Increased urinary kallikrein-like activity in the syndrome of inappropriate secretion of antidiuretic hormone.

The role of the kallikrein system in the natriuresis of SIADH was studied in 3 patients. Following free water intake, serum Na decreased. Urinary Na excretion, urinary aldosterone excretion and urinary kallikrein-like activity (UKaV) increased. Significant relationships were observed between UKaV and urinary aldosterone excretion during the study. Further, there were significant relationships between serum Na and UKaV, and between uric acid clearance and UKaV. In 1 patient, who was observed for a longer period, a significant relationship was observed between Na clearance and UKaV. We conclude that UKaV is increased during hyponatremia in SIADH by volume expansion. This increase in UKaV may play a role in the natriuresis in SIADH.