The effects of two pure synthetic atrial natriuretic factors, Atriopeptin (AP) I and AP II, on the whole kidney glomerular filtration rate (GFR), sodium and potassium excretion (UNaV, UKV), urine flow rate (V) and arterial blood pressure (BP) were studied in adult male Sprague-Dawley rats. The variables were measured during a control period and during 70 min of continuous intravenous infusion of AP I or AP II at a rate of 10 micrograms h-1 kg-1 body wt. A time control group was studied in parallel to see whether the variables under study changed with time. The AP I infusion did not affect GFR (change from 1.34 +/- 0.10 to 1.24 +/- 0.04 ml min-1 g-1 kidney wt), but was clearly natriuretic (UNaV changed from 0.071 +/- 0.011 to 0.229 +/- 0.038 mumol min-1 g-1 kidney wt, P less than 0.01). The UKV increased from 0.504 +/- 0.073 to 1.138 +/- 0.121 mumol min-1 g-1 kidney wt, (P less than 0.001) and V from 1.88 +/- 0.10 to 2.94 +/- 0.15 microliter min-1 g-1 kidney wt, (P less than 0.001). Urine osmolality (Uosm) and BP were unaffected. During AP II infusion GFR remained unchanged but was slightly below the pre-infusion level during the last infusion period (1.05 +/- 0.07 as against 1.37 +/- 0.09 ml min-1 g-1 kidney wt, P less than 0.05). Despite this fact, UNaV was significantly elevated throughout the infusion period.(ABSTRACT TRUNCATED AT 250 WORDS)