Vasopressin turnover in the hypothalamus of rats exposed to low and high ambient temperature

Abstract

Thermal stressors such as low and high ambient temperature elicit an abundance of neuroendocrine responses including activation of the hypothalamo-pituitary-adrenal (HPA) axis, and arginine-vasopressin (AVP) release (1, 2). The exposure to heat, unlike cold, represents not only an unpleasant experience, but a threat to the osmotic homeostasis as well. Since AVP has long been recognized as a hormone involved in the modulation of HPA axis activity (3), along with its well known peripheral effects, the aim of this study was to elucidate the hypothalamic AVP turnover in acutely heat and cold exposed rats. Rats were exposed to high (38°C) or low (4°C) ambient temperature for 60 minutes. Western blot was employed for determination of hypothalamic AVP levels, and difference in AVP content between supraoptic (SON) and paraventricular nucleus (PVN) was detected using immunohistochemical analysis. The obtained results show that both exposure to high and low ambient temperature increased hypothalamic AVP level, although with different intensity since the level was higher under heat conditions. On the other hand, pattern of AVP level changes in PVN and SON was stressor-specific, given that cold exposure mainly increased the SON AVP level, while heat exposure affected the PVN AVP content more. In conclusion, our results directly confirmed the positive correlation between temperature stressors and changes in hypothalamic AVP content, rising new questions about the origin of AVP secreted during various and often different needs of the organism.