Studies of alpha-adrenoceptor antagonists on sympathetic mydriasis in rabbits.
This study was undertaken to identify the alpha-adrenergic receptor type responsible for sympathetically evoked mydriasis in pentobarbital-anesthetized rabbits. Frequency-response curves of pupillary dilation were generated by stimulation of the preganglionic cervical sympathetic nerve (1-64 Hz). Evoked mydriatic responses were inhibited by systemic administration of nonselective alpha-adrenergic antagonists, phentolamine (0.3-10 mg/kg) and phenoxybenzamine (0.03-0.3 mg/kg), as well as the selective alpha(1)-adrenergic antagonist, prazosin (0.1-1 mg/kg). The alpha(2)-adrenergic antagonist, RS 79948 (0.3 mg/kg, i.v.) was without inhibitory effect, but potentiated the mydriatic response. In addition, the selective alpha(1A)-adrenoceptor antagonist, 5-methylurapidil (0.1-1 mg/kg, i.v.), antagonized the elicited mydriasis in a dose-dependent fashion. Unlike previous observations that prazosin does not block the adrenoceptor in rabbit iris dilator muscle, our results suggest that prazosin is effective in inhibiting neuronally elicited mydriasis in this species, and that alpha(1A)-adrenoceptors appear to mediate the response.
Yu
Yongxin
Y
Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City 73190, USA. yongxin-yu@ouhsc.edu
Koss
Michael C
MC
D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D015878:Mydriasis / Q000378:metabolism / Q000503:physiopathology*; D009184:Mydriatics / Q000494:pharmacology*; D009287:Naphthyridines / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011680:Pupil / Q000187:drug effects*; D011817:Rabbits; D013564:Sympathetic Nervous System / Q000503:physiopathology*
D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D007546:Isoquinolines; D009184:Mydriatics; D009287:Naphthyridines; D010879:Piperazines; C104875:RS 79948-197; D010643:Phenoxybenzamine; C057446:5-methylurapidil; D011224:Prazosin; D010646:Phentolamine