Model of plasma calcium regulation: system oscillations induced by growth

The process of growth was included in a model for simulation of calcium homeostasis in the chick, using data of carcass composition and a model of growth and energy intake. Computer simulations, made for chickens between 0 and 10 wk of age, predicted oscillations in plasma calcium and its major regulatory systems. Analysis of the oscillations indicated a periodicity of approximately 55 h. The oscillations were proportionally dependent on the rate of growth, disappearing almost completely when growth rate was made equal to zero. Subject to the validity of the model, it is suggested that the oscillations in plasma calcium and some of the components of the regulatory systems are induced by a continuous perturbation (growth) resulting in a dual response to the main regulatory hormone, parathyroid hormone, one rapid with a response time of minutes (bone), and one delayed, with a response time of hours (calcium absorption via the metabolism of 1,25-dihydroxychole-calciferol). It is also suggested that some of the normal variance and some of the rhythmicity observed previously in various components of the calcium regulatory system may be the results of spontaneous oscillations.