Biliary excretion in foreign compounds. Sulphonamide drugs in the rat

Biliary excretion in foreign compounds. Species difference in biliary excretion

1. The biliary excretion of injected [(14)C]aniline, [(14)C]benzoic acid, 4-amino-hippuric acid and 4-acetamidohippuric acid in six or eight species of animal (rat, dog, hen, cat, rabbit, guinea pig, rhesus monkey and sheep) was studied. 2. These compounds, with molecular weights in the range 93-236, are poorly excreted in the bile in all the species examined and, in effect, there is little significant species difference in the extent of their biliary excretion. 3. Compounds of higher molecular weight (355-495) were also studied, namely succinylsulphathiazole, [(14)C]stilboestrol glucuronide, sulphadimethoxine N(1)-glucuronide and phenolphthalein glucuronide. 4. With these compounds a clear species difference in the extent of biliary excretion was found, the rat, dog and hen being good excretors, the rabbit, guinea pig and monkey poor excretors, and the cat and sheep taking an intermediary position. 5. There was a general trend for biliary excretion to be higher in all species when the compounds were of higher molecular weight. 6. These results are discussed in their relation to species differences in drug metabolism.

Biliary excretion of [C]succinylsulphathiazole in the rat and rabbit

1. After intravenous injection about 30% of the dose (20mg./kg.) of succinylsulphathiazole is excreted unchanged in the bile in 3hr. by the rat, whereas only about 1% is excreted by the rabbit. When the renal pedicles are ligated the biliary excretion of succinylsulphathiazole in the rat increases to about 80% of the dose, but in the rabbit under these conditions the biliary excretion is only 2% of the dose. 2. In the rat, the sulphonamide readily enters the liver and biliary excretion occurs against a concentration gradient from liver to bile; further, the excretory process can be saturated, and can be depressed by the simultaneous administration of phenolphthalein glucuronide or bile salts. 3. In the rabbit, these conditions have not been found; succinylsulphathiazole does not readily enter the liver from the plasma, there is no transfer of the drug from the liver cells to the bile against a concentration gradient, and no saturation or depression of the biliary excretion of succinylsulphathiazole is found. 4. It is suggested that two factors responsible, at least partly, for the low biliary excretion of succinylsulphathiazole in the rabbit are the poor entry of the sulphonamide into the liver in this species and a deficiency of the concentrative mechanism for its excretion in the bile.

The fate of ethyltin and diethyltin derivatives in the rat

1. Ethyltin trichloride does not appear to be metabolized by the rat. When given orally excretion occurs almost entirely in the faeces, and when given intraperitoneally it occurs exclusively in the urine. Biliary excretion is almost negligible. 2. Di[1-(14)C]ethyltin dichloride has been synthesized. When given intraperitoneally it is excreted in the urine and faeces in the ratio about 1:2. Both the urine and faeces contain ethyltin(3+) and diethyltin(2+). Diethyltin is also excreted extensively in the bile. Di[(14)C]ethyltin is not converted into (14)CO(2) in the rat. 3. About 50% of the injected diethyltin dichloride is de-ethylated to ethyltin(3+). Since ethyltin and diethyltin are found in the urine and faeces after intraperitoneal injection of diethyltin dichloride and since only diethyltin is excreted in the bile, then the de-ethylation of diethyltin occurs in the body tissues and the gut. 4. The conversion of diethyltin into ethyltin has been demonstrated in a preparation of rat caecal contents, but not in liver homogenates. 5. The dealkylation of diethyltin(2+) to ethyltin(3+) in the rat is discussed and it is suggested that the ethyl group is lost as ethane.

Prediction of biliary excretion in rats and humans using molecular weight and quantitative structure-pharmacokinetic relationships

The aims were (1) to evaluate the molecular weight (MW) dependence of biliary excretion and (2) to develop quantitative structure-pharmacokinetic relationships (QSPKR) to predict biliary clearance (CL(b)) and percentage of administered dose excreted in bile as parent drug (PD(b)) in rats and humans. CL(b) and PD(b) data were collected from the literature for rats and humans. Receiver operating characteristic curve analysis was utilized to determine whether a MW threshold exists for PD(b). Stepwise multiple linear regression (MLR) was used to derive QSPKR models. The predictive performance of the models was evaluated by internal validation using the leave-one-out method and external test groups. A MW threshold of 400 Da was determined for PD(b) for anions in rats, while 475 Da was the cutoff for anions in humans. MW thresholds were not present for cations or cations/neutral compounds in either rats or humans. The QSPKR model for human CL(b) showed a significant correlation (R (2) = 0.819) with good prediction performance (Q (2) = 0.722). The model was further assessed using a test group, yielding a geometric mean fold-error of 2.68. QSPKR models with significant correlation and good predictability were also developed for CL(b) in rats and PD(b) data for anions or cation/neutral compounds in rats and humans. Both CL(b) and PD(b) data were further evaluated for subsets of MRP2 or P-glycoprotein substrates, and significant relationships were derived. QSPKR models were successfully developed for biliary excretion of non-congeneric compounds in rats and humans, providing a quantitative prediction of biliary clearance of compounds.

Disposition in rats of the carbohydrate polymer in Ferastral--an iron-poly (sorbitol-gluconic acid) complex

The disposition and pharmacokinetics in rats of 14C-sorbitol-Ferastral has been studied as an initial step towards elucidating the metabolic fate of the polymeric organic moiety. The period of time studied was 24 h. Following i.v. administration of a dose corresponding to 10 mg/kg of iron approximately 60% of the isotope was found in the urine after this period of time. A further 3% was demonstrated in the faeces whilst the expired air accounted for about 10% in the form of 14CO2. Thus, a relatively large proportion of the radiolabel was promptly excreted via the kidneys whilst the expired air and probably bile constituted secondary excretion routes. The physico-chemical nature of the urinary product was similar to the parent carbohydrate compound. The residual 14C radioactivity was distributed mainly between the liver, which contained approximately 45% of the retained label, carcass with 36% and large intestine with 7%. The plasma disappearance pattern was biphasic. Similar experiments with the 14C-sorbitol polymer starting material were performed for purposes of comparison.

Phenolphthalein induces thymic lymphomas accompanied by loss of the p53 wild type allele in heterozygous p53-deficient (+/-) mice

Epidemiology studies have indicated that many human cancers are influenced by environmental factors. Genetically altered mouse model systems offer us the opportunity to study the interaction of chemicals with genetic predisposition to cancer. Using the heterozygous p53-deficient (+/-) mouse, an animal model carrying one wild type p53 gene and one p53 null allele, we studied the effects of phenolphthalein on tumor induction and p53 gene alterations. Earlier studies showed that phenolphthalein caused carcinogenic effects in Fisher 344 rats and B6C3F1 mice after a 2-yr dosing period (Dunnick and Hailey, Cancer Res. 56: 4922-4926, 1996). The p53 (+/-) mice received phenolphthalein in the feed at concentrations of 200, 375, 750, 3,000, or 12,000 ppm (approximately 43, 84, 174, 689, or 2,375 mg/kg body weight/day or 129, 252, 522, 2,867, or 7,128 mg/m2 body surface area/day) for up to 6 mo. A target organ cancer site that accumulated p53 protein in the B6C3F1 mouse (i.e., thymic lymphoma) was also a target site for cancer in the p53 (+/-) mouse. In the p53 (+/-) mouse, treatment-related atypical hyperplasia and malignant lymphoma of thymic origin were seen in the control and dosed groups at a combined incidence of 0, 5, 5, 25, 100, and 95%, respectively. Twenty-one of the thymic lymphomas were examined for p53 gene changes, and all showed loss of the p53 wild type allele. Chemical-induced ovarian tumors in the B6C3F1 mouse showed no evidence for p53 protein accumulation and did not occur in the p53 (+/-) mouse. The p53-deficient (+/-) mouse model responded to phenolphthalein treatment with a carcinogenic response in the thymus after only 4 mo of dosing. This carcinogenic response took 2 yr to develop in the conventional B6C3F1 mouse bioassay. The p53-deficient (+/-) mouse is an important model for identifying a carcinogenic response after short-term (< 6 mo) exposures. Our studies show that exposure to phenolphthalein combined with a genetic predisposition to cancer can potentiate the carcinogenic process and cause p53 gene alterations, a gene alteration found in many human cancers.

Effect of various antidotes on biliary excretion of arsenic in isolated perfused livers of guinea pigs after acute experimental poisoning with As2O3

The effect of the dithiols British Anti-Kewisite (BAL), dimercaptopropanesulfonic acid (DMPS), dimercaptosuccinic acid (DMSA) and a new metal binding agent 2,3-bis-(acetylthio)- propanesulfonamide (BAPSA) on the biliary excretion of arsenic in perfused livers of guinea pigs after acute experimental poisoning with As2O3 was investigated. Guinea pigs received As2O3, 10.0 mg/kg subcutaneously at 9 a.m. as a single injection. One hour after the injection the livers were perfused (2.5 ml x min.-1 x g-1 liver) with Krebs-Henseleit buffer and glucose for 80 min. After 40 min. of saline perfusion (control) 0.1 or 0.7 mmol/l BAL, DMSA, DMPS, or BAPSA were added to the perfusate and arsenic elimination in the bile and effluent perfusate was measured. The biliary excretion of arsenic in control livers between 40 and 80 min. was 0.7% of the total arsenic liver content before perfusion (= arsenic liver content after perfusion + portion excreted in the bile+perfusate). After antidote addition (0.1 mmol/l) the excretion was 0.2% for livers perfused with BAL, 6.8% for DMSA, 10.6% for DMPS, and 11.1% for BAPSA, respectively. After 0.7 mmol/l antidote the excretion of arsenic was 0.1% in livers perfused with BAL, 9.6% for DMSA, 12.3% for DMPS, and 13.3% for BAPSA, respectively. Except BAL, all compounds and most effectively BAPSA increased biliary excretion of arsenic. This indicates that excretion of arsenic which normally is mainly renal is shifted towards faecal excretion by the dithiols.

An evaluation of the low-pH enzymatic assay of urinary D-glucaric acid, and its use as a marker of enzyme induction in exocrine pancreatic disease

We have evaluated a low-pH enzymatic method for measuring urinary D-glucaric acid, and its usefulness as a marker of 'enzyme induction' in patients with exocrine pancreatic disease. The coefficient of variation lay between 7.5 and 10.9% for within-batch precision, and between 7.9 and 19.8% for between-batch precision. The useful range of the method was 20-200 mumol/l, with a lower detection limit of 11 mumol/l. The molar concentration ratio of D-glucaric acid to creatinine in urine correlated with the 8-h output of D-glucaric acid (p less than 0.005): both indices were significantly higher in a group of 29 patients with exocrine pancreatic disease than in controls (median ratios 4.6 and 2.9 X 10(-3), p less than 0.005; median outputs 14.0 and 8.8 mumol/8 h, respectively, p less than 0.005). Comparison with the results of theophylline tests in the same group of patients showed that whereas 72% of patients had theophylline clearances higher than the highest value in controls, 45% of the group had increased D-glucaric acid/creatinine ratios, whilst only 21% had increased outputs of D-glucaric acid. Paradoxically, in patients with established liver disease in whom drug metabolism was impaired urinary D-glucaric acid values were amongst the highest encountered in the study. Thus, the obvious advantages of the method--non-invasive, simple, reproducible, inexpensive, easily applied to out-patients--are offset by an unacceptably low predictive value as an indicator of microsomal 'enzyme induction'.

Enterohepatic circulation of vitamin D: a reappraisal of the hypothesis

Vitamin-D metabolites in bile were investigated after oral and intravenous doses of radioactively labelled vitamin D had been given to six patients with T-tube biliary drainage after cholecystectomy. The vitamin was mainly excreted as highly polar inactivation products and less than 4% of the metabolites in bile were present as 25-hydroxyvitamin D or its glucuronide conjugate. There was insufficient vitamin D or 25-hydroxyvitamin D in bile for the reabsorption of these metabolites to make a significant contribution to normal vitamin-D status. Therefore interference with an enterohepatic circulation of vitamin-D metabolites cannot be a cause of vitamin-D deficiency.

Metabolic oxidation of the ethynyl group in 4-ethynylbiphenyl

1. 4-Ethynylbiphenyl undergoes extensive metabolism in the rat and the rabbit, involving aromatic hydroxylation and oxidation of the ethynyl group. No metabolites containing the intact ethynyl group were detected. 2. In the rat unchanged 4-ethynylbiphenyl was concentrated initially in the adipose tissue. No other tissues accumulated significant amounts of radioactivity. 3. The major metabolites were the same in both the rat and the rabbit, namely 4'-hydroxybiphenyl-4-ylacetic acid (90-95% of dose) and biphenyl-4-ylacetic acid (2-10% of dose). 4. Excretion was slower in the rat than in the rabbit, probably because of greater biliary and faecal excretion in the rat. Biliary excretion and enterohepatic circulation of biphenyl-4-ylacetic acid and 4'-hydroxybiphenyl-4-ylacetic acid were demonstrated in the rat.

The absorption and elimination of ICI 74,917 in man

1 The pharmacokinetics of ICI 74,917 were studied in both asthmatic patients and normal volunteers. 2 The tritiated compound was administered to the lungs by inhalation from an aerosol and a bronchoscope, and by intravenous, oral and buccal routes. Radioactivity was measured in plasma, urine, faeces, sputum and exhaled air. 3 After bronchoscopic administration 63% of the available dose was absorbed; after aerosol administration 8% was absorbed from the lung and more than 50% swallowed. 5 Intravenous studies indicated that the drug is excreted in the bile and urine in the ratio 2:1. 5 Minimal oral and no buccal absorption occurred. 6 There was no evidence of tritium exchange or drug metabolism. 7 The mean terminal half-life following administration by all route was 16.1 hours. However, the majority of the dose was rapidly excreted. 8 Aerosol administration is the method of choice for the clinical use of ICI 74,917.

Excretion of pyrrolic metabolites in the bile of rats given the pyrrolizidine alkaloid retrorsine or the bis-N-ethylcarbamate of synthanecine A

(1) A comparison has been made in male rats between the biliary excretion of pyrrolic metabolites from the pyrrolizidine alkaloid retrorsine and a synthetic analogue 1-methyl-2,3-pyrroline-bis-N-ethyl-carbamate (Synthanecine A bis-N-ethylcarbamate). (2) When bile duct-cannulated rats were given retrorsine (40 mg/kg) and the bile collected at 1 h intervals, the relative concentration of pyrrolic metabolites was greatest in the first 1 h sample and was negligibly small by 7 h after dosing. By 7 h, about 25% of the dose had been excreted as pyrrolic metabolites. (3) In rats given [3H]synthanecine A bis-N-ethylcarbamate (40 mg/kg), the amounts of radioactivity and the relative levels of pyrrolic metabolites in the bile were greatest in the first 0.5 h sample and became negligibly small by 4 h after dosing. Within this time, about 25% of the dose had been excreted as [3H]radioactivity in the bile only about 5% as pyrrolic metabolites. (4) When rats were given [3H]2,3-bishydroxymethyl-1-methyl pyrrole (10 mg/kg), a proposed pyrrolic metabolite of synthanecine A bis-N-ethylcarbamate, about 17% of the dose was excreted for as [3H]radioactivity in the bile but only about 3% could be accounted for as pyrrolic metabolites. (5) Thin-layer chromatography of bile from rats given [3H]2,3-bishydroxy-methyl-1-methylpyrrole or [3H]synthanecine A bis-N-ethylcarbamate showed little redioactivity or Ehrlich-positive pyrrolic metabolites with an RF value corresponding to that of 2,3-bishydroxymethyl-1-methylpyrrole. A large proportion of the radioactivity label and most of the Ehrlich positive pyrrolic metabolites were associated with highly polar derivatives at the origin of the TLC plate. (6) It was concluded that biliary excretion plays an important role in the disposal of metabolites from both retrorsine and synthanecine A bis-N-ethyl-carbamate though not for the parent compounds. The expected hydroxy-methyl pyrrolic metabolites undergo further modification to more polar derivatives. In the case of retrorsine, these retained their abilities to react with Ehrlich reagent, while with pyrrolic metabolites from synthanecine A bis-N-ethylcarbamate, substatial conversion to Ehrlich negative derivatives occurred. (7) When bile of rats given [3H]synthanecine A bis-N-ethylcarbamate was injected intraduodenally into recipient animals, reabsorbtion of the radioactive label accounted for less than 4% of the dose given to the donor animals, indicating the enterohepatic circulation is probably only of minor importance influencing the elimination of these compounds.

Streptozotocin: its excretion and metabolism in the rat

The excretion of radioisotope following the administration of three specifically 14C-labelled forms of streptozotocin was investigated in the rat using ureter and bile duct cannulation techniques. The urine collected during the first hour following the administration of the drug contained the highest proportion of injected radioactivity (approximately 34% with (3'-methyl-14C)-streptozotocin and approximately 40% each with (1-14C)-and (2'-14C)-streptozotocin. Over the entire experimental period (6 hours), approximately 70% of the injected radioactivity of (1-14C)- and (2'-14C)-streptozotocin appeared in the urine. With (3'-methyl-14C)-streptozotocin, only 53% of the injected radioactivity appeared in the urine over the same period. In contrast to the high urinary excretion, less than 3% of the injected radioactivity from all three radiolabelled streptozotocin samples appeared in the bile. The in vivo and in vitro metabolism of streptozotocin was also investigated. In addition to substantial amounts of unchanged drug, three radiolabelled metabolites (two major and one minor) were detected in the urine during the 6 hour collection period following the administration of (1-14C)- and (2'-14C)-streptozotocin. In contrast, only unchanged (3'-methyl-14C)-streptozotocin was detected in the urine collected over the same period following the administration of the methyl labelled drug. The two major metabolites were also produced when (1-14C)-and (2'-14C)-streptozotocin were incubated with a rat liver supernatant fraction (100,000 X g). The liver was further demonstrated to be the major site of metabolism in isolated liver perfusion studies in which both (1-14C)- and (2'-14C)-streptozotocin were quantitatively converted to the two major metabolites. The two major metabolites of (1-14C)-streptozotocin, whether produced in vivo or in vitro, were chromatographically homogenous with the two major metabolites formed from (2'-14C)-streptozotocin. Nicotinamide pretreatment had no apparent effect on the urinary excretion of streptozotocin and its metabolites.

The properties of uridine diphosphate glucuronyltransferase(s) which catalyse the synthesis of steroid glucuronides in microsomal fractions from guinea-pig liver

The properties of the UDP-glucuronyltransferase(s) of guinea-pig liver that catalyse the synthesis of steroid glucuronides were examined. There are many similarities between apparently different substrate-specific forms of these enzymes in that all are activated by bivalent metal ions, and all contain at least 2 thiol groups important for enzyme activity. On the other hand, there are significant differences between the enzymes conjugating steroids and those conjugating non-steroids. Only the latter are activated by UDP-N-acetylglucosamine, which enhances their relatively poor affinity for UDP-glucuronic acid. The steroid-conjugating forms of UDP-glucuronyltransferase are not activated by UDP-N-acetylglucosamine and have relatively high apparent affinities for UDP-glucuronic acid. The rate of glucuronidation of testosterone was inhibited by treatment with phospholipase A. Treatment with cholate or Triton X-100 did not enhance the rates of glucuronidation of any steroid tested. The data indicate several similarities between different forms of UDP-glucuronyltransferase, suggesting that there is a large family of related proteins. At the same time there are important differences in the parameters that modulate the rates of different glucuronidation reactions.

The distribution and kinetics of sulphacetamide in leukaemic mice

1 During the first 90 min following oral administration of sulphacetamide, there was a rapid decline in plasma drug concentration in control mice whereas a progressive increase in sulphacetamide concentration was observed in leukaemic mice. 2 Similar changes in the kinetics of sulphacetamide distribution were observed in the liver, spleen and muscle. 3 While the concentration of sulphacetamide remained quite constant in the brain and fat tissue of control mice, a progressive increase in drug concentration was observed in the brain and fat tissue of leukaemic mice. 4 Some of these changes in the kinetics of sulphacetamide tissue distribution are compatible with delay in gastrointestinal absorption of the drug and its accumulation in the ascitic fluid.

Bile and urine as complementary pathways for the excretion of foreign organic compounds

1. The urinary and biliary excretion in the rat of 30 aromatic compounds with mol. wt. of 100-850, and largely excreted unchanged, has been studied. 2. These compounds fall into three groups as regards their pattern of elimination, which is related to mol. wt: group 1, with mol. wt. less than 350 and the major route of elimination the urine. When urinary excretion is prevented by ligating the renal pedicles the biliary excretion remains low. group 2, with mol, wt. of 450-850 which are excreted predominantly in bile. Even when the bile duct is obstructed, only small amounts of these compounds are found in urine. group 3, with mol. wt. of 350-450, which are eliminated extensively in both urine and bile. When one of these routes is blocked excretion by the other increases. 3. These studies emphasize the interrelationship of urine and bile as excretory routes for organic compounds. Urine and bile are complementary pathways; the extent of urinary excretion is greatest for the compounds of lowest mol. wt. and tends to decrease as mol. wt. increases and biliary excretion becomes more extensive.

Biliary excretion of xenobiotics

The biliary route is very important for the elimination of some foreign compounds from the body. For many of these compounds, an increase in the rate at which they are excreted into the bile will decrease their toxicity and vice versa. A number of factors which are known to alter the biliary excretion of xenobiotics, as well as the current concepts of the physiological mechanisms responsible for the excretion of foreign compounds, have been enumerated. However, much remains still to be understood; essentially nothing is known at the subcellular level about the biliary excretion of foreign compounds. It has recently been concluded that our knowledge of the biliary excretion of compounds is about 40 years behind that of the renal excretion mechanism.

Molecular weight as a factor in the excretion of monoquaternary ammonium cations in the bile of the rat, rabbit and guinea pig

1. The excretion in the bile and urine of intraperitoneally injected (14)C-labelled monoquaternary ammonium or pyridinium cations was measured in bile-duct-cannulated rats (ten compounds) and in guinea pigs and rabbits (six compounds). 2. Seven of these, namely N-methylpyridinium, tetraethylammonium, trimethylphenylammonium, diethylmethylphenylammonium, methylphenyldipropylammonium, dibenzyldimethylammonium and tribenzylmethylammonium, were excreted largely unchanged in the bile and urine. 3. 3-Hydroxyphenyltrimethylammonium, 3-bromo-N-methylpyridinium and cetyltrimethylammonium were metabolized to an appreciable extent in the rat. 4. In intact rats intraperitoneally injected trimethylphenylammonium (mol.wt. 136) was excreted mainly in the urine, dibenzyldimethylammonium (mol.wt. 226) was excreted in roughly equal amounts in the urine and faeces, and tribenzylmethylammonium (mol.wt. 302) was excreted mainly in the faeces. The faecal excretion of these compounds corresponded to their biliary excretion in bile-duct-cannulated rats. About 3-4% of tribenzyl[(14)C]methylammonium was eliminated as (14)CO(2). 5. In rats the extent of biliary excretion of four cations with molecular weights in the range 94-164 was less than 10% of the dose, whereas that of five cations with molecular weights 173-302 was greater than 10%. These results and other data from the literature suggested that the molecular weight needed for the biliary excretion of such cations to an extent of 10% or more of the dose was about 200+/-50. Studies with six cations in guinea pigs and rabbits suggest that this value applies also to these species. 6. The results suggest that the threshold molecular weight for the appreciable (>10%) biliary excretion of monoquaternary cations is different from that for anions (Millburn et al., 1967a; Hirom et al., 1972b). With rats, guinea pigs and rabbits, no significant species difference was noted, whereas with anions there is a marked species difference.

Effect of 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525-A) on sulphacetamide distribution and excretion in rats

1. Administration of 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525-A), 40 mg/kg, i.p., simultaneously or 40 min before sulphacetamide sodium, 100 mg/kg, i.p., was associated with a three-fold increase in sulphacetamide plasma concentration of rats. This effect was no longer evident after 30 minutes.2. The augmentation in sulphacetamide plasma concentration was associated with parallel increases in the muscle, kidney and brain tissue. The stomach was the only organ that contained less sulphacetamide.3. When sulphacetamide was administered i.v., a similar phenomenon was observed but the differences were less marked.4. Pretreatment with SKF 525-A was associated with decreased excretion of sulphacetamide by the kidney.5. It is concluded that SKF 525-A may alter the distribution and excretion of drugs as well as inhibiting drug metabolizing enzymes.

Species variations in the threshold molecular-weight factor for the biliary excretion of organic anions

1. The excretion in the bile and urine after intravenous injection of 16 organic anions having molecular weights between 355 and 752 was studied in female rats, guinea pigs and rabbits. 2. These compounds were mostly excreted unchanged, except for three of them, which were metabolized to a slight extent (<7% of dose). 3. The rat excreted all the compounds extensively (22-90% of dose) in the bile. 4. In guinea pigs four of the compounds with mol.wt. 355-403 were excreted in the bile to the extent of 7-16% of the dose, four with mol.wt. 407-465 to the extent of 25-44% and eight compounds with mol.wt. 479-752 to the extent of 44-100%. 5. In rabbits four compounds with mol.wt. 355-465 were excreted in the bile to the extent of 1-8% of the dose, two compounds with mol.wt. 479 and 495 to the extent of 24 and 22%, and six compounds with mol.wt. 505-752 to the extent of 31-94%. 6. These results, together with those of other investigations from this laboratory, are discussed and the conclusion is reached that there is a threshold molecular weight for appreciable biliary excretion (i.e. more than 10% of dose) of anions, which varies with species: about 325+/-50 for the rat, 400+/-50 for the guinea pig and 475+/-50 for the rabbit. 7. Anions with molecular weights greater than about 500 are extensively excreted in the bile of all three species. 8. That proportion of the dose of these compounds which is not excreted in the bile is excreted in the urine, and in the three species, bile and urine are complementary excretory pathways, urinary excretion being greatest for the compounds of lowest molecular weight and tending to decrease with increasing molecular weight. 9. Some implications of this interspecies variation in the molecular-weight requirement for extensive biliary excretion are discussed.

The fate of ( 14 C)disodium cromoglycate in man

The fate of [14C]disodium cromoglycate (DSCG) has been examined in 12 asthmatic patients. Maximum plasma concentrations (mean 9.2 ng/ml) were obtained within 15 min of inhaling DSCG (20 mg) and the average plasma half-life was 81 min. Although absorption from the lung is rapid, most of the inhaled dose is swallowed. Only 2.0% of the dose was excreted in the urine, and 84% was recovered from the faeces. DSCG is poorly absorbed from the gastrointestinal tract, only 0.4 % of an oral dose (20 mg) appeared in the 24 h urine and 83 % was recovered from the faeces. Intravenous administration of DSCG resulted in approximately equal amounts (30–50% of dose) being excreted via the urine and faeces. No metabolites of DSCG were detected chromatographically.

Steroid metabolism in the cat. Biliary and urinary excretion of metabolites of [4-14C]cortisone

1. [4-(14)C]Cortisone was administered to anaesthetized male cats as a single injection or as a 45-60min. infusion. 2. After the single dose a total of 69.6-89.6% of the radioactivity was excreted in bile, and 0.5-7.1% in urine. After infusion total recovery in bile was 73.4-92.1%, and 1.2-1.7% in urine. 3. When bile and urine samples were hydrolysed successively by beta-glucuronidase, cold acid and hot acid, most of the radioactivity was converted into substances not extractable from neutral aqueous solution by ethyl acetate-ether. 4. In bile, metabolites hydrolysable by beta-glucuronidase were found in only small proportions (3-4%) of the dose.