Target Organ Toxicity and Leukopenia in Fischer 344 Rats Given Intravenous Doses of Vinblastine and Desacetyl Vinblastine

Target Organ Toxicity and Leukopenia in Fischer 344 Rats GivenIntravenous Doses of Vinblastine and Desacetyl Vinblastine.ZIMMERMANN, J. L., TODD, G. C., AND TAMURA, R. N. (1990). FundamAppl Toxicol 17, 482–493. The toxicity and leukopeniaproduced by vinblastine or desacetyl vinblastine were establishedin 1-month studies in rats. Groups of male Fischer 344 ratswere given weekly intravenous doses of vinblastine or desacetylvinblastine at doses of 0.08, 0.16, 0.32, 0.64, or 1.28 mg/kg.The target organ toxicity was similar for both compounds. Decreasedcell production in the thymus, testes, and bone marrow was producedin the animals of the two highest dose groups for both compoundswith the degree of seventy greater in the highest dose group.All high dose rats (1.28 mg/kg) given desacetyl vinblastineand three rats given vinblastine died prior to study termination.Body weight loss was more pronounced in high dose rats givendesacetyl vinblastine, but at lower doses there were no significantdifferences in body weight reduction for rats receiving eithercompound. Leukopenia occurred at all dose levels of 0.32 mg/kgand higher. During the first 2 weeks of the study, rats given1.28 mg/kg of desacetyl vinblastine had a greater leukopenicresponse than rats given 1.28 mg/kg of vinblastine. It is concludedthat both compounds produced similar target organ toxicity andleukopenia without deaths at doses of 0.32 and 0.64 mg/kg givenonce a week for 4 weeks. At the high dose (1.28 mg/kg) desacetylvinblastine was more toxic than vinblastine resulting in greatermortality and body weight reduction.     

Structure-activity relationships of dimeric Catharanthus alkaloids. 1. Deacetylvinblastine amide (vindesine) sulfate.

Exploration of the effects of "minor" structural differences on the antitumor activity and toxicity of dimeric Catharanthus alkaloids resulted in the preparation of deacetylvinblastine amide (vindesine, VDS) from either vinblastine (VLB) or deacetylvinblastine. Adequate amounts of vindesine for biological testing were prepared by preferential hydrazinolysis of the C23-ester in the vindoline moiety of VLB, followed by hydrogenolysis of the resulting deacetylvinblastine hydrazide. Vindesine in its activity spectrum against rodent tumor systems resembles vincristine (VCR) rather than its parent VLB, while its neurotoxic potential appears to be less than that of VCR. The experimental models developed to estimate this potential include in vitro measurements of axoplasmic transport effects in the cat sciatic nerve and the estimation of neuromuscular disturbances in chickens and monkeys by vindesine in comparison with VCR. A radioimmunoassay for VLB, VCR, and VDS, developed by means of deacetylvinblastine acid azide, has been used to study the pharmacokinetics of vindesine in man. The clinical investigation of vindesine is in progress. Deacetylvinblastine, in contrast to earlier reports, showed activity against several murine tumor systems.     

Toxicology of indecainide hydrochloride after intravenous administration to rats and dogs

Subchronic 1-month intravenous toxicity studies on indecainide, an antidysrhythmic agent, were conducted in rats and dogs. Rats (10 males, 10 females/group) were given daily intravenous (i.v.) doses of 0, 3, 6, or 9 mg/kg of indecainide for 1 month. 6 Of 10 males and 1 of 10 females given 9 mg/kg died during the test period. All but 2 animals from the other test groups survived. The high end of these daily doses was close to the acute single lethal dose, and the deaths were not unexpected. There were no treatment-related hematologic or serum chemistry changes in the surviving animals. No treatment-related histopathologic changes occurred in any of the animals. Groups of dogs (2 males, 2 females per group) were given daily i.v. injections of 0, 1.5, 3, or 4.5 mg/kg of indecainide for 1 month. 2 Of 4 dogs died after receiving multiple daily doses of 4.5 mg/kg. No treatment-related histopathologic changes were present in these animals. Dogs given doses of 1.5 or 3 mg/kg tolerated daily injections of the compound with no overt signs of toxicity and without hematologic, serum chemistry or histologic changes. Electrocardiograms revealed prolonged PR, QRS, and QT intervals in dogs from all three dose groups. Rats and dogs tolerated daily intravenous doses of indecainide as high as 6 and 3 mg/kg, respectively, with no evidence of any effect of treatment except the expected pharmacological action on the myocardium.     

Experimental systemic toxicology of 4'-epidoxorubicin, a new, less cardiotoxic anthracycline antitumor agent

The acute and chronic iv toxicity of 4'-epidoxorubicin, a new antitumor anthracycline antibiotic, was compared with doxorubicin. The LD50 of 4'-epidoxorubicin was 16.07 mg/kg in mice, 14.27 mg/kg in rats, and about 2 mg/kg in dogs; the LD50 of doxorubicin was 11.98 mg/kg in mice, 10.51 mg/kg in rats, and about 2.5 mg/kg in dogs. Rats and dogs were also dosed iv for 91 days (3 injections/week) with 4'-epidoxorubicin or doxorubicin at doses of 0.128, 0.32, and 0.8 mg/kg to rats and 0.064, 0.16, and 0.4 mg/kg to dogs. A comprehensive toxicological evaluation of the animals was carried out before, throughout, and at the end of the study. High-dose 4'-epidoxorubicin induced toxic clinical signs in dogs, and in both species caused loss of body weight, antiproliferative effects on blood-forming organs and testes, and degenerative lesions in kidneys and heart. The cardiac damage was moderate in rats and very mild in dogs; only three male rats died at this dose. The medium dose induced less pronounced changes and no heart lesions and the low dose was practically nontoxic. Doxorubicin showed similar antiproliferative activity, but more evident toxic effects, especially on the heart; many rats given the high dose died and some at the medium dose showed initial cardiac lesions. Thus 4'-epidoxorubicin appeared less toxic than doxorubicin; in particular cardiac damage was much less evident in animals chronically injected with the new drug.     

Toxicity of intraperitoneally administered antitumour drugs in athymic rats

The toxicity of eight anticancer drugs given intraperitoneally to athymic rats was investigated to define the maximum tolerable doses (MTD). Drugs were given once weekly. Toxicity was assessed as percentage loss of body weight (LBW%) or percentage toxic death rate (TDR%) during the first week after drug administration. LBW% and TDR% were significantly correlated, r = 0.58 p less than 0.00001. From the regression equation for the relationship between LBW% and TDR%, 10 percent TDR (LD10), usually regarded as equivalent to MTD in animals, was found to correspond to 14 percent LBW. From the individual regression equations for LBW% and dose for each of six drugs, MTDs were calculated to be as follows; doxorubicin 7 mg/kg, cyclophosphamide 100 mg/kg, mitomycin C 1.8 mg/kg, cisplatin 8 mg/kg, vindesine 0.8 mg/kg and vincristine 0.9 mg/kg. LD10 was found to be 40 mg/kg for both carmustine (BCNU) and etoposide.     

Bromocriptine self-administration and bromocriptine-reinstatement of cocaine-trained and heroin-trained lever pressing in rats

Rats were trained to lever press for intravenous cocaine (1.0 mg/kg/injection) and then switched to bromocriptine (0.3, 1.0, or 3.0 mg/kg/injection) on a FR-1 reinforcement schedule. Bromocriptine sustained responding at all three doses; hourly drug intake increased linearly with log-dose. In a second experiment, animals were trained to respond for cocaine (1.0 mg/kg/injection) or heroin (0.1 mg/kg/injection) reinforcement; drug was available for the first 2 h of each daily session; saline was substituted for cocaine or heroin for 5 subsequent hours. One hour into each saline substitution session, an intravenous injection of saline or bromocriptine (0.0, 0.5, 1.0, or 2.0 mg/kg) was given. Bromocriptine reinstated both cocaine-trained and herointrained lever pressing; under these conditions, the drug was most effective in the heroin-trained animals. Reinforcing doses of clonidine (0.0625 and 0.125 mg/kg), methohexital, and nicotine (0.05 and 0.1 mg/kg), and a sub-intoxicating dose of ethanol (2 g/kg) failed to reinstate cocaine-trained responding. These data indicate that bromocriptine has cocaine-like and heroin-like stimulus and reinforcing effects.     

Disruptions of the hypothalamo-pituitary-adrenal axis increase anticancer drug lethality in the rat

We have previously shown that toxicity of the anticancer agent hydroxyurea (HU) in the rat is markedly increased by hypophysectomy or adrenalectomy. In this study, we investigated whether increased toxicity in ablated animals is a unique feature of HU or it is shared with other anticancer agents; the toxic effects of five such drugs have been compared in intact, hypophysectomized (HYX) and adrenalectomized (ADX) rats. Bis-chloroethyl-nitrosourea (BCNU, 5–10 mg/kg), busulfan (0.1–10 mg/kg), cyclophosphamide (25–125 mg/kg), 5-fluorouracil (15–75 mg/kg) and vindesine (0.1–0.5 mg/kg) were given to intact and endocrine-ablated rats, and lethality was recorded over 3 weeks. It was found that mortality was low or absent in intact rats, whereas (with the exception of HYX rats receiving the highest dose of busulfan) it was dramatically increased by both hypophysectomy and adrenalectomy. However, replacement treatments with long-acting tetracosactrin and corticosterone to HYX and ADX rats respectively afforded significant protection against BCNU toxicity only. We conclude that the integrity of the hypothalamo-pituitary-adrenal axis is needed to tolerate the toxicity of various anticancer drugs, although complex mechanisms appear to underlie such protective effect.     

Acute and subchronic toxicology of LY-195115 in rats and dogs

LY-195115 is a new (investigational) inotropic agent. When given orally to either young adult rats or mice, single doses of 2500 or 5000 mg/kg were tolerated with minimal lethality. Clinical signs included muscle weakness, hypoactivity, and evidence of hemorrhage. Dogs and monkeys survived a single oral dose of 10 and 5 mg/kg, respectively; however, there was sinus tachycardia for 6-8 h post dose in both species. Rats (20/sex/group) were fed diets containing LY-195115 in concentrations of 0, 0.005, 0.025, or 0.1% for 3 months. The average daily intake of the compound was approximately 0, 3.5, 17, or 70 mg/kg in both sexes. Deaths occurred only in the high-dose group. Body weight gain, food consumption, and efficiency of food utilization were significantly reduced in males in the 0.1% dose group and animals of both sexes in this group had changes in hematology, clinical chemistry, and urinalysis parameters indicative of renal damage. Crystals containing LY-195115 were present in the urine of animals from the 0.025% and 0.1% treatment groups. Secondary hydronephrosis due to kidney stone formation was observed on gross and microscopic pathologic evaluation in the males of the 0.025% group and animals of both sexes in the 0.1% group. In addition, periarteritis was present in the adventitia and muscularis of small and medium-sized arteries in the pancreas, lymph node, kidney, and stomach of some animals in all LY-195115 treatment groups. No overt signs of toxicity were produced in beagle dogs (4/sex/group) given daily oral doses of 0.03, 0.12, or 0.5 mg/kg of LY-195115 for 3 months. The only adverse effect was the occurrence of focal subendocardial fibroplasia in the heart in 2 high-dose male dogs. Thus, subchronic exposure of rats to doses of LY-195115 as high as 70 mg/kg produced minimal mortality, renal toxicity, and mild, limited vascular changes, while dogs tolerated doses up to 0.5 mg/kg with no evidence of any effect of treatment except minimal histological changes in the heart consequent to the expected cardiotonic action of the compound.     

Lack of carcinogenicity of chlorpyrifos insecticide in a high-dose, 2-year dietary toxicity study in Fischer 344 rats.

Chlorpyrifos (CPF) was administered daily in the feed to evaluate toxicity and oncogenicity potential in male and female Fischer 344 rats, according to U.S. EPA guidelines. Doses for the 2-year study were based on findings in a 13-week feeding study in which lower body weights, urinary perineal staining, adrenal cortical vacuolization, and inhibition (slightly more than 60%) of brain cholinesterase (ChE) occurred at 15 mg/kg/day. The high dose in the subsequent 2-year study was 10 mg/kg/day, with lower doses of 0, 0.05, 0.1, or 1.0 mg/kg/day chosen to define dose-response patterns. Rats given 10 mg/kg/day for 2 years were healthy and there was no evidence of premature deaths. Mild toxicity occurred only in rats given 10 mg/kg/day and consisted of perineal urine soiling in females and a 6-8% body-weight decrease in males. Males given 10 mg/kg/day also had increased adrenal weights and vacuolation of the adrenal zona fasciculata. ChE was considered a measure of exposure. Plasma, RBC, and brain ChE activities were inhibited in rats given 10 mg/kg/day, and the plasma and RBC ChE activities were inhibited in rats given 1.0 mg/kg/day. Chronic exposure to 0.1 mg/kg/day was considered a threshold exposure level for inhibition of plasma ChE. Rats given 10 mg/kg/day, considered a maximum-tolerated dose, had approximately 60% chronic inhibition of brain ChE. This group had similar numbers and types of neoplasms as control rats. Consequently, CPF was not carcinogenic at dose levels up to 10 mg/kg/day.     

Vinblastin-23-oyl amino acid derivatives: chemistry, physicochemical data, toxicity, and antitumor activities against P388 and L1210 leukemias

The dimeric alkaloids vinblastine (VLB) and vincristine (VCR) differ structurally only in the functional group on the dihydroindole nitrogen. The semisynthetic derivative vindesine (VDS) differs slightly from VLB by having an amide group instead of an ester group. However, these minor distinctions are responsible for profound differences in the oncolytic spectrum, potency, and toxicity of these compounds. Vinblastin-23-oyl amino acid derivatives were synthesized by linking amino acid carboxylic esters to the vinblastin-23-oyl moiety through an amide linkage. Studies were extended to explore the influence of the nature of the amino acid, the ester alkyl chain lengths, the stereoisomerism of the amino acid, or the reacetylation of the hydroxyl group (position O-4) of the vindoline moiety. The present study deals with the synthesis of 21 vinblastin-23-oyl amino acid derivatives, some of their physicochemical data, the acute toxicity in mice, and therapeutic activities of these derivatives against the P388 and L1210 leukemias in comparison with VDS, VBL, and VCR.     

Preclinical toxicologic evaluation of nadolol, a new beta-adrenergic antagonist.

Nadolol, 2,3-cis-5-[3-[)1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,2,3,4-tetrahydro-2,3-naphthalenediol, is a potent new β-adrenergic blocking agent that has undergone extensive safety evaluation in animals. In 1-month parenteral studies, no signs of toxicity were observed in rats given as much as 25 mg of nadolol/kg daily ip or in dogs given 12.5 mg/kg daily iv. Nadolol did not produce signs of toxicity in monkeys given daily oral doses of up to 250 mg/kg for 3 months. Mice and rats given daily doses of 500 and 1000 mg/kg, respectively, in the diet in 2-year studies showed no evidence of toxicity or carcinogenicity. In a 1-year oral study in dogs, nadolol was administered at daily doses of 24, 60, and 150 mg/kg. The only significant effect observed was a slight, dose-related decrease in tolerance to an intravenous glucose load. Nadolol produced no significant changes in a fertility and reproductive study in rats and in teratologic studies in rats and hamsters at daily doses of up to 300 mg/kg. In rabbits, nadolol was embryotoxic and fetotoxic at 100 and 300 mg/kg, but not at 50 mg/kg. No significant effects were noted in an oral perinatal and postnatal study in rats with doses of up to 1800 mg/kg. There were no indications of teratogenicity resulting from the administration of nadolol to any of the species studied. The results of these studies indicate that nadolol has a low order of toxicity and lacks teratogenic and carcinogenic potential in the species studied.     

Adrenal steroid release by vinblastine sulfate and its contribution to vinblastine sulfate effects on rat thymus

Measurement of plasma 11-hydroxycorticosteroid levels after vinblastine sulfate (VLB) injection (1 mg/kg) into nonadrenalectomized rats showed that corticosteroid levels were elevated by a factor of two over control level within 3 hr after injection, increasing to a factor of four within 12 hr. Since adrenal steroids were known to cause thymic involution associated with an inhibition of nucleic acid synthesis, VLB effects on thymus were compared in adrenalectomized and nonadrenalectomized rats. VLB (0.33–1.0 mg/kg) caused thymic weight loss in adrenalectomized rats. Incorporation of [¹⁴C]thymidine and [³H]uridine into cold-acid-insoluble material by thymocytes, obtained from adrenalectomized rats after they had been injected with similar doses of VLB, was also inhibited. The magnitude of each of these effects was similar to that seen in nonadrenalectomized rats. It was concluded that adrenal steroid release did not play a major role in the thymolytic effects of VLB. Adrenalectomized rats were shown to be more sensitive to the lethal effects of VLB than were nonadrenalectomized rats. Small doses of cortisol administered simultaneously with VLB could protect rats from the lethal effects of this agent.     

Concerted role of carboxylesterases in the potentiation of carbofuran toxicity by iso-OMPA pretreatment

Pretreatment of rats with the nonspecific esterase inhibitor iso-OMPA (1 mg/kg sc) 1 h prior to carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl N-methylcarbamate, 0.5 mg/kg sc) administration potentiated carbofuran toxicity by more than threefold. Neither iso-OMPA nor carbofuran in the given doses produced any gross toxic signs. Rats receiving combined treatment, however, showed severe hypercholinergic signs (salivation, tremors, muscle fasciculations, and convulsions) within 5-10 min following carbofuran administration, and the severity was comparatively greater than that observed with an acute dose of carbofuran (1.5 mg/kg sc). Rats pretreated with iso-OMPA (0.5 mg/kg) died within 10-15 min following the acute dose of carbofuran (1.5 mg/kg). Each drug when given alone (1.0 mg/kg iso-OMPA, 0.5 mg/kg carbofuran) caused a significant (p less than .01) inhibition of carboxylesterase (CarbE) activity in brain structures (cortex, stem, striatum, and hippocampus), skeletal muscle (hemidiaphragm), liver, and plasma, whereas acetylcholinesterase (AChE) activity remained significantly (p greater than .01) unchanged. The maximal CarbE inactivation in plasma (less than 14% remaining activity) following either drug indicated a tremendous nonspecific binding to non-AChE serine-containing enzymes. iso-OMPA pretreatment markedly potentiated carbofuran's anticholinesterase activity both in neuronal and in nonneuronal tissues. It can be concluded that iso-OMPA pretreatment potentiates carbofuran toxicity either by preventing nonspecific binding of carbofuran to CarbE and/or possibly by inhibiting its detoxification.     

Preliminary toxicity studies on bis-[beta-(N,N-dimorpholino) ethyl] selenide (MOSE). A new radioimaging agent

The present study describes the acute toxicity of MOSE, a proposed radioimaging agent for brain scintigraphy . Acute intraperitoneal administration of MOSE in mice revealed an LD50 between 1.35 and 6.25 g/kg, with convulsions preceding death. Intravenous administration of MOSE in rats resulted in an LD50 between 400 and 800 mg/kg, with death also preceded by convulsions. The rabbit was more sensitive to the acute effects of MOSE than the rat. The LD50 for MOSE given i.v. in the rabbit was 80 mg/kg. The predominant toxic sign was convulsions, which immediately preceded death at high doses. At intermediate doses convulsions were elicited, followed by a period of lethargy which gave way to hyperactivity on the following day. Normal appearances were restored within a week. Hematology and blood chemistries were similar to controls, except for increased serum LDH in animals receiving MOSE when sampled two weeks after dosing. Repeated administration of MOSE by the intravenous route in rabbits at a dose rate of 1 mg/kg/da, five days per week for two weeks, resulted in no signs of toxicity. Hematology, clinical chemistry, and histology revealed no changes in animals receiving MOSE when compared to control. It was concluded that barring any unusual susceptibility in man, the proposed diagnostic dose to man is unlikely to precipitate any acute toxic effects.     

Cefepime (diHCl/L-arginine blend): intravenous continuous infusion and/or single dose subcutaneous toxicity study in rats and dogs]

To investigate single dose toxicity of cefepime (CFPM diHCl/L-arginine blend), the test drug was administered to rats [Crj: CD (SD)] of both sexes at dose levels of 500, 1,000 and 2,000 mg/kg using intravenous continuous infusion or subcutaneous injection, and to male beagle dogs at 1,000 and 2,000 mg/kg using intravenous continuous infusion. As the control, two additional groups of each animals were given either saline or L-arginine alone which was used in the test formulation to adjust pH values of CFPM diHCl solutions. The obtained results are summarized as follows: 1. Rats dosed with 2,000 mg/kg CFPM through intravenous continuous infusion showed slightly decreased spontaneous physical activity. One male rat dosed with L-arginine alone via continuous infusion also showed slightly decreased activity. Slight to severe inflammatory reactions at injection sites including sloughing of the tail were prominent at doses of 1,000 or 2,000 mg/kg of CFPM, or L-arginine alone. Average body weights of rats in the test groups of either sex were comparable to the controls in all of the dose groups of the same sex during the 14-day test period. 2. Rats receiving 2,000 mg/kg CFPM in single subcutaneous injection showed slightly diminished activities. Slight to moderate reactions occurred around the injection site (viz., hardening, depilation, scab-formation and necrosis) in rats injected any of the 3 doses of CFPM. Though body weight gains were slightly retarded in male rats receiving 2,000 mg/kg CFPM during the last half of the observation period, such weight gain retardation was not observed in rats of other dose groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of unit dose and route of administration on self-administration of morphine

Rats were implanted with intravenous or intragastric cannulas and allowed to self-administer morphine sulfate in doses of 0 (saline), 0.03, 0.1, 0.3, 1.0, 3.0, and 10.0 mg/kg/infusion. For the intravenous route the number of infusions decreased with increasing unit dose, while the amount self-administered was directly related to unit dose. However, for the intragastric route the number of infusions first increased and then decreased as unit dose was elevated, while the amount self-administered again increased with unit dose. Comparisons between routes showed that for intragastric subjects the number of infusions and amount self-administered both were lower at the two lowest doses but higher for all other doses. These results support the expectation that intravenous injection should produce more potent reinforcing effects than intragastric administration.     

In vivo and in vitro pharmacokinetics and metabolism of vincaalkaloids in rat. II. Vinblastine and vincristine

Vinblastine and Vincristine pharmacokinetics, including tissue distribution, metabolism and biliary excretion, were investigated, using both "in vitro" and "in vivo" models, after i.v. injections in rats. Plasma kinetic curves were best fitted to a two-compartment open model. The average terminal half-lives of VLB and VCR were 14.3 h and 7.5 h, respectively. The systemic clearance and apparent distribution volume for VLB, respectively 1.49 l/h/kg and 11.46 l/kg, were significantly greater than those of VCR, 0.12 l/h/kg and 0.41 l/kg. VCR was found to be widely distributed in tissues after i.v. injections in rats. The highest drug accumulation site was the intestine (122.0 ng/g wet tissue at 24 h). Liver and kidneys also retained high proportions of drug (respectively, 47.0 ng/g and 44.4 ng/g at 24 h). Biliary excretion was more rapid for VCR (42.7% of total radioactivity excreted over 24 h) than VLB (28.2% of total dose over 24 h). For both molecules, the percentage of radioactivity excreted in bile over 30-48 h ranged between 40-50% of total dose. At high doses, either biliary excretion rate or cumulated excretion was reduced. High performance liquid chromatography analysis of bile samples revealed four biotransformation products for VLB and three for VCR. When incubated in freshly isolated rat hepatocytes, VLB penetrated more rapidly and intensely into the cells (more than 90% of total dose taken up over 20 min) than VCR (only about 40% accumulated), probably through a passive diffusion mechanism followed by tight cellular binding. "In vitro" metabolism patterns were similar to those found "in vivo", except for the most polar metabolites observed "in vitro". Two anti-Vinca monoclonal antibodies with different specificities were used to test VCR metabolite immunoreactivities. The results suggested that some structural modifications occurred in the catharantine moiety of the molecule but that the dimeric structure seemed to be well conserved after biotransformation.     

Testicular toxicity in F344 rats by aminophenylnorharman, formed from norharman and aniline.

9-(4'-Aminophenyl)-9H-pyrido[3,4-b]indole [aminophenylnorharman (APNH)] is a novel mutagenic heterocyclic amine, produced by the reaction of norharman with aniline in the presence of S9 mix. In the present study, the acute toxicity of this compound was investigated in male F344 rats. Ten-week-old animals were treated with a single intragastric injection of APNH at doses of 45 or 90 mg/kg body wt and euthanized 1, 3, or 6 days afterward. When APNH was administered at a dose of 90 mg/kg, vacuolation of Sertoli cells in the testis was seen at 1 day after treatment. The testicular damage had markedly progressed by day 6, with multinucleated giant cells and loss of round spermatids in the seminiferous tubules observed in groups 1 and 2 of the four histological categories of spermatogenesis. Numbers of spermatogonia were also decreased by APNH treatment. No toxic changes were observed in Leydig cells under these conditions and serum follicle-stimulating hormone and luteinizing hormone concentrations were also unchanged from control values. Such severe testicular damage was not observed at any time point at the 45 mg/kg dose level of APNH. Moreover, neither norharman nor aniline alone exerted acute testicular toxicity at doses equivalent to 90 mg/kg of APNH. In addition to the testicular lesions, erosive changes of urinary bladder, thymic atrophy, and panmyelophthisis were evident in rats given APNH at 90 mg/kg.     

HIGHLIGHT: Dose-Dependent Metabolism of Benzene in Hamsters, Rats, and Mice

The disposition of oral doses of [¹⁴C]benzene was investigatedusing a range of doses that included lower levels (0.02 and0.1 mg/kg) than have been studied previously in rat, mouse,and in hamster, a species which has not been previously examinedfor its capacity to metabolize benzene. Saturation of metabolismof benzene was apparent as the dose increased, and a considerablepercentage of the highest doses (100 mg/kg) was exhaled unchanged.Most of the remainder of the radioactivity was excreted as metabolitesin urine, and significant metabolite-specific changes occurredas a function of dose and species. Phenyl sulfate was the predominantmetabolite in rat urine at all dose levels (64–73%) ofurinary radioactivity), followed by prephenylmercapturic acid(10–11%). Phenyl sulfate (24–32%) and hydroquinoneglucuronide (27–29%) were the predominant metabolitesformed by mice. Mice produced considerably more muconic add(15%), which is derived from the toxic metabolite muconaldehyde,than did rats (7%) at a dose of 0.1 mg/kg. Unlike both ratsand mice, hydroquinone glucuronide (24–29%) and muconicacid (19–31%) were the primary urinary metabolites formedby hamsters. Two metabolites not previously detected in theurine of rats or mice after single doses, 1,2,4-trihydroxybenzeneand catechol sulfate, were found in hamster urine. These dataindicate that hamsters metabolize benzene to more highly oxidized,toxic products than do rats or mice.     

Low doses of naloxone and MIF-1 peptides increases fluid consumption in rats

Three studies were done with albino rats to determine the effects of low doses of opiate antagonists on fluid intake. In Experiment 1, male rats were deprived of water for 12 hr and then randomly injected IP with 0.0, 0.01, 0.1, 1.0 or 10.0 mg/kg of naloxone. Ten min later they were given free access to a 20% sucrose solution and consumption was measured for the next 30 and 60 min on 2 consecutive days. Only animals injected with 1.0 or 10.0 mg/kg drank significantly less than controls. The other doses were not reliably different from controls but on Day 1 animals injected with 0.01 mg/kg of naloxone drank slightly more than controls. Experiment 2 followed the same procedure with lower doses of 0.0, 0.001, 0.01, and 0.1 mg/kg of naloxone. Although the effect of 0.1 mg/kg of naloxone was again not significant, this time animals injected with 0.001 and 0.01 mg/kg of naloxone consumed reliably more fluid than controls. Experiment 3 extended the findings to a peptide with opiate antagonistic properties and its analogs. Male and female rats were randomly assigned to receive an IP injection of 0.0, 0.01, 0.1, or 1.0 mg/kg of naloxone, MIF-1 (Pro-Leu-Gly-NH₂), the pGlu analog (pGlu-Leu-Gly-NH₂), or Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH₂). Measurement of intake occurred every 30 min or 600 min. Consumption was significantly increased. Rats injected with MIF-1 drank the most, followed in order by those injected with the pGlu analog, naloxone, Tyr-MIF-1, and controls. Dose was also reliable in a dose-dependent fashion, with animals receiving the lowest dose of 0.01 mg/kg drinking the most. None of the groups drank less than the controls. Sex was also significant in interactions with substance and dose. The results suggest that in some situations low doses of opiate antagonists may facilitate fluid consumption even though high doses are known to suppress the same behavior. The data also support the role of MIF-1 and MIF-1 analogs as opiate antagonists.