title: Pharmacological evidence of a role for prejunctional imidazoline (I(1)) receptors in ocular function.
abstract: Imidazoline and guanidiniun-substituted isoindoline compounds have been reported to demonstrate affinity for the putative imidazoline receptors (I(1)) and alpha-2 (alpha(2)) adrenoceptors. The purpose of this study was to determine the relative contribution of I(1) receptors to ocular actions of moxonidine (MOX) and brimonidine (BRIM) by utilizing relatively selective alpha(2) and I(1) antagonists. MOX, an alpha(2)/I(1) receptor agonist, BRIM, a selective alpha( 2) agonist, efaroxan (EFA), an I(1)/alpha(2) antagonist and rauwolscine (RAU), a relatively selective alpha(2) antagonist, were utilized to study alterations in sympathetically evoked contractions of the cat nictitating membrane (CNM). MOX (1-10 microg) suppressed, dose dependently, contractions of the CNM elicited by electrically stimulating the cervical preganglionic sympathetic trunk. The suppressive effect of MOX was antagonized more effectively by EFA (333 microg) than by rauwolscine (333 microg). In contrast, RAU, but not EFA, completely reversed the suppressive effects of BRIM on electrically induced contractions of the CNM. In conclusion, these in vivo data suggest that I(1) receptors are involved in the pre-junctional (neuronal) modulation of contractions in the CNM (Supported by NIH grant EY06338).
authors.affiliation: Department of Pharmacology, Merck and Co, Merck Research Laboratories, WP46-200, West Point, PA, USA. miller_ogidigben@merck.com
authors.forename: Miller J
authors.initials: MJ
authors.lastname: Ogidigben
authors.forename: David E
authors.initials: DE
authors.lastname: Potter
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001572:Benzofurans / Q000494:pharmacology; D000068438:Brimonidine Tartrate; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D007093:Imidazoles / Q000494:pharmacology; D054755:Imidazoline Receptors; D009541:Nictitating Membrane / Q000187:drug effects / Q000502:physiology*; D009799:Ocular Physiological Phenomena; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology; D011955:Receptors, Drug / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001572:Benzofurans; D007093:Imidazoles; D054755:Imidazoline Receptors; D010975:Platelet Aggregation Inhibitors; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug; C410887:imidazoline I1 receptors; D015016:Yohimbine; D000068438:Brimonidine Tartrate; C043482:moxonidine; C062597:efaroxan