Theophylline-Induced Hypocalcemia in Sheep

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Abstract
Intravenous infusion of theophylline at rates of 1 and 2 mg/kg/min. caused marked hypocalcemia in intact sheep. The plasma concentration of NEFA increased. The lipolytic but not the hypocalcémie effect of theophylline was completely inhibited by nicotinic acid. This fact suggested that lipid mobilization and hypocalcemia were not related. The effects of parathyroid hormone are mediated by 3′, 5′AMP, and methyl xanthines are known to inhibit the inactivation of 3′, 5′AMP. There is, however, evidence in the literature that excessive amounts of 3′, 5′AMP inhibit rather than increase bone resorption. It was therefore suggested that the used amounts of theophylline caused an excessive accumulation of 3′, 5′AMP in bone tissue, so that bone resorption was inhibited and hypocalcemia developed.