Superovulatory Response, Oocyte Spontaneous Activation, and Embryo Development in WMN/Nrs Inbred Rats

Abstract

WMN/Nrs inbred rats have been widely used in radiation biology for years. However, their reproductive profile has never been examined. We examined various reproductive characteristics of WMN/Nrs inbred rats such as superovulatory response, oocytes spontaneous activation (OSA), and embryo development in vitro and in vivo. Superovulation was induced in 3-to 9-week-old females by injection of 150 IU/kg PMSG and 150 IU/Kg hCG by 48 h apart. Only 8-and 9-week-old animals superovulated averaging 31.4 and 43.9 oocytes, respectively, and superovulation did not depend on estrous cycle. Animals 3-7 weeks of age did not superovulate. Because Wistar strains have been known to show a high incidence of OSA, factors expected to affect OSA in WMN/Nrs, including the time interval of various steps from euthanasia to oocyte recovery, incubation media, estrous cycle, and anesthetic treatments, were examined. The time from animal euthanasia to oviduct excision was the only factor shown to affect OSA. We also compared in vitro and in vivo embryo developmental competence between embryos obtained by natural ovulation and superovulation. Although percent in vitro development of 2-cell embryos to blastocysts was similar for embryos obtained by natural ovulation (63.7%) and superovulation (69.7%), fetus development after oviductal transfer of 2-cell embryos was significantly lower in embryos obtained by superovulation than in those obtained by natural ovulation (60.2% vs. 87.5%, P=0.02). Our results provide important normative data regarding future applications of rat assisted reproductive technologies (ARTs) such as in vitro fertilization and cryopreservation in WMN/Nrs strain and may be applicable to other strains of laboratory rats.

Fertilizability of Superovulated Eggs by Estrous Stage-independent PMSG/hCG Treatment in Adult Wistar-Imamichi Rats

“…The low value of mating and ovulation rate in immature rats has been reported in other strains [19, 28] and our present result consists with these previous reports. On the other hand, the fertilization efficiency of eggs obtained from mated and ovulated rats were not significantly different between immature and adult rats (Table 7).…”

“…According to Kagabu’s [16, 18] and our previous [20] data, efficient superovulation can be induced for at least eight weeks (10–18 weeks of age) in adult, whereas efficient superovulation can be induced for only two weeks (4–6 weeks of age) in immature rats. In comparison with other strains [1, 2, 4, 6, 19, 28], WI rats are superior to other strains in the number of obtained eggs. In addition, WI rats are also superior to other strains in handling.…”

“…There are various methods to induce superovulation in laboratory rats, such as injection of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) [1, 2, 4, 12, 22, 25], continuous infusion of follicle stimulating hormone [5, 30], and injection of inhibin antiserum [14, 15]. Among these methods, PMSG/hCG treatment is widely used as a simple and effective method to induce superovulation [4, 28]; however, it is known that response to PMSG/hCG treatment varies by strain [1, 4, 6, 19, 20, 22, 25, 28] and with age [16, 18,19,20, 22, 28]. Thus, there is no universal protocol to induce superovulation with PMSG/hCG in rats.…”

Impact of the use of gonadotropins on embryonic development - a rat model

“…4 (18.2) (a) 0.045 are also reported in literature (Popova et al, 2002;; Kito et al, 2010). It is important to emphasize that it is possible to collect as many as 33 structures from only one animal;; consistent collection of large numbers of structure per animal could minimize the number of animals needed in future studies.…”

White tea intake interferes with the expression of angiogenic factors in the corpora lutea of superovulated rats

“…The hormonal protocol for superovulation was the same as that of Kito et al . (). Forty‐eight hours after the hormonal treatment, the rats were weighed, anaesthetised with ether and then euthanised through exsanguination.…”