Association of different zinc concentrations combined with a fixed caffeine dose on plasma and tissue caffeine and zinc levels in the rat

Because caffeine and tissue levels of Zn are closely related, the objectives of this study were to determine the changes in plasma caffeine levels over a period of 5 h when different concentrations of Zn combined with a fixed concentration of caffeine were injected into the femoral vein of rats and to determine the relationship between tissue levels of caffeine and Zn at 5 h postinjection. Rats were divided into three groups: group 1, 220 µg caffeine; group 2,220 µg caffeine + 8 µg Zn/g body weight (BW); group 3, 220 µg caffeine +16 µg Zn/g BW. Blood from groups 1 and 3 was collected at 3 min, 30 min, 1h, 3h, and 5h to determine the pharmacokinetics of caffeine. All groups were killed at 5 h. Caffeine and Zn concentrations of the brain, kidney, heart, and liver of all groups were determined. The plasma-caffeine curve in group 3 showed a lower concentration at 3 min and a slower caffeine-elimination rate during the first 3 h. Brain and kidney caffeine levels remained constant in all groups, whereas caffeine levels were increased in the heart in group 2 and in the liver in group 3. Zn concentrations in the brain and kidney were lower in group 2 compared with groups 1 and 3 and higher in group 3 compared to groups 1 and 2. Zn concentration in the heart was the same among the three groups but was increased in the liver in group 3 compared to groups 1 and 2. Therefore, we concluded that caffeine combined with Zn affects caffeine pharmacokinetics. With caffeine intake, levels of Zn (16 µg/g BW) that are slightly higher than the daily requirements (12 µg/g BW) may prevent a reduction of Zn in tissue. In addition, caffeine’s effects on Zn concentration among organs are different.