Reduced urinary kallikrein activity in rats developing spontaneous hypertension

Urinary kallikrein activity, intake, and excretion of sodium and water were measured in metabolic balance studies on spontaneously hypertensive rats (SHR) of the Okamoto-Aoki strain and normotensive Wistar-Kyoto rats (WKY) on a normal sodium diet from 4 through 15 wk of age. Urinary excretion of active and total kallikrein was significantly lower in SHR at all ages examined and represented a stable percentage of the values in age-matched WKY throughout development, on the average 69.5 and 67.4%, respectively. SHR exhibited a lower urinary excretion of sodium and water than WKY, a higher cumulative sodium balance at all ages studied, and a higher cumulative water balance only at ages 7 and 8 wk. The slopes of the regression lines correlating urinary kallikrein to systolic arterial pressure and to urinary excretion and cumulative balance of sodium and water were always significantly less in SHR than in WKY. The results of the present study indicate that SHR developing hypertension exhibit a precocious and stable abnormality in renal excretion of kallikrein activity.