In the present study the effects of exogenous and endogenous nitric oxide (NO) on intestinal bacteria and on the intestinal tissue integrity have been investigated in healthy rats and in rats receiving bacterial endotoxin (LPS). A segment of jejunum was taken in order to evaluate tissue damage and hematoxylin-eosin staining; microbiological studies were carried out collecting stool samples. Administration of LPS (5 mg kg-1 i.v.) induced a moderate jejunal damage, which was completely prevented by N-G-nitro-L-arginine methyl ester (L-NAME, 5 mg kg-1 s.c.), thus suggesting a damage of endogenous NO on the intestinal mucosa; sodium nitroprusside (SNP, 10 mg kg-1 os) reduced significantly jejunal damage induced by LPS. Endogenous NO produced by the administration of LPS resulted to be cytotoxic for all examined aerobic and anaerobic bacteria, while exogenous NO, released from SNP, showed an inhibitory effect only on Entero. faecalis and E. coli growth. From our data, it seems reasonable to conclude that high local levels of NO are required in order to observe jejunal damage and cytotoxic effects on aerobic and anaerobic faecal flora.
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