cAMP stability

[mellott james bs bioc]

	In my biochemistry class , we're talking about glycolysis , TCA , etc.,
and one of the topics is the regulation of glycogen through a cAMP pathway . It
is my understanding that a high concentration of cAMP is needed for the 
continuous activation of Protein kinase , and to inactivate the kinase , the 
concentration of cAMP is lowered through the activity of a phosphodiesterase . 
I recall hearing that caffeine stabilizes the concentration of cAMP in such a
pathway , and I was wondering , since caffeine and adenine have similar 
structures , if caffeine acts as a competitive inhibitor with cAMP for the 
phosphodiesterase . 
	Thanks in advance for any comments and/or references you can give me .