Atrial Natriuretic Peptide and the Natriuresis Due to Acute β-Blockade in Conscious Hypertensive Rats

Acute beta-adrenoceptor blockade in rats is known to produce a natriuresis of hitherto uncertain cause. To investigate this phenomenon plasma atrial natriuretic peptide (ANP) concentrations were measured in groups of conscious metoprolol-treated and control rats. In the active treatment group the blood pressure decreased slowly, as expected, settling at a lower level after 2 hours, and the mean sodium excretion doubled 1 hour after metoprolol administration. This natriuretic effect was maximal after 40-60 minutes and thereafter slowly declined towards basal values. The period of enhanced sodium excretion was associated with a significant rise (68%) of the mean ANP plasma concentration. It suggested that this increase in plasma ANP concentration can mediate the acute natriuretic effect beta-adrenoceptor blockade.