Hurwitz, S., Institute of Animal Science, The Volcani Center, Bet Dagan, 50250, Israel, The Department of Biochemistry, University of California, Riverside, California, 92521, United States
Miller, B., Institute of Animal Science, The Volcani Center, Bet Dagan, 50250, Israel, The Department of Biochemistry, University of California, Riverside, California, 92521, United States
Norman, A.W., Institute of Animal Science, The Volcani Center, Bet Dagan, 50250, Israel, The Department of Biochemistry, University of California, Riverside, California, 92521, United States

Computer simulation of calcium homeostasis in chicks predicted an oscillatory behavior of bone calcium flow and kidney 25‐hydroxyvitamin D3‐1 hydroxylase with a periodicity of 56 h and a 9 h phase difference between the two signals. In growing chickens subjected to a light: dark cycle of 22:2 h, and intravenously dosed with 45Ca, the temporal changes in plasma 45Ca could be described by an exponential decline with superimposed diurnal oscillations. The activity of the renal 25‐hydpoxyvitamil D3‐1‐hydroxylase in chicks subjected to a 12:12 h light: dark cycle ALSO followed diupnal oscillations, with a ladir at the beginning of the light period and a peak 12 h later. The production of 1,25‐dihydroxyvitamin D3 by primary cultures of chicken kidney cells mscillated with a periodicity of 5.6 h or shorter. It is suggested that despite the differences in phase and periodicity between the simulation predictions and actual results, the oscillations in both 1‐hydroxylase and bone calcium flow could be coupled through the hormonal systems involved in regulation of plasma calcium. Copyright © 1994 Wiley‐Liss, Inc.