ROLE OF PERFUSATE HYDROGEN-ION ACTIVITY IN KALLIKREIN RELEASE FROM ISOLATED RAT KIDNEYS

The present experiments were performed to investigate whether renal ka llikrein release by isolated perfused rat kidneys correlates with acid -base-related parameters. Kallikrein excretion per millilitre of glome rular filtrate was inversely correlated with perfusate pH (r = -0.49, P < 0.001) and HCO3- concentration (r = -0.46, P < 0.005). A direct re lationship between kallikrein excretion per millilitre of glomerular f iltrate and urinary Na+/K+ ratio was found (r = 0.59, P < 0.001). Some 86% of the variability (F ratio 110, P < 0.00001) of urinary kallikre in activity was attributable to the perfusate pH and the urinary catio n ratio. Therefore, urinary kallikrein activity was highly correlated with perfusate H+ activity corrected by the urinary Na+/K+ ratio (r = 0.92, P < 0.0001). Kallikrein secretion into the distal tubular fluid appears to be regulated by blood Hf activity, and modulated by factors that affect the distal Na+ and K+ handling. The HCO3- excretion rate was inversely correlated with the urinary kallikrein activity (r = -0. 62, P < 0.001). This finding confirms previous data from the author's laboratory showing a kallikrein involvement in the regulation of HCO3- secretion in rats and rabbits. Kallikrein probably transduces the sen sing of interstitial fluid H+ activity by the connecting tubule cells into an appropriate translocation of HCO3- or H+ to the tubular lumen by the intercalated cells.