ABSTRACT
To investigate where oestrogens act to induce an increase in the tonic release of prolactin, the effect of ovariectomy alone or of ovariectomy plus oestradiol benzoate treatment (10 μg/day for 7 days) (OeB10) on the morning prolactin serum level in adult female rats was determined after each of the following procedures: frontal hypothalamic deafferentation (FHD) (a semi-lunar cut at the caudal border of the optic chiasma, separating the anterior hypothalamus from the preoptic area); medial hypothalamic deafferentation (MHD) (a similar cut, but separating the anterior from the posterior half of the hypothalamus); sham deafferentation; an electrolytic lesion of the arcuate-median eminence area (Arcuate-ME lesion); hypophysectomy and pituitary autotransplantation beneath the kidney capsule. The rats were ovariectomized 1 week after the latter procedure, or 3 weeks after the others, and OeB10 or oil vehicle treatment was begun one week after ovariectomy.
FHD, the Arcuate-ME lesion and pituitary autotransplantation markedly increased the basal prolactin level; MHD induced a much smaller increase. The level fell after ovariectomy only in the FHD group. A sharp and equal increase in the prolactin level occurred in the FHD, MHD and sham operation groups in response to OeB10; a much smaller and more variable increase occurred in the Arcuate-ME and pituitary autotransplantation groups.
The results suggest that oestrogens increase the tonic release of prolactin only in part by a direct action on the pituitary, and more importantly by acting on the posterior half of the hypothalamus or on areas with lateral, superior, or posterior afferent connections to this site.