PubMed Health⌕ Search

Biomedical subjects

T V Zenser

Publications and source records attributed to T V Zenser.

At least 109 records · Page 6Linked to original sources
PubMed1982

Anaerobic metabolism and nuclear binding of the carcinogen 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT).

The anaerobic reductive metabolism of the urinary tract carcinogen 2-amino-4-(5-nitro-2-furyl)-[2-14C]-thiazole ([14C]ANFT) was examined in vitro using rabbit liver and kidney microsomes. The intermediate(s) produced during the reduction binds to tRNA, DNA, and protein. ANFT reduction was inhibited by oxygen, required NADPH and was not inhibited by SKF-525A or allopurinol. No binding to tRNA or DNA was observed if the nucleic acids were added at the end of the incubation. The covalent binding of an ANFT metabolite(s) to nucleic acids and protein was inhibited by the antioxidants vitamin E and butylated hydroxytoluene. The stoichiometry of microsomal reduction shows 3 mol of NADPH were used/mol of ANFT reduced. In inner medullary microsomes, the apparent Km and Vmax were 0.05 mM and 0.92 nmol/mg/min, respectively. Two metabolites from the anaerobic incubation of ANFT were isolated. The metabolites were tentatively identified as 1-(2-amino-4-thiazolyl)-3-cyano-1-propanone and 2-amino-4-(5-hydroxyl-amino-2-furyl)thiazole.

Anaerobiosis↗
PubMed1982

Modulation of renal production of 24,25- and 1,25-dihydroxyvitamin D3 in young and adult rats by dietary calcium, phosphorus, and 1,25-dihydroxyvitamin D3.

The purpose of this study was to examine the effects of dietary calcium (Ca), phosphorus (P), and vitamin D3 metabolites on the renal metabolism of 25-hydroxyvitamin D3 (25OHD3) to either 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] or 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3] in the rat. The regulation of 25OHD3 metabolism was studied in both young and adult rats, since previous studies have suggested a change in the renal metabolism of 25OHD3 with age. Renal 25OHD3 metabolism was measured in vitro by incubating renal cortical slices with tritiated 25OHD3 and quantifying tritiated metabolites by high pressure liquid chromatography. The apparent Michaelis constant for the conversion of 25OHD3 to 1,25-(OH)2D3 in this system was 1.16 microM. Experiments were conducted in rats fed a vitamin D-deficient diet containing either 0.02% Ca (low Ca) or 1.20% Ca (high Ca) for 4 weeks. Young rats (4 weeks old) fed the low Ca diet demonstrated a 2.8-fold increase in 1,25-(OH)2D3 production, but no change in 24,25-(OH)2D3 production compared to young rats fed the high Ca diet. Adult rats (12 months old) fed the low Ca diet showed no change in 1,25-(OH)2D3 production, but exhibited a decrease in 24,25-(OH)2D3 production compared to adult rats fed the high Ca diet. Repletion of the young rats fed the low Ca diet with 1,25(OH)2D3 resulted in a marked decrease in 1,25-(OH)2D3 production and an increase in 24,25-(OH)2D3 production. Repletion of the adult rat resulted in no change in 1,25-(OH)2D3 production, but a significant increase in 24,25-(OH)2D3 production. When young rats were fed diets containing various levels of Ca and P, it was found that 1,25-(OH)2D3 production was inversely correlated with plasma Ca over the range 4--13 mg/dl. Since the plasma Ca level of the adult rat was 11-12 mg/dl regardless of diet, this high concentration may explain the lack of 1,25-(OH)2D3 production observed in the adult.

24,25-Dihydroxyvitamin D 3↗
PubMed1982

Differential effects of parathyroid hormone on the renal 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 production of young and adult rats.

In young rats, PTH markedly stimulates the renal conversion of 25-hydroxyvitamin D3 (25OHD3) to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], the biologically active form of vitamin D3. With increasing age, serum 1,25-(OH)2D3 decreases while serum PTH increases. Therefore, the effect of PTH on the renal metabolism of 25OHD3 to 24,25-(OH)2D3 or 1,25-(OH)2D3 was compared in young and adult rats. Rats were housed in the dark and fed a low Ca, vitamin D-deficient diet for 4-6 weeks, and thyroparathyroidectomy was performed. Renal 25OHD3 metabolism was measured in vitro by incubating renal cortical slices with tritiated 25OHD3 and quantifying tritiated metabolites by high pressure liquid chromatography. When young (2 months old) thyroparathyroidectomized (TPTX) rats were repleted with PTH by ip injection, 1,25-(OH)2D3 production increased 61%, and 24,25-(OH)2D3 production decreased to 40%. When adult (13 months old) TPTX rats were repleted with PTH, there was no increase in 1,25-(OH)2D3, but 24,25-(OH)2D3 production decreased to 43%. When PTH was added in vitro by incubating renal slices from young TPTX rats for 4 h, 1,25-(OH)2D3 production increased 68%, and 24,25-(OH)2D3 production decreased to 71%. In slices from adult rats, 24,25-(OH)2D3 production was decreased significantly to 71%, and 1,25-(OH)2D3 production was unaffected by PTH. The PTH-stimulated increase in the cAMP content of renal slices from adult rats was 75% that of slices from young rats. These studies demonstrate that PTH modulates renal 24,25-(OH)2D3 production in the adult. However, PTH does not modulate renal 1,25-(OH)2D3 production in the adult under the same conditions that produce a PTH effect in the young animal.

24,25-Dihydroxyvitamin D 3↗
PubMed1982

Independent mechanisms for bradykinin-mediated prostaglandin E2 and cyclic GMP syntheses in rabbit renal inner medulla slices.

The relationship between bradykinin-mediated prostaglandin (PG)E2 and cyclic GMP syntheses was investigated using rabbit renal inner medullary slices. Media PGE2 and slice cyclic GMP content were determined by specific radioimmunoassays. Effects of the time of incubation, the cyclic nucleotide phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine, the prostaglandin synthesis inhibitor aspirin and calcium exclusion were examined. Maximal bradykinin-mediated increases in cyclic GMP preceded increases in PGE2 synthesis. 1-Methyl-3-isobutylxanthine increased basal and bradykinin-mediated cyclic GMP content 6- to 10-fold, but reduced basal and bradykinin-mediated PGE2 synthesis. 1-Methyl-3-isobutylxanthine did not alter arachidonic acid-mediated PGE2 synthesis and did not uncover an arachidonic acid-dependent increase in the cyclic GMP content. Aspirin completely inhibited basal, bradykinin- and arachidonic acid-mediated PGE2 synthesis but did not alter basal or bradykinin-dependent cyclic GMP production. Neither exogenous cyclic GMP nor dibutyryl cyclic GMP altered basal or bradykinin-mediated increases in PGE2 synthesis. Exclusion of calcium from the media resulted in reduced basal synthesis of both PGE2 and cyclic GMP and prevented the increases caused by bradykinin. Arachidonic acid increases in PGE2 were not altered by calcium exclusion. The results indicate that bradykinin-dependent renal medullary slice synthesis of cyclic GMP and PGE2 are not dependent upon one another. However, they both require calcium. Some of the physiological effects of bradykinin on renal function may be mediated by cyclic GMP and others by PGs.

1-Methyl-3-isobutylxanthine↗
PubMed1981

6-Ketoprostaglandin E1 stimulation of rat and rabbit renal adenylate cyclase-cyclic AMP systems.

6-Ketoprostaglandin E1 effects on rat and rabbit renal adenylate cyclase-cyclic AMP systems were examined. Adenylate cyclase activity was assessed in the 1000 X g fractions prepared from different areas of kidney. 6-Ketoprostaglandin E1 caused a dose-dependent increase in rat cortical and medullary adenylate cyclase activity with 8 x 10(-6) M being the lowest effective concentration. Combinations of maximal stimulatory concentrations of 6-ketoprostaglandin E1 and prostaglandin I2 caused stimulation similar to that seen with either agent alone. In contrast, the combination of either prostaglandin with parathyroid hormone (cortex) or antidiuretic hormone (medulla) resulted in enzyme activity significantly greater than with either agent alone. Similar results were observed in the rabbit. In addition, rabbit cortical and medullary slice cyclic AMP content was increased by 6-ketoprostaglandin E1. Maximal stimulatory effects of 6-ketoprostaglandin E1 on adenylate cyclase activity and cyclic AMP content were similar to prostaglandin I2. Therefore, the similarity in physiologic actions of 6-ketoprostaglandin E1 and prostaglandin I2 may be due to the stimulation of adenylate cyclase by both agents. These prostaglandins and the polypeptide hormones appear to activate different renal adenylate cyclase-cyclic AMP systems.

Adenylyl Cyclases↗
PubMed1981

Mass spectrometry of 2-substituted 5-nitro-2-furyl thiazoles. Identification of microsomal nitroreduction products by electron impact mass spectrometry.

The electron impact mass spectral fragmentation of nitro heterocyclic carcinogens N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide, 2-amino-4-(5-nitro-2-furyl)thiazole, 2-methyl-4-(5-nitro-2-furyl)thiazole and 2-methylamino-4-(5-nitro-2-furyl)thiazole were studied. The molecular ions undergo two modes of cleavage: one giving [M-84]+ ions which include the 2-substituted thiazole ring, while the other gives rise to the fragment [M-74]+ ions. The products of anaerobic microsomal nitroreduction of 2-methyl-4-(5-nitro-2-furyl)thiazole were isolated and purified by high-pressure liquid chromatography. The metabolites undergo different fragmentation patterns compared to the parent nitro analogs. Metabolites from anaerobic enzymatic reduction showed identical gas chromatographic, high-pressure liquid chromatographic and thin-layer chromatographic properties to the chemically synthesized material. The metabolites were identified as 1-(2-methyl-4-thiazolyl)-3-cyano-1-propenone and 1-(2-methyl-4-thiazolyl)-3-cyano-1-propane by mass spectral fragmentation pattern.

Animals↗
PubMed1981

Renal metabolism of drugs and xenobiotics.

The renal cortex, outer medulla and inner medulla exhibit different profiles of drug metabolism. Mixed-function oxidase activity was present in cortex but not inner medulla. Cooxidation by prostaglandin endoperoxide synthetase was detected in inner medulla but not cortex. Both mixed-function oxidase and cooxidation were demonstrable in outer medulla. Urinary bladder carcinogens such as FANFT and benzidine and the renal carcinogen diethylstilbestrol were cooxidized by prostaglandin endoperoxide synthetase. Cooxidation could be a mechanism of activation of urinary bladder carcinogens and of nephrotoxic agents.

Animals↗
PubMed1981

Conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 in renal slices from the rat.

Isolated renal cortical slices were used to study the conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and 24,25-dihydroxyvitamin D3 [24,25](OH2)D3] by the rat kidney. Production of 1,25-(OH)2D3 and 24,25-(OH)2D3 was linear with time (30-90 min) and tissue weight (40-250 mg). Production of 1,25-(OH)2D3 was greatest (134 +/- 17 pg/mg tissue.h) in animals fed a low calcium, vitamin D-deficient diet. The greatest 24,25-(OH)2D3 production (106 +/- 17 pg/mg tissue.h) was seen in animals fed a high calcium, vitamin D-replete diet, 1,25-(OH)2D3 production was reduced to 23% of maximum by the addition of 1.2% calcium or 0.8% strontium to the vitamin D-deficient, low calcium diet. Production of 1,25-(OH)2D3 and 24,25-(OH)2D3 was greatly reduced in renal cortical slices that had been heated before incubation. Slices of renal medulla produced only small amounts of 1,25-(OH)2D3 compared to slices of renal cortex. These studies provide direct evidence for the production of 1,25-(OH)2D3 and 24,25-(OH)2D3 by the mammalian renal cortex. They also demonstrate that this production may be modulated by dietary calcium, strontium, and vitamin D.

24,25-Dihydroxyvitamin D 3↗
PubMed1981

Solute concentration affects bradykinin-mediated increases in renal prostaglandin E2.

The effects of solute concentration on the bradykinin-mediated increase in inner medullary slice prostaglandin E2 (PGE2) synthesis were investigated. PG content was determined by specific RIA. Bradykinin stimulation was prevented by the addition of the following solutes to Krebs buffer: 1.0 M urea, 0.5 or 1.0 M NaCl, 0.5 or 1.0 M mannitol, 1.0 M urea plus 0.5 M NaCl, or 1.0 M mannitol plus 0.5 M NaCl. By contrast, basal PGE2 synthesis was increased by 1.0 M mannitol or by 1.0 M mannitol plus 0.5 M NaCl, but decreased by 1.0 M urea. Urea elicited a concentration-dependent, reversible inhibition of bradykinin stimulation, with 0.01 M urea being the lowest effective concentration. By contrast, basal PGE2 synthesis was only reduced at a urea concentration greater than 0.6 M. Arachidonic acid-mediated increases in both PGE2 and PGF2 alpha synthesis were not prevented by 1.0 M urea. The latter suggests that neither PG endoperoxide synthetase nor PG endoperoxide E isomerase are inhibited by urea. The data indicate that different hypertonic solutions have different effects on basal PG production, but all inhibit bradykinin stimulation.

Animals↗
PubMed1981

Inhibition of bradykinin stimulation of renal medullary prostaglandin E2 synthesis by phosphodiesterase inhibitors.

Effects of phosphodiesterase inhibitors DL-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro-20) and 1-methyl-3-isobutylxanthine (MIX) on prostaglandin E2 (PGE2) synthesis were examined using rabbit renal inner medullary slices incubated in Krebs' buffer with or without 1 mM RO-20 or 2 mM MIX. Basal and bradykinin-mediated PGE2 synthesis were inhibited in a dose-dependent, reversible manner by both RO-20 and MIX. Arachidonic acid-mediated increases in PGE2 synthesis were not inhibited. By contrast, 1 mM aspirin completely inhibited PGE2 synthesis. Phosphodiesterase inhibitors increased slice cyclic AMP content more than 6-fold. However, this elevation in tissue cyclic AMP content did not appear to be the cause of decreased PGE2 synthesis. Exogenous 3 mM cyclic AMP and 3 mM dibutyryl cyclic AMP did not alter PGE2 synthesis. 2',5'-Dideoxyadenosine, an inhibitor of adenylate cyclase, prevented RO-20 and MIX-mediated increases in cyclic AMP but had no effect on PGE2 synthesis. Exogenous 3 mM cyclic GMP and dibutyryl cyclic GMP did not alter PGE2 synthesis. Neither RO-20 nor MIX had a direct effect on PG endoperoxide synthetase. These results indicate MIX and RO-20 inhibit renal medullary PGE2 production by limiting the availability of arachidonic acid. These effects of MIX and RO-20 on PGE2 synthesis are not secondary to their effects on cyclic nucleotide phosphodiesterase.

1-Methyl-3-isobutylxanthine↗
PubMed1981

Transport of the renal carcinogen 3-hydroxymethyl-1-([3-(5-nitro-2-furyl)allydidene]amino) hydantoin by renal cortex and cooxidative metabolism by prostaglandin endoperoxide synthetase.

Transport of the renal carcinogen 3-hydroxymethyl-1-([3-(5-nitro-2-furyl)-allydidene]amino) hydantoin (HMN) by the renal cortex and metabolism by the kidney was evaluated. Organic acid and base transport by renal cortical slices was determined using [131I]Hippuran and [14C]tetraethylammonium, respectively. HMN caused a dose-dependent reversible inhibition of [131]Hippuran accumulation but did not alter [14C]tetraethylammonium uptake. By contrast, benzidine inhibited organic base but not acid transport. The decrease in absorbance at 405 nm was used as an index of microsomal metabolism of HMN. Reduced nicotinamide adenine dinucleotide phosphate-dependent metabolism of HMN was not observed with either cortical or medullary microsomes. However, there was prostaglandin endoperoxide synthetase-mediated metabolism of HMN. Specific substrate, cofactor, and inhibitor studies suggest that metabolism occurs by the prostaglandin hydroperoxidase activity of prostaglandin endoperoxide synthetase. At least one product of HMN metabolism was characterized and shown to be different from HMN by its high-pressure liquid chromatographic and ultraviolet spectral properties. The renal mixed-function oxidases system, lipid peroxidation, nitroreduction, and lipoxygenase did not seem to be involved in HMN metabolism. These results are consistent with the hypothesis that the kidney is a site for cooxidative metabolism of chemicals which elicit carcinogenic and nephrotoxic effects in the kidney. Facilitated transport of HMN into renal tissue by the organic acid transport system may explain the greater potential for HMN to elicit renal carcinogenesis compared to other tissues.

Animals↗
PubMed1981

Aspirin inhibition of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide-induced lesions of the urinary bladder correlated with inhibition of metabolism by bladder prostaglandin endoperoxide synthetase.

The effects of aspirin on N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide (FANFT) -induced urinary bladder lesions, endogenous bladder prostaglandin E2 synthesis, and the metabolism of FANFT by bladder epithelial microsomes were examined. Rats were fed 0.5% aspirin and/or a diet containing 0.1% or 0.2% FANFT. Bladder lesions were observed with light and scanning electron microscopy, and the prostaglandin E2 content of rat bladder was measured by radioimmunoassay. Metabolism of FANFT was measured by decreased absorbance at 400 nm. Aspirin inhibited the appearance of hyperplastic lesions induced by feeding 0.1% or 0.2% FANFT for 6 or 12 weeks. Aspirin reduced bladder prostaglandin E2 content at 1, 2, 6, and 13 weeks compared to corresponding control values. Rat and rabbit microsomal metabolism of FANFT were dependent upon specific fatty acid substrate and prevented by specific inhibitors (including aspirin) of prostaglandin endoperoxide synthetase. Other inhibitor and substrate specificity studies suggest that FANFT was not metabolized by xanthine oxidase, lipoxygenase, lipid peroxidation, or mixed-function oxidases. These results suggest that the metabolism of FANFT by prostaglandin endoperoxide synthetase may be involved in the metabolic activation of FANFT necessary for the induction of bladder cancer in rats.

Animals↗
PubMed1981

Prostaglandin hydroperoxidase-mediated 2-amino-4-(5-nitro-2-furyl) [14C]thiazole metabolism and nucleic acid binding.

Prostaglandin hydroperoxide-mediated metabolism and binding of 2-amino-4-(5-nitro-2-furyl) [14C]thiazole ([14C]ANFT) metabolite to nucleic acids and proteins were investigated with rabbit bladder transitional epithelial and solubilized ram seminal vesicle microsomes. Metabolism was assessed by spectrophotometric and radiochemical techniques. Substrate and inhibitor studies are consistent with both metabolism and binding of [14C]ANFT occurring by the prostaglandin hydroperoxidase activity of prostaglandin endoperoxide synthetase. The ratio of the rates of [14C]ANFT product formation is approximately 3:7:10 (organic soluble:non-trichloroacetic acid precipitable: trichloroacetic acid precipitable) over a wide range of arachidonic acid concentrations. Approximately 2 and 1% of the total [14C]ANFT metabolized binds to transfer RNA and DNA, respectively. The metabolite isolated from the organic phase had a chromatographic profile and ultraviolet spectra different from authentic ANFT. If transfer RNA or DNA is added at the end of a 5-min incubation, no binding to nucleic acids was observed. The demonstration of prostaglandin hydroperoxidase-mediated covalent binding to nucleic acids is consistent with the involvement of this enzyme in 5-nitrofuran-induced bladder carcinogenesis.

Animals↗
PubMed1981

Microsomal nitroreductase activity of rabbit kidney and bladder: implications in 5-nitrofuran-induced toxicity.

Reductive metabolism of the aromatic nitro group of 5-nitrofurans is thought to be an important step in the mechanism of their toxicity. Microsomal nitroreductase activity with p-nitrobenzoic acid and N-[4-(5-nitro-2-furyl)-2-thiazolyl[formamide (FANFT) as substrates was assessed in the renal cortex, outer medulla, inner medulla, bladder transitional epithelial and non-epithelial bladder tissue. Cortex and transitional epithelial tissue contained the most p-nitrobenzoic acid reductase activity. However, FANFT reductase activity was similar in all areas tested except nonepithelial bladder tissue, which was 10% of the others. FANFT reduction was inhibited by oxygen, but not by carbon monoxide, allopurinol or aspirin and required NADPH. These results are consistent with NADPH-cytochrome c reductase catalyzed FANFT reduction. In medullary microsomes, the apparent Km and Vmax were 0.125 mM and 0.84 nmol/mg of protein per min, respectively. Transitional epithelial microsomes incorporated approximately 1 and 10% of the total [2-14C]FANFT metabolized into t-RNA and trichloroacetic acid-precipitable material, respectively. Two products of FANFT reduction were demonstrated by high-pressure liquid chromatography. One product was reversibly oxidized to FANFT and the other was tentatively identified by mass spectral analysis as an open chain nitrile. In view of the relatively low oxygen tension in the renal inner medulla and bladder mucosa, these results suggest that medullary and transitional epithelial nitro-reductases may be involved in the pathogenesis of 5-nitrofuran toxicity.

Animals↗