Acid fecal recovery

Despite these difficulties the use of the silica gel technique for the solid probe/quadrupole mass spectrometer system holds promise for the analysis of some nutritionally important metals Both zinc and copper have been extracted successfully from serurn and zinc has also been extracted from urine and feces by using an anion exchange purification Biorad A61X8 (100-200 mesh) chloride form) anion exchange resin has been used to separate copper and zinc from acidic solutions (6) We have adapted this method to the separation of these two metals from acidic solutions of AAS standards urine serum and deproteinated fecal homogenate by elution with sucessively dilute acid solutions Recovery of an isotopic spike ai subsequent mass spectral analysis has been demonstrated with a Zn spike added to 1ml aliquots of a Fisher Certified AA Standard (zinc concentration Img/ml) Results of this experiment are shown in Table III ... 

Metabolic Transit of Lysinoalanine. Urinary and Fecal Excretion of Protein-Bound Lysinoalanine (113). Three different alkali-treated proteins (lactalbumin, fish protein isolate, and soya protein isolate) containing, respectively, 1.79, 0.38, and 0.14 g of lysinoalanine/16 g nitrogen were given to rats and the urines and feces were collected. Lysinoalanine was measured before and after acid hydrolysis. The fecal excretion varied from 33 to 51% of the total ingested lysinoalanine and the urinary excretion varied from 10 to 25%. The higher level of lysinoalanine found after acid hydrolysis indicates that a certain quantity is excreted in the urines as combined lysinoalanine (see Table VII). The total recovery was inferior to the ingested quantity (50 to 71%) indicating that the molecule is transformed or retained in the body of the rat. 

Feces The amount of feeal homogenate needed for the desired level of radioactivity per injection is determined. The feeal homogenate is extracted with three volumes of an appropriate solvent (e.g., aeetonitrile, acetonitrile/ methanol, acetonitrile/acidic acid). The fecal homogenate/solvent mixture is vortexed and sonicated and centrifuged. The extraction is repeated at least one more time to recover a desirable >85% of radioactivity. The sample is combined, dried, reconstituted in an appropriate solvent (e.g., 20-40% acetonitrile in water), vortexed and centrifuged at 3000 x g for 5 min. The aliquots of the reconstituted sample are counted by LSC to determine the final recovery of radioactivity (>80% desired). 

Colonic reabsorption of secondary bile acids seems to be clearly established. The presence of deoxycholic acid as a normal biliary constituent indicates that it has been absorbed from the colon. Furthermore, the human bile contains a variety of other bacterial transformation products such as lithocholic acid and other cholanic acids, some of which may have been further metabolized by the liver (44-47). In contrast to the case in some other mammalian species, human liver is not able to convert deoxycholic acid back to cholic acid. Colonic perfusion with different labeled bile acids has clearly shown that colonic absorption takes place in man (48). Administration of labeled cholic acid into the lumen of the large bowel during operation for cholecystectomy is followed by the appearance of labeled cholic acid and deoxycholic acid in the T-tube bile, the recovery from the T-tube being about 60% of the dose (49). This clearly shows that cholic acid is converted to deoxycholic acid in the human colon and that both of them are absorbed from the large bowel. Colonic reabsorption has been calculated to amount to 200 mg/ day (49). The colonic absorption of secondary bile salts could be even higher if the physical state of some bile acids were not unfavorable for absorption. Lithocholic acid, for example, is a very nonpolar compound and precipitates in the colonic content in addition, it and other secondary bile acids as well are partially associated with fecal debris and bacteria (41). As a result of poor absorption, the amount of secondary bile acids, other than deoxycholic acid, is usually low in human bile. After a continuous biliary drainage, secondary bile acids disappear from the bile in a few days (49-51). 

Quantitative recoveries of endogenously labeled bile acids in homogenized human feces can be obtained by continuous extraction for 48 hr with hot chloroform-methanol, 1 1 (18). After saponification, acidification, and continuous diethyl ether extraction, the bile acids are purified on silicic acid (Section IIIB 4 and Ref. 18) to give one mono- and disubstituted, and one trisubstituted bile acid fraction. For identification purposes further subfractionation can be made [see Table V (69, 77, 126, 127)]. The subfrac-ticns are subsequently subjected to small-scale preparative thin-layer chromatography of methylated bile acids. The fractions eluted from the thin-layer plates are next subjected to peak-shift analyses followed by final identification by gas chromatography-mass spectrometry. When the fecal bile acid composition has been elucidated in this way the mono-, di- and trisubstituted bile acids from the first silicic acid column may be quantitated after methyla-tion and by analysis on QF-1. These results are then compared with those obtained after trifluoroacetylation of the bile acid methyl esters. (18). 

Although fermentation of fiber tends to reduce its effectiveness as a source of fecal bulk, it has other very important benefits. The absorption and metabolism of short-chain fatty acids derived from carbohydrate fermentation provides the route for the recovery of energy from undigested polysaccharides. Butyrate functions as the preferred source of energy for the colonic mucosal cells, whilst propionate and acetate are absorbed and metabolized systemically. There continues to be much debate about the importance of butyrate for the colon. In vitro, butyrate causes differentiation of tumor cells, suppresses cell division, and induces programed cell death (apoptosis). These effects are thought likely to suppress the development of cancer, but it is not yet entirely clear whether they also occur in the intact intestine. Research continues on the importance of butyrate and other short-chain fatty acids for human health. 

---