Renal effects of adrenomedullin in the rat

We investigated the effects of a constant infusion of adrenomedullin (ADM) on renal hemodynamics and fluid electrolyte excretion in the rat. Following baseline measurements, eight rats received an intravenous infusion of 5 micrograms of rat ADM (167 ng/min) for 30 min at 10 microliters/min. Eight additional rats received 0.9% saline at 10 microliters/min instead of ADM. Renal function was measured during this period and for two consecutive 20-min periods following termination of the ADM or vehicle infusion. Mean arterial pressure decreased from a baseline of 113 +/- 3 to 102 +/- 1 mm Hg at 25 min of ADM infusion and returned towards control after the ADM infusion was terminated. This modest hypotensive effect was associated with an increase in heart rate from 366 +/- 10 to 384 +/- 9 bpm, which continued to remain elevated after the ADM infusion was stopped. Urinary sodium excretion increased from 348 +/- 57 to 813 +/- 172 nEq/min during ADM infusion and continued to increase to 1141 +/- 347 nEq/min after the infusion of ADM was terminated. Urinary potassium excretion increased from 1.94 +/- 0.22 to 2.75 +/- 0.24 microEq/min during ADM infusion. Urine flow tended to increase (P = 0.08) from 7.0 +/- 0.5 to 8.1 +/- 0.6 microliters/min during ADM infusion and continued to increase to 9.7 +/- 1.5 microliters/min after the infusion was stopped. Renal plasma flow increased from 3.22 +/- 0.22 to 3.82 +/- 0.20 ml/min/g kidney wt during ADM infusion and continued to increase to 4.14 +/- 0.22 ml/min/g kidney wt after the ADM infusion was stopped. Glomerular filtration rate averaged to 1.11 +/- 0.07 ml/min/g kidney wt during baseline and did not significantly change during or after ADM infusion. These results indicate that a constant infusion of adrenomedullin, at a dose that results in a minimal hypotensive effect increases renal plasma flow and urinary sodium excretion in the rat.