ABSTRACT
Plasma renin activity (PRA) was studied during delivery in umbilical cord venous blood
and serially in the first 48 hours of life. PRA after cesarean section without labor,
15.2 ± 2.3 ng/ml/hr (mean and SEM), was less than after cesarean section with labor,
44.1 ± 8.9 (P <.02), and vaginal delivery, 34.7 ± 4.3 (P <.05). PRA decreased during
the first 30 minutes after vaginal delivery from 34.7 ± 4.3 ng/ml/hr to 19.3 ± 3.5
(P <.01); PRA subsequently increased by four hours of life to 38.6 ± 6.7 mg/ml/hr
(P <.05) and remained elevated throughout the 48-hour study period. These data show
that PRA is stimulated during labor, decreases postnatally, and is again restimulated
in the early newborn period.
