DYNORPHIN-A (1-13) IN THE BRAIN SUPPRESSES EPINEPHRINE-INDUCED VENTRICULAR PREMATURE COMPLEXES AND VENTRICULAR TACHYARRHYTHMIAS

The objectives of this study were to test the hypothesis that dynorphin in the central nervous system modulates epinephrine-induced cardiac arrhythmias and that central cholinergic mechanisms are operative in this action of dynorphin. Cardiac arrhythmias were produced by continuous intravenous infusion of epinephrine, in Wistar rats, previously instrumented with catheters in the lateral cerebral ventricle, femoral vein and femoral artery. Epinephrine produced ventricular premature complexes and later the development of fatal ventricular fibrillation. Dynorphin A (1-13), 5 or 20 mug (3 or 12 nM) administered into the lateral cerebral ventricle (ICV), significantly (P < 0.05) increased the threshold for development of cardiac arrhythmias. Dynorphin A (1-13), 20 mug, increased the epinephrine dose at the occurrence of ventricular premature beats to 171 +/- 8 (mean +/- 1 S.E.M.) compared to 120 +/- 5 mug epinephrine/kg in the control group and increased the dose at the onset of fatal arrhythmias to 186 +/- 8 compared to 141 +/- 10 mug epinephrine/kg in the control group. The action of dynorphin was significantly (P < 0.05) antagonized by the kappa opioid antagonist MR2266. Atropine sulfate, administered ICV or intravenously, produced a dose dependent antagonism of this action of dynorphin A (1-13). This was not due to the peripheral effects of atropine, as atropine methylnitrate, which does not cross the blood brain barrier, did not oppose the effects of dynorphin A (1-13). These data indicate (i) dynorphin A (1-13) increases the threshold for or suppresses the manifestions of epinephrine-induced ventricular arrhythmias, (ii) dynorphin's action on cardiac arrhythmias is mediated through central cholinergic rather than peripheral parasympathetic mechanisms (iii) dynorphin may play a role as an endogenous opioid within the brain that modulates cardiac arrhythmias in circumstances of elevated circulating epinephrine concentration.