Modulation of growth hormone secretion by thermogenically derived free fatty acids in the perinatal lamb.

To evaluate the hypothesis that the rapid fall in circulating GH concentrations at birth is secondary to the initiation of nonshivering thermogenesis and the consequent rise in FFA levels, a series of experiments was performed in late-gestation fetal sheep. By sequentially cooling the fetus by means of a coil placed around the fetal thorax, ventilating with oxygen via an exteriorized tracheostomy tube, and separating the fetus from the placenta by occluding the umbilical cord, nonshivering thermogenesis could be induced in utero. In the first protocol (n = 6) cooling alone had no effect on fetal plasma FFA levels, oxygenation elevated FFAs slightly from 64 +/- 7 mu Eq/liter to 183 +/- 29 mu Eq/liter, and cord occlusion caused a further marked rise (P less than 0.005) to 635 +/- 69 mu Eq/liter. Neither cooling nor ventilation affected fetal plasma GH concentrations which fell (P less than 0.001) from 160 +/- 17 ng/ml to 65 +/- 13 ng/ml upon cord occlusion. When the cord occluder was removed FFA levels fell...