BLUNTED NATRIURETIC RESPONSE TO ENDOGENOUS ATRIAL-NATRIURETIC-PEPTIDEDURING RAPID CARDIAC PACING IN ANESTHETIZED DOGS

1. We investigated whether diuresis and natriuresis induced by endogen ous atrial natriuretic peptide (ANP) were blunted during rapid cardiac pacing. 2. Changes in plasma ANP renal function and haemodynamics dur ing rapid cardiac pacing were studied in anaesthetized closed-chest do gs. Dogs were paced via the right ventricle at a rate of 200 b.p.m. (m oderate pacing) or 250 b.p.m. (severe pacing) for 180 min. 3. The maxi mal increases in plasma ANP and urinary excretion of cGMP during sever e pacing were four-and three-fold higher, respectively, than those dur ing moderate pacing. Despite the higher concentration of plasma ANP, t he maximal increases in urine volume, urinary excretion of sodium and fractional excretion of sodium during severe pacing were similar to th ose during moderate pacing. Mean arterial pressure and renal vascular resistance were decreased only by severe pacing. The increase in total peripheral resistance during severe pacing was significantly smaller than that during moderate pacing. However, the glomerular filtration r ate was kept at basal levels by both moderate and severe pacing. 4. Th ese results suggest that there are certain mechanisms that counteract renal tubular sodium reabsorption induced by endogenous ANP under cond itions of severe pacing. The suppression occurs at tubular sites but n ot at glomerular sites. One of the possibilities for the suppression i s the decrease in renal perfusion pressure accompanied by decreases in peritubular capillary hydrostatic pressure.