The contribution of alpha2-adrenoceptor and opioid receptor mechanisms to antinociception differs in Lewis and Fischer 344 rats.
Lewis and Fischer 344 (F344) rats differ in their physiological and pharmacological responses to a variety of environmental stimuli, which have been partially attributed to endogenous opioid function. Since opioid and alpha(2)-adrenoceptor mechanisms are closely related, we have comparatively examined the contribution of both systems to antinociception in female Lewis and F344 rats by the tail-flick method. Basal responses of F344 and Lewis rats were found to be similar, both showing a slight but significant increase in reaction time along the experimental period which was not completely reversed by naloxone. Morphine exhibited a bell-shaped dose-response curve in Lewis rats, these animals being more sensitive than F344 at 1 and 5 mg/kg but less sensitive at 10 mg/kg. Clonidine up to 0.1 mg/kg was more active in F344 rats. The alpha(2)-adrenoceptor antagonist yohimbine provoked a higher hyperalgesic effect in Lewis rats and decreased morphine antinociception in both strains. The existence of a balanced contribution of opioid and alpha(2)-adrenoceptor mechanisms to control pain transmission in both strains is discussed.
Herradón
Gonzalo
G
Laboratorio de Farmacologia, Universidad de San Pablo CEU, Urb. Montepríncipe, 28668 Boadilla, Madrid, Spain.
Morales
Lydia
L
Pérez-García
Carmen
C
Alguacil
Luis F
LF
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D011917:Rats, Inbred Lew; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology*; D011957:Receptors, Opioid / Q000187:drug effects* / Q000502:physiology; D013045:Species Specificity; D013997:Time Factors; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000701:Analgesics, Opioid; D018341:Receptors, Adrenergic, alpha-2; D011957:Receptors, Opioid; D015016:Yohimbine; D009270:Naloxone; D009020:Morphine; D003000:Clonidine