Cryoactivation of inactive renin in human plasma.

The mechanism of the increase in renin activity in human plasma which had been kept -5 degrees C for 4 days (cryoactivation) was investigated. From the results of clinical studies, it is likely that the controling mechanism of inactive renin has something in common with that of active renin. The experimental data showed that the increase in renin activity of human plasma by cryoactivation was closely correlated to the increase obtained by incubation with trypsin (r = 0.88, p less than 0.001, n = 10). Soybean trypsin inhibitor, aprotinin and di-isopropylfluorophosphate (DFP) inhibited cryoactivation, indicating that the cryoactivation is due to the action of a trypsin-like serine enzyme. Trypsin which had no effect on plasma renin activity in the presence of the same amount of soybean trypsin inhibitor at 37 degrees C, activated the renin activity during cold incubation, suggesting that the dissociation of the trypsin-inhibitor complex may have taken place at a low temperature. Endogenous trypsin inhibitor is also likely to lose its affinity to endogenous trypsin-like enzyme at a low temperature.