Pharmacological evidence of a role for prejunctionalimidazoline (I1) 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 (a 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 a 2 and I 1 antagonists. MOX, an a 2 /I 1 receptor agonist, BRIM, a selective a 2 agonist, efaroxan (EFA), an I 1 /a 2 antagonist and rauwolscine (RAU), a relatively selective a 2 antagonist, were utilized to study alterations in sympathetically evoked contractions of the cat nictitating membrane (CNM). MOX (1-10 µg) 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 µg) than by rauwolscine (333 µg). 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).