Urinary kallikrein and plasma renin activity in normal human pregnancy.

Urinary kallikrein excretion (UK), plasma renin activity (PRA), and 24-hour urine volume, sodium, and potassium excretion rates were determined sequentially in 16 normal pregnant women. Throughout gestation, UK was significantly elevated as compared to values obtained in 13 control women (1466 +/- 152 vs 375 +/- 90 U/g creatinine). The highest level was observed in Period 2 of gestation, corresponding to Weeks 17 to 24. PRA was also significantly elevated during pregnancy (11.97 +/- 1,35 vs 1.06 +/- 0.90 ng/ml/hr), with the highest level in Period 2. Mean 24-hour urine volume, sodium, and potassium excretion rates were significantly higher during pregnancy. Nor correlation was found between UK and: PRA, urine volume, and sodium and potassium excretions. These findings indicate a consistent activation of the renal-kallikrein-kinin system during pregnancy. We postulate that this vasodilator system might play a role in the maintenance of normotension in pregnancy, counteracting tha effect of the renin-angiotensin-aldosterone system.