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Biomedical subjects

D E Rickert

Publications and source records attributed to D E Rickert.

At least 73 records · Page 4Linked to original sources
PubMed1976

Studies on the biological disposition of diethylstilbestrol in rats and humans.

Studies were conducted to elucidate the processes involved in the biological disposition of diethylstilbestrol (DES). The apparent biological half-life of [14C] DES decreased with increasing age in immature rats. The half-life of DES in adult rats (14 min) was reached between the 15th and 25th day after birth. Comparison of the intestinal absorption of [14C] DES and [14C]DES monoglucuronide showed the unconjugated drug to be absorbed much more rapidly. Hydrolysis of the conjugate took place in the lower intestine, and this permitted the drug to undergo enterohepatic cycling.

Age Factors↗
PubMed1975

Cyproheptadine and beta cell function in the rat: insulin secretion from pancreas segments in vitro.

Pancreatic islet cell vacuolization, hyperglycemia, and glucose intolerance develop in rats after oral administration of cyproheptadine (CPH). In order to determine whether these effects were associated with abnormal insulin secretion, pancreas segments from CPH-treated and control rats were compared for their ability to secrete insulin in response to several stimuli. Oral administration of CPH (45 mg/kg/day) to rats for 1 or 8 days inhibited glucose-mediated insulin secretion from pancreas segments obtained 3 and 24 hr after the last dose of the drug. Insulin secretion had returned to normal by 48 hr after drug administration. Intraperitoneal administration of the drug was less effective than oral administration in inhibiting in vitro insulin secretion. Other stimuli for insulin secretion (tolbutamide, glucagon, L-leucine, and dibutyryl 3',5'cyclic AMP), like glucose, were incapable of releasing normal amounts of insulin from pancreas segments of CPH-treated rats. CPH and a metabolite, desmethyl-CPH, inhibited glucose-stimulated insulin secretion when added in vitro to pancreas segments from control rats. This suggests that the inhibition of insulin secretion in pancreas segments taken from animals treated with CPH could be due, at least in part, to the presence of drug and its metabolite in the tissue. A previously observed reduction in the pancreatic content of insulin in CPH-treated rats may also contribute to the abnormal insulin release in animals given the drug.

Administration, Oral↗
PubMed1975

Cyproheptadine-induced depletion of insulin in the rat.

The pancreotoxicity of cyproheptadine (CPH) in rats was characterized through measurement of proinsulin and insulin levels in the pancreas as well as plasma immunoreactive insulin (IRI) and glucose levels at various times during and after drug treatment. Daily oral doses of CPH (45 mg/kg) depleted pancreatic IRI to 25% of control within 3 days. Pancreatic IRI levels showed no further decrease during the rest of a 2-week treatment period and returned to normal levels 2 days after withdrawal of the drug. Pancreatic proinsulin levels were not significantly changed by CPH treatment, and the decrease in pancreatic IRI can be ascribed primarily to a decrease in insulin. Nonfasting hyperglycemia was evident after two doses of CPH and persisted throughout the treatment period. Plasma IRI was not significantly altered compared to control and was inappropriately low for the hyperglycemia that was produced by CPH. Daily doses of CPH given i.p. (45 mg/kg) caused a transient decrease in pancreatic IRI, but hyperglycemia did not occur. Lower i.p. doses (22.5 mg/kg/day) caused a sustained decrease in pancreatic IRI content to 45% of control after 2 weeks and hyperglycemia was evident throughout the treatment period. No changes in pasma IRI were observed as a result of drug treatment even though blood glucose was elevated. These results suggest that biochemical changes affecting insulin synthesis and/or storage are associated with previously reported CPH-induced morphologic alterations in the rat beta-cell.

Animals↗
PubMedDate not supplied

Induction of hepatic and testicular lesions in Fischer-344 rats by single oral doses of nitrobenzene.

Since the acute toxicity of nitrobenzene (NB) in rats has not been characterized, experiments were performed to ascertain the possible deleterious effects of NB in different tissues of the male Fischer-344 rat. Rats were given single oral doses of NB (50-450 mg/kg) and at the time of sacrifice, 25 tissues were removed and examined histologically by light microscopy. Histopathological changes induced by a single oral dose of NB consistently involved only the liver and testes. One rat receiving 450 mg NB/kg had a microscopic cerebellar lesion. Hepatic centrolobular necrosis appeared inconsistently in rats given various doses of NB, while hepatocellular nucleolar enlargement was consistently detected in rats given doses of NB as low as 110 mg/kg. These data suggest that nucleolar enlargement was independent of cell death and subsequent regeneration. Testicular lesions were confined to the seminiferous tubules and consisted of necrosis of the primary and secondary spermatocytes with the appearance of multinucleated giant cells between one and four days after administration of NB 300 mg/kg. Necrotic debris and decreased numbers of spermatozoa were seen in the epididymis as early as three days after NB administration. The NB-induced methemoglobinemia does not appear to be solely responsible for the formation of early lesions in the rat liver, testes, or brain, since sodium nitrite administration, at dosages which produced methemoglobinemia equivalent to that of NB, did not produce any histopathological changes. Thus, the observed liver and testicular damage are probably due to a direct effect of NB or its metabolites.

Administration, Oral↗
PubMedDate not supplied

In vitro activation of 2-aminobenzyl alcohol and 2-amino-6-nitrobenzyl alcohol, metabolites of 2-nitrotoluene and 2,6-dinitrotoluene.

Previous results have suggested that key intermediates in the activation of 2-nitrotoluene and 2,6-dinitrotoluene are 2-aminobenzyl alcohol and 2-amino-6-nitrobenzyl alcohol, respectively. In order to determine the metabolic pathway(s) involved in the activation steps, calf thymus DNA and [14C]-2-aminobenzyl alcohol or [14C]-2-amino-6-nitrobenzyl alcohol were incubated with male Fischer-344 rat hepatic cytosol and PAPS, microsomes and NADPH, or microsomes and cytosol with PAPS, NADPH, and acetyl coenzyme A. DNA was isolated and analyzed for radiolabel bound covalently. Analysis of the incubations containing [14C]-2-aminobenzyl alcohol revealed radiolabel bound covalently to DNA, as well as one major metabolite labile in both sulfatase and acid. The appearance of each required the presence of PAPS and cytosol and was inhibited by the sulfotransferase inhibitor 2,6-dichloro-4-nitrophenol. Neither NADPH nor acetyl coenzyme A played a role in the generation of detectable 14C bound to nucleic acids. 2-Amino-6-nitrobenzyl alcohol was converted to metabolites capable of binding to calf thymus DNA when incubated with cytosol and PAPS or with microsomes and NADPH. However, when cytosol and microsomes were incubated together, activation of 2-amino-6-nitrobenzyl alcohol appeared to require only PAPS, suggesting a minor role for NADPH-dependent enzymes in its activation. The results suggest that the metabolite of 2-nitrotoluene responsible for binding covalently to DNA is 2-aminobenzyl sulfate. There may be more than one pathway involved in the formation of metabolite(s) of 2,6-dinitrotoluene that bind covalently to DNA.

Acetyl Coenzyme A↗
PubMedDate not supplied

Hepatic macromolecular covalent binding and intestinal disposition of [14C]dinitrotoluenes.

The covalent binding to hepatic RNA, DNA, and protein of a highly genotoxic dinitrotoluene (DNT) isomer (2,6-DNT) was compared with that of a less genotoxic DNT isomer (2,4-DNT) after oral administration to male Fischer-344 rats. Covalent binding to each macromolecular species was proportional to dose (10 or 35 mg/kg) for each isomer, but that due to 2,6-DNT was always 2-5-fold higher than that due to 2,4-DNT. There was no selectivity of either isomer for any macromolecule. The time course of appearance and disappearance of covalently bound material was similar regardless of isomer or dose administered. Little covalently bound material was present until 8 h after the dose. Covalent binding peaked between 12 and 24 h and then slowly declined. The half-lives of covalently bound material were independent of the isomer administered, ranging from 2.9 to 5.0 d for RNA and protein and from 5.1 to 7.9 d for DNA. Both isomers disappeared from the small intestine rapidly, and covalent binding to hepatic macromolecules became significant only after the isomeric dinitrobenzyl alcohol glucuronides had appeared in the small intestine. The concentration of alcohol glucuronides in the intestine declined prior to peak covalent binding in the liver. The data suggest that covalent binding to hepatic macromolecules qualitatively reflects the differences in genotoxicities between the two isomers. The time course of intestinal disposition of the two isomers supports previous reports that suggest that activation of both isomers requires oxidation to the corresponding benzyl alcohol, glucuronidation, excretion in the bile, deconjugation, and further metabolism by intestinal microorganisms, followed by reabsorption.

Animals↗
PubMedDate not supplied

Metabolism of chloronitrobenzenes by isolated rat hepatocytes.

The metabolism of radiolabeled monochloronitrobenzene isomers was compared in isolated hepatocytes and hepatic subcellular fractions from male Fischer-344 rats. 2-Chloronitrobenezene was converted by isolated hepatocytes to 2-chloroaniline, 2-chloroaniline-N-glucuronide, and S-(2-nitrophenyl)glutathione in approximately equal quantities (13-19% of the added substrate in 90 min). The major metabolite formed from 3-chloronitrobenzene by isolated hepatocytes was 3-chloroaniline (31% of the added substrate in 90 min). Smaller amounts of 3-chloroaniline-N-glucuronide and 3-chloroacetanilide were formed (7 and 17% of the added 3-chloronitrobenzene, respectively, in 90 min). 4-Chloronitrobenzene was metabolized to 4-chloroacetanilide, 4-chloroaniline, and S-(4-nitrophenyl)glutathione in approximately equal amounts (10-15% of the added substrate in 90 min). Studies with hepatic microsomes showed that reduction of the chloronitrobenzenes to chloroanilines was inhibited by SKF 525-A, metyrapone, and carbon monoxide, suggesting that cytochrome P-450 played a role in the reaction. Thus, the major difference in the in vitro hepatic metabolism of the three isomers of chloronitrobenzene is the failure of 3-chloronitrobenzene to be converted to a glutathione conjugate.

Animals↗
PubMedDate not supplied

Metabolism of acrylonitrile to 2-cyanoethylene oxide in F-344 rat liver microsomes, lung microsomes, and lung cells.

The metabolism of acrylonitrile to the epoxide, 2-cyanoethylene oxide (ANO) was examined in rat liver microsomes, lung microsomes, and isolated enriched lung cell preparations. GC/high resolution MS was used to quantitate ANO in microsomal and cellular extracts by monitoring the fragment ion C2H3N (m/z 41.0265). The limit of detection was 0.05 pmol of ANO/0.5 microliter of standard solution, microsomal extract, or cellular extract injected onto the column, and the linear range of analysis was 0.05 to 12.5 pmol of ANO. Kinetic parameters of Vmax, V/K, and Km were calculated for microsomal ANO formation. Liver microsomes were quantitatively more active than lung microsomes on a mg of protein basis. The Vmax (pmol of ANO formed/min/mg of protein) was 666.61 for liver and 45.07 for lung microsomes. The V/K (pmol of ANO/min/mg of protein/microM) was 12.83 for liver and 0.02 for lung microsomes. The apparent Km was 51.93 microM and 1853.83 microM for liver and lung microsomes, respectively. When calculated as nmol of ANO formed/min/nmol of microsomal P-450, the Vmax for lung was equivalent to the Vmax for liver. ANO formation in the rat lung was cell specific. The rates of metabolism in the Clara cell-enriched fraction, the alveolar type II cell-enriched fraction, and the cell suspension were 2.55, 0.38, and 0.67 pmol of ANO formed/min/mg of protein, respectively. No metabolism was observed in the endothelial (small) cell-enriched fraction or in the alveolar macrophages. The results suggest that the lung contributes to the metabolism and disposition of inhaled acrylonitrile.

Acrylonitrile↗
PubMedDate not supplied

Loss of rat liver microsomal cytochrome P-450 during methimazole metabolism. Role of flavin-containing monooxygenase.

The role of flavin-containing monooxygenase (FMO) in the decrease in cytochrome P-450 content during the microsomal metabolism of methimazole (N-methyl-2-mercaptoimidazole) was investigated by heat inactivation of FMO. Incubation of liver microsomes from untreated Fischer 344 rats with NADPH and methimazole resulted in a 25% loss of cytochrome P-450 detectable as its ferrous-carbon monoxide complex. The same extent of cytochrome P-450 loss was observed with 1 and 20 mM methimazole, suggesting saturation of the process. There was no significant loss of cytochrome P-450 when microsomal FMO was heat-inactivated prior to incubation with NADPH and methimazole. Heat pretreatment of the microsomes did not affect cytochrome P-450 concentrations and cytochrome P-420 was not observed. These results indicate that FMO-catalyzed metabolism of methimazole is necessary for the loss of cytochrome P-450 in microsomes from untreated rats. Sulfite and N-methylimidazole, the ultimate products of methimazole metabolism, did not cause a significant loss of cytochrome P-450. There was no loss of cytochrome P-450 when glutathione was included in the incubation with methimazole, suggesting that cytochrome P-450 loss was due to an interaction with oxygenated metabolites of methimazole formed by FMO. Losses of cytochrome P-450 were also observed after incubation of microsomes from phenobarbital- (31%) of beta-naphthoflavone-pretreated rats (44%) with NADPH and methimazole. In contrast to microsomes from untreated rats, heat inactivation of FMO did not prevent the loss of cytochrome P-450 in microsomes from the pretreated rats. These results indicate that both phenobarbital and beta-naphthoflavone induce isozymes of cytochrome P-450 capable of directly activating methimazole.

Animals↗
PubMedDate not supplied

Isomer- and sex-specific bioactivation of mononitrotoluenes. Role of enterohepatic circulation.

2-Nitrotoluene (2NT) induces DNA repair in the in vivo-in vitro hepatocyte unscheduled DNA synthesis assay in male, but not female, Fischer-344 rats. 3-Nitrotoluene (3NT) and 4-nitrotoluene (4NT) are inactive in both sexes. The structurally related rat hepatocarcinogen, 2,6-dinitrotoluene, which also displays a sex-specific toxicity, requires biliary excretion for bioactivation. Therefore, the role of enterohepatic circulation in the development of the isomer- and sex-specific hepatic bioactivation of the mononitrotoluenes was studied in male and female Fischer-344 rats. Male rats excreted 28.6, 10.8, and 9.8% of a dose (200 mg/kg) of 2NT, 3NT, or 4NT, respectively, in the bile 12 hr after the dose. Female rats excreted 9.6, 4.3, and 1.3% of a dose of 2NT, 3NT, or 4NT, respectively, in the bile 12 hr after the dose. Of the 2NT-related material excreted in the bile, 77% in males (22.0% of the dose) and 86% in females (8.3% of the dose) was 2-nitrobenzyl glucuronide. Of the 3NT-related material excreted in the bile, 28% in males (2.8% of the dose) and 16% in females (0.7% of the dose) was 3-nitrobenzyl glucuronide. Of the 4NT-related material excreted in bile, 9% in males (0.9% of the dose) and 7% in females (0.1% of the dose) was 4-nitrobenzyl glucuronide. Inhibition of enterohepatic circulation by bile duct cannulation resulted in a decrease in hepatic macromolecular covalent binding by 98, 75, and 78% in male rats, and by 85, 44, and 45% in female rats after 2NT, 3NT, or 4NT, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Metabolism of dinitrobenzenes by rat isolated hepatocytes.

The metabolism of radiolabeled dinitrobenzene (DNB) isomers was compared in hepatocytes and hepatic subcellular fractions isolated from male Fischer-344 rats. Under aerobic conditions, reduction was the major metabolic pathway for m- and p- DNB in hepatocytes with m- and p-nitroaniline accounting for 74.0 +/- 1.2 and 81.0 +/- 0.6% (mean +/- SE, n = 4), respectively, of the radioactivity present after a 30-min incubation. The major metabolite of o-DNB in similar incubations was S-(2-nitrophenyl)glutathione which represented 48.1 +/- 5.5% of the total radioactivity; o-nitroaniline accounted for 29.5 +/- 2.1% of the radioactivity. Incubations of DNBs with microsomes produced nitroanilines as well as nitrosonitrobenzenes and nitrophenylhydroxylamines. Reduction of o- and m-DNB by microsomes was NADPH-dependent. Reduction of p-DNB could be supported by NADH as well as NADPH, although the rate of reduction was slower with NADH. o- and p-DNB were reduced to nitroanilines 3-5 times faster than m-DNB in hepatocyte and microsomal incubations. Conjugation of o- and p-DNB, but not m-DNB, with glutathione occurred in cytosol incubations although only o-DNB formed the glutathione conjugate in intact hepatocytes. Thus, there are substantial isomeric differences in the aerobic metabolism of the DNBs by rat hepatic enzymes.

Animals↗