Studies on Growth Hormone Secretion in Starved Rats under Urethane Anesthesia

Abstract

Adult male wistar rats averaging 200 g each were subjected to food removal for 1--6 days or fed ad libitum throughout (controls). Plasma GH levels and pituitary GH contents were measured by radioimmunoassay. The GH responses to intravenous injection of TRH (2.5 microgram/100 g B.W.), PGE1(5 microgram/100 g B.W.), LH-RH (1 microgram/100 g B.W.) and Chlorpromazine (CPZ, 100 microgram/100 g B.W.) were tested under urethane anesthesia. Circulating GH levels were significantly increased by prolonged starvation, while pituitary GH contents progressively decreased with increased periods of starvation. In addition, following the TRH administration, plasma GH levels increased in starved rats compared to the control rats. A similar effect was also observed with PGE1. In contrast, the administration of CPZ, which was reported to act at the hypothalamic level, failed to potentiate GH release in starved rats under urethane anesthesia. These observations suggest an increased susceptibility of starved rats to urethane anesthesia with the administration of TRH and PGE1 in the GH secretory mechanism. In addition, the fact that no further potentiation of GH release was observed by CPZ treatment may indicate an abnormality of the hypothalamic dopaminergic mechanism in starved animals.