Comparative gavage subchronic toxicity studies of o-chloroaniline and m-chloroaniline in F344 rats and B6C3F1 mice.

ortho-Chloroaniline (o-CA) andmeta-chloroaniline (m-CA) are chemical intermediates for pigment production in the textile industry. Comparative subchronic gavage studies were conducted to determine the effect of structure on toxicity.o-CA orm-CA was administered to 10 animals/sex/species in deionized water at dosages of 0, 10, 20, 40, 80, and 160 mg/kg for 13 weeks. Blood samples for clinical pathology were collected after 3 and 23 days in rats and at study termination (Day 93) in rats and mice. No mortalities occurred that could be directly attributed to treatment. Transient clinical signs of toxicity observed after dosing included cyanosis in rats and ataxia and tremors in mice. Methemoglobin formation was directly related to dosage (rats and mice) and duration of treatment (rats). At study termination, Heinz body formation in erythrocytes in association with decreased hemoglobin, hematocrit, and red blood cell count was a prominent treatment-related effect. Enlarged spleens (gross necropsy observation) and increased spleen weight were treatment effects of each chemical in both species. Microscopic lesions typical of increased red blood cell production were found in hematopoietic tissues (bone marrow, spleen, and liver), while lesions due to increased red cell destruction were found in these tissues and also the kidneys (rats). Microscopic changes were more frequently seen and severe, and involved more body organs, in rats than mice, and in m-CA-treated animals thano-CA-treated animals. Sex differences in lesion incidence/severity were not evident.

Adrenal gland: structure, function, and mechanisms of toxicity.

The adrenal gland is one of the most common endocrine organs affected by chemically induced lesions. In the adrenal cortex, lesions are more frequent in the zona fasciculata and reticularis than in the zona glomerulosa. The adrenal cortex produces steroid hormones with a 17-carbon nucleus following a series of hydroxylation reactions that occur in the mitochondria and endoplasmic reticulum. Toxic agents for the adrenal cortex include short-chain aliphatic compounds, lipidosis inducers, amphiphilic compounds, natural and synthetic steroids, and chemicals that affect hydroxylation. Morphologic evaluation of cortical lesions provides insight into the sites of inhibition of steroidogenesis. The adrenal cortex response to injury is varied. Degeneration (vacuolar and granular), necrosis, and hemorrhage are common findings of acute injury. In contrast, chronic reparative processes are typically atrophy, fibrosis, and nodular hyperplasia. Chemically induced proliferative lesions are uncommon in the adrenal cortex. The adrenal medulla contains chromaffin cells (that produce epinephrine, norepinephrine, chromogranin, and neuropeptides) and ganglion cells. Proliferative lesions of the medulla are common in the rat and include diffuse or nodular hyperplasia and benign and malignant pheochromocytoma. Mechanisms of chromaffin cell proliferation in rats include excess growth hormone or prolactin, stimulation of cholinergic nerves, and diet-induced hypercalcemia. There often are species specificity and age dependence in the development of chemically induced adrenal lesions that should be considered when interpreting toxicity data.

Inhalation toxicity of potassium octatitanate fibers (TISMO) in rats following 13 weeks of aerosol exposure.

One hundred and forty male and 140 female rats were divided into 1 control and 3 test groups of 35 rats each, per sex, and exposed by whole-body inhalation to test compound at target concentrations of 0, 1 mg/m(3) (1700 fibers/cm(3), 123 WHO fibers/cm(3)), 10 mg/m(3) (5900 fibers/cm(3), 952 WHO fibers/cm(3)), and 100 mg/m(3) (112,700 fibers/cm(3), 7440 WHO fibers/cm(3)) for 6 h/day, 5 days/wk for 13 wk. Ten rats from each group were killed after 13 wk of exposure and 13 wk of recovery, respectively, for histopathological evaluation. The other 15 rats from each group were killed to study lung clearance after 91 days of exposure, and approximately 1.5 and 3 mo of recovery following the end of the 13 wk of exposure. The mean fiber length of the chamber atmosphere was 2.8, 2.7, and 2.8 microm, while the mean fiber width was 0.48, 0.48, and 0.45 microm for the 1-, 10-, and 100-mg/m(3) chambers, respectively. In the 1-mg/m(3) (123 WHO fibers/cm(3)) exposure group, inhaled particles were mostly retained in a few fiber-laden alveolar macrophages (AMs) within the alveoli adjacent to alveolar ducts without any adverse tissue response throughout 13 wk of exposure and following 13 wk of recovery. This exposure concentration was considered to be a no-observable-adverse-effect level (NOAEL), since the alveoli containing fiber-laden AMs preserved normal structure. After 13 wk of exposure to 10 mg/m(3) (952 WHO fibers/cm(3)), fiber-laden AMs were mainly retained at the alveoli adjacent to the alveolar ducts. Infrequently, slight fibrotic thickening was observed in the alveolar ducts and adjoining alveoli, with proliferating fibroblasts and hyperplastic Type II pneumocytes, and microgranulomas. Occasionally, trace amounts of collagenous material were deposited in the thickened alveolar ducts and adjoining alveolar walls. In addition, minimal alveolar bronchiolarization was occasionally found in the alveoli adjacent to the terminal bronchioles. The peribronchial lymphoid tissue and thymic lymph nodes contained migrated fiber-laden AMs. After 13 wk of recovery, fiber-laden AMs had mostly disappeared from alveoli located in the peripheral acini, but they localized in the alveolar ducts region, suggesting there was active lung clearance of fibers by the AMs via airways. Thickened alveolar ducts and adjacent alveoli were decreased in thickness, a reversible change manifested by reduction of proliferating Type II pneumocytes and fibroblasts. Collagenized fibrosis was slightly more pronounced in the thickened alveolar ducts and adjoining alveoli. The lung response following 13 wk of exposure to 100 mg/m(3) (7440 WHO fibers/cm(3)) and after 13 wk of recovery was similar to those findings of the 952 WHO fibers/cm(3) group but more pronounced, demonstrating a clear concentration-related response. Alveolar ducts and adjoining alveolar walls in the central acini were irregularly thickened with more frequent evidence of minimal collagenized fibrosis. The lung burden and clearance of fibers were estimated by measuring the total content of titanium (Ti) in the lungs, but high variability of Ti content in control and exposed groups prevented meaningful lung clearance analysis.

Life experiences among urban adolescents: examining the role of context.

Interest in the influence of context on the psychosocial development of adolescents led to the examination of neighborhood effects on the experience of adolescent life stress. Because of concerns regarding the population and ecological validity of existing measures of adolescent life events, the research group developed a scale for the measurement of life events among urban adolescents based on data from focus group interviews in the community of interest. Investigators utilized three strategies to examine the impact of neighborhood on adolescents' perceptions of life stress in a sample of 114 adolescents (mean age = 15). Results indicated that life stress in the peer domain varied by the adolescent's neighborhood of residence. In addition, family/community stress was linearly related to neighborhood indices of economic resources.

Reduction of the cardiotoxicity of doxorubicin in rabbits and dogs by encapsulation in long-circulating, pegylated liposomes.

The relative cardiotoxicity of pegylated (STEALTH) liposomal doxorubicin (PL-DOX; Doxil) was compared to nonliposomal doxorubicin (Adriamycin) in rabbits and dogs treated i.v. for up to 22 weeks. No histological evidence of cardiotoxicity was seen in dogs treated with placebo liposomes or PL-DOX every 3 weeks for a total of 10 doses (cumulative doxorubicin dose = 10 mg/kg) either 1 or 5 weeks post-treatment. All dogs treated with the same cumulative dose of free doxorubicin showed marked cardiotoxicity (vacuolization and myofibrillar loss in the myocardium) at both time points. In rabbits, progressive cardiomyopathy was seen in both treatment groups, but was more frequent and severe with free doxorubicin (67% of doxorubicin-treated rabbits, cumulative dose = 12 to 14 mg/kg versus 16% of PL-DOX-treated animals, cumulative dose = 14 to 21 mg/kg). Five doxorubicin-treated rabbits died of congestive heart failure or with histologic evidence of cardiotoxicity (median severity score = 6). No PL-DOX-treated rabbits died of congestive heart failure, although two animals that died early showed microscopic evidence of mild cardiotoxicity (median severity score = 2.5). Cardiotoxicity increased during the post-treatment period in both treatment groups. Rabbits received up to 50% more PL-DOX with no increase in cardiotoxicity. Thus, results in two species demonstrate that the cardiotoxicity of doxorubicin is significantly decreased when administered as PL-DOX. Significantly more PL-DOX can be given without incurring an increased risk of cardiomyopathy. Recent clinical studies have confirmed that PL-DOX is also less cardiotoxic than the same dose of unencapsulated doxorubicin in humans.

Acute cardiotoxicity of the Anti-HIV dideoxynucleoside, F-ddA, in the rat.

2'-beta-Fluoro-2',3'-dideoxyadenosine (F-ddA), an acid-stable, purine dideoxynucleoside with in vitro anti-HIV activity, has been selected by the NCI as a clinical trial candidate. A recent report that high, single doses of F-ddA produce cardiotoxicity in rats prompted the present investigation whose objective was to quantitate this effect and establish a relationship between this toxicity and F-ddA plasma concentrations. Microscopic examination of cardiac tissues for degenerative lesions established the effects of F-ddA and ddA on three iv schedules [daily x 1(2.5-250 mg/kg); daily x 5(125, 250 mg/kg), and BID x 1 (250 mg/kg)] as well as one oral schedule [BID x 1 (500 mg/kg) using 8- to 12-week old female Sprague-Dawley rats. For both F-ddA and ddA, the group mean severity of the cardiac lesions was dose-dependent and proportional to the measured plasma concentrations of the undeaminated parent drugs. F-ddI and ddI, were essentially nontoxic in this study (iv, 250 mg/kg, daily x 1 and daily x 5), since plasma concentrations exceeding 2 mM produced only minimal cardiac lesions. The cardiomyopathy of F-ddA was minimal to mild for all iv doses except 250 mg/kg (daily x 1) and usually was greater than that of ddA at any given dose. This is a consequence of the fact that F-ddA is deaminated 20 times more slowly than ddA, resulting in higher plasma concentrations of F-ddA relative to ddA at any given time for any given dose. Neither F-ddA nor ddA was more cardiotoxic on a repeated iv schedule (daily x 5) than when administered only once, suggesting that rat cardiotoxicity is related Cmax rather than total exposure. In this most sensitive species, the formation of cardiac lesions above the background level is associated with i.v. F-ddA administration when the F-ddA plasma concentration approaches 300 microM, 30-50 times the anticipated therapeutic level in humans.

Use of ex vivo magnetic resonance imaging to detect onset of vigabatrin-induced intramyelinic edema in canine brain.

Vigabatrin (VGB) causes intramyelinic edema (microvacuolation) in brain of dogs and rodent, which has encouraged development of noninvasive methods to monitor for this effect during clinical trials. We report the qualitative ex vivo magnetic resonance imaging (MRI) changes observed in a neuropathology study in dogs to detect time of onset and regression of VGB-induced intramyelinic edema. Beagles were randomly assigned to 18 groups of 6 dogs per group and administered vigabatrin orally (p.o.) at a dose of 300 mg/kg/day (2 males, 2 females) or placebo (1 male, 1 female). Animals were killed and examined at weekly intervals during the 12 weeks of treatment and at 1, 2, 4, 8, 12, and 16 weeks after discontinuation of drug treatment. Myelin microvacuolation in thalamus, hypothalamus, and fornix were noted histologically after 4-5 weeks of treatment. Increases in MRI T2 intensity were observed in hypothalamus after 4 weeks and in thalamus and columns of the fornix after 7 weeks. Both MRI T2 intensity and microvacuolation continued to increase during 12-week VGB treatment. When VGB treatment was discontinued after 12 weeks, both MRI T2 intensity and microvacuolation began to decrease. Sixteen weeks after VGB discontinuation, histopathology had returned to normal and MRI examination demonstrated a marked trend toward reversal of the increased T2 signal intensity. MRI thus has potential as a noninvasive surveillance technique in certain experimental and clinical conditions associated with intramyelinic edema.

MRI monitoring of vigabatrin-induced intramyelinic edema in dogs.

Chronic administration of vigabatrin (gamma-vinyl GABA) in dogs produces reversible microvacuolation (intramyelinic edema) in discrete brain regions. Histologic changes are most notable in the columns of the fornix and regions of the hypothalamus, thalamus, optic tract, and hippocampus. In an attempt to image these changes in vivo, we performed high-field MRI on seven treated and four control dogs at baseline and after 15 weeks of dosing with vigabatrin (300 mg/kg/d). All dogs underwent parallel electrophysiologic assessment to determine the effects of vigabatrin on afferent conduction. At 15 weeks, all treated dogs showed increased T2- and decreased T1-weighted signals, with changes from baseline most prominent in the columns of the fornix and to a lesser degree in the surrounding hypothalamus and thalamus. MRIs performed on control dogs were unremarkable. We then perfused a random selection of four treated and two control dogs and imaged their brains ex vivo prior to sectioning. Ex vivo imaging confirmed the in vivo findings and strongly correlated with both electrophysiologic and subsequent histopathologic findings. Imaging was repeated in the surviving dogs 5 and 12 weeks after discontinuation of dosing. Signal abnormalities in the treated dogs progressively diminished during recovery, paralleling the electrophysiologic and histopathologic results. These findings demonstrate that MRI can detect signal changes anatomically congruent with vigabatrin-induced intramyelinic edema and suggest that MRI may provide a useful noninvasive tool for monitoring patients during clinical trials.

Sequential neuropathology of dogs treated with vigabatrin, a GABA-transaminase inhibitor.

Vigabatrin (Sabril) is a gamma-aminobutyric acid-transaminase (GABA-T) inhibitor that is effective in the treatment of certain types of drug-resistant or uncontrolled epilepsy but is known to cause microscopic vacuolation (intramyelinic edema) in the brains of treated rats, mice, and dogs. The effects of high oral doses (300 mg/kg/day) of vigabatrin administered orally to Beagle dogs were studied during treatment weeks 1-12 and recovery weeks 13, 14, 16, 20, 24, and 28. Emesis, loose stools, and anorexia and 3 drug-related deaths were observed during the first 4 wk of treatment but were virtually nonexistent thereafter because of adaptation to the drug aided by food supplementation. In more sensitive areas of the brain (columns of the fornix, thalamus, and hypothalamus), microscopic quantitative differences between background vacuolation in controls and drug-related vacuolation in treated dogs could be delineated after 4 wk, generally reached highest levels of severity between 8 and 12 wk, and were reversible upon cessation of dosing. Inhibition of brain GABA-T and elevation of brain GABA were noted after 1 wk of treatment. During the course of treatment vigabatrin ranged between 4-17 nmol/ml (plasma) and 42-1,570 nmol/ml [cerebrospinal fluid (CSF)] while CSF GABA concentrations were 4-32 nmol/ml (treated dogs) and 0.1-0.6 nmol/ml (control dogs). Although the cause of vigabatrin-induced microvacuolation is unknown, the results of the study demonstrated that GABA-T inhibition with subsequent GABA elevation occurred within the first week of treatment and was followed by the onset of detectable microvacuolation several weeks later.

Three-month effects of MDL 19,660 on the canine platelet and erythrocyte.

Nine male and nine female Beagle dogs were divided into three groups and administered orally 0, 15, or 30 mg/kg/day of the antidepressant compound MDL 19,660(5-(4-chlorophenyl)-2,4-dihydro-2,4-dimethyl-3H-1,2,4-triazole-3-t hione) for 3 months to determine the long-term effects on hemopoietic cells. Compared to a control platelet range of 353,000-452,000/microliters, a thrombocytopenia reached lowest mean levels of 135,000/microliters in the 15 mg/kg/day dogs after 2 weeks and 81,000/microliters in the 30 mg/kg/day dogs after 1 week. Subsequently, platelet numbers progressively increased and by the end of the study averaged 222,000/microliters and 203,000/microliters in dogs administered 15 and 30 mg/kg/day. Ultrastructural study of the platelet increase in the 30 mg/kg/day dogs revealed more smaller discoid platelets but no change in percentage platelets with vacuolar degeneration. Histologically, megakaryocyte hyperplasia was present in the sternal marrows and spleens of treated dogs. These observations suggest that increased thrombopoiesis rather than reduced destruction was involved in this partial recovery of platelet numbers during continuous treatment. Concurrently, cyclic formation of reticulocytes and Heinz bodies occurred in dogs given 30 mg/kg/day of MDL 19,660. These dogs had slightly lower erythrocyte counts, hemoglobin levels, and hematocrits in association with hemosiderosis (spleen, liver), extramedullary hematopoiesis (spleen), and bone marrow hypercellularity. These findings indicate that both destructive and regenerative processes followed MDL 19,660-induced Heinz body formation.

Effects of high-dose gamma-vinyl GABA (vigabatrin) administration on visual and somatosensory evoked potentials in dogs.

gamma-Vinyl GABA (GVG, vigabatrin) is a GABA transaminase-inhibiting antiepileptic agent. In dogs, chronic GVG administration produces reversible microvacuolation (intramyelinic edema) in discrete brain regions and slowing in central afferent transmission as measured by somatosensory evoked potentials (SEPs). Because this microvacuolation is especially prominent in the optic tract, this study tested the sensitivity of visual evoked potentials (VEPs) to GVG-induced changes in conduction. We also replicated the earlier SEP findings. Eight beagles received daily oral vigabatrin at the maximum tolerated dose (300 mg/kg/day); four were placebo controls. Cortical VEPs and SEPs were recorded using scalp needle electrodes at baseline and every 2 weeks throughout treatment. One treatment dog died at 2 weeks. The remainder showed an increase in central latencies beginning at 6 weeks, attaining significance (p < 0.05) at 8 and 10 weeks for SEPs and VEPs, respectively. No changes occurred in peripheral or spinal conduction in treated dogs, or in any measure in control dogs. Three GVG and two control dogs were followed after drug was withdrawn; both VEP and SEP measures returned to baseline values within 5 weeks. These findings support the use of VEPs and SEPs to monitor patients receiving vigabatrin therapy.

Thrombocytopenia in rats and dogs administered the antidepressant compound MDL-19,660.

Two-week oral administration of MDL-19,660, a triazole antidepressant compound, resulted in a dose-related thrombocytopenia in rats given 40-360 mg/kg/d and dogs treated with 5-50 mg/kg/d. Consumptive loss of platelets was not apparent since splenomegaly, hemorrhage, microscopic thrombi or prolonged coagulation times (prothrombin and activated partial thromboplastin) were not observed. Platelet production did not appear to be impaired since megakaryocytes in the bone marrow of treated animals were similar in number or slightly increased compared to control animals. Although the pathogenesis of this thrombocytopenia is presently unknown, intravascular destruction by immune mechanisms or direct drug-related effects seems most likely.

Chronic toxicity studies with vigabatrin, a GABA-transaminase inhibitor.

The GABA-transaminase inhibitor, vigabatrin, has been shown to have a rather low degree of acute toxicity in several animal species. Oral administration of the drug at 1,000 mg/kg/day for 2-4 weeks caused decreased food consumption and weight loss with resultant prostration and death in both rats and dogs. Dosages of 200 mg/kg/day were tolerated for a year without clinical signs in dogs, although rats suffered reduced weight gains and convulsions after 3-4 months when given the drug in the diet. The convulsions continued to occur frequently throughout the one-yr study, but abated 3-4 months after cessation of treatment. The only consistent histopathologic evidence of toxicity in rats and dogs has been the finding of intramyelinic edema (microvacuolation) in the brain, most notably in certain areas of white matter (cerebellum, reticular formation and optic tract in rats and columns of fornix and optic tract in dogs). No lesions were found in the spinal cord or peripheral nervous system. It took several weeks for the microvacuolation to develop, even at high dosages, but it did not continue to progress thereafter, even though a slight effect was noted at dosages as low as 30-50 mg/kg/day after one yr of treatment. The intramyelinic edemia disappeared within a few weeks after treatment was withdrawn. No residual effects were observed in dogs, whereas rats exhibited swollen axons and microscopic mineralized bodies in the cerebellum. Monkeys exhibited no adverse clinical effects except for occasional loose stools at 300 mg/kg/day. After 16 months of oral treatment at 300 mg/kg/day any suggestion of intramyelinic edema was considered to be equivocal, and there was no evidence of any effect in the 50 or 100 mg/kg/day monkeys after 6 yr of treatment. Higher doses caused chronic diarrhea, thus limiting the dosage in this species. Vigabatrin was shown to be well absorbed in rat, dog and man, whereas dose-limited absorption occurred in the monkey. Metabolism is practically nil in all 4 species and the primary elimination pathway is by glomerular filtration. Because vigabatrin is an irreversible inhibitor of GABA-transaminase and the enzyme has a slow turnover rate, plasma levels of the drug are not indicative of its pharmacologic activity. For this reason cerebrospinal fluid levels of GABA and vigabatrin were evaluated, with considerable species differences being noted. The significance of these differences in relation to the differences in toxic response is discussed.

Short-term studies of MDL 19,660-induced canine thrombocytopenia.

After 2 days of dosing, platelet counts progressively declined in dogs treated orally with 30 mg/kg/day of the antidepressant compound MDL 19,660 for 8 days. Accompanying the decrease in platelet counts was an increase in both large and vacuolated degenerating platelets. Upon cessation of dosing, the platelet counts returned to levels equal to or exceeding predosing levels within 4-7 days. Co-administration with aspirin, a known antiaggregating agent, had no protective effect on the drug-induced thrombocytopenia. In vitro testing of normal canine platelets in the presence of MDL 19,660 further revealed that spontaneous aggregation did not occur and that ADP-induced aggregation was inhibited. Drug-related platelet loss was also not prevented by the co-administration of prednisone, a steroid with immunosuppressive effects and inhibitory properties against reticuloendothelial cell phagocytosis of platelets. The results of the present investigation indicate that MDL 19,660 may produce in the dog a reversible thrombocytopenia in the form of vacuolar degeneration and subsequent destruction of the platelet by means other than aggregation or steroid-responsive mechanisms.

Degeneration of the rat and canine adrenal cortex caused by alpha- (1,4-dioxido-3-methylquinoxalin-2-yl) -N-methylnitrone (DMNM).

The antibacterial drug alpha- (1,4-dioxido-3-methylquinoxalin-2-yl)-N-methylnitrone (DMNM) given at a dose of 22.5 mg/kg/bid to 4 dogs for 14 days caused diminished adrenal cortical reserves as determined by decreased plasma corticol (3 dogs) and lower aldosterone levels (4 dogs) following the intravenous infusion of ACTH. A dose of 100 mg/kg/day of DMNM administered to rats for 31 or 35 days resulted in significant decreases in blood glucose. Histologically, the adrenal glands of both species treated with DMNM for a maximum period of 21 days (dogs) and 35 days (rats) had widespread granular and vacuolar degeneration of the cortex. The degeneration, as demonstrated in treated rats, began in the zona reticularis and inner regions of the zona fasciculata and eventually involved the entire cortex including the zona glomerulosa. As a result of treatment, significant ultrastructural alterations within cells of the rat and canine adrenal cortex consisted of degeneration of the mitochondria and an increase in the numbers and lipolysis of lipid droplets. The ultrastructure of the zona reticularis and fasciculata was most severely affected.

Degeneration of the rat and canine adrenal cortex caused by alpha-(1,4-dioxido-3-methylquinoxalin-2-yl)-N-methylnitrone (DMNM).

The antibacterial drug alpha-(1,4-dioxido-3-methylquinoxalin-2-yl) N-methylnitrone (DMNM) given at a dose of 22.5 mg/kg bid to four dogs for 14 days caused diminished adrenal cortical reserves as determined by decreased plasma cortisol (three dogs) and lower aldosterone levels (four dogs) following the intravenous infusion of ACTH. A dose of 100 mg/kg/day of DMNM administered to rats for 31 or 35 days resulted in significant decreases in blood glucose. Histologically, the adrenal glands of both species treated with DMNM for a maximum period of 21 days (dogs) and 35 days (rats) had widespread granular and vacuolar degeneration of the cortex. This degeneration in treated rats began in the zona reticularis and inner regions of the zona fasciculata and eventually involved the entire cortex including the zona glomerulosa. As a result of treatment, significant ultrastructural alterations within cells of the rat and canine adrenal cortex consisted of degeneration of the mitochondria and an increase in the numbers and lipolysis of lipid droplets. The ultrastructure of the zona reticularis and fasciculata was most severely affected.

Dose related induction of the drug metabolizing enzymes of rat liver by cilobamine.

Cilobamine , an antidepressant, was investigated for its influence on the hepatic drug metabolizing enzymes ( DME ) of male Charles River CD rats. Cilobamine doses (3, 10, 30, 100, and 300 mg/kg po, as free base) were compared to sodium phenobarbital (PB) doses (3, 10, 30, 100, and 200 mg/kg po, as free acid). Compounds were given daily for 4 days and all tests were done on Day 5. Ethylmorphine n-demethylase, aniline hydroxylase, microsomal cytochrome P-450 content, relative liver weight, and recoverable microsomal protein were quantitated. The results indicated that cilobamine was an inducer of the DME but not as potent as PB. Cilobamine did not exert any inductive responses at 3 mg/kg. At 10 and 30 mg/kg some but not all test systems were increased. However, at 100 and 300 mg/kg all were increased. PB increased all systems at all doses studied. Electron micrographs of livers of rats given 100 mg/kg of cilobamine or PB revealed hypertrophy of the smooth endoplasmic reticulum. The time course of induction in rats given 100 mg/kg po showed that responses in the cilobamine rats peaked after the second dose and plateaued with later doses. Responses in PB rats increased markedly after one dose and showed a continual increase with later doses. Induction of the DME was also demonstrated in female rats.

Intestinal changes caused by DL-alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase.

Subacute (2 week) oral or intravenous administration of DL-alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), caused diarrhea and frequent emesis as early as 4 to 5 days in dogs (dose greater than or equal to 200 mg/kg/day). Diarrhea also occurred in monkeys after 1 week of treatment with an intravenous dose of 1000 mg/kg/day. Especially evident in the treated dogs with diarrhea were fluid loss, hemoconcentration, and decreased serum sodium and chloride which were findings totally reversible about 2 weeks after cessation of dosing. As a result of treatment with the highest intravenous dosage (1000 mg/kg/day), villous atrophy of the mucosa was observed by light and scanning electron microscopy in the canine small intestine. Transmission electron microscopy demonstrated that the most significant alterations of the canine intestinal tract involved the microvilli of epithelial cells which became shorter and were frequently less numerous or absent along focal areas of the plasma membrane. Intestinal mucosal levels of putrescine, especially in the duodenum and jejunum, were decreased as demonstrated in the monkeys following intravenous treatment with 100, 300, or 1000 mg/kg/day of DFMO. The results of this investigation are consistent with the hypothesis that the inhibition of ODC activity and subsequent altered polyamine metabolism may lead to delayed maturation of the intestinal epithelial cells and the impaired development of their microvilli, causing fluid loss due to reduced absorptive surface area.

Adrenocortical degeneration in dogs, monkeys, and rats treated with alpha-(1,4-dioxido-3-methylquinoxalin-2-YL)-N-methylnitrone.

The antibacterial compound alpha-(1,4-dioxido-3-methylquinoxalin-2-yl)-N-methylnitrone (DMNM), which was administered for a maximum period of 90 days, was given orally at 0, 7.5, 15.0 or 22.5 mg/kg/day for dogs; 0, 15, 50 or 100 mg/kg/day for rats; and 35 mg/kg/day for monkeys. Reduced food consumption and weight gain, depression, debility, and deaths occurred starting at doses (mg/kg/day) of 15 in dogs, 35 in monkeys and 50 in rats. Frequent emesis and occasional black, tarry feces were also observed in most treated dogs. Necropsy examinations revealed small, pale adrenal glands in rats given a dose of 50 mg/kg/day and gastrointestinal hemorrhage in dogs administered 15.0 or 22.5 mg/kg/day of DMNM. Microscopically, vacuolar degeneration of the canine, monkey and rat adrenal cortex was seen at all dosages and appeared to progress from the zona reticularis to the zona glomerulosa. In rats treated with 50 mg/kg/day of the drug chronic lesions of adrenal cortical fibrosis, atrophy, and nodular hyperplasia were also detected. The only other significant microscopic lesions consisted of mild testicular atrophy and occasional gastric erosions in dogs treated with 7.5 mg/kg/day of DMNM.