Release of active and inactive renin by the pig kidney during development

The release of both active and acid-activatable (inactive), renin was determined in piglets ranging in age from 3 to 53 days. The concentration of active renin in arterial plasma during control periods decreased from 4.4 +/- 1.1 ng/ml in 3--5-day-old animals to 0.7 +/- 0.1 ng/ml in 42-53-day-old animals, while the rate of release of active renin was unchanged (11.8 +/- 5.1 ng/min and 7.5 +/- 3.4 ng/min, respectively). Both isoproterenol and furosemide stimulated release of renin in all age animals while propranolol supressed renin release. The data indicate that the qualitative control of renin release is similar in animals of various ages and stages of development. However, the differences in the concentration of renin in plasma of newborn and more mature animals may depend on factors other than release of renin by the kidney. Newborn animals release both active and inactive renin from the kidney.