Effect of acute volume expansion associated with salt load on the profile of plasma angiotensins in rats

We measured the changes produced in renin and the peptide components of the circulating renin-angiotensin system by acute volume expansion alone or associated with salt load in rats. With both maneuvers, there was a decrease of plasma renin activity (PRA) and plasma angiotensin (Ang) concentrations, but the changes were more pronounced in the salt-load group. In contrasting to Ang I and Ang II, plasma Ang-(1-7) concentration decreased significantly only within 60 min of 5.0% NaCl infusion (19.5 +/- 2.9 vs 30.5 +/- 1.9 pg/ml in the control group). As expected, plasma vasopressin increased markedly in the animals submitted to acute salt load (144.0 +/- 42.0 vs 5.0 +/- 0.2 pg/ml in the control group). The dissociation between the changes in plasma Ang-(1-7) and that of other plasma angiotensins is consistent with our previous studies using chronic salt load, and suggests that during acute volume expansion associated with salt load Ang I is preferentially converted to Ang-(1-7). In contrast to vasopressin, however, plasma Ang-(1-7) concentration increased only after chronic salt load, suggesting that this angiotensin may be more involved with long-term mechanisms of control of hydromineral balance.