Neurohypophyseal response to dehydration in the spontaneously hypertensive rat

Experiments were performed to evaluate the effect of dehydration on neurohypophyseal hormone secretion, both vasopressin and oxytocin, fluid balance, and blood pressure in male spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar Kyoto (WKY). Metabolic studies showed that the antidiuretic response to dehydration (24 and 48 hours of water deprivation) was significantly depressed (p less than 0.01) in the hypertensive animals. They responded inappropriately to dehydration with a greater loss of water and sodium and a larger increase in hematocrit. In contrast, the vasopressin response (both urinary excretion and plasma levels) was increased. The peak plasma levels were 25.3 pg/ml (SHR) compared to 16.6 pg/ml (WKY), while the urinary excretion was 22.5 ng/24 hrs (SHR) vs 9.0 ng/24 hrs (WKY). Dehydration also elicited a stimulation of oxytocin secretion, with no differences observed in the responses of the groups. Blood pressure was significantly greater in the SHR and it did not change during dehydration. These results provide further support for the idea that hypertension is associated with abnormalities in the control of fluid/electrolyte balance.