Selection and interpretation of clinical pathology indicators of hepatic injury in preclinical studies.

This position paper delineates the expert recommendations of the Regulatory Affairs Committee of the American Society for Veterinary Clinical Pathology for the use of preclinical, clinical pathology endpoints in assessment of the potential for drug-induced hepatic injury in animals and humans. Development of these guidelines has been based on current recommendations in the relevant preclinical and human clinical trial literature; they are intended to provide a method for consistent and rigorous interpretation of liver-specific data for the identification of hepatic injury in preclinical studies and potential liability for hepatic injury in human patients.

Oral toxicity study of 2-pentenenitrile in rats with reproductive toxicity screening test.

A combined repeated-dose toxicity study with reproduction was conducted with 2-pentenenitrile (2-PN). Rats (10/sex per dose level) were dosed with 2-PN once daily by gavage at dose levels of either 0, 1, 3, or 10 mg kg(-1) day(-1) for 28 days, prior to and during cohabitation, and through day 3 of lactation. General clinical observations were recorded daily; body weights were recorded weekly. A neurobehavioral evaluation consisting of a functional observational battery and motor activity was conducted in all parental rats (10/sex per group). Clinical pathology parameters (hematology, clinical chemistry, coagulation) were measured in parental rats. Pup weights and clinical signs were recorded at birth and on lactation day 4. Parental rats were given a gross pathological examination, organ weights were obtained, and histological examination was conducted for the control and 10 mg kg(-1) day(-1) groups. No effects were seen with regard to mortality, clinical signs, functional observational battery and motor activity, hematology, or organ weights. Females receiving 10 mg/kg and males from all dose groups showed lower body weight gains and feed efficiency. Increased albumin concentrations were seen in both sexes given 10 mg/kg. Females in the 10 mg/kg group showed degeneration of the olfactory mucosa. No effects on the numbers of pups born, number surviving to lactation day 4, pup weight, and no gross anatomical development changes were observed. Under the conditions of this study, the no-observed-effect level (NOEL) for systemic toxicity in rats was 3 mg kg(-1) day(-1), based on degeneration of olfactory mucosa in females at 10 mg kg(-1) day(-1). The NOEL for reproductive and neurobehavioral toxicity in rats and for toxicity to offspring was 10 mg kg(-1) day(-1), the highest dose level tested.

Automated and semiautomated analysis of rat alkaline phosphatase isoenzymes.

A semiautomated quantitative assay for rat serum alkaline phosphatase (ALP) isoenzyme determination was developed, incorporating selective precipitation of bone alkaline phosphatase (BALP) with wheat germ lectin and differential inhibition with levamisole for determination of intestinal alkaline phosphatase (IALP). The assays for each isoenzyme were linear over a broad range of activities. The within-run and between-run coefficients of variation were less than 11% for all 3 isoenzymes. Dilution of serum with saline results in an artifactual overestimation of BALP activity. Comparison of ALP and ALP isoenzyme activity in rats of various ages showed that BALP activity drops dramatically with increasing age of rats. IALP activity is greater in immature rats compared to that in mature rats. While there was no difference between male and female rats at 4 wk of age with regard to total ALP activity and activity of any of the isoenzymes, total ALP activity and activity of the individual isoenzymes were higher in males than in females at most ages over 4 wk. Gavage with corn oil resulted in increased serum IALP activity, and bile duct ligation resulted in increased liver alkaline phosphatase activity. This combined assay for the 3 ALP isoenzymes in rat serum is an efficient means of analysis of large numbers of samples and should increase markedly the specificity of serum ALP activity in identifying the target organ in toxicologic studies when serum ALP activity is increased.

Inhalation toxicity of methylglutaronitrile in rats.

Methylglutaronitrile (MGN) is a high-boiling (263 degrees C) solvent/intermediate used in the fiber industry. Twenty male rats per group were exposed nose-only to condensation aerosol/vapor concentrations of approximately either 5, 25, or 200 mg/m3 of MGN for 6 h/day, 5 days/week over a 4-week period. Ten rats/group were sacrificed one day after the final exposure and the remaining rats after a four-week recovery period. No effects were observed in clinical observations during the exposure period, but body-weight depression was observed in the 200 mg/m3 group. The 200 mg/m3 group showed minimal decreases in red blood cell count, hemoglobin, and hematocrit values accompanied by increases in reticulocytes. There were no other effects observed in clinical or pathologic evaluations in the study. A neurobehavioral battery of tests (including grip strength, functional observational battery, and motor activity tests) given at the end of the exposure and recovery periods showed no MGN effects. During the 4-week recovery, body weights in the 200 mg/m3 group returned to normal and the hematologic findings in all groups were normal. Based on the above findings of body weight depression at 200 mg/m3, the no-observed-adverse-effect level (NOAEL) for this study was considered to be 25 mg/m3.

Recessive resistance to thyroid hormone in mice lacking thyroid hormone receptor beta: evidence for tissue-specific modulation of receptor function.

The diverse functions of thyroid hormone (T3) are presumed to be mediated by two genes encoding the related receptors, TRalpha and TRbeta. However, the in vivo functions of TRalpha and TRbeta are undefined. Here, we report that targeted inactivation of the mouse TRbeta gene results in goitre and elevated levels of thyroid hormone. Also, thyroid-stimulating hormone (TSH), which is released by pituitary thyrotropes and which is normally suppressed by increased levels of thyroid hormone, was present at elevated levels in homozygous mutant (Thrb-/-) mice. These findings suggest a unique role for TRbeta that cannot be substituted by TRalpha in the T3-dependent feedback regulation of TSH transcription. Thrb-/- mice provide a recessive model for the human syndrome of resistance to thyroid hormone (RTH) that exhibits a similar endocrine disorder but which is typically caused by dominant TRbeta mutants that are transcriptional inhibitors. It is unknown whether TRalpha, TRbeta or other receptors are targets for inhibition in dominant RTH; however, the analysis of Thrb-/- mice suggests that antagonism of TRbeta-mediated pathways underlies the disorder of the pituitary-thyroid axis. Interestingly, in the brain, the absence of TRbeta may not mimic the defects often associated with dominant RTH, since no overt behavioural or neuroanatomical abnormalities were detected in Thrb-/- mice. These data define in vivo functions for TRbeta and indicate that specificity in T3 signalling is conferred by distinct receptor genes.