| RESEARCH PAPER
|Year : 1983 | Volume
| Issue : 4 | Page : 279-291
Interactions of digoxin with autonomic drugs in isolated frog heart
HC Tripathi, PK Das
The effect of digoxin was studied, in graded concentrations of 2,8 and 32 'g/ml, on isolated straub's preparation of hypodynamic heart. Maximal positive inotropic activity was produced by 2 and 8 ug/ml of digoxin while the effect of 32 ug/ml was toxic.Potentiation of the positive inotropic activity of digoxin by physostigmine and inhibition by atropine, suggest that the action of digoxin is possibly mediated through the release of aceytlcholine. The positive intropic effect of digoxin was found to be decreased by pretreatment of heart with guanethidine, propranolol or phentolamine. These results are suggestive of probable release of catecholamines, potentiating the positive inotropic action of digitalis. Digoxin produced dose-dependent negative chronotropic effect, Pretreatment with physostigmine or atropine decreased the negative chronotropic action of digoxin. Guanethidine pretreatment with propranolol resulted in decreased negative chronotropic activity of digoxin. Digoxin was also found to produce occasional drop beats in concentration of 8-32 ug/ml. Physostigmine pretreatment slightly increased while atropine pretreatment slightly decreased the incidence of digoxin-induced drop beats. These results indicate that the conduction block in frog heart produced by digoxin was potentiated by cholinergic activity and inhibited by anti-cholinergic agents. Propranolol pretreatment was found to increase the incidence of drop beats in frog hearts. It is possible that in the frog heart, besides direct action of digoxin, there were adrenergic and cholinergic mediated actions. Blockade of adrenergic receptors produced a relative dominance of cholinergic activity potentiating the conduction block. In isolated frog heart, vagal stimulation-induced cardiac standstill or vagal stimulation-induced positive inotropic activity in atropine pretreated hearts, was not affected by digoxin treatment. These results suggest that in the existing experimental setup, the endorgan heart response to autonomic stimulation remained unaffected by digoxin treatment.
H C Tripathi
Source of Support: None, Conflict of Interest: None