The influence of angiotensin II and aldosterone on the diuretic effects ofatrial natriuretic peptide in isolated perfused rat kidneys

The diuretic effects of atrial natriuretic peptide (ANP) are known to be re duced if renin-angiotensin-aldosteron system (RAAS) activity is increased. Studies of ANP-effects in intact organisms are hampered by the vasodilating action of this hormone, decreasing arterial blood pressure and thereby the diuretic activity of ANP itself. To investigate whether increased concentr ations of angiotensin II (AII) or of aldosterone (ALD) determine ANP-unresp onsiveness we studied three groups of kidneys perfused for 180 minutes with a constant perfusion pressure of 100 mmHg: a control group (n = 5), an ATT /ANP group (n = 6), first subjected to AII and subsequently to hANP, and an ALD/ANP group (n = 4), in which ALD instead of AII was used. We observed a n increase of urine flow above control levels after ANP in kidneys pretreat ed with AII, while such an effect could not be demonstrated after pretreatm ent with ALD. This suggests that the blunted diuretic effect of ANP during increased RAAS activity is more determined by ALD than by ALI.