Role of vasoactive intestinal peptide and 5-HT2 receptor subtype in serotonin stimulation of basal and thyrotropin-releasing-hormone-induced prolactin release in vitro from rat pituitary cells.
We have previously demonstrated that 5-HT stimulates not only basal but also thyrotropin-releasing-hormone (TRH)-induced prolactin (PRL) release by acting directly at the pituitary gland level. In the present report, the participation of an autoparacrine action of VIP in the stimulatory effects of 5-HT and the involvement of the 5-HT2 receptor type in mediating serotonin-induced PRL release have been examined. Cultured anterior pituitary cells from ovariectomized adult rats were incubated for 1 h in 1 ml of T3-supplemented medium with or without the test substances. The results obtained in the presence of T3 confirm our previous observations, since treatment of the cells with 5-HT caused dose-dependent increases in basal PRL release, with an approximate EC50 of 3.68 x 10(-8) M, and led to a significant potentiation (1.3-fold) of the TRH-induced PRL release. In order to evaluate the possible participation of vasoactive intestinal peptide (VIP) as mediator of the effects of 5-HT on PRL release, cells were incubated in the presence of 5-HT alone (3-1,000 nM) or 100 nM 5-HT plus 30 nM TRH, with or without 200 nM VIP antagonist (VIP-At): [D,4-Cl-Ph6,Leu17]VIP. VIP-At partially inhibited the release of PRL induced by 5-HT, both basal and TRH-stimulated release. The stimulatory effect of 5-HT, however, was not eliminated by VIP-At, since the PRL released in response to 5-HT was still over the respective control ones. These results further support the findings suggesting that 5-HT acts directly at pituitary level by stimulating PRL release. Addition of the 5-HT2 receptor antagonist, ketanserin (1 microM) into the incubation medium resulted in the loss of cellular responsiveness to 5-HT, preventing not only the stimulatory effect of 5-HT on the basal but also on the TRH-induced PRL release. In conclusion, the results further strengthen the possibility that 5-HT increases the basal PRL release and potentiates the stimulatory effect of TRH by acting directly at the level of the lactotropes. These effects are not simply a consequence of autoparacrine action of VIP. In addition, it was shown that ketanserin completely antagonizes PRL response to 5-HT, indicating the involvement of the 5-HT2 receptor type in mediating PRL release.
Apfelbaum
M E
ME
Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D007650:Ketanserin / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013268:Stimulation, Chemical; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014660:Vasoactive Intestinal Peptide / Q000502:physiology*
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; D014660:Vasoactive Intestinal Peptide; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D007650:Ketanserin