Cerebral extract from morphine-tolerant rats shows antiopiate properties in guinea pig ileum bioassay

Pharmacological Research Communications
G GiagnoniE Gori

Abstract

The existence of an endogenous antiopiate system which counteracts endogenous opiate effects has been proposed. The present study set out to seek substance/s with morphine-antagonist activity in the brain and serum of morphine-tolerant rats. Cerebral extracts were partly purified on Sephadex G 25 and serum was ultrafiltered through membranes with pore diameter smaller than 0.005 micron. On the guinea pig ileum myenteric plexus longitudinal muscle a fraction of the cerebral extract and the serum ultrafiltrate in toto did increase electrically induced contractions, and antagonized the depressant effect of morphine. The serum ultrafiltrate also enhanced longitudinal smooth muscle tone. Preliminary findings suggest that levels of endogenous morphine-antagonist substance/s are higher in morphine-tolerant rats than in controls. Only cerebral extract, not serum ultrafiltrate, inhibited [3H]-naloxone binding to cerebral opiate receptors. In the guinea pig bioassay both the cerebral extract and serum ultrafiltrate antagonized, to some extent, the inhibition elicited by morphine, norepinephrine and adenosine. These observations support the existence of endogenous compound/s which may be functional antagonist/s of opiates and play a role ...Continue Reading

References

Jun 1, 1994·Pharmacology, Biochemistry, and Behavior·C D McLachlanG J Coleman

Citations

Mar 1, 1974·Nature·W A Klee, R A Streaty
Jan 1, 1969·Proceedings of the Society for Experimental Biology and Medicine·G Ungar, L Galvan
Aug 1, 1984·Proceedings of the National Academy of Sciences of the United States of America·J TangE Costa

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