Association Des Physiologistes: 61ème Réunion, Bordeaux 14-17 Septembre 1993

Exogenous spermine induces maturation of the liver in suckling rats

In the present study, we investigated the effects of spermine on postnatal liver maturation in suckling rats. The animals were given spermine either per os (8 micromol) or by intraperitoneal injection (1 micromol), once daily for three or five days. The percentage of liver cells in different cell cycle phases and of diploid cells in the parenchyma was estimated. The protein content, ornithine aminotransferase (OAT) activity, and content of DNA polyamines and receptors for polymeric immunoglobulins (RPI) were also measured in liver extracts. The ingestion of spermine had the following effects: the percentage of the cells in S and G2M phases of the cell cycle diminished the percentage of diploid cells increased the content of polymeric immunoglobulin receptors increased; the OAT activity increased; the contents of putrescine and spermidine decreased and almost reached adult values; and the spermidine/spermine ratio became similar to that observed in the liver of adult rats. These phenomena were detected 40 hours after the beginning of oral spermine treatment. The intraperitoneal injection of spermine had no effect on the OAT activity, but it decreased the spermidine content and enhanced the spermine content. Our data demonstrated for the first time that dietary polyamines play a role in the initiation of liver postnatal maturation in suckling rats.

Analysis of structural and biochemical events occurring in the small intestine after dietary polyamine ingestion in suckling rats

In the present investigation, we analyzed the mechanism involved in spermine-induced intestinal maturation in suckling rats. Spermine was given orally to suckling pups and biochemical as well as morphological parameters were studied at different times after the beginning of the treatment. Eight hours after administration, spermine produced cell elimination at the villus tops and a decrease in intestinal DNA and protein content. In parallel, protein and DNA concentration and disaccharidase activity were enhanced in the chyme. These transitory alterations were not induced by growth inhibition, as DNA synthesis was not modified, although a brief decrease in protein synthesis was observed. Spermine was not metabolized in cytotoxic products: rat pretreatment with MDL72527 (an inhibitor of polyamine oxidase) did not avoid the decrease in disaccharidase activity and in DNA and protein content. Three days after treatment, sucrase and maltase activity was higher in rats treated with spermine and MDL72527 than that in animals receiving spermine alone. Lactulose or acetylspermine ingestion induced intestinal maturation. Our data suggest that dietary polyamines exert a direct and specific maturational effect on rat small intestine and that an early decrease in lactase activity plays an important role in this phenomenon.