Actions and pharmacokinetic properties of the α2-adrenergic agents, medetomidine and atipamezole, in rainbow trout (Oncorhynchus mykiss) |
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Authors: | T E Horsberg J F Burka R A R Tasker |
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Institution: | The Norwegian School of Veterinary Science, PO Box 8146 Dep., N-0033 Oslo, Norway;*Atlantic Veterinary College, UPEI, Charlottetown PE, C1A 4P3, Canada |
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Abstract: | The effects of medetomidine and atipamezole were examined in rainbow trout. Medetomidine proved to be an effective sedative but not an anaesthetic; its effects were antagonised by atipamezole. The clinical signs of medetomidine sedation were rapid settling to the bottom of the tank followed by progressive ataxia. The sedative effect was dose-dependent: at 1 mg/l, one of 6 fish rested on its side after 10 min, whereas at 20 mg/l all 6 rested on their sides. No loss of consciousness occurred. Atipamezole at 6 times the medetomidine concentration antagonised sedation. The average time before fish exposed to medetomidine alone showed avoidance reactions was 10 h, more than 5 times longer than the mean time in fish exposed to medetomidine and then atipamezole. During exposure to medetomidine (5 mg/l) opercular movement rate decreased from 80/min to 20/min. The nature of opercular excursions also changed from being rapid and shallow to slow and deep. Respiratory movements increased after transfer to the bath containing atipamezole. Medetomidine had a marked effect upon skin colour, with fish becoming very pale a few min after exposure. Normal pigmentation was not restored until 4.5 days after exposure to medetomidine alone, but returned to normal after 10 min exposure to atipamezole solution. The half-life (t1/2 lambdaz) for medetomidine was 5.5 h. For atipamezole, it was 8.6 h. |
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