Effect of Starvation on Hypothalamic Content of “Somatotropin Releasing Factor” and Pituitary Growth Hormone Content12

Abstract

The effects of acute starvation on hypothalamic content of "somatotropin releasing factor" (SRF) and on pituitary growth hormone content were studied in rats. After complete food removal for 5-7 days or after ad lib. feeding, adult male donor rats were decapitated and their hypothalami were removed and extracted with cold 0.1 [image] HCl. The neutralized extract was injected into the left common carotid artery of adult male recipient rats and 30 min. later the rats were sacrificed and their pituitaries were removed. The pituitaries were assayed for somatotropin (STH) by the standard tibia test in young hypophysectomized rats. A log-dose relationship was demonstrated between the dose of hypothalamic extract injected and the amount of STH released by the recipient''s pituitary indicating that rat hypothalamic extract contains a factor which stimulates STH release. When the hypothalami of starved rats were compared with hypothalami of ad lib. fed controls in 2 separate experiments, it was found that starvation markedly reduced the hypothalamic content of SRF. The hypothalami of the ad lib. fed rats showed approximately 5 times as much capacity to release pituitary STH as the hypothalami of the starved rats. Starvation also reduced the pituitary content of STH by 40[long dash]50%. These results suggest that acute starvation in rats results in decreased synthesis and release of SRF by the hypo-thalamus, and this in turn results in depressed production and release of STH by the pituitary.