Diurnal rhythms in calcium and phosphate metabolism in rodents and their relations to lighting and feeding schedules.

Diurnal fluctuations in serum Ca, inorganic phosphorus, Mg, and alkaline phosphatase activity and their relations to lighting and feeding schedules were investigated in nocturnal rats and diurnal asiatic chipmunks. The following results were obtained: all parameters in the animals fed ad libitum and adapted to a regulated light-dark cycle (with light from 7.00 to 19.00 h) showed diurnal rhythms; under the same experimental condition, the patterns of the rhythms in the nocturnal rat and the diurnal asiatic chipmunk were nearly 180 degrees out of phase with each other; under the continuous lighting condition for more than 10 days, the diurnal rhythms of the parameters in rats decreased in their amplitudes, and phase shifts or marked modulations in the diurnal curves occurred when the time of availability of food was restricted from 9.00 to 17.00 h without altering the lighting schedule. The above findings support an idea that the rhythmicity is one of the essential features involved in the Ca metabolism. It is demonstrated that the environmental photofraction is one of the essential factors in generating or in maintaining the circadian rhythm of Ca metabolism as in other physiological processes and that the feeding time also could have a marked effect on the diurnal rhythm in the Ca metabolism.