Hyperlipidemia induced by a cholesterol-rich diet leads to enhanced peroxynitrite formation in rat hearts

OBJECTIVE

We investigated the influence of experimental hyperlipidemia on the formation of cardiac NO, superoxide, and peroxynitrite (ONOO(-)) in rat hearts.

METHODS

Wistar rats were fed 2% cholesterol-enriched diet or normal diet for 8 weeks. Separate groups of normal and hyperlipidemic rats were injected twice intraperitoneally with 2 x 20 micromol/kg FeTPPS (5,10,15,20-tetrakis-[4-sulfonatophenyl]-porphyrinato-iron[III]), a ONOO(-) decomposition catalyst, 24 h and 1 h before isolation of the hearts.

RESULTS

A cholesterol diet significantly decreased myocardial NO content, however, myocardial Ca(2+)-dependent and Ca(2+)-independent NO synthase activity and NO synthase protein level did not change. Myocardial superoxide formation and xanthine oxidase activity were significantly increased; however, cardiac superoxide dismutase activity did not change in the cholesterol-fed group. Dityrosine in the perfusate, a marker of cardiac ONOO(-) formation, and plasma nitrotyrosine, a marker for systemic ONOO(-) formation, were both elevated in hyperlipidemic rats. In cholesterol-fed rats, left ventricular end-diastolic pressure (LVEDP) was significantly elevated as compared to controls. Administration of FeTPPS normalized LVEDP in the cholesterol-fed group.

CONCLUSION

We conclude that cholesterol-enriched diet-induced hyperlipidemia leads to an increase in cardiac ONOO(-) formation and a decrease in the bioavailability of NO which contributes to the deterioration of cardiac performance and may lead to further cardiac pathologies.

A peptidomic analysis of human milk digestion in the infant stomach reveals protein-specific degradation patterns

In vitro digestion of isolated milk proteins results in milk peptides with a variety of actions. However, it remains unclear to what degree protein degradation occurs in vivo in the infant stomach and whether peptides previously annotated for bioactivity are released. This study combined nanospray LC separation with time-of-flight mass spectrometry, comprehensive structural libraries, and informatics to analyze milk from 3 human mothers and the gastric aspirates from their 4- to 12-d-old postpartum infants. Milk from the mothers contained almost 200 distinct peptides, demonstrating enzymatic degradation of milk proteins beginning either during lactation or between milk collection and feeding. In the gastric samples, 649 milk peptides were identified, demonstrating that digestion continues in the infant stomach. Most peptides in both the intact milk and gastric samples were derived from β-casein. The numbers of peptides from β-casein, lactoferrin, α-lactalbumin, lactadherin, κ-casein, serum albumin, bile salt-associated lipase, and xanthine dehydrogenase/oxidase were significantly higher in the gastric samples than in the milk samples (P < 0.05). A total of 603 peptides differed significantly in abundance between milk and gastric samples (P < 0.05). Most of the identified peptides have previously identified biologic activity. Gastric proteolysis occurs in the term infant in the first 2 wk of life, releasing biologically active milk peptides with immunomodulatory and antibacterial properties of clinical relevance to the proximal intestinal tract. Data are available via ProteomeXchange (identifier PXD000688).

Administration of procyanidins from grape seeds reduces serum uric acid levels and decreases hepatic xanthine dehydrogenase/oxidase activities in oxonate-treated mice

In this study we have investigated the effects of administration of procyanidins from grape seeds on serum uric acid levels in a model of hyperuricaemia in mice pretreated with oxonate, as well as the xanthine dehydrogenase and xanthine oxidase activities in mouse liver in vivo. The procyanidins, when orally administered to the oxonate-pretreated hyperuricaemic mice, were able to elicit a dose-dependent hypouricaemic effect. At a dose of 400 mg/kg for 3 days, the serum urate levels of the oxonate-pretreated mice were not different from the normal mice. In addition, the hepatic activities of xanthine dehydrogenase and xanthine oxidase in the procyanidins-treated mice were found to decrease significantly. However, the hypouricaemic effects observed in the experimental animals did not seem to parallel the changes in xanthine dehydrogenase and xanthine oxidase activities, implying that the procyanidins might be acting via other mechanisms apart from simple inhibition of enzyme activities. Furthermore, the procyanidin-treated animals exhibited normal growth while the allopurinol-treated animals exhibited some retarded growth. These results demonstrated for the first time that the procyanidins from grape seeds possess in vivo urate-lowering activities. The potential application of these natural compounds in the treatment of hyperuricaemia is discussed.

Comparative histochemical and immunohistochemical study on xanthine oxidoreductase/xanthine oxidase in mammalian corneal epithelium

We have previously found that xanthine oxidase (one form of xanthine oxidoreductase that generates reactive oxygen species, such as superoxide radicals and hydrogen peroxide) is present in corneal epithelium of normal rabbit eye. It was suggested that the reactive oxygen species contribute to additional eye damage related to prolonged continuous contact lens wear and irradiation of the eye with UV-B light. To further explore the potential danger of xanthine oxidase as a source of reactive oxygen species, we have examined in the present paper whether xanthine oxidoreductase and xanthine oxidase are present in corneal epithelium of other mammalian species, employing immunohistochemical and enzyme histochemical methods. In corneal epithelium of normal eyes of ox, pig, guinea-pig, and rat xanthine oxidoreductase activity was detected by the tetrazolium salt reduction method and xanthine oxidase activity was localized by a method based on cerium ions capturing hydrogen peroxide. For the immunohistochemical demonstration of the enzymes, rabbit anti-bovine xanthine oxidase antibody, rabbit anti-human xanthine oxidase antibody and monoclonal mouse anti-human xanthine oxidase/xanthine dehydrogenase/aldehyde oxidase antibody were used. The immunohistochemical and enzyme histochemical results show that xanthine oxidoreductase and xanthine oxidase are present both as proteins and as active enzymes in the corneal epithelium of all animals studied. It is hypothesized that under various pathological states, xanthine oxidase-generated reactive oxygen species might contribute to eye damage.

High levels of xanthine oxidoreductase in rat endothelial, epithelial and connective tissue cells

The localization of xanthine oxidoreductase activity was investigated in unfixed cryostat sections of various rat tissues by an enzyme histochemical method which specifically demonstrates both the dehydrogenase and oxidase forms of xanthine oxidoreductase. High activity was found in epithelial cells from skin, vagina, uterus, penis, liver, oral and nasal cavities, tongue, esophagus, fore-stomach and small intestine. In addition activity was demonstrated in sinusoidal cells of liver and adrenal cortex, endothelial cells in various organs and connective tissue fibroblasts. Xanthine oxidoreductase produces urate which is a scavenger of oxygen-derived radicals. Because the enzyme is found in epithelial and endothelial cells which are subject to relatively high oxidant stress, it is postulated that in these cells xanthine oxidoreductase is involved in the antioxidant enzyme defense system. In addition, a possible role for the enzyme in proliferation and differentiation processes is discussed.

Nitric oxide mediates murine cytomegalovirus-associated pneumonitis in lungs that are free of the virus

4 wk after intraperitoneal inoculation of 0.2 LD50 (50% lethal dose) of murine cytomegalovirus (MCMV) in adult BALB/c mice, MCMV remained detectable in the salivary glands, but not in the lungs or other organs. When the T cells of these mice were activated in vivo by a single injection of anti-CD3 monoclonal antibody, interstitial pneumonitis was induced in the lungs that were free of the virus with an excessive production of the cytokines. In the lungs of such mice persistently infected with MCMV, the mRNA of the cytokines such as IL-2, IL-6, TNF-alpha, and IFN-gamma were abundantly expressed 3 h after the anti-CD3 injection, and the elevated levels continued thereafter. A marked expression of inducible nitric oxide synthetase (iNOS) was then noted in the lungs, suggesting that such cytokines as TNF-alpha and IFN-gamma may have induced iNOS. Although the increase in NO formation was demonstrated by the significant elevation of the serum levels of nitrite and nitrate, the interstitial pneumonitis was not associated with either increased superoxide formation or peroxynitrite-induced tyrosine nitration. Nevertheless, the administration of an NO antagonist also alleviated the interstitial pneumonitis provoked by anti-CD3 mAb. Based on these findings, it was concluded that MCMV-associated pneumonitis is mediated by a molecule of cytokine-induced NO other than peroxynitrite.

Xanthine oxidase/dehydrogenase is present in human placenta

Xanthine dehydrogenase/oxidase (XDH, EC 1.1.1.204, XO, EC 1.2.3.2) produces uric acid, and in the oxidase form also generates the free radical superoxide. Previous reports failed to demonstrate XDH/XO activity in human placenta. Our objective was to determine evidence of XDH/XO in human placenta. We developed a cDNA probe for human XDH/XO and used it to detect mRNA by Northern hybridization. Immunohistochemical localization of the enzyme in placental tissue was performed using a specific antibody for XDH/XO and ABC-peroxidase. Enzyme activity assay was determined by the conversion of [14C] xanthine to [14C] uric acid. mRNA was detected in all placental samples (n = 4). Villous and non-villous trophoblast cells expressed immunohistochemical staining for XOD (n = 4). Enzyme activity was detected in all placentae (n = 6). Despite previous reports, we found mRNA, XDH/XO protein and enzyme activity in human placenta localized to trophoblast cells. Enzyme activity was much lower than in liver. Several conditions in the maternal-fetal unit could potentially increase XDH/XO activity and conversion of the enzyme to its oxidase form.

Xanthine oxidase activity in mouse pancreas: effects of caerulein-induced acute pancreatitis

The development of acute pancreatitis involves a number of pathophysiological changes which result in pancreatic tissue damage. Data from several models of acute pancreatitis suggest that the in vivo conversion of the enzyme xanthine dehydrogenase to xanthine oxidase may cause tissue damage by the subsequent generation of oxygen-derived free radical products. In the present studies, acute pancreatitis was induced in mice by the administration of supramaximal secretory doses of caerulein, a cholecystokinin analogue. Pancreatic xanthine oxidase activity was observed to occur in the dehydrogenase form in both control and treated mice. Artifactual conversion to the oxidase form could be induced by exclusion of 2-mercaptoethanol and phenylmethylsulfonyl fluoride from the buffer during tissue preparation. These data indicate that no significant conversion of xanthine dehydrogenase to oxidase is associated with this model of acute pancreatitis in mice.

Increasing the resolution of polyacrylamide gel electrophoresis by varying the degree of gel crosslinking

Resolution of polyacrylamide gel electrophoresis may be substantially improved by taking advantage of the gel sieving effects of varying concentrations of bisacrylamide crosslinker. A dilution procedure is described which permits simultaneous variation of both total acrylamide concentration and percent crosslinking within a single linear regression alaysis.

Gene expression in Drosophila: post-translational modification of aldehyde oxidase and xanthine dehydrogenase

Maroon-like homozygotes are completely deficient for xanthine dehydrogenase (XDH) and aldehyde oxidase (AO), however, ma-l is not a structural locus for either enzyme. Quantitative immunoelectrophoresis of ma-l and wild type extracts suggests that the ma-l function must be post-translational. To determine whether the ma-l function involves some direct physical changes in XDH and/or AO the enzymes were characterized with respect to temperature sensitivity and behavior in gel sieving electrophoresis. Since the XDH and AO from complementary ma-l heterozygotes is more thermolabile and different in shape from wild type XDH and AO, we conclude that ma-l is involved in a post-translational modification of these enzymes.

Comparative localization of aldehyde oxidase and xanthine oxidoreductase activity in rat tissues

The distribution of aldehyde oxidase activity was evaluated in unfixed cryostat sections from tissues of male Wistar rats using a tissue protectant, polyvinyl alcohol, with Tetranitro BT as a final electron acceptor. The distribution of aldehyde oxidase activity was compared with that of xanthine oxidoreductase. The enzyme histochemical method demonstrated aldehyde oxidase activity in the epithelium of the tongue, renal tubules and bronchioles, as well as in the cytoplasm of liver cells. Such activity was not detected in oesophagus, stomach, spleen, adrenal glands, small or large intestine or skeletal and heart muscle fibres. In contrast, xanthine oxidoreductase activity was demonstrated in the tongue, renal tubules, bronchioles, oesophageal, gastric, small and large intestinal epithelial cells, adrenal glands, spleen and liver cytoplasm but not in skeletal and heart muscle fibres. The significance of the ubiquitous distribution of aldehyde oxidase activity, especially in surface epithelial cells from various tissues, except for the gastrointestinal tract, is unclear. However, aldehyde oxidase may possess some physiological activity other than in the metabolism of N-heterocyclics or of certain drugs.

Histochemistry of oxidases in several tissues of bivalve molluscs

Various tissues of the marine bivalve Mytilus galloprovincialis were analysed histochemically for oxidases capable of generating reactive oxygen species (ROS) using the cerium-DAB technique. Incubations were performed on unfixed cryostat sections using polyvinyl alcohol and semipermeable membranes. High xanthine oxidoreductase and D-amino acid oxidase (DAOX) activities were observed in kidney epithelial cells of mussels. DAOX also presented a strong activity in all the digestive epithelia. No xanthine oxidase activity was observed in any of the mussel tissues tested suggesting the presence of an enzyme only showing dehydrogenase activity. Mannitol oxidase, associated with special organelles called 'mannosomes' of terrestrial gastropods, presented a weak activity in the stomach epithelium and a strong specific activity in the haemocytes. Only DAOX presented a discrete granular distribution compatible with a peroxisomal compartmentalization. No urate oxidase activity could be demonstrated in tissues of mussels. These observations suggest a role for peroxisomes in ROS generation and determine the tissues capable of producing oxygen radicals in the digestive gland. This study raises the question of the behaviour of these enzymes in conditions in which ROS-generating organic xenobiotics are accumulated in the digestive gland of molluscs.

Effects of omeprazole and gentamicin on the biochemical and histopathological alterations of the hypoxia/ reoxygenation induced intestinal injury in newborn rats

We utilized a newborn rat model of hypoxia/reoxygenation (H/R) that resembles human necrotizing enterocolitis (NEC) to investigate the effects of omeprazole and/or gentamicin on the formation of free oxygen radicals (FOR) and bowel histopathology. For H/R, 1-day-old rats were placed into a chamber of 100% CO2 for 5 min, then they were reoxygenized for the next 5 min. The rats (n = 70) were divided into seven groups: group 1 (control), group 2 (H/R), group 3 (omeprazole), group 4 (H/R + omeprazole), group 5 (gentamicin), group 6 (H/R + gentamicin), group 7 (H/R + omeprazole + gentamicin). Gentamicin and/or omeprazole were given orally for 3 days, then all animals were killed; bowel specimens were harvested. Histopathologic injury scores (HIS) and malonyldialdehyde (MDA) and XO/(XO+XDH) rates (XO; xanthine oxidase, XDH; xanthine dehydrogenase) were measured, which reflect the FOR levels. In group 2, the HIS was significantly higher than groups 4 and 6. The mean MDA values in groups 1-7 were as follows: 54.16, 104.2, 56.85, 63.43, 62.31, 76.85, 79.13, respectively. The mean XO/(XO + XDH) levels were 0.306, 0.461, 0.286, 0.335, 0.323, 0.410, 0.375 from groups 1 -7, respectively. Group 2 rats had significantly more MDA and XO/(XO + XDH) rates versus other groups (P < 001). Histopathologic injury and biochemical results were significantly more severe in group 2 than in groups 4 and 6 (P < 001). There was no difference between groups 1 and 4 according to XO/(XO + XDH) rates. In newborn rats, H/R produces FOR, which cause serious intestinal damage. Omeprazole and/or gentamicin reduce biochemical and histopathologic bowel damage. This effect was more obvious in omeprazole treated rats. We think omeprazole may open new insights into the treatment of H/R related bowel injuries like NEC.

Xanthine oxido-reductase activity in ischemic human and rat intestine

We measured time course and extent of xanthine dehydrogenase (XD) to xanthine oxidase (XO) conversion in ischemic human and rat intestine. To model normothermic no-flow ischemia, we incubated fresh biopsies for 0, 2, 4, 8 and 16h. At t = 0h, XO was less in humans than in rats (P < 0.0004), while XD was essentially the same (P = NS). After 16h incubation at 37 degrees C, there was no appreciable XD-to-XO conversion and no change in neither XO nor XD activity in human intestine. In contrast, the rat intestine had XO/(XO + XD) ratio doubled in the first 2h and then maintained that value until t = 16 h. In conclusion, no XO-to-XD conversion was appreciable after 16 h no-flow normothermic ischemia in human intestine; in contrast, XO activity in rats increased sharply after the onset of ischemia. An immunohistochemical labelling study shows that, whereas XO + XD expression in liver tissue is localised in both hepatocytes and endothelial cells, in the intestine that expression is mostly localised in epithelial cells. We conclude that XO may be considered as a major source of reactive oxygen species in rats but not in humans.

Hypouricemic and uricosuric actions of AA-193 in a hyperuricemic rat model

In normal rats, consecutive administrations of AA-193 for 7 days maintained the dose-dependent uricosuric activity without significant changes of the plasma urate level. In clearance studies, AA-193 produced an increase in the fractional excretion of urate (FEua) namely an inhibition of the net urate reabsorption in the nephron, which was probably dependent on the plasma concentration of the agent. During in vitro studies, 1 mmol/L AA-193 had no effect on liver uricase activity and 0.2 mmol/L AA-193 did not inhibit xanthine dehydrogenase activity. Therefore, it is unlikely that AA-193 at physiologic doses has a significant effect on either the production or degradation of urate. To assess the hypouricemic effect of AA-193 derived from its uricosuric effect, we used uricase-inhibited rats produced by oxonate feeding. In the hyperuricemic rat model, consecutive administrations of AA-193 for 7 days increased urate excretion and decreased the plasma urate level. We conclude that AA-193 has a hypouricemic effect caused by increases in urate excretion in hyperuricemic rats.

Splenectomy influences endotoxin-induced bacterial translocation

To determine whether splenectomy affects the antibacterial defenses of the gut, experiments were performed using bacterial translocation (BT) as a marker of intestinal barrier failure. The incidence of BT was measured 8 days after splenectomy or sham-splenectomy in mice receiving or not receiving endotoxin (0.1 mg IP). Splenectomy does not appear to promote BT from the gut, since the incidence of bacterial translocation after splenectomy or sham-splenectomy (5%) were not different. A second experiment was performed to determine whether the resistance to endotoxin-induced BT was modified after splenectomy. The incidence of endotoxin-induced BT was 73% in the unoperated control group, 59% in the sham-splenectomy group, but 23% in the splenectomy group (p less than 0.002). Thus, splenectomy but not sham-splenectomy increased the resistance of otherwise healthy mice to endotoxin-induced BT.

Lung oxidant changes after zymosan peritonitis: relationship between physiologic and biochemical changes

Our purpose was to determine the effect of non-bacteria-dependent systemic inflammation on the degree and time course of lung oxidant activity and antioxidant defenses, comparing these changes with lung, physiologic, and histologic alterations. Adult male rats were given intraperitoneal zymosan (0.7 mg/g body weight) and were fluid resuscitated. Oxidant changes were measured as lung tissue oxidized glutathione (GSSG) and malondialdehyde (MDA) content, antioxidant defenses as tissue reduced glutathione (GSH), and catalase. Animals were killed at 4, 12, and 24 h, and at 5, 10, and 30 days. Lung data were compared with that found in liver. We noted a 45% mortality in the first 18 to 36 h with all remaining animals surviving. In the first 24 h, we noted a doubling of lung MDA and an 80% conversion of tissue GSH to GSSG compared with less than 5% in control animals, indicating a severe oxidant stress. These findings corresponded with marked increase in lung neutrophils. Arterial pressure (PaO2) was significantly decreased from a control of 95 +/- 4 mm Hg to 80 +/- 5 mm Hg and 75 +/- 4 mm Hg at Days 5 and 10, respectively, but returned toward control by 30 days. Lung GSSG and MDA remained significantly increased for the 30-day period, whereas amounts of the antioxidants, catalase, and GSH returned to control after 24 h. The ongoing oxidant stress corresponded with marked mononuclear cell infiltration and interstitial thickening, which persisted over the 30-day period even after peritonitis had completely resolved.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of lipid peroxidation products (malondialdehyde, 4-hydroxynonenal) on xanthine oxidoreductase prepared from rat liver

Depending on metabolic conditions, xanthine oxidoreductase acts as either a dehydrogenase (XDH) or an oxidase (XOD). The metabolism of hypoxanthine and xanthine by the oxidase is associated with the production of reactive oxygen radicals. Reaction of reactive oxygen radicals with polyunsaturated fatty acids (lipid peroxidation) leads to the formation of malondialdehyde (MDA) and 4-hydroxynonenal (HNE), known to modify proteins by reaction with NH2- and SH-groups. Therefore, these aldehydes could influence both the activity of xanthine oxidoreductase and the XOD/XDH ratio. We found that incubation of xanthine oxidoreductase with MDA leads to an initial increase in XDH activity and to a continuous decrease in XOD activity, whereby the total activity decreases. This was in contrast to the effects of HNE which did not alter the XDH activity; XOD was however activated. This demonstrates that the lipid peroxidation products MDA and HNE are able to modify xanthine oxidoreductase similarly to a feed-back mechanism.

Relationship between liver oxidant stress and antioxidant activity after zymosan peritonitis in the rat

OBJECTIVE

To determine the effect of a severe nonbacterial-dependent peritonitis on the degree and time course of liver oxidant stress and antioxidant activity.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal laboratory.

SUBJECTS

Thirty-eight male Sprague-Dawley rats were injected with zymosan 0.75 mg/g body weight, mixed in mineral oil, and fluid resuscitated.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Oxygen consumption (VO2), base deficit, and blood gases were determined. Liver tissue oxidized and reduced glutathione, malondialdehyde catalase, xanthine oxidase, and xanthine dehydrogenase were measured and data were compared with both a pair-fed and an ad libitum fed group over a 24-hr period. We noted a 30% mortality rate with animals dying between 20 and 24 hrs. Peak decrease in VO2 occurred at 12 hrs, corresponding with a metabolic acidosis. Marked liver oxidant stress was seen at 4 hrs with oxidized glutathione increased from a control value of 0.2 +/- 0.1 to 1.1 +/- 0.2 mg/g of tissue, while reduced glutathione decreased from a control value of 1.8 +/- 0.1 to 0.3 +/- 0.1 mg/g. By 24 hrs, oxidized glutathione activity was no longer increased, but reduced glutathione concentrations were still markedly decreased. Tissue catalase was also significantly decreased at the 24-hr period. Liver malondialdehyde was increased at 24 hrs when the peak decrease in antioxidants was evident. Liver xanthine oxidase activity increased significantly from 15 +/- 3 to 45 +/- 8 mumol uric acid/min/g by 4 hrs and remained increased, with the initial increase predating evidence of impaired perfusion. Pair-fed animals demonstrated no changes in oxidant or antioxidant activity.

CONCLUSIONS

We conclude that a marked increase in liver oxidant stress and decrease in antioxidant activity occurs in the first several hours after the onset of nonbacterial peritonitis. An early increase in liver xanthine oxidase activity may be a source of the oxidants. Decreased liver antioxidant activity persists well after the oxidant stress resolves.

Change of xanthine dehydrogenase and xanthine oxidase activities in rat brain following complete ischaemia

We studied the activities of xanthine dehydrogenase and xanthine oxidase in rat forebrain after complete ischaemia. Complete ischaemia was induced by decapitation after transcardiac infusion with saline. The activities of xanthine dehydrogenase and xanthine oxidase immediately after ischaemia were 93.3 +/- 38.7 and 18.8 +/- 7.7 microU/mg protein, respectively, and at 24 h after ischaemia were 183.5 +/- 75.1 and 60.8 +/- 15.2 microU/mg protein, respectively. The ratios of xanthine dehydrogenase/xanthine oxidase immediately and 24 h after ischaemia were 5.04 +/- 1.03 and 3.04 +/- 0.99, respectively. These data indicate that xanthine dehydrogenase and xanthine oxidase activities were maintained even 24 h after complete ischaemia. Conversion of xanthine dehydrogenase to xanthine oxidase proceeds slowly during complete ischaemia.

Xanthine oxidase/dehydrogenase in mammary gland of mouse: relationship to mammogenesis and lactogenesis in vivo and in vitro

Xanthine oxidase/dehydrogenase (XO/XDH) increases at mid gestation in mammary gland but not in liver of the mouse and remains elevated until the pups are weaned at 20 d post partum. The increase in enzyme activity is due neither to alteration in activators or inhibitors nor to a production of a variant enzyme with altered catalytic properties. The increase is preceded in vivo by a surge of prolactin-like activity (placental lactogen) in plasma, and prolactin is required for induction of XO/XDH in explant culture in vitro. Induction of XO/XDH in vivo and in vitro precedes the full histological differentiation of the gland. In addition, induction of XO/XDH in vitro occurs more rapidly and at lower concentrations of prolactin than does histological differentiation. Thus although XO/XDH is present in milk, increased XO/XDH activity is an early event in mammogenesis in vivo and in vitro rather than a terminal component of differentiation.

Quantitative in situ analysis of xanthine oxidoreductase activity in rat liver

The tetrazolium salt method previously developed for the detection of xanthine oxidoreductase activity in unfixed cryostat sections has been validated for quantitative purposes. The specificity of the enzyme reaction was studied by incubating unfixed cryostat sections of rat liver in test medium containing the substrate hypoxanthine, in control medium that lacked the substrate, and in medium containing substrate and allopurinol, a specific inhibitor of xanthine oxidoreductase activity. The specific reaction rate was determined cytophotometrically by subtracting the amount of final reaction product generated in the control reaction from that formed in the test reaction. Highest specific enzyme activity in rat liver was found when the incubation medium contained 18% (w/v) polyvinyl alcohol, 100 mM phosphate buffer, pH 7.8, 0.45 mM 1-methoxyphenazine methosulfate, 5 mM tetranitro BT, and 0.5 mM hypoxanthine. Enzyme activity was present in liver parenchymal cells and in sinusoidal cells (endothelial and Kupffer cells) and was completely inhibited by allopurinol. A linear relationship was observed between the specific amount of final reaction product generated at 37 degrees C and incubation time at least up to 21 min, as well as section thickness up to 12 microns. Xanthine oxidoreductase activity, expressed as mumoles substrate converted per cm3 tissue/min, was 1.61 +/- 0.34 in pericentral areas and 1.24 +/- 0.16 in periportal areas. These values are similar to biochemical data reported in the literature. In conclusion, the tetrazolium method to detect xanthine oxidoreductase activity in unfixed cryostat sections of rat liver gives a reliable reflection of in situ activity.