Jpn. J. Pharmacol. 81 (1), 34 - 37 (1999)

Antinociceptive Effect of R-(+)-Hyoscyamine on the Conjunctival Reflex Test in Rabbits

Carla Ghelardini1, Nicoletta Galeotti1, Lia Fantetti1, Fulvio Gualtieri2,
Serena Scapecchi2 and Alessandro Bartolini1

1Department of Pharmacology, University of Florence, Viale G. Pieraccini, 6, I-50139 Florence, Italy
2Department of Pharmaceutical Sciences, University of Florence, Via G. Capponi, 9, I-50121 Florence, Italy

Abstract: R-(+)-Hyoscyamine (1 - 10 g/kg, s.c.) dose-dependently increased the local anesthetic effect of procaine (50 g/ml) and lidocaine (50 g/ml) in the conjunctival reflex test in the rabbit. This potentiating effect is completely prevented by the M1 antagonist dicyclomine (10 mg/kg, s.c.). The intensity of R-(+)-hyoscyamine antinociception was comparable to that induced by morphine (2 mg/kg, s.c.) and minaprine (15 mg/kg, s.c.), used as analgesic reference drugs. In the same experimental conditions, the S-(-)-enantiomer of atropine (0.1 - 10 g/kg, s.c.), was completely ineffective. The present results confirm the ability of R-(+)-hyoscyamine to produce a paradoxical antinociceptive effect mediated by a cholinergic mechanism not only in rodents but also in the rabbit.

Keywords: Atropine, R-(+)-Hyoscyamine, Antinociception, Local anesthetics, Cholinergic system

Copyright The Japanese Pharmacological Society 1999

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