Effects of Suckling on Hypothalamic LH-Releasing Factor and Prolactin Inhibiting Factor, and on Pituitary LH and Prolactin

Abstract

The effects of suckling on the hypothalamic content of luteinizing hormone-releasing factor (LRF) and on prolactin inhibiting factor (PIF), and on pituitary concentration of LH and pro-lactin were studied in lactating rats. On postpartum day 18, lactating mother rats were killed by guillotine. Regular cycling rats of the same strain served as controls. Anterior pituitary halves incubated with hypothalamic extract from suckled rats released significantly less LH but more prolactin into the medium than the corresponding control pituitary halves incubated with hypothalamic extract from cycling rats. Pituitary LH concentration was significantly decreased and pituitary prolactin was significantly increased in the suclked rats when compared with the cycling controls. Suckling also signifi-cantly reduced pituitary, ovarian and uterine weights. These observa-tions indicate that the suckling acts on the hypothalamus to depress release of LRF and PIF, the former resulting in inhibition of pituitary LH release and the latter in increased prolactin release.