Minerals and Trace Elements Effect of Dietary Caffeine and Theophylline on urinary Calcium Excretion in the Adult Rat SUSAN J. WHITING1 ANDHANNAH L WHFTNEY Department of Home Economics, Mount Saint Vincent University, Halifax, Nova Scotia, Canada B3M 2J6 ABSTRACT The chronic effects of dietary caffeine or theophylline on urinary calcium excretion were investigated in the adult male rat. When caffeine was added at two concentrations, 0.75 and 1.50 g/kg diet, 24-h urinary calcium excretion rose 300 and 450% on d 7, and 200 and 330% on d 14, respectively. There were no changes in the 24-h urinary excretion of phosphate, sulfate, sodium and cAMP nor did urine volume change. The high dose of caffeine was compared to an equimolar dose of theophylline ( 1.39 g/kg diet) in both Wistar and Sprague-Dawley rats. Urinary calcium excretion in theophylline-treated rats was significantly greater than in caffeine-treated rats on all sampling days and in both strains of rat; the calciuric effect lasted at least 22 d. When rats were given indomethacin (3.3 mg/kg diet) the calciuria induced by caffeine and theophylline was abolished, and sodium excretion in all groups was reduced by 35-50%, but urine volume was unchanged. The calciuria of methylxanthine feeding may result from a prostaglandin-mediated process distinct from diuresis. J. Fiutr. 117: 1224-1228, 1987. INDEXING KEY WORDS: •calcium •caffeine •theophylline •indomethacin •calciuria Caffeine, a common component of the human diet, has recently been shown to influence calcium metab olism in humans (1, 2). Caffeine intake was found to be positively associated with urinary calcium excretion in a study of dietary intakes and calcium balances of perimenopausal women (1). The relationship between caffeine and calcium excretion has also been directly examined in a short-term (3-h) study of adults that showed that urinary calcium excretion increased upon administration of a single 300-mg dose of caffeine (2). Because caffeine ingestion has been found to be signif icantly correlated to a decrease in bone mineral content of adult women (3), it is of special interest to explore the relationship between caffeine ingestion and cal cium metabolism. The purpose of the experiments described in this pa per was to examine the chronic effects on calcium ex cretion of caffeine and theophylline ingestion in the rat. It has been shown recently that rats injected with large doses of caffeine demonstrate an elevated urinary calcium excretion (4). We looked first at the effects of feeding two doses of caffeine on urinary excretion of calcium, sodium, phosphate, cyclic AMP and urine vol ume. We then compared the effects of feeding caffeine to those produced by feeding another methylxanthine, theophylline, which is a more potent diuretic than caf feine in the rat (5). Because prostaglandin production is involved in methylxanthine-induced diuresis (5) and in caffeine-induced calciuria found in human subjects (6), we also administered the prostaglandin synthesis inhibitor, indomethacin, to determine whether xan- thine-induced calciuria is abolished in rats by blocking prostaglandin formation. MATERIALS AND METHODS Animals. Male Wistar rats (Charles River, LaSalle, Que.) were used in experiments 1 and 2. Male Sprague- Dawley rats (Canadian Hybrid Farms, Kentville, NS) were used in experiment 3. In all experiments, rats were randomly assigned to one of three groups and housed individually in wire-bottom metabolism cages with lighting regulated to give a 12-h light-dark cycle. All animals were acclimated to a control diet for 1 wk before the collections. Food and water were provided ad libitum throughout. Body weights and feed intakes were recorded weekly and biweekly, respectively. 'Supported by giants from the Natural Sciences and Engineering Research Council (NSERC) of Canada and from Mount Saint Vincent University. 0022-3166/87 $3.00 ©1987 American Institute of Nutrition. Received 2 June 1986. Accepted 3 March 1987. 1224 by guest on August 19, 2015 jn.nutrition.org Downloaded from