Subchronic Oral Administration Research Articles

In vivo neuroprotective effects of the novel imidazolyl nitrone free-radical scavenger ( Z)-α-[2-thiazol-2-yl)imidazol-4-yl]- N- tert-butylnitrone (S34176)

Herein, we report an extensive investigation of the neuroprotective effects of the compound ( Z)-α-[2-thiazol-2-yl)imidazol-4-yl]- N- tert-butylnitrone (S34176) and the prototypic nitrone α-phenyl- N- tert-butylnitrone (PBN), in different in vivo paradigms of neuronal degeneration. Administration of S34176 (75 mg/kg i.p.) 30 min before transient (10 min) global ischaemia in Wistar rats significantly prevented delayed neuronal cell death in the hippocampal CA1 area 7 days post-ischaemia (24% vs. 73% in ischaemia control; P<0.05) whereas PBN was inactive under similar conditions. Furthermore, oral administration of S34176 (30 mg/kg) 60 min before and during (1×30 mg/kg p.o.) 6 days post-ischaemia, in combination with an acute post-ischaemia sub-protective dose (3×10 mg/kg i.p.) of the glutamate receptor antagonist, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), resulted in an increased neuroprotective action (29% cell loss in drug-treated vs. 84% in ischaemia control P<0.001) compared to either compound alone. S34176 (20 mg/kg i.p.) also partially prevented kainic acid-induced neuronal cell death at 7 days post-exposure in the CA1 (41% in drug-treated vs. 74% for kainate-treated controls; P<0.01) and CA3 hippocampal region (22% vs. 53%; P<0.01). Under similar conditions, S34176 administered orally (40 mg/kg) produced a more marked protection against kainate-induced neuronal cell loss in the CA1 (13% in drug-treated vs. 82%; P<0.001) and CA3 areas (10% vs. 52%; P<0.001). Sub-chronic oral administration of S34176 (10 mg/kg) also partially reduced kainate-induced hippocampal cell death in the CA1 (53% vs. 77%; P<0.01) and CA3 (23% vs. 53%; P<0.01) areas. Dopamine depletion in the striatum of C57BL/6 mice induced by systemic d-methamphetamine injection was significantly reduced by S34176 (40±5% vs. 11.5±8%; P<0.001) (150 mg/kg i.p.) whereas PBN was inactive under similar conditions. S34176 represents a new centrally acting nitrone-based radical scavenger with neuroprotective properties in in vivo models of delayed neuronal cell death, and supports the therapeutic potential of this class of compound for the treatment of cerebral pathologies implicating chronic neurodegeneration.

Prophylactic clarithromycin to treat Mycobacterium avium in HIV patients receiving zidovudine may significantly increase mortality by suppressing lymphopoiesis and hematopoiesis

The increased mortality observed when human immunodeficiency virus (HIV)-infected individuals are treated with clarithromycin (CLA) as prophylaxis for disseminated infection with organisms of the Mycobacterium avium complex (MAC) suggests that CLA might possess immunosuppressive activities. To test this possibility, we assessed the immunological response of BALB/c mice following subchronic (28 days) oral administration of CLA alone or in combination with zidovudine (ZDV). Because normal hematopoiesis is needed to maintain the immune system, we also examined the effect of these drugs given individually or in combination on several hematological parameters. The major effect of administration of 500 mg/kg CLA was a marked decrease in the lymphocyte/neutrophil ratio, and the only evidence of hematotoxicity in mice treated with 240 mg/kg ZDV alone was mild macrocytic anemia. However, treatment with a combination of CLA and ZDV resulted in severe hematotoxicity, evidenced by a significant ( p<0.01) decrease in the number of circulating erythrocytes, neutrophils, and lymphocytes and a 67% drop in splenic cellularity ( p<0.01). Treatment with CLA or ZDV alone or both drugs in combination had no effect on lymphocyte function, determined by measuring the ex vivo proliferative activity of splenocytes in response to alloantigens or a B cell mitogen, lipopolysaccharide (LPS). However, because of the cellular depletion in the spleen, overall immune responses in this organ decreased significantly ( p<0.05) in mice treated with CLA plus ZDV. These data suggest that interactions between CLA and ZDV warrant further evaluation because these drugs are given in combination to persons with advanced HIV infection.

Huperzine A attenuates cognitive deficits and hippocampal neuronal damage after transient global ischemia in gerbils

The protective effects of huperzine A on transient global ischemia in gerbils were investigated. Five min of global ischemia in gerbils results in working memory impairments shown by increased escape latency in a water maze and reduced time spent in the target quadrant. These signs of dysfunction are accompanied by delayed degeneration of pyramidal hippocampal CA1 neurons and by decrease in acetylcholinesterase activity in the hippocampus. Subchronic oral administration of huperzine A (0.1 mg/kg, twice per day for 14 days) after ischemia significantly reduced the memory impairment, reduced neuronal degeneration in the CA1 region, and partially restored hippocampal choline acetyltransferase activity. The ability of huperzine A to attenuate memory deficits and neuronal damage after ischemia might be beneficial in cerebrovascular type dementia.

Effects of telmisartan on renal excretory function in conscious dogs.

The present study investigated the effects of telmisartan, a selective AT1 receptor antagonist, on renal function in dogs. Conscious female dogs were treated with (i) vehicle (controls) and three doses of telmisartan (0.03 mg/kg, 0.1 mg/kg and 0.3 mg/kg) administered intravenously; (ii) vehicle and three doses of telmisartan (0.3 mg/kg, 1.0 mg/kg and 3.0 mg/kg) administered orally; or (iii) 1.0 mg/kg per day telmisartan orally for 12 days. Eight dogs were used for each experiment. Each of the four treatments in (i) and (ii) was administered 7 days apart. During the 6 h after intravenous administration, urine volume was significantly higher in dogs treated with telmisartan 0.1 mg/kg (8.5 +/- 1.6 ml/kg) and 0.3 mg/kg (7.0 +/- 0.9 ml/kg) than controls (2.7 +/- 0.3 ml/kg; P < 0.05), and renal sodium excretion was increased significantly with telmisartan 0.03 mg/kg (803 +/- 124 micromol/kg), 0.1 mg/kg (1039 +/- 213 micromol/kg) and 0.3 mg/kg (966 +/- 161 micromol/kg) versus controls (159 +/- 21 micromol/kg; P < 0.05). Oral telmisartan at doses of 1.0 mg/kg and 3.0 mg/kg also produced significant increases in urine volume (7.2 +/- 1.1 ml/kg and 6.6 +/- 1.2 ml/kg, respectively) and renal sodium excretion (599 +/- 146 micromol/kg and 555 +/- 131 micromol/kg, respectively) compared with controls (2.8 +/- 0.5 ml/kg and 80 +/- 33 mciromol/kg; P < 0.05) over the 6-h post-dose period. Telmisartan at all intravenous doses and at 3.0 mg/kg orally increased the urinary excretion of chloride significantly over the 6-h post-dose period compared with vehicle alone. The excretion of potassium and creatinine were unchanged by any treatment. Telmisartan 1.0 mg/kg administered orally for 12 days produced similar results. In conclusion, acute intravenous or oral as well as subchronic oral administration of telmisartan to conscious dogs promotes diuresis and natriuresis without affecting potassium or creatinine excretion.

Effects of Jiawey Siwu on Rat Activity

Jiawey siwu (JS) is a modified formula of siwu with the addition of Ginseng Radix and Eucommiae Cortex. We studied the CNS effect of JS on pentobarbital-induced hypnosis in ICR mice after acute oral administration. We also investigated the motor activity and exercise performance effects of JS in SD rats after subchronic (12 days) and chronic (8 weeks) oral administration with an activity cage and rotarod, respectively. The duration of pentobarbital-induced hypnosis was significantly decreased in mice after acute oral administration of 0.21, 1.05 or 4.2 g/kg JS. The time of ambulatory activity and time on the rotarod significantly increased in rats after subchronic and chronic oral administration of 1.05 g/kg JS, respectively. These results indicate that JS potentially increased the excitability of the CNS in mice, as well as increasing motor activity and physical endurance in rats.

Toxicological evaluation and classification of the genotoxic, carcinogenic, reprotoxic and sensitising potential of tris(2-chloroethyl)phosphate

Tris(2-chloroethyl)phosphate is used as flame-proofing additive in polyurethane foam and paints. The substance was not mutagenic in the Salmonella/microsome test in 6 of 7 studies, two of which were performed on behalf of BG Chemie as part of its 'Programme for the Prevention of Health Hazards Caused by Industrial Substances'. No mutagenic potential has been detected in mammalian cells in vitro (mouse lymphoma test, reverse mutation and HPRT test). The substance produces no chromosome aberrations in vitro, but does cause questionable to significant increases in the sister chromatid exchange rate. Two in vivo micronucleus tests performed on behalf of BG Chemie have given no indications of clastogenicity, while a further test was inconclusive. A test involving Drosophila (interchromosomal mitotic recombination) was also negative. Overall, tris(2-chloroethyl)phosphate appears to have no genotoxic potential. According to the EU (European Union) classification criteria, the substance has not been classified as mutagenic in Germany. Summarising the existing studies on the carcinogenic potential of tris(2-chloroethyl)phosphate, kidney tumours as well as tumours of the Harderian gland were present at below the maximum tolerable dose, the kidney tumours arising in two different species (rats, mice) and in mice in two studies. These tumours do not spontaneously occur, and their incidence was also increased in comparison with historical control data. However, only at systemic toxic doses was the incidence of carcinomas of the kidney significantly increased. Below systemic toxic doses, only the benign kidney tumours were significantly increased, but this was dose-dependent. In conclusion, the data show a carcinogenic potential of tris(2-chloroethyl)phosphate, possibly with an epigenetic mechanism. A supporting indication is provided by two of three in vitro cell transformation tests with positive results. Therefore, the carcinogenicity has been classified as EU category C2 in Germany. Tris(2-chloroethyl)phosphate is not embryotoxic or teratogenic in rats with oral administration, even at doses that are maternally toxic, and does not impair postnatal development in the offspring. Accordingly, the developmental reproductive toxicity has not been classified in Germany. However, the substance adversely affects sperm and its motility with subchronic oral administration to rats and mice. Toxic effects on reproduction were seen in both generations in a 2-generation study in Swiss CD1 mice. The classification of the reproductive toxicity, endpoint fertility, has been suggested by BG Chemie to be RF2 according to the EU classification criteria, which is still under discussion and will be concluded by the time of the congress (in the meantime, the substance has been classified as RF2 in Germany.) There were no indications of skin-sensitising potential in a Buehler test in guinea pigs. Accordingly, no classification is necessary.

Hematological and Biochemical Parameters in the Rat Following Subchronic Oral Administration of Dodine (n-Dodecylguanidine Acetate)

The subchronic toxicity following oral administration of Dodine was studied in male and female rats. Animals received 5, 10, or 20 mg/kg of the product suspended in carboxymethyl cellulose daily for 90 days. Control animals received 10 ml/kg of the vehicle. No clinical signs of toxicity were observed in the treated animals. The body weight changes were slightly higher in the Dodine-treated animals than in controls of both sexes. The males receiving the lowest dose showed a marked increase in urea. There was a significant decrease in the aspartate amino transferase activity and bilirubin content of the males treated with the highest dose. Severe histological changes were found in heart, liver, and kidneys at the three doses in both sexes.

Subchronic Toxicity Study of Tetrahydroisohumulone and Hexahydroisohumulone in the Beagle Dog

Hops and hop extracts are approved and widely used bittering agents in the brewing of beer. During recent years, preisomerized α hop acids and reduced preisomerized α hop acids have been introduced as effective and economical bittering agents that may be added late in the brewing process. Although hops have been used for centuries, there are few studies in the literature on the safety of this ingredient. The study herein was conducted to determine the effects associated with subchronic oral administration of the reduced preisomerized hop acids, hexahydroisohumulone and tetrahydroisohumulone, in the dog. The results show that these materials are generally well tolerated in the dog. At high dose levels they induce vomiting, and much of the material administered was excreted in the faeces. The no-observed-adverse-effect level (NOAEL) of the compounds were 50 and 100 mg/kg body weight, respectively. Consumption of these ingredients by adult humans drinking 1 litre of beer daily is less than 0.25 mg/kg body weight; their use is thus associated with wide safety margins.

2,5-Hexanedione concentrations and morphological changes within the eye of albino rat

Exposure to 2,5-hexanedione (2,5-HD), a major n-hexane metabolite, can cause loss of photoreceptor cells, particularly when combined with light energy. The aims of this study were to document the levels of 2,5-HD reached in relation to time in retina, aqueous humor, and serum of the Sprague-Dawley albino rat after: (1) a single oral administration of 2,5-HD (0.04 g/ kg body wt.) by tube feeding; and (2) after subchronic oral administration of 2,5-HD. In addition, morphometric analysis of the retina was carried out to evaluate cell loss at the end of administration and after various periods of recovery. The 2,5-HD concentration in retinal tissue, aqueous humor, and serum reached a peak within 1 h after exposure to a single dose of 2,5-HD. Twenty four hours after the exposure, only a minor amount of 2,5-HD could be detected in the retina and aqueous humor. When 2,5-HD was administered subchronically (0.04 g/kg body wt. per day, for 35 days) no loss of photoreceptor cells was seen immediately after the end of exposure or at the end of a 4-week recovery period. Rats exposed to 0.60 g/kg body wt. per day for 11 days showed no significant loss of photoreceptor cells immediately after the end of exposure but there was a substantial loss of photoreceptor cells after 2 and 4 weeks of recovery. The results demonstrate that 2,5-HD reaches the aqueous humor and retina, and penetrates blood-aqueous humor/retina barriers after oral administration. Moreover, retinal degeneration seen in the animals may be directly caused by 2,5-HD and these changes are dose dependent.

Biochemical and Morphologic Characterization of Acrylamide Peripheral Neuropathy

To determine whether reduced Na+/K+-ATPase activity might be involved in acrylamide (ACR)-induced peripheral axon swelling and degeneration, rubidium (Rb+) transport was measured as an index of enzyme function. x-ray microanalysis was used to quantify elemental Rb uptake and accumulation in internodal myelinated axons, mitochondria, Schwann cells, and myelin of rat tibial nerve cryosections. Results demonstrated impairment of Rb uptake in tibial axons from orally intoxicated (2.8 mM ACR for 34 days), moderately affected rats. In severely affected oral rats (49 days), complete inhibition of Rb transport and frank axon degeneration were evident. However, in moderate-to-severely affected rats exposed to ACR via ip injection (50 mg/kg/day for 11 days), neither structural nor enzymatic changes were present in tibial fibers. These findings in nerve cryosections suggested inhibition of axolemmal Na+pump activity and degeneration were dependent upon route of ACR administration. This possibility was substantiated by a quantitative longitudinal morphometric study of conventionally fixed tibial nerve. Oral ACR treatment (2.8 mM ACR for 15–49 days) was associated with progressive axon degeneration, which was preceded by atrophy. Axonal swellings were rarely (<1%) observed. In contrast, ip ACR injection (50 mg/kg/day for 5–11 days) produced classic behavioral neurotoxicity but did not alter axon morphology in tibial nerve. Thus, fiber degeneration and decreased Na+pump activity were consequences of subchronic oral ACR administration. This parallel expression suggests a mechanistic relationship. However, the corresponding general neurotoxicological significance is unclear since, behavioral toxicity induced by ip ACR develops without structural and enzymatic changes in tibial nerve.

Effects of subchronic administration of metrifonate on cholinergic neurotransmission in rats.

The effects of subchronic oral administration of metrifonate, a long-acting cholinesterase (ChE) inhibitor, on cholinergic neurotransmission were assessed in young adult male Wistar rats. Animals were treated twice daily with metrifonate. In a pilot study testing a 100 mg/kg dose of metrifonate for up to 14 days, ChE activity was found to steadily decrease to reach maximum inhibition levels of about 55%, 80% and 35% in brain, erythrocytes and plasma. Steady-state inhibition levels were attained by the 10th day of treatment. When metrifonate-treatment was discontinued, ChE activity in plasma returned to control levels within another day, while erythrocyte and brain ChE activity took more than 2 weeks to recover. In subsequent dose-response studies, metrifonate treatment was given for 3 and 4.5 weeks at doses of 0, 12.5, 25, 50, and 100 mg/kg, to different groups of animals, respectively. Correlation analysis indicted that brain ChE inhibition was more accurately reflected by erythrocyte than by plasma ChE inhibition, although all effects were highly correlated. The changes in ChE activity were not paralleled by changes in other parameters of the cholinergic neurotransmission, such as acetylcholine synthesis rate or acetylcholine receptor binding. It is therefore concluded that repeated administration of metrifonate to rats induces a long-lasting inhibition of ChE activity in a dose-related and predictable manner, which is neither subject to desensitization nor paralleled by counterregulatory downregulation of muscarinic or nicotinic receptor binding sites in brain.

Absorption, Distribution and Excretion of GT31-104, a Novel Bile Acid Sequestrant, in Rats and Dogs After Acute and Subchronic Administration

The absorption, distribution, and excretion of GT31-104, a novel bile acid sequestrant, was studied in rats and dogs after both acute and subchronic oral administration. The polyallylamine backbone of GT31-104 was labeled with tritium and one of the alkyl side chains was labeled with 14C. The mean blood and plasma concentration of [3H,14C]GT31-104 in rats, in both treatment regimens, was negligible at all time points, with the highest amount observed being 0.69 µg eq/g blood; in dogs the mean blood and plasma concentration of [3H,14C]GT31-104 was below the limit of quantitation (<0.001% total dose) at all time points. In both rats and dogs, the mean total urinary excretion of [3H,14C]GT31-104 was ∼0.06% of the total dose. The fecal excretion data indicates that both 3H- and 14C-derived radioactivity was excreted entirely in the feces. Mean total radioactivity excreted in the feces ranged from ∼95 to 105% in the rats and 92 to 102% in the dogs. Across the different treatment regimens, in both species, tissue concentrations were negligible (<0.01% total dose) and no differences in tissue profile were noted, indicating that there was no effect of pretreatment on [3H,14C]GT31-104 absorption. GT31-104 was extracted with water, and the water-soluble portion contained radioactivity that would correlate to 60.19% of the 3H dose and 0.41% of the 14C dose; this portion probably accounted for the negligible radioactivity observed systemically. Analysis of gastrointestinal (GI) tract tissues with contents indicated that GT31-104 is rapidly cleared from the GI tract. These data indicate that GT31-104 is not absorbed from the GI tract in rats and dogs.

Inhibition of hepatic xenobiotic metabolism and of glutathione-dependent enzyme activities by zinc ethylene-bis-dithiocarbamate in the rabbit.

Effects of either a single (300 mg/kg) or a subchronic (0.3 and 0.6% for 70 days) oral administration of a dithiocarbamate fungicide (zinc ethylene-bis-dithiocarbamate, zineb) on hepatic drug metabolism and on the activity of several glutathione-dependent enzymes were investigated in male New Zealand White rabbits. While a pronounced reduction in the rate of oxidative biotransformations occurred after either single or repeated exposure, both cytochrome P450 and total haem content were lowered following acute challenge to zineb. None of the experimental protocols affected microsomal carboxylesterase but induced a marked increase in glutathione content and none of the examined glutathione-dependent enzymes was altered by the single administration of zineb, whereas the subchronically exposed rabbits showed a fall in the activities of both total glutathione S-transferase and selenium-independent glutathione peroxidase. In the 0.6% treated animals, a decrease in class mu glutathione S-transferase and glyoxalase I, and an increase in thiol-transferase activities were also recorded. It is concluded that (1) zineb is able to selectively impair oxidative drug metabolism with possible different mechanism(s) according to the duration of the exposure, (2) only the subchronic treatment affects glutathione-dependent enzymes, (3) the decrease in glutathione S-transferase activity would seem to be ascribed to a direct interaction with the fungicide.

Hepatic involvement of two chlorinated propenes following repeated oral exposure in the rat

The comparative toxicity of two chlorinated propene isomers, 1,2,3-trichloropropene (TRCP) and 1,1,2,3-tetrachloropropene (TECP), was investigated via subchronic oral administration to rats for 4 weeks. Test groups, each consisting of 5 male and 5 female rats, were exposed to 0, 3, 10, 30, 100 or 300 mg/kg/d TRCP or TECP by gavage. A separate corn oil control group was used for each chloropropene. While all rats of both sexes given 300 mg/kg/d TRCP died, only 1 female exposed to 300 mg/kg TECP died. Mean body weights were reduced in male rats given 100 mg/kg/d TRCP. With TECP, dose-related reductions in mean body weight and food consumption were seen at 100 and 300 mg/kg/d. Moderate fatty changes in the livers of high-dose TRCP-treated rats which died during the first study week were probably related to chloropropene exposure. Treatment-related necrotic/degenerative lesions of the liver were seen in both male and female rats administered 300 mg/kg/d TECP.

Assessment of hepatic indicators of subchronic carbon tetrachloride injury and recovery in rats

To determine the course of hepatic recovery from subchronic oral administration of carbon tetrachloride (CCl 4), male F-344 rats were gavaged with 0, 20, or 40 mg CCl 4/kg, 5 days/week, for 12 weeks. Exposure to CCl 4 caused dosage-dependent increases in relative liver weight and the serum levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase, and cholesterol as well as a dosage-dependent decrease in hepatic cytochrome P450. Centrilobular hepatocellular vacuolar degeneration, necrosis, and cirrhosis occurred at both 20 and 40 mg/kg, with dosage-dependent severity. Reversibility of these reported effects varied with parameter. By Day 8 postexposure, necrosis had disappeared and all serum indicators and cytochrome P450 had returned to control levels. By Day 15 postexposure, the severity of the vacuolar degeneration had decreased. Reversibility of cirrhosis was dosage dependent; complete recovery occurred in the low- but not the high-dose group by Day 15. The disappearance of the increase in relative liver weight was also dependent on dosage; the low- but not the high-dose group had returned to the control level by Day 22. In an attempt to measure persistent hepatic damage, liver uptake relative to the spleen was determined for a sulfur colloid labeled with technetium-99m and for tritiated 2-deoxyglucose. Neither method consistently measured hepatic damage in cirrhotic livers due, in part, to the high degree of variability in the tracer uptake data.

Myopathic Alterations in Extraocular Muscle of Rats Subchronically Fed Pyridostigmine Bromide

To determine if alterations in extraocular muscle morphology occur after subchronic oral administration of pyridostigmine bromide, rats were continuously fed 90 mg/kg in meal and examined at 1, 2, 4, 7, and 15 days. Within the first day, blood acetylcholinesterase activity was reduced by 87% and remained inhibited by 74-91% during the study. Light microscopy demonstrated that by day 1 approximately 3% of the extraocular myofibers were shrunken and invaded by inflammatory cells. The most severe degenerative changes consisting of vacuoles and inflammatory cell infiltration occurred at day 1 with progressively less severe changes at days 2 and 4. At days 7 and 15, 1.3-4.5% of the myofibers still exhibited damage. Ultrastructurally, all presynaptic areas were normal but the postsynaptic areas of affected myofibers at days 1, 2, and 4 showed myofilament and Z-band dissolution, mitochondrial inclusions, subneural fold and T-tubule/sarcoplasmic reticulum vacuolization and subneural fold depth reduction. By days 7 and 15, these changes were diminished in some cases and in others alterations appeared similar to day 1. We conclude that subchronic feeding of pyridostigmine bromide induces myopathic rather than neurogenic changes in rat extraocular muscle and that the myopathy is different in these muscles than in the diaphragm from the the same rats.

Tolerance and sensitization to chronic and subchronic oral caffeine: Effects of wheelrunning in rats

Twenty-four male Sprague-Dawley rats were tested for wheelrunning in conjunction with chronic (continuous) or subchronic (alternate day) oral caffeine administration. As expected, chronic administration led to complete tolerance to caffeine's locomotor stimulant effect, while subchronic administration produced sensitization. Results confirm earlier reports of enhanced stimulation with spaced administration of caffeine and tolerance with chronic administration.

Subchronic toxicity evaluation of tridecyl acetate in rats

Tridecyl acetate was administered to male and female Sprague-Dawley rats by oral gavage, 5 days per week for 13 weeks (90 days). Treated rats received daily doses of 0.1, 0.5, or 1.0 g/kg/day and control rats received distilled water at a dose of 1.0 g/kg/day. After 45 days an interim termination was made to evaluate potential hematologic or hepatic effects of tridecyl acetate. Blood samples were collected for routine hematology and serum chemistry determinations and liver tissue was obtained for histological examination. After 90 days all animals were necropsied. Blood samples were obtained and selected organs were weighed and prepared for histological examination. Treatment-related effects observed in the mid and high dose groups consisted of (1) increased liver weights and/or liver/body weight ratios in both sexes at the interim and 13 week termination, (2) increased kidney weights and/or kidney/body weight ratios in both sexes at the terminal necropsy, (3) histopathologic evidence of hydrocarbon nephrophathy in males, and (4) a slight decrease in serum glucose levels in male rats at both the interim and terminal necropsies. The increases in liver weight are believed to be a normal physiological response to a chemical challenge. The nephropathy produced by tridecyl acetate is characteristic of that produced by a diverse group of hydrocarbons and, to date, appears to be limited to male rats. The low dose in this study was a no observed effect level. These results are indicative of an overall low degree of systemic toxicity following subchronic oral administration of tridecyl acetate at doses up to 1 g/kg body weight.

Model systems for detecting the hepatic toxicity of pyrrolizidine alkaloids and pyrrolizidine alkaloid N-oxides

Indicine N-oxide (INO) is a pyrrolizidine alkaloid (PA) with antitumor activity in animals and humans. Prior studies showed that despite the known hepatic toxicity of the PAs, INO did not produce hepatic toxicity in animals but caused unpredictable lethal hepatic toxicity in humans. In this study we have attempted to find a model system for predicting the hepatotoxic potential of antitumor PAs. Primary cultures of rat hepatocytes showed toxicity only with the most hepatotoxic PAs such as lasiocarpine, but did not detect toxicity with other PAs. Subchronic intraperitoneal administration of PAs to weanling rats and adult mice produced, in surviving animals, hepatic megalocytosis and centrilobular necrosis with heliotrine (H) and 9-O-( R(−)-2-(4′-chlorophenyl)-2-hydroxybutyryl)retronecine N-oxide (RC1NO) but only megalocytosis with INO. Thus, despite previous reports, weanling rats offered no advantage over adult mice for detecting significant hepatic toxicity with PAs. Phenobarbital pretreatment of the mice did not increase the hepatic toxicity of any of the PAs. Subchronic oral administration of PAs to adult mice produced hepatic megalocytosis and centrilobular necrosis in surviving animals with H and RC1NO and megalocytosis with INO. Animals that died acutely following oral administration of INO showed hepatic centrilobular necrosis. Administration of several courses of INO intravenously to dogs produced histological evidence of centrilobular hemorrhagic necrosis. It is concluded that there is no single animal model that will predict hepatic toxicity of the type seen in humans with the antitumor PAs. A combination of studies using adult mice and dogs and lethal doses of the PAs offers the best way of detecting potential hepatic toxicity.

Myopathic changes in diaphragm of rats fed pyridostigmine bromide subchronically

To determine if alterations in muscle morphology occur after subchronic oral administration of pyridostigmine bromide, rats were fed 90 mg/kg continuously in meal and examined at 1, 2, 4, 7, and 15 days. Within the first day, cholinesterase activity was reduced by 87% and remained inhibited by 74–91% for the entire course of the feeding. Light microscopy demonstrated that by the first day approximately 1 in 100 myofibers was shrunken and contained centralized nuclei. Electron microscopic examination showed that white presynaptic areas of neuromuscular junctions were relatively unaffected by this dose, postsynaptic areas invariably showed maximal changes. Ultrastructural alterations included disruption of myofilaments, mitochondrial changes consistent with accumulation of calcium, and nuclear alterations. These effects appeared not to be cumulative and were greatly diminished by 15 days even under constant drug administration and inhibition of cholinesterase activity. We conclude that subchronic feeding of pyridostigmine bromide induces primarily myopathic rather than neurogenic changes in the diaphragm and that some mechanism of accommodation may be activated that minimizes continued muscle injury.