Effect of adenosine on synthesis and release of cyclic AMP by cultured vascular cells from swine.

Both endothelial and smooth muscle cells cultured from swine aorta responded to adenosine by elevating cAMP levels. cAMP was found both intracellularly and released into the incubation medium. Total cAMP in endothelial cells in buffer alone was 2 pmol cAMP/10(6) cells. Total cAMP reached a maximum stimulated level of 2 times control at 640 microM adenosine. The level of cAMP in unstimulated smooth muscle cells was 7 pmol/10(6) cells. Total cAMP was increased 2-fold at 10 microM adenosine and reached a maximum stimulated level of as much as 20 times control at 640 microM adenosine. Kinetics of release of cAMP from smooth muscle cells show that fractional release rates were increased 2 to 7 fold by 10 microM adenosine and 7 to 29 fold by 160 microM adenosine. These experiments indicate that adenosine specifically stimulates release of cAMP as well as synthesis. The phosphodiesterase inhibitor 3-isobutyl-l-methylxanthine (IBMX) had complex effects on the distribution of cAMP between the cells and medium. The data are consistent with the model that IBMX is a low affinity competitive inhibitor of adenosine, and is itself slightly effective as an agonist for release.