Conditions for maximal synthesis of cyclic AMP by mouse macrophages in response to beta-adrenergic stimulation

The synthesis of cyclic AMP by mouse peritoneal macrophages in response to stimulation by isoproterenol was studied as a function of drug concentration, incubation time and cell density. Cyclic AMP levels of macrophages increased 3 to 3.5 times over the control level 20 sec after the addition of 10(-3) M isoproterenol. Under these conditions the dose response could be followed down to an isoproterenol concentration of 10(-6) to 10(-7) M. When cell suspensions were inactivated as early as 1 sec after the addition of the drug, the increase in cyclic AMP was much greater (153 vs. 25 pmol/10(7) cells). Macrophage suspensions of high cell density were less responsive than those of low cell density. In the absence of any inhibitor of phosphodiesterase, the stimulatory effect of isoproterenol was always of short duration. The maximum effect of beta-adrenergic stimulation probably occurs in less than 1 sec at a cell density less than 2 x 10(6) cells/ml. The beta-blocking drug Visken abolished the observed effects.