CIRCADIAN VARIATION IN THE NATRIURESIS PRODUCED BY POTASSIUM INTAKE IN THE RAT

To determine if there was an endogenous circadian regulation of the re nal natriuretic response to acute potassium loading, unanesthetized ra ts, either fed or fasted, were given an intragastric infusion of KCl o ver 100 min at the times of maximum and minimum circadian sodium excre tion, i.e. in the early dark and early light phase of a 12 hour dark/l ight cycle. During KCl infusion plasma potassium concentration as well as sodium and potassium excretion progressively increased. Cumulative sodium excretion was greater in dark than light phase, and was greate r in fed than fasted rats. Sodium excretion was greater at any given e levated level of plasma potassium in the dark than light phase. The re sults suggest that reported variations in the effects of high potassiu m diets on sodium excretion, blood pressure, or circulatory pathology in hypertension, may in part be explained by variations in the time of oral potassium intake.