Control of pituitary FSH synthesis by hypothalamic factors in rats.

Electrolytic lesions placed in the median eminence of adult male rats are followed, in 7--10 days, by a significant decrease in pituitary FSH concentration. The intravenous injection of a hypothalamic extract prepared from normal animals induces, in 45 minutes, a significant increase in the amounts of FSH stored in the pituitary of median eminence-lesioned animals. The concentration of FSH in the pituitary of lesioned animals is also increased to normal by the intravenous injection of an extract prepared from the isolated hypothalamic island of animals previously submitted to a total "hypothalamic deafferentation", in spite of the fact that this does not contain any FSH-RF activity. It is suggested that the hypothalamus possesses separate humoral factors for the regulation of the release and of the synthesis of pituitary FSH.