Hypoxemia increases renin secretion rate in anesthetized newborn lambs

Abstract

The response of renin secretion rate (RSR) to acute systemic hypoxemia (mean arterial p0 2 34±8 torr) was studied in mechanically ventilated, anesthetized newborn lambs 5–10 days of age (n=6). Ventilation of these lambs with room air (normoxemia) was followed by administration of low oxygen inhaled gas mixture (f i0 2 0.11) which was associated with no change in arterial pC0 2, pH, mean arterial pressure (MAP), renal blood flow (RBF, measured by electromagnetic flow probe), and calculated renal vascular resistance (RVR). Arterial plasma renin activity (PRA A 4.28±1.73 to 6.46±3.00 ng AI/ml · hr), renal vein plasma renin activity (PRA RV, 6.26±3.79 to 11.44±7.11 ng AI/ml · hr) and renin secretion rate (RSR, 19.86±21.70 to 51.32±48.54 units/min · KgBW) increased significantly (p<0.05) in response to hypoxemia. Restoration of normoxemia (arterial p0 2 100±18 torr) was associated with significant decline in MAP (to 65±14 mmHg) and RBF (to 9.0±2.1 ml/min · KgBW) and further increases in PRA A (to 8.98±3.40 ng AI/ml · hr), PRA RV (to 19.04±10.62 ng AI/ml · hr) and RSR (to 88.6±77.6 units/min · KgBW). PRA A correlated strongly with PRA RV (r=0.84) and RSR (r=0.60) in these lambs. These results suggest that PRA A, PRA RV and RSR increase in response to hypoxemia in anesthetized lambs by a mechanism other than renal arterial baroreceptor stimulation, although this mechanism may be active during recovery from hypoxemia. Furthermore, PRA A closely approximates RSR in newborn lambs under these conditions.