Effect of [ d-Trp 6]LHRH infusion on prolactin secretion by perifused rat pituitary cells

Abstract

The effect of a superactive agonistic analog of luteinizing hormone-releasing hormone (LHRH), [ d-Trp 6]LHRH on prolactin (PRL) secretion by perifused rat pituitary cells was investigated. Constant infusion of [ d-Trp 6]LHRH (0.5 ng/min) for 2–3 h elicited a significant decrease in PRL secretion by these cells. This decrease in PRL release started ca. 30 min after the beginning of the infusion with the LHRH analog and lasted up to 1.5–2 h. [ d-Trp 6]LHRH significantly stimulated luteinizing hormone (LH) secretion during the first 30 min of peptide infusion; thereafter, LH levels began to return to control values. In animals pretreated in vivo with 50 μg of [ d-Trp 6]LHRH (s.c.) 1 h before sacrifice, PRL secretion by the rat pituitary cell perifusion system was significantly lower than vehicle-injected controls throughout the entire [ d-Trp 6]LHRH infusion period. On the other hand, thyrotropin-releasing hormone (TRH)-stimulated PRL secretion was slightly, but significantly impaired by [ d-Trp 6]LHRH infusion, while dopamine (DA) inhibition of PRL release was unaffected by this same treatment. These results reinforce previous observations of a modulatory effect of [ d-Trp 6]LHRH, probably mediated by pituitary gonadotrophs, on PRL secretion by the anterior pituitary. In addition, our findings suggest that basal PRL secretion by the lactotroph may be dependent on a normal function of the gonadotroph. The collected data from this and previous reports support the existence of a functional link between gonadotrophs and lactotrophs in the rat pituitary gland.