The effects of angiotensin II, saralasin, and furosemide on inactive renin in the fetal lamb.

The effects of angiotensin II, saralasin, and furosemide on plasma prorenin (inactive renin, cryoactivated, and trypsin activated) were studied in the fetal lamb. Cryorenin and trypsin-activated renin decreased from 4.0 +/- 1.0 ng/ml/hr of plasma renin activity (PRA) and 7.3 +/- 1.0 to 0.05 +/- 0.01 and 1.7 +/- 1.0 (P less than 0.01), respectively, after 15 min of angiotensin II infusion; active renin did not statistically decrease. Cryoactivated and trypsin-activated renin increased from 2.2 +/- 0.5 ng/ml/hr (mean +/- S.E.) and 4.9 +/- 0.9 of PRA to 4.6 +/- 1.0 and 8.5 +/0 1.5, respectively, after 30 min (P less than 0.05) of the saralsin (10 micrograms/kg/min) infusion, whereas active renin showed no change. Furosemide increased cryorenin and trypsin-activated renin in parallel to active renin from 2.9 +/- 1.1 ng/ml/hr and a6.9 +/- 1.5 of PRA to 5.0 +/- 1.0 and 11.2 +/- 1.5 at 65 min, respectively (P less than 0.05). These data show that prorenin levels are high in the fetal lamb, angiotensin II can inhibit prorenin but not renin, and a negative feedback loop exists between angiotensin II and prorenin, but not renin.