AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 5 684-R687, Copyright © 1984 by American Physiological Society
Calcium metabolism in birds: computer simulation of response to 1,25-dihydroxycholecalciferol
S. Hurwitz, S. Fishman, A. Bar and H. Talpaz
A simulation model of calcium metabolism in the chick has been used to
evaluate the response of the systems that regulate plasma calcium to a
continuous input of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] from the
intestine. The results of simulation showed that the concentration of the
vitamin D metabolite in the intestine increased during the first 24 h and
thereafter decreased slightly due to suppression of endogenous hormone
production. Metabolite accumulation was accompanied by an increase in
calcium absorption, with a lag period of about 4 h. Most of the increase in
absorbed calcium was excreted in the urine, with a lesser change in net
bone calcium uptake. Plasma calcium increased with time, in proportion to
the intake of the exogenous hormone. The validity of the predicted
steady-state plasma calcium levels, and bone and kidney calcium flows, is
discussed. The results of the simulation demonstrate the importance of the
vitamin D-intestinal axis in regulation of plasma calcium.
