Increase of renal sympathetic nerve activity by metoprolol or propranolol in conscious spontaneously hypertensive rats.

1 Mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were recorded in conscious spontaneously hypertensive rats (SHR). 2 Infusion of metoprolol (4 mumol kg-1 h-1) or propranolol (1.5 mumol kg-1 h-1) reduced HR and significantly increased RSNA. 3 Administration of metoprolol caused a sustained decrease of MAP starting in the third hour of infusion. In contrast, administration of propranolol induced a biphasic response in MAP. It is suggested that the increase of RSNA after both beta-adrenoceptor blocking drugs is due to a decrease in arterial baroreceptor activity.