Interrelationships between the hypothalamus, pituitary gland, ovary, adrenal gland, and the open period for LH release in the hen (Gallus domesticus).

The asynchronous ovulatory cycle of the hen is believed to be the consequence of two interacting systems, one of which is circadian and regulates the timing of the preovulatory LH surge. In support of this proposition, the open period for LH release was shown to oscillate with the same periodicity as the photoschedule when the hens were exposed to 14 L:7 D, 14 L:10 D, and 14 L:14 D. In addition, it was demonstrated that follicular maturation is not affected by or synchronized with the photoperiod. The physiological system that transduces the light/dark cycle into an open period for LH release has not been identified although circumstantial evidence supports the idea that the adrenal gland plays a role in this function. This evidence includes the anatomical juxtaposition of the left ovary and adrenal gland, innervation of steroid-producing cells within the follicle by nerve tracts passing through the adrenal glands, the ability of injections of metyrapone to alter the timing of preovulatory LH release, the ability of injections of corticosterone to induce ovulation when a mature follicle is present in the ovary, and the ability of dexamethasone or infusions of corticosterone to block ovulation. Recently we have also shown that infusions of corticosterone will block the gonadotropic effect of PMSG, will inhibit the photoperiodic response, and do not affect the release of LH in response to injections of GnRH. The addition of corticosterone to incubations of dispersed granulosa cells does not affect their response to LH. These data suggest that corticosterone may modulate the responsiveness of the hypothalamus to tropic stimuli and demonstrate that exposure to corticosterone can alter the responsiveness of some ovarian tissues to gonadotropins.