Studies on flavonoid metabolism. Metabolism of (+)-[14C]catechin in the rat and guinea pig

1. The fate of (+)-[U-(14)C]catechin and (+)-[ring A-(14)C]catechin has been studied in the guinea pig and rat. 2. (+)-[U-(14)C]Catechin was shown to give rise to labelled phenolic acids, labelled phenyl-gamma-valerolactones and (14)CO(2). 3. (+)-[ring A-(14)C]-Catechin did not give rise to labelled phenolic acids, but labelled phenyl-gamma-valerolactones were detected together with a higher proportion of (14)CO(2). 4. Administered [(14)C]delta-(3-hydroxyphenyl)-gamma-valerolactone gave rise to labelled m-hydroxyphenylpropionic acid in the rat whereas administered [(14)C]m-hydroxyphenylpropionic acid gave rise to a compound yielding labelled m-hydroxybenzoic acid on hydrolysis. 5. The distribution of radioactivity in the urine and faeces of (+)-[(14)C]catechin-fed animals is described; a high proportion of residual radioactivity was found in urine that had been exhaustively extracted with diethyl ether.     

Metabolism of sodium oestrone [35S]sulphate in the guinea pig

Intraperitoneal administration of sodium oestrone [(35)S]sulphate to male and female free-ranging guinea pigs is followed by excretion of most of the radioactivity mainly as inorganic [(35)S]sulphate in the urine within 72h. The remainder of the radioactivity in the urine was found in oestrone [(35)S]sulphate, two unidentified metabolites (A and B) and traces of oestradiol-17beta 3-[(35)S]sulphate. When injected intraperitoneally into animals with bile-duct and bladder cannulae, most of the dose was excreted in the bile. Unchanged oestrone [(35)S]sulphate was the main biliary component excreted in males and females, but the latter also excreted appreciable amounts of oestradiol-17beta 3-[(35)S]sulphate and metabolites A and B. The urine from these animals also contained these metabolites, inorganic [(35)S]sulphate and also oestrone [(35)S]sulphate, but in small amounts. Metabolite A was present only in samples from males. Whole body radioautography pinpointed the liver and kidney as the possible sites of metabolism of the ester. The ester underwent little desulphation in the isolated perfused female guinea-pig liver and in animals in which kidney function had been eliminated, and was excreted unchanged in the bile. These results and the observed low oestrogen sulphatase and arylsulphatase C activities found in guinea-pig liver and kidney support the view that the two enzymes are identical.     

Metabolism of [14C]diethylstilboestrol epoxide by rat liver in vitro.

1. The trans-epoxide of diethylstilboestrol and its pinacolone were synthesized chemically and the pinacolone shown to be formed from the epoxide by a non-enzymic process. 2. [14C]Diethylstiboestrol epoxide was converted by rat liver microsomal fraction into 4'-hydroxypropiophenone by a new type of cleavage reaction involving mono-oxygenase. Conditions for the formation of this metabolite and also water-soluble products were investigated together with the effect of inhibitors. A sex-difference in the conversion of diethylstilboestrol epoxide into 4'-hydroxypropiophenone and to polar and water-soluble products was observed. 3. Diethylstilboestrol epoxide was found to be a relatively stable compound that did not form a glutathione conjugate readily without further microsomal activation. A purified preparation of epoxide hydratase did not enhance its rate of conversion into the pinacolone. 4. Diethylstilboestrol epoxide was found to have about one-tenth the oestrogenic activity of diethylstilboestrol as measured by the increase in uterine weight or the induction of peroxidase in immature rat uteri. It was inactive as a mutagen when tested for its ability to inhibit bacteriophage phi X174 DNA viral replication. 5. The possible role of diethylstilboestrol epoxide as an intermediate in the metabolism of diethylstilboestrol and in mediating the harmful effects of this synthetic estrogen is discussed.     

Metabolism of [4-14C] testosterone in the rat uterus in vitro.

In view of the uterine action of androgens we have investigated in vitro the metabolism of [4-14C]-testosterone in uterine tissue of ovariectomized rats. After purification of the extracts on Amberlite XAD-2 the metabolites have been isolated by gel. Five metabolites were isolated and identified during these incubation studies: 4-androstene 3,17-dione, 17beta-hydroxy-5alpha-androstan-3-one, 5 alpha-androstane-3alpha17beta-diol, 4-androstene-3 beta, 17beta-diol and 4-androstene-3alpha, 17beta-diol. Furthermore, two polar C19O3-metabolites and one isopolar to 5 alpha-androstane-3, 17-dione have also been detected. The metabolites were characterized by radioactive gas chromatogrphy, and determination of the relative specific activity in the eluates of Sephadex column chromatography. The identification of allylic alcohols was complemented by their oxidation to 4-androstene-3,17-dione. The present data show that activity of 17beta,3alpha- and 3beta-hydroxysteroid-oxidoreductase and 5alpha-ring-reductase are involved in the metabolism of testosterone in vitro in the rat uterus. The very low 5 alpha-reductase activity under the experimental conditions used in this work explains the formation of allylalcohols as the principal metabolites of testosterone in the rat uterus.     

Thermophilic Anaerobic Biodegradation of [14C]Lignin, [14C]Cellulose, and [14C]Lignocellulose Preparations

Thermophilic (55°C) anaerobic enrichment cultures were incubated with [¹⁴C-lignin]lignocellulose, [¹⁴C-polysaccharide]lignocellulose, and kraft [¹⁴C]lignin prepared from slash pine, Pinus elliottii, and ¹⁴C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

The incorporation of [14C] lysine into the protein of the guinea pig central auditory system

The incorporation of [¹⁴C]lysine into various brain proteins was studied. The proteins of different areas of the auditory system and cortical subcellular fractions were analysed using a disc electrophoretic technique that allows both protein and radioactivity assays along the gels. The highest level of incorporation was found in the mid brain nuclei, particularly the inferior colliculus, and was lowest in the auditory cortex proteins. This was true for both saline soluble proteins and proteins solubilized by Triton X-100 treatment. Of the subcellular fractions, the highest level of activity was found in the microsomal fraction. Considerable radioactivity was also found in the proteins isolated from the synaptosome-rich fraction. Of particular interest in this fraction was a slow migrating protein band which was soluble in Triton X-100, had a high specific activity, and appeared to be synaptosome specific. These observations are in concurrence with the hypothesis that the nerve ending contains protein synthesizing machinery.     

Metabolism of [1-14C]glyoxylate, [1-14C]-glycollate, [1-14C]glycine and [2-14C]-glycine by homogenates of kidney and liver tissue from hyperoxaluric and control subjects

1. The metabolism of [1-(14)C]glyoxylate to carbon dioxide, glycine, oxalate, serine, formate and glycollate was investigated in hyperoxaluric and control subjects' kidney and liver tissue in vitro. 2. Only glycine and carbon dioxide became significantly labelled with (14)C, and this was less in the hyperoxaluric patients' kidney tissue than in the control tissue. 3. Liver did not show this difference. 4. The metabolism of [1-(14)C]glycollate was also studied in the liver tissue; glyoxylate formation was demonstrated and the formation of (14)CO(2) from this substrate was likewise unimpaired in the hyperoxaluric patients' liver tissue in these experiments. 5. Glycine was not metabolized by human kidney, liver or blood cells under the conditions used. 6. These observations show that glyoxylate metabolism by the kidney is impaired in primary hyperoxaluria.     

Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.     

Long-term Metabolism of [14C]Sugars in Stored Potatoes

[¹⁴C]Sucrose, [¹⁴C]glucose and [¹⁴C]fructose were introducedinto potato tubers held at 10 °C and the redistributionof label chased over a 65 d period in storage. Respiratory losseswere identical in all treatments, as was the partitioning of¹⁴C between soluble and insoluble forms. Sucrose was the predominantlabelled sugar in the tubers after 20 h, regardless of the original[¹⁴C]sugar introduced, and was loaded and distributed throughoutthe tubers by the internal phloem system. After 20 h the proportionsof labelled sugars bore no relationship to those of the unlabelledendogenous sugars. However, with time the percentage of ¹⁴Cin sucrose fell while that in glucose increased and by 65 dthe proportions of the labelled sugars more closely resembledthe endogenous pools. Fructose represented a consistently lowproportion of both the labelled and unlabelled sugars. By 21d a considerable proportion of the soluble ¹⁴C had been convertedto starch (approx. 25% of the total tuber 14C), this value remainingrelatively constant for the remainder of the storage period.Sprouts which formed on the tubers contained up to 6% of thetotal tuber ¹⁴C but less than 0.2% of the tuber dry matter.It is suggested that the bulk of the translocated [¹⁴C]sucroseentered the symplast and exchanged slowly with the bulk of thesugars in the storage cell vacuoles. [¹⁴C]sugars, phloem loading, starch, potato tuber, Solunum tuberosum, cold storage