Effect of atrial natriuretic peptide on vasa recta blood flow in the rat.

To determine whether synthetic atrial natriuretic peptide (ANP) increases renal medullary blood flow and if so whether the increase mediates the diuresis and natriuresis induced by ANP, inner medullary vasa recta blood flow in the exposed left renal papilla of anesthetized Munich Wistar rats weighing between 102 and 161 g was measured by fluorescence videomicroscopy. The rats were maintained in a euvolemic state by the infusion of albumin. Synthetic ANP (Auriculin B) was administered intravenously as 2.5 micrograms/kg body wt prime and as a continuous infusion of 0.2 microgram X min-1 X kg body wt-1 to the experimental group (n = 7). Within 2 min after ANP was given, urine flow and sodium excretion increased (29.4 +/- 3.8 to 50.4 +/- 5.8 microliter X min-1 X kidney wt-1, P less than 0.01, and 3.39 +/- 0.57 to 6.05 +/- 0.95 mueq X min-1 X g kidney wt-1, P less than 0.01, respectively), but vasa recta blood flow in descending (DVR) or ascending (AVR) vasa recta did not change significantly (9.5 +/- 2.3 to 10.0 +/- 2.8 nl/min in DVR and 5.3 +/- 1.0 to 6.1 +/- 1.2 nl/min in AVR). Forty-five minutes after ANP was begun, urine flow and sodium excretion increased further (77.1 +/- 11.1 microliter X min-1 X g kidney wt-1 and 12.0 +/- 2.15 mueq X min-1 X g kidney wt-1, respectively), and by this time vasa recta blood flow had increased significantly to 14.0 +/- 2.6 in DVR, P less than 0.01, and 9.8 +/- 1.2 in AVR, P less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)