AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 6 1173-R1181, Copyright © 1987 by American Physiological Society
Model of plasma calcium regulation: system oscillations induced by growth
S. Hurwitz, S. Fishman and H. Talpaz
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.
