Effects of caffeine on the osteoblasts: Changes in biochemical parameters. For the bone cells culture, intracellular total protein, alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) synthesis were increased gradually while the prostaglandin E2 (PGE2) synthesis decreased during the 7 days' culture period. At the same time, ALP, LDH, and PGE2 secretion into medium decreased, while the total protein in the culture medium was relatively stationary. After adding 10 mM caffeine to the osteoblasts cell culture for 3 to 7 days, the intracellular ALP content decreased significantly, while the ALP secreted into medium was relatively preserved. The intracellular LDH decreased significantly and the LDH in the medium increased significantly at the presence of 10 mM caffeine for 3 to 7 days. Both the intracellular PGE2 and the PGE2 secreted into medium decreased significantly at the 3rd and 7th day's culture. At the same time, total protein contents were relatively preserved.