Intracerebroventricular administration of canatoxin to rats increases the circulating levels of luteinizing hormone.

Recent evidence has implicated the central nervous system as a target organ for canatoxin, a toxic protein present in Canavalia ensiformis seeds. This toxin activates the lipoxygenase pathway of arachidonic acid metabolism and can thus induce the release of substances mediated by lipoxygenase products. In the present study, the circulating levels of luteinizing hormone (LH) were measured by RIA in male Wistar rats (200-240 g) after the administration of canatoxin into the lateral cerebral ventricle. Canatoxin (0.5-2 micrograms in 2 microliters daily for 3 days) caused a dose- and time-dependent increase in the plasma levels of LH. The total dose of canatoxin used is subconvulsive. At 2, 4 and 24 h after 2 micrograms of canatoxin LH levels were increased by 10%, 43% and 61%, respectively, compared to vehicle-injected animals (0.18 +/- 0.03 ng/ml). This response to 2 micrograms of canatoxin was not attenuated by pretreatment with two different lipoxygenase inhibitors, nordihydroguaiaretic acid (NDGA, 125 mg/kg) or esculetin (ECLT, 125 mg/kg), ip, 1 h before each canatoxin (CNTX) injection; % increase in LH with CNTX alone: 61%; CNTX+NDGA: 54%; CNTX+ECLT:76%; N = 5/group. These data show that intracerebral injection of CNTX in rats increases circulating levels of LH via a mechanism that is independent of the lipoxygenase pathway.

Intracerebroventricular administration of canatoxin to rats increases the circulating levels of luteinizing hormone

Recent evidence has implicated the central nervous system as a target organ for canatoxin, a toxic protein present in Canavalia ensiformis seeds. This toxin activates the lipoxygenase pathway of arachidonic acid metabolism and can thus induce the release of substances mediated by lipoxygenase products. In the present study, the circulating levels of luteinizing hormone (LH) were measured by RIA in male Wistar rats (200-240 g) after the administration of canatoxin into the lateral cerebral ventricle. Canatoxin (0.5-2 micrograms in 2 microliters daily for 3 days) caused a dose- and time-dependent increase in the plasma levels of LH. The total dose of canatoxin used is subconvulsive. At 2, 4 and 24 h after 2 micrograms of canatoxin LH levels were increased by 10 per cent , 43 per cent and 61 per cent , respectively, compared to vehicle-injected animals (0.18 +/- 0.03 ng/ml). This response to 2 micrograms of canatoxin was not attenuated by pretreatment with two different lipoxygenase inhibitors, nordihydroguaiaretic acid (NDGA, 125 mg/kg) or esculetin (ECLT, 125 mg/kg), ip, 1 h before each canatoxin (CNTX) injection; per cent increase in LH with CNTX alone: 61 per cent ; CNTX+NDGA: 54 per cent ; CNTX+ECLT:76 per cent ; N = 5/group. These data show that intracerebral injection of CNTX in rats increases circulating levels of LH via a mechanism that is independent of the lipoxygenase pathway

Further studies on the hypoxia produced by canatoxin in rats.

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.

Further studies on the hypoxia produced by canatoxin in rats

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 ug/kg, ip, N=6) and isoproterenol (100 ug/kg, ip, N+6) partially blocked (% variation of pO2:CNTX alone: -26.67 ñ 2.56, N=6; with cyproheptadine: 16.15 ñ 2.97*, N=6; with isoproterenol: 17.73 ñ 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 atrophine (2 mg/kg, ip, N=6). The hypoxemic effect of canatoxin (100 ug/kg iv 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

Alterations in rat carbohydrate metabolism induced by canatoxin as a probable consequence of primary hypoxia.

1. Canatoxin, a protein displaying lipoxygenase-activating properties isolated from Canavalia ensiformis seeds, induces hypoxia and hyperglycemia in male rats. 2. Liver glycogen, blood glucose and lactate levels were measured in male and female rats after canatoxin (50 mU, iv) injection. Increased levels of serum glutamic oxaloacetic transaminase activity were used as an indicator of hepatic injury. 3. There was no sex-related difference observable during canatoxin-induced hypoxia but male and female rats did show different patterns of metabolic change and hepatic injury after toxin administration. Increased blood glucose and lactate levels, liver glycogenolysis and hepatic injury were observed in male rats while female rats showed only hypoglycemia and glycogenolysis. 4. Pretreatment of male rats with either glucose, diazepam or hexamethonium abolished both the hypoxia and hepatic injury and the metabolic alterations produced by toxin injection. 5. The results suggest that the metabolic alterations and hepatic injury detected after canatoxin injection may be a consequence of primary hypoxia.

Alterations in rat carbohydrate metabolism induced by canatoxin as a probable consequence of primary hypoxia

Canatoxin, a protein displaying lipoxygenase-activating properties isolated from Canavalia ensiformis seeds, induces hypoxia and hyperglycemia in male rats. Liver glycogen, blood glucose and lactate levesls were measured in male and female rats after canatoxin (50 mU, iv) injection. Increased levels of serum glutamic oxaloacetic transaminase activity were used as an indicator of hepatic injury. There was no sex-related difference observable during canatoxin-induced hypoxia but male and female rats did whow different patterns of metabolic change and hepatic injury after toxin observed in male rats while female rats showed only hypoglycemia and glycogenolysis. Pretreatment of male rats with either glucose, diazepam or hexamethonium abolished both the hypoxia and hepatic injury and the metabolic alterations produced by toxin injection. The results suggest that the metabolic alterations and hepatic injury detected after canatoxin injection may be a consequence of primary hypoxia

Involvement of lipoxygenase and cyclo-oxygenase pathways in hypoxia and metabolic alkalosis produced by canatoxin in rats.

This paper reports on the metabolic alkalosis produced in rats by canatoxin, a neurotoxic principle extracted from Canavalia ensiformis seeds. Rats receiving canatoxin showed increased blood bicarbonate concentration with alkaline pH and no change in pCO2. A fall in pO2 was also seen. A dose-dependent relationship between pO2 decrease and bicarbonate increase was also observed with the toxin, suggesting that hypoxia may result from respiratory compensation. Canatoxin-induced hypoxia was both lipoxygenase and cyclo-oxygenase dependent but metabolic alkalosis was only blocked with cyclo-oxygenase inhibitors. Canatoxin activates the lipoxygenase pathway and probably increases leukotriene (LT) production. Since LT may release cyclo-oxygenase products, this may explain the metabolic alkalosis observed with canatoxin.