Different mechanisms controlling FSH and LH release in Japanese quail (Coturnix coturnix japonica): evidence for an inherently spontaneous release and production of FSH.

Plasma concentration of FSH and LH and their content in the adenohypophyses of Japanese quail were estimated by homologous radioimmunoassays based on chicken hormones. The results consistently showed that the plasma concentration of FSH was slightly higher than that of LH, although the FSH content in the adenohypophysis was much lower than that of LH in immature, mature and acutely photostimulated quail. These results prompted experiments in vitro to determine whether the difference was intrinsic. Adenohypophyses were collected and each cut mid-sagittally into two halves; one half was incubated for 20 h with or without chicken hypothalamic extract, and the medium was changed every 1 or 2 h to estimate the FSH and LH released. The other half served to estimate the initial content of FSH and LH in the adenohypophysis. The amount of FSH released was three times more than the original content even when adenohypophyses were incubated without hypothalamic extract, and the residual FSH content in the pituitary after 20 h of incubation was equal to the initial FSH content. In contrast, under the same incubation conditions, little LH was released and the residual LH content was decreased. When hypothalamic extract was added to the medium, LH release was enhanced sixfold compared with the control, whereas the increase in FSH was less than twofold. Spontaneous FSH release was markedly decreased in a Ca2+-deficient incubation medium, suggesting that the release was not due to leakage but to an active secretion mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)