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Physiological Effects of Caffeine in the Rat: Extracellular Cyclic AMP Status, Growth Pattern and Glucose Metabolism in Adipose Tissue

Department of Nutrition, University of Montreal, C.P. 6128, Succursale A, Montreal, Quebec, Canada H3C 3J7

The authors investigated the effect of moderate caffeine intake on overall cyclic adenosine monophosphate (AMP) metabolism in the rat and its relationship to growth and glucose metabolism in adipose tissue. Male Sprague-Dawley weanling rats were divided into control and treatment groups. The latter received caffeine via drinking water (0.06 mg/ml H₂O) during a 4-week period whereas controls received water only. At weekly intervals, urinary cyclic AMP excretion, food intake and weight gain were measured. Plasma cyclic AMP caffeine and glucose were determined at moment of death and in vitro lipogenesis and glycogen synthesis from [6-¹⁴C]glucose in epididymal adipose tissue were assayed. Although urinary cyclic AMP excretion was negatively correlated to caffeine intake during the 2nd week of the experiment, this did not reach significant levels, nor did this trend continue into the 4th week. Growth pattern and food efficiency were similar in both groups as were blood glucose and cyclic AMP values at moment of death. In vitro glycogen synthesis from [6-¹⁴C] glucose in adipose tissue showed a 40% increase, this parameter being positively correlated with plasma caffeine concentration. Glucose uptake and lipogenesis were unaltered in epididymal fat pads. These data suggest that regular intake of a moderate dose of caffeine leads to homeostasis of overall cyclic AMP metabolism and of selected physiological parameters under study. Alteration of glycogen synthesis in adipose tissue is discussed in relation to documented effects of caffeine ingestion on catecholamine secretion.

KEY WORDS: • caffeine • extracellular cyclic AMP • adipose tissue

¹ To whom reprint requests should be sent: Nutrition Department, Sunnybrook Medical Centre 2075 Bayview Ave., Toronto, Ontario, Canada M4V 3M5.

² Supported by studentship from Medical Research Council of Canada.

³ Supported by Fonds internes de l'Universite de Montreal.

Manuscript received 22 July 1980.