Baroreflex control of renal nerve activity in conscious animals

This study quantitates the effect of three different doses of vasopressin on the arterial baroreflex control of renal sympathetic nerve activity and heart rate. The lowest dose of vasopressin (0.4 mU/kg X min), which had no significant effect on resting mean arterial pressure, heart rate, or renal sympathetic nerve activity, increased the inhibitory influence of arterial baroreflexes on renal sympathetic nerve activity in response to an increase in pressure. During infusions of higher doses of vasopressin (1.5 and 3.0 mU/kg X min), which significantly decreased resting heart rate and renal sympathetic nerve activity but had no significant effect on mean arterial pressure, the mean arterial pressure-renal sympathetic nerve activity relation showed a significant decrease in maximum renal sympathetic nerve activity when compared with control. The highest dose of vasopressin resulted in a significant shift of the relation to the left toward lower pressures and in a decrease in maximum gain. The relation exhibited a parallel shift toward lower pressure, with no change in gain, at the higher dose of vasopressin. Based on these results, we conclude that vasopressin exerted a dose-related effect on arterial baroreflex such that lower doses of vasopressin may sensitize the central baroreflex neurons to afferent input, while the higher doses of vasopressin caused direct excitations of these neurons, resulting in a reduction in resting sympathetic outflow.