Subacute Doses Research Articles

Antispermatogenic effects of cyclophosphamide in the Syrian hamster.

Cyclophosphamide is an alkylating antineoplastic drug and has been shown to impair spermatogenesis after chronic exposures. The purpose of this investigation was to determine the effect of cyclophosphamide on sperm production in hamsters following subacute intraperitoneal (ip) exposures. The Syrian hamster, Mesocricetus auratus, aged 10-11 wk, received single daily ip doses for 4 d ranging from 10 to 250 mg cyclophosphamide/kg body weight. Control hamsters received an equivalent volume of phosphate-buffered saline solution. Testis weight, caudal sperm number, and sperm morphology were monitored for 12 wk. Cyclophosphamide failed to induce sperm abnormalities. Testis weight and sperm count were slightly suppressed at wk 1 and 4 before returning to normal at wk 12. This study showed that subacute doses of cyclophosphamide in hamsters did not significantly affect the sperm production as previously reported in other animals.

Attenuation of phenobarbital-induced deficits in coordinated locomotion during subacute exposure.

The effects of phenobarbital on coordinated locomotion were measured in rats trained to criterion to avoid electric shock by running treadmill fashion along a motor driven belt. Two phenobarbital groups (35 and 50 mg/kg) and saline controls were injected for 29 consecutive days. Testing was carried out on Drug Days 1, 15, and 29. On Drug Day 1, disturbances in gait and balance were reflected by an increased time off belt for the phenobarbital groups. In addition, both groups demonstrated a significant improvement in performance over the three 2-min trial test sessions. Deficits were further reduced on Drug Day 15, and by Drug Day 29, the performance of rats treated with 35 mg/kg was equivalent to control values while that of the 50 mg/kg group had improved by more than 90%. There was no corresponding change in plasma levels of phenobarbital during subacute dosing. After a one month drug withdrawal period, treatment with phenobarbital again produced coordination deficits which were equivalent to those seen on Drug Day 1. These data demonstrate that an attenuation of the effects of phenobarbital on coordination can begin within minutes of the initial test session and is most likely due to behavioral processes (i.e., acute functional tolerance). In addition, results suggest that further drug exposure may play a role in the carry-over of functional tolerance from one drug test session to the next.

The effects of maternal murine cytomegalovirus infection on the mouse conceptus at different gestational stages.

The effects of murine cytomegalovirus (MCMV) on the prenatal development of the CD-1 mouse were investigated. Two sets of experiments were performed. In the first, mice were inoculated with different doses of MCMV on gestational day 7, and in the second, pregnant animals were inoculated with a subacute injection dose at different gestational stages. The effects of maternal infection on pregnancy in terms of maternal sickness, embryo lethality, date of parturition, litter size, postnatal death, and pups' body weight on d 1 and d 3 postpartum were investigated. High-dose MCMV infection on d 7 of pregnancy resulted in a significant increase in early embryo resorption and also in a reduction of the neonatal body weight of surviving pups. Two gestational stages were identified as being especially susceptible to MCMV infection. Most embryonic death as indicated by resorption rates was found after treatment on d 9, whereas perinatal death was most frequent when treatment was done on d 13 of gestation. Still births and neonatal death within 24 h of birth were found commonly in this latter group, which also showed the most pronounced growth retardation. The phenomenon of delay in time of parturition was noted and found to be most significant in groups of animals that were inoculated on d 3 or d 13. This investigation suggests that the effects of MCMV on the CD-1 mouse vary greatly with the age of the embryo and the course of the infection.

Evaluation of genotoxic potential of khat (Catha edulis) in Swiss albino mice.

Genotoxicity of the methanolic extract of khat (Catha edulis) has been evaluated on the male germ cells using the dominant lethal assay procedure in Swiss albino mice. The extract was administered at a dose of 500 mg/kg orally once daily, for five days. Following this sub-acute dose regimen, the effect of khat was studied during the different stages of spermatogenic cycle on the rate of pregnancy and post-implantation losses. Khat reduced the percent pregnancy rates and increased the mean post-implantation losses in the treated group. The increase was found to be statistically significant in the post-meiotic stages.

Cerebral citric acid cycle enzymes in methionine sulfoximine toxicity.

The activity levels of pyruvate dehydrogenase, enzymes of the citric acid cycle, aspartate and alanine aminotransferases, and NADP+-isocitrate dehydrogenase were determined in the cerebral cortex, cerebellum, brain stem, corpus striatum, hippocampus, and midbrain regions of normal rats and rats injected with acute and subacute doses of methionine sulfoximine (MSI). In both conditions there was an elevation in the activities of pyruvate dehydrogenase and all the enzymes of the citric acid cycle except malate dehydrogenase, whereas the activities of aminotransferases and NADP+-isocitrate dehydrogenase were suppressed in all the cerebral regions. It is suggested that the operational rates of the citric acid cycle would be enhanced in MSI-induced hyperammonemia and that there might be a derangement in the transport of reducing equivalents across mitochondrial membranes. It has been suggested that the convulsant action of the drug is due to its effects on ionic gradients and may not be due to depletion of alpha-ketoglutarate from the citric acid cycle.

Suppression of the enzymes of glutamate metabolism in cortical synaptosomes in methionine sulfoximine toxicity

Enzymes of glutamate metabolism were studied in synaptosomes prepared from normal rats and those treated with acute (300 mg/kg) and subacute (150 mg/kg) doses of the convulsant methionine sulfoximine (MSO). The activities of glutamine synthetase, glutamate dehydrogenase and aspartate aminotransferase were inhibited in the synaptosomes of drug treated animals. It is suggested that MSO would suppress the formation of glutamine and glutamate and consequently the releasable pool of glutamate, aspartate and GABA. These neurotransmitters would be depleted irom the nerve endings. It is also indicated that the ammonia accumulated would affect the cerebral functioning by interfering with the maintenance of ionic gradients.

A social interaction model of anxiety sensitive to acutely administered benzodiazepines

AbstractActive social interaction (SI) and aggression (AGG) were recorded separately during 5‐min observation periods of pairs of male Wistar rats. There was little difference between the levels of SI in undrugged animals across ten different experimental conditions, involving the manipulation of environmental and social stimuli. When animals were housed and tested together, no increases in SI were observed with acute administration of chlordiazepoxide (CDZP, 8 mg/kg PO) irrespective of other environmental changes. When the only potentially anxiogenic stimulus used was a novel partner, a large increase in SI was observed with CDZP. With the exception of strong lighting, combinations of this and other stimuli resulted in smaller increases. When animals were housed and familiarized together but tested with a novel partner, the large increase in SI induced by CDZP was not associated with changes in locomotor activity and was maintained after subacute dosing when decreases in motor activity were absent. Furthermore, similar increases were observed with other benzodiazepines after acute administration in this protocol. This modified method of SI in the rat is more sensitive to the anxiolytic activity of benzodiazepines leading to their detection after acute administration.

Intoxication with four synthetic pyrethroids fails to show any correlation between neuromuscular dysfunction and neurobiochemical abnormalities in rats

The neurological effects of four synthetic pyrethroids resmethrin, permethrin, cypermethrin, and deltamethrin have been investigated in the rat to establish whether there is a correlation between the clinical-functional status of the animal and peripheral nerve damage as measured biochemically. Neuromuscular dysfunction was assessed by means of the inclined plane test and peripheral nerve damage by reference to beta-glucuronidase and beta-galactosidase activity increases in nerve tissue homogenates from treated and control animals. A transient functional impairment was found in animals treated with any one of the four pyrethroids tested and in all cases this was maximal at the end of the 7 day subacute dosing regimen. Significant increases in beta-glucuronidase and beta-galactosidase were found 3-4 weeks after the start of dosing in the distal portion of the sciatic/posterior tibial nerves from permethrin, cypermethrin, and deltamethrin treated animal; but no changes were found in remesthrin-dosed animals. It is concluded therefore, that there is no direct correlation between the time-course of the neuromuscular dysfunction and the neurobiochemical changes. This suggests that these pyrethroids have at least two distinct actions--a short-term pharmacological effect and at near-lethal dose levels a more chronic neurotoxic effect that results in sparse axonal nerve damage.

Comparisons between carcinogenic potency and mutagenic potency to Salmonell in a series of derivatives of 4-dimethylaminozobenzene (DAB)

8 derivatives of the rodent liver carcinogen 4-dimethylaminoazobenzene (DAB), all of known carcinogenicity in rodents, have been evaluated in the 3 major variants of the Salmonella mutation assay; the standard plate test of Ames et al., the pre-incubation assay of Yahagi et al. and the fluctuation assay of Gatehouse, Altough 4 of these chemicals were reported to be non-carcinogenic, and 4 to be of greater carcinogenic potency than DAB, each was mutagenic in a least 2 of the assays. Furthe, no quantitative correlation between carcinogenic and mutagenic potency was evident in any of the assays employed. The parent carcinogen DAB, 5-dimethylaminophenylazoindazole (a non-carcinogenic bacterial mutagen) and 6-dimethylaminophenylazobenzthiazole (a carcinogen bacterial mutagen) were administered to rats via intraperitoneal injection, followed, 26 h later, by a sub-acute dose of [ 14C]dimethylnitrosamine. The histopathological of the extent and nature of methylation by DMN of the DNA in the livers according to the method of O'Connor. Disturbances in both the pathological and DNA-related parameters were observed for the 2 carcinogens while control levels were seen for the non-carcinogen. Within this context the value of short-term assays conducted in vivo is discussed, especially their potential to identify potent mammalian carcinogens from among a collection of structurally related bacterial mutagens.

Genetic activity of vinylidene chloride in yeast

Vinylidene chloride (VDC) was tested for its ability to induce both point mutation and mitotic gene conversion in a diploid strain (D7) of the yeast Saccharomyces cerevisiae in a suspension test with and without a mammalian microsomal activation system, and in the intrasanguineous host-mediated assay in mice. In suspension tests with D7, VCD was toxic but not genetically active without microsomal activation. When a mouse liver 10000X g supernatant was included in the suspension tests, dose-related increases in both point mutation and mitotic gene conversion were seen at survival levels greater than 50%, at doses of VCD above 20 mM. In the host-mediated assay, VDC induced both point mutation and mitotic gene conversion when recovered from the liver and kidneys after both acute and sub-acute dosing. Yeasts recovered from the lungs showed little, if any, increase in either point mutation or mitotic gene conversion.

Effects of sulphur dioxide on southern bean mosaic and maize dwarf mosaic

Sub-acute doses of sulphur dioxide (SO 2) (either 262 or 524 μ m −3) for 5–10 days caused small but consistent increases in the titre of southern bean mosaic virus (SBMV) in ‘Bountiful’ bean and maize dwarf mosaic virus (MDMV) in maize. Exposure to SO 2 also increased infection and intensified symptoms caused by MDMV. Sulphur uptake by the host plant was not affected by either virus; however, pre- and post-inoculation exposures of bean plants to SO 2 resulted in greater than additive effects on sulphur uptake.

A study on the toxicity and the biochemical effects of ethylene dibromide in the Japanese quail.

1. The acute oral LD50 and chronic LC50 toxicity values for ethylene dibromide (EDB) were estimated for japanese quail. 2. Single sub-acute oral and intraperitoneal doses of EDB (1/2 LD50) and chronic oral doses of EDB (1/3 LC50) were administered to quail in order to characterise the sub-lethal effects of EDB residues. 3. At 24 h after sub-acute dosing, relative liver weight, plasma aspartate aminotransferase (AT) [EC 2.6.1.1] and L-iditol (sorbitol) dehydrogenase (SDH) [EC 1.1.1.14] were elevated and decreases were found in hepatic total lipid, total protein, AT and glutamic dehydrogenase (NAD (P)+) (GDH) and plasma cholinesterase (ChE) [EC 3.1.1.8] and total lipid. 4. Following chronic administration, elevations in relative liver weight, plasma ChE and total lipid, haemoglobin and haematocrit were found and hepatic AT, GDH and total lipid were decreased. 5. The changes in hepatic and plasma enzymes and constituents are discussed in relation to possible biphasic effects resulting from EDB exposure.

Effect of citreoviridin, a mycotoxin from Penicillium citreoviride, on kinetic constants of acetylcholinesterase and ATPase in synaptosomes and microsomes from rat brain

The subcutaneous injection of acute (6 mg/kg) and subacute doses of citreoviridin, a toxin from Penicillium citreoviride NRRL 2579, inhibited brain synaptosomal (Na + + K +)-ATPase whereas in microsomes, both (Na + + K +)-ATPase and Mg 2+-ATPase activities are significantly stimulated in a dose-dependent manner. In vitro, both Mg 2+ and (Na + + K +)-ATPase activities are inhibited in synaptosomal as well as in microsomal fractions. Kinetic parameters obtained from double reciprocal plots indicate that under in vivo conditions citreoviridin increases V max and K m values of microsomal (Na + + K +)-ATPase and Mg 2+-ATPase, whereas in synaptosomes Mg 2+-ATPase, V max and K m are unaltered but (Na + + K +)-ATPase V max is decreased and K m increased. In vitro, both Mg 2+ and (Na + + K +)-ATPase K m values are increased and V max values are decreased in the synaptosomal as well as in the microsomal fractions. On the other hand, AChE V max values are decreased and K m values are increased in the synaptosomes under both in vivo and in vitro conditions. In microsomes, in vivo, the V max values are decreased and K m values are unaltered while in vitro both are unaltered. These results indicate that citreoviridin neurotoxicity may be related to the altered enzymatic activities.

Lethality of sub-acute insecticidal doses to the Japanese beetle

Lethality of sub-acute insecticidal doses to the Japanese beetle

Effects of subacute doses of psychotropic drugs on the sleep cycle in the Cat: Attempt to use a data processing system

An automatic acquisition and processing system for the identification of the sleep cycle states in the freely moving cat, which uses as the only input the electrocorticogram, is described. Its reliability has been verified by comparing the automatic identification process with visual reading of the polygraphic recordings of the generally used parameters. The effects of subacute doses of some benzodiazepines, chlorpromazine, thioridazine and DL 308-IT, a new psychotropic drug under clinical investigation, are also reported.

Synergism of the toxicity of physostigmine and neostigmine by lithium or by a reserpine-like agent (Ro4-1284)

A single sublethal i.p. dose of lithium chloride (300 mg/kg or 7.1 meq/kg) followed 12 h later by an otherwise sublethal s.c. dose of physostigmine sulfate (1.0 mg/kg) resulted in 90% mortality among male rats following a pronounced cholinergic syndrome, including convulsions. This confirms a previous report of a lethal synergism of physostigmine after subacute dosing with lithium. Mortality could be completely prevented by 1.0 mg/kg of atropine sulfate given 3- min before physostigmine, but was incompletely, if at all, reduced by selective peripheral cholinergic blockers, methylatropine bromide (0.5, 1.5 mg/kg) or glycopyrrolate (1 mg/kg). This suggested a predominantly central site for the toxic interaction. However, a similar synergism of lethality caused by neostigmine methylsulfate (0.3 mg/kg, s.c.) after treatment with lithium, which could be eliminated by methylatropine or glycopyrrolate, indicates that lithium may also produce lethal synergism of a cholinesterase (ChE) inhibitor that does not act centrally. Ro4-1284, an agent that has reserpine-like actions, was tested in combination with physostigmine or neostigmine; it showed synergism of toxicity nearly the same as in the case of lithium plus the cholinergic agents. These findings support the hypothesis that lithium causes the toxic synergism via a reduction of adrenergic activity, leading to an imbalance between adrenergic and cholinergic influences and a consequent failure to tolerate the effects of the ChE inhibitors. A potential hazard for the clinical use of physostigmine and neostigmine, concurrently with lithium or reserpine-like agents, it suggested.

Changes in hepatic polyamine levels during acute and chronic administration of aflatoxin B 1 to rats

A subacute dose of aflatoxin B 1 (3 mg/kg body weight) increases liver putrescine levels within 1 hr after administration, with high levels persisting over 24 hr. Higher doses of the carcinogen elicited larger increases in liver polyamine levels. A marked elevation of putrescine, spermidine and spermine were noted in aflatoxin B 1-induced preneoplastic liver. Pretreatment of rats with phenobarbital prior to aflatoxin B 1 administration resulted in no synergistic or additive effects.

Effect of subacute dosing and phenobarbital and 3-methylcholanthrene pretreatment on the metabolism of acetaminophen in rats.

The metabolism of 14C-ring-labelled acetaminophen was studied in male Wistar rats. Pretreatment with phenobarbital increased the initial rate of elimination of 14C from the blood and increased the amount of acetaminophen glucuronide excreted in the urine. Pretreatment with 3-methylcholanthrene did not significantly affect the rate of elimination from the blood and decreased the amount of acetaminophen glucuronide in the urine. Daily dosing with acetaminophen for up to 3 weeks increased the rate of elimination of 14C from the blood after 4 h, and increased the urinary excretion of both total 14C and the glucuronide and sulfate conjugates. Subacute dosing with acetaminophen had a diuretic effect but this did not correlate with the increased excretion of the drug. It is concluded that acetaminophen elimination is increased by phenobarbital pretreatment and by subacute dosing with acetaminophen, but by different mechanisms.

Effects of Stock or Purified Diet on Rat Liver Enzymes Involved in the Synthesis of Dimethyl Selenide

Rats fed either a stock deit or a purified diet based on casein were tested for their ability to convert 75Se-sodium selenite to volatile selenium (dimethyl selenide) in vivo. This conversion was also studied in liver and kidney in vitro. When injected with a subacute dose of selenite (2 mg Se/kg), rats previously fed stock diet volatilized more than twice as much of the dose compared to rats fed the purified diet, confirming earlier findings. Parallel dietary effects were also observed in vitro using subcellular fractions incubated with 75Se-selenite, glutathione, TPNH, and S-adenosylmethionine. The 9-000 X g supernate prepared from rats fed stock diet synthesized dimethyl selenide at approximately twice the rate of that prepared from rats fed purified diet. A fourfold higher activity was observed with liver microsomal fractions from rats fed the stock diet, whereas cytosol was slightly more active in rats fed the purified diet. Kidney fractions showed analogous changes with diet, although the activity of kidney microsomal fraction was very low. Only minor differences in the levels of glutathione reductase, nonspecific disulfide reducatse, and non-protein thiols were observed in liver and kidney from rats fed the two diets. Considering the effects of diet on the various enzymes known from our previous studies to be involved in dimethyl selenide synthesis, it was concluded that the enhanced ability of rats fed stock diet to synthesize dimethyl selenide results from the induction of a liver microsomal enzyme, apparently a Se-methyltransferase, caused by unknown substances in the stock diet.

Dietary fat alteration of plasma cholinesterase response to malathion

This study revealed the influence of organophosphate pesticides on cholinesterase levels of male Sprague-Dawley rats. Subjects were fed fat-free, normal-fat, and high-fat test diets. Sub-acute doses of malathion were given subcutaneously and cholinesterase levels were determined. Malathion was chosen because it is the least toxic of the organophosphate cholinesterase-inhibiting pesticides. Statistical analysis of the data showed that malathion does inhibit blood cholinesterase to the greatest degree in normal-fat diet animals, with the least effect on high-fat groups and fat-free subjects fall in between the two groups.