Cardiovascular effects of angiotensin II and vasopressin in intact awake rats

1. In this study we evaluated, in intact awake rats, the effects of angiotensin II (AII) and vasopressin (AVP) on venous tone to explain their different hemodynamic effects. 2. Cardiac index (CI) was measured by thermodilution. AII and AVP were infused at the doses adjusted to increase mean arterial pressure 25, 50 and 70% above baseline. Lower doses of AVP than AII were necessary to increase mean arterial pressure at the same levels. 3. To study whether the different effects of AII and AVP on CI may be explained by their different actions on the venous system, changes in venous tone were evaluated by measuring mean circulatory filling pressure (MCFP) and determining the pressure gradient for venous return (PGVR). 4. AVP induced a decrease in CI from 32.5 +/- 2.2 to 23.1 +/- 1.7 and 15.4 +/- 0.8 ml/min/100 g (P < 0.01) with the second and third level of increase in afterload respectively, whereas AII at the same levels of afterload decreased CI from 34.8 +/- 1.3 to 28.3 +/- 2.3 and 23.4 +/- 1.7 ml/min/100 g (P < 0.01). Furthermore, the rise in total peripheral resistances (TPR) was greater with AVP than with AII at the highest level of afterload (P < 0.05). Heart rate significantly decreased more in the animals infused with AVP than with AII. 5. There were no changes in MCFP and PGVR with either AII or AVP. 6. These results indicate that in intact awake rats the larger fall in CI induced by AVP can not be explained only by a greater decrease in HR since at highest levels of afterload AVP decreased SV.(ABSTRACT TRUNCATED AT 250 WORDS)