Role of cardiac atria in the human renal response to changing plasma volume

We examined the role of cardiac atria in the renal response to sequential volume expansion and contraction, during and directly following water immersion. In immersed healthy volunteers (group 1, n = 9) atrial diameter, plasma levels of atrial natriuretic peptide (ANP), and natriuresis increased, whereas renal vascular resistance (RVR) and filtration fraction declined. Each parameter changed in an opposite direction postimmersion. An analysis of transglomerular dextran transport suggests that transglomerular hydraulic pressure difference (delta P) changed in parallel with filtration fraction. Baseline atrial diameter, plasma ANP, RVR, and filtration fraction were significantly elevated in nine recipients of denervated cardiac allografts (group 2). Atrial diameter and plasma ANP changed in parallel with group 1 during and after immersion. However, corresponding reciprocal changes in RVR were smaller and filtration fraction remained constant throughout. From transglomerular dextran transport, we compute that delta P increased progressively during and after immersion, suggesting predominant efferent arteriolar tone. The postimmersed state was associated also with enhanced sodium retention despite sixfold higher plasma ANP than in group 1. These findings are consistent with an effect of cardiac denervation to leave unopposed efferent sympathetic nervous traffic to the kidney. They suggest that the latter is an important modulator of the renal response to changing plasma volume in humans.