Short lasting increase in urinary specific kallikrein activity during long term administration of furosemide

Furosemide was administered for seven days to normal rats. Urinary kallikrein excretion showed a biphasic response during the seven consecutive days of study. During the initial three days only the kininogenase activity showed a significant increase without any variation in the excretion of the immunoreactive kallikrein. The specific urinary kininogenase activity was therefore enhanced. After three days of furosemide administration, both the urinary kininogenase activity and urinary immunoreactive kallikrein were augmented. The urinary specific kininogenase activity was that time no more different when compared to the basal value. Considering the delay time of three days, this second part of the response could be a mineralocorticoid mediated effect. In this respect, kidney level of immunoreactive and kininogenase activity of kallikrein are also increased after seven days of furosemide administration. However the short lasting increase in urinary specific kininogenase activity observed during the initial three days is due to a change in the ratio active versus inactive kallikrein without any variation of total kallikrein. It is possible that this immediate response results of a direct effect of furosemide acting either on the preferential excretion of the active form or on the activation of the prokallikrein in the urine.