Rilmenidine produces mydriasis in cats by stimulation of CNS alpha 2-adrenoceptors.
1. Experiments were undertaken to determine if the imidazoline/alpha2-adrenoceptor agonist, rilmenidine, would produce mydriasis in cats and, if so, to delineate its site of action and determine if this effect is mediated by imidazoline receptors or alpha2-adrenoceptors. 2. Rilmenidine produced dose-related pupillary dilator responses in pentobarbital anaesthetized cats that were independent of sympathetic innervation to the iris but were dependent upon intact parasympathetic neuronal tone. The ED50 for rilmenidine-induced pupillary dilation was approximately 200 microg kg(-1), i.v., and was sustained for at least 1 h. 3. The highly selective alpha2-adrenoceptor antagonist, RS-79948, administered either before or after rilmenidine, antagonized rilmenidine-induced mydriasis. Neuronally induced reflex inhibition of parasympathetic nerve activity was also inhibited by administration of RS-79948. 4. These results suggest that rilmenidine acts like clonidine to produce pupillary dilation by inhibition of parasympathetic tone to the iris sphincter and that this central nervous system parasympatho-inhibition is mediated by alpha2-adrenoceptors, rather than imidazoline receptors.
Koss
M C
MC
Department of Cell Biology, University of Oklahoma College of Medicine, PO Box 26901, Oklahoma City, OK 73190, USA.
D058647:Adrenergic alpha-2 Receptor Agonists; D000818:Animals; D002415:Cats; D002490:Central Nervous System / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D009184:Mydriatics / Q000494:pharmacology*; D010080:Oxazoles / Q000494:pharmacology*; D011680:Pupil / Q000187:drug effects* / Q000502:physiology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D000077769:Rilmenidine
D058647:Adrenergic alpha-2 Receptor Agonists; D009184:Mydriatics; D010080:Oxazoles; D018341:Receptors, Adrenergic, alpha-2; D000077769:Rilmenidine