Bathgate R A, Parry L J, Fletcher T P, Shaw G, Renfree M B, Gemmell R T, Sernia C
Institute for Hormone and Fertility Research, University of Hamburg, Germany.
Adv Exp Med Biol. 1995;395:639-55.
Unlike eutherian mammals which secrete only oxytocin (OT), marsupials secrete the typically reptilian mesotocin (MT) and/or OT as their oxytocic peptides. Our laboratories have been conducting research on various aspects of the roles of OT-like peptides in three marsupials, the brushtail possum, the northern brown bandicoot and the tammar wallaby. By providing information on the functions of OT-like peptides in these species we hope to provide some clues as to the evolution of neurohypophysial hormones in marsupials. Brain and peripheral distributions of OT-like peptides have been studied in the possum and bandicoot. As in eutherian mammals, OT-like peptides are distributed throughout the brain and are present in the testis, corpus luteum, prostate and adrenal glands. Studied on the regulation of release of MT into plasma in the possum show that it is regulated by similar mechanisms to OT release in eutherian mammals. OT receptors have been characterized and localized in the possum and the tissue distributions and pharmacological characteristics of the receptor are similar to both the sheep and rat OT receptors. The marsupial OT receptor shows no pharmacological specificity for MT over OT which is reflected in the similar potency of these peptides in eliciting contractions of the uterus of the tammar wallaby in vitro. MT seems to play an important but not essential role in parturition in the tammar. MT concentrations are increased immediately after delivery in the tammar but infusion of an OT antagonist before expected birth delays but does not prevent parturition. The presence of OT receptors in the marsupial mammary gland and the sensitivity of the gland to exogenous OT and stimulation of mesotocinergic neurones demonstrates that these peptides are important for marsupial lactation. Our data suggest that the presence of MT with or without OT in marsupials is a result of a neutral mutation rather than functional evolution.
与仅分泌催产素（OT）的真兽类哺乳动物不同，有袋类动物分泌典型的爬行类中催产素（MT）和/或OT作为其催产肽。我们的实验室一直在研究OT样肽在三种有袋类动物——帚尾袋貂、北褐袋狸和袋鼬中的作用的各个方面。通过提供这些物种中OT样肽功能的信息，我们希望能为有袋类动物神经垂体激素的进化提供一些线索。已经在袋貂和袋狸中研究了OT样肽在大脑和外周的分布。与真兽类哺乳动物一样，OT样肽分布于整个大脑，并且存在于睾丸、黄体、前列腺和肾上腺中。对袋貂中MT释放到血浆中的调节研究表明，其受与真兽类哺乳动物中OT释放类似的机制调节。已经对袋貂中的OT受体进行了表征和定位，该受体的组织分布和药理学特性与绵羊和大鼠的OT受体相似。有袋类OT受体对MT的药理学特异性并不高于OT，这反映在这些肽在体外引起袋鼬子宫收缩的效力相似。MT似乎在袋鼬的分娩中起重要但非必需的作用。袋鼬分娩后MT浓度立即升高，但在预期分娩前注入OT拮抗剂会延迟但不会阻止分娩。有袋类乳腺中存在OT受体以及该腺体对外源OT的敏感性和中催产素能神经元的刺激表明，这些肽对有袋类动物的泌乳很重要。我们的数据表明，有袋类动物中MT的存在与否是中性突变而非功能进化的结果。
