Studies on the source of cyclic AMP in canine gastric juice

The possibility that cyclic AMP in gastric juice is derived from plasma by simple clearance was evaluated. The effect of exogenous cyclic AMP administration (1 mg/min) on radioimmunoassayable cyclic AMP in plasma and gastric juice was studied in dog stomach during histamine (8--16 micrograms/kg/hr) infusion. Experiments were performed in vagally denervated fundic (Heidenhain) and in innervated gastric pouches. During infusion of cyclic AMP with histamine, plasma cyclic AMP concentration rapidly increased 500-fold. Simultaneously, gastric juice cyclic AMP levels decreased almost 50%. In contrast, dibutyryl cyclic AMP infusion increased gastric juice cAMP concentration 5-fold, suggesting that the gastric mucosa is more permeable to dibutyryl cyclic AMP. In Heidenhain pouch experiments the clearance of dibutyryl cyclic AMP into gastric juice was only 1.5% of the clearance of aminopyrine. It appears that plasma clearance of cyclic AMP fails to account for most of the cyclic AMP present in gastric juice.