Morphometric analyses of adrenal gland growth in fetal and neonatal sheep. I. The adrenal cortex.
This, the first linear morphometric analysis of the epigenesis of the fetal mammalian adrenal cortex, has shown that in the fetal sheep during the latter two thirds of gestation and in the newborn lamb, there are two periods of rapid growth separated by a period of much reduced growth. The fetal ages studies were 53 days (0.36 gestation), a period when the fetal adrenal cortex is actively steroidogenic; 100 days (0.68 gestation), a period of adrenocortical quiescence; 130 days (0.88 gestation), the period of increasing responsiveness to ACTH and cortisol production; 144 days (0.98 gestation), the period of maximal adrenocortical steroidogenesis; and 2 days postpartum, when cortisol production is normally maintained. The first adrenocortical growth period extends to mid-gestation, then growth slows to 0.85 gestation when the second growth period begins. The changes between the first growth period (0.36 gestation) and the period of quiescence (0.68 gestation) are characterised by the attainment of normal adrenocortical zonation and the separation of the medulla. The rate of adrenocortical cell division slows and the zona fasciculata cells become smaller in size. The volume density of the adrenocortical blood sinusoids decreases significantly. The onset of the second growth phase is associated with the previously reported increased levels of fetal plasma ACTH at 0.85 gestation and is expressed initially as a hypertrophic response. Cellular hypertrophy increases from 0.88 gestation to 0.98 gestation and then declines over the birth period. The rate of adrenocortical cell division increases from 0.88 gestation and maintains a maximal rate from 0.98 gestation to 2 days postpartum. These interactions of cellular hypertrophy and hyperplasia, which result in adrenocortical growth, may be explained as a response to fetal ACTH, which has the ability to stimulate the production of peptide growth and differentiation factors, e.g. IGF-II, and cortisol, which then control adrenocortical development in an autocrine and paracrine fashion.
Boshier
D P
DP
Department of Anatomy, School of Medicine, University of Auckland, New Zealand.
Holloway
H
H
D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000302:Adrenal Cortex / Q000196:embryology* / Q000201:enzymology; D000818:Animals; D000831:Animals, Newborn; D001699:Biometry; D002452:Cell Count; D002454:Cell Differentiation; D005314:Embryonic and Fetal Development; D005865:Gestational Age; D009929:Organ Size; D012756:Sheep / Q000196:embryology*
D015096:3-Hydroxysteroid Dehydrogenases