Gabapentin action and interaction on the antinociceptive effect of morphine on visceral pain in mice.
OBJECTIVE
Visceral pain is one of the most common forms of pain and for which new drugs would be welcome. The aim of this study was to investigate whether gabapentin inhibits induced abdominal contractions in mice and to examine the effect of its co-administration with morphine.


METHODS
A total of 96 mice received acetic acid intraperitoneally after administration of saline or gabapentin (1, 5, 10, 50 and 100 mg kg(-1)) or morphine (0.25, 0.5, 1, 3 and 5 mg kg(-1)) or a combination of morphine and gabapentin. Other groups also received naloxone. The number of writhes were counted.


RESULTS
Both gabapentin and morphine reduced writhing in a dose-dependent manner. The number of writhes was decreased significantly by gabapentin (50 and 100 mg kg(-1)) and morphine (0.5, 1, 3 and 5 mg kg(-1)) (P < 0.001). Also, the lowest dose of morphine 0.25 mg kg(-1) when combined with low doses of gabapentin significantly decreased the number of writhes (P < 0.005). The combination of a low effective dose of gabapentin (50 mg kg(-1)) with a low dose of morphine decreased the writhing by 94% as compared to the controls. The antinociceptive effect of combined administration was not reversed by naloxone.


CONCLUSIONS
These data demonstrated the comparable efficacy of gabapentin with morphine in visceral pain. Also, the results showed that the combination of doses of gabapentin and morphine, which were ineffective alone, produced a significant analgesic effect in the writhing model of pain. This may be clinically important in the management of visceral pain.
Meymandi
M-S
MS
Physiology and Pharmacology Department, Neuroscience Research Center, Kerman University of Medical Sciences, 22 Bahman Blvd., 76169-1411 Kerman, Iran. manzume@yahoo.com
Sepehri
G
G
D019342:Acetic Acid / Q000008:administration & dosage; D000588:Amines / Q000494:pharmacology*; D000700:Analgesics / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D000077206:Gabapentin; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy*; D010147:Pain Measurement / Q000187:drug effects; D012965:Sodium Chloride / Q000008:administration & dosage; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D000588:Amines; D000700:Analgesics; D000701:Analgesics, Opioid; D003509:Cyclohexanecarboxylic Acids; D009292:Narcotic Antagonists; D009270:Naloxone; D012965:Sodium Chloride; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D009020:Morphine; D019342:Acetic Acid