Effect of Angiotensin II on Blood Volume and Water Intake in the Rat

Abstract

Experiments were performed to investigate whether the copious drinking of rats infused with angiotensin II results from a reduction in plasma volume. Angiotensin II (Hypertensin, CIBA) dissolved in 0.9% NaCl was infused through a jugular cannula into conscious, unrestrained rats at a rate of 0.72 ± 0.015 μg kg−1 min−1 for a 30 min period. The amount of angiotensin II required to induce the first drinking response was 6.43 ± 0.667 μg/kg body weight and the latency to drink following the initiation of the infusion was 9.1 ± 0.97 min. The average intake of water during the first drinking bout was 6.3 ± 0.43 ml/kg. The total intake of water during the 30 min infusion period was 13.0 ± 1.37 ml/kg. Plasma volume and hematocrit were determined before and during the angiotensin II infusion. Blood samples were obtained from the jugular cannula before the infusion began and again either 1, 2, 3, 4, 5, 10, 15, or 30 min after the infusion began. The same determinations were also made either when angiotensin II initiated drinking, 2 min or 8 min thereafter. There were no significant changes in either plasma volume or hematocrit. It is concluded that angiotensin-induced drinking does not occur because of hypovolemia produced by angiotensin II.