title: Alpha and beta adrenergic receptors of canine lung tissue identification and characterization of alpha adrenergic receptors by two different ligands.
abstract: Adrenergic receptors of canine peripheral lung tissues were measured by direct binding techniques using [3H]dihydroergocryptine ([3H]DHE), [3H]prazosin and [3H]dihydroalprenolol ([3H]DHA). All three ligands bound to canine lung tissue with saturability, stereospecificity and reversibility. Adrenergic agonists competed for binding of [3H]DHE and [3H]prazosin in the order: 1-epinephrine greater than 1-norepinephrine greater than d-epinephrine greater than d-norepinephrine greater than 1-isoproterenol. Adrenergic antagonists competed for binding of [3H]prazosin in the order: prazosin greater than phentolamine greater than yohimbine. Inhibition curves of [3H]DHE by prazosin or yohimbine were biphasic suggesting two subtypes of binding sites. Maximum binding capacities of [3H]DHE ranged from 30.6 to 42.7 fmol/mg protein. [3H]prazosin from 18.3 to 26.9 fmol/mg protein and [3H]DHA from 135.2 to 359.4 fmol/mg protein. When both [3H]DHE and [3H]prazosin were used in the same membrane preparation, specific binding of [3H]DHE was always more than that of [3H]prazosin. Since [3H]prazosin is considered to bind to alpha 1 adrenergic receptors specifically and [3H]DHE is considered to bind alpha 2 adrenergic receptors nonselectively, the difference between the numbers of the specific binding sites of these two ligands should represent alpha 2 adrenergic receptors. Alpha 2 adrenergic receptor density ranged from 9.5 to 21.1 fmol/mg protein. Our results suggest the existence of both alpha 1 and alpha 2 adrenergic receptors in canine peripheral lung tissue. Approximately 40% of alpha adrenergic receptors were alpha 2. The ratio of alpha/beta adrenergic receptors ranged from 1:3.3 to 1:10.4. The ratio of alpha 1/beta adrenergic receptors ranged from 1:6.7 to 1:21.1.
mesh_terms: D000818:Animals; D001665:Binding Sites; D004082:Dihydroalprenolol / Q000378:metabolism; D004088:Dihydroergotoxine / Q000378:metabolism; D004285:Dogs; D007700:Kinetics; D008168:Lung / Q000032:analysis*; D011224:Prazosin / Q000378:metabolism; D011869:Radioligand Assay; D011941:Receptors, Adrenergic / Q000032:analysis* / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000032:analysis*; D011943:Receptors, Adrenergic, beta / Q000032:analysis*; D014316:Tritium
chemical_list: D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D014316:Tritium; D004088:Dihydroergotoxine; D004082:Dihydroalprenolol; D011224:Prazosin