Inhibitory effect of epinephrine on renal potassium secretion: A micropuncture study

The effect of epinephrine on renal potassium excretion was examined in the rat. In group I KCl was infused acutely to increase plasma K [P(K)] by 2.0 meq/liter; urinary K excretion [U(K)V] rose by 1.22 μeq/min. In group II rats, which received a similar dose of KCl but with epinephrine, the increase in P(K) (Δ = 0.8 meq/liter, P < 0.001) was blunted and U(K)V was reduced (Δ = 0.23 μeq/min, P < 0.001). To determine whether the reduction in U(K)V resulted from the smaller increase in P(K) or from a direct action of epinephrine on renal K transport, a third group of animals received a lower dose of KCl. Despite similar P(K) levels, the epinephrine group excreted significantly less K in the urine (0.61 vs. 0.93 μeq/min). In group IV propranolol was infused with KCl; U(K)V was modestly increased. The effects of epinephrine on U(K)V were unrelated to changes in glomerular filtration rate, urine flow, or U(Na)V. Micropuncture results showed that at comparable P(K) levels epinephrine had no direct effect on K secretion by the distal tubule but indirectly inhibited K secretion in this nephron segment by reducing P(K). In addition, epinephrine reduced K addition at tubular sites beyond the late distal tube, most likely in the collecting tubule.