The effects of salt loading on the renin-angiotensin control of blood pressure in the newborn lamb.

Abstract

Summary: The renin-angiotensin system control of newborn blood pressure was studied in six sets of twin newborn lambs. The mean aortic blood pressure and plasma renin activity (PRA) was 79.6 ± 0.96 mmHg (mean and S.E.) and 6.88 ± 0.83 ng/ml/h in the chronically salt-loaded lambs (10 mEq/kg/day for 5 days); 86.16 ± 1.8 mmHg (P < 0.001) and 20.48 ± 2.46 ng/ml/h (P < 0.001), respectively in the control lambs. PRA and % change after angiotensin 11 blockade with saralasin was greater in the control lambs, 181.5 ± 6.09 ng/ml/h and 780% than in the chronically salt-loaded lambs, 40 ± 10.47 and 480%, P < 0.001. Blood pressure decreased 10 mmHg only in the control lambs, P < 0.001. An angiotensin 11 dose of 0.25 μg/kg/min increased blood pressure 32 ± 3.1 mmHg in control mambs, and 0.10 μg/kg/min increased blood pressure 32 ± 3.2 mmHg in acutely salt-loaded (10 mEq/kg in 20 ml 5% dextrose/water) lambs. PRA and mean aortic blood pressure decreased in the acutely salt-loaded lambs from 22.3 ± 3.0 ng/ml/h and 86.6 ± 1.0 mmHg to 11.3 ± 1.1 and 76.4 ± 0.8, P < 0.01, respectively. These data show that sodium loading will suppress the basal renin-angiotensin system levels, and mean aortic blood pressure; decrease the hypotensive and PRA responses to saralasin; and increase the pressor responsiveness to angiotensin 11.