Effects of physiological increments in renal arterial plasma osmolality on renin secretion rate

The present study was performed in anesthetized dogs to examine the effects of physiological increments in renal arterial plasma osmolality on basal renin secretion rate and on the response of renin secretion rate to RNS. Three concentrations of hypertonic NaCl were infused into the renal artery (i.r.a.) at 0.38 ml/min for 3 min; i.r.a. Hypertonic NaCl at 0.45M, 0.9M, and 1.8M increased the renal arterial plasma osmolality by 6 +/- 2, 8 +/- 2, and 28 +/- 9 mOsm/kg H2O, respectively. NaCl, 0.45M, did not affect renal function, whereas both 0.9M and 1.8M NaCl increased renal blood flow and urinary sodium excretion; neither 0.45M, 0.9M, nor 1.8M NaCl affected renin secretion rate. RNS was applied at two different frequencies: LFRNS and HFRNS. LFRNS did not affect renal blood flow, whereas HFRNS reduced renal blood flow by 50%. Both LFRNS and HFRNS increased renin secretion rate significantly. An i.r.a. infusion of 0.9M NaCl increased urinary sodium excretion and reduced the renin secretion rate response to LFRNS (-52% +/- 15, p less than 0.02) and HFRNS (-25% +/- 8, p less than 0.01). These findings demonstrate that increases in renal arterial plasma osmolality within the physiological range increase renal blood flow but do not affect renal secretion rate. The renal secretion rate response to RNS is attenuated by increased renal arterial plasma osmolality, an effect consistent with increased sodium chloride delivery to the distal tubular macula densa receptor.