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Calcium Dynamics: A Model System Approach^1,2,

Institute of Animal Science and Department of Statistics and Experiment Design, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

A computerized model used to simulate calcium metabolism in growing chicks combines growth equations with differential equations that account for the amount and action of various components of the plasma calcium regulating subsystems—intestine, kidney and bone. These in turn are modulated by the calcium-regulating hormones: parathyroid hormone and 1,25-dihydroxycholecalciferol. Simulation with this model indicated oscillations in the plasma calcium concentration in growing chicks under normal dietary conditions. The oscillations diminish in amplitude and finally disappear when dietary calcium concentrations are either reduced or elevated. These oscillations, triggered by the perturbation imposed by growth, are the result of the dual action of parathyroid hormone on bone on the one hand and on intestinal calcium absorption via the 1,25-dihydroxycholecalciferol synthesizing system on the other and the difference in the response time between the two subsystems. Simulation also predicts that at high or low intakes of calcium, the capacity of the control systems is exceeded and oscillations in plasma calcium diminish and finally disappear. Bone calcium, simulated for different calcium concentrations, mimics documented experimental results (J. Nutr. 73: 177–185, 1961).

KEY WORDS: • calcium homeostasis • models • biological oscillations

¹ Contribution No. 1601-E, 1986 Series, from the Agricultural Research Organization, Bet Dagan, Israel.

² This symposium, the 51st Annual Poultry Nutrition Conference: Metabolic Aspects of Calcification in Avians, was presented at the 70th Annual Meeting of the Federation of American Societies for Experimental Biology, St. Louis, MO, April 13–18, 1986. It is supported by grants from Church & Dwight, Co., Degussa Corp., Hoffmann-LaRoche, Lilly Research Laboratories, Merck & Co., Pfizer, Inc., Rhône-Poulenc, Inc., Monsanto Co., Purina Mills, Inc., Nutrius, Inc. and Shaver Farms Ltd.

Manuscript received 11 June 1986. Revision accepted 30 September 1986.