Fecal excretion rate

The majority of ultratrace elements are metals, and their fecal excretion rate is greater than 50% (Table 4.19). Fecal excretion of lead by people with a mixed diet is astonishingly low (50%), while the apparent absorption rate is very high (40% on average). The daily lead intake of test popula-... 

The fecal excretion rates of the ultratrace elements strontium, titanium, uranium and chromium were 90-99%, and the appa-... 

Fecal excretion of the nutritional vanadium intake amounts to 96% in both sexes, and to 79% in lactating tvomen (Tables 27.5 and 27.6). Most of the ingested vanadium is not absorbed, and the form of the diet (mixed or ovo-lacto-vegetarian) has no effect on the fecal excretion rate (see Table 27.5). On average, adults of both sexes and with either form of diet eliminate 4% of the nutritional vanadium intake renally (range 2-6%). 

The rate of cholate synthesis in man is about 200-300 mg/day, as measured by isotope dilution studies. The chenodeoxycholate synthesis rate is similar, so that the total primary bile salt synthesis is about 400-600 mg daily for a healthy adult, and when in the steady state this amount is also the daily fecal excretion rate (12). 

In a study of pregnant rats that were exposed to radiolabeled methyl parathion by single dermal application, half-life elimination rate constants for various tissues ranged from 0.04 to 0.07 hour, highest values noted in plasma, kidneys, and fetus. Of the applied radioactivity, 14% was recovered in the urine in the first hour postapplication. By the end of the 96-hour study, 91% of the applied dose had been recovered in the urine. Fecal excretion accounted for only 3% of the administered dose (Abu-Qare et al. 2000). 

The large contribution of the fecal route to excretion of absorbed americium appears to be the result of excretion of americium into the bile. In monkeys that received an intravenous injection of americium citrate,241 Am was detected in gall bladder bile and its concentration increased as the relative rate of fecal excretion increased over time post injection (Durbin 1973). Durbin (1973) estimated that at bile production rates similar to humans, biliary excretion could have accounted for most, if not all, of the fecal excretion of americium observed in the monkeys. 

Fig. 2 Pharmacokinetic profiles of occluded and non-occluded systems. (A) Total urinary and fecal excretion. (B) Time of maximal excretion rate (hr). (From Ref. °l)...

The model simulations were in close agreement with the observed results from the distribution and metabolism studies. Physiological processes that were highlighted by the results and the discrepancies that did occur include the probable active transport into the brain (versus passive diffusion) of a methyl-mercury-cysteine complex, the bidirectional transport of methylmercury between the gut lumen and gut tissue as a more important determinant of methylmercury fecal excretion than biliary secretion, the importance for the determination of methylmercury half-life in rats of the recycling of mercury from ingested hair, and the need for better estimates of the rate constants for the demethylation of methylmercury in order to adapt the model to other species. 

The nonionic contrast media are highly hydrophilic. When given orally, iohexol is absorbed Ifom normal bowel (785). In dogs, approximately 2% of the oral dose is absorbed and excreted in the urine within 6 h, and about 4%of the dose is absorbed and excreted in cats. Using I-labeled iohexol, Mutzel and Speck (267) found intestinal absorption to be about 2% of the intravenous dose given at 60 mg I/mL body weight to male rats. The urinary excretion from the rat was 91.5 3.6% of the administered dose of I-labeled iohexol, and the fecal excretion 6.8 2.7% of the dose 24 h after intravenous injection. In the dog the urine contained 81 9% of the administered dose within 3 h after injection. Total recovery from urinary excretion in the dogduringthe 7 days after injection was 98 4% of the dose and total recovery from fecal excretion was 0.95 0.45%. Healthy volunteers excreted 84% of the dose in urine within 4 h and 100% of the dose within 24 h after intravenous injection at the rate of 25 mL/min of iohexol at a... 

The excretion of nonionic iopamidol was studied in healthy subjects at several dose levels by use of two different solution concentrations of 200 and 300 mg I/mL, which were administered intravenously at a rate of 20 and 39 mL/min, respectively (760). Urinary elimination of iopamidol was rapid at all dose levels, with more than half of the dose excreted by the kidneys in the first 2 h after injection. Total urinary recovery within 72-96 h after injection was more than 90%, and the fecal recovery for the same period was about 1% of the administered dose. C-Labeled iopamidol was also included in this study for quantitation and the search for metabolic products of iopamidol, of which none was found. In dogs the urinary and fecal excretion of iopamidol at 72 h were 94.8 1.2 and 0.63 0.32%, respectively, of the injected dose at the dose level of 50 mg I/kg body weight. At a higher dose level of 200 mg I/kg, these excretions were 93.4 1.5 and 3.17 1.39%, respectively (195). The... 

Strontium that has been absorbed from the gastrointestinal tract is excreted primarily in urine and feces. In two dial painters, rates of urinary and fecal excretion of radium approximately 10 years after the exposure were approximately 0.03 and 0.01% of the body burden, respectively (Wenger and Soucas 1975). The urine fecal excretion ratio of 3 that was observed in the radium dial workers is consistent with ratios of 2-4 observed several days to weeks after subjects received an intravenous injection of SrCl2 (Bishop et al. 1960 Blake et al. 1989a, 1989b Newton et al. 1990 Samachson 1966 Snyder et al. 1964 Uchiyama et al. 1973). Thus, urine appears to be the major route of excretion of absorbed strontium. The observation of fecal excretion of radioactive strontium weeks to decades after an oral exposure or over shorter time periods after an intravenous exposure suggests the existence of a mechanism for transfer of absorbed strontium into gastrointestinal tract, either from the bile or directly from the plasma. Evidence for direct secretion of strontium from the plasma into the intestine is provided by studies in animals (see Section 3.5.1). The available information does not address the extent to which biliary excretion may also contribute to fecal excretion of strontium. 

The excretion of macro elements occurs via the feces, urine, and stveat, though the first two routes represent the main pathways. Typically, fecal excretion accounts for only 2-7% of the sodium intake. The apparent absorption rate of sodium has been found to vary between 93 and 98%. On average, the apparent absorption rate of macro elements by ovolactovegetarians is lower... 

Tab. 4.5 Fecal excretion and apparent absorption rates of ash and macro elements by ad ults ...

Fecal excretion of the macro elements was, on average, 3% for sodium, 19% for potassium, 28% for ash, 36% for phosphorus, 69% for magnesium, and 84% for calcium. The apparent absorption rate is negatively correlated with fecal excretion of the macro elements. The real absorption rate of all these elements is higher than the apparent absorption rate, mainly due to the salivary, biliary and pancreatic excretion of absorbed macro elements into the intestine. 

Tab. 4.12 Fecal excretion and apparent absorption rate of trace elements by adults ...

The phytin-rich nutrition of ovolactovegetar-ians lowers the availability of strontium and increases fecal excretion of this alkali metal. The apparent absorption rate of strontium in vegetarians, like that of calcium, is significantly lower than in people with a mixed diet. 

Fecal excretion of sodium is limited to 1 -2%, which is extremely low in comparison to other elements. The apparent absorption rate of sodium is 98%, and this compares... 

Inhibition of Lipid Absorption - Agents which decrease the absorption of dietary lipids specifically by inhibiting pancreatic lipase may be suitable for the treatment of obesity. The reduced rate of lipid absorption produced by fenfluramine in rats is probably due to an inhibition of pancreatic lipase. The structural features of a series of phenethylamines, including fenfluramine, required for lipase inhibition have been described using partially purified rat and human pancreatic lipase. Pluronic L-101, a hydrophobic surfactant is a potent inhibitor of pancreatic lipase vitro and reduces body weight gain and carcass lipid after chronic administration to rats. Fecal excretion of dietary lipid is enhanced by Pluronic L-101, thus supporting its action as a lipase inhibitor. 

A. Specific levels. Elemental and inorganic mercury follow a biphasic elimination rate (initially rapid, then slow), and both urinary and fecal excretion occur. The urinary elimination half-life is approximately 40 days. 

Conflicting results were also observed in animals consuming 20% chitin. Their hemoglobin value (13.7 1.1 g Hb/dl) would have been expected to be lower considering the manner in which animals voided Fe via fecal excretion over time (Figure 5). At the rate of Fe loss observed, total depletion of Fe was probable after 23 days on the diet or shortly thereafter. 

Urinary and fecal excretion for each of the three experiments is shown in Figure 4. The amounts excreted are very small and a descending excretion rate is observed in each case. Apparent differences may not be real, considering the small quantities which are being measured. 

Cholestyramine resin forms a nonabsorbable complex with bile salts in the gut lumen and increases fecal excretion about three times and may thus be expected to have an effect on bile salt pool size and synthesis rates similar to ileectomy (18). 

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