Hypothalamo-adenohypophyseal-thyroid and gonadal interrelationships in the chick embryo: I. Differential effect of ectopic pituitary grafts on plasma total T 4 and testosterone levels

Abstract

Plasma total thyroxine (T 4) and testosterone concentrations of Day 15.5 intact, surgically partially decapitated (hypothalamo-hypophyseoprivic) and partially decapitated chick embryos with adenohypophyseal transplants were determined by radioimmunoassay of the same plasma sample. Decapitation in both male and female chick embryos at 33–38 h of incubation results in plasma thyroxine and testosterone levels which are statistically significantly lower than those of intact embryos. The addition of a single adenohypophyseal transplant to the chorioallantoic membrane (CAM) of male and female decapitated embryos only partially restores plasma thyroxine levels to intact levels. However, the same procedure results in plasma testosterone levels which are higher than those of both decapitated and intact individuals. The data suggest that in the developing chick embryo there are differences in dependence of the thyroid and the gonads upon a functional hypothalamo-adenohypophyseal unit. The possible differential regulatory effects of the hypothalamus on the adenohypophyseal-thyroid and adenohypophyseal-gonadal components of the hypothalamic-adenohypophyseal-thyroid and hypothalamic-adenohypophyseal-gonadal axes are discussed.