Effect of theophylline on calcium metabolism and circulating vitamin D metabolites.
Theophylline has been shown to induce the hepatic microsomal enzyme system. These same enzymes increase the metabolism of vitamin D and 25-hydroxyvitamin D when induced by chronic barbiturate or phenytoin administration. To assess the long-term effects of theophylline on vitamin D and calcium metabolism, young rats were treated for 4 weeks with constant subcutaneous theophylline infusions. Theophylline-treated animals had a significantly increased urinary calcium excretion (p less than 0.0001), a significantly decreased total body calcium per gram body weight (p less than 0.05), and significantly decreased serum 25-hydroxy-vitamin D concentrations (p less than 0.002) when compared to control animals. These alterations in the concentration of 25-hydroxyvitamin D may impair the ability to increase 1,25-dihydroxyvitamin D-dependent intestinal calcium absorption to compensate for excessive urinary calcium losses. These data suggest that theophylline promotes skeletal calcium loss, and its use may be a risk factor for the development of osteopenia in humans.
Fortenbery
E J
EJ
Department of Radiology, Nuclear Medicine Service, Fitzsimmons Army Medical Center, Aurora, CO 80045.
McDermott
M T
MT
Duncan
W E
WE
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002112:Calcifediol / Q000097:blood*; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000378:metabolism*; D007260:Infusion Pumps; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D051381:Rats; D013806:Theophylline / Q000494:pharmacology*
D010281:Parathyroid Hormone; D013806:Theophylline; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium