title: Influence of chronic treatment of rats with isoprenaline and calcium channel blockers on response of isolated right ventricle to noradrenaline.
abstract: Influence of chronic treatment of rats with and calcium channel blockers (CCBs) and isoprenaline (ISP) on responses to noradrenaline (NA) was investigated on electrically--driven isolated right ventricle preparations. The ventricles were obtained from animals treated with chronic ISP or CCBs alone and chronic nifedipine, verapamil, diltiazem or nimodipine plus chronic ISP. A decreased response to NA as evidenced by an increase in EC50 for contraction which was observed in chronic ISP- treated preparations may be due to development of desensitisation (down-regulation) of beta-adrenoceptors. In chronic CCB-treated preparations there was a significant decrease in the EC50 of NA and decreased contractile response suggesting an increase in the beta-adrenoceptors and decreased availability of calcium, respectively. In chronic CCBs + ISP treated preparations further decreases in the EC50 values were observed suggesting that the voltage gated L-type Ca2+ channels may be affected directly or indirectly by change in beta-adrenoceptor activity. By the above results a proposed mechanism of interrelationship of beta-adrenoceptors with voltage gated L-type calcium channels in cardiac muscle is supported.
authors.affiliation: Department of Pharmacology, Pramukhswami Medical College, Karamsad, India.
authors.forename: P
authors.initials: P
authors.lastname: Bhugra
authors.forename: O D
authors.initials: OD
authors.lastname: Gulati
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000008:administration & dosage*; D020746:Calcium Channels, L-Type / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000008:administration & dosage*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000008:administration & dosage*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D007545:Isoproterenol; D009638:Norepinephrine