Zheng T, Villalobos C, Nusser K D, Gettys T W, Faught W J, Castaño J P, Frawley L S
Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston 29425, USA.
Am J Physiol. 1997 Feb;272(2 Pt 1):E282-7. doi: 10.1152/ajpendo.1997.272.2.E282.
It is clear that alpha-melanocyte-stimulating hormone (alpha-MSH), released by the hypophysial neurointermediate lobe, is a mediator of suckling-induced prolactin release, but several questions surrounding its role remain unresolved. Accordingly, the objectives of the present study were 1) to establish whether alpha-MSH could bind in a reversible manner to a specific secretory type cell within the adenohypophysis (AP), 2) to resolve the issue of whether the peptide could compete with dopamine for the same receptor binding site, and 3) to seek a functional signaling correlate for alpha-MSH binding. In pursuit of these objectives, we subjected pituitary cells from lactating rats to alpha-MSH receptor autoradiography, AP hormone immunocytochemistry, or digital imaging fluorescence microscopy with fura 2 as a calcium-sensitive probe. Our results show that alpha-MSH binding is restricted to mammotropes and that a specific subpopulation of these express functional alpha-MSH receptors that are coupled to a Ca2+ signaling pathway. Moreover, alpha-MSH does not compete with dopamine antagonists/agonists for the same binding site.
显然，由垂体神经中间叶释放的α-黑素细胞刺激素（α-MSH）是哺乳诱导催乳素释放的介质，但围绕其作用的几个问题仍未解决。因此，本研究的目的是：1）确定α-MSH是否能以可逆方式与腺垂体（AP）内特定的分泌型细胞结合；2）解决该肽是否能与多巴胺竞争同一受体结合位点的问题；3）寻找α-MSH结合的功能性信号相关物。为实现这些目标，我们对哺乳期大鼠的垂体细胞进行了α-MSH受体放射自显影、AP激素免疫细胞化学或使用fura 2作为钙敏感探针的数字成像荧光显微镜检查。我们的结果表明，α-MSH结合仅限于促乳腺细胞，并且这些细胞中的特定亚群表达与Ca2+信号通路偶联的功能性α-MSH受体。此外，α-MSH不与多巴胺拮抗剂/激动剂竞争同一结合位点。
