Effect of Hypothalamic Implants of GH on Anterior Pituitary Weight and GH Concentration

Abstract

Hypothalamic implants of GH mixed with cholesterol produced a reduction in both absolute and relative weight of the anterior pituitary within 7 days of implantation on comparison with either normal or cholesterol-implanted controls. Similar implants of LH or prolactin failed to modify pituitary weight. The reduction in pituitary weight persisted for an additional 7 days and was associated with a reduction in pituitary GH concentration at 14 days as estimated by bioassay. Small decreases in body weight gain were apparent on comparison with cholesterol-implanted controls at 4–7 after implantation which indicate that endogenous plus exogenous GH release may have been reduced in the rats with GH implants. A dose-response relationship was evident between the dose of GH implanted and the reduction in pituitary weight. Implants of GH in a variety of hypothalamic loci were effective and a minimal effect was exerted by implants of the hormone in the cerebral cortex. It is concluded that GH acts centrally on the hypothalamo-pituitary region to inhibit its own secretion. (Endocrinology85: 725, 1969)