Effects of prolonged caffeine consumption on cardiac contractile function in rats.

The purpose of the study was to explore effects of prolonged caffeine administration on the contractile function and myocardial energy metabolites of the isolated rat heart. Caffeine treatment for 1 week (10 mg/kg, i.p., twice a day) was followed by unchanged pump function of the isolated heart, but reduced maximal left ventricular (LV) systolic pressure by 14% (p < 0.05). Caffeine consumption during 8-9 weeks (0.1% water solution) was also followed by unchanged maximal pump function but increased maximal double product (LV developed pressure multiplied by heart rate) by 23% (p < 0.05). The hearts of caffeine-consumed rats also maintained a higher level of the pump function at a high rate of atrial electrostimulation. The myocardial content of adenosine triphosphate (ATP), creatine phosphate, as well as creatine was slightly but insignificantly increased after caffeine consumption. Results show that in the course of prolonged caffeine treatment, the maximal myocardial contractile function first decreases and then increases, showing adaptation of the heart.