Plasma ubiquinone, alpha-tocopherol and cholesterol in man.

Plasma ubiquinone, coenzyme Q10 or CoQ10 has been analyzed in plasma together with alpha-tocopherol and free cholesterol in healthy sedentary male subjects (SS), endurance trained male athletes (ET) and male patients with severe ischemic heart disease (IHD). Higher means were found in SS compared to both IHD and ET. Moreover, the ratios CoQ10 and alpha-tocopherol over free cholesterol were higher. In all groups significant relationships were found between the two products of the mevalonate pathway: CoQ10 and cholesterol (r ranged 0.66-0.86, p less than 0.01). The two lipophilic antioxidants, CoQ10 and alpha-tocopherol, were interrelated only in IHD (r = 0.86, p less than 0.001), borderline in SS (r = 0.51, p less than 0.05) but not in ET. It is assumed that plasma free cholesterol reflects the capacity to transport lipids and lipophilic compounds in blood. With metabolic stress and an elevated radical formation as in IHD and ET, the lower CoQ10 and alpha-tocopherol to cholesterol ratios mirror a subsequent toll on the scavenging potential. The difference in LDL levels between IHD and ET and the different storage capacity of CoQ10 and alpha-tocopherol might explain the tight coupling in IHD but not in ET. It is possible that the toll reflects both an intra- and extracellular radical quenching activity. The joint effect of the two lipophilic, extracellular antioxidants CoQ10 and alpha-tocopherol role in protecting e.g. LDL particles from peroxidation is suggested.     

The quantitative estimation of toluene skin absorption in man

Summary The absorption of toluene through the skin of the hand and the forearm in men was investigated experimentally. Both the absorption of liquid toluene and the absorption from aqueous solutions were studied using the direct method. It was stated that under the experimental conditions the rate of absorption of liquid toluene was 14–23 mg/cm²/h.In mean concentrations of 180–600 mg/1 the rate of absorption of toluene from aqueous solutions was 160-600 g/cm²/h and increased according to the increase of toluene concentration.     

Percutaneous absorption of m-xylene in man

Summary Percutaneous absorption of m-xylene was studied in volunteer experiments by means of monitoring xylene concentrations in blood and in exhaled air, and urinary methylhippuric acid excretion. Compared to normal working practices a rather extreme skin exposure, i.e. immersion of both hands in liquid xylene resulted in an estimated absorption of 35 mg xylene in 15 min which equals an estimated pulmonary retention within the same time period at TLV air.level of 100 ppm. The observed absorption rate for m-xylene was approximately 2 g/cm²/min. The penetration of xylene was fairly rapid, peak concentrations appearing in the draining venous blood 4–6 min after exposure. Further absorption took place for five hours, however, after the termination of exposure and the removal of the contaminant by alcohol and water rinsing. It was found, as expected, that venous blood from a contaminated area exhibits a much higher concentration of the contaminant than mixed venous blood. To exclude this error in biological monitoring of xylene (and other skin penetrating solvents) exposure, exhaled air determinations are recommended. As a sporadic finding in the investigation, a symptom-free subject with previous history of atopic dermatitis developed toxic eczema of the hands after xylene exposure and exhibited a three times greater absorption of the compound than the average for the rest of the group.     

Egg sphingomyelin lowers the lymphatic absorption of cholesterol and alpha-tocopherol in rats

Evidence indicates that phosphatidylcholine (PC) inhibits the intestinal absorption of cholesterol (CH) in rats. This study was designed to determine whether sphingomyelin (SM), structurally similar to PC, also inhibits the lymphatic absorption of CH. Sprague-Dawley rats with lymph cannulae were infused at 3.0 mL/h for 8 h via a duodenal catheter with a lipid emulsion [33.3 kBq 14C-CH, 20.7 micromol CH, 451.7 micromol triolein, 3.1 micromol alpha-tocopherol (alphaTP), 75.4 nmol retinol and 396.0 micromol sodium taurocholate in 24 mL of PBS (pH, 6.5)], without egg SM (SM0) as control, or with 5.0 micromol/h (SM5) or 10.0 micromol/h (SM10). Egg SM lowered the lymphatic absorption of 14C-CH in a dose dependent manner. Likewise, SM lowered the lymphatic absorptions of alphaTP and fatty acid (oleic acid), whereas it had no effect on retinol absorption. SM at a high dose (SM10) lowered the lymphatic outputs of both PC and SM, whereas there was no such effect at a lower dose (SM5). These results indicate that luminal egg SM has an inhibitory effect on the intestinal absorption of CH and other lipids of relatively high hydrophobicity. Our findings suggest that SM, if ingested in sufficient amounts, may inhibit the intestinal absorption of dietary lipids including cholesterol and alphaTP.     

Rice and iron absorption in man

Several studies suggest that iron absorption is low from rice-based meals. Comparisons of the effect of rice starch and wheat starch on iron absorption showed that rice had no effect on absorption. Observed differences in effects on iron absorption between different batches of rice starch could be explained by differences in the phytate content. Phytate is always present in rice grains. The content varies markedly depending on the method of milling. In polished rice, the content of phytate-P varied between 11.5 and 66 mg/100 g rice (data from 45 rice mills in Thailand). The bioavailability of iron in a meal composed of meat, a vegetable and rice varied about threefold (22.1-7.5 per cent) depending on the different phytate content of the rice (4 levels between 30 and 175 mg phytate-P were studied). The inhibitory effect of the phytate in rice was overcome by adding different amounts of an ascorbic acid-rich vegetable (green collard) to the meals.     

Percutaneous absorption of solvent vapors in man

It is known from industrial experience and experimental studies that percutaneous absorption of concentrated liquid solvents may be considerable and even hazardous if large enough areas of skin are exposed for long periods of time. Percutaneous penetration of xylene, styrene, toluene, 1,1,1-trichloroethane and tetrachloroethylene vapors at ambient air concentrations of 600 ppm for 3.5 h was studied in a dynamic exposure chamber with a restricted number of human volunteers. Although the small number of exposed persons precluded conclusive quantitation of absorption and valid intercompound comparisons, aromatic solvents and tetrachloroethylene appear to penetrate skin much more readily than 1,1,1-trichloroethane. Skin penetrating properties of solvents seem, under the circumstances, to be associated primarily with lipid solubility. It was approximated that percutaneous exposure (total body surface) to 600 ppm of xylene vapor for 3.5 h corresponded to an equally long inhalation exposure of less than 10 ppm. Similar percutaneous exposure to 1,1,1,-trichloroethane corresponded to an inhalation exposure of only 0.6 ppm. Disease-affected skin may display altered permeability characteristics, and one volunteer with atopic dermatitis exhibited a more than three times larger absorption of xylene vapor when compared to subjects with normal skin. It may be concluded that in the work environment percutaneous absorption of solvent vapors from the surrounding air through undamaged skin is likely to be insignificant.     

The 'anomalous' absorption of labelled and unlabelled vitamin C in man

Previous studies of vitamin C absorption in man using stable isotope probes have given results which cannot easily be reconciled with those obtained using non-isotope measurement. In order to investigate some of the apparent paradoxes we have conducted a study using two consecutive doses of vitamin C, one labelled and one unlabelled, given 90 min apart. Compatibility of the experimental results with two feasible models was investigated. In Model 1, ingested vitamin C enters a pre-existing pool before absorption, which occurs only when a threshold is exceeded; in Model 2, ingested vitamin C is exchanged with a pre-existing flux before absorption. The key difference between these two models lies in the predicted profile of labelled material in plasma. Model 1 predicts that the second unlabelled dose will produce a secondary release of labelled vitamin C which will not be observed on the basis of Model 2. In all subjects Model 1 failed to predict the observed plasma concentration profiles for labelled and unlabelled vitamin C, but Model 2 fitted the experimental observations. We speculate on possible physiological explanations for this behaviour, but from the limited information available cannot unequivocally confirm the model structure by identifying the source of the supposed flux.     

Percutaneous absorption of 2-butoxyethanol in man

The percutaneous absorption of the commonly used glycol ether 2-butoxyethanol (ethylene glycol monobutyl ether) was investigated in 12 exposure experiments with five men. The subject kept two or four fingers immersed in neat butoxyethanol for 2 h. Arterialized capillary blood samples were collected from the other hand before, during, and up to 4 h after the exposure and analyzed for butoxyethanol by gas chromatography. Urine was collected for 24 h and analyzed for the metabolite butoxyacetic acid, also by gas chromatography. The presence of butoxyethanol in blood and of butoxyacetic acid in urine confirmed that butoxyethanol enters the systemic circulation in man in vivo during dermal exposure. Percutaneous uptake rates were calculated from measured blood levels of butoxyethanol with the use of kinetic parameters (clearance and volume of distribution) obtained in earlier experiments with the same subjects. The uptake rates ranged from 7 to 96 nmol.min-1.cm-2. The results indicate that persons exposing large portions of their skin to butoxyethanol are at risk of absorbing acutely toxic doses.     

The absorption,metabolism, and excretion of xylenes in man

Summary Fifteen exposure experiments were carried out, in which four persons each, were simultaneously exposed to a defined concentration of o-, m-, and p-xylene vapors and also to their mixture at a ratio of 1:1:1. The concentrations were in all cases around 0.2 mg/l (Czechoslovakian MAC) or around double the amount. The period of exposure amounted to exactly 8 h.It was ascertained that the pulmonary retention is practically identical in all persons and in all isomers and amounts to 63.6 ± 4.2%. Its extent does not depend upon inoculation level, nor upon the duration of the exposure. During the period of desaturation the lungs excrete approximately 5% of the total amount retained in the organism. Xylene excretion via urine is quite negligible and amounts to a thousandth of 1%.The chief metabolites are toluic acids which are excreted in conjugated form with glycine as so-called toluric (=methylhippuric) acids. Free toluic acids, toluylglucuronic acids, and hydroxytoluic acids do not occur in the urine of persons exposed to a reasonable concentration of xylene vapors.The excreted amounts of toluric acids reach a maximum in the portion of urine collected at the end of exposure; then they decrease rapidly, but trace amounts can be still observed even after 4–5 days. The excretion takes a similar course in different persons and at different intensity of exposure. During the last 2 h of exposure a mean of 23.6% is excreted and in 8 h of exposure 71.7% of the amount excreted within 24 h.The side metabolites of xylenes are compounds hydroxylated on the aromatic nucleus. After exposure to o-xylene the presence of 2.3- and 3.4-xylenol was observed in urine; after exposure to m-xylene the presence of 2.4 xylenol, and finally after exposure to p-xylene the presence of 2.5-xylenol. The excretion of xylenols reaches a maximum as a rule just after termination of exposure.It was proved by balance calculation that of the total amount of xylene retained in the organism during exposure, more than 95% is excreted in the form of toluric acid (o-97.1; m-99.2; p-95.1%) and only a small part in form of xylenol (o-0.86; m-1.98; p-0.05%).     

Phosphatidylcholine inhibits and lysophosphatidylcholine enhances the lymphatic absorption of alpha-tocopherol in adult rats

This study was conducted to compare the effects of enterally infused phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) on the lymphatic absorption of alpha-tocopherol (alphaTP) in male rats. In expt. 1, bile-diverted rats with mesenteric lymph cannulas were infused at 3.0 mL/h for 8 h with a lipid emulsion containing 5.0 micromol alphaTP, 565 micromol 14C-triolein (14C-OA) and 396 micromol Na+-taurocholate with 80 micromol 1,2-dipalmitoyl PC (DPPC) or 1,2-dilinoleoyl PC (DLPC) or without PC (NoPC) in 24 mL phosphate-buffered saline (pH 6.6). In expt. 2, the effects of 1,2-dioleoyl PC (DOPC) and 1-oleoyl-2-hydroxy-PC (lysoPC) on alphaTP and 14C-cholesterol absorption were compared in rats with lymph cannulas. When DPPC or DLPC was infused, the lymphatic absorption of alphaTP was lowered drastically. The cumulative absorptions of alphaTP in rats infused with DPPC and DLPC were 45 and 52%, respectively, of the control values (NoPC). No significant difference was noted between the PC groups. In contrast, the absorption of 14C-OA was increased by 42 to 43% in rats infused with DPPC or DLPC compared with that in NoPC rats. Phospholipid outputs also were significantly higher in DPPC (34.0 +/- 5.5 micromol /8 h) and DLPC (32.4 +/- 2.4 micromol /8 h) rats than in NoPC rats (21.2 +/- 4.2 micromol /8 h). When lysoPC was infused, the absorptions of alphaTP and 14C-cholesterol were increased markedly compared with those for DOPC, with no significant difference in PL output between groups infused with DOPC and lysoPC. These observations provide clear evidence that PC present in a lipid emulsion inhibits alphaTP absorption, whereas it enhances the absorption of fat. The data also demonstrate that lysoPC simultaneously increases the absorption of alphaTP and cholesterol. The findings indicate that luminal PC inhibits the absorption of alphaTP and that hydrolysis of PC is critical to improving the intestinal absorption of the vitamin.     

Dietary L-carnitine enhances the lymphatic absorption of fat and alpha-tocopherol in ovariectomized rats

This study was conducted to determine whether the feeding of dietary L-carnitine (CN) improves the intestinal absorption of fat and alpha-tocopherol (alphaTOH) in ovariectomized (OX) rats. OX adult rats were weight-matched and assigned to 2 groups fed a modified AIN-93G diet containing alphaTOH-stripped soybean oil without (-CN) or with (+CN) supplemental CN at 150 mg/kg diet. At 5 wk, each rat with a lymph cannula was infused intraduodenally at 3.0 mL/h with a lipid emulsion consisting of 565 micromol triolein labeled with (14)C ((14)C-OA), 3.6 micromol alphaTOH, and 396 micromol sodium taurocholate in 24 mL PBS buffer. Lymph was collected hourly for 8 h and analyzed for lipids. The lymphatic absorption of alphaTOH for 8 h in +CN rats (899 +/- 201 nmol) was higher (P < 0.05) than in -CN rats (587 +/- 92 nmol). The absorption of (14)C-OA in +CN rats (53.5 +/- 4.0% dose/8 h) also was increased (P < 0.05) compared with -CN rats (47.6 +/- 5.0% dose/8 h). Lymph flow did not differ between the groups. When bile was diverted but with infusion of sodium taurocholate, the lymphatic absorption of lipids did not differ. The present study provides evidence that dietary CN enhances the rates and amounts of lymphatic absorption of alphaTOH and fat in OX rats. Our findings suggest that dietary CN may influence the process of lipid packaging and absorption by the enterocyte in OX rats, and may explain in part the increased status of alphaTOH in CN-fed animals.     

Guar delays intestinal calcium absorption in man

The effect of guar on the absorption of the calcium isotope 45Ca was measured in six normal subjects. Values for the delay before the initial rise of radioactivity in plasma (delta t) and the initial fractional absorption rate (alpha) were derived using a non-linear curve-fitting computer programme. Guar significantly reduced the fraction of 45Ca absorbed between 15 and 120 min. Guar increased the delay before the initial rise of radioactivity in plasma and reduced the initial fractional absorption rate. The results show that a dietary fibre which does not bind calcium in vitro reduces the rate of calcium absorption in man.     

Lead absorption in man from dietary sources

Summary The change in lead concentrations in foods and beverages has been examined during cooking processes in aqueous lead solutions. All of the foods examined-carrots, cabbage, peas, and macaroni—showed a significant uptake of lead in excess of the quantity of water regain that took place during cooking. Lesser quantities of lead were taken into carrots when cooked in solutions containing various concentrations of sodium chloride.Conversely, there were decreases in the concentrations of lead in both tea and coffee during preparation. A linear association between the concentration of lead in running tap water and kettle water in samples suggested that kettles do not contribute further to lead exposure. These experiments emphasize the dangers to man of lead exposure from domestic water supplies.