Verburg-van Kemenade B M, Jenks B G, Visser T J, Tonon M C, Vaudry H
Peptides. 1987 Jan-Feb;8(1):69-76. doi: 10.1016/0196-9781(87)90167-7.
This study considers the possible involvement of the tripeptide TRH (thyrotropin releasing hormone) in the physiological regulation of melanophore stimulating hormone (MSH) secretion from the pars intermedia of the toad, Xenopus laevis. TRH was shown to stimulate release of MSH from superfused neurointermediate lobes obtained from white-background adapted animals, but had no effect on secretion from lobes of black-background adapted animals. Immunohistochemical analysis revealed a rich TRH-containing neuronal network terminating in the neural lobe of the Xenopus pituitary. Plasma levels of TRH, determined with a specific radioimmunoassay, proved to be extremely high and no significant difference in this level could be found between white- and black-adapted animals. Plasma TRH probably originates from the skin, and our results show that its concentration is within the effective concentration range established for this peptide in stimulating MSH release from the pars intermedia. Therefore, while both our superfusion and immunohistochemical results argue favourably for a function of TRH in the regulation of MSH secretion, we conclude that, in any regulatory role, it would likely have to function within the pars intermedia at concentrations exceeding the high plasma values. While TRH could be involved in short-term activation of the secretory process in white-background adapted animals or in animals undergoing the initial stages of black background adaptation, our results indicate that this peptide may have no function in the maintenance of secretion from the pars intermedia of animals fully adapted to black background.
本研究探讨了三肽促甲状腺激素释放激素（TRH）可能参与蟾蜍非洲爪蟾中间叶促黑素（MSH）分泌的生理调节过程。研究表明，TRH能刺激从适应白色背景的动物获取的经体外灌流的神经中间叶释放MSH，但对适应黑色背景的动物的叶分泌无影响。免疫组织化学分析显示，非洲爪蟾垂体神经叶中有丰富的含TRH神经元网络。用特异性放射免疫测定法测定的血浆TRH水平极高，在适应白色和黑色背景的动物之间未发现该水平有显著差异。血浆TRH可能起源于皮肤，我们的结果表明其浓度处于该肽刺激中间叶释放MSH的有效浓度范围内。因此，虽然我们的灌流和免疫组织化学结果都有力地支持TRH在调节MSH分泌中起作用，但我们得出结论，在任何调节作用中，它可能必须在中间叶内以超过高血浆值的浓度发挥作用。虽然TRH可能参与适应白色背景的动物或处于黑色背景适应初始阶段的动物分泌过程的短期激活，但我们的结果表明，该肽可能对完全适应黑色背景的动物中间叶的分泌维持没有作用。
