PROLACTIN IMPLANTS IN THE HYPOTHALAMUS INHIBIT PROLACTIN SURGES DURING PREGNANCY AND ALTER PROLACTIN-RELEASE IN RESPONSE TO DOPAMINE RECEPTOR BLOCKADE

The purpose of this study was to determine whether prolactin (PRL) could exert a negative feedback on it's own secretion during pregnancy and following ovariectomy, and to determine the possible mechanism by which this feedback acts. Implantation of ovine PRL into the arcuate nucleus-median eminence area of the hypothalamus completely inhibited the nocturnal PRL surge during pregnancy in the rat, and lowered baseline PRL to almost undetectable levels in the ovariectomized rat. When ovariectomized rats implanted with ovine PRL in the hypothalamus were injected with the dopamine receptor blocker domperidone the PRL response was significantly lower than in control rats implanted with albumin. Pregnancy increased the ability of domperidone to cause PRL release following ovine PRL implantation compared to what occurred in ovariectomized rats. These results suggest that PRL implantation increases the secretion of dopamine from the tuberoinfundibular neurons, resulting in a decrease in PRL secretion.