Increased Renin Activity after Cold Storage of Human Plasma

The velocity of angiotensin generation during incubation for 3 h at 37 °C increased up to 600% if plasma (EDTA) from normal men was first preincubated for 3 days at 4 °C. Longer preincubation (9–31 days) generally resulted in additional potentiation that continued to be expressed during incubation periods of 3–48 h at 37 °C. The effect is not abolished in the presence of up to 200 μg/ml of neomycin sulfate. Recovery of synthetic angiotensin I added to both cold-stored and control plasma is about 90% after 3 h of contact at 4 °C. The cause of potentiation has not been established, but possibilities under investigation include renin activation and preferential degradation of a renin inhibitor.