Burns G, Almeida O F, Passarelli F, Herz A
Department of Neuropharmacology, Max Planck Institute for Psychiatry, Planegg/Martinsried, Federal Republic of Germany.
Endocrinology. 1989 Sep;125(3):1365-72. doi: 10.1210/endo-125-3-1365.
It is well established that in the pituitary gland corticotropin-releasing hormone (CRH) stimulates the release of beta-endorphin (beta-E) via a cAMP-linked mechanism. Studies of the mechanisms underlying the CRH stimulation of beta-E release from rat hypothalamic slices perifused in vitro are reported in this paper. The data indicate that both a cAMP-dependent and non-cAMP-dependent mechanism mediate the action of CRH in the hypothalamus. The presence of a cAMP-linked mechanism was suggested by the finding that cholera toxin (0.1-10 nM) and forskolin (2.5 x 10(-6) M), both of which act to raise intracellular cAMP levels, stimulated the release of beta-E. In both cases, no further stimulation was seen upon addition of CRH (10(-8)M). However, it was also found that preincubation of the tissue with pertussis toxin (PTX; 100 ng/ml) prevented both the CRH- and forskolin-stimulated release of beta-E. This indicated that, in addition to the cAMP-linked mechanism, a further messenger system which is connected to a PTX-sensitive G-protein may also play a role. The latter observation also implied that a further substance, which utilizes a separate second messenger system, might be involved in the CRH stimulation of beta-E release. In this regard the role of arginine vasopressin (AVP) was investigated due to the known interaction between CRH and AVP in the pituitary gland. AVP (10(-12) to 10(-6)M) itself potently and dose-dependently stimulated beta-E release, producing a maximal increase of 220% above basal levels. The AVP-induced release of beta-E was abolished in PTX-pretreated hypothalami. The apparently obligatory requirement of AVP for the CRH-stimulation of beta-E release was illustrated by the finding that blockade of AVP receptors using the AVP antagonist d(CH2)5 [Tyr(OEt)2,Val4]-AVP almost completely attenuated the CRH-stimulated release of beta-E. Furthermore, in the presence of a high concentration of AVP (10(-6)M) no further stimulation of release was seen with CRH (10(-8)M). These data therefore strongly indicate that CRH acts via the intermediacy of AVP to release beta-E from hypothalamic slices in vitro and that two separate second messenger systems are involved: a cAMP-linked mechanism connected to a cholera toxin-sensitive G-protein (CRH) and a second system linked to a PTX-sensitive G-protein (AVP).
垂体中促肾上腺皮质激素释放激素（CRH）通过一种与环磷酸腺苷（cAMP）相关的机制刺激β-内啡肽（β-E）释放，这一点已得到充分证实。本文报道了对体外灌流的大鼠下丘脑切片中CRH刺激β-E释放的潜在机制的研究。数据表明，cAMP依赖性和非cAMP依赖性机制均介导了CRH在下丘脑中的作用。霍乱毒素（0.1 - 10 nM）和福斯高林（2.5×10⁻⁶ M）均可提高细胞内cAMP水平，二者均刺激了β-E的释放，这一发现提示存在与cAMP相关的机制。在这两种情况下，加入CRH（10⁻⁸ M）后未见进一步刺激。然而，还发现用百日咳毒素（PTX；100 ng/ml）预处理组织可阻止CRH和福斯高林刺激的β-E释放。这表明，除了与cAMP相关的机制外，另一种与对PTX敏感的G蛋白相连的信使系统可能也发挥作用。后一观察结果还暗示，另一种利用独立第二信使系统的物质可能参与了CRH对β-E释放的刺激。鉴于CRH与抗利尿激素（AVP）在垂体中的已知相互作用，本文研究了AVP的作用。AVP（10⁻¹²至10⁻⁶ M）本身能有效且剂量依赖性地刺激β-E释放，使释放量比基础水平最大增加220%。在经PTX预处理的下丘脑中，AVP诱导的β-E释放被消除。使用AVP拮抗剂d(CH2)5 [Tyr(OEt)2,Val4]-AVP阻断AVP受体几乎完全减弱了CRH刺激的β-E释放，这一发现说明了AVP对CRH刺激β-E释放的明显必要性。此外，在高浓度AVP（10⁻⁶ M）存在的情况下，加入CRH（10⁻⁸ M）未见释放进一步增加。因此，这些数据有力地表明，CRH通过AVP的介导作用使体外下丘脑切片释放β-E，且涉及两个独立的第二信使系统：一个与对霍乱毒素敏感的G蛋白相连的cAMP相关机制（CRH）和另一个与对PTX敏感的G蛋白相连的系统（AVP）。
