Comparative study of active and inactive plasma renin in healthy infants and adults.

Active, inactive and total plasma renin activity (obtained after cryoactivation), active, inactive and total plasma renin concentration (obtained after acid activation) and plasma angiotensin II were measured in 20 healthy infants and in 20 healthy adults. Active plasma renin activity but not active plasma renin concentration or plasma angiotensin II were significantly higher in the infants. In the latter both cryoactivation and acid activation resulted in a nearly 100% increase of the mean active plasma renin activity or active plasma renin concentration. Therefore the active fraction represented 0.5 of total renin with both methods. This was different in adults, where acid activation was more effective than cryoactivation. In adults, plasma angiotensin II was correlated only with active plasma renin activity and active plasma renin concentration; in contrast, plasma angiotensin II of infants was correlated with both active plasma renin activity, and with inactive plasma renin activity.