This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart 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 Hashimoto, Y. Articles by Tanaka, T. Search for Related Content PubMed PubMed Citation Articles by Hashimoto, Y. Articles by Tanaka, T.

Exogenous 20K Growth Hormone (GH) Suppresses Endogenous 22K GH Secretion in Normal Men

Institute of Biological Science (Y.H., M.H., K.M.), Mitsui Pharmaceuticals, Inc., Chiba 297-0017; Clinical Development Department (T.K., A.M., Y.S.), Mitsui Pharmaceuticals, Inc., Tokyo 103-0027; Komagome-higashi Clinic (M.T.), Kiyaku-kai Medical Corporation Hohsen Clinic, Tokyo 170-0003; and Department of Endocrinology and Metabolism (T.T.), National Children’s Medical Research Center, Tokyo 154-8509, Japan

Address correspondence and requests for reprints to: Yoshihide Hashimoto, Ph.D., Senior Scientist, Institute of Biological Science, Mitsui Pharmaceuticals, Inc., 1900–1 Togo, Mobara, Chiba 297-0017, Japan.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
The physiological and pharmacological functions of the 20-kDa human GH (20K-hGH) isoform are unknown. We conducted a pharmacokinetic study of recombinant 20K-hGH in human subjects (Phase I clinical trial). Placebo or 20K-hGH was administered sc to normal men (20–31 yr of age, n = 6–8 per group) at 2100 h. Serum 20K- and 22K-hGH levels were monitored every 30 min for 24 h by specific enzyme-linked immunosorbent assays. Serum free fatty acid, insulin-like growth factor I, insulin, and glucose levels were measured for 24 h. In the placebo group, the secretion profiles of endogenous 20K- and 22K-hGH were pulsatile and similar to each other. The proportion of 20K- to 22K-hGH was fairly constant. In the 20K-hGH-treated groups, serum 20K-hGH levels increased in a dose-dependent manner over the dose range of 0.01–0.1 mg/kg. Maximum serum 20K-hGH levels were reached at 3–4 h and decreased with half-lives of 2–3 h. Marked suppression of endogenous 22K-hGH secretion was observed in a time-dependent manner. Serum free fatty acid and insulin-like growth factor I levels were significantly elevated (P < 0.01) at 4, 8, and 12 h and at 8, 12, and 24 h after 20K-hGH administration, respectively. Serum insulin and glucose levels did not change significantly within 24 h. These results suggested that: 1) regulation of 20K-hGH secretion is physiologically the same as that of 22K-hGH; 2) the pharmacokinetics after sc injection of 20K-hGH are comparable with those of 22K-hGH; 3) 20K-hGH regulates hGH secretion through "GH-induced negative feedback mechanisms"; and 4) administration of 20K-hGH is expected to exert GH actions (growth-promoting activity and lipolytic activity). Monitoring of serum 20K- and 22K-hGH levels may be useful in evaluating the effects of administered GH isoforms on their own release from the pituitary.

	Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
THE 20-kDa HUMAN GH (20K-hGH) is a naturally occurring isoform lacking residues 32–46 of 22K-hGH (1, 2, 3). This deleted region is involved in the interface with both the hGH receptor (4) and the PRL receptor (5) in 22K-hGH. The 20K-hGH comprises approximately 10% of pituitary hGH, but its physiological and pharmacological functions remain to be elucidated (6, 7). The 20K-hGH stimulates linear growth in hypophysectomized rats (8), exerts lipolytic activity in vitro (9), and binds to hGH receptors (10) similarly to 22K-hGH, but differs in some metabolic effects, such as acute insulin-like activity (11) and binding to lactogenic receptors (12, 13). Recently, recombinant 20K-hGH has been produced in high purity and in large amounts (9). We have also constructed an enzyme-linked immunosorbent assay (ELISA) system, which specifically reacts with 20K-hGH but not 22K-hGH (14, 15). The ELISA system has been applied to the determination of serum 20K-hGH levels in both normal subjects and patients with endocrine or metabolic disorders (15, 16). The level of circulating 20K-hGH was highly correlated to that of 22K-hGH in both normal subjects and patients, and the proportion of 20K-hGH in each individual subject was fairly constant even after pharmacological and physiological stimuli. Here, we conducted a pharmacokinetic study of recombinant 20K-hGH in human subjects (Phase I clinical trial). The aim of the present study was to investigate: 1) physiological secretion profiles of serum 20K- and 22K-hGH; 2) the pharmacokinetics after sc injection of 20K-hGH; and 3) the GH actions of 20K-hGH [i.e. its effects on peripheral 22K-hGH, insulin-like growth factor I (IGF-I), free fatty acid (FFA), insulin, and glucose levels].

	Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Subjects and protocol

Thirty-two healthy male subjects, aged 20–31-yr-old, were studied after giving their informed consent. The protocol for the study was approved by the Kiyaku-kai Medical Corporation Hohsen Clinic (Tokyo, Japan) Institutional Review Board for human investigation. The study was performed according to a double-masked, randomized and noncrossover protocol. Four groups of eight individuals (six on active, two on placebo) received a single sc dose of 20K-hGH: 0.01, 0.025, 0.05, and 0.1 mg/kg. Treatment was sequential; beginning with the lowest dose of 20K-hGH, the tolerability of each level was established before the next higher dose was administered. Placebo or 20K-hGH was administered sc into the thigh at 2100 h. Blood samples were collected every 30 min for 24 h, except at 16.5 and 20.5 h for meals, centrifuged, and the resulting serum samples were frozen and kept at -80 C until assay.

Adverse events

Healthy male volunteers tolerated exposure to single doses of 0.01–0.1 mg/kg 20K-hGH well. Few adverse effects were observed. Those that were seen were predominantly mild, with no apparent relationship to the dose, and were similar between the 20K-GH-treated and placebo groups. For example, transient increases in temperature were observed in four subjects: one who received placebo, two who received 20K-hGH 0.01 mg/kg, and one who received 20K-hGH 0.1 mg/kg.

Materials

Recombinant 20K-hGH (Lot DB9805) (9) was prepared for clinical use at a concentration of 2 mg/mL in sodium phosphate solution containing creatinine, polysorbate 80, L-arginine and D-mannitol.

Assays

Serum 20K- and 22K-hGH were measured by specific ELISAs, as described previously (15). Briefly, in 20K-hGH ELISA, 0.1 mL assay buffer and 0.025 mL standard or serum samples were added to monoclonal anti-20K-hGH antibody (D05; Mitsui Pharmaceuticals, Inc., Tokyo, Japan)-precoated microtiter plates, followed by incubation for 2 h at room temperature. After washing, 0.1 mL peroxidase-labeled anti-20K-hGH monoclonal antibody (POD-D14; Mitsui Pharmaceuticals, Inc., 0.5 mg/L) was added and incubated for 2 h at room temperature. After washing, 0.1 mL TMB/H₂O₂ substrate was added, followed by incubation for 30 min at room temperature. The absorbances were read with a microtiter plate reader at 450 nm (reference, 620 nm) after stopping the enzyme reaction. In 22K-hGH ELISA, the microtiter plates were coated with monoclonal anti-hGH antibody (A36020047P; BiosPacific, Inc., Emeryville, CA). Other procedures were the same as described above, except that the concentration of POD-D14 was 0.05 mg/L. The cutoff values were 10 pg/mL for 20K-hGH and 100 pg/mL for 22K-hGH. Serum IGF-I and insulin were determined with an immunoradiometric assay kit (Somatomedin C; Chiba-Corning, Inc. Tokyo, Japan) and a RIA kit (Phadisef Insulin; Pharmacia-Upjohn, Tokyo, Japan), respectively. Serum nonesterified FFA and glucose were measured with commercial kits using an auto-analyzer (TBA-80FR; Toshiba, Tokyo, Japan).

Statistical analysis

The results are expressed as means ± SD unless otherwise noted. Differences between groups were evaluated by ANOVA using the computer software StatLight (Yukms Corp., Tokyo, Japan), with P < 0.05 taken to indicate significance.

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Physiological 24-h secretion profiles of serum 20K- and 22K-hGH

Fig. 1 shows the 24-h profiles of serum 20K- and 22K-GH levels in a representative subject for each of the groups. In the placebo group (Fig. 1A), a large degree of variability was noted between subjects, and the secretion profiles of endogenous 20K- and 22K-hGH were typical pulsatile (17) and similar to each other. The proportion of 20K-hGH to 22K-hGH was fairly constant (ca. 5%). In the 20K-hGH-treated groups (Fig. 1, B-E), serum 20K-hGH levels increased within 30 min after injection, reached a peak between 2 and 6 h, and decreased by the end of the sampling period. In contrast, the spontaneous 22K-hGH surges were suppressed after a delay of a few hours after injection, especially at higher doses.

View larger version (43K): [in this window] [in a new window]   Figure 1. Individual representative 24-h serum 20K-hGH (•) and 22K-hGH () profiles in normal men administered the placebo (A) in comparison with those in normal men administered 20K-hGH at the indicated doses (B-E). Placebo and 20K-hGH (0.01–0.1 mg/kg) were administered at 2100 h. In the placebo group, the typical pulsatile pattern of hGH secretion was observed.

Serum 20K-hGH levels after a single sc injection of 20K-hGH are shown in Fig. 2A. In the placebo group, mean 24-h serum 20K-hGH levels were 0.13 ± 0.12 ng/mL. Serum 20K-hGH level increased in a dose-dependent manner. The pharmacokinetic parameters of 20K-hGH are summarized in Table 1. Maximum serum 20K-hGH levels (C_max) after injection were reached at 3–4 h, declining thereafter with a mean half-life (T_1/2) of 2–3 h. There was a linear relationship between dose and C_max or area under the serum level-time curve (AUC), indicating linear pharmacokinetics.

View larger version (37K): [in this window] [in a new window]   Figure 2. Mean serum 20K-hGH (A) and 22K-hGH (B) levels in normal men after single sc administration of placebo and 20K-hGH. Sera were analyzed by 20K-hGH and 22K-hGH ELISA, respectively. The values are means ± SE (n = 6–8). Placebo and 20K-hGH (0.01–0.1 mg/kg) were administered at 2100 h. In the placebo group, the typical nyctohemeral variations in hGH secretion were observed.

Fig. 2B illustrates serum 22K-hGH levels after 20K-hGH administration. In the placebo group, mean 24-h serum 22K-hGH levels were 2.5 ± 1.7 ng/mL, and the typical nyctohemeral variations in hGH secretion (17) were observed. The AUC_{0–12 h} of serum 22K-hGH was almost 3-fold higher than the AUC_{12–24 h}. In the 20K-hGH-treated groups (0.01, 0.025, 0.05, and 0.1 mg/kg), mean 24-h serum 22K-hGH levels were 1.1 ± 0.4, 0.6 ± 0.6, 0.9 ± 0.9, and 0.9 ± 0.7 ng/mL, respectively. Serum 22K-hGH levels decreased in a time-dependent manner. Although the mean serum 22K-GH levels after injection were not different even at higher doses compared to the placebo group during the first 4 h, the 22K-hGH levels were reduced even at lower doses from approximately 4–6 h up to 12 h. During the subsequent 24-h observation period, the 22K-hGH levels gradually returned to the placebo level. Fig. 3 summarizes the AUC of serum 22K-hGH over 6 h, which was used as an index of total 22K-hGH secretion. There were no significant changes in the AUC_{0–6 h} between the 20K-hGH-treated and placebo groups. Marked suppression of the AUC_{6–12 h} (P < 0.01) was observed at all doses, and almost 10-fold reductions were seen in comparison to the placebo group. Both the AUC_{12–18 h} and AUC_{18–24 h} tended to be suppressed in the 20K-hGH-treated groups, although differences were not significant compared with the placebo group.

View larger version (33K): [in this window] [in a new window]   Figure 3. Endogenous 22K-hGH secretion (AUC; ng Eh/mL per 6 h) in normal men after placebo and 20K-hGH administration. Each bar represents the mean ± SE (n = 6–8). **, P < 0.01 (vs. placebo by the Kruskal-Wallis and Steel test). Administration of 20K-hGH (0.01–0.1 mg/kg) resulted in marked reduction in AUC6–12 h of 22K-hGH, but no significant differences were observed between AUC0–6 h, AUC12–18 h and AUC18–24 h of 22K-hGH.

The 20K-hGH-treated groups showed significant elevations in serum FFA and IGF-I levels with different time courses after 20K-hGH administration (Fig. 4). Serum FFA levels increased more rapidly than that of IGF-I, with maximum levels at 4–8 h. The FFA levels were significantly higher than those of the placebo group at 4, 8, and 12 h (P < 0.01), and returned to the control levels by 24 h (Fig. 4A). On the other hand, serum IGF-I levels were not increased significantly at 4 h, but were increased at 8, 12, 24 (Fig. 4B), and 36 h (data not shown) (P < 0.01). Serum insulin and glucose levels were not changed significantly during the 24-h observation period (data not shown).

View larger version (22K): [in this window] [in a new window]   Figure 4. Mean serum FFA (A) and IGF-I (B) increases () over the basal values after placebo and 20K-hGH administration in normal men. Placebo and 20K-hGH (0.01–0.1 mg/kg) were administered at 2100 h. The values are means ± SE (n = 6–8).

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

We found that the 24-h profile of 20K-hGH secretion in the placebo group was similar to that of 22K-hGH and that the proportion of 20K- to 22K-hGH was fairly constant. These observations suggested that regulation of 20K-hGH secretion is physiologically the same as that of 22K-hGH. Baumann and Stolar (25) suggested that 20K- and 22K-hGH may be stored together in secretory granules in the somatotroph and, hence, released together in response to various stimuli. Our observations support this hypothesis. Furthermore, these results suggested that the endogenous kinetics of 20K-hGH may be comparable with those of 22K-hGH. Interestingly, the pharmaco-kinetics after sc injection of recombinant 20K-hGH were nearly comparable with those of recombinant 22K-hGH (26, 27). In 20K-hGH-treated groups, the serum 20K-hGH levels contained both exogenously administered and endogenously secreted 20K-hGH, but the endogenous 20K-hGH levels were ignored in this study because the mean secreted 20K-hGH levels in the placebo group were fairly low (0.13 ± 0.12 ng/mL). It has been reported that 20K-hGH is cleared more slowly than 22K-hGH in rats (28, 29), but this observation has not been confirmed in guinea pigs (30). These discrepancies may be related to the differences in the species studied (rat, guinea pig, human) and/or assay methods used.

We have demonstrated the time course of the suppressive effect induced by exogenous 20K-hGH on endogenous 22K-hGH secretion in humans. The reduction of serum 22K-hGH level after 20K-hGH administration required a period of ca. 4 h, and the level tended to recover by 24 h. However, the delay in suppression of endogenous 22K-hGH by exogenous 20K-hGH is difficult to define precisely because of the intermittent nature of hGH secretion. Additional studies are required to clarify the time lag between 20K-hGH exposure and suppression of endogenous 22K-hGH. In previous studies (31, 32), single intramuscularly or sc administration of hGH (with monitoring of the resulting plasma profiles) showed a delayed and prolonged suppressive effect on rat GH secretion. The time course of endogenous GH suppression in rats was similar to but faster than that in humans reported here. The fast time course in rats was probably due to the rapid absorption of hGH in this species (14, 33). Willoughby et al. (31) suggested that suppression is achieved through metabolic or other intermediary processes, rather than acutely by a direct membrane effect of the hGH molecule.

The marked suppression of endogenous 22K-hGH secretion occurred in parallel with the FFA elevation; serum FFA levels increased with maximum levels at 4–8 h and recovered by 24 h after 20K-hGH administration. In contrast, serum IGF-I levels increased after 8 h and were prolonged up to 24 h or more, and no increase in circulating glucose levels was observed for 24 h. Our data are consistent with those of Rosenthal et al. (34), who found that 6-h methionyl 22K-hGH infusion raised plasma FFA levels but not IGF-I or glucose levels and blunted GHRH-induced GH secretion in normal men. Of the main hGH-dependent substances, elevation of FFA rather than IGF-I levels may play a leading role at least in the marked 22K-hGH suppression at AUC_{6–12 h} after a single sc administration of 20K-hGH. Administration of FFA markedly reduced the basal GH secretion and blocked GH secretion induced by pharmacological and physiological stimuli in humans (23, 35). Recently, Briard et al. (36) reported that FFA acts both at the hypothalamic level, through increased somatostatin secretion, and at the pituitary level in sheep.

The suppression of 22K-hGH secretion was observed even at the lowest dose of 20K-hGH administered (0.01 mg/kg), with a C_max of 8.1 ± 4.1 ng/mL. Rosenthal et al. (34) reported that the GHRH-induced GH response in humans was significantly inhibited during 6-h methionyl 22K-hGH infusion, whereas the plasma GH level remained constant (9–13 ng/mL). Therefore, the effect of 20K-hGH on negative feedback may be as potent as that of 22K-hGH.

There are experimental limitations to differentiating between exogenous and endogenous hGH in humans. The time course of GH-induced negative feedback in humans can only be studied indirectly by using the peripheral GH response to GH provocation (21, 34, 37, 38) or the amplitude of sleep-related GH secretion (20) as an indicator of suppression of GH secretion. Our observations extended these studies and indicated that an exogenously administered GH isoform could suppress the other endogenously secreted GH isoform in a time-dependent manner. The proportion of 20K- to 22K-hGH is fairly constant under physiological conditions. Therefore, by measuring the serum 20K- and 22K-hGH levels and using the other hGH isoform as an indicator of the endogenous hGH, it may be possible to monitor the internal behavior of exogenously administered hGH in clinical application of 20K-hGH and, especially, 22K-hGH. Measurement of serum 20K- and 22K-hGH may be useful in evaluating the effects of circulating GH isoforms on their own release from the pituitary.

	Acknowledgments

 
We thank Drs. Kohei Yazawa, Fumiaki Ikeda, and Masaru Honjo for advice and encouragement during these studies. We also thank Ms. Noriko Takayama, Ms. Keiko Kawano, and Ms. Hiromi Takeda for technical assistance.

Received August 3, 1999.

Revised October 12, 1999.

Accepted October 20, 1999.

	References

Top Abstract Introduction Subjects and Methods Results Discussion References

 

1. Lewis UJ, Bonewald LF, Lewis LJ. 1980 The 20,000 dalton variant of human growth hormone: location of the amino acid deletions. Biochem Biophys Res Commun. 92:511–516.[CrossRef][Medline]
2. DeNoto FM, Moore DD, Goodman HM. 1981 Human growth hormone DNA sequence and mRNA structure: possible alternative splicing. Nucleic Acids Res. 9:3719–3730.[Abstract/Free Full Text]
3. Cooke NE, Ray J, Watson MA, Estes PA, Kuo BA, Liebhaber SA. 1988 Human growth hormone gene and the highly homologous growth hormone variant gene display different splicing patterns. J Clin Invest. 82:270–275.
4. De Vos AM, Ultsch M, Kossiakoff AA. 1992 Human growth hormone and extracellular domain of its receptor: crystal structure of the complex. Science. 255:306–312.[Abstract/Free Full Text]
5. Cunningham BC, Bass S, Fuh G, Wells JA. 1990 Zinc mediation of the binding of human growth hormone to the human prolactin receptor. Science. 250:1709–1712.[Abstract/Free Full Text]
6. Lewis UJ, Dunn JT, Bonewald LF, Seavey BK, VanderLaan WP. 1978 A naturally occurring structural variant of human growth hormone. J Biol Chem. 253:2679–2687.[Free Full Text]
7. Baumann G. 1991 Growth hormone heterogeneity: genes, isohormones, variants, and binding proteins. Endocr Rev. 12:424–449.[Abstract]
8. Lewis UJ, Markoff E, Culler FL, Hayek A, VanderLaan WP. 1987 Biologic properties of the 20K-dalton variant of human growth hormone: a review. Endocrinol Jpn. 34:73–85.[Medline]
9. Uchida H, Naito N, Asada N, et al. 1997 Secretion of authentic twenty kilodalton human growth hormone (20K hGH) in Escherichia coli and properties of the purified product. J Biotechnol. 55:101–112.[CrossRef][Medline]
10. Wada M, Ikeda M, Takahashi Y, et al. 1997 The full agonistic effect of recombinant 20 kDa human growth hormone (hGH) on CHO cells stably transfected with hGH receptor cDNA. Mol Cell Endocrinol. 133:99–107.[CrossRef][Medline]
11. Kostyo JL, Skottner A, Brostedt P, et al. 1987 Biological characterization of purified native 20-kDa human growth hormone. Biochim Biophys Acta. 925:325–331.[Medline]
12. Wada M, Uchida H, Ikeda M, et al. 1997 The 20 kDa human growth hormone (hGH) differs from the 22 kDa hGH in the complex formation with cell surface hGH receptor and hGH-binding protein circulating in human plasma. Mol Endocrinol. 12:146–156.[Abstract/Free Full Text]
13. Tsunekawa B, Wada M, Ikeda M, Uchida H, Naito N, Honjo M. 1998 The 20-kilodalton (kDa) human growth hormone (hGH) differs from the 22-kDa hGH in the effect on the human prolactin receptor. Endocrinology. 140:3909–3918.[Abstract/Free Full Text]
14. Hashimoto Y, Ikeda I, Ikeda M, et al. 1998 Construction of a specific and sensitive sandwich enzyme immunoassay for 20 kDa human growth hormone. J Immunol Methods. 221:77–85.[CrossRef][Medline]
15. Tsushima T, Katoh Y, Miyachi Y, et al. 1999 Serum concentration of 20K human growth hormone (20K hGH) measured by a specific ELISA. J Clin Endocrinol Metab. 84:317–322.[Abstract/Free Full Text]
16. Ishikawa M, Yokoya S, Tachibana K, et al. 1999 Serum levels of 20-kilodalton human growth hormone are parallel with 22-kilodalton human growth hormone in normal and short children. J Clin Endocrinol Metab. 84:98–104.[Abstract/Free Full Text]
17. Berg GVD, Veldhuis JD, Frölich M, Roelfsema F. 1996 An amplitude-specific divergence in the pulsatile mode of growth hormone (GH) secretion underlies the gender difference in mean GH concentrations in men and premenopausal women. J Clin Endocrinol Metab. 81:2460–2467.[Abstract]
18. Dieguez C, Page MD, Scanlon MF. 1988 Growth hormone neuroregulation and its alterations in disease state. Crin Endocrinol (Oxf). 28:109–143.
19. Abrams RL, Grumbach MM, Kaplan SL. 1971 The effect of administration of human growth hormone on the plasma growth hormone, cortisol, glucose, and free fatty acid response to insulin: evidence for growth hormone autoregulation in man. J Clin Invest. 50:940–950.
20. Mendelson WB, Jacobs LS, JC Gillin. 1983 Negative feedback suppression of sleep-related growth hormone secretion. J Clin Endocrinol Metab. 56:486–488.[Abstract]
21. Pontiroli AE, Lanzi LD, Monti E, Sandoli E, Pozza G. 1991 Growth hormone (GH) autofeedback on GH response to GH-releasing hormone. Role of free fatty acids and somatostatin. J Clin Endocrinol Metab. 72(2):492–495.
22. Berelowitz M, Szabo M, Frohman LA, Firestone S, Chu L, Hintz RL. 1981 Somatomedin C mediates growth hormone negative feed-back by effects on both hypothalamus and the pituitary. Science. 212:1279–1281.[Abstract/Free Full Text]
23. Casanueva FF, Villanueva L, Dieguez C, et al. 1987 Free fatty acids block growth hormone (GH) releasing hormone-stimulated GH secretion in man directly at the pituitary. J Clin Endocrinol Metab. 65:634–642.[Abstract]
24. Dieguez C, Casanueva FF. 1995 Influence of metabolic substrates and obesity on growth hormone secretion. Trends Endocrinol Metab. 6:55–59.
25. Baumann G, Stolar MW. 1986 Molecular forms of human growth hormone secreted in vivo: nonspecificity of secretory stimuli. J Clin Endocrinol Metab. 62:789–790.[Abstract]
26. Urae A, Irie S, Amamoto T, Kumamoto M, Urae R, Morise H. 1992 Clinical trial phase I of LY137998 -biological equivarence test of the products manufactured by new method (2 cistron) and conventional method (1 cistron). Clin Report. 26:1063–1084.
27. Ho KY, Weissberger AJ, Stuart MC, Day RO, Lazarus L. 1989 The pharmacokinetics, safety and endocrine effects of authentic biosynthetic human growth hormone in normal subjects. Clin Endocrinol. 30:335–345.[Medline]
28. Baumann G, Stolar MW, Buchanan TA. 1985 Slow metabolic clearance rate of the 20,000-dalton variant of human growth hormone: implications for biological activity. Endocrinology. 117:1309–1313.[Abstract]
29. Baumann G, Shaw MA. 1990 Plasma transport of the 20,000-daltone variant of human growth hormone (20K): evidence for a 20K-specific binding site. J Clin Endocrinol Metab. 71:1339–1343.[Abstract]
30. Fairhall KM, Carmignac DF, Robinson ICAF. 1992 Growth hormone (GH) binding protein and GH interactions in vivo in the guinea pig. Endocrinology. 131:1963–1969.[Abstract]
31. Willoughby JO, Menadue M, Zeegers P, Wise PH, Oliver JR. 1980 Effects of human growth hormone on the secretion of rat growth hormone. J Endocrinol. 86:165–169.[Abstract]
32. Lanzi R, Tannenbaum GS. 1992 Time course and mechanism of growth hormone’s negative feedback effect on its own spontaneous release. Endocrinology. 130:780–788.[Abstract]
33. Clark RG, Morthnsen DI, Carlsson LMS, et al. 1996 Recombinant human growth hormone (GH)-binding protein enhances the growth-promoting activity of human GH in the rat. Endocrinology. 137:4308–4315.[Abstract]
34. Rosenthal SM, Kaplan SL, Grumbach MM. 1989 Short term continuous intravenous infusion of growth hormone (GH) inhibits GH-releasing hormone-induced GH secretion: a time-dependent effect. J Clin Endocrinol Metab. 68:1101–1105.[Abstract]
35. Imaki T, Shibasaki T, Shizume K, et al. 1985 The effect of free fatty acids on growth hormone-releasing hormone-mediated GH secretion in man. J Clin Endocrinol Metab. 60:290–294.[Abstract]
36. Briard N, Rico-gomez M, Guillaume V, et al. 1998 Hypothalamic mediated action of free fatty acid on growth hormone secretion in sheep. Endocrinology. 139:4811–4819.[Abstract/Free Full Text]
37. Rosenthal SM, Hulse JA, Kaplan SL, Grumbach MM. 1986 Exogenous growth hormone inhibits growth hormone-releasing factor-induced growth hormone secretion in normal men. J Clin Invest. 77:176–180.
38. Pontiroli AE, Lanzi R, Pozza G. 1989 Inhibition of the growth hormone (GH) response to GH-releasing hormone by constant Met-GH infusions. J Clin Endocrinol Metab. 68:956–959.[Abstract]

This article has been cited by other articles:

				H. Liu, D. M. Bravata, I. Olkin, A. Friedlander, V. Liu, B. Roberts, E. Bendavid, O. Saynina, S. R. Salpeter, A. M. Garber, et al. Systematic Review: The Effects of Growth Hormone on Athletic Performance Ann Intern Med, May 20, 2008; 148(10): 747 - 758. [Abstract] [Full Text] [PDF]

				M. Hayakawa, Y. Shimazaki, T. Tsushima, Y. Kato, K. Takano, K. Chihara, A. Shimatsu, and M. Irie Metabolic Effects of 20-Kilodalton Human Growth Hormone (20K-hGH) for Adults with Growth Hormone Deficiency: Results of an Exploratory Uncontrolled Multicenter Clinical Trial of 20K-hGH J. Clin. Endocrinol. Metab., April 1, 2004; 89(4): 1562 - 1571. [Abstract] [Full Text] [PDF]

				K.-C. Leung, C. Howe, L. Y.-Y. Gui, G. Trout, J. D. Veldhuis, and K. K. Y. Ho Physiological and pharmacological regulation of 20-kDa growth hormone Am J Physiol Endocrinol Metab, October 1, 2002; 283(4): E836 - E843. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart 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 Hashimoto, Y. Articles by Tanaka, T. Search for Related Content PubMed PubMed Citation Articles by Hashimoto, Y. Articles by Tanaka, T.