ACCUMULATION OF CAMP AUGMENTS DYNAMIC VAGAL CONTROL OF HEART-RATE

Recent investigations in our laboratory using a Gausslan white noise p erturbation technique have shown that simultaneous sympathetic stimula tion augmented the gain of the transfer function from vagal stimulatio n frequency to heart rate response. Ro-ct ever, the mechanism of that augmentation remains to be elucidated. In this study, we examined in a nesthetized rabbits how three pharmacological interventions known to c ause intracellular accumulation of cAMP affected the transfer function . Isoproterenol (0.3 mu g.kg(-l) . min(-1) iv) increased the dynamic g ain of transfer function from 7.12 +/- 0.67 to 12.4 +/-1.21 beats.min( -1).Hz(-1). (P < 0.05) without changing the corner frequency or the la g time. Similar augmentations were observed when forskolin (5 mu g. kg (-1).min(-1) iv) or theophylline (20 mg/kg iv) was administered under conditions of P-adrenergic blockade. These results suggest that the ac cumulation of cAMP at postjunctional effector sites contributes, at le ast in part, to the sympathetic augmentation of the dynamic vagal cont rol of heart rate.