Canatoxin, a
convulsant neurotoxin from the seeds of Canavalia ensiformis, induces
lipoxygenase-dependent
hypoxia in rats which is blocked by
hexamethonium. The purpose of the present study was to examine the relationship between
canatoxin-induced
hypoxia and bronchoconstriction. Since several effects of the toxin are very similar to those described for
morphine and
opioid-like
peptides, the effects of
opioid antagonists were also investigated. Pretreatment of male, adult Wistar rats (200-250 g) with
cyproheptadine (80 micrograms/kg, ip, N = 6) and
isoproterenol (100 micrograms/kg, ip, N = 6) partially blocked (% variation of pO2: CNTX alone: -26.67 +/- 2.56, N = 6; with
cyproheptadine: -16.15 +/- 2.97*, N = 6; with
isoproterenol: -17.73 +/- 1.93*, N = 6; *P < 0.05 as compared to CNTX alone) the
hypoxia but no effect was observed with
diphenhydramine (2 mg/kg, ip, N = 6) or
atropine (2 mg/kg, ip, N = 6). The hypoxemic effect of
canatoxin (100 micrograms/kg, i.v., 20 min, N = 6) was also almost completely blocked with either
naloxone (1 mg/kg, sc, N = 6) or
naltrexone (5 mg/kg, sc, N = 6). The results presented here provide evidence suggesting that both
opioid peptides and bronchoconstriction seem to play a role in the
hypoxia caused by
canatoxin.