Specificity of the Vascular Smooth Muscle Contractile Response to a Labile Digitalis-like Factor in Peritoneal Dialysate: The Influence of Potassium

Although multiple lines of evidence have suggested that a circulating endogenous digitalis-like factor (DLF) might contribute to the pathogenesis of sodium-sensitive hypertension, the subject remains controversial. This study was designed to compare the influence of potassium on vascular responses to an endogenous DLF isolated from peritoneal dialysate (PD) in volume-expanded patients with other sodium pump inhibitors, such as ouabain and bufalin, and the influence of serotonin as an index of specificity. An increase in bath potassium (K+) concentration from 2.7 to 10 mmol/L relaxed bovine facial artery precontracted with serotonin, but induced a secondary paradoxical contractile response in vascular-smooth muscle (VSM) precontracted with ouabain, bufalin, or the endogenous DLF from PD. There was a strong correlation between the primary contraction induced by each sodium pump inhibitor, and the magnitude of the paradoxical secondary contractile response. The increase in potassium concentration did not influence ouabain binding in the 20 min required for the experimental protocol, although binding was decreased after 120 min. The findings indicate that the VSM contractile response induced by the agent isolated from PD reflects VSM sodium pump inhibition, supporting its candidacy as a circulating regulator of the sodium pump.