Growth Hormone in Encephalectomized Rat Fetuses, with Comments on the Effects of Anesthetics

Abstract

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 to deprive 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 4 groups of fetuses studied: controls from intact females (1.38 .+-. 0.19 .mu.g/gland), controls from females submitted to surgery on day 19 (1.47 .+-. 0.13 .mu.g/gland), surgically encephalectomized fetuses (1.13 .+-. 0.12 .mu.g/gland) and sham-operated fetuses (1.19 .+-. 0.10 .mu.g/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 < 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 < 0.01) or pentobarbital (P < 0.05); 30 min later, it had increased by 40% (P < 0.025). The release of GH in the fetus can apparently be modified by anesthetics; some GH still is evidently released by the pituitary gland in the absence of the hypothalamus.