Germfree rats

The DE of pectin is slightly decreased in the upper part of GI and as well as in caecum and colon of germfree rats (Table 2). 

In intestinal contents and faeces from germfree rats quite high amounts of galacturonan were found, especially in the case of the pectin with the highest DE (Table 3). The isolated pectins were depolymerized to a small extent. The molecular weight distribution of pectins from intestinal contents and faeces remained relatively unchanged (Figures 1 and 2). 

Figure I. Pectins isolated from contents of of ileum, caecum and colon as well as from from faeces of a germfree rat (DE 92.6%).

Figure 2. Pectins isolated from faeces of germfree rats (collecting period I).

Robert A, Asano T Resistance of germfree rats to indomethacin-induced intestinal lesions. Prostaglandins 1977 14 333-341. 

B. S. Reddy, T. Narasawa, J. H. Weisburger and E. L. Wynder, Promoting effect of sodium deoxycholate on colon adenocarcinomas in germfree rats, J. Natl. Cancer Inst., 1976, 56(2), 441. 

The experiments with germfree rats also indicated that MAP metabolites were able to undergo enterohepatic circulation. 

Pentachloromethylthiobenzene (PCMTB) is metabolized in rats to bis-(methylthio)tetrachlorobenzene (bis-MTTCB) by a microflora dependent pathway that involves biliary excretion of the mercapturate precursors and the action of a microfloral C-S lyase (8). The results of metabolism studies in rats are outlined in table III. Eighty-one percent of single oral doses of labeled PCMTB were excreted with the feces as bis-MTTCB and nonextractable residues in about equal amounts. Germfree rats excreted about 88 percent of the dose with the feces as at least two mercapturic acids (I, II, fig. 3 ). The major metabolite in the urine from both conventional and germfree rats was the mercapturic acid. 

Seventy-four percent of oral doses of PCMTB-l C were excreted in the bile by conventional rats. Most of this (50 to 70%) has been characterized to be products of the MAP (8). Neither of the mercapturates shown in fig. 3 were secreted in the bile therefore, the mercapturic acids that were excreted with the germfree rat feces had to have been formed either by metabolism of the precursors of the mercapturic acid by the intestinal mucosa, or by the tissues during enterohepatic circulation of these precursors. Comparison of the rates of excretion of oral doses of PCMTB- C given to germfree and conventional rats indicate that there was enterohepatic circulation of the in the germfree rats. Conventional rats excreted more than 80 percent of the dose in the feces within two days while it took at least eight days for the germfree rats to excrete 80 percent of the dose in the feces. 

The importance of the gut microflora in the metabolism of isoflavones has been demonstrated. Antibiotic administration blocks isoflavone metabolism and germfree animals do not excrete metabolites. Moreover, only germfree rats colonized with microflora from a good equol producer excrete equol when fed soy. ... 

Sulfoxide Reduction. Reduction of the sulfoxide of the mercapturic acid of 2-chloro-f+-isopropylacetanilide by Intestinal microflora has been shown in vitFo (9), but has not been demonstrated to occur in tissues. The excretion of this mercapturate sulfoxide, which is excreted into the intestine with the bile, in feces from germfree rats dosed with the acetanilide is vivo evidence for the reductive function of the intestinal microflora (49) in MftP catabolism. This reduction, in addition to deacetylation, is another source for cysteine conjugates which can be translocated to the tissues for metabolism or excretion, or remain in the intestine and further catabolized by the microflora. 

C]-Benzo[a]pyrene was administered to male germfree rats (Yang et al. 1994). Urine was collected 24 hours before and every 24 hours for 7 days after administration. Urinary metabolites, consisting of 9% ofthe administered radioactivity, were fractionated by lipophilic ion exchange chromatography, and characterized by reversed-phase HPLC, ultraviolet spectrometry, and gas... 

Yang Y, Sjovall J, Rafter J, et al. 1994. Characterization of neutral metabolites of benzo[a]pyrene in urine from germfree rats. Carcinogenesis 15(4) 681-687. 

Reddy, B.S., Narasawa, T., Weisburger, J.H., Wynder, E.L., Promoting Effect of Sodium Deoxycholate on Colon Adenocarcinomas in Germfree Rats. J. Natl. Cancer Inst., 1976, 56, 441-442. 

Similar data have been reported for liver cholesterol levels in rats (7). Germfree and conventional rats fed a cholesterol-free diet had similar liver cholesterol levels however, as the amount of cholesterol in the diet was increased, the liver cholesterol levels of the germfree rats rose three times higher than did those of the comparable conventional rats. In these rats, the serum cholesterol levels did not change with microbiological status or dietary cholesterol. 

The time required for the conventional rats to excrete one-half of the administered isotope was calculated to be 2 days. The germfree rats required... 

Portman and Murphy (24) reported that the type of diet had an influence on turnover of cholic acid in conventional rats. Gustafsson and Norman (25) have investigated whether this effect is seen in germfree rats. In their study, they concluded that no significant difference existed in the percent of bile acid in the cecum of their rats among different groups of animals kept on different diets or between germfree and conventional ani-... 

As will be discussed below, the fecal bile acid excretion of germfree subjects is only one-half that of comparable conventional subjects. Wost-mann (unpublished data) has observed that the biliary bile acid flow in the germfree rat was three times greater than in the conventional rat. Since the pool sizes were essentially similar (22), this implies that the absorptive capacity and the number of cycles through the enterohepatic system were markedly greater in germfree rats than in conventional rats. 

Gustafsson et al. (22) studied the fecal excretion of cholic acid-i C metabolites in conventional and germfree rats. The mean daily excretion of labeled cholic acid and its metabolites was 18.9 mg/kg body weight for the conventional group and 8.2 mg/kg body weight for the germfree group. As mentioned above, their techniques would not uniformly label the bile acid pool however, their other techniques may have caused inclusion of the muricholic acids in their assay. 

Kellogg and Wostmann (14) studied the fecal bile acid excretion of germfree and conventional rats by direct chromatographic procedures. The germfree rats average 11.3 2.4 mg and the conventional rats 21.4 9.9 mg of bile acid/kg body wt/day p < 0.005) (Table III and Fig. 1). The coefficients of variation were 21 and 46%, respectively, suggesting that at least half of the quantitative variation seen in fecal bile acid excretion in the conventional animal was derived from effects of the intestinal microflora. 

In a later experiment, the same group (22) studied the effect of monoassociation of rats with E. coli. They found that there was no increase in bile acid excretion compared to that of germfree rats and identified 3a, 12a-dihydroxy-7-ketotaurocholanic acid and 3a,7j, 12a-trihydroxytaurocholanic acid as new bile acids in the feces of the E. coli associated rats. Only the 3a, 12a-dihydroxy-7-keto derivative was formed in vitro by E. coli, and this compound was metabolized by the rat to 3a,7j, 12a-trihydroxy- and 3a,7a,12a-trihydroxytaurocholanic acids. 

The Discrimination of Urinary Odors from Germfree Rats... 

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