Reducing effect of atrial natriuretic factor on Na, K-ATPase activity in rat kidney.

This study was designed to examine the effect of the rat atrial extract (RAE) and synthetic rat ANF123-150 (rANF) on the renal Na, K-ATPase activity in Wistar anesthetized rats. Na, K-ATPase activity was assayed by measuring the amount of inorganic phosphate liberated from ATP. RAE from 40.3, 80.6 mg of tissue and rANF in the following doses: 0.043, 0.087, 0.173, 0.260 nM/kg/min reduced Na, K-ATPase activity by 59, 64 and 11, 34, 37, 45% respectively in the renal medulla but not in the cortex. It was associated with the increase in diuresis and natriuresis. Five and ten minutes after the end of rANF administration, Na, K-ATPase activity was decreased by 78 and 57% respectively, diuresis and natriuresis were significantly higher than the control. After fifteen minutes enzyme activity returned to normal, diuresis and natriuresis were increased. After thirty minutes there was a 37% increase in Na, K-ATPase activity but diuresis and natriuresis were still higher than control values. We conclude that the inhibition of Na, K-ATPase in the medulla of the rat kidney is one of the mechanisms of ANF action.