title: Estrogen modulates in vitro atrial bradycardia induced by Indian red scorpion venom via G-protein coupled mechanisms.
abstract: Role of estrogen on cardiac dysrhythmia produced by Indian red scorpion (Mesobuthus tamulus) venom was examined using rat right atrial preparations in vitro. In females, the M. tamulus venom produced an increase, a decrease and an increase in rate at 0.03, 0.3 and 3 microg/ml of venom, respectively, producing N-shaped response curve, whereas no such response pattern was observed in males. Force of contraction in females was increased at all the concentrations of the venom, while in males the increase was seen only at 3 microg/ml. Castration of male rats did not alter the venom response to female type, while 'estrogenisation of castrated male rats' (pseudofemales) produced a response similar to females. Tamoxifen reversed the venom-induced responses both in females and pseudofemales. Further in females, the venom action at 0.3 microg/ml was blocked by atropine. Response at this concentration was also blocked by pertussis toxin and methylene blue. Results suggest that the cholinergic component of venom response is modulated by estrogen receptors via G(i)-protein-guanylyl cyclase mechanism.
authors.affiliation: Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi-221 005, India.
authors.forename: Anitha B
authors.initials: AB
authors.lastname: Alex
authors.forename: Sadhana
authors.initials: S
authors.lastname: Kanoo
authors.forename: Shripad B
authors.initials: SB
authors.lastname: Deshpande
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001285:Atropine / Q000494:pharmacology; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000187:drug effects* / Q000378:metabolism; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D006325:Heart Atria / Q000187:drug effects* / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009919:Orchiectomy; D037342:Pertussis Toxin / Q000494:pharmacology; D051381:Rats; D011960:Receptors, Estrogen / Q000187:drug effects* / Q000378:metabolism; D012604:Scorpion Venoms / Q000633:toxicity*; D012737:Sex Factors; D013629:Tamoxifen / Q000494:pharmacology
chemical_list: D000889:Anti-Arrhythmia Agents; D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D004967:Estrogens; D018727:Muscarinic Antagonists; D011960:Receptors, Estrogen; D012604:Scorpion Venoms; D013629:Tamoxifen; D001285:Atropine; D037342:Pertussis Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D006162:Guanylate Cyclase; D008751:Methylene Blue