C. Ghelardini et al., Antinociception induced by amitriptyline and imipramine is mediated by alpha(2A)-adrenoceptors, JPN J PHARM, 82(2), 2000, pp. 130-137
The involvement of alpha(2)-adrenoceptors in the antinociception induced by
the tricyclic antidepressants amitriptyline and imipramine was investigate
d in mice by using the hot-plate and abdominal constriction tests. The anti
nociception produced by amitriptyline (15 mg/kg, i.p.) and imipramine (15 m
g/kg, i.p.) was prevented by reserpine (2 mg/kg, i.p.) and yohimbine (3 - 1
0 mg/kg, i.p.) but not by naloxone (1 mg/kg, i.p.), atropine (5 mg/kg, i.p.
), CGP 35348 (100 mg/kg, i.p.) and prazosin (1 mg/kg, i.p.). On the basis o
f the above data, it can be postulated that amitriptyline and imipramine ex
erted their antinociceptive effect by activation of alpha(2)-adrenoceptors.
Administration of the alpha(2A)-adrenoceptor antagonist BRL 44408 (1 mg/kg
, i.p,) prevented amitriptyline and imipramine antinociception, whereas the
alpha(2B/C)-adrenoceptor antagonist ARC239 (10 mg/kg, i.p.) was ineffectiv
e. These data indicate that the enhancement of the pain threshold produced
by amitriptyline and imipramine is mediated by activation of alpha(2A)-adre
noceptors. Neither tricyclic antidepressants nor the antagonists used impai
red mouse performance evaluated by the rota-rod and hole-board tests.