Alpha2-adrenoceptors do not mediate reflex mydriasis in rabbits.

Abstract

The aim of this study was to identify receptors that mediate reflex mydriasis in pentobarbital-anesthetized rabbits, in which the cervical sympathetic nerve was sectioned unilaterally. Voltage-response curves of pupillary dilation were generated bilaterally by stimulation of the sciatic nerve. Evoked mydriatic responses were mediated mainly by efferent parasympathetic innervation, and, to a lesser extent, by sympathetic innervation. The alpha-adrenergic antagonist, phenoxybenzamine (0.3 mg/kg, intravenously (i.v.)), antagonized mydriasis of the neurally intact eye, but not that on the sympathectomized side. The alpha2-adrenergic antagonist, RS 79948 (0.3 mg/kg, i.v.), potentiated mydriasis of the normal eye, but was without either a potentiating or inhibitory effect on the mydriasis of the sympathectomized eye. In addition, the dopamine-receptor antagonist, haloperidol (1 mg/kg, i.v.), inhibited evoked mydriasis of the sympathectomized eye. These results suggest that, unlike some other species (cats and rats), alpha2-adrenoceptors do not mediate reflex mydriasis elicited by sciatic-nerve stimulation in the rabbit, and support the previous finding in humans that dopamine receptors may mediate this response.

• Authors: Yongxin Yu, Michael C Koss
• Journal: Journal of ocular pharmacology and therapeutics : the official journal of the Association for Ocular Pharmacology and Therapeutics (J Ocul Pharmacol Ther) Vol. 20 Issue 6 Pg. 479-88 (Dec 2004) ISSN: 1080-7683 [Print] United States
• PMID: 15684808 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Adrenergic alpha-2 Receptor Antagonists
• Adrenergic alpha-Antagonists
• Dopamine Antagonists
• Isoquinolines
• Naphthyridines
• RS 79948-197
• Receptors, Adrenergic, alpha-2
• Receptors, Dopamine
• Phenoxybenzamine
• Haloperidol

Topics

• Adrenergic alpha-2 Receptor Antagonists
• Adrenergic alpha-Antagonists (administration & dosage, pharmacology)
• Anesthesia
• Animals
• Dopamine Antagonists (administration & dosage, pharmacology)
• Dose-Response Relationship, Drug
• Drug Synergism
• Electric Stimulation
• Haloperidol (administration & dosage, pharmacology)
• Injections, Intravenous
• Isoquinolines (administration & dosage, pharmacology)
• Male
• Models, Neurological
• Mydriasis (chemically induced, physiopathology)
• Naphthyridines (administration & dosage, pharmacology)
• Phenoxybenzamine (administration & dosage, pharmacology)
• Rabbits
• Receptors, Adrenergic, alpha-2 (physiology)
• Receptors, Dopamine (physiology)
• Reflex, Pupillary (drug effects, physiology)
• Sciatic Nerve (physiology, surgery)
• Sympathectomy