Inhibition of furosemide-induced natriuresis by acetylsalicylic acid in dogs.

The effect of intravenously administered acetylsalicylic acid (ASA) has been investigated in two sets of experiments in conscious dogs. In the first part of the study ASA 70-90 mg/kg was infused for 40 min. Urine flow, free water clearance, renal blood flow and urinary excretion of sodium did not change significantly as compared to placebo treated animals. This is in contrast to the effects of comparable ASA doses in the pentobarbital anaesthetized dog. In the second part of the study the effects of pre-treatment with the same ASA doses of 5 ml 0.6% NaCl (placebo) on some renal effects of furosemide 1 mg/kg (intravenously) were investigated. In the placebo group acute furosemide treatment increased CIN in five out of six dogs and CPAH in all six dogs, these increases being most prominent the first 10 min after drug administration. After pre-treatment with ASA the initial increases in CIN and CPAH were almost abolished. CIN was reduced by 23.8% and CPAH by 30.6% during the first six clearance periods (0-6- min) after diuretic treatment in the ASA group as compared to the placebo group. Although urinary sodium excretion also increased in ASA pre-treated dogs, the effect of furosemide was greater in all dogs in the placebo group (P less than 0.05), and the effect of furosemide on fractional tubular reabsorption of sodium was significantly attenuated after pre-treatment with ASA.