Total 14C Radioactivity Research Articles

Uptake, translocation, and metabolism of sulfamethazine by Arabidopsis thaliana: distinguishing between phytometabolites and abiotic transformation products in the media

Plant accumulation of antibiotic residues presents potential risks to human and ecosystem health. However, the phytometabolic pathways of antibiotics following plant uptake are still largely uncharacterized. This study investigated the phytometabolism of sulfamethazine (SMT) by Arabidopsis thaliana, using 14C-labeled and unlabeled SMT. SMT was accumulated in both roots and shoots of axenic A. thaliana plants (123.7 ± 12.3 and 22.7 ± 1.0 µg/kg fw, respectively) after 21 days of exposure. However, the parent 14C-SMT accounted for only 1.7 ± 0.01% of the total 14C-radioactivity in plant tissues. The majority of 14C-radioactivity taken up by plants was present as bound residues (42.0–68.2% of initially applied 14C-SMT), while extractable 14C-residues accounted for only 7.7–12.6%. A. thaliana metabolized SMT primarily through glycosylation at the N4-nitrogen atom. Additionally, other products, including pterin-SMT, methylsalicylate-SMT, N4-formyl-SMT, desulfo-SMT, hydroxyl-SMT, N4-acetyl-SMT, desamino-SMT, and 2-amino-4,6-dimethylpyrimidine, were also identified. Notably, a portion of the extractable metabolites was excreted into the culture media, requiring characterization of these metabolites as either excreted phytometabolites or abiotic transformation products of SMT based on comparisons between experimental and control reactors.

Determination of the absolute oral bioavailability of niraparib by simultaneous administration of a 14C-microtracer and therapeutic dose in cancer patients

IntroductionNiraparib (Zejula™) is a poly(ADP-ribose) polymerase inhibitor recently approved by the US Food and Drug Administration for the maintenance treatment of patients with recurrent platinum-sensitive epithelial ovarian, fallopian tube, or primary peritoneal cancer who are in a complete or partial response to platinum-based chemotherapy. The pivotal phase III clinical trial has shown improved progression-free survival in patients receiving niraparib compared with those receiving placebo.PurposeSince niraparib is administered orally, it is of interest to investigate the oral bioavailability (Fpo) of this novel compound, which is the aim of this study.MethodsSix patients received an oral therapeutic dose of 300 mg niraparib, followed by a 15-min intravenous infusion of 100 µg 14C-niraparib with a radioactivity of approximately 100 nCi. The niraparib therapeutic dose was measured in plasma using a validated liquid chromatography–tandem mass spectrometry method, whereas the total 14C-radioactivity and 14C-niraparib plasma levels were measured by accelerator mass spectrometry and a validated high performance liquid chromatography assay with AMS.ResultsThe Fpo of niraparib was determined to be 72.7% in humans.

Long-term fate of the herbicide mefenacet in a rice-grown lysimeter over a period of 6 consecutive years

To show the long-term fate of the herbicide mefenacet in rice paddies, [aniline-14C]mefenacet was applied to a lysimeter of loamy soil with a depth of 1 m, and rice plants were cultivated for 6 consecutive years according to the conventional methods in Korea. Mineralization of [14C]mefenacet to 14CO2 and volatilization from the soil surface were 12.01 and 0.02 %, respectively, of the originally applied amount during the first 23 weeks following application. Throughout the 6-year period, the total proportion of 14C-radioactivity that leached through the lysimeter soil was 0.778 % of the original radioactivity. The total 14C-radioactivity absorbed and translocated by rice plants throughout the 6 years was 2.46 % of the applied 14C. Measurement of the 14C-radioactivity distributed in each part of the rice plant (the straw, the ears without rice grain, the chaff, and the brown rice grain) indicated that the amount of 14C in straw was 25.87 times higher than that in brown rice grain over the 6 years. The 14C-radioactivity remaining in the soil layer after 6 years was 44.58 % of that applied, 91.45 % of which was distributed in the upper 0–20-cm layer. These results strongly indicate that mefenacet moved downward very slowly and more than half of the herbicide applied was released into the air, mainly through mineralization to CO2 in soil during the experimental period.

Fate and bioavailability of 14C-pyrene and 14C-lindane in sterile natural and artificial soils and the influence of aging

Soil organic matter is used to extrapolate the toxicity and bioavailability of organic pollutants between different soils. However, it has been shown that other factors such as microbial activity are crucial. The aim of this study was to investigate if sterilization can reduce differences in the fate and bioavailability of organic pollutants between different soils. Three natural soils with increasing total organic carbon (TOC) content were collected and three artificial soils were prepared to obtain similar TOCs. Soils were sterilized and spiked with 14C-pyrene and 14C-lindane. Total 14C radioactivity, HPCD extractability, and bioaccumulation in Eisenia fetida were measured over 56 days. When compared to non-sterile soils, differences between the natural and artificial soils and the influence of soil-contaminant contact time were generally reduced in the sterile soils (especially with middle TOC). The results indicate the possibility of using sterile soils as “the worst case scenario” in soil ecotoxicity studies.

Abstract 747: Absorption, distribution, metabolism, and excretion of 14C-Labeled tivantinib (ARQ 197) in healthy male subjects

Abstract Background: Tivantinib (ARQ 197), a selective, oral, non-ATP-competitive, small-molecule inhibitor of c-MET receptor tyrosine kinase, is being evaluated in combination with other agents in non-small cell lung cancer, colorectal cancer, and hepatocellular carcinoma (HCC), and as a single-agent in HCC. This study assessed the absorption, distribution, metabolism, and excretion of tivantinib in healthy subjects. Methods: A phase 1, open-label study was conducted in healthy, male, nonsmoking subjects (age, 18 to 45 years; body mass index, 19 to 29 kg/m2). A single 360-mg oral dose of 14C-tivantinib (∼250 αCi) was administered ∼5 min after consumption of a standard high-fat meal. Blood, feces, and urine samples were collected for tivantinib and radioactivity analysis for a maximum of 16 days postdose. Study endpoints included pharmacokinetic parameters associated with total radioactivity in blood and plasma and tivantinib in plasma, mass balance (rate and extent of excretion) of total 14C radioactivity in urine and feces, and adverse events (AEs). Plasma, urine, and fecal samples were also analyzed for metabolite identification. Results: Six subjects (all CYP2C19 extensive metabolizers) participated in this study. Median time to maximal concentration (tmax) for tivantinib in plasma and total radioactivity in plasma and whole blood were 4, 6, and 6 hours, respectively. Mean terminal half-life (t1/2) for tivantinib in plasma and total radioactivity in plasma and whole blood were 11.7, 20.7, and 13.6 hours, respectively. Based on area under the curve (AUC), tivantinib constituted ∼12% of total radioactivity in plasma, indicating the existence of substantial amounts of circulating tivantinib metabolite(s). Eight tivantinib metabolites were identified in plasma, and 4 were considered major metabolites based on their relative plasma exposure. The mean whole blood to plasma AUCinf ratio (AUCb:AUCp) was 0.609, indicating that most of the total radioactivity resided in plasma and was not highly associated with red blood cells. Mean ± SD recovery of radioactivity in feces and urine was 87.2% (feces = 68.2% ± 3.80%; urine = 19.0% ± 2.42%). Parent tivantinib was not detected in urine and trace amounts were detected in feces. Urinary and fecal metabolites were oxidative and subsequently conjugated molecules. Three subjects (50%) experienced 12 treatment-emergent adverse events; were mild in severity and none resulted in treatment discontinuation. Conclusions: Tivantinib was rapidly absorbed and metabolized after oral administration, and 87% of total radioactivity was recovered in urine and feces. Parent tivantinib was not detected in urine and only trace amounts were detected in feces. The fact that all the urinary and fecal metabolites are oxidative and subsequent conjugated molecules suggests near complete absorption of tivantinib when administered under fed conditions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 747. doi:1538-7445.AM2012-747

Impulse-response studies on tracer doses of [14C]lignocaine and its multiple metabolites in the perfused rat liver.

The outflow-concentration-time profiles for lignocaine (lidocaine) and its metabolites have been measured after bolus impulse administration of [14C]lignocaine into the perfused rat liver. Livers from female Sprague-Dawley rats were perfused in a once-through fashion with red-blood-cell-free Krebs-Henseleit buffer containing 0 or 2% bovine serum albumin. Perfusate flow rates of 20 and 30 mL min-1 were used and both normal and retrograde flow directions were employed. Significant amounts of metabolite were detected in the effluent perfusate soon after lignocaine injection. The early appearance of metabolite contributed to bimodal outflow profiles observed for total 14C radioactivity. The lignocaine outflow profiles were well characterized by the two-compartment dispersion model, with efflux rate << influx rate. The profiles for lignocaine metabolites were also characterized in terms of a simplified two-compartment dispersion model. Lignocaine was found to be extensively metabolized under the experimental conditions with the hepatic availability ranging between 0.09 and 0.18. Generally lignocaine and metabolite availability showed no significant change with alterations in perfusate flow rate from 20 to 30 mL min-1 or protein content from 0 to 2%. A significant increase in lignocaine availability occurred when 1200 microM unlabelled lignocaine was added to the perfusate. Solute mean transit times generally decreased with increasing flow rate and with increasing perfusate protein content. The results confirm that lignocaine pharmacokinetics in the liver closely follow the predictions of the wellstirred model. The increase in lignocaine availability when 1200 microM unlabelled lignocaine was added to the perfusate is consistent with saturation of the hydroxylation metabolic pathways of lignocaine metabolism.

Chlorophenoxyacetic acid and chloropyridylphenylurea accelerate translocation of photoassimilates to parthenocarpic and seeded fruits of muskmelon ( Cucumis melo)

We compared the effect of p-chlorophenoxyacetic acid ( p-CPA) and 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) on parthenocarpic and seeded muskmelon ( Cucumis melo) fruits in regards to fruit development and the transport of photoassimilates from leaves exposed to 14CO 2 to the developing fruits. Ten days after anthesis (DAA), the fresh weight, total 14C-radioactivity and contents of 14C-sucrose and 14C-fructose were higher in the CPPU-induced parthenocarpic fruits than in seeded fruits. However, at 35 DAA, fresh weight and sucrose content in mesocarp, placenta and empty seeds of the parthenocarpic fruits were lower than in seeded fruits. Also, total 14C-radioactivity and 14C-sugar content of the parthenocarpic fruits were lower as well as the translocation rate of 14C-photoassimilates into these fruits. Application of p-CPA to the parthenocarpic fruits at 10 and 25 DAA increased fresh weight and sugar content. Moreover, these treatments elevated the total 14C-radioactivity, 14C-sucrose content and the translocation rate of 14C-photoassimilates. The 14C-radioactivity along the translocation pathway from leaf to petiole, stem, lateral shoot and peduncle showed a declining pattern but dramatically increased again in the fruits. These results suggest that the fruit's sink strength was regulated by the seed and enhanced by the application of p-CPA.

Glyceroneogenesis Is the Dominant Pathway for Triglyceride Glycerol Synthesis in Vivo in the Rat

Triglyceride synthesis in mammalian tissues requires glycerol 3-phosphate as the source of triglyceride glycerol. In this study the relative contribution of glyceroneogenesis and glycolysis to triglyceride glycerol synthesis was quantified in vivo in adipose tissue, skeletal muscle, and liver of the rat in response to a chow diet (controls), 48-h fast, and lipogenic (high sucrose) diet. The rate of glyceroneogenesis was quantified using the tritium ([(3)H(2)]O) labeling of body water, and the contribution of glucose, via glycolysis, was determined using a [U-(14)C]glucose tracer. In epididymal and mesenteric adipose tissue of control rats, glyceroneogenesis accounted for approximately 90% of triglyceride glycerol synthesis. Fasting for 48 h did not alter glyceroneogenesis in adipose tissue, whereas the contribution of glucose was negligible. In response to sucrose feeding, the synthesis of triglyceride glycerol via both glyceroneogenesis and glycolysis nearly doubled (versus controls); however, glyceroneogenesis remained quantitatively higher as compared with the contribution of glucose. Enhancement of triglyceride-fatty acid cycling by epinephrine infusion resulted in a higher rate of glyceroneogenesis in adipose tissue, as compared with controls, whereas the contribution of glucose via glycolysis was not measurable. Glyceroneogenesis provided the majority of triglyceride glycerol in the gastrocnemius and soleus. In the liver the fractional contribution of glyceroneogenesis remained constant (approximately 60%) under all conditions and was higher than that of glucose. Thus, glyceroneogenesis, in contrast to glucose, via glycolysis, is quantitatively the predominant source of triglyceride glycerol in adipose tissue, skeletal muscle, and liver of the rat during fasting and high sucrose feeding.

Green tea catechins inhibit pancreatic phospholipase A 2 and intestinal absorption of lipids in ovariectomized rats

This study was conducted to examine whether the inhibition of intestinal lipid absorption by green tea is associated with the inhibitory effect of its catechins on pancreatic phospholipase A 2 (PLA 2). PLA 2 activity was assayed by using 1,2-dioleoylphosphatidylcholine (DOPC), porcine pancreatic PLA 2 and catechins at varying concentrations (0.075–1.80 μmol/L). The amount of 1-oleoyl-2-hydroxyphosphatidylcholine liberated was determined by HPLC. The percentage of inhibition of PLA 2 by catechins at 0.6 μmol increased in the order of (−)-epicatechin (23.3%), (+)-catechin (CAT; 24.8%), (−)-epigallocatechin (25.7%), (−)-epicatechin gallate (39.7%) and (−)-epigallocatechin gallate (EGCG; 64.9%). In an in vivo study, ovariectomized rats with lymph cannula were infused intraduodenally for 8 h with a triolein emulsion containing [dioleoyl-1- 14C]-phosphatidylcholine, DOPC, α-tocopherol (αTOH) and retinol (ROH) without (CAT0) or with CAT or EGCG. The lymphatic total 14C-radioactivity was significantly lowered by EGCG (45.5±4.9% dose) compared with CAT (56.2±5.2% dose) and CAT0 (64.7±2.0% dose). The 14C-radioactivity remaining in the small intestinal lumen and cecum was higher in EGCG (24.1% dose) than in CAT (9.5% dose) and CAT0 rats (9.0% dose). Significantly less 14C radioactivity was incorporated into lymph triacylglycerol and cholesteryl ester in EGCG rats. The absorption of αTOH, used as a marker of extremely hydrophobic lipids, was significantly lower in EGCG (7.8±1.7 μmol) than in CAT (14.4±2.8 μmol) and CAT0 rats (16.8±2.1 μmol). The absorption of ROH was unaffected, whereas oleic acid output was lower in EGCG rats. The results show that EGCG inhibits the intestinal absorption of lipids, which is in part associated with its inhibition of phosphatidylcholine hydrolysis. Data suggest that EGCG may inhibit the absorption of other highly lipophilic organic compounds.

Effect of tamoxifen and raloxifene on cholesterol transformation to bile acids in ovariectomized rats

Tamoxifen is used as adjuvant therapy for prevention and treatment of metastatic breast cancer, whereas raloxoifene is approved for osteoporosis and is being investigated for breast cancer prevention. The most important aspects of these therapies are focused on their influence on bone and lipid metabolism. Several studies have reported the effect of tamoxifen and raloxifene on plasma lipids. Approximately 40% of total cholesterol removal occurs by conversion to bile acids, a process that takes place in the liver. The aim of the present study was to evaluate the influence of tamoxifen and raloxifene on the conversion of cholesterol to bile acids in estrogen-deficient in rats. The study included 40 female Wistar rats, divided into four groups: sham-operated controls, ovariectomized controls, ovariectomized rats treated with tamoxifen and ovariectomized rats treated with raloxifene. After 42 days of drug administration, bile was collected under anesthesia following administration of radioactive [4-14C]cholesterol and assayed for total 14C radioactivity; 14C-labeled bile acids were determined by the use of isotopic techniques after initial separation by thin-layer chromatography. Ovariectomy caused decreased excretion of bile and bile acids. Administration of tamoxifen and raloxifene significantly reduced the excretion of 14C-labeled bile and bile acids compared with ovariectomized controls. Tamoxifen therapy significantly reduced the excretion of taurocholic acid and glycochenodeoxycholic plus glycodeoxycholic acids, and excretion of cholic, litocholic and chenodeoxycholic plus deoxycholic acids was increased. Raloxifene significantly reduced the excretion of taurocholic, glycocholic and litocholic acids, taurochenodeoxycholic plus taurodeoxycholic acids, as well as chenodeoxycholic plus deoxycholic acids. The results of the present study suggest that tamoxifen and raloxifene did not reverse the changes in bile composition induced by estrogen deficiency. The decreased concentration of trihydroxy bile acids during therapy with raloxifene might decrease the risk of gallstone formation, although this hypothesis requires further investigation.

Long-term fate of the herbicide cinosulfuron in lysimeters planted with rice over four consecutive years.

In order to elucidate the long-term fate of the sulfonylurea herbicide cinosulfuron, the 14C-labelled chemical was applied to a clay loam soil, encased in two lysimeters, 22 days after rice (Oryza sativa L.) transplanting, and rice plants were grown for four consecutive years. Throughout the experimental period, leaching through soil profiles, absorption and translocation by rice plants, and distribution of 14C by downward movement in the soil layers were clarified. The total volume of leachates collected through the lysimeter soil over the four years amounted to 168 and 146 L in lysimeters I and II, respectively. The leachates contained 2.43% and 2.99% of the originally applied 14C-radioactivity, corresponding to an average concentration of 0.29 and 0.41 microg/L as the cinosulfuron equivalent in lysimeters I and II, respectively. The total 14C-radioactivity translocated to rice plants in the third and fourth year was 0.69% and 0.60% (lysimeter I), and 1.02% and 0.84% (lysimeter II) of the 14C applied, respectively. Larger amounts of cinosulfuron equivalents (0.54-0.75%) remained in the straw in the fourth year than in any other parts. The 14C-radioactivities distributed down to a depth of 70 cm after four years were 56.71-57.52% of the 14C applied, indicating the continuous downward movement and degradation of cinosulfuron in soil. The non-extractable residues were more than 88% of the soil radioactivity and some 45-48% of them was incorporated into the humin fraction. The 14C-radioactivity partitioned into the aqueous phase was nearly 30% of the extractable 14C, suggesting strongly that cinosulfuron was degraded into some polar products during the experimental period. It was found out in a supplemental investigation that flooding and constant higher temperature enhanced mineralization of [14C]cinosulfuron to 14CO2 in soil, indicating the possibility of chemical hydrolysis and microbial degradation of the compound in the flooded lysimeter soil.

Absorption, Metabolism, and Excretion of Intravenously and Orally Administered [14C]Telmisartan in Healthy Volunteers

The study was conducted in healthy male volunteers to evaluate the absorption, metabolic pattern, and mode of elimination of telmisartan, a nonpeptide angiotensin II receptor antagonist. [14C]telmisartan was administered orally in solution as a single 40 mg dose to 5 subjects. A further 5 subjects received short-term intravenous infusion of [14C]telmisartan 40 mg. Measurement of total 14C radioactivity in plasma showed that about 50% was absorbed following oral administration, with maximum plasma concentration observed after 0.5 to 1 hour. Absolute bioavailability was 43%. On average, 84% of total radioactivity in plasma reflected the parent compound. The remainder of total radioactivity could be ascribed to the glucuronide conjugate of telmisartan, which represented the only metabolite in man. About 99.5% of telmisartan was bound to plasma protein, mainly to albumin and alpha-1-acid glycoprotein. Telmisartan was reversibly distributed into erythrocytes. More than 90% of administered dose was excreted within 120 hours, and the excretion balance was complete 144 hours after dosing. Radioactivity was almost exclusively (> 98%) excreted via the feces; urinary excretion accounted for < 1% of the dose, irrespective of the route of administration. In the small fraction excreted into urine, the glucuronide conjugate of telmisartan was predominant. Although some telmisartan glucuronide was detected in plasma, only unchanged drug was identified in the feces. No changes in vital signs, electrocardiogram, or clinical laboratory tests were detected following telmisartan administration, and adverse events, predominantly unrelated to treatment and of mild intensity, were infrequent. One subject fainted and, on another occasion, reported faintness; these events were probably due to the antihypertensive action of the intravenous study medication.

Pharmacokinetics and pharmacodynamics of fluoroquinolones

'Division of Clinical Pharmacology, Department of Medicine, Albany Medical College, Albany, New York, USA; 21NSERM U479, Service d'Hematologie et d'Immunologie Biologiques, CHU Xavier BICHAT, Paris, France; 3Department of Infectious Diseases, Uppsala University Hospital, Uppsala, Sweden; 4Hoechst Marion Roussel Inc, Bridgewater, New Jersey, USA; 5Med Klinik 111, Frankfurt a m Main, Germany; 61nstitute for Biomedical & Pharmaceutical Research, Nurnberg Herodsberg, Germany; 7Hoechst Marion Roussel AG, Clinical Development, Frankfurt a m Main, Germany

Colorimetric versus radioimmunological measurement of glycated and non-glycated serum albumin after affinity chromatography

Affinity chromatography by m-aminophenylboronic acid has been proposed for routine measurement of glycated albumin. We assayed glycated and non-glycated fractions of serum albumin (HSA) eluted by affinity chromatography columns by both a specific RIA method for the human serum albumin (HSA) and by a colorimetric method. Sixteen diabetic patients presented a significantly higher percentage of glycated-HSA than 7 control subjects with both methods, and a strong correlation was found between the values obtained with the two methods. RIA was able to detect a significant concentration of glycated-HSA in all normal subjects, while the colorimetric method was not. The accuracy of separation between the glycated and non-glycated fractions of albumin was tested using [14C]glucose as tracer. When [14C]glycated-HSA purified by Sephadex G25 filtration was chromatographed using the m-aminophenylboronic acid, only 5.3% of the total 14C-radioactivity present in the solution was recovered in the bound fraction, while 44.0% was eluted in non-protein-bound fraction and 54.7% was retained in the column. Our findings confirm that affinity chromatography by m-aminophenylboronic acid can be a useful tool in the monitoring of short glycemic control of diabetic patients. Our data also indicate that the affinity chromatography with m-aminophenylboronic acid does not accurately discriminate between glycated and non-glycated fraction of HSA.

Rapid Clearance of Xanthines from Airway and Pulmonary Tissues

The airway and pulmonary fate of two antiasthma xanthines was examined in a guinea pig perfused lung preparation where the airway mechanics and airway microvascular perfusion are maintained at near normal values. 14C-theophylline or 14C-enprofylline was infused for 10, 30, and 300 s into the pulmonary artery of the guinea pig isolated lung. The radioactivity increased rapidly (within 10 s) in tracheobronchial as well as in lung tissue, confirming that the large airway microcirculation was well supplied also by the perfusion. The effluent concentrations of total 3H and 14C radioactivity at the onset, during, and after intrapulmonary infusion of 14C-labeled xanthines and 3H-sucrose were closely associated, suggesting that the xanthines, like sucrose, largely distributed in extracellular fluid and were not taken up by the tissues. No metabolites of enprofylline or theophylline could be detected in the lung tissue or lung effluent, suggesting that xanthines are not biotransformed by the guinea pig lung. After intratracheal instillation of 14C-theophylline, the peak radioactivity in the lung effluent appeared in the second 15-s fraction after instillation, and after 10 and 60 min, 68.1 +/- 4.7% and 86.9 +/- 8.4%, respectively, of the given dose had appeared in the lung effluent. The present data suggest a mainly extracellular distribution and a rapid clearance of xanthines from the lung and airway tissues. The rapid disappearance of topical theophylline may explain the lack of success of inhalation therapy with this drug.

266 GLUCONEOGENESIS BY THE FETAL SHEEP KIDNEY

We have consistently noted glucose release by the kidney of the unstressed fetal sheep, but it is not known whether this glucose is produced by gluconeogenesis or by glycogenolysis. To examine this question, we infused 14C-lactate intravenously into 5 healthy fetal sheep (mean gestational age 130 days) which had catheters chronically placed in the fetal descending aorta (FA), renal vein (RV), and inferior vena cava. We measured 14C-glucose and glucose concentrations in the RV and FA, total 14C-radioactivity and lactate concentration in the FA, and renal blood flow by the radioactive microsphere method. We calculated glucose flux across the kidney by the Fick method. Lactate specific activity was not measured; since total 14C-radioactivity may include 14C-metabolites of lactate, we could not calculate the actual quantity of glucose produced from lactate. We could, however, measure the minimum amount of glucose produced from lactate. We found net glucose release by the kidney (mean 3.0 mg/min/100 g kidney); at least 23% of this glucose was produced from lactate (0.7 mg/min/100g kidney).The unstressed fetal sheep kidney is therefore able to produce glucose by gluconeogenesis. This new glucose may be used by the kidney or may contribute to total fetal glucose supply. (Supported by HD 17618.)

Fate of 3,3′‐dichlorobenzidine in soil: Persistence and binding

AbstractThe fate of the carcinogen 3,3′‐dichlorobenzidine (DCB) in soil was evaluated with regard to persistence and binding. A Brookston clay loam soil was amended with 4 or 40 ppm 14C‐DCB and incubated under aerobic conditions for 32 weeks or under anaerobic conditions for 1 year. Mineralization occurred very slowly in aerobic soil and did not occur in anaerobic soil. Total 14C radioactivity in soil remained essentially constant during the incubations, demonstrating that volatile losses of DCB or DCB decomposition products did not occur in our incubation system. DCB was shown to bind strongly to soil. After 32 weeks of incubation, approximately 90% of the applied radioactivity remained in soil after extraction with ethyl acetate and methanol. The loss of solvent‐extractable DCB occurred mostly in the first several weeks of incubation and was accompanied by an increase in alkali‐extractable DCB. These data strongly suggest the formation of covalent linkages between DCB and soil humic components as the primary fate of DCB in the Brookston soil. The significance of humus‐bound DCB residues as potential sources of future contamination is essentially unknown.

FATE OF 3,3′-DICHLOROBENZIDINE IN SOIL: PERSISTENCE AND BINDING

The fate of the carcinogen 3,3′-dichlorobenzidine (DCB) in soil was evaluated with regard to persistence and binding. A Brookston clay loam soil was amended with 4 or 40 ppm 14C-DCB and incubated under aerobic conditions for 32 weeks or under anaerobic conditions for 1 year. Mineralization occurred very slowly in aerobic soil and did not occur in anaerobic soil. Total 14C radioactivity in soil remained essentially constant during the incubations, demonstrating that volatile losses of DCB or DCB decomposition products did not occur in our incubation system. DCB was shown to bind strongly to soil. After 32 weeks of incubation, approximately 90% of the applied radioactivity remained in soil after extraction with ethyl acetate and methanol. The loss of solvent-extractable DCB occurred mostly in the first several weeks of incubation and was accompanied by an increase in alkali-extractable DCB. These data strongly suggest the formation of covalent linkages between DCB and soil humic components as the primary fate of DCB in the Brookston soil. The significance of humus-bound DCB residues as potential sources of future contamination is essentially unknown.

Metabolism of 2-methoxyestrone in normal men.

We studied, in four normal men, the metabolism of 2-methoxyestrone (2-MeOE1) using pulse injections of either [3H]2MeOE1 (two men) or [14C]methoxy-2-MeOE1 plus [3H]2-MeOE1 (two men) by analysis of blood samples drawn at increasing time intervals after the pulse and of urine collected for 5 days. The disappearance from the blood of radioactivity as 2-MeOE1 could be characterized as a function that was the sum of three exponentials. The mean +/- SE value for the initial volume of distribution was 32 +/- 9 liters, and the mean MCR was 2470 +/- 770 liters/day. The disappearance of total 3H radioactivity from the blood was considerably slower, with a mean MCR of 290 +/- 30 liters/day, indicating the presence of a slowly turning over pool of 2-MeOE1 metabolites, probably including the 2-MeOE1 3-sulfate conjugate. The disappearance of total 14C radioactivity was slower than that of total 3H, indicating considerable demethylation of 2-MeOE1 with a very slow excretion of 14C from the released methyl group. In none of the subjects could we find in the blood radioactivity as unconjugated [3H]2-hydroxyestrone ( [3H]2-OHE1). However, examination of the urine indicated that considerable demethylation of [3H]2-MeOE1 had occurred. At least 64% of the urinary 3H-containing metabolites from the mixed dose had lost the 14C-bearing methoxylcarbon atom. The fractionated metabolites were qualitatively and quantitatively similar to those found earlier for [3H]2-OHE1. We conclude that 2-MeOE1, which of itself has little biological activity, can act as a pool of potentially active 2-OHE1 in the tissues.

The pharmacokinetics of tetroxopim in the dog

The pharmacokinetics and metabolism of the newly developed antibacterial tetroxoprim (TXP) were investigated in four male beagle dogs using a 2-(14C)-labelled drug. TXP was administered intravenously and orally at doses of 5 mg/kg bodyweight. Counting of the total 14C-radioactivity shows that the drug was absorbed completely and eliminated almost exclusively by the kidneys. The quantitative absorption of TXP from the canine gastro-intestinal tract was ascertained by comparison of the AUC-values and the renal recoveries of unchanged drug following i.v. and oral dosage. The terminal half-lives of non-metabolized compound in plasma were 4.64 and 4.83 for i.v. and oral dosing respectively. Following either i.v. or oral TXP administration, the major route of excretion was renal elimination of the compound as its major metabolite U-1 (81-82.2% of dose) and as unchanged mother substance (11.4-12.3% of dose).