Inhibition of arginine vasopressin-stimulated Na+ K+ ATPase activity by difluoromethyl ornithine in the rat renal medulla.

Arginine vasopressin (AVP) stimulates Na+ K+ ATPase and ornithine decarboxylase (ODC) activity in the rat medullary thick ascending limb. The effect of difluoromethyl ornithine (DFMO), a specific inhibitor of ODC activity, on AVP-stimulated Na+ K+ ATPase activity was evaluated using a cytochemical bioassay. Peaks in Na+ K+ ATPase activity in cultured rat renal segments which occurred after tissue had been exposed to 1 fmol AVP/l were completely inhibited by the addition of 20 mmol DFMO/l to the culture medium containing AVP. The addition of 20 mmol DFMO/l to the culture medium containing AVP in the concentration range 0.001-10 fmol/l inhibited completely the stimulation of Na+ K+ ATPase activity by AVP. The response of Na+ K+ ATPase to increasing doses of ATP (10-40 g polypeptide/l) was not influenced by the addition of 20 mmol DFMO/l to the culture medium containing AVP, suggesting that the prevention of AVP-stimulated Na+ K+ ATPase activity by DFMO was not due to a direct effect on the enzyme.