[Effects of atrial natriuretic polypeptide on arterial pressure and renal sympathetic nerve activity in anesthetized rats].

The effects of atriopeptin III (AP III) on the arterial pressure (AP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were investigated in anesthetized rats. The results were as follows: (1) In intact rats (n = 12), following intravenous injection of AP III (50 micrograms/kg), systolic arterial pressure (SAP) decreased by 23.0 +/- 1.66 mmHg (M +/- SE, P less than 0.001), HR decreased by 9 +/- 3.5 beats/min (P less than 0.05), and RSNA decreased by 4.89 +/- 2.95% (P greater than 0.05). After vagotomy, the decrease in SAP following iv. AP III showed no significant difference with that of intact rats. HR showed no change, while there was a small increase in RSNA (P greater than 0.05); (2) In the intact vagi but sinoaortic denervated rats (n = 7), intravenous AP III decreased SAP by 27.4 +/- 3.25 mmHg (P less than 0.001), HR by 13 +/- 3.1 beats/min (P less than 0.01), and RSNA by 11.67 +/- 1.95% (P less than 0.001). After vagotomy, the decrease in SAP following i.v. AP III was attenuated, HR showed no significant change, but there was a small but significant increase in RSNA (P less than 0.05); (3) Following intravenous injection of nitroprusside, SAP decreased significantly. Such a hypotensive effect was associated with an increase in RSNA in either the intact or the vagotomized rats. The results indicate that (1) the hypotensive effect of AP III was mediated partly by vagi; (2) in the sinoaortic denervated rats AP III could reflexly inhibit RSNA by activation of vagal afferent fibers.