Urinary kallikrein excretion can predict the blood pressure response to a single oral dose of captopril.

The antihypertensive efficacy of ACE inhibitors depends in theory from the blockade of the angiotensin II formation but also from the inhibition of kinin breakdown. To test whether a blunted activity of the kallikrein-kinin system might account for the failure of ACE inhibitors in lowering BP in patients in whom the renin-angiotensin system is not enhanced, thirty-one essential hypertensives with normal or low PRA were evaluated before and after a single oral dose (50 mg) of captopril. A significant fall both in systolic and diastolic blood pressure (BP) was obtained in the subgroup of patients who were classified as "normal kallikrein hypertensives" according to whether their pretreatment urinary kallikrein excretion was within the normal range, while no significant change in BP was observed in "low kallikrein hypertensives". Furthermore the mean percentage fall in mean BP, throughout the 2 hours following captopril administration, was significantly related to the basal value of urinary kallikrein excretion (r = 0.47, p less than 0.05) in the entire group of patients. Our results suggest that a blunted activity of the kallikrein system might be responsible for failure of captopril in lowering BP in patients in whom the renin-angiotensin system is not pathogenetically implicated.