Hypothalamic and extrahypothalamic-limbic system vasopressin concentration under exposure to hyperosmolarity, hypovolemia and heat stress

Abstract

The distribution of vasopressin (AVP) in different brain structures in response to osmotic and/or hypovolemic stress under normo- and hyperthermic conditions was investigated. Fourteen groups of male albino rats (Zabar strain) were exposed to different combinations of the stressors and AVP concentration in the plasma (PL), pituitary (PT) hypothalamus (HY) and extrahypothalamic-limbic system (Exhy-LS), were measured by radioimmunoassay. Hyperosmolarity and hypovolemia under normothermia brought about an elevation in PL AVP, concomitantly with a decrease in Exhy-LS AVP concentration. In contrast, thermal stress superimposed on these stressors resulted in a parallel rise in Exhy-LS and PL AVP concentration. Under the latter conditions the rise in rectal temperature (Tre) coincided with an increase in Exhy-LS ( Y = −564+15.5 X; r = 0.83) and a decrease in HY AVP concentration ( Y = 9054 − 215 X; r = 0.88). The results infer a possible role of AVP during normal thermoregulatory activity. The study also confirms earlier reports suggesting that the limbic system is the site where AVP exerts its effect on thermoregulation.