Institute for Small Animal Research, Dörnbergstrasse 25-27, 3100 Celle, FRG. Institute for Hormone and Fertility Research, Grandweg 64, 2000 Hamburg 54, FRG.
J Neuroendocrinol. 1992 Jun;4(3):347-51. doi: 10.1111/j.1365-2826.1992.tb00178.x.
The avian hypothalamic nonapeptide arginine vasotocin (AVT) is released from axon terminals in the neural lobe upon the application of osmotic stimuli. We have investigated whether, and to what extent, hormone secretion from the neurohypophysis is related to gene expression in the hypothalamus. Results from hybridization experiments with an AVT-specific cDNA probe indicate that in adult chickens stimulated by water deprivation or by hypertonic saline (2% w/v) drinking water, an upregulation of the AVT mRNA pool takes place, since consistently higher AVT mRNA levels compared to controls were monitored in osmotically challenged birds. This stimulatory effect was even visible at the transcriptional level after 19 h of water deprivation when osmolality was still near the basal value. In hens osmotically challenged by hypertonic saline drinking water for 5 days, a dissociation between osmolality and AVT plasma concentration was visible: extremely high plasma osmolality was accompanied by only moderately increased plasma AVT concentration. This might be caused either by exhaustion of stored hormone, or by downregulation of the system after chronic challenge. The latter suggestion is supported by the fact that the AVT mRNA concentration after 5 days of hypertonic saline challenge was well below the AVT mRNA levels of the groups with the more short-term stimuli of water deprivation for 19 or 48 h. In 30-day-old chicks the hypothalamic AVT mRNA concentration hardly reached 70% of the adult value, although AVT plasma concentrations were similar to those in the mature bird. We conclude that osmotic challenge of the hypothalamo-neurohypophysial system not only causes secretion of AVT from stores in the neural lobe but is accompanied by upregulation of AVT gene expression. Upregulation already occurs after marginal increase in plasma osmolality, as seen after 19 h of water deprivation in hens. In 30-day-old chicks gene expression is only slightly upregulated after short-term water deprivation while increase in plasma AVT is even greater compared to hens.
禽类下丘脑神经肽精氨酸血管加压素（AVT）在受到渗透刺激时从神经垂体轴突末端释放。我们研究了神经垂体激素的分泌与下丘脑基因表达之间是否以及在何种程度上相关。使用 AVT 特异性 cDNA 探针进行杂交实验的结果表明，在因限水或饮用高渗盐水（2%w/v）而受到刺激的成年鸡中，AVT mRNA 池发生上调，因为与对照组相比，渗透刺激鸟类的 AVT mRNA 水平始终更高。在因限水而受到 19 小时刺激时，即使在渗透压仍接近基础值的情况下，这种刺激作用甚至在转录水平上也是可见的。在因限水而受到 5 天刺激的母鸡中，渗透压和 AVT 血浆浓度之间出现了分离：极高的血浆渗透压伴随着仅适度增加的血浆 AVT 浓度。这可能是由于储存的激素耗竭所致，也可能是由于慢性刺激后系统下调所致。5 天高渗盐水刺激后 AVT mRNA 浓度远低于因限水 19 或 48 小时的短期刺激组的 AVT mRNA 水平，这支持了后一种假设。在 30 日龄小鸡中，下丘脑 AVT mRNA 浓度几乎达不到成年鸡的 70%，尽管 AVT 血浆浓度与成熟鸟类相似。我们得出的结论是，对下丘脑-神经垂体系统的渗透刺激不仅会导致神经垂体中 AVT 的储存分泌，还伴随着 AVT 基因表达的上调。在上调发生之前，就已经出现了如在母鸡中因限水 19 小时导致的轻微血浆渗透压增加。在 30 日龄小鸡中，短期限水后基因表达仅略有上调，而血浆 AVT 增加量甚至比母鸡更大。
