Diuretic response of a second infusion of atrial natriuretic polypeptide into anesthetized dogs

We examined the diuretic effects of a second infusion of atrial natriuretic polypeptide (ANP). Intrarenal infusion of ANP (50 ng X kg-1 X min-1) for 30 min to anesthetized dogs had no significant effect on mean arterial blood pressure (MABP), renal blood flow (RBF) and glomerular filtration rate (GFR), whereas there was an increase in urine flow (V) and urinary excretion of sodium (UNaV) from 7.5 +/- 1.5 to 34.1 +/- 9.4 microliters/g X min, from 0.97 +/- 0.20 to 4.38 +/- 1.32 microEq/g X min, respectively. When the same dose of ANP was infused 1 h after the first administration, V and UNaV were increased from 12.4 +/- 1.8 to 62.5 +/- 18.8 microliters/g X min, from 1.72 +/- 0.57 to 7.18 +/- 2.68 microEq/g X min, respectively. A second infusion of ANP caused a greater absolute increase in UNaV than did the first infusion but proportionally the increase in UNaV with the second ANP infusion was much the same. The present study shows that acute ANP infusion has no tachyphylaxis on the natriuretic response. These data will aid in establishing a bioassay for natriuretic response in vivo, thereby leading to elucidation of the physiological action of ANP.