Liver snips. A simple, rapid and reproducible method for studying metabolism in small fragments of tissue, as applied to glucuronidation in rat liver

The sibutramine metabolite M2 improves muscle glucose uptake and reduces hepatic glucose output: preliminary data

The satiety agent sibutramine acts in part through a primary amine metabolite, M2. To investigate whether M2 could affect glycaemia independently of satiety and weight loss, groups of normal mice received a single dose of M2 (1 or 10 mg/kg) and food was withheld. Compared with controls (who received vehicle only), M2 (10 mg/kg) decreased basal plasma glucose concentrations, with a maximal decrease of about 25% at 48 hours (p < 0.05). Soleus muscles were isolated from the mice at intervals: insulin-mediated glucose uptake by the muscles from controls progressively decreased over 24 hours whereas uptake was maintained by muscles from M2-treated mice. Hepatic gluconeogenesis was reduced about 40% by liver snips isolated from M2-treated mice after 24 hours (p < 0.05). These preliminary results suggest that the M2 metabolite of sibutramine can reduce glycaemia, maintain insulin-mediated muscle glucose uptake and reduce hepatic gluconeogenesis independently of satiety and weight loss.

Metabolism of sitosteryl beta-D-glucoside and its nutritional effects in rats

[4-14C]Sitosteryl beta-D-glucoside, intragastrically administered to rats, was not absorbed by the intestinal mucosa. At three hr after the application, radioactivity was concentrated almost exclusively in the digesta of stomach, small intestine as well as cecum and colon, whereas only low proportions of radioactively labeled compounds were found in the various tissues of the gastrointestinal tract. Minor proportions of labeled metabolites of [4-14C]sitosteryl beta-D-glucoside, such as sitosterol and sitosteryl esters, were formed in the small intestine in vivo and in slices of small intestine in vitro. In the tissues of cecum and colon as well as the digesta derived from them, high proportions of labeled coprositostanol, i.e. 24 alpha-ethyl-5 beta-cholestan-3 beta-ol, that obviously had been formed by bacterial degradation of the substrate were detected. The feeding of sitosteryl beta-D-glucoside (0.5 g/kg body weight X day) over a period of four weeks did not alter significantly body weights or organ weights of rats. Analyses of steryl lipids of the various organs and tissues confirmed the findings obtained with the radioactive substrate: neither sitosteryl beta-D-glucoside nor sitosterol or sitosteryl esters derived therefrom had been transported in appreciable amounts to organs and tissues outside the alimentary canal during the feeding period. Minor proportions of unmetabolized sitosteryl beta-D-glucoside were detected in the tissues of stomach and intestine, whereas large proportions of the substrate were found in feces of rats that had received the sitosteryl beta-D-glucoside-containing diet; coprositostanol was found in feces of these animals in high proportions as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic lipoprotein biosynthesis

Methods for the study of hepatic lipoprotein synthesis and secretion have been described, and the advantages of each system discussed. Attention has been focused on intact cell systems. The isolated perfused liver constitutes a standard of comparison for all others, even though it, too, has limitations. Table IV below gives our assessment of some of the advantages and disadvantages of the techniques for studying hepatic lipoprotein biosynthesis.

The temporary postnatal decline in glucuronidation of certain phenols by rat liver

A temporary but marked postnatal decline in UDP-glucuronosyltransferase activity occurs in homogenates and microsomes from rat liver. The profile of this trough and its time of occurrence (maximal over 13-16 days) are almost identical with the two substrates 2-aminophenol and 1-naphthol, whose rates of glucuronidation differ 10-fold. The trough is greatest with digitonin-activated preparations, least with fresh latent ('native') enzyme and intermediate when the native enzyme is treated with its specific activator UDP-N-acetylglucosamine (UDP-GlcNAc). Less detailed evidence supports similar conclusions with 4-nitrophenol as substrate. The trough is not due to the presence of an inhibitor of the transferase in rat liver at 15 days of age. Over the whole perinatal period, including the time of the trough, the enzyme in homogenates can be activated by UDP-GlcNAc; the microsomal enzyme is activated to a rather lesser degree perinatally, and evidence suggests this may be due to artefacts introduced during tissue fractionation. When the overall process of glucuronidation is studied in snips of intact liver offered high concentrations of the two different phenols, the trough is again evident over the same period as observed with broken cells, and of equal depth for both substrates. The infant rat is therefore probably less able to glucuronidate hepatically these phenols over the suckling or early weaning period than are the adult, late foetus or newborn, and may be especially incompetent at 13-16 days of age.