Hoffman G E, McDonald T, Figueroa J P, Nathanielsz P W
Department of Physiology, University of Pittsburgh, School of Medicine, Pa.
Neuroendocrinology. 1989 Dec;50(6):633-43. doi: 10.1159/000125292.
Both oxytocin (OXY) and arginine vasopressin (AVP) enhance the effects of corticotropin-releasing factor on ACTH release by the pituitary. One of these, AVP, plays a role in the control of fluid balance and responses to hypoxemic stress in the fetal sheep. To determine the possibility that OXY also participates in fetal neuroendocrine events, OXY-containing neuronal structures must first be demonstrated within the fetal endocrine hypothalamus. OXY-immunoreactive elements were examined in fetal sheep hypothalami late in gestation and compared to AVP-containing structures using immunocytochemical procedures. Six fetal sheep ranging from 126 to 144 days gestational age were delivered via cesarian section from timed pregnant Rambouillet-Columbia ewes and killed by an overdose of anesthesia. The fetal head was perfused via bilateral carotid catheters and processed for immunocytochemical localization of OXY or AVP using the avidin-biotin complex procedure. At all fetal ages examined, OXY- and AVP-containing neurons were found within the paraventricular nuclei (PVN), supraoptic nuclei (SON) and accessory magnocellular hypothalamic nuclei. OXY-containing neurons were found principally in the SON and PVN. They were generally less numerous and less intensely stained than the AVP neurons. In the SON, they concentrated along the dorsal borders of the nucleus above the AVP neurons. In PVN, clusters of OXY cells were located along the dorsal and lateral borders of the nucleus surrounding the AVP neurons; in the periventricular division, they were intermingled with the AVP neurons. Small numbers of OXY axons were located in the external zone of the median eminence; whereas most OXY axons extended into the hypothalamo-neurohypophyseal tract and posterior lobe of the pituitary. A few of the OXY axons in the pituitary stalk were diverted to the pars intermedia. Likewise, some of the OXY fibers from the external zone of the median eminence entered the pars tuberalis but were rarely found in the distal lobe of the pituitary. In contrast, AVP axons richly innervated the external zone of the median eminence, and neural lobe. Like OXY, AVP axons from the median eminence and the pituitary stalk sent projections to the adenohypophysis. AVP fibers in the pars distalis frequently contacted corticotropes and were more numerous than OXY fibers in this region. These data provide anatomical evidence that OXY and AVP may directly regulate the fetal adenohypophysis. Of these two neuropeptides, AVP predominates anatomically.
催产素（OXY）和精氨酸加压素（AVP）均可增强促肾上腺皮质激素释放因子对垂体促肾上腺皮质激素（ACTH）释放的作用。其中，AVP在调节绵羊胎儿的水平衡及对低氧应激的反应中发挥作用。为确定OXY是否也参与胎儿神经内分泌活动，必须首先在胎儿内分泌下丘脑内证实含OXY的神经元结构。采用免疫细胞化学方法，对妊娠晚期绵羊胎儿下丘脑内的OXY免疫反应性成分进行检测，并与含AVP的结构进行比较。从定时妊娠的朗布依埃-哥伦比亚母羊经剖宫产取出6只妊娠126至144天的绵羊胎儿，过量麻醉致死后，经双侧颈动脉导管对胎儿头部进行灌注，并采用抗生物素蛋白-生物素复合物方法进行OXY或AVP的免疫细胞化学定位。在所检查的所有胎儿年龄段，室旁核（PVN）、视上核（SON）和下丘脑大细胞附属核内均发现含OXY和AVP的神经元。含OXY的神经元主要见于SON和PVN。与AVP神经元相比，它们的数量通常较少，染色也较浅。在SON中，它们集中在核的背侧边缘，位于AVP神经元上方。在PVN中，OXY细胞簇位于围绕AVP神经元的核的背侧和外侧边缘；在室周部，它们与AVP神经元相互交织。少量OXY轴突位于正中隆起的外侧区；而大多数OXY轴突延伸至下丘脑-神经垂体束和垂体后叶。垂体柄中的一些OXY轴突转向中间部。同样，来自正中隆起外侧区的一些OXY纤维进入结节部，但在垂体远侧部很少发现。相反，AVP轴突大量支配正中隆起的外侧区和神经叶。与OXY一样，来自正中隆起和垂体柄的AVP轴突向腺垂体发出投射。远侧部的AVP纤维常与促肾上腺皮质激素细胞接触，且在该区域比OXY纤维数量更多。这些数据提供了解剖学证据，表明OXY和AVP可能直接调节胎儿腺垂体。在这两种神经肽中，AVP在解剖学上占主导地位。
