The Effect of Beta Adrenergic Stimulation on Proximal Tubular Sodium Reabsorption 1

Summary

Studies were designed to determine whether beta adrenergic stimulation has a direct effect on proximal tubular sodium transport. The recollection micropuncture technique was utilized before and during the intrarenal infusion of isoproterenol, 0.018 μg/kg/min, the highest dose of the drug which had no renal or systemic hemodynamic effects. In the first group of five studies, the tubular fluid to plasma inulin (TF/P inulin) ratio was 1.47 ± 0.04 SEM and 1.46 ± 0.08 before and during beta stimulation, respectively. In a second group of six experiments in which alpha blockade was maintained throughout with phenoxybenzamine, 0.09 μg/kg/min, the TF/P inulin ratio was again unchanged at 1.48 ± 0.09 in the control period and 1.52 ± 0.09 in the experimental period. Nephron filtration rate and absolute reabsorption were unchanged in both groups of studies. In addition, total GFR, renal plasma flow, sodium excretion and mean arterial pressure were unchanged during isoproterenol infusion. From these data, there is no indication that beta stimulation has an inhibitory effect on proximal tubular sodium reabsorption.