The Effects of Quinestrol As a Contraceptive in Mongolian Gerbils (Meriones Unguiculatus)
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Exp. Anim. 60(5), 489–496, 2011 —Original— The Effects of Quinestrol as a Contraceptive in Mongolian Gerbils (Meriones unguiculatus) Xiao-Hui LV and Da-Zhao SHI College of Agriculture and Biotechnology, China Agricultural University, Beijing 100193, China Abstract: The contraceptive effects of quinestrol in Mongolian gerbils were examined. The results showed that body weight significantly increased after quinestrol treatment, except in the group that received the highest dose. The gonadosomatic index of ovaries decreased, whereas that of uteri increased, and uterine edema appeared after quinestrol treatment. Histological examination revealed that the ovaries had a lack of mature follicles and corpora lutea and that the myometrium and endometrium of the uteri became thin after quinestrol treatment. Persistent estrous appeared after quinestrol treatment, and time to persistent estrous shortened with increasing doses of quinestrol. Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels decreased, whereas estradiol (E2) and progesterone (P4) levels increased after quinestrol treatment, and the effects were dose-dependent. During gestation, the serum E2 levels in the different treatment groups were not significantly different. During gestation in the control groups, the serum P4 levels from days 0 to 15 were higher than in the quinestrol-treated groups; however, they did not show significant differences from days 18 to 24. Doses of 0.1 to 2.7 μg/g quinestrol over 6 days completely inhibited fertility. Birth time was prolonged with increasing doses of quinestrol. The findings suggest that quinestrol has marked estrogenic effects in Mongolian gerbils and may inhibit follicle maturation and ovulation through lowered gonadotropin levels. Uterine edema and abnormal E2 and P4 levels during gestation are important causes of pregnancy failure in quinestrol-treated Mongolian gerbils. Quinestrol causes prolonged inhibition of fertility in Mongolian gerbils. Key words: fertility control, Mongolian gerbils, quinestrol Introduction They are the main reservoir host of Yersinia pestis, which causes plague [20]. Therefore, Mongolian gerbil The Mongolian gerbil (Meriones unguiculatus, Milne populations are important to control. Additionally, the Edwards, 1867) belongs to the subfamily Gerbillinae Mongolian gerbil has been extensively used as an and is mainly distributed across the arid steppes, experimental animal model in neuroscience, physiology, semideserts and adjacent farming-pastoral areas of North reproduction, and behavioral research [28]. China, Mongolia, and the Baikal Lake region of Russia Control of fertility in rodent populations was first sug- [20, 28]. Mongolian gerbils cause serious damage to gested by Knipling [17], with use of chemosterilants for crops in agricultural areas when present in large numbers. rodent control suggested later by Davis [3]. The (Received 30 March 2011 / Accepted 4 June 2011) Address corresponding: D.-Z. Shi, College of Agriculture and Biotechnology, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian District, Beijing 100193, China 490 X.-H. LV AND D.-Z. SHI advantage of chemosterilants over conventional ment period. These smears were considered to represent poisoning has been shown theoretically in the prevention estrous (cornified cells) [29]. Five randomly selected of rat reproduction [18]. Synthetic estrogens had been gerbils per group were sacrificed by ether inhalation on studied for control of rodent populations [9, 13, 22]. the first day after quinestrol administration. Blood Quinestrol is a synthetic estrogen with marked estrogenic samples (0.5–0.6 ml) were collected via orbital venous effects and prolonged activity [10, 24, 25], and it is an puncture following light ether anesthesia before eutha- effective contraceptive in women. Additionally, nasia. The ovaries and uteri were weighed and col- quinestrol has been shown to reduce the fertility of rats lected for histological analysis. The remaining half of [2, 11, 27]. To our knowledge, the application of the virgin female gerbils were paired with experienced quinestrol for fertility control in Mongolian gerbils has males and examined by vaginal smear the next morning. not been previously reported, nor have the effects of The first day sperm was found in a vaginal smear was quinestrol in Mongolian gerbils been studied. The designated as day 0 of gestation. The male was removed objectives of this study were to confirm whether when the female was confirmed pregnant. The parturi- quinestrol inhibits fertility in Mongolian gerbils and to tion day was regarded as the last day of gestation. Blood study its effects as a contraceptive in this species. samples (0.2–0.3 ml) were taken every 3 days during gestation. The birth time (the period from the day sperm Materials and Methods was first detected in vaginal smears to the day of partu- rition) and litter size were recorded. Animals The Mongolian gerbils used in this study were from Histological study of sex organs a domesticated colony bred from animals captured in the Ovaries and uteri were fixed in 4% paraformaldehyde, Xilinguole League of Inner Mongolia. The gerbils were gradually dehydrated in ethanol and embedded in paraf- maintained at 23 ± 1°C, with automatically controlled fin, sectioned at 5μ m and stained with eosin and hema- lighting from 0700 to 2100 h (14 h light : 10 h dark). toxylin for histological examination. The sections were The Mongolian gerbils were provided with a food mix- observed by light microscopy. ture containing equal parts of corn and sunflower seeds, and they were given water ad libitum. Fifty virgin fe- Hormone assays male, 4-month-old gerbils (55–65 g) with regular estrous Serum was separated by centrifugation at 1,000 × g cycles, as confirmed by vaginal smear [29], were used. for 20 min at 4°C and stored at –80°C until assayed. The study was conducted according to Guidelines for Concentrations of FSH and LH were measured using rat Animal Experiments and approved by the Animal Care ELISA kits (EIAab Science Co., Ltd., Wuhan, China), and Use Committee at the China Agricultural Univer- as described and validated previously [30]. The mini- sity. mum detectable dose was 0.078 mIU/ml for FSH and 0.195 mIU/ml for LH, respectively. The intra- and in- Experimental design terassay variations for FSH and LH were 4.8 and 7.4%, Quinestrol (Zizhu Medicine Co., Ltd., Beijing, China) respectively. Serum E2 and P4 levels were determined was dissolved in peanut oil. Fifty virgin female gerbils by a chemiluminescence immunoassay (CLIA) [21] us- were randomly divided into five groups. The gerbils ing CLIA kits (Furui Biotechnology Co., Ltd., Beijing, were given quinestrol intragastrically daily at single China). The minimum detectable dose was 1.50 pg/ml doses of 0, 0.1, 0.3, 0.9, and 2.7 μg/g body weight (BW) for estradiol and 0.05 ng/ml for progesterone. The intra- for 6 days [32]. The control group was given peanut oil. and interassay variations for both were less than 10% The feeding habits of all experimental groups were ob- and 15%, respectively. served. The body weight of all animals was measured daily. Vaginal smears were also taken daily to assess the Statistical analysis effect of quinestrol on the estrous cycles during the treat- The data were analyzed by one-way ANOVA with QUINESTROL EFFECTS IN MONGOLIAN GERBILS 491 Table 1. Effects of quinestrol on the body weights and gonadosomatic indices of Mongolian gerbils Gonadosomatic index Initial body Final body Dose (μg/g) N (gonad weight/body weight × 1000) weight (g) weight (g) Ovaries Uteri 0 5 59.72 ± 2.55 61.44 ± 2.46 0.43 ± 0.11 2.21 ± 0.45 0.1 5 58.72 ± 1.95 64.57 ± 1.51 0.28 ± 0.03 16.81 ± 2.17* 0.3 5 57.37 ± 1.01 60.42 ± 1.64 0.28 ± 0.03 14.72 ± 2.08* 0.9 5 56.53 ± 1.88 59.86 ± 2.44 0.47 ± 0.03 15.24 ± 1.96* 2.7 5 59.01 ± 2.02 59.00 ± 1.33 0.25 ± 0.01 6.89 ± 0.79 * Significant compared with the control groups (P<0.05). Tukey’s test for post hoc multiple comparison analysis. quinestrol treatment (Table 1). The gonadosomatic in- Pearson correlation coefficients were calculated. Values dices of the uteri from groups treated with 0.1–0.9 μg/g were considered statistically significant at P<0.05 and quinestrol were significantly higher than those of the highly significant at P<0.01. The analyses were per- groups treated with 0 and 2.7 μg/g quinestrol (P<0.05). formed using SPSS 16.0 for Windows. Data are pre- The correlation coefficients between the quinestrol sented as means ± SEM. doses and the gonadosomatic indices of uteri were not significant. The percentages of uterine edema were 60, Results 100, 100, and 80% after quinestrol treatment at 0.1, 0.3, 0.9, and 2.7 μg/g, respectively. Histologic examination Effects of quinestrol on body weight and sex organs of uteri treated with quinestrol showed thinning of the The feeding habits of gerbils from all experimental myometrium and endometrium (Fig. 1G–J). Addition- groups were unaltered during the course of the study. ally, the endometrium showed reduced epithelial hyper- There was no significant difference in initial and final plasia, few profound glands, hyalinized stroma, and body weights for the gerbils in the different groups shedding cilia. (Table 1). However, each group exhibited a significant increase in final body weight compared with initial body Effects of quinestrol on estrous cycles weight (P<0.05), except for the group treated with the The regular estrous cycle of Mongolian gerbils was dose of 2.7 μg/g quinestrol. There was a significant interrupted treatment with 0.1–2.7 μg/g doses of quin- negative correlation between dosage and the change in estrol. Persistent estrous appeared in quinestrol-treated body weight (r=–0.392, P<0.01).