Releasing Factors and LH in the Plasma of Intact and Hypophysectomized Chickens

Abstract

One of the more interesting problems of reproductive endocrinology lies in the mechanism of control of the ovulatory cycle of birds. An indeterminate layer like the domestic hen must have a mechanism which assures her that not more than one ovum is matured and ovulated on each successive day while the polytocous mammal must be able to mature groups of eggs at genetically predetermined intervals which are then ready for simultaneous ovulation. The daily ovulation of a single ovum clearly calls for a hypothalamo-hypophysial control mechanism which is distinctly different from the one which must prevent such an event and assure a much wider chronological spacing between single or multiple ovulations. It is now clear that in mammals a neurohumoral hypothalamo-hypophysial feed-back system operates in controlling the long interval ovulatory sequences. In the chicken it appears probable but not yet certain that a hypothalamic releasing factor system exists similar to the one in mammals. It is also well established that in mammals the gonadal steroids form an important link in the hypothalamo-hypophysial-gonadal (HHG) feed-back system. In some mammals, such as the reflex ovulators, a neural component also participates in the HHG system.