Prolactin releasing action of the hypothalamic extract in last stage of pregnant rats (author's transl)

Abstract

Regulation of prolactin secretion in pituitary is considered to be mostly carried with the action of prolactin inhibiting factor in hypothalamus. We have investigated on the subject of prolactin releasing factor in the hypothalamus of rats in last stage of pregnancy using puerperal and ovariectomized rats as recipients. After prepared the cell-free system of pregnant rat hypothalamus with sonic oscillator, supernatant was produced by ultracentrifuge (25,000 X g, 30 min.) and utilized for the experiments. When the extract was injected intramuscularly to puerperal rats (48-60 hours after delivery), serum prolactin values increased gradually to 3 times of control values, but pituitary prolactin values showed the variation with decrease and recovery. The control values were obtained by determination after injection of cerebral cortical extract to puerperal rats. After administration of a extract of non-pregnant rat hypothalamus to puerperal rats, serum prolactin values decreased and pituitary prolactin values increased antagonistically. In the ovariectomized rats pretreated with estradiol and progesterone, serum prolactin values increased in 1 hour after administration of the extract of pregnant rat hypothalamus, but pituitary prolactin values did not show any variation. The present experiment suggests that the prolactin secretion promoting factor exists in the hypothalamus of pregnant rats and predominates over as compared with PIF in last stage of pregnancy.