Oscillatory behavior of control-systems of calcium homeostasis in chickens.

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-hydroxyvitamin D3-1-hydroxylase in chicks subjected to a 12:12 h light: dark cycle ALSO followed diurnal oscillations, with a nadir 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 oscillated 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.