EFFECT OF ATRIAL-NATRIURETIC-PEPTIDE ON CELLULAR ELEMENT CONCENTRATIONS IN RAT PROXIMAL TUBULES - EVIDENCE FOR INHIBITION OF THE SODIUM-PUMP

1. In order to further define the action of atrial natriuretic peptide (ANP) on proximal tubular (PT) transport, combined clearance and elec tron microprobe X-ray (EMPX) experiments were performed on five male W istar rats infused with ANP (0.16 nmol/kg per h) and nine control anim als. 2. Electron microprobe X-ray analysis of PT cell electrolytes (mm ol/kg wet weight) revealed a similar [Na](i) in both the control and A NP treated groups (16.4 +/- 0.4 vs 16.5 +/- 0.4; P = 0.894). [Cl](i) w as lower in the ANP treated animals (14.8 +/- 0.3 vs 12.0 +/- 0.3; P<0 .0001) as was [K](i)(131.4 +/- 1.4 vs 114 +/- 1.7; P<0.0001). The PT c ells in the ANP treated group had a significant reduction in dry weigh t (20.1 +/- 0.3 g% vs 19.0 +/- 0.3 g%; P<0.024), indicating significan t cell swelling. Thus, despite a normal [Na](i), there was net accumul ation of Nai following ANP treatment. 3. These results are consistent with accumulation of Na-i due to inhibition of the Na pump followed by cell swelling and subsequent regulatory volume decrease with exit of K and Cl. These results are the first to show the effect of ANP on PT intracellular electrolytes.