This source (http://udel.edu/~danikoll/metabolism.html http://udel.edu/~danikoll/metabolism.html) validates your point that caffeine has an indirect rather than

This source (http://udel.edu/~danikoll/metabolism.html http://udel.edu/~danikoll/metabolism.html) validates your point that caffeine has an indirect rather than direct effect on cAMP: "Caffeine competitively inhibits phosphodiesterase, the enzyme that degrades cyclic AMP...By blocking the degradation process of cyclic AMP, caffeine indirectly affects regulation of cAMP-dependent protein kinases". TIL.