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

5-羟色胺（5-HT）抑制猪子宫纵肌（LM）和圆肌（CM）的自发收缩，但纵肌对5-HT的敏感性高于子宫肌。本实验旨在阐明5-HT受体亚型介导的抑制、抑制的亚细胞机制以及5-HT受体亚型肌肉层依赖性抑制的机制。根据5-HT受体激动剂（5-carboxamidotryptamine> - 5-HT>5-methoxytryptamine>8-羟基-2-（二正丙胺）四乙胺）和5-HT受体拮抗剂（methothepin > methylseride > metgoline >mianserin>氯氮平>spiperone）的排序，证明5-HT_7受体介导5-HT对子宫肌收缩性的抑制。抑制机制：5- ht对猪肌层的抑制作用提示：5-HT_7受体激活→Gs激活→腺苷酸环化酶激活→cAMP升高→[Ca^<…More 2+>]i和Ca^<2+>-收缩因子敏感性降低→肌肉收缩性抑制。5- ht_7受体分布：LM和CM层含有一类Kd值相似的[^3H]5-羧氨基色胺结合位点。CM组的Bmax是LM组的4倍。分子研究（逆转录聚合酶链反应）表明，5-HT_7受体mRNA在CM中的表达高于LM， 5- ht使两层肌肉中cAMP均升高，但CM中的增加量高于LM。因此，我们认为5-HT对收缩力的不同抑制是由于5-HT_7受体的肌层依赖性分布（CM>LM）导致cAMP的肌层相关积累（CM>LM）引起的。5-HT_7受体在猪子宫内的异质分布与其他受体（肌碱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>CM）的分布有很大的不同。肌层依赖性抑制：5-HT_7和β_2-肾上腺素受体介导的途径是猪肌层的主要抑制机制，并以平滑肌层依赖性的方式抑制收缩性（LM: β_2-肾上腺素受体，CM: 5-HT_7受体）。不同地区对5-HT和异丙肾上腺素的反应不同，可能与5-HT受体的优势亚型和β_2-肾上腺素受体的密度不同有关。生物活性肽和一氧化氮在调节猪子宫收缩性中不发挥显著的生理作用（作为抑制剂）。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