The hormonal activities associated with the cephalic and caudal regions of the cockerel pars distalis

Abstract

The regional distribution of tropic hormone activities in the avian pars distalis was studied by transplanting the cephalic, middle, and caudal regions of the pars distalis of day-old cockerels onto the chorioallantoic membrane of 10-day-old partially decapitated (“hypophysectomized”) embryos. Bioassay was based on body growth (assessed by body weights and third toe lengths) and the growth and histological maturation of the adrenal and thyroid glands and the gonads. The experimental design consisted of normal embryos, hypophysectomized embryos, hypophysectomized embryos with one cephalic region graft, hypophysectomized embryos with one middle region graft, and hypophysectomized embryos with one caudal region graft. All embryos were examined at the end of 20 days of incubation. Hypophysectomy severely retarded growth, vitelline, and chorioallantoic vascular shutdown, yolk sac retraction, feather, and skin development and normal maturation of endocrine target organs. All regions of the pars distalis may contain a grwothsustaining activity (STH? and/or prolactin?) capable of normalizing the length of the third toe in hypophysectomized embryos. The cells of each region apparently retained a normal histological appearance in the grafts. Probable ACTH, TSH, and FSH activities were exclusively associated with the cephalic region of the pars distalis whereas a presumed LH activity originated from the caudal region of the gland. A STH activity may occur throughout the gland but there was no indication of the presence or distribution of MSH or prolactin activities. The data indicate that the secretory repertoire of the pars distalis cells did not apparently change over a 10-day period; in the absence of the hypothalamus or even when the regions were isolated. This indicates that perhaps the hypothalamus in day-old cockerels is not important for the maintenance of the secretory integrity or regional differentiation of pars distalis cells. Apparently the cells of one region do not stimulate or inhibit the secretory differentiation of the other region.