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T V Zenser

Publications and source records attributed to T V Zenser.

At least 91 records · Page 5Linked to original sources
PubMed1984

Forskolin increases 1,25-dihydroxyvitamin D3 production by rat renal slices in vitro.

Renal production of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] from 25-hydroxyvitamin D3 (25OHD3) is increased by PTH. The complete mechanism by which PTH modulates renal 25OHD3 metabolism is not known, but there is some evidence that the stimulation of renal cAMP production by PTH may be important. Therefore, we have used forskolin, a direct activator of adenylate cyclase in the intact tissue, to further investigate the role of cAMP in regulating renal 25OHD3 metabolism. The effect of forskolin on renal 25OHD3 metabolism and renal adenylate cyclase activity was measured using isolated renal slices from thyroparathyroidectomized rats previously fed a vitamin D-deficient, low calcium diet. Forskolin added to renal slices in vitro for 4 h increased renal 1,25-(OH)2-D3 production in a concentration-dependent manner. In separate experiments, forskolin was found to increase tissue cAMP in a concentration-dependent manner when added for 5 min. The concentration of forskolin necessary for half-maximal stimulation of adenylate cyclase was 10 microM, and that needed for half-maximal stimulation of 1,25-(OH)2-D3 production was 1 microM. PTH added to renal slices also increased renal 1,25-(OH)2-D3 production, but the effects of PTH and forskolin were not additive. Inclusion of 1,25-(OH)2-D3 in the incubation medium blocked the effect of forskolin on 1,25-(OH)2-D3 production, but it did not block the effect of forskolin on tissue cAMP content. These studies support the concept that forskolin and PTH modulate renal 25OHD3 metabolism though a cAMP-dependent pathway. However, this pathway may be further regulated at sites distal to cAMP production by compounds such as 1,25-(OH)2-D3.

Animals↗
PubMed1984

Effects of hypophysectomy and growth hormone treatment on renal hydroxylation of 25-hydroxycholecalciferol in rats.

Growth hormone stimulates intestinal calcium absorption. This action has been linked to vitamin D metabolism. We have investigated the effects of hypophysectomy and GH treatment on renal metabolism of 25-hydroxycholecalciferol (25-OH-D3). Renal hydroxylation of 25-OH-D3 was measured in vitro using the renal slice technique. Experiments were performed in young F344 rats fed a vitamin D-replete, low calcium diet for 4 weeks. In hypophysectomized rats, renal conversion of 25-OH-D3 to 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was markedly reduced compared with sham-operated rats. Renal conversion of 25-OH-D3 to 24,25-(OH)2D3 was markedly increased in hypophysectomized rats compared with sham-operated rats. Treatment of hypophysectomized rats with rat GH (rGH) for 10 days resulted in a significant increase in renal conversion of 25-OH-D3 to 1,25-(OH)2D3 and a significant decrease in conversion to 24,25-(OH)2D3. Rat GH treatment caused no significant changes in serum levels of immunoreactive parathyroid hormone. Serum calcium concentrations were similar in all groups, and serum phosphorus was low in hypophysectomized rats. Treatment of hypophysectomized rats with ovine GH for 6 days caused changes which were much less pronounced than those induced by rGH. Renal conversion of 25-OH-D3 to 1,25-(OH)2D3 and 24,25-(OH)2D3 correlated well with growth rate (weight gain). These results suggest that GH, either directly or indirectly, modulates renal metabolism of 25-OH-D3.

24,25-Dihydroxyvitamin D 3↗
PubMed1984

Antithyroid drugs interact with renal medullary prostaglandin H synthase.

The antithyroid drugs propylthiouracil and methimazole exert their effects on the thyroid gland by inhibiting thyroid peroxidase. In addition to this effect, these drugs have been reported to inhibit prostaglandin production in both the thyroid gland and the kidney. The purpose of our studies was to evaluate the mechanism of the effects of these drugs on prostaglandin production. Both propylthiouracil and methimazole reversibly inhibited prostaglandin E2 production in both inner medullary slices and isolated renal papillary collecting tubule cells. The inhibition of arachidonic acid-induced increases in PGE2 production indicated that the effects of methimazole and propylthiouracil were on the enzyme complex prostaglandin H synthase, and not on the phospholipase mechanisms responsible for the release of arachidonic acid from tissue phospholipids. Propylthiouracil inhibited both arachidonic acid and hydrogen peroxide-dependent binding of 14C-N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide to protein, indicating that the effect of propylthiouracil is on the hydroperoxidase and not on the cyclooxygenase component of prostaglandin H synthase. Our data also indicate the potential of the antithyroid drugs for inhibition of metabolism of drugs and xenobiotics by prostaglandin H synthase. Metabolism of both methimazole and propylthiouracil by the hydroperoxidase component of prostaglandin H synthase was demonstrated. It is proposed that this interaction with the hydroperoxidase component of prostaglandin H synthase is at least in part the mechanism by which propylthiouracil and methimazole inhibit prostaglandin production. The inhibition of tissue peroxidase provides these agents with the capability to prevent the peroxidatic metabolism of drugs and xenobiotics.

Animals↗
PubMed1984

Metabolic activation of carcinogenic aromatic amines by dog bladder and kidney prostaglandin H synthase.

Microsomal enzyme preparations from dog liver, kidney, and bladder were used to assess the prostaglandin H synthase-catalyzed activation of carcinogenic aromatic amines to bind covalently to proteins and nucleic acids. Benzidine, a urinary bladder carcinogen, bound to protein of bladder transitional epithelial and renal inner and outer medullary microsomes and was dependent upon addition of arachidonic acid, but not upon reduced nicotinamide adenine dinucleotide phosphate. Bladder transitional epithelial microsomes also activated o-dianisidine, 4-aminobiphenyl, and 2-naphthylamine to bind to protein and transfer RNA and benzidine and O-dianisidine to bind DNA. Cosubstrate and inhibitor specificities were consistent with activation by prostaglandin H synthase. Binding of benzidine to protein was not observed with either hepatic or renal cortical microsomes upon addition of arachidonic acid or reduced nicotinamide adenine dinucleotide phosphate. Prostaglandin H synthase and mixed-function oxidase-catalyzed bindings of 2-naphthylamine to protein and to transfer RNA were compared using liver and bladder microsomes. Only mixed-function oxidase-catalyzed binding was observed in liver, and only prostaglandin H synthase-catalyzed binding was observed in bladder. The rate of binding catalyzed by bladder microsomes was considerably greater than that catalyzed by hepatic microsomes. In addition, the bladder content of prostaglandin H synthase activity was approximately 10 times that of kidney inner medullary, a tissue reported to have a relatively high content of this enzyme in other species. These results are consistent with involvement of bladder transitional epithelial prostaglandin H synthase in the genesis of primary aromatic amine-induced bladder cancer.

Amines↗
PubMed1983

In vitro modulation of renal 25-hydroxyvitamin D3 metabolism by vitamin D3 metabolites and calcium.

It has been shown that 1,25-dihydroxyvitamin D3 (1,25-(OH)2-D3) and dietary Ca modulate renal metabolism of 25-hydroxyvitamin D3 (25-OH-D3) to 1,25-(OH)2-D3 and 24,25-dihydroxyvitamin D3 (24,25-(OH)2-D3) in the rat. However, it is not known if 1,25-(OH)2-D3 and Ca act directly on the kidney to modulate 25-OH-D3 metabolism or indirectly through other mechanisms, such as the modulation of parathyroid hormone secretion. Therefore, we have used isolated renal cortical slices from the rat to study the effect of 1,25-(OH)2-D3 and Ca in vitro on renal 25-OH-D3 metabolism. Incubation of renal slices from rats fed a vitamin D-deficient, low-Ca diet with 50 nM 1,25-(OH)2-D3 for 3 h resulted in a significant decrease in 1,25-(OH)2-D3 production and a significant increase in 24,25-(OH)2-D3 production. Increasing media Ca concentration from 0.5 to 2.5 mM resulted in a significant decrease in 1,25-(OH)2-D3 production but no change in 24,25-(OH)2-D3 production. The inhibitory effect of 1,25-(OH)2-D3 was blocked by cycloheximide, but the inhibitory effect of Ca was not blocked by cycloheximide. Renal 1,25-(OH)2-D3 production was inhibited to a greater extent by incubation with 1,25-(OH)2-D3 and Ca together than by incubation with 1,25-(OH)2-D3 and Ca separately. These studies indicate that 1,25-(OH)2-D3 and Ca act directly on the kidney to modulate renal 25-OH-D3 metabolism. They also suggest that the mechanism of modulation is different for each agent.

Animals↗
PubMed1983

Renal disease profoundly alters cortical interstitial cell function.

Interstitial cells were cultured from explants of the unilaterally hydronephrotic, contralateral, and normal kidneys. Two types of cells were identified in culture, macrophages, and cells which were tentatively identified as fibroblasts. Cells grew at a significantly faster rate in hydronephrotic compared to contralateral or normal kidneys. Cells from the hydronephrotic kidney increased prostaglandin (PG)E2 production in response to bradykinin. Cells from contralateral and normal renal cortex did not increase PGE2 production in response to bradykinin. These results indicate hydronephrosis induces functional changes in interstitial cells cultured from the cortex of hydronephrotic compared to contralateral and normal kidneys. The induction of increased PGE2 synthesis and bradykinin responsiveness in hydronephrotic cortex could be related to the exaggerated prostaglandin synthesis known to occur in hydronephrotic cortex. In hydronephrosis, cortical interstitial cells elaborate increased amounts of substances such as prostaglandins which have the capacity to modulate important parameters of renal function.

Animals↗
PubMed1983

Prostaglandin H synthase metabolism of the urinary bladder carcinogens benzidine and ANFT.

Prostaglandin H synthase (PHS) and horseradish peroxidase catalyze the oxidation of benzidine to the same free radical species. No radical was observed if either benzidine, H2O2 or enzyme was omitted. The similarity of the fine structure of this radical to a computer-simulated model suggests the presence of a free cation radical of benzidine. Neither superoxide nor hydroxyl radicals appear to be involved in the co-oxidation of benzidine or 2-amino-4-(5-nitro-2-furyl)-thiazole (ANFT) by PHS. Production of the benzidine radical by PHS was inhibited by ANFT, acetaminophen, cyanide and ascorbate. ANFT was metabolized by PHS but not by horseradish peroxidase. ANFT had no effect on either radical production or 14C-metabolism of benzidine by horseradish peroxidase. These results indicate that different peroxidases may exhibit specificity with respect to the carcinogens they activate. The free radical cation of benzidine may be the electrophilic intermediate responsible for PHS-catalyzed binding of benzidine to protein and nucleic acids.

Animals↗
PubMed1983

Prostaglandin hydroperoxidase-catalyzed activation of certain N-substituted aryl renal and bladder carcinogens.

Certain carcinogens are thought to induce renal and bladder cancer following metabolic activation. We propose a model system for this activation and provide supporting experimental evidence. This model proposes that renal and bladder carcinogens' entry into the urinary tract is facilitated, that carcinogens are activated by the prostaglandin hydroperoxidase activity of prostaglandin endoperoxide synthetase (PES), and that activation results in covalent binding to nucleic acids which can initiate carcinogenesis. Benzidine and the 5-nitrofuran HMN were shown to inhibit uptake of organic anions and cations, respectively. Carcinogen binding to DNA was dependent upon specific unsaturated fatty acid substrates and prevented by specific inhibitors of PES, i.e., aspirin. Activation with organic peroxides or H(2)O(2) was inhibited by antioxidants but not aspirin. Horseradish peroxidase (HRP) metabolized benzidine but not ANFT. Acetaminophen and the 5-nitrofurans ANFT and HMN prevented PES (14)C-benzidine metabolism. However, only acetaminophen inhibited HRP metabolism of benzidine. The only aerobic metabolism we have observed of 5-nitrofurans is PES-catalyzed. Aspirin (0.5% in the diet) inhibited rat bladder hyperplastic lesions induced by feeding 0.1% or 0.2% FANFT for 6 or 12 weeks. Aspirin reduced bladder prostaglandin synthesis and PES metabolism of FANFT. After one year of an ongoing long-term study, gross examination reveals bladder tumors in 85% of the rats fed 0.2% FANFT and in only 37% of the rats fed FANFT plus 0.5% aspirin.

Amines↗
PubMed1983

Effects of Mycobacterium bovis (strain BCG) on the interstitial cells of hydronephrotic, contralateral, and normal rabbit kidneys.

Studies were undertaken to determine the effect of viable organisms of Mycobacterium bovis, strain Bacillus Calmette Guerin (BCG), on cell growth characteristics and phagocytic properties of cells from surgically-induced unilaterally hydronephrotic, contralateral, and normal rabbit kidneys. A single intravenous administration of 8 X 10(8) BCG organisms was given at the time of ureteral ligation. Four days after injection, explants were removed from the hydronephrotic, contralateral, and normal kidneys. Two cell types, fibroblasts and mononuclear phagocytes, grew from these explants. BCG caused a marked increase in the rate of growth of cells from the hydronephrotic and contralateral kidneys. There was no measurable effect of BCG on cells from the normal kidney.

Animals↗
PubMed1983

Peroxidase metabolism of the urinary bladder carcinogen 2-amino-4-(5-nitro-2-furyl)thiazole.

Metabolism of 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT) by a variety of different peroxidases was examined. Metabolism of ANFT was measured by the binding of radiolabeled substrates to protein and DNA. Prostaglandin hydroperoxidase but not horseradish peroxidase, lactoperoxidase, or chloroperoxidase metabolically activated ANFT. All four peroxidases catalyzed the binding of benzidine to protein and DNA. With peroxide substrates, peroxidase-catalyzed binding of both carcinogens was observed with or without molecular oxygen. Arachidonic acid-dependent binding of ANFT and benzidine by prostaglandin endoperoxide synthetase was inhibited by anaerobic conditions and aspirin. Chloroperoxidase activation of benzidine was also inhibited by aspirin. Vitamin E inhibited activation of both carcinogens by all enzymes examined. Prostaglandin hydroperoxidase-catalyzed binding of benzidine to protein was inhibited by the 5-nitrofurans ANFT and 3-hydroxymethyl-1-(([3-(5-nitro-2-furyl)allydidene] amino))hydantoin and acetaminophen, while only acetaminophen inhibited horseradish peroxidase-catalyzed binding. These results indicate that different peroxidases may exhibit specificity with respect to their activation of carcinogens. Only prostaglandin hydroperoxidase activated the 5-nitrofuran ANFT, while a number of peroxidases activated the aromatic amine benzidine.

Anaerobiosis↗
PubMed1983

Comparative effects of prostaglandin H synthase-catalyzed binding of two 5-nitrofuran urinary bladder carcinogens.

Understanding the role of prostaglandin H synthase (PHS) in the carcinogenic process and the metabolic steps involved in the activation of carcinogens will facilitate experiments using pharmacological agents to prevent carcinogenesis. This study assesses the relative amounts of PHS-catalyzed binding of the urinary tract carcinogens [2-14C]-N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide (FANFT) and [2-14C]-2-amino-4-(5-nitro-2-furyl) thiazole (ANFT). Binding to protein and nucleic acid was assessed using PHS prepared from ram seminal vesicle, dog bladder transitional epithelium and rabbit renal inner medulla. PHS-catalyzed binding of ANFT was significantly greater than FANFT in each tissue. Substrate and inhibitor experiments were consistent with the prostaglandin hydroperoxidase activity of PHS catalyzing the binding of FANFT and ANFT. Oxygen was required for metabolism with arachidonic acid but not with peroxide as cosubstrate. The amount of PHS-catalyzed ANFT binding to protein was at least 4-fold greater than FANFT. Whereas a significant amount of FANFT was bound to protein, no FANFT binding to DNA could be detected. By contrast, PHS catalyzed the binding of ANFT to both protein and DNA. A PHS-catalyzed metabolite of ANFT was tentatively identified as the 4-keto analog by mass spectral analysis. The lower rate of PHS-catalyzed metabolism of FANFT compared to ANFT and the lack of detectable FANFT binding to DNA suggest that the metabolic steps involved in the initiation of FANFT-induced bladder cancer include 1) deformylation of FANFT to ANFT, 2) PHS-catalyzed activation of ANFT and 3) binding of an activated ANFT metabolite(s) to DNA.

Animals↗
PubMed1983

Prostaglandin H synthase-catalyzed activation of benzidine: a model to assess pharmacologic intervention of the initiation of chemical carcinogenesis.

Carcinogens which cause cancers in tissues distal to their entry are thought to require metabolic activation before covalent binding to macromolecules. The hydroperoxidase component of prostaglandin H synthase (PHS) activates certain carcinogens and a model describing this process is presented. The procarcinogen benzidine was used to identify sites at which microsomal PHS-catalyzed binding might be inhibited by pharmacologic agents. Activation of benzidine was determined by assessing free radical cation formation and covalent binding to protein. Reduction of benzidine diimine to diamine was also assessed. This study provides the first demonstration of inhibition of PHS-activated benzidine binding by propylthiouracil, methimazole, MK447, vitamin C and phenidone. The agents tested identified the following sites at which PHS-catalyzed binding of benzidine can be prevented: 1) inhibition of generation of the peroxide cosubstrate for benzidine oxidation; 2) inhibition of prostaglandin hydroperoxidase; 3) reduction of oxidized intermediate(s) to the parent compound; and 4) conjugation of the activated intermediate(s). This study provides a basis for further investigations of the pharmacologic intervention of chemical carcinogenesis.

Animals↗
PubMed1983

Effect of aspirin on metabolism of acetaminophen and benzidine by renal inner medulla prostaglandin hydroperoxidase.

The effect of in vivo and in vitro aspirin treatment on renal inner medullary prostaglandin hydroperoxidase-catalyzed metabolism of acetaminophen and benzidine was examined. Metabolism was assessed by the binding of [3H]acetaminophen and [14C]benzidine to TCA-precipitable material. Microsomes were prepared from control or aspirin-treated rabbits. Aspirin, whether administered in vivo (15 mg/kg i.v.) or added in vitro (2 mM), had no effect on peroxide-initiated metabolism. By contrast, arachidonic acid-initiated metabolism was completely prevented by both in vivo and in vitro aspirin. Salicylate did not inhibit either arachidonic acid- or peroxide-dependent metabolism. The antioxidant glutathione (1 mM) completely inhibited both peroxide- and arachidonic acid-initiated metabolism. Aspirin treatment completely inhibited metabolism of arachidonic acid by medullary microsomes. Thus aspirin does not inhibit the hydroperoxidase component of prostaglandin endoperoxide synthetase, and co-oxidation of acetaminophen and benzidine may proceed in the presence of aspirin. Co-oxidation may be involved in the genesis of the nephrotoxicity of mixed analgesic abuse.

Acetaminophen↗
PubMed1982

Mass spectrometry of 2-substituted-4-arylthiazoles. II--Identification of microsomal nitroreduction product by mass spectrometry.

Electron impact fragmentation of 2-methyl-4-(4-nitrophenyl)-thiazole and 2-amino-4-(4-nitrophenyl)-thiazoles were studied. Prominent fragment ions result from: (1) elimination of an NO2 radical and of a neutral NO molecule; (2) 1,2 cleavage of the thiazole ring in both compounds to give a phenoxythiirene ion; and (3) subsequent cleavage of this phenoxythiirene ion to give the common ions [C7H5]+ and [C5H3]+. An anaerobic microsomal nitroreduction product of 2-methyl-4-(4-nitrophenyl) thiazole was isolated and its structure was determined by electron impact, chemical ionization and high resolution mass spectrometry to be 2-methyl-4-(4-aminophenyl)-thiazole.

Animals↗
PubMed1982

Changes in hepatic microsomal membrane fluidity with age.

There are changes in the mixed function oxidase enzymatic activities of rat hepatic microsomal membranes with age. However, the protein components of the mixed function oxidase system do not appear to change with age. The purpose of this study was to detect possible changes in the fluidity of the lipid component of the microsomal membrane with age. Hepatic microsomes were isolated by differential centrifugation from uninduced, male CFN rats aged 3, 12 and 26 mo. The microsomal membrane fluidity was measured using electron paramagnetic resonance after incorporation of a 5-nitroxide stearic acid spin label into the membrane. The order parameter S decreased with age from 0.586 +/- 0.003 (3 mo) to 0.581 +/- 0.002 (12 mo) to 0.569 +/- 0.003 (26 mo) at 30 degrees C. This indicated an increase in membrane fluidity with age. In membranes labeled with the 16-nitroxide stearic acid, a similar increase in membrane fluidity with age was observed. The order parameter of microsomal membranes from 3 and 26 mo rats was measured over the temperature range 10 degrees to 31 degrees C in steps of 0.9 degrees C. A plot of the log of S versus the reciprocal temperature revealed a phase transition at 24 degrees C in membranes from 26 mo rats, but no phase transition was observed in 3 mo old rats in this temperature range. The change in fluidity of the hepatic microsomal membrane with age may account for some of the observed changes in membrane-bound mixed function oxidase activities with age.

Aging↗