Ojeda S R, Negro-Vilar A
Endocrinology. 1985 May;116(5):1763-70. doi: 10.1210/endo-116-5-1763.
The present in vitro experiments were performed to examine the involvement of Ca+2 in the mechanism by which prostaglandin E2 (PGE2) induces LHRH release from the median eminence (ME) of the hypothalamus. Stepwise decreases in the Ca+2 concentration of the incubation medium reduced the LHRH response to PGE2. Nevertheless, neither complete omission of Ca+2 (residual Ca+2 concentration, 3.5 microM) nor chelation of residual Ca+2 with EGTA prevented the stimulatory effect of the PG, suggesting that a significant portion of the PGE2 effect on LHRH release is independent of extracellular Ca+2. Blockade of Ca+2 influx with verapamil, a Ca+2 entry blocker, demonstrated that this component of the PGE2 effect is completely independent of inward Ca+2 movement. Depletion of intraterminal Ca+2 stores by exposure of the MEs to the Ca+2 ionophore A23187 in medium without Ca+2 containing EGTA almost completely obliterated the subsequent LHRH response to PGE2, indicating that normal intraterminal Ca+2 levels are important for the PGE2 effect to occur. Preloading the ME terminals with 45Ca+2 and subsequent stimulation with PGE2 demonstrated that even in the absence of extracellular Ca+2, PGE2 stimulates Ca+2 efflux from the terminals, and this Ca+2 movement occurs temporarily associated with LHRH release. Depolarization of ME terminals with 56 mM K+ in the presence of normal Ca+2 concentration resulted in massive efflux of 45Ca+2 and a greater LHRH response than that produced by PGE2, suggesting that the effect of PGE2 is not the consequence of a nonspecific general depolarization of ME nerve terminals. Thus, although a full LHRH response to (exogenous) PGE2 necessitates normal extraterminal Ca+2 concentrations, the results indicate that translocation of Ca+2 from intracellular stores is an event involved in the mechanism by which PGE2 releases LHRH.
进行了目前的体外实验，以研究Ca+2在前列腺素E2（PGE2）诱导下丘脑正中隆起（ME）释放促性腺激素释放激素（LHRH）的机制中的作用。孵育培养基中Ca+2浓度的逐步降低减少了LHRH对PGE2的反应。然而，完全去除Ca+2（残余Ca+2浓度为3.5 microM）或用乙二醇双四乙酸（EGTA）螯合残余Ca+2均不能阻止前列腺素的刺激作用，这表明PGE2对LHRH释放的显著部分作用独立于细胞外Ca+2。用Ca+2通道阻滞剂维拉帕米阻断Ca+2内流表明，PGE2作用的这一组成部分完全独立于内向Ca+2移动。通过将ME暴露于不含Ca+2但含有EGTA的培养基中的Ca+2离子载体A23187来耗尽终末内Ca+2储存，几乎完全消除了随后LHRH对PGE2的反应，表明正常的终末内Ca+2水平对于PGE2作用的发生很重要。用45Ca+2预加载ME终末并随后用PGE2刺激表明，即使在没有细胞外Ca+2的情况下，PGE2也会刺激Ca+2从终末流出，并且这种Ca+2移动与LHRH释放暂时相关。在正常Ca+2浓度存在下用56 mM K+使ME终末去极化导致45Ca+2大量流出，并且LHRH反应比PGE2产生的反应更大，这表明PGE2的作用不是ME神经终末非特异性一般去极化的结果。因此，尽管对（外源性）PGE2的完整LHRH反应需要正常的终末外Ca+2浓度，但结果表明Ca+2从细胞内储存的转运是PGE2释放LHRH的机制中涉及的一个事件。
