Tachyphylaxis to beta-adrenoceptor agonists in guinea pig airway smooth muscle in vivo and in vitro.
Beta-Adrenoceptor tachyphylaxis was induced by incubating spirally cut guinea pig tracheas with isoproterenol (2.4 x 10(-7) M) for 20 min. This incubation reduced the relaxant effects of catecholamines but not of dibutyryl cyclic AMP, theophylline or sodium nitrite. Tracheas incubated with norepinephrine, phosphodiesterase inhibitors or cyclic nucleotides became tachyphylactic to isoproterenol. Pretreatment with indomethacin prevented induction of tachyphylaxis. Incubation with adenosine, methoxamine or sodium nitrite did not induce beta-adrenoceptor tachyphylaxis. When we gave isoproterenol intramuscularly to guinea pigs, airway sensitivity to aerosolized histamine was unchanged but the toxicity of parenterally administered histamine was increased. A prolonged treatment with isoproterenol reduced airway sensitivity to histamine aerosols; this reduced sensitivity was reversed by indomethacin. Thus, beta-adrenoceptor tachyphylaxis may not explain increased toxicity of parenteral histamine after isoproterenol treatment. Elevated levels of cyclic AMP and an increased synthesis of prostaglandins may result in diminished response to beta-receptor stimulation.
Tachyphylaxis to beta-adrenoceptor agonists in guinea pig airway smooth muscle in vivo and in vitro. Beta-Adrenoceptor tachyphylaxis was induced by incubating spirally cut guinea pig tracheas with isoproterenol (2.4 x 10(-7) M) for 20 min. This incubation reduced the relaxant effects of catecholamines but not of dibutyryl cyclic AMP, theophylline or sodium nitrite. Tracheas incubated with norepinephrine, phosphodiesterase inhibitors or cyclic nucleotides became tachyphylactic to isoproterenol. Pretreatment with indomethacin prevented induction of tachyphylaxis. Incubation with adenosine, methoxamine or sodium nitrite did not induce beta-adrenoceptor tachyphylaxis. When we gave isoproterenol intramuscularly to guinea pigs, airway sensitivity to aerosolized histamine was unchanged but the toxicity of parenterally administered histamine was increased. A prolonged treatment with isoproterenol reduced airway sensitivity to histamine aerosols; this reduced sensitivity was reversed by indomethacin. Thus, beta-adrenoceptor tachyphylaxis may not explain increased toxicity of parenteral histamine after isoproterenol treatment. Elevated levels of cyclic AMP and an increased synthesis of prostaglandins may result in diminished response to beta-receptor stimulation.