Water Rehydration Blunted Vasopressin, Angiotensin II And HSP70 Responses To High Environmental Temperature Without Altering Plasma Osmolality In Male Sprague-Dawleys Rats

Abstract

Chronic exposure to high environmental temperature (HET) is a reno-cardiovascular risk factor. Studies have shown that HET alters body fluid balance and elevates plasma osmolality, with the consequent release of angiotensin II and arginine vasopressin (AVP), which play key roles in the pathophysiology of some forms of hypertension. This study investigated the effect of water rehydration on plasma osmolality, angiotensin II, arginine AVP and heat shock protein (HSP70) during chronic exposure to HET. Eighteen (18) male Sprague-Dawley rats (n = 6/group, 8 weeks old, weight: 90-100g) were either kept in an environmental chamber maintained at a HET (38.5±0.5oC) 4hrs daily with (RH) or without access to water (H) compared to control rats (C), maintained at a room temperature of 25 ± 0.5oC oC. The experiment lasted 8 weeks. There was a significant increase in plasma osmolality (P<0.05), fluid balance (P<0.001), angiotensin II (P<0.01), AVP (P<0.001) and HSP 70 (P<0.05) in rats (H) exposed to HET compared to control. However, with water rehydration in rats (RH) exposed to similar HET, increases were only noticed in plasma osmolality (P<0.01) and fluid balance (P<0.001), with no significant rise in AVP, angiotensin II and HSP70 compared to control. Meanwhile, AVP was significantly lower (P<0.01) in RH compared to H rats, whereas plasma osmolality, fluid balance, angiotensin II and HSP70 were not significantly different in H and RH rats. The result suggests that water rehydration during prolong exposure to hot environment blunts AVP, angiotensin II and HSP 70 responses to persistent hyperosmolality