[Relaxing effect of isoprenaline on the contracture of the guinea-pig taenia coli].
The relaxing effect of isoprenaline on [Na+]o-free induced contracture of the guinea-pig taenia coli was investigated in presence of phentolamine (10(-5)M), an alphareceptor blocking agent. This action of isoprenaline showed dose-dependency (ED 50: 10(-5)M) and was abolished completely by beta-receptor blocking agent (propranolol, 10(-5)M). The effect of isoprenaline (10(-5)M) disappeared gradually during long exposure to [Na+]o-free solution and when short application of sodium ions to the perfusing solution, the effect of isoprenaline was restored. Pretreatment of [K+]o-free solution or ouabain (10(-5)M) enhanced the effect of isoprenaline. The effect of isoprenaline is inhibited by ouabain (10(-5)M) by about 50%. These observations strongly suggest that the inhibitory effect of isoprenaline may be mainly mediated through activation of Na-pump. However, direct activation of the drug on Na+-Ca2+ exchange, Ca-pump, or Ca-uptake into cellular Ca store sites can not be ruled out.
D000818:Animals; D003106:Colon / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007477:Ions; D007545:Isoproterenol / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000502:physiology; D012964:Sodium / Q000502:physiology
D007477:Ions; D010042:Ouabain; D012964:Sodium; D007545:Isoproterenol; D011188:Potassium