Biology of Reproduction, Vol 6, 258-263, Copyright © 1972 by Society for the Study of Reproduction

Reduction of Plasma Progesterone Levels in Pituitary-Autografted Rats Following Treatment with Hypothalamic Extract

¹ Department of Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45219

Subcutaneous administration of crude hypothalamic extract from 15 to 30 days after autotransplantation of the pituitary to the kidney capsule reduced the concentration of plasma progesterone but had no significant effect on 20-hydroxypregn-4-en-3-one levels. A similar regimen of cerebral cortical extract given to pituitary-autografted rats had no effect on the plasma concentration of either progestin. The decreased progesterone titer following treatment with hypothalamic extract was not accompanied by structural luteolysis of corpora lutea. Also, plasma prolactin levels were not reduced and plasma LH was not elevated following the chronic administration of hypothalamic extract. Dialysis of hypothalamic extract did not remove the material which lowered plasma progesterone indicating that the active substance was larger than hypothalamic hypophysiotrophic hormones. These results suggest that material present in crude hypothalamic extract acts directly at the ovarian level to inhibit progesterone Secretion.