. Ronnemaa Nutrient Intake, Weight, and Leu7Pro Polymorphism in Prepro-Neuropeptide Y in Children J. Clin. Endocrinol. Metab., November 1, 2006; 91(11): 4664 - 4668. [Abstract] [Full Text] [PDF]

				U. Jaakkola, T. Kuusela, T. Jartti, U. Pesonen, M. Koulu, T. Vahlberg, and J. Kallio The Leu7Pro Polymorphism of PreproNPY Is Associated with Decreased Insulin Secretion, Delayed Ghrelin Suppression, and Increased Cardiovascular Responsiveness to Norepinephrine during Oral Glucose Tolerance Test J. Clin. Endocrinol. Metab., June 1, 2005; 90(6): 3646 - 3652. [Abstract] [Full Text] [PDF]

				R. R. Kraemer, R. J. Durand, E. O. Acevedo, L. G. Johnson, G. R. Kraemer, E. P. Hebert, and V. D. Castracane Rigorous Running Increases Growth Hormone and Insulin-Like Growth Factor-I Without Altering Ghrelin Experimental Biology and Medicine, March 1, 2004; 229(3): 240 - 246. [Abstract] [Full Text] [PDF]

				K. Pettersson-Fernholm, M. K. Karvonen, J. Kallio, C. M. Forsblom, M. Koulu, U. Pesonen, J. A. Fagerudd, and P.-H. Groop Leucine 7 to Proline 7 Polymorphism in the Preproneuropeptide Y Is Associated With Proteinuria, Coronary Heart Disease, and Glycemic Control in Type 1 Diabetic Patients Diabetes Care, February 1, 2004; 27(2): 503 - 509. [Abstract] [Full Text] [PDF]

				J. Kallio, U. Pesonen, U. Jaakkola, M. K. Karvonen, H. Helenius, and M. Koulu Changes in Diurnal Sympathoadrenal Balance and Pituitary Hormone Secretion in Subjects with Leu7Pro Polymorphism in the Prepro-Neuropeptide Y J. Clin. Endocrinol. Metab., July 1, 2003; 88(7): 3278 - 3283. [Abstract] [Full Text] [PDF]

				P. Lucidi, G. Murdolo, C. Di Loreto, A. De Cicco, N. Parlanti, C. Fanelli, F. Santeusanio, G. B. Bolli, and P. De Feo Ghrelin Is Not Necessary for Adequate Hormonal Counterregulation of Insulin-Induced Hypoglycemia Diabetes, October 1, 2002; 51(10): 2911 - 2914. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kallio, J. Articles by Koulu, M. Search for Related Content PubMed PubMed Citation Articles by Kallio, J. Articles by Koulu, M.