The inhibin B response to a motilin receptor agonist in male rats.

BACKGROUND: In a repeat oral dose toxicity study, all of 16 male rats given 100 mg/kg/day GSK1322888 sustained testicular injury after 4 weeks of treatment; the findings were not reversible after 12 weeks off-dose. The current study was conducted to further characterize testicular toxicity and to explore the possible relationship between onset of lesions, and changes in circulating hormone levels. METHODS: Male Sprague Dawley rats were orally administered 30 or 100 mg/kg/day GSK1322888 for 2 weeks with a 4-week off-dose period. Blood was collected via tail vein twice during the treatment period (days 4 and 11) and three times during the off-dose period (days 28, 36, and 42) for measurement of serum testosterone, dihydrotestosterone, and Inhibin B, luteinizing hormone, and follicle stimulating hormone concentrations. A histopathologic examination of testes was performed at the end of the treatment and off-dose periods. RESULTS: At 100 mg/kg/day, microscopic findings of the testis (degeneration of the germinal epithelium) were evident for 9 of 10 male rats on day 14 and all 10 rats at the end of the 4-week recovery period. There was no testicular toxicity observed at 30 mg/kg/day. During all stages of evaluation, there was no apparent difference among control and treated animals in hormone concentrations. CONCLUSION: There was poor correlation between changes in serum levels of Inhibin B and testis histopathology. Based on these observations, the utility of Inhibin B as a hormonal marker for germ cell toxicity is limited.

The potential role for corticosterone in the induction of cleft palate in mice after treatment with a selective NK-1 receptor antagonist, casopitant (GW679769B).

BACKGROUND: Casopitant is a potent and selective NK-1 receptor antagonist that has shown clinical efficacy in the prevention of chemotherapy-induced and postoperative-induced nausea and vomiting. METHODS: In an embryo-fetal development study, pregnant mice were given vehicle (sterile water) or doses of 30, 100, or 300 mg/kg/day casopitant on Gestation Day (GD) 6 to 15. Fetuses were evaluated for external, visceral, and skeletal abnormalities on GD 18. In a follow-on study to investigate casopitant-induced hormonal changes during the developmental period for palate formation, pregnant mice were given vehicle (sterile water) or 300 mg/kg/day casopitant once daily on GD 6 to 13. Blood was collected on GD 13 at various time-points for measurement of plasma adrenocorticotropic hormone and corticosterone (CRT) concentrations. RESULTS: There was no evidence of developmental toxicity in mice at 30 or 100 mg/kg/day but 9% of fetuses at 300 mg/kg/day had cleft palate. Mice are sensitive to glucocorticoid-induced cleft palates, and NK-1 antagonists are known to modulate the hypothalamic-pituitary-adrenal axis leading to increases in corticosterone. On GD 13, mean plasma adrenocorticotropic hormone levels at 300 mg/kg/day were elevated by approximately twofold from vehicle-treated levels at 1 hr post-dose and mean plasma CRT levels were elevated by 3, 5, and 10-fold at 0.5, 1, and 2 hr post-dose, respectively. CONCLUSIONS: The increased level of CRT was in the range previously shown in the literature to cause cleft palates in mice and was likely the underlying mechanism behind casopitant-induced cleft palate in mice.