Influence of rat plasma and of various cations on the anti-eledoisin activity of morin.

1. The musculotropic activity of eledosin on the isolated guinea-pig ileum is antagonized by morin, a flavonoid derivative.2. The anti-eledoisin activity of morin is abolished by fresh rat plasma and by deproteinized rat plasma, but not by deionized plasma.3. Cupric acetate can restore the inhibitory property of the deionized plasma and can also inactivate morin.4. This effect of rat plasma and of cupric acetate is inhibited by (-)-penicill-amine and by N-acetyl-(+/-)-penicillamine.5. It is concluded that, when in contact with rat plasma, morin is probably inactivated as a consequence of the formation of a complex with the plasma copper.