<prompt> Caffeine, a methyl xanthine, has been added to a variety of cell types. Which one of the following would be expected in various cell types treated with caffeine and epinephrine?Decreased activity of liver PKADecreased activity of muscle PKAIncreased activity of liver pyruvate kinaseDecreased activity of liver glycogen synthase  <response>: If the phosphodiesterase that degrades cAMP were inhibited an effect of caffeine in the presence of epinephrine, cAMP levels would be elevated. PKA would become more active in the liver and muscle; pyruvate kinase would become less active in the liver; and glycogen synthase activity would be decreased in both the muscle and the liver. Phosphorylase activity would be increased in both the muscle and the liver owing to constant phosphorylation by phosphorylase kinase, which is activated by PKA. 