Jain S K, Zelena D
Department of Zoology, Dr H.S. Gour University, India.
Endocr Regul. 2013 Apr;47(2):65-74. doi: 10.4149/endo_2013_02_65.
Although prolactin (PRL) plays an important role in the milk production, it has also many other functions. PRL secretion can be inhibited by dopamine and stimulated by serotonin, thyrotropin releasing hormone (TRH), and vasoactive intestinal peptide (VIP). However, the exact mechanisms of PRL regulation are still not fully understood. Glutamate is also a potent elevator of PRL secretion. It has several receptors: ionotropic NMDA (N-methyl-D-aspartate) and non-NMDA as well as metabotropic receptors. Our interest was to find out whether endogenous glutamate may act at the hypophyseal level and affect the PRL regulating neurotransmitters (dopamine, serotonin, TRH, VIP).
MK-801 as NMDA blocker and GYKI52466 as a non-NMDA antagonist were used in this study. For dopamine and serotonin experiments intraperitoneal drug administration and blood sampling were applied. On the other hand, TRH and VIP effect on PRL secretion was studied in in vitro conditions by incubating them with a half 300*300nm choppered anterior pituitary gland of the adult male rats.
The basal PRL levels were not influenced by the glutamate antagonists used either alone or combined in both in vivo and in vitro conditions. We failed to reveal interaction between dopamine-, serotonin-, and TRH-induced PRL rise and antagonists treatment. MK-801 had a significant inhibitory effect on VIP-induced PRL changes.
Our data confirmed the regulatory role of dopamine, serotonin, and TRH on PRL secretion, however, the interaction between these and glutamatergic systems was not confirmed, at least not via the ionotropic receptors. On the other hand, the endogenous glutamate can through the NMDA receptor subtype contribute to the VIP-induced PRL secretion at the level of the anterior pituitary. This regulation may be especially important during suckling and stress response when rapid release of PRL is required.
尽管催乳素（PRL）在乳汁分泌中起重要作用，但它还有许多其他功能。多巴胺可抑制PRL分泌，而血清素、促甲状腺激素释放激素（TRH）和血管活性肠肽（VIP）则可刺激其分泌。然而，PRL调节的确切机制仍未完全明确。谷氨酸也是PRL分泌的有力促进剂。它有几种受体：离子型N-甲基-D-天冬氨酸（NMDA）受体和非NMDA受体以及代谢型受体。我们感兴趣的是，内源性谷氨酸是否可能在垂体水平起作用，并影响调节PRL的神经递质（多巴胺、血清素、TRH、VIP）。
本研究使用MK-801作为NMDA阻滞剂，GYKI52466作为非NMDA拮抗剂。在多巴胺和血清素实验中，采用腹腔内给药和采血。另一方面，通过将TRH和VIP与成年雄性大鼠的半块300*300nm切碎的垂体前叶一起孵育，在体外条件下研究它们对PRL分泌的影响。
在体内和体外条件下，单独或联合使用谷氨酸拮抗剂均未影响基础PRL水平。我们未能发现多巴胺、血清素和TRH诱导的PRL升高与拮抗剂治疗之间的相互作用。MK-801对VIP诱导的PRL变化有显著抑制作用。
我们的数据证实了多巴胺、血清素和TRH对PRL分泌的调节作用，然而，这些与谷氨酸能系统之间的相互作用未得到证实，至少不是通过离子型受体。另一方面，内源性谷氨酸可通过NMDA受体亚型在前叶垂体水平促进VIP诱导的PRL分泌。在需要快速释放PRL的哺乳和应激反应期间，这种调节可能尤为重要。
