Johnson M S, Mitchell R, Thomson F J
University Department of Pharmacology, Medical Research Council, Edinburgh, UK.
Mol Cell Endocrinol. 1992 Jun;85(3):183-93. doi: 10.1016/0303-7207(92)90257-7.
The priming effect of LHRH in vitro (which results in increased responsiveness of gonadotropes to both LHRH receptor-mediated and receptor-independent stimuli) is brought about by an unknown mechanism. The present results indicate that induction of the LHRH priming effect is inhibited in a concentration-dependent manner by the protein kinase C (PKC) inhibitors staurosporine, K252a, H7 and by the novel highly-selective PKC inhibitor, Ro 31-8220. In contrast, a range of other compounds that are relatively selective inhibitors of other kinases such as tyrosine kinases and Ca2+/calmodulin-dependent kinases were unable to prevent priming. The PKC inhibitors prevented priming without affecting initial LHRH-induced gonadotropin secretion. Thus, the priming-elicited increment in secretion was selectively removed, restoring hormone release to the level measured during an initial response to LHRH. Similar results were obtained on different days of the estrous cycle where the magnitude of the priming effect varies. Experiments on the time course of PKC inhibitor action revealed that the critical period was in the induction of the priming effect, not its expression. The PKC inhibitors had neither acute nor delayed effects on gonadotropin secretion induced by ionomycin. Staurosporine, K252a and Ro 31-8220 inhibited LHRH priming with identical potencies to their inhibition of phorbol ester-induced gonadotropin secretion. The reduced potency of H7 seen on LHRH priming compared to phorbol ester-induced gonadotropin release parallels results seen with this inhibitor on phorbol ester-induced secretion of growth hormone (Johnson and Mitchell (1989) Biochem. Soc. Trans. 17, 751-752) and on the pharmacological characteristics of PKCs partially purified from anterior pituitary tissue. In all aspects of this study, effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion appeared to be entirely similar.
促性腺激素释放激素（LHRH）的体外启动效应（导致促性腺细胞对LHRH受体介导和受体非依赖性刺激的反应性增加）是由一种未知机制引起的。目前的结果表明，蛋白激酶C（PKC）抑制剂星形孢菌素、K252a、H7以及新型高选择性PKC抑制剂Ro 31-8220以浓度依赖性方式抑制LHRH启动效应的诱导。相反，一系列相对选择性抑制其他激酶（如酪氨酸激酶和Ca2+/钙调蛋白依赖性激酶）的其他化合物无法阻止启动。PKC抑制剂在不影响初始LHRH诱导的促性腺激素分泌的情况下阻止启动。因此，启动引发的分泌增加被选择性消除，使激素释放恢复到对LHRH初始反应期间测量的水平。在发情周期的不同日子也获得了类似结果，其中启动效应的大小有所不同。关于PKC抑制剂作用时间进程的实验表明，关键时期在于启动效应的诱导，而非其表达。PKC抑制剂对离子霉素诱导的促性腺激素分泌既无急性影响也无延迟影响。星形孢菌素、K252a和Ro 31-8220抑制LHRH启动的效力与其抑制佛波酯诱导的促性腺激素分泌的效力相同。与佛波酯诱导的促性腺激素释放相比，H7对LHRH启动的效力降低，这与该抑制剂对佛波酯诱导的生长激素分泌的作用结果（Johnson和Mitchell（1989年）《生物化学学会会刊》17，751 - 752）以及从垂体前叶组织部分纯化的PKC的药理学特性相似。在本研究的所有方面，对促黄体生成素（LH）和促卵泡生成素（FSH）分泌的影响似乎完全相似。
