Responsiveness to tyramine in isolated lung parenchymal strip of guinea-pig and rat.
The effects of alpha/beta-adrenoceptor agonists in isolated lung parenchymal strip are well characterized but information related to indirectly acting sympathomimetic agents is scarce. In the present study the response to tyramine was analyzed in lung strips from guinea-pig and rat. Tyramine elicited a dose-related contraction of the lung strip with an EC50 of 1.12 X 10(-4) M in the guinea-pig and 4.28 X 10(-4) M in the rat. Incubation with propranolol did not modify the tyramine-induced contraction but blocked the relaxation which occasionally appeared at low concentrations of tyramine. No tachyphylaxis to tyramine was detected. Cocaine (3 X 10(-5) M) and reserpine significantly increased the EC50 values of tyramine. In reserpine-treated animals, phentolamine (both animal species), clemizole (guinea-pig) and methysergide (rat) displaced to the right the concentration-response curve to tyramine but the dose ratios were significantly lower than those obtained for their specific agonists. These results suggest that in addition to the adrenergic component (catecholamine release and direct alpha-adrenoceptor activation) there is an important contribution of other receptor systems such as histamine (guinea-pig) and 5-hydroxytryptamine (rat) to the contractile response to tyramine in lung tissue.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D003042:Cocaine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008168:Lung / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014439:Tyramine / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D011433:Propranolol; D003042:Cocaine; D000109:Acetylcholine; D014439:Tyramine