Functional study for physiological role of 5-hydroxytryptamine7 receptors in porcine myometrium

5-羟色胺(5-羟色胺)抑制猪子宫纵肌和环肌的自发收缩，但环肌对5-羟色胺的抑制作用比环肌敏感。本实验旨在阐明5-羟色胺受体亚型对5-羟色胺的抑制作用、抑制的亚细胞机制以及5-羟色胺受体亚型对肌层依赖性抑制的机制：根据5-羟色胺受体激动剂(5-carboxamidotryptamine&gt；5-HT&gt；5-methoxytryptamine&gt；的排列顺序8-羟基-2-(二正丙氨基)四氢呋喃和5-羟色胺受体拮抗剂(methiothepin&gt；methysergide&gt；metergoline&gt；mianserin&gt；clozapine&gt；spiperone)，证实了5-HT7受体介导了5-羟色胺抑制子宫肌层收缩的作用。抑制机制：对5-羟色胺诱导的抑制作用的分析表明，猪子宫肌层中发生了以下一系列事件：5-HT7受体激活、→激活、Gs的→激活、腺苷环化酶→的激活、cAMP中→的增加、[Ca^&lt；…]的降低更多的2+和2+-敏感性的收缩元件→抑制肌肉收缩。5-HT7受体分布：光层和CM层只有一类具有相似Kd值的5-氨基色胺结合部位。分子研究(逆转录-聚合酶链式反应)显示，5-HT7受体mRNA在CM和LM中的表达均高于LM。5-羟色胺增加了两个肌层中cAMP的含量，但CM的增加幅度高于LM。因此，5-羟色胺对心肌收缩的不同抑制作用是由于5-HT7受体的肌层依赖性分布(CM&GT；LM)引起的。5-HT7受体的这种异质性分布是非常独特的，不同于猪子宫中存在的其他受体(M_3受体、组胺H_1受体、内皮素A受体、β和α2-肾上腺素受体，LM和GT；CM)。肌层依赖性抑制：5-HT_7和β_2-肾上腺素受体介导的通路是猪子宫肌层的主要抑制机制，并以平滑肌层依赖的方式参与收缩抑制(LM：β_2-肾上腺素受体，CM：5-HT_7受体)。5-羟色胺和异丙肾上腺素的反应因区域不同而不同，可能与5-羟色胺受体的优势亚型和β_2-肾上腺素受体密度的不同有关。生物活性多肽和一氧化氮在猪子宫收缩调节中没有明显的生理作用(作为抑制剂)。较少

5-Hydroxytryptamine (5-HT) inhibits the spontaneous contraction in longitudinal (LM) and circular muscles (CM) of the porcine uterus but CM is more sensitive to 5-HT than LM.The present experiments were designed to clarify the 5-HT receptor subtype mediating the inhibition, subcellular mechanisms of the inhibition and mechanisms underlying the muscle layer-dependent inhibition by 5-HTReceptor subtype : On the basis of ranking order of 5-HT receptor agonists (5-carboxamidotryptamine>5-HT>5-methoxytryptamine>8-hydroxy-2-(di-n-propylamino) tetralin) and 5-HT receptor antagonists (methiothepin>methysergide>metergoline>mianserin>clozapine>spiperone), it was demonstrated that the 5-HT_7 receptor mediated the inhibition of myometrial contractility by 5-HT.Inhibitory mechanism : Analysis of the 5-HT-induced inhibition suggested a following cascade of events in the porcine myometrium : 5-HT_7 receptor activation→activation of Gs→activation of adenylate cyclase→increase in cAMP→decrease in [Ca^< … More 2+>]i and Ca^<2+>-sensitivity of the contractile elements→inhibition of muscle contractility.5-HT_7receptor distribution : LM and CM layers contained a single class of [^3H]5-carboxamidotryptamine binding sites with a similar Kd value. However, Bmax in the CM was 4-times higher than that in the LM.The molecular study (reverse transcription polymerase chain reaction) demonstrated that the expression of 5-HT_7 receptor mRNA in the CM was higher than that in the LM.5-HT increased the cAMP in both muscle layers, but the increment in the CM was higher than that in the LM.Therefore, it was suggested that the different inhibition of the contractility by 5-HT was caused by muscle layer-related accumulation of cAMP (CM>LM), due to muscle-layer dependent distribution (CM>LM) of 5-HT_7 receptors. This heterogeneous distribution of 5-HT_7 receptor is quite unique and different from that of other receptors (muscarinc M_3 receptor, histamine H_1 receptor , endothelin A receptor, β and α2-adrenaline receptors, LM>CM) present in the porcine uterus.Muscle layer-dependent inhibition : 5-HT_7 and β_2-adrenaline receptor-mediatd pathways were the main inhibitory mechanisms in the porcine myometrium and shared in the inhibition of contractility in a smooth muscle layer-dependent manner (LM : β_2-adrenoceptors, CM : 5-HT_7 receptors). The responses of 5-HT and isoproterenol differ from region to region, probably because of differences in the dominant subtype of 5-HT receptors and density of β_2-adrenaline receptors. Bioactive peptides and nitric oxide do not play a significant physiological role (as inhibitory agents) in the regulation of porcine uterine contractility. Less