The regulatory mechanism of endothelin on the secretion of the pituitary horones

1. (1)采用免疫组织化学方法研究了内皮素-3 （ET3）样免疫反应性在牛蛙垂体组织中的分布。et3免疫反应细胞（ET3-ir）与LH和FSH免疫反应细胞相对应。在男性垂体中，仅观察到少量ET3-ir细胞。(2)胶体金免疫电镜分析显示，在同一分泌颗粒内存在et3样物质和促性腺激素。这些结果提示ET3可能作为一种自分泌和/或旁分泌激素参与调节垂体功能。以大鼠ET B受体（ET_B受体）的425-439氨基酸残基为靶点，制备抗血清。在大鼠正中隆起和血管终板中可见大量ET_B受体免疫反应纤维。抗黄体生成素释放激素（LHRH）抗血清双标记研究显示，ET_B受体样免疫反应性与LHRH免疫反应纤维在这些区域相关。然而，在lhrh免疫反应体中未检测到ET_B受体样免疫反应性。这一结果表明，ET通过末端场轴突上的ET_B受体影响LHRH神经元系统。研究ET-1对大鼠离体神经叶抗利尿激素（VP）释放的影响。此外，血管紧张素II （ANG II）的作用也被研究，因为它与ET-1和VP在轴突末端的相同分泌颗粒中共定位。ET-1诱导VP释放增加，随后在其退出后下降到基础水平。ANGⅱ也能刺激VP的释放。这些结果强烈提示ET-1和ANG II直接作用于神经叶，刺激VP的释放。然而，这些肽的作用位点尚不清楚。

1. (1) The distribution of endothelin-3 (ET3)-like immunoreactivity in the bullfrog pituitary was investigated immunohistochemically. ET3-immunoreactive (ET3-ir) cells were found to correspond to cells showing LH- and FSH -immunoreactivities. In the male pituitary, only a few ET3-ir cells were observed. (2) Immuno-electron microscopic analysis using colloidal gold revealed the co-existence of ET3-like substance (s) and gonadotropins within the same secretory granules. These results suggest the possible participation of ET3 in regulating pituitary function as an autocrine and/or paractrine hormone.2. Antisera were raised against amino-acid residues 425-439 of the rat ET B receptor (ET_B receptor). Massive ET_B receptor immunoreactive fibers were observed in the median eminence and organum vasculosum lamina terminalis of rats. Double labeling studies with antiluteinzing hormone-releasing hormone (LHRH) antiserum revealed that ET_B receptor-like immunoreactivity associated with LHRH-immunoreactive fibers in these areas. However, ET_B receptor-like immunoreactivity was not detected in LHRH-immunoreactive somata. This result suggests that ET affects the LHRH neuronal systems via ET_B receptors on the axon at the terminal field.3. Effects of ET-1 on the release of vasopressin (VP) from the isolated neural lobe of the rat were investigated. In addition, effects of angiotensin II (ANG II) were also investigated, because it colocalizes with ET-1 and VP in the same secretory granules in the axon terminals. ET-1 induced an increase in VP release, followed by a decline to basal levels upon its withdrawal. The VP release was also stimulated by ANG II.These results strongly suggest that ET-1 and ANG II act directly on the neural lobe to stimulate the release of VP.However, the sites of action of these peptides are not clear.