Alpha and beta adrenergic receptors of canine lung tissue identification and characterization of alpha adrenergic receptors by two different ligands.
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.
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
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D014316:Tritium; D004088:Dihydroergotoxine; D004082:Dihydroalprenolol; D011224:Prazosin