AJP - Regulatory, Integrative and Comparative Physiology, Vol 237, Issue 5 311-R317, Copyright © 1979 by American Physiological Society
Endogenous nature of circadian rhythms in calcium metabolism
J. F. Staub, A. M. Perault-Staub and G. Milhaud
Rats studied when the lights are on from 0600 to 1800 daily and fed only in
the dark period displayed circadian rhythms in plasma calcium (ionized and
total) and 45Ca concentrations, 6 and 8 days after 45Ca administration. In
rats fed a calcium-deficient diet, the amplitude of daily variation of
plasma ionized and total calcium increased markedly whereas plasma 45Ca
daily fluctuation remained essentially unchanged. In the calcium-deficient
rats, significant correlations between plasma calcium and 45Ca and between
plasma calcium and magnesium were observed throughout the 24 h; circadian
periodicity of calcium metabolism persisted in rats fasted overnight,
regardless of the illumination schedule. Normal daily fluctuations in
plasma 45Ca, lost after thyroparathyroidectomy (TPTX), were restored by
feeding the TPTX rats a high-calcium diet. These results demonstrate
clearly that circadian rhythms of calcium metabolism occurred irrespective
of the light-dark schedule, the calcium supply through intestines and the
thyroparathyroid system. An attractive suggestion is that circadian
rhythmicity originates as a result of dynamic properties involving
nonlinear processes of calcium metabolism.
