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Original Studies |
Department of Physiological Sciences, Eastern Virginia Medical School (M.G.L., G.J.P.), Norfolk, Virginia 23501; and the Departments of Obstetrics/Gynecology/Reproductive Sciences and Physiology, Center for Studies in Reproduction, University of Maryland School of Medicine (E.D.A.), Baltimore, Maryland 21201
Address all correspondence and requests for reprints to: Gerald J. Pepe, Ph.D., Department of Physiological Sciences, Eastern Virginia Medical School, P.O. Box 1980, Norfolk, Virginia 23501-1980. E-mail: gjp{at}borg.evms.edu
| Abstract |
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-hydroxylase-C17,20
lyase (P-450c17) enzyme that catalyzes the synthesis of C19
steroids used for placental estrogen production. The development of the
transitional zone comprised of cortical cells that express the P-450c17
and the 3ß-hydroxysteroid dehydrogenase-isomerase (3ßHSD) enzymes
for cortisol production, and the definitive zone, which expresses
3ßHSD, but not P-450c17, for mineralocorticoid synthesis, does not
occur until relatively late in gestation. Although ACTH is considered
essential to fetal adrenal growth and function, the role that ACTH has
in the development of the transitional and definitive zones, is less
clear. To answer this question, the width of these zones was determined
by immunocytochemical expression of P-450c17 and/or 3ßHSD in fetal
adrenal glands obtained on day 100 (mid) of gestation (term = day
184) from baboons in which ACTH was administered to the fetus on days
9599 of gestation or on day 165 (late) of gestation from baboons in
which fetal ACTH was suppressed by treatment of the mother and fetus
with betamethasone on days 150164 of gestation. At midgestation, the
fetal adrenal was comprised almost exclusively of fetal zone cells and
a small definitive zone (38 ± 2 µm in width), but was
essentially devoid of a transitional zone (7 ± 2 µm). Treatment
with ACTH enhanced (P < 0.05) the width of the
transitional zone (67 ± 4 µm), but not the size of the
definitive zone (10 ± 4 µm). In late gestation, the width of
the definitive zone, although 2-fold greater than that on day 100, was
smaller (P < 0.05) than that of the transitional
zone (120 ± 15 µm), which greatly exceeded that at
midgestation. Treatment with betamethasone in late gestation eliminated
the transitional zone, but had no effect on the size of the definitive
zone (120 ± 8 µm). These findings indicate that the development
of the baboon fetal adrenal transitional zone late in gestation is
dependent on fetal pituitary ACTH. In contrast, the ontogenesis of the
definitive zone at midgestation and its growth in late gestation occur
in the relative absence of ACTH. | Introduction |
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-hydroxylase-C17,20-lyase (P-450c17) enzyme essential for the
production of the C19 androgen dehydroepiandrosterone and its sulfate
that serve as requisite precursors for placental estrogen production
(5). In contrast, the transitional zone, which expresses both the
3ß-hydroxysteroid dehydrogenase-isomerase (3ßHSD) and the P-450c17
enzymes for the production of cortisol, and the definitive zone, which
expresses 3ßHSD, but not P-450c17, for the production of aldosterone
(1, 6), do not develop in the fetal adrenal gland until relatively late
in gestation. In the baboon (7, 8) and rhesus monkey (9), ACTH of fetal
pituitary origin (10) is essential to the developmental expression in
late gestation of the messenger ribonucleic acids (mRNAs) and proteins
for 3ßHSD and P-450c17 in and de novo cortisol production
by the fetal adrenal (11, 12). It would appear, therefore, that ACTH is
important to development of the transitional zone, although this
remains to be confirmed by analysis of zone-specific expression of
3ßHSD and P-450c17. Moreover, it is not known whether fetal pituitary
ACTH is also required for development of the definitive zone. To answer
these questions, the current study compared the cellular expression of
3ßHSD and P-450c17 in fetal adrenal glands obtained at midgestation
from baboons in which the fetus was administered ACTH and in late
gestation from animals treated with betamethasone, which we previously
demonstrated inhibited fetal pituitary POMC mRNA/ACTH (8)
expression. | Materials and Methods |
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Fetal adrenal glands were obtained from baboons (Papio anubis) via cesarean section on day 100 (mid) or day 165 (late) of gestation (term = day 184). Baboon fetuses of midgestation were untreated (n = 5) or treated with ACTH (n = 4; Cortrosyn, Organon, Inc., West Orange, NJ) administered via maternal transabdominal im injection once daily to the fetus (25 µg/100 µL saline) on days 9599 of gestation. In late gestation, baboons were untreated (n = 5) or treated with betamethasone (Celestone Soluspan, Schering AG, Chicago, IL) administered to the mother (6 mg) and fetus (0.6 mg) every other day between days 150164 of gestation (n = 3).
Immunocytochemistry
Baboon fetal adrenals were fixed in 10% formalin and embedded in paraffin. Sections (4 µm) through the central portion of the gland were mounted onto SuperFrost microscope slides (Fischer Scientific, Arlington VA), deparaffinized by heating at 60 C (15 min) followed by three washes in xylene, dehydrated in graded ethanols (8), and treated with H2O2 in methanol (0.3% for 3ßHSD and 3.0% for P-450c17) to block endogenous peroxidase.
For analysis of 3ßHSD, alternate sections were preblocked for 30 min with 5% normal goat serum (Vector Laboratories, Inc., Burlingame, CA) in phosphate-buffered saline and incubated (4 C) overnight with a rabbit polyclonal antibody to antihuman 3ßHSD (supplied by Dr. Ian Mason, University of Edinburgh, Edinburgh, Scotland) diluted 1:5000 in 5% normal goat serum. After treatment with biotinylated goat antirabbit IgG (Vector Laboratories, Inc.), sections were incubated with avidin DH and horseradish peroxidase (Vectastain Elite Kit, Vector Laboratories, Inc.) and color developed with imidazole and diaminobenzidine. Sections were lightly counterstained with Gills hematoxylin (Fisher Scientific), and an average of six randomly selected areas (157 x 130 µm)/section (n = 48 sections/fetal adrenal) were examined using an Optiphot-2 microscope attached to a video-based Image 1 Analysis System (Universal Imaging Corp., West Chester, PA) to determine the width (microns) of the cell layer expressing 3ßHSD (7, 8).
For analysis of P-450c17, alternate adrenal sections were placed in Coplin jars containing 10 mmol/L sodium citrate buffer (pH 6.0; Sigma Chemical Co., St. Louis, MO) and microwaved (model JE 1540, 900W, General Electric) for 5.5 min. After cooling for 30 min, sections were washed, preblocked as for 3ßHSD, and incubated (4 C) overnight with a rabbit polyclonal antibody to antihuman P-450c17 (supplied by Dr. M. Waterman, Vanderbilt University School of Medicine, Nashville, TN) diluted 1:2000. After incubation with biotinylated goat antirabbit IgG, avidin, and biotinylated horseradish peroxidase (Vector Laboratories, Inc.), sections were incubated with H2O2, imidazole, and diaminobenzidine and examined by light microscopy as described for 3ßHSD. The mean width of cells adjacent to the capsule not expressing P-450c17 was determined by image analysis.
As described by Mesiano et al. (6), the mean width (microns) of the layer of cells expressing 3ßHSD was defined as the total width of the definitive and transitional zones. The width of this cell layer not expressing P-450c17 was defined as the definitive zone (3ßHSD positive; P-450c17 negative). This value was then subtracted from the total width of the 3ßHSD cell layer to determine the width of the transitional zone (3ßHSD and P-450c17 positive). The fetal zone was defined as those cortical cells that expressed P-450c17 but not 3ß-HSD.
Statistics
The effects of development, betamethasone, and ACTH on the width of the definitive or the transitional zones were compared by ANOVA with multiple comparison of the means by the Newman-Keuls statistic. Students t tests for dependent observations were used to compare the respective widths of the definitive and transitional zones in all groups.
| Results |
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| Discussion |
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The results of present study also indicate that the size of the
definitive zone, like that of the transitional zone, was increased
between mid- and late gestation. However, in contrast to the
transitional zone, treatment with ACTH at mid-gestation or
suppression of endogenous ACTH by betamethasone in late gestation did
not alter the width of the definitive zone. Hypophysectomy of the sheep
fetus at mid- to late gestation also had no effect on the apparent
width of the fetal adrenal glomerulosa (i.e. definitive
zone), as based on histology, although the size of the developing
fasiculata (i.e. transitional zone) was dramatically reduced
(14). Histological (15, 16) and stereological (17) analyses of the
human fetal adrenal have also shown that growth of the zona glomerulosa
was not affected by fetal anencephaly, i.e. in the absence
of ACTH. It appears, therefore, that the development of the definitive
zone of the fetal adrenal is regulated by factors other than ACTH.
Earlier studies in the adult rat also demonstrated that the width of
the zona glomerulosa of the adrenal was not significantly affected by
hypophysectomy, i.e. removal of pituitary ACTH (18). In the
adult adrenal, glomerulosa cell function is regulated by angiotensin II
via interaction with the AT1 receptor.
Interestingly, human fetal adrenal cortical cells primarily express the
AT2 receptor (19). The AT1
receptors apparently are only expressed in a few layers of cortical
cells at the periphery (presumed definitive zone) of the fetal adrenal
gland (19). Studies of the regulation and role of
AT1 and AT2 receptors in
the primate fetal adrenal gland, however, remain to be performed.
Activin and inhibin have also been postulated to modulate fetal adrenal
development (1). Recently, we demonstrated that the baboon fetal
adrenal expresses abundant quantities of inhibin
-subunit in fetal
zone cells throughout the course of gestation (20). However, inhibin
-subunit was not detected in the outer layer of definitive zone
cells expressing 3ßHSD in late gestation. Although the role of
inhibin on adrenal cellular maturation remains to be determined,
in vitro studies suggest that the presence of
-subunit
may serve to limit the production of activins (dimers of ß-subunits),
which have been shown to inhibit fetal adrenal cell proliferation as
well as stimulate ACTH-dependent cortisol production (21). Finally, we
previously demonstrated that estrogen of placental origin acts on the
baboon fetal adrenal gland in vitro (22) and in
vivo (23) to suppress ACTH-dependent dehydroepiandrosterone
production by fetal zone cells, apparently by interaction with the
estrogen receptor, which is expressed in the cells of the fetal zone
(24). Interestingly, estrogen receptor was also expressed in relatively
high levels in definitive zone cells, and therefore, estrogen may also
act to coordinate the development and/or function of the baboon fetal
adrenal definitive zone.
In summary, the current study demonstrated that the development of the baboon fetal adrenal transitional zone late in gestation is dependent on fetal pituitary ACTH. In contrast, the ontogenesis of the definitive zone at midgestation and its growth and development in late gestation occurred in the relative absence of ACTH, suggesting that factors other than ACTH regulate maturation of the primate fetal adrenal definitive zone.
| Acknowledgments |
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| Footnotes |
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Received April 21, 1999.
Revised June 28, 1999.
Accepted July 1, 1999.
| References |
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-hydroxylase/17,20-lyase, and 3ß-hydroxysteroid dehydrogenase
isomerase steroidogenic enzymes in human and rhesus monkey fetal
adrenal glands: reappraisal of functional zonation. J Clin
Endocrinol Metab. 77:11841189.[Abstract]
5-3ß-hydroxysteroid dehydrogenase and
17
-hydroxylase-17,20-lyase activity. Endocrinology. 128:23952401.
-inhibin. Biol Reprod. 61:142146.
and ß in the baboon fetal adrenal gland. Endocrinology.
In press.
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