A Comparative Study to Evaluate Chronotropic and Inotropic Effects of Nimodipine and Verapamil on Intact Frog's Heart

Abstract

Background: Nimodipine and verapamil are calcium channel blocking drugs. These drugs differ chemically hence their pharmacological actions are also different. Verapamil has predominant action on myocardial calcium channels while nimodipine acts more on Ca++ channels of vascular smooth muscle. Nimodipine has established use in subarachnoid haemorrhage. In this study effect of nimodipine on cardiac muscle has been compared with verapamil. Both the inotropic and chronotropic effects are compared. Method: After stunning and pithing of frog, its heart was exposed and the apex was attached to force transducer of Power Lab. Frog's Ringer solution was used as the nutrient medium. Drug solutions were applied directly on the heart and effects were observed and recorded on power lab monitor. Result: Verapamil produced characteristic negative inotropic and chronotropic effect on intact frog's heart (p<0.05). Nimodipine produced positive inotropic and negative chronotropic effect on intact frog's heart. As 't' test show value of 0.01 regarding force of contraction and 0.007 regarding heart rate as compared to normal baseline reading. On comparison between nimodipine and verapamil regarding force of contraction and heart rate the P values are 0.01 and 0.16. Conclusion: In conclusion, nimodipine produced positive inotropic and negative chronotropic effect on intact frog's heart. On comparison with verapamil, nimodipine has increased force of contraction of heart while verapamil has significantly reduced force of contraction of heart. Regarding heart rate both drugs decrease the rate of heart contraction. Clinically, after this observation nimodipine will be helpful for patients with subarachnoid haemorrhage along with cardiac failure.