Critical Time in the Hypothalamic Control of the Pituitary-Adrenal System in Fetal Rats: Observations in Fetuses Subjected to Hypervitaminosis A and Hypothalamic Destruction

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Abstract
The time of onset of hypothalamic regulation of the pituitary-adrenal system in fetal rats was assessed by induction of fetal exencephaly by maternal hypervitaminosis A and destruction of the fetal hypothalamic area with an electrocoagulator. The effects of such experiments were compared with those of fetal hypophysectomy (surgical decapitation). In fetuses decapitated and autopsied at various stages between the 17th and the 22nd day of gestation, the adrenals stopped growing from the day of decapitation. Brains of exencephalics at all stages from the 16th to 22nd days were everted and more or less degenerated, but pituitaries always persisted. The adrenals of such exencephalics grew nearly to thesame extent as did those of non-exencephalics until the 20th day after which they stopped growing despite the presence of the anterior pituitary. When hypothalamic destruction took place on day 17 of gestation, there was no alteration in adrenal growth during the subsequent day. Between the 18th and the 20th day, the destruction caused slight retardation of adrenal growth. After the 20th day, the destruction completely stopped adrenal growth as did fetal decapitation. These results suggest that in fetal rats, hypothalamic control of the pituitary-adrenal system begins to operate between the 18th and the 22nd day of gestation. (Endocrinology93: 1, 1973)

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