title: Mydriatic and antinociceptive effects of intrathecal dexmedetomidine in conscious rats.
abstract: A comparison was made of the dose-effect relationship of intrathecally applied dexmedetomidine as concerns its mydriatic and antinociceptive effects in rats. Pupil diameter was measured with a photographic method without anesthesia. Antinociception was measured by means of the tail-withdrawal test. The intrathecal (i.t.) administration of dexmedetomidine led to dose-dependent antinociception (P < 0.05) and mydriasis (P < 0.001). Both effects reached their maximum 10 min after drug application. The tail-withdrawal latency was prolonged by 9 micrograms dexmedetomidine. Mydriasis appeared on administration of a 1 microgram dose and its degree was proportional to the dexmedetomidine dosage up to 12 micrograms. A significant correlation was not found between pupil diameter and tail-withdrawal latency in the same rat after any dexmedetomidine dose. Based on the present experiments, we conclude that the mydriatic effect of i.t. dexmedetomidine appears at a lower dose than its antinociceptive effect. Our results suggest that the assessment of pupillary response is a sensitive method for estimation of the supraspinal effect of i.t. administered alpha 2-adrenoceptor agonists.
authors.affiliation: Department of Physiology, Albert Szent-Györgyi Medical University, Szeged, Hungary.
authors.forename: G
authors.initials: G
authors.lastname: Horváth
authors.forename: M
authors.initials: M
authors.lastname: Kovács
authors.forename: M
authors.initials: M
authors.lastname: Szikszay
authors.forename: G
authors.initials: G
authors.lastname: Benedek
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D007278:Injections, Spinal; D008297:Male; D020926:Medetomidine; D015878:Mydriasis / Q000139:chemically induced; D010147:Pain Measurement; D011680:Pupil / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000316:Adrenergic alpha-Agonists; D000700:Analgesics; D007093:Imidazoles; D020926:Medetomidine