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 > 1-norepinephrine > d-epinephrine > d-norepinephrine > 1-isoproterenol. Adrenergic antagonists competed for binding of [3H]prazosin in the order: prazosin > phentolamine > 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 alpha1 adrenergic receptors specifically and [3H]DHE is considered to bind alpha2 adrenergic receptors nonselectively, the difference between the numbers of the specific binding sites of these two ligands should represent alpha2 adrenergic receptors. Alpha2 adrenergic receptor density ranged from 9.5 to 21.1 fmol/mg protein. Our results suggest the existence of both alpha1 and alpha2 adrenergic receptors in canine peripheral lung tissue. Approximately 40% of alpha adrenergic receptors were alpha2. The ratio of alpha/beta adrenrgic receptors ranged from 1:3.3 to 1:10.4. The ratio of alpha1/be ta adrenergic receptors ranged from 1:6.7 to 1:21.1.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)