Apfelbaum M E
Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
Neuroendocrinology. 1998 Jan;67(1):45-50. doi: 10.1159/000054297.
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.
我们之前已经证明，5-羟色胺（5-HT）不仅能刺激基础催乳素（PRL）释放，还能通过直接作用于垂体水平来刺激促甲状腺激素释放激素（TRH）诱导的PRL释放。在本报告中，我们研究了血管活性肠肽（VIP）的自分泌作用在5-HT刺激效应中的参与情况，以及5-HT2受体亚型在介导血清素诱导的PRL释放中的作用。将来自成年去卵巢大鼠的培养垂体前叶细胞在1毫升添加了T3的培养基中孵育1小时，培养基中添加或不添加测试物质。在存在T3的情况下获得的结果证实了我们之前的观察结果，因为用5-HT处理细胞会导致基础PRL释放呈剂量依赖性增加，其近似半数有效浓度（EC50）为3.68×10⁻⁸ M，并导致TRH诱导的PRL释放显著增强（1.3倍）。为了评估血管活性肠肽（VIP）作为5-HT对PRL释放影响的介质的可能参与情况，细胞在单独存在5-HT（3 - 1000 nM）或100 nM 5-HT加30 nM TRH的情况下孵育，同时添加或不添加200 nM VIP拮抗剂（VIP-At）：[D,4-Cl-Ph6,Leu17]VIP。VIP-At部分抑制了5-HT诱导的PRL释放，包括基础释放和TRH刺激的释放。然而，5-HT的刺激作用并未被VIP-At消除，因为对5-HT作出反应而释放的PRL仍高于各自的对照值。这些结果进一步支持了以下发现，即5-HT通过刺激PRL释放直接作用于垂体水平。在孵育培养基中添加5-HT2受体拮抗剂酮色林（1 μM）导致细胞对5-HT的反应性丧失，不仅阻止了5-HT对基础PRL释放的刺激作用，也阻止了其对TRH诱导的PRL释放的刺激作用。总之，这些结果进一步增强了以下可能性，即5-HT通过直接作用于催乳细胞水平来增加基础PRL释放并增强TRH的刺激作用。这些效应并非简单地是VIP自分泌作用的结果。此外，研究表明酮色林完全拮抗PRL对5-HT的反应，表明5-HT2受体亚型参与介导PRL释放。
