Plasma active and inactive renin concentrations in children.

Plasma active and inactive renin concentrations (PARC and PIRC) were measured by immunoradiometric assay. Age-related changes in PARC, PIRC and the ratio of PARC/PIRC were studied in 78 normal children, age 1 month to 15 years. The effects of upright position for 15 min were also investigated in 7 postmenarcheal girls. PARC and PIRC in infants were significantly higher than in older children and their ratio of PARC/PIRC was significantly lower than in prepubertal children. During puberty, PARC, PIRC and their ratio were higher in premenarcheal girls than in postmenarcheal girls. In the upright position, PARC, PIRC and the ratio were increased significantly. These finding suggest that: (1) the production of inactive renin is increased but the activation of renin may be lowered in infants; (2) the activation of renin is affected by the menstrual cycle, and (3) the production and activation of renin are increased during short term standing.