CIRCADIAN-RHYTHMS OF PLASMA-CONCENTRATIONS OF NA-EXCRETION IN NORMAL AND DIABETIC RATS( AND K+ AND THEIR URINARY)

The effects of streptozotocin induced diabetes (50 mg/Kg) on the circa dian rhythms in the excretion of sodium and potassium as well as their plasma concentration rhythms were investigated. Control (C) and diabe tic (D) rats were studied during a light-dark (12h:12h) cycle and fed ad libitum. Statistically significant circadian rhythms were found for sodium and potassium excretion in C rats. The orthophases of both rhy thms occurred in the dark phase, the potassium one occurring before th at of sodium. In D rats there is increased excretion of both sodium an d potassium with the rhythmicity maintained for sodium excretion only, which has an earlier orthophase than in the C rats. Plasma sodium and potassium concentrations showed a statistically significant circadian pattern in C rats, with orthophase in the light phase. This rhythmici ty only appears in plasma potassium concentration for D rats, with ort hophase at the end of the dark phase. The results in diabetic rats may suggest that the glomerular filtration rate (GFR) and/or tubular reab sorption rhythms are still contributing to the sodium excretory rhythm , and that the loss of the circadian rhythm in sodium plasma concentra tion has no influence on the sodium excretion rhythm. Nevertheless, th e loss of the potassium excretion rhythm may suggest a disruption of t he variations in the secretory process, as this excretion seems to be independent of the plasma potassium concentration rhythm, which is not lost in D rats.