Pituitary GH and Hypothalamic GHRF After Median Eminence Implantation of Ovine or Human GH

The effects of implanting human or ovine GH in the median eminence were measured on pituitary GH concentration, hypothalamic content of growth hormone releasing factor (GHRF) and serum prolactin activity. Adult female rats implanted with human or ovine GH showed a significant decrease in pituitary GH concentration and in hypothalamic GHRF content when compared with controls 7 days after implantation. Pituitary weights were also decreased in GH implanted rats. There were no significant changes in body weight or ovarian or uterine weights. Rats implanted with human GH showed decreased serum prolactin and atrophy of the mammary glands when compared with pre-implantation levels or controls implanted with cocoa butter. These results suggest that human and ovine GH act via the hypothalamus to decrease pituitary GH concentration. They also indicate that human GH, like prolactin from other species, can decrease serum prolactin levels and induce mammary gland regression when implanted in the median eminence of rat...