催产素及其受体与哺乳动物的生殖

OXYTOCIN AND ITS RECEPTOR IN MAMMALIAN REPRODUCTION

催产素 (OT)是一种 9肽激素 ,主要由哺乳动物下丘脑产生 ,以神经内分泌、旁分泌或自分泌形式 ,在哺乳动物生殖过程中发挥重要作用。催产素受体 (OTR)是与G 蛋白相耦联的膜蛋白 ,通过激活磷脂酶C发挥其生理作用。OT在交配、分娩、哺乳时由神经垂体 (垂体后叶 )脉冲式释放 ,促进子宫平滑肌和乳腺肌上皮细胞收缩 ,利于精子运行、胎儿娩出和射出乳汁 ;OT在中枢神经系统中参与调节母性行为 ;在性腺中促进某些物种的黄体形成。OT与PGF2α共同作用使有蹄动物黄体退化。以上过程都依赖于OT和OTR基因的时空特异性表达 ,多种激素参与它们的表达调控。但OT的生理作用有时也可被其它途径所替代。

The nonapeptide hormone oxytocin, synthesized mainly in the mammalian hypothalamus, plays an important role in mammalian reproduction through the neuroendocrine, autocrine or paracrine pathways. Oxytocin receptor is a member of the G-protein-coupled receptor superfamily, consisting of seven hydrophobic transmembrane α-helices, and acts through the activation of phospholipase C. Oxytocin released from neurohypophysis can stimulate the contraction of uterine smooth muscle at term and that of myoepithelial cells that surround the alveoli of the mammary gland during lactation. The secretion of oxytosin is a typical neuroendocrine response and can be stimulated by various physiological and environmental stimulation such as the suck ling of the young animals during lactation, light-dark rhythm and the suppression of fetus on the uterus and vagina. Oxytocin is involved in the regulation of maternal behavior in the central nervous system. OTR are expressed in the brain of many mammals, though its distribution in the central nervous system may be different among species. The OTR expression in brain is regulated by the steroid hormones. OT may play a role in the process of leuteinization in some species. Oxytocin also cooperates with prostaglandin F 2α to elicit the leuteolysis of ungulates. OT secreted from the large luteal cells binds the OTR expressed by uterine epithelium cells, so as to stimulated the production of prostaglandin, forming a positive feedback that responsible for the luteolysis. During pregnancy recognition, the trophoblast cells secret interferon-τ, which inhibits the expression of OTR in the uterus. The block of OT-OTR interaction are necessary for the suevival of corpus luteum during pregnancy. But it is possible that other mechanism of luteolysis and maternal pregnancy recognition may be exist in other species. All of these processes depend on the temporal-spatial expression of OT and OTR genes. Several hormones are involved in the regulation of their expression. Some physiological functions of oxytocin can be substituted for by other redundant mechanisms, since in the mice whose OTR gene have been knocked out, some of the physiological processes, but not all, are interfered.