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Department of Neonatology (S.B.-D., P.S.), Meyer Childrens Hospital, Haifa 31096, Israel; Division of Endocrinology (N.Z.-L., M.L., Z.H.), Meyer Childrens Hospital, Haifa 31096, Israel; Department of Radiology (M.E.), Rambam Medical Center, Haifa 31096, Israel; Endocrine Laboratory (Z.S.-O.), Rambam Medical Center, Haifa 31096, Israel; and Faculty of Medicine (P.S., Z.H.), Technion-Israel Institute of Technology, Haifa 31096, Israel
Address all correspondence and requests for reprints to: Nehama Zuckerman-Levin, M.D., Pediatric Endocrinology, Meyer Childrens Hospital, POB 9602, Haifa 31096, Israel. E-mail: zuckerln{at}netvision.net.il.
| Abstract |
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Hypothesis: Placental factors up-regulate dehydroepiandrosterone sulfate (DHEA-S) generation. Hence, regardless of age, parturition will result in fetal adrenal involution and decline in DHEA-S levels.
Subjects and Methods: Premature neonates (n = 30) with gestational age 2635 wk were studied. Adrenal volume by ultrasonography and serum DHEA-S, cortisol, and androstendione levels were followed weekly between d 1 and 28 of life.
Results: Serum DHEA-S was high on d 1 of life, declining rapidly regardless of gestational age during the first week of life (P < 0.001), and serum androstenedione and cortisol levels followed a similar pattern. Androstenedione levels showed a rise as of d 21 of life in boys but not in girls. The adrenals decreased in ultrasonographic volume from d 1 to 14 of life (P < 0.001), regardless of gestational age.
Conclusions: Involution of the adrenal is faster than previously reported and, regardless of gestational age, occurs within the first week of life in terms of hormone secretion and within 2 wk in adrenal size. Involution involves a decline in DHEA-S but also in androstenedione and cortisol secretion, with a change in enzymatic activity. Males and females differ in their androstenedione levels and enzymatic activity. Parturition itself is the basis for fetal adrenal involution, supporting a key role for placental factors in maintaining the fetal adrenal and generating adrenal androgens.
| Introduction |
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5 3ß-hydroxysteroids due to low 3ß-hydroxysteroid dehydrogenase (3ß-HSD) expression in the fetal zone (3, 4, 5, 6). In utero the generation of dehydroepiandrosterone (DHEA) parallels the increase in fetal size during the second and third trimester of pregnancy (7). At the end of a full pregnancy, DHEA/DHEA sulfate (DHEA-S) levels are high and are greater than adult blood levels. After birth, the fetal adrenals undergo involution, losing in a month 50% of their mass (1). Adrenal involution is followed by rapid decline in androgen secretion (8, 9, 10, 11). The working hypotheses of the study were that if placental factors up-regulate adrenal androgens production, then parturition, regardless of age, would result in a rapid decline in neonatal DHEA-S levels. On the other hand, if fetal factors are the drive for fetal DHEA/DHEA-S generation, premature parturition would result in a delayed adrenal involution. Toward these hypotheses, the adrenal involution of 30 premature neonates was studied by means of hormone secretion and adrenal ultrasonography.
| Subjects and Methods |
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Thirty consecutive premature newborns (2635 wk gestational age; 18 males and 12 females) were included in this prospective study (Table 1
). The Helsinki Committees of the Rambam Medical Center and the Israel Ministry of Health approved the protocol, and parents signed informed consents. Eight infants were delivered by cesarean section, the others by spontaneous delivery. Subjects were excluded from the study if they had any of the following: massive intracranial bleeding, chromosomal or genetic aberrations, ambiguous genitalia, or abnormal thyroid function tests. Subjects were divided into three subgroups according to the following gestational ages: group A, 2628 wk; B, 2932 wk; C, 3335 wk. Blood samples were taken in small volumes as part of routine blood tests in these patients.
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Adrenal gland volume (cubic centimeters) by ultrasonography was measured in groups A and B at d 1, 7, 14, 21, and 28.
For a rough indirect estimation of 3ß-HSD, DHEA-S sulfotransferase, and sulfatase activity, we calculated the androstenedione/DHEA-S ratio, and for 17 hydroxylase activity, we calculated the androstenedione/cortisol ratio.
Methods
The volume of the adrenal gland was calculated according to the two-limb model as previously suggested (12), whereby each limb is assumed to be cylindrical, using the sagittal, axial, and coronal dimensions, and the calculated ultrasonographic volume is presented in cubic centimeters. The ultrasound scanner used a 5 MHz transducer (model SSD-1400; Aloka Co., Tokyo, Japan). Serum levels of cortisol and DHEA-S were measured by competitive immunoassays with the Immulite Analyzer (Diagnostic Products Corp., Los Angeles, CA). Androstenedione levels were measured by a double antibody RIA kit (Diagnostic Systems Laboratories, Webster, TX). Cross-reactivity of DHEA-S was 0.1% with androstenedione and less than 0.01% with cortisol. Cross-reactivity of cortisol with androstenedione and DHEA-S was less than 0.01%, and cross-reactivity of androstenedione was 0.04% with cortisol and less than 0.01% with DHEA-S.
Statistical methods
Statistical analysis used separate variance t-test. Differences were regarded significant with P values of less than 0.05.
| Results |
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Serum androstenedione levels followed a similar pattern, declining by 53, 68, and 80% in groups A, B, and C, respectively (P < 0.001), from d 1 to 7.
Androstenedione level showed a rise, as of d 21 of life, with a different pattern in male and female newborns (Fig. 4B
). After a decrease in androstenedione levels on d 7 in both boys and girls (P < 0.0001), boys demonstrated a significant rise in androstenedione levels as of d 21 of life (P < 0.0012). Androstenedione levels in boys were higher than in girls in all postpartum days (P < 0.014).
Absolute levels and percent decrease of all three hormones did not correlate with gestational age.
When estimating enzyme activity, one has to consider the three orders of magnitude higher serum levels of DHEA-S compared with androstenedione and cortisol.
Figure 5
shows that the androstenedione/DHEA-S ratio in boys increases from d 1 to 7 (P < 0.01), decreases from d 7 to 14 (P < 0.03), and increases from d 14 to 28 (P < 0.0004), whereas in girls this ratio decreases (P < 0.04). Ratios were higher in boys than in girls on d 21 and 28 postpartum (P < 0.01).
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| Discussion |
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This pattern of rapid involution was demonstrated in all neonates, regardless of their gestational age. The present findings disagree with previous reports that involution of the adrenal is related to gestational age rather than birth (15, 16). That study used urinary levels of 3ß-OH-5ene steroids as a measure of urinary fetal zone steroids and suggested that the fetal adrenals maintain high androgen levels for 34 wk after term. The urinary metabolites were inversely correlated to ACTH levels (16).
Measuring adrenal volume by ultrasonography bares a methodological difficulty, because the shape of the gland is multipart. We used a model based on a two-limb shape of the adrenal gland (12) and assumed each limb to be cylindrical. The width and length are in the same order as other reports of ultrasonographic adrenal size (12, 17), although it is hard to evaluate the precise anatomical size of the glands, and the ultrasonographic volumes given are meant for between-group and over-time comparison only.
Serum cortisol levels were within normal adult reference for 0800 h cortisol on d 1 and declined within 7 d, regardless of gestational age, confirming previous reports (18, 19). These documented cortisol levels are in accordance with a reference level of this age group and have to be considered in the context of infants under stress because involution of the fetal zone precedes the full development of the definitive zone (20, 21, 22).
Serum androstenedione levels paralleled the pattern of a rapid decrease of DHEA-S and cortisol but were followed in males only by an increase in androstenedione levels as of d 21 of life. This pattern of rise in male neonates is similar to that reported for testosterone (23), and it seems to be due to gonadal secretion. Gonads may also be responsible for the higher androstenedione levels in boys vs. girls after parturition. The data show an increase in the androstenedione/DHEA-S ratio, reflecting an increase in the combined activity of 3ß-HSD, DHEA-S sulfotransferase, and sulfatase. The latter is highly expressed in the placenta, and parturition eliminates this activity.
Indeed, low 3ß-HSD activity is characteristic of the fetal zone compared with the definitive zone cells (1). Lower activity of the enzymes on the first day of life reflects the disappearance of the placenta, and the later rise in boys demonstrates gonadal activity, seen in boys but not in girls.
We also show a rise in 17-hydroxylase activity during the same time period, which is noted more in boys. Fetal adrenal produces androgens due to increased 17-hydroxylase activity, enhanced by cytochrome b5 (24, 25). Parturition followed by adrenal involution involves a low 17-hydroxylase activity, which was demonstrated in our subjects. Rise in enzyme activity in boys is also connected to gonadal contribution.
Previous studies investigated the possible placental factors that maintain the fetal adrenal and might disappear at parturition. Coculture of placental tissue with ACTH-stimulated fetal adrenal cells demonstrated inhibition of cortisol production in the fetal adrenal (26). In vitro studies in human fetal adrenal cells (27, 28, 29) and in human adrenal microsomes (30) showed that estrogens inhibit adrenal 3ß-HSD activity. Indeed, fetal unconjugated levels of total estrogen (estrone, estradiol, and estriol) from the placenta dramatically rise from 1720 wk gestation to term (31), and estrogen levels increase in direct correlation with the adrenal weight and the DHEA-S pool (32). A recent study in baboons questioned the role of estrogens in fetal adrenal zone development and suggested that estrogens act as a feedback system to control physiological secretion of estrogen precursors (33). Studies in vivo demonstrated that IGF-II of placental or adrenal origin is another possible regulator of fetal adrenal development and a mediator of ACTH action (34, 35). Increased placental CRH production at the end of gestation, together with various growth factors, may exert direct stimulation of fetal adrenal steroidogenesis (35, 36) and elevation of estrogen levels.
We conclude that parturition itself is the basis for fetal adrenal involution and for neonatal recovery of the definitive adrenal enzyme activity after birth.
| Footnotes |
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First Published Online October 31, 2006
1 S.B.-D. and N.Z.-L. contributed equally to this work, and both are to be considered first authors. ![]()
Abbreviations: DHEA, dehydroepiandrosterone; DHEA-S, DHEA sulfate; 3ß-HSD, 3ß-hydroxysteroid dehydrogenase.
Received December 15, 2005.
Accepted October 23, 2006.
| References |
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-hydroxylase/17, 20-lyase, and 3 ß-hydroxysteroid dehydrogenase isomerase steroidogenic enzymes in human and rhesus monkey fetal adrenal glands: reappraisal of functional zonation. J Clin Endocrinol Metab 77:11841189[Abstract]This article has been cited by other articles:
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