Coadministration Of Indomethacin Research Articles

Insulin inhibits acetylcholine responses in rat isolated mesenteric arteries via a non-nitric oxide nonprostanoid pathway.

Hyperinsulinemia is a risk factor for hypertension and arteriosclerosis. The mechanism by which it contributes to disease progression is not known. The present study examines the effects of insulin on endothelium-derived relaxing factors. Segments of rat mesenteric arterioles and aorta were set up for isometric recordings. The effect of insulin (1 mU/mL) on acetylcholine responses was examined with and without nitro-L-arginine, indomethacin, KCl (40 mmol/L), and apamin+charybdotoxin. Incubation with insulin (maximum response to acetylcholine 90.9+/-8.7% versus 90.7+/-4.5% for before versus after insulin, respectively), nitro-L-arginine, indomethacin, or high K(+) alone had no effect on these responses in mesenteric arterioles. Apamin+charybdotoxin significantly blunted responses to acetylcholine. When coincubated with nitro-L-arginine but not with indomethacin or high K(+), insulin blunted the maximum response to acetylcholine (from 84.8+/-8.2% to 40.7+/-10.2% for before versus after insulin, respectively; P<0.01). When coincubated with apamin+charybdotoxin, insulin had no further effect. Coadministration of indomethacin with nitro-L-arginine had no greater effect than did nitro-L-arginine alone. The addition of insulin, together with nitro-L-arginine and indomethacin, significantly decreased the maximal response to acetylcholine from 96.6+/-5.3% to 52.9+/-10.8% (P<0.01). In the aorta, nitro-L-arginine abolished acetylcholine responses. Coadministration with insulin had no further effect. We conclude that insulin attenuates acetylcholine responses mediated by endothelium-derived hyperpolarizing factor in small but not large arteries. This effect of insulin is apparent only when NO is blocked and may be important in the development of hypertension or arteriosclerosis when reduced NO function has been reported.

Latanoprost and brimonidine: therapeutic and physiologic assessment before and after oral nonsteroidal anti-inflammatory therapy

PURPOSE: To assess, before and during oral nonsteroidal anti-inflammatory drug coadministration, latanoprost’s and brimonidine’s hypotensive action in eyes at risk of glaucomatous progression, assessing the effect of each drug on ocular perfusion and visual function. METHODS: Twenty consenting adults with open-angle glaucoma or ocular hypertension underwent a double-masked, bilateral, randomized prospective study. Treatment started with either latanoprost 0.005% in the morning and placebo in the evening, or brimonidine 0.2% twice daily in one eye; after 1 week starting the other in the fellow eye. After another week, oral indomethacin 25 mg four times a day, commenced for 2 more weeks. Intraocular pressure, ocular circulation, and visual function were monitored pretreatment, after unilateral monotherapy (day 7), bilateral ocular therapy (day 14), and coadministered oral indomethacin (day 28). Intrasubject differences (interocular and intraocular relative to baseline) were determined by two-tailed paired t test. RESULTS: A loss of the significance of intraocular pressure reduction with brimonidine was noted after oral indomethacin coadministration (−14%; P = .004 for brimonidine alone versus −11%; P = .3 with indomethacin). Significant intraocular pressure reduction with latanoprost persisted despite indomethacin (−25%; P < .0001 for latanoprost alone versus −30%; P < .0001 with indomethacin). Pulsatile ocular blood flow increased 40% with latanoprost, but was unchanged with brimonidine (interdrug difference, P = .004). Midperipheral retinal microcirculation increased 23% ( P = .03) with latanoprost. Humphrey perimetry and contrast sensitivity remained consistently at or above baseline with both latanoprost and brimonidine. Indomethacin had no significant effect on ocular perfusion or visual function measures. CONCLUSIONS: Circulatory and hydrodynamic findings differed substantially for the two drugs. The loss of significance of intraocular pressure reduction with brimonidine during indomethacin treatment may be clinically important.

Indomethacin prevents the development of experimental ammonia-induced brain edema in rats after portacaval anastomosis

Patients with fulminant hepatic failure (FHF) die with brain edema, exhibiting an increased cerebral blood flow (CBF) at the time of cerebral swelling. Mild hypothermia prevents brain edema in experimental models and in humans with FHF, an effect associated with normalization of CBF. To study the effects of alterations of CBF on the development of brain edema, we administered intravenous (IV) indomethacin to rats receiving an ammonia infusion after portacaval anastomosis. This model predictably develops brain edema and a marked increase in CBF at 3 hours of infusion. Brain water was measured with the gravimetry technique; CBF was monitored with both laser Doppler flowmetry and radioactive microspheres, whereas intracranial pressure (ICP) was monitored with a cisterna magna catheter. Coadministration of indomethacin prevented the increase in CBF seen with ammonia alone (110 ± 19% vs. −2 ± 9%) as well as the increase in brain water (80.86 ± 0.12% vs. 80.18 ± 0.06%) and the increase in ICP. Plasma ammonia and brain glutamine levels were markedly elevated in the ammonia-infused group and unaffected by indomethacin. However, ammonia uptake by the brain was significantly reduced by indomethacin. Levels of 6-keto-PGF1α, a stable metabolite of prostacyclin, were reduced in the cerebrospinal fluid (CSF) of indomethacin-treated animals. As with mild hypothermia, avoiding cerebral vasodilatation with indomethacin will prevent the development of brain edema in this hyperammonemic model. Cerebral vasoconstriction reduces cerebral ammonia uptake and, if selective to the brain, may be of benefit in FHF. (HEPATOLOGY 2001;34:249-254.)

Amniotic fluid prolactin is decreased by experimental intrauterine infection or interleukin-1beta infusion but not via prostaglandins in pregnant rhesus macaques.

Amniotic fluid contains a high concentration of prolactin produced and secreted by the decidua. In vitro models have suggested that bacterial products inhibit prolactin secretion by decidual cells. To further examine this potentially important regulatory mechanism in the whole animal, chronically instrumented pregnant rhesus monkeys were prepared. Experimental infection was induced by intraamniotic or choriodecidual inoculation of 10(3)-10(6) group B streptococcus. Alternatively, interleukin (IL)-1beta was infused into the amniotic cavity. Finally, indomethacin was coadministered with IL-1beta to block the production of prostaglandins (PGs). The average prolactin level prior to inoculation (0 h) equaled 34.0 +/- 6.4 microg/ml. There was a 40% decrease in prolactin by 37 h postinfection (n = 6) and a 71% decrease between 61 and 72 h postinfection (n = 3, p < 0.01 vs. before infection). Infusion of IL-1beta also caused a decrease in amniotic fluid prolactin. There was a 42% decrease in prolactin between 0 and 24 h postinfusion (p < 0.05) and a 66% decrease between 25 and 72 h after IL-1beta infusion (p < 0.05; n = 6). Coadministration of indomethacin with IL-1beta prevented the accompanying increase in PGs but did not prevent the decrease in prolactin (n = 5). Amniotic fluid prolactin levels in untreated monkeys were stable and without a prepartum decline during the sampling period from 130 to 166 days of gestation. In summary, intrauterine bacterial infection decreases amniotic fluid prolactin, and IL-1beta mimics this effect. The effect of IL-1beta on amniotic fluid prolactin does not appear to be mediated by PGs and may involve a direct effect of IL-1beta on decidual cells.

Geranylgeranylacetone and cetraxate hydrochloride increase UDP-galactosyltransferase activity in rat gastric mucosa.

UDP-galactosyltransferase (UDP-Gal-T) is a key enzyme in the synthesis of mucus glycoprotein which plays an important role in gastric mucosal defensive mechanisms. Analysis of gastric UDP-Gal-T activity should clarify the mechanisms of the action of antiulcer drugs regarding gastric defensive factors. Here, we examined UDP-Gal-T activity in rat gastric mucosa treated with the antiulcer drugs geranylgeranylacetone (GGA) and cetraxate hydrochloride (CET). The effects of coadministration of indomethacin and exogenous administration of prostaglandins (PGs) were also studied. GGA and CET significantly increased UDP-Gal-T activity, and coadministration of indomethacin inhibited the increase of enzyme activity. UDP-Gal-T activity level with GGA was significantly higher than the control level, even in the presence of indomethacin. With CET, however, this was not the case. Among PGs, PGE1 significantly increased enzyme activity. Concomitant administration of PGE1 and GGA or CET increased UDP-Gal-T activity even with indomethacin to the levels achieved when these antiulcer drugs were administered without indomethacin. Our findings suggest that GGA and CET exert antiulcer effects by increasing mucus glycoprotein synthesis and that endogenous PG synthesis may be involved in this process. However, mechanisms not mediated by endogenous PGs may also exist in the stimulatory action of GGA on UDP-Gal-T activity.

Counteraction of the Embryolethal Effects, But Not the Maternal Toxicity, of Bropirimine and Tilorone by Coadministration of Indomethacin

Bropirimine and tilorone are immunomodulators with experimental antiviral and antitumor activities. In earlier studies, treatment with bropirimine resulted in either death of the entire litter, if given once on specific days during or prior to the period of organogenesis, or litter survival comparable with that of controls. For example, bropirimine and tilorone were both found to be embryolethal when administered orally at 400 mg/kg to Upj:TUC(SD)spf rats on day 10 of gestation. Previous studies also have shown that coadministration of progesterone with either of these immunomodulators could prevent the embryolethality but not the pronounced maternal toxicity seen concurrently. Thus, bropirimine and tilorone appear to affect maternal support of the pregnancy rather than having a direct effect on the embryos. Since administration of bropirimine or tilorone appears to mimic the luteolytic effects of prostaglandin F2a, it was hypothesized that coadministration of the prostaglandin synthesis inhibitor indomethacin might prevent such embryolethality. Thus, indomethacin was administered s.c. in combination with bropirimine or tilorone (400 mg/kg orally on day 10 of gestation), at 0.4 or 0.8 mg/rat on days 9-11 (bropirimine experiment) or days 9-12 of gestation; the dams were killed on day 13, at which time the status of each conceptus was ascertained. Although unable to prevent maternal toxicity, which was found 24 h after administration of either immunomodulator, coadministration of indomethacin resulted in a decrease in the embryolethality associated with administration of either immunomodulator on day 10 of gestation. No live embryos were found on day 13 of gestation in five of six pregnant dams given bropirimine only, whereas in the drug-combination groups six of seven (indomethacin at 0.4 mg/day) and six of eight (indomethacin at 0.8 mg/day) pregnant dams had litters containing live embryos. In the tilorone experiment, six of eight litters were completely lost in utero in the group receiving the immunomodulator only. However, only one of four surviving dams had no live embryos in the drug-combination group that received indomethacin at 0.4 mg/day, with all eight surviving dams having live embryos in the group that received 0.8 mg/day of this drug. The results of this study and of earlier combination experiments with progesterone support the following hypothesis: bropirimine or tilorone administration to Upj:TUC-(SD)spf rats on day 10 of gestation inhibits progesterone production by the corpora lutea by a mechanism involving prostaglandin synthesis, resulting in a disruption in maternal support to the pregnant uterus and subsequent embryolethality.

Growth Hormone-Induced Glomerular Hyperfiltration Is Dependent on Vasodilating Prostanoids

Exogenous growth hormone (GH) and insulin-like growth factor (IGF)-I induce an increase of renal hemodynamics in normal subjects, but the precise mechanism mediating this phenomenon has not been explored in humans. We investigated whether the renal response to exogenous GH requires the presence of vasodilating prostaglandins (PG). In 10 healthy normotensive women with normal renal function, the effect of recombinant human (rh)GH on glomerular filtration rate (GFR) was examined using an intraindividual cross-over design. The subjects were studied under conditions of normal hydration and controlled sodium and protein intake without and with coadministration of indomethacin, 150 mg/d. rhGH, 4.5 IU twice per day, was administered by subcutaneous self-injection for 3 days. GFR was measured as inulin clearance (Cin) in the morning hours in the fasting state in supine position before and after 3 days of rhGH treatment. Baseline GFR was 115.7 +/- 10.1 (SD) mL/min/1.73 m2. Three days of treatment with rhGH caused a 50% increase in serum IGF-I values and GFR increased by 10% to 127.9 +/- 11.7 mL/min/1.73 m2 (P < 0.03). The study was repeated under coadministration of indomethacin, which was started 2 days before application of rhGH. Despite a similar increase in serum IGF-I values, the increase in GFR was completely blocked by indomethacin. Urinary PGE2 excretion was not stimulated by rhGH, but decreased by 50% during indomethacin treatment, as expected. These findings suggest that the increase of GFR during GH treatment in humans is mediated by or requires the presence of vasodilating prostanoids.

Identification of non-cyclooxygenase-derived prostanoid (F2-isoprostane) metabolites in human urine and plasma.

Free radicals are thought to play an important role in many types of tissue injury. Recently, we reported that a series of prostaglandin F2-like compounds (F2-isoprostanes) capable of exerting potent biological activity are produced in vivo by free radical-induced lipid peroxidation. Their formation is independent of the cyclooxygenase enzyme and has been shown to increase profoundly in animal models of free radical injury and lipid peroxidation. We now report the identification of F-ring isoprostane metabolites in human urine and plasma utilizing a gas chromatographic/mass spectrometric assay for the major urinary metabolite of prostaglandin D2 (9 alpha,11 beta-dihydroxy-15-oxo-2,3, 18,19-tetranorprost-5-ene-1,20-dioic acid). Evidence confirming these metabolites as tetranor, dicarboxylic acid compounds containing one double bond, cis-cyclopentane ring hydroxyls, and one keto group similar in structure to the major urinary metabolite of prostaglandin D2 was obtained by analysis of human urine by electron ionization mass spectrometry. Levels of these metabolites in normal human urine were determined and found to be unaffected by cyclooxygenase inhibitors. Evidence that these metabolites arise from F2-isoprostanes was obtained by demonstrating that (a) marked increases in plasma levels and urinary excretion of these metabolites, which were unaffected by coadministration of indomethacin, occurred in rats administered CCl4 to induce F2-isoprostane formation and (b) marked increases in levels of these metabolites in plasma and urine resulted from the intravenous infusion of F2-isoprostanes into a rat. Quantification of these isoprostane metabolites in urine and plasma may provide a reliable index of endogenous isoprostane production which could prove to be an important advance in our ability to assess oxidant stress in vivo in humans.

Importance of endogenous prostaglandins for the toxicity of cyclosporin A to rat endocrine and exocrine pancreas?

Previous work has shown that cyclosporin A is toxic to the endocrine and exocrine pancreas. The aim of this study was to examine whether endogenous eicosanoids play a role in controlling cyclosporin A induced toxicity. Rats were treated for eight days with indomethacin (2 mg/kg, twice daily) in addition to cyclosporin A (5 or 10 mg/kg daily). Effects of drug treatments on exocrine (as assessed by amylase and protein secretion into the pancreatic juice) and endocrine (as assessed by the glucose dependent insulin release) pancreatic functions, and pancreatic formation of prostaglandins and thromboxane were evaluated. Treatment with cyclosporin A in the doses used did not inhibit eicosanoid formation by the pancreatic tissue ex vivo. Indomethacin caused significant inhibition of pancreatic formation of prostaglandin E2, 6k prostaglandin F1 alpha and thromboxane B2. Combined treatment with indomethacin and cyclosporin A (5 or 10 mg/kg) augmented cyclosporin A induced pancreatic toxicity with further impairment of insulin release, amylase secretion, and pancreatic juice protein content, but did not result in more pronounced inhibition of pancreatic eicosanoid formation. The increased toxicity of the combined treatment was, however, associated with raised cyclosporin A whole blood concentrations. The data suggest that the potentiation of pancreatic toxicity of cyclosporin A observed during coadministration of indomethacin is not the result of suppression of endogenous pancreatic eicosanoid biosynthesis, but more likely results from altered cyclosporin A pharmacokinetic which may be caused by an interference of indomethacin with the hepatic cytochrome P-450 dependent monooxygenase involved in cyclosporin A metabolism. The possibility that coadministration of non-steroidal antiinflammatory drugs aggravates toxic effects in cyclosporin A treated patients should be considered.

Bay K 8644 is a negative inotrope in the presence of arachidonic acid but not eicosapentaenoic acid.

The inotropic and radioligand binding characteristics of arachidonic acid (AA) and the fish oil derivative, eicosapentaenoic acid (EPA), were studied. AA alone was a concentration-dependent negative inotrope in isolated hamster papillary muscles. The negative inotropic effect of AA was enhanced 500-fold by the coadministration of indomethacin (cyclo-oxygenase inhibitor) and caffeic acid (lipoxygenase inhibitor). The dihydropyridine calcium channel agonist Bay K 8644 (BK) was a concentration-dependent positive inotrope. BK in the presence of AA was a concentration-dependent negative inotrope. The negative inotropic effect of BK in the presence of AA was blocked by caffeic acid but not indomethacin. EPA alone was a concentration-dependent negative inotrope. EPA had no effect on the positive inotropic effect of BK. Scatchard analyses of [3H]nitrendipine (dihydropyridine) binding to cardiac membranes in the presence of AA or EPA resulted in a decrease in the KD (-1/slope) with no effect on Bmax (x intercept). Kinetic studies further revealed that both AA and EPA enhanced the off rate of [3H]nitrendipine binding. These data suggest that both AA and EPA mediate similar direct negative inotropic effects through cardiac sarcolemmal calcium channels. A unique effect on E-C coupling by AA, not shared by EPA, is mediated through the lipoxygenase pathway (leukotrienes). AA and its eicosanoid products may play critically important roles in regulating myocardial contractility during acute and chronic myocardial ischemia. Differences between AA and EPA may contribute to the beneficial effects of dietary fish oils enriched in EPA.

Uterine activity and decidual prostaglandin production in women in early pregnancy in response to mifepristone with or without indomethacin in vivo

Mifepristone stimulates uterine activity in pregnant women in the first trimester. In-vitro studies have shown that the addition of mifepristone to culture medium increases the ability of decidual cells to generate prostaglandins. In this study, pregnant women of less than 56 days gestation were treated with mifepristone (600 mg) 24, 36 or 48 h prior to surgical termination of pregnancy. Another cohort of women were similarly treated with mifepristone, but also received indomethacin (100 mg b.d.). Control groups, given indomethacin alone (100 mg b.d. for 48 h) or no treatment, were also included. Uterine activity was measured immediately prior to surgical termination of pregnancy and the ability of decidua obtained at operation to generate prostaglandins in culture was measured. Uterine activity was increased in all groups pretreated with mifepristone, an increase which was not prevented by co-administration of indomethacin. In the groups pretreated with mifepristone 36 h previously, the production of prostaglandin F2 alpha (PGF2 alpha) by decidua in vitro was increased. In the group in whom indomethacin was given in addition to mifepristone 36 h prior to the study, there was a marked reduction in the ability of decidua to generate PGF2 alpha. In spite of this suppression, the increase in uterine activity was similar to the group which had not received indomethacin. These results suggest that factors other than an increase in decidual prostaglandin production are responsible for the increase in uterine activity seen following mifepristone administration in vivo.

Prevention of benzene-induced myelotoxicity by nonsteroidal anti-inflammatory drugs.

Benzene affects hematopoietic progenitor cells leading to bone marrow depression and genotoxic effects such as micronucleus formation. Progenitor cell proliferation and differentiation are inhibited by prostaglandins produced by macrophages. Administration of benzene to DBA/2 or C57BL/6 mice caused a dose-dependent bone marrow depression and a significant increase in marrow prostaglandin E level and both were prevented by the coadministration of indomethacin and other inhibitors of the cyclooxygenase component of prostaglandin H synthase. Levels of benzene that decreased bone marrow cellularity also caused genotoxic effects measured as increased micronucleated polychromatic erythrocytes in peripheral blood, which was also prevented by the coadministration of indomethacin. These results suggest a possible role for prostaglandin synthase in benzene myelotoxicity; a mechanism by which this might occur is presented.

Prevention of Benzene-Induced Myelotoxicity by Nonsteroidal Anti-Inflammatory Drugs

Benzene affects hematopoietic progenitor cells leading to bone marrow depression and genotoxic effects such as micronucleus formation. Progenitor cell proliferation and differentiation are inhibited by prostaglandins produced by macrophages. Administration of benzene to DBA/2 or C57BL/6 mice caused a dose-dependent bone marrow depression and a significant increase in marrow prostaglandin E level and both were prevented by the coadministration of indomethacin and other inhibitors of the cyclooxygenase component of prostaglandin H synthase. Levels of benzene that decreased bone marrow cellularity also caused genotoxic effects measured as increased micronucleated polychromatic erythrocytes in peripheral blood, which was also prevented by the coadministration of indomethacin. These results suggest a possible role for prostaglandin synthase in benzene myelotoxicity; a mechanism by which this might occur is presented.

Prevention of benzene-induced myelotoxicity and prostaglandin synthesis in bone marrow of mice by inhibitors of prostaglandin H synthase

Administration of benzene to mice causes bone marrow toxicity and elevations in prostaglandin E2 (PGE2), a negative regulator of myelopoiesis. In these experiments, benzene (400 mg/kg; 2×/day for 2 days) administered to DBA/2 or C57B1/6 mice decreased bone marrow cellularity and myeloid progenitor cell development (measured as colony-forming units per femur) by 40%. When inhibitors of the cyclooxygenase component of prostaglandin H synthase (PHS) (either indomethacin, 2 mg/kg; aspirin, 50 mg/kg; meclofenamate, 4 mg/kg) were coadministered with benzene, myelotoxicity and the elevation in bone marrow PGE level were prevented. Additionally, when indomethacin (1 μM) was added to cultures of bone marrow cells from benzene-treated mice, myeloid progenitor cell development was the same as the controls. The doses of indomethacin used had no affect on the hepatic conversion of benzene to its major metabolite, phenol. Using purified PHS, indomethacin (10 μM) inhibited the arachidonic acid-dependent oxidation of hydroquinone to p-benzoquinone, a putative reactive metabolite of benzene. Indomethacin (10 μM) had no effect on the H2O2-driven oxidation of hydroquinone catalysed by either PHS-peroxidase or myeloperoxidase. Coadministration of the benzene metabolites, phenol and hydroquinone, has been reported previously to reproduce the myelotoxicity of benzene. In our studies, phenol and hydroquinone (50 mg/kg each; 2×/day for 2 days) decreased bone marrow cellularity by 40%; however, coadministration of indomethacin (2 mg/kg) or meclofenamate (4 mg/kg) with these metabolites did not prevent the decrease in bone marrow cell number. Our results implicate marrow PHS in mediating the short-term myelotoxicity of benzene.

Defibrotide reduces infarct size in a rabbit model of experimental myocardial ischaemia and reperfusion.

1. Defibrotide, a single-stranded polydeoxyribonucleotide obtained from bovine lungs, has significant anti-thrombotic, pro-fibrinolytic and prostacyclin-stimulating properties. 2. The present study was designed to evaluate the effects of defibrotide on infarct size and regional myocardial blood flow in a rabbit model of myocardial ischaemia and reperfusion. 3. Defibrotide (32 mg kg-1 bolus + 32 mg kg-1 h-1, i.v.) either with or without co-administration of indomethacin (5 mg kg-1 x 2, i.v.) was administered 5 min after occlusion of the left anterior-lateral coronary artery and continued during the 60 min occlusion and subsequent 3 h reperfusion periods. 4. Defibrotide significantly attenuated the ischaemia-induced ST-segment elevation and abolished the reperfusion-related changes (R-wave reduction and Q-wave development) in the electrocardiogram. In addition, defibrotide significantly improved myocardial blood flow in normal and in ischaemic, but not in infarcted sections of the heart. The improvement in blood flow in normal perfused myocardium, but not in the ischaemic area was prevented by indomethacin. 5. Although the area at risk was similar in all animal groups studied, defibrotide treatment resulted in a 51% reduction of infarct size. Indomethacin treatment abolished the reduction of infarct size seen with defibrotide alone. 6. The data demonstrate a considerable cardioprotective effect of defibrotide in the reperfused ischaemic rabbit myocardium. This effect may be related, at least in part, to a stimulation of endogenous prostaglandin formation. Other possible mechanisms are discussed.

The prevention of benzene-induced genotoxicity in mice by indomethacin

Benzene is a myelotoxin which affects hemopoietic progenitor cells leading to bone-marrow depression as well as a genotoxin which causes chromosomal abnormalities including micronucleus formation. We have demonstrated previously that benzene administered to DBA/2 or C57B1/6 mice causes bone-marrow depression and increased prostaglandin E 2 levels in bone marrow; both of these effects can be prevented by the coadministration of indomethacin, a selective inhibitor of prostaglandin synthase. We report, herein, that benzene (400–600 mg/kg body weight), under conditions where it depresses bone-marrow cellularity, also induces an increase in the frequency of micronucleus formation in polychromatic erythrocytes of C57B1/6 mice which is also prevented by the coadministration of indomethacin at levels that do not inhibit cytochrome P450 or myeloperoxidase. In Swiss Webster wild-type mice doses of benzene from 400 to 1000 mg/kg were without effect on marrow cellularity, but did induce the formation of micronucleated polychromatic erythrocytes which could be prevented by indomethacin. In contrast, DBA/2 mice, a strain highly sensitive to benzene, exhibited significant bone-marrow depression at a dose of benzene of 100 mg/kg body weight. Even at this low dose, benzene is too toxic toward developing erythrocytes to allow the evaluation of micronucleus formation. The frequency of induction of micronucleated polychromatic erythrocytes by benzene thus depends on the strain of mouse used. Furthermore, micronucleus formation appears to be an early and very sensitive indicator of benzene toxicity. A possible role for prostaglandin H synthase in the geno- and myelo-toxicity of benzene is discussed.

Decreased hepatic microsomal cytochrome P450 due to indomethacin: Protective roles of 16,16-dimethylprostaglandin F 2α and inducing agents

Indomethacin administration to rats caused a dose-dependent decrease in hepatic microsomal cytochrome P450, aminopyrine N-demethylase, ethoxyresorufin O-de-ethylase and benzyloxyresorufin O-debenzylase, accompanied by selective alterations in microsomal sodium dodecylsulphate polyacrylamide gel electrophoretograms. High doses (⪖8.5 mg/kg) caused the disappearance of certain of the SDS-PAGE proteins tentatively identified as being different forms of cyt. P450, together with either increases, decreases or no change in some of the non-cyt. P450 proteins in the electrophoretogram. Concomitant administration of 16,16-dimethylprostaglandin F 2α gave dose-dependent protection against the deleterious effects of indomethacin on the enzymic and electrophoretic parameters of cyt. P450, but did not prevent the changes due to indomethacin in the non-cyt. P450 proteins on the electrophoretogram. In contrast, prior phenobarbitone or 3-methylcholanthrene induction prevented the effects of indomethacin on both cyt. P450 and the other microsomal proteins. Concomitant administration of SKF-525A exacerbated the effects of indomethacin on cyt. P450 and the other proteins. Indomethacin coadministration with 3-methylcholanthrene resulted in the major 3MC-induced putative cyt. P450 apoprotein having a lower mol. wt than usual. Conversely, indomethacin did not prevent the induction by SKF-525A of a different putative cyt. P450 apoprotein, despite causing decreases in cyt. P450 as determined spectrophotometrically and enzymologically. The results indicate that indomethacin rather than one of its metabolites is responsible for the decrease in cyt. P450 and that the mechanisms of protection by prostaglandin and inducing agents are, respectively, different.