Growth hormone in encephalectomized rat fetuses, with comments on the effects of anesthetics.

Plasma and pituitary immunoreactive growth hormone (GH) was measured in 21.5-day-old rat fetuses under various experimental conditions. Encephalectomy on day 19.5 was used as a method for depriving the fetus of its hypothalamus. The fetuses were recovered on day 21.5 under maternal pentobarbital anesthesia. Total encephalectomy or partial encephalectomy (ablation of superficial brain structures) similarly affected fetal growth. The mean GH contents of the pituitaries were not significantly different in the four groups of fetuses studied: controls from intact females (1.38 +/- 0.19 mug/gland), controls from females submitted to surgery on day 19 (1.47 +/- 0.13 mug/gland), surgically encephalectomized fetuses (1.13 +/- 0.12 mug/gland), sham-operated fetuses (1.19 +/- 0.10 mug/gland). The mean plasma GH levels were the same in control fetuses of intact females (147 +/- 8 ng/ml) and in control fetuses of females submitted to surgery (168 +/- 9 ng/ml). The values were lower in sham-operated fetuses (118 +/- 11 ng/ml) and considerably reduced (P less than 0.001) in encephalectomized fetuses (60 +/- 8 ng/ml). Plasma GH was higher in the fetuses of females killed less than 2 min earlier, than in the fetuses of anesthetized females. In dams anesthetized with pentobarbital or ether, the fetal plasma levels of GH were not different after 15 or 45 min of maternal anesthesia. Under maternal urethane anesthesia, the fetal plasma GH was at 15 min significantly lower than it was under (P less than 0.01) or pentobarbital (P less than 0.05); 30 min later, it had increased by 40% (P less than 0.025). It appears that the release of GH in the fetus can be modified by anesthetics, and that some GH still is released by the pituitary gland in the absence of the hypothalamus.