The influence of intravenous infusion of electrolytes on the diurnal excretory rhythms

In freely moving rats the diurnal variation in electrolyte excretion was studied. Food was available during either the dark or the light period. The lights were on from 0800–2000; the dark phase extended from 2000–0800 hrs. The electrolyte excretory rhythms were studied during a control period, in which the minerals were present in the food, and during experimental periods, when successive minerals were not present in the food but were instead given by constant intravenous infusion. For both groups the excretory rhythms of K, Mg and P persisted during continuous infusion but the times of maximum and minimum excretion differed. Day-fed animals exhibited a remarkable decrease in amplitude during the mineral infusion period. In contrast, the calcium excretory pattern was only influenced by the feeding period.