The dose-response relation for the antinociceptive effect of morphine in a fish, rainbow trout.
There have been suggestions that analgesics be used by fish researchers. But in the absence of dose-response data for morphine, this suggestion seems imprudent. The purpose of the present study was to develop a dose-response relationship in fish using six doses of morphine. The response (movement of the fins or tail) to a noxious stimulus (electrical shock to the face region) was monitored before and after a dose of morphine intraperitoneally (i.p.). The i.p. dose of morphine ED(50) in rainbow trout was 6.7 ± 0.8 mg/kg (n = 12 at each dose). The plasma morphine concentration EC(50) was 4.1 ± 1.5 mg/L. In a second experiment, rainbow trout tested with equal amounts of morphine and naloxone (30 mg/kg) showed that the antinociceptive effect of morphine was blocked by naloxone. It has been suggested that stress-induced analgesia has been a confounding factor in some fish studies. However, plasma cortisol levels in our study indicated that stress was not a confounding factor in the present experiments. The ED(50) for morphine in fish was higher than that reported for humans or other mammals. Our observation showing a dose-response relation for morphine using a noxious stimulus supports arguments for its effectiveness as an antinociceptive drug in fish.
Biomedical Sciences, AVC-UPEI, Charlottetown, PE, Canada.
S G
SG
Jones
C
C
Kamunde
K
K
Lemke
E D
ED
Stevens
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D006854:Hydrocortisone / Q000097:blood; D009020:Morphine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D017686:Oncorhynchus mykiss / Q000097:blood*; D010146:Pain / Q000517:prevention & control / Q000662:veterinary*; D013312:Stress, Physiological / Q000187:drug effects
D000701:Analgesics, Opioid; D009020:Morphine; D006854:Hydrocortisone