The Role of the Adrenergic Nervous System in the Renal Response To Acute Extracellular Fluid Volume Expansion. ∗

Summary

The role of the adrenergic nervous system in the renal response to acute extracellular fluid (ECF) volume expansion was examined in the same dogs before and after catecholamine depletion with reserpine. In the control experiments before reserpine, acute ECF volume expansion produced marked increases in glomerular filtration rate (GFR). pamino-hippurate clearance (C_PAH), mean arterial pressure (MAP), urine flow (V), sodium excretion (U_NaV) and osmolar clearance (Cosm). One week later the same animals were studied under the same experimental conditions except for generalized impairment of the adrenergic nervous system secondary to catecholamine depletion with reserpine. The ECF volume expansion produced very similar increases in GFR, C_PAH and filtered loads of sodium (F_Na) before and after reserpine; however, the MAP, and thus renal perfusion pressures, were significantly lower after reserpine. Diminished urine flows (V), sodium excretion rates (U_NaV) and osmolar clearances (Cosm) occurred after reserpine and correlated closely with the level of MAP. Since the F_Na were comparable before and after reserpine, the effect of the lower MAP after reserpine on U_NaV appeared to be related to a relatively greater tubular reabsorption of sodium. This study indicates, therefore, that the role of adrenergic nervous system in the renal pressure-flow relationships is an important factor in the natriuretic response to acute ECF volume expansion in dogs.