Plasma vasopressin concentration and renin in the rat: effect of hydration and hemorrhage

In order to investigate effects of hydration state, different techniques of collecting blood samples, and of acute, stepwise hemorrhage, we studied plasma vasopressin (AVP) concentration, and plasma renin activity (PRA) in 80 female Wistar rats. Plasma AVP was decreased following hydration with 10 ml of water (1.0 +/- 0.3 pg/ml, mean +/- S.E.M.) as compared to controls (6.1 +/- 2.0 pg/ml), while withdrawal of water for 48 hours stimulated AVP release (29 +/- 8 pg/ml). AVP values in jugular venous blood during light ether anesthesia (9.6 +/- 4 pg/ml) were slightly higher than in trunk blood following decapitation (2.7 +/- 0.7 pg/ml). There was no effect of sham gastric lavage on AVP. PRA was slightly increased in trunk blood and in jugular venous blood following ether anesthesia, and 5-fold increased following 48 h of water withdrawal. In aortic blood obtained during ether anesthesia, AVP-levels were 12- to 560-fold those in control trunk blood. Rapid hemorrhage, 2.0 ml stepwise, resulted in corresponding increases of AVP blood concentration, presumably due to hypothalamohypophyseal ischemia. PRA values showed a similar, albeit less pronounced increase. These results show the importance of controlling conditions of blood sample collection for AVP and PRA analysis, and demonstrate massive release of AVP in response to acute hemorrhage. The amount of AVP released is well about the threshold for pressor activity, and may be of importance in vasoconstrictive adaptation to acute hypovolemic hypotension.