To investigate the significance of impaired insulin secretion on preimplantation embryo development, outbred ICR female mice received an injection of a single dose of streptozotocin 200 mg.kg-1 14-17 days before fertilization. Oocytes were collected 24-26 h after hCG injection. Morphological evaluation revealed a lower percentage of oocytes with second polar bodies from streptozotocin-treated females in comparison with controls. Furthermore, in this group the incidence of degenerated embryos significantly increased after 120 h in vitro cultivation. Insulin (5 U per 100 g b.w.) administered twice daily to streptozotocin-treated mice significantly improved the Embryonic development. Morphological analysis of oocyte maturation in streptozotocin-treated mice showed no significant differences in comparison with control mice. It could be concluded that marked changes in preimplantation embryo development were detected in outbred ICR mice after streptozotocin administration and this process was partly reversible by insulin treatment. Furthermore, it was shown that the process of fertilization was negatively influenced and that during in vitro cultivation the delayed effects of impaired insulin secretion resulted in an increase of embryo degeneration at the time following the third mitotic cleavage.
To investigate the significance of impaired insulin secretion on preimplantation embryo development, outbred ICR female mice received a single injection of streptozotocin 130 mg (low) and 160 mg (subdiabetic) kg-1, 14-17 days before fertilization. Preimplantation embryos were collected on day 3 of pregnancy, four to eight-cell embryos were cultured in vitro 48 h (day 5) and their cell number was estimated. After spontaneous ovulation, the significantly different distribution pattern in comparison with the controls was detected only in preimplantation embryos isolated from subdiabetic (160 mg.kg-1 streptozotocin) mice. Furthermore, the incidence of degenerated embryos was significantly increased after 48 h in vitro cultivation. The analysis of cell number distribution in embryos after cultivation in vitro indicated a significant delay in cell proliferation in both experimental groups (130 and 160 mg.kg-1 streptozotocin) in comparison with control mice. After superovulation, the only significant difference was foTund in the distribution pattern of embryos isolated on day 3 of pregnancy from subdiabetic (160 mg.kg-1 streptozotocin) mice. No significant differences were found after embryo cultivation in vitro. It could be concluded th at, in outbred ICR mice, lower streptozotocin treatment (130 mg.kg-1) influenced only cell distribution of in vitro cultured embryos after spontaneous ovulation. In ICR mice, marked changes in preimplantation embryo development were detected only after subdiabetic (160 mg.kg-1) streptozotocin treatment. During in vitro cultivation delayed effects of impaired insulin secretion resulted in an increase of embryo degeneration at the time after the third mitotic cleavage. Our results indicate that the effects of impaired maternal insulin secretion on preimplantation embryo development in mice are marked and consistent after spontaneous ovulation. Suiperovulation apparently disguises subtle changes in preimplantation embryo development after low and subdiabetic streptozotocin treatment.
To estimate the significance of insulin in the regulation of preimplantation embryo growth, female mice received a single subdiabetogenic dose of streptozocin (65 mg/kg intraperitoneally) 8-11 days or 14-17 days before fertilization. Mean glycaemia levels and the number of embryos per mouse did not differ significantly between the streptozocin-treated and control groups. Morphological analysis of preimplantation embryos collected on day 3 of pregnancy revealed significant changes in the distribution pattern of preimplantation embryo stages recovered from streptozocin-treated females. Continuous insulin treatment of streptozocin-treated mice improved the impaired development of preimplantation embryos only in short-lasting experiments. After a long subdiabetic period (14-17 days) the incidence of degenerated embryos was increased in both streptozocin-treated groups. It can be concluded that the subdiabetic state in female mice impairs preimplantation embryo development which could partly be prevented by insulin treatment.
The influence of estradiol and testosterone on body growth of young male Wistar rats was investigated. In the first experiment, estradiol was given to intact ad libitum fed male rats at 32, 37 and 42 days of age. Moreover, two untreated groups of animals were used: one was fed rcstrictedly according to the food intake of animals receiving estradiol and another was fed ad libitum. The animals were sacrificed at 47 days of age. Both untreated groups of animals achieved significantly higher body weight and length of tibia than estradiol treated animals. Also the growth of the tail of untreated animals was more intensive than that of estradiol treated animals. In the second experiment, estradiol was given to intact ad libitum fed male rats at 30, 35 and 45 days of age. Moreover, testosterone was given to a half of these animals at 45, 50 and 55 days of age. The animals were sacrificed at 60 days of age. Administration of testosterone significantly increased the growth of the tail and tibia in comparison to the animals which did not receive testosterone after estradiol administration. The results of the present study show that the inhibitory effect of estradiol on body growth of young male rats is not only the result of decreased food intake and that testosterone can improve the skeletal growth of male rats altered by previously given estradiol.
The effect of oestradiol administration and restricted feeding on longitudinal tibia growth was investigated in immature male rats. The restrictedly fed animals had a significantly longer tibia, greater thickness of the growth plate, faster rate of longitudinal tibial growth as well as the greater rate of [methyl-3H]thymidine incorporation into the growth plate of the tibia compared with oestradiol-treated animals. The results indicate that, in immature male rats, exogenous oestradiol can decrease the longitudinal growth of the tibia (at least partly due to inhibition of cell proliferation in the growth plate) independently of its anorexic effect.