OBJECTIVES: Our purpose was to determine whether chronic physiologic elevations in plasma angiotensin II levels decrease plasma renin concentration, alter the relationship between active renin and prorenin in fetal plasma and kidney, and depress the expression of renal renin messenger ribonucleic acid in the fetus.

STUDY DESIGN: Seventeen chronically catheterized ovine fetuses at approximately 130 days' gestation were infused with either angiotensin II (48.9 ± 3.5 ng/kg · min) or vehicle (5% glucose in water) for 72 hours.

RESULTS: Mean arterial pressure increased significantly by 1 hour of infusion and continued to increase throughout the infusion. The plasma active renin concentration was significantly decreased by 1 hour of the infusion, whereas the prorenin concentration was not decreased until 24 hours of the infusion. After 72 hours of angiotensin II infusion the renal tissue prorenin content decreased (21.5 ± 5.1 ng/mg · hr angiotensin I vs 46.4 ± 6.6 ng/mg · hr angiotensin I in the control animals, p = 0.01), whereas the active renin concentration did not change (26.6 ± 5.1 ng/mg · hr angiotensin I vs 35.1 ± 5.4 ng/mg · hr angiotensin I in the control animals, p = 0.28). The renal renin messenger ribonucleic acid expression tended to be lower in the angiotensin II–treated fetuses (p = 0.10).

CONCLUSION: Chronic physiologic increases in fetal plasma angiotensin II suppress the secretion of active and prorenin and alter the relationship between processing and secretion of renin in the fetal kidney. (Am J Obstet Gynecol 1997;176:931-7.)