Alpha 2-adrenoceptor agonists potentiate responses mediated by alpha 1-adrenoceptors in the cat nictitating membrane.
Alpha 1 but not alpha 2-adrenoceptors mediate contractions of the cat nictitating membrane. The contractions of this tissue evoked by alpha 1-adrenoceptor agonists, but not those evoked by angiotensin II, are potentiated by pre-dosing with alpha 2-adrenoceptor agonists. This potentiation is reversed by the alpha 2-adrenoceptor antagonist, WY 26392. Pressor responses evoked by alpha 1-adrenoceptor agonists or angiotensin II were not affected by alpha 2-adrenoceptor agonists. Contractions of the nictitating membrane evoked by noradrenaline were reduced by pretreatment with WY 26392. These results suggest that in some tissues the role of alpha 2-adrenoceptors may be to modulate responses to alpha 1-adrenoceptors, rather than to evoke a discrete response themselves.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D000068438:Brimonidine Tartrate; D002415:Cats; D003000:Clonidine / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009541:Nictitating Membrane / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011807:Quinolizines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000959:Antihypertensive Agents; D011807:Quinolizines; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D000804:Angiotensin II; D010656:Phenylephrine; D000068438:Brimonidine Tartrate; C038537:Wy 26392; D003000:Clonidine; D009638:Norepinephrine