Age-related differences in the stoichiometry of the renin-angiotensinogen reaction in rat plasma

Generation of immunoreactive angiotensin I (AI) in plasma of either adult or 10-day-old rats proceeded via first-order kinetics. Although the concentration (Vmax) of renin was 5-fold greater in neonatal compared to adult plasma, the specific activity (kapp/Vmax) of the enzyme was 2-fold greater in adults. Both enzymes exhibited a similar affinity (Km) for angiotensinogen; and at both ages, the generation of AI was limited by insufficient endogenous substrate to sustain maximum rates. In conclusion, although the catalytic properties of renin do not change with age, subtle differences in the stoichiometry of the reaction may have profound implications in determining compensatory mechanisms involved in renin-dependent regulation of homeostasis in developing animals.