Collaborative work on evaluation of ovarian toxicity. 7) Effects of 2- or 4- week repeated dose studies and fertility study of cyclophosphamide in female rats.

The main focus of this study was to determine the optimal administration period concerning the toxic effects on ovarian morphological changes in the repeated dose toxicity study. In order to assess the morphological and functional changes induced in the ovary by cyclophosphamide (CP), the compound was administrated to female rats at dose levels of 0, 5, 10 and 20 mg/kg for the repeated dose toxicity study for 2 or 4 weeks, and at 0, 5, 10, and 20 mg/kg for the female fertility study from 2 weeks prior to mating to Day 7 of pregnancy. In the repeated dose toxicity study, increases in large sized atretic follicles, atrophy of corpora lutea were observed in the 20 mg/kg group in the 4-week study by the histopathological examination of the ovaries. There were no drug-related changes in the ovary in the 2-week study. In the female fertility study, the numbers of implantation were slightly decreased and the corpora lutea of pregnancy was not observed in the 20 mg/kg group. The dose-dependent increase in the incidence of post-implantation loss was observed, and no abnormalities were observed in the estrus cycle and mating in all treated groups. From these findings, the histopathological changes in the ovary are important endpoints for the evaluation of drug-induced ovarian damage as well as caesarean section. In conclusion, a 4-week administration period is sufficient to detect the ovarian toxicity of CP in the repeated dose toxicity study.

Hypothermia-related testicular toxicity of reserpine in mice.

Local cooling of the testis was reported to cause testicular abnormality, but there is no information regarding the effect of whole body cooling, such as hypothermia on spermatogenesis. We investigated whether hypothermia would cause testicular toxicity in mice. Male mice were administered with a single intraperitoneal dose of 100mg/kg of reserpine. The rectal temperature decreased to 29 degrees C 6h post dosing and thereafter sustained at lower values (24-25 degrees C) until 96 h post dosing. The histopathological examination of the testis showed nuclear vacuolation of round spermatids at stages I-V in mice examined 24, 48, 72 and 96 h post dosing. The lesions were more severe in the groups examined 72 and 96 h post dosing than in the groups examined 24 and 48 h post dosing. These results suggested that hypothermia condition at lower than 30 degrees C and sustained for more than 18 h could induce nuclear vacuolation of round spermatids at stages I-V in the testis. In order to demonstrate that the testicular lesion in the reserpine-treated mice was induced by hypothermia, mice were given a single intraperitoneal dose of 100mg/kg of reserpine, and each dosed group was housed under different environmental conditions for 72 h; one consisted of housing the mice individually at room temperature, and the other consisted of housing the mice individually under heated condition. In the mice administered with reserpine and housed at room temperature, hypothermia below 30 degrees C with a minimal of 26 degrees C was observed for 66 h. In contrast, the mice administered with reserpine and housed under heated condition maintained the rectal temperature of 33-36 degrees C. Nuclear vacuolation of round spermatids at stages I-V in the testis was observed in reserpine-treated mice maintained at room temperature, but not in reserpine-treated mice kept under heated condition. These data strongly indicated that nuclear vacuolation of round spermatids at stages I-V observed in reserpine-treated mice was related to hypothermia.

Attenuated stress-induced catecholamine release in mice lacking the vasopressin V1b receptor.

Vasopressin V(1b) receptor is specifically expressed in the pituitary and mediates adrenocorticotropin release, thereby regulating stress responses via its corticotropin releasing factor-like action. In the present study we examined catecholamine release in response to two types of stress in mice lacking the V(1b) receptor gene (V(1b)R(-/-) mice) vs. wild-type mice. There were no significant differences in the basal plasma levels of catecholamines between the two genotypes. In response to stress induced by forced swimming, norepinephrine (NE), but not epinephrine (E) or dopamine (DA), was increased in wild-type mice, whereas the increases in NE and DA were not observed in V(1b)R(-/-) mice. In wild-type mice, E, but not NE or DA, was increased in response to social isolation stress, whereas the increase in E was not observed in V(1b)R(-/-) mice. These results suggest that the V(1b) receptor regulates stress-induced catecholamine release. Because it has been suggested that arginine-vasopressin (AVP) is related to the development of depression, we also evaluated immobility time in the forced swimming test, and we found no significant change in V(1b)R(-/-) mice. Taken together, these findings suggest that, in addition to the previously elucidated effect on the hypothalamic-pituitary-adrenal axis, vasopressin activity via V(1b) receptors regulates stress-induced catecholamine release.