Central depressive effects of Magnolia extracts 4421 Muscle relaxant effect

Watanabe et al. (1973) reported the central depressive effect of extracts of Magnolia. After intraperitoneal administration of the water extract (1 g/kg), mice developed muscle weakness in 2-3 min, followed by cessation of breathing and heart beat in a few minutes. In contrast, no marked behavioral symptoms, except for a slight decrease in spontaneous motor activity for a short period, were produced by oral administration of the water extract (2 g/kg). In the case of the ether extract, however, both oral and intraperitoneal administrations resulted in strong muscle relaxation and disruption of clinging to a steel net for up to 90-120 min, without death. The ED50 values for the muscle relaxant effect of intraperitoneally administered ether extract of Magnolia and its alkaline soluble fraction were estimated to be 582 mg and 580 mg, respectively (Watanabe et al., 1975). The ethanol extract showed an intermediate effect between those of the water and ether extracts. These results indicate that the strong lethal effect of intraperitoneally injected water extract is caused by the peripherally mediated curare-like muscle relaxant action of magnocurarine and its related compounds (Tomita et al, 1951), and the ether extract shows a central depressive action. The known chemicals in the ether extract are essential oils such as pinenes, camphene, limonene, and a-, P- and y-eudesmol (Fujita et al., 1973a; Itokawa, 1986) and phenolic compounds such as magnolol, honokiol and magnaldehyde (Fujita et al., 1972, 1973b,c; Yamazaki, 1986; Yahara et al., 1991).

4.4.2.2 Anticonvulsive effect

The central depressive effect of the ether extract of Magnolia is also supported by its anticonvulsive effect. The intraperitoneal pretreatment of mice with the ether extract (1 mg/kg, 50 min before) and its alkali-soluble fraction completely protected the convulsions and death caused by strychinine (1 mg/kg s.c.) and picrotoxin (7.5 mg/kg s.c.), and the tremor induced by oxotremorine (1 mg/kg i.p.). The same pretreatment with the ether extract antagonized the pentetrazol (120 mg/kg s.c.)-induced extensor tonus and death, but not the convulsive twitch.

The ether extract of Magnolia and the alkali-soluble fractions inhibited the spinal reflexes, the crossed extensor reflex responding to the stimulation of the central end of the cut sciatic nerve, in young chicks (ED50 48.8 mg/kg and 21.2 mg/kg, respectively) (Watanabe et al., 1973). This effect was antagonized by strychnine (0.5 mg/kg i.p.). The tonic extensor convulsion produced by intracerebroventricular injection of penicillin G potassium (50 |ig) in mice was also inhibited by Magnolia ether extract (ED50 530 mg/kg) and its alkali-soluble fraction (ED50 251 mg/kg).

It was noted that the anticonvulsive potentials of the ether extract were approximately half those of the alkali-soluble fraction, suggesting that multiple compounds having different chemical characteristics are responsible for the anticonvulsive effect of the ether extract.

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