Mezey E, Kiss J Z
National Institute of Mental Health, LCB, Bethesda, Maryland 20892.
Endocrinology. 1991 Oct;129(4):1814-20. doi: 10.1210/endo-129-4-1814.
Magnocellular hypothalamic neurons in the rat supraoptic nucleus (SON) normally produce either vasopressin (VP) or oxytocin (OT). Here we demonstrate that many magnocellular neurons in the SON of lactating rats synthesize both hormones at the same time. We show the colocalization of the messenger (m) RNA that encodes the VP precursor with OT-neurophysin; OT mRNA with VP-neurophysin, the C-terminal glycopeptide of the VP precursor, and VP itself, and the presence of both mRNAs in the same cell. At the light microscopic level quantitative studies show that on the second day of lactation, 17% of the SON neurons produce both hormones, on the fifth day 13%, and on the ninth day 9%. Two days after lactation the number of cells that are positive for both hormones returns to the control level (2-3%). We also show by means of electron microscopic immunohistochemistry that both peptides (or their precursors) are present in the same neurosecretory vesicles in nerve endings in the posterior lobe of lactating rats. At the electron microscopic level quantitative studies show that on the second day of lactation 21% of the terminals contain mixed vesicles; this number increases to 24% by the fourth day and is down to 5% by the 15th day, a level similar to that found in control rats. Since the double-labeled cells seemed to be producing additional VP as opposed to OT, we hypothesized that the former should affect urinary osmolality. Urine samples of lactating rats show a significant (5-fold) increase in urine osmolality during lactation (highest on the second day). The increase in osmolality correlated with the increase in the number of VP positive cells during lactation. We suggest that magnocellular neurons that ordinarily synthesize little or no VP can produce this antidiuretic hormone to help the animal compensate for the loss of water associated with lactation.
大鼠视上核（SON）中的大细胞性下丘脑神经元通常只产生血管加压素（VP）或催产素（OT）其中一种激素。在此我们证明，哺乳期大鼠SON中的许多大细胞性神经元可同时合成这两种激素。我们展示了编码VP前体的信使核糖核酸（mRNA）与OT-神经垂体素的共定位；OT mRNA与VP-神经垂体素、VP前体的C末端糖肽以及VP自身的共定位，以及两种mRNA在同一细胞中的存在情况。在光学显微镜水平进行的定量研究表明，在哺乳期第二天，17%的SON神经元产生两种激素，第五天为13%，第九天为9%。哺乳期结束两天后，两种激素均呈阳性的细胞数量恢复到对照水平（2%-3%）。我们还通过电子显微镜免疫组织化学方法表明，两种肽（或其前体）存在于哺乳期大鼠后叶神经末梢的同一神经分泌小泡中。在电子显微镜水平进行的定量研究表明，在哺乳期第二天，21%的终末含有混合小泡；到第四天这个数字增加到24%，到第15天降至5%，这一水平与对照大鼠中发现的水平相似。由于双标记细胞似乎产生的是额外的VP而非OT，我们推测前者应该会影响尿渗透压。哺乳期大鼠的尿液样本显示，哺乳期期间尿渗透压显著升高（5倍）（第二天最高）。渗透压的升高与哺乳期期间VP阳性细胞数量的增加相关。我们认为，通常很少合成或不合成VP的大细胞性神经元能够产生这种抗利尿激素，以帮助动物补偿与泌乳相关的水分流失。
