Temporal Synergism of Prolactin and Adrenal Steroids in the Regulation of Fat Stores

Abstract

SummaryDaily variations in fattening responses to prolactin may be phased or driven by injections of adrenal steroids in a fish, Fundulus grandis, a lizard, Anolis carolinensis, and a pigeon, Columba livia. Daily injections of prolactin about 24 hr after injections of adrenocortical hormones favor the accumulation of fat stores; whereas daily injections of prolactin 6 hr after the adrenal steroids cause losses in fat. An experiment on the fish indicated that the rhythm of fat responsiveness to prolactin is capable of self-sustaining circadian oscillations on continuous light following initial synchronization by exogenous hydrocortisone. An experiment on the pigeon indicated that a daily rhythm of cropsac sensitivity to prolactin may also be driven by daily injections of corticosterone, but the temporal pattern of the adrenal steroid and prolactin that favors cropsac proliferation is not in the same phase relations with those that favor accumulation of body fat, liver fat, and increases in intestinal weight. It is concluded that a temporal synergism of prolactin and the adrenal steroids is an important organizational unit in the vertebrate system.