TY - JOUR T1 - STUDIES WITH CHOLECYSTOKININ <em>IN VITRO.</em> IV. EFFECTS OF CHOLECYSTOKININ AND RELATED PEPTIDES ON PHOSPHODIESTERASE JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 535 LP - 548 VL - 183 IS - 3 AU - M. SAMIR AMER AU - G. R. McKINNEY Y1 - 1972/12/01 UR - http://jpet.aspetjournals.org/content/183/3/535.abstract N2 - Cholecystokinin, gastrin and pentapeptide stimulated cyclic 3', 5'-adenosine monophosphate-phosphodiesterase (PDE) from a number of rabbit tissues including the gall bladder. The stimulation is effected by a shift in activity from a high Km form of PDE (PDE-I) to a low Km form (PDE-II) of the enzyme. At low concentrations the peptides stimulated the enzyme and when added in high concentrations they inhibited the enzyme activity. Tetrapeptide consistently inhibited PDE activity. The hypothesis is presented that gastrin and cholecystokinin may act via stimulation of PDE and a resultant decrease in intracellular cyclic 3', 5'-adenosine monophosphate levels. This hypothesis is in harmony with most of the known physiology and pharmacology of these hormones. Further-more, it provides an explanation for the antagonism between each of these hormones and secretin on gastric acid secretion. © 1972 by The Williams &amp; Wilkins Co. ER -