Effects of brain natriuretic peptide on renal nerve activity in conscious rabbits

Responses of renal nerve activity (RNA) to intravenous infusion of brain natriuretic peptide (BNP) were examined in chronically instrumented conscious rabbits with all baroreflexes intact, sinoaortic baroreceptor denervation (SAD), and SAD plus vagotomy. In intact rabbits, an infusion of BNP at a rate of 0.3 microgram.kg-1.min-1 for 30 min decreased mean arterial pressure (MAP) by 8 +/- 1 mmHg and increased RNA by 48 +/- 4% but did not alter heart rate (HR). The decrease in MAP in SAD rabbits (20 +/- 3 mmHg) was greater than in intact rabbits, whereas RNA increased less (21 +/- 7%). After SAD plus vagotomy, BNP lowered MAP by 25 +/- 4 mmHg, whereas RNA was not altered significantly. To further examine the effects of BNP on baroreflex control of HR and RNA, the baroreceptors were stimulated or unloaded by raising or lowering MAP by injections of phenylephrine or glyceryl trinitrate, respectively. The maximum change in each HR or RNA response to phenylephrine or glyceryl trinitrate was plotted against the maximum change in each MAP response and a logistic function curve was fitted to the MAP-HR and MAP-RNA relationship. BNP did not alter the slope of either curve but shifted both curves to the left. These results indicate that 1) in intact rabbits, BNP increases RNA due to sinoaortic and cardiopulmonary baroreflexes and 2) BNP resets the baroreflex control of HR and RNA to a lower arterial pressure.