The effect of hypothalamic paraventricular nuclear lesions placed at 108-110 days gestational age on plasma ACTH concentrations in the fetal sheep

Lesions that completely destroyed the paraventricular nucleus of the hypothalamus were placed in fetal sheep (n = 4) at 108-110 days of gestational age. These fetuses were then subjected to hypotension (50% of initial mean fetal arterial blood pressure), hypoxaemia (a decrease in fetal PaO₂ ≥ 5 torr) and bolus injection of corticotropin releasing factor (CRF-1.0 μg iv) in random order on successive days. The lesioned fetuses produced significantly less ACTH after hypotension (+ 10 min: 35.7 ± 26.9 vs. 358.0 ± 99.7 and +30 min: 28.2 ± 12.2 vs. 238.0 ± 73.0 pg.ml^-1) (P < 0.05), hypoxaemia (+40 min: 23.5 ± 9.3 vs. 198.3 ± 75.8 and +60 min: 32.3 ± 18.8 vs. 295.3 ± 99.9 pg.ml^-1) (P < 0.05) and intravenous administration of 1 μg CRF (+15 min: 32.0 ± 16.8 vs. 145.7 ± 25.0 and +60 min: 33.0 ± 23.3 vs. 161.3 ± 43.1 pg.ml^-1) (P < 0.05). Our experiments suggest an important role for the fetal paraventricular nucleus in control of ACTH secretion. They also indicate that impairment of paraventricular nucleus function at this stage of fetal life may have a detrimental effect on the ability of the anterior pituitary to secrete ACTH in response to exogenous CRF.