Effects of hyperstimulation with gonadotrophins and age of females on oocytes and their metaphase II status in rats

Abstract

The present study was undertaken to evaluate the effects of hyperstimulation and aging on the number and proportion of oocytes in the metaphase II stage in female Wistar rats. It explored the validity of the hypothesis that a combination of hyperstimulation with pregnant mare serum gonadotrophins (PMSG) and age could compromise, to a greater extent, the oocyte quality as indicated by the proportion of ovulated oocytes in the metaphase II stage. Female Wistar rats were stimulated with varying doses of PMSG and human chorionic gonadotrophins (hCG) and the number and proportion of ovulated oocytes in the metaphase II stage were examined and compared between different groups of young adult (8–10 weeks old) and aging (30–32 weeks old) female rats. While spontaneous ovulation occurred in all young adult rats, only 50% of the aging rats did. The ovulation rate in aging rats was increased from 50 to 93% when non‐PMSG‐stimulated rats were given a dose of 10 IU of hCG at proestrus. The lower number of ovulated oocytes noted, even in those hyperstimulated with high doses of PMSG/hCG, also indicated a reduction in fertility in aging rats. Under the influence of high doses of PMSG, all aging rats ovulated, but as with the young adult rats, a higher dose of hCG was needed to achieve the maximum number of ovulated oocytes from the PMSG‐induced expanded pool of preovulatory follicles. However, the average number of ovulated oocytes in aging rats was, nevertheless, still significantly lower than in young adult rats even when approximation of weight was considered. No consistent significant difference in proportion of normal oocytes was noted within groups and between young adult and aging rats. A lower proportion of ovulated oocytes was arrested at the metaphase II stages when rats, whether they were young adult or aging, were hyperstimulated with 40 IU of PMSG. However, this proportion was restored to normal (about 100%) when a higher dose of hCG, which is a signal responsible for initiating oocyte maturation, was used. Results of the present study showed that there appears to be an age‐related reduction of sensitivity of the preovulatory follicles to the ovulation induction signal of hCG and thus higher doses of hCG were needed to ovulate the PMSG‐induced expanded pool of dominant follicles. In older rats, apart from the obvious depletion of the pool of follicles, the evidence from the present study suggests that some of these older rats do have follicles, but that these were unable to develop to preovulatory follicles, probably because of the absence of sufficiently high levels of gonadotrophins essential for the initiation of folliculogenesis. PMSG‐hyperstimulation can affect nuclear maturation; the proportion of ovulated oocytes not arrested at the metaphase II stage was higher. However, the proportion of ovulated oocytes at the metaphase II was restored to normal by increasing the dose of hCG use. Hence, meiotic aberration in rats is not age‐dependent but rather dependent on the amplitude of the luteinizing hormone...

The long-term effects of superovulation on fertility and sexual behavior of male offspring in mice

“…It has been reported that superovulation of female mice delayed embryonic and fetal development [3,34]. The possible explanation is that superovulation increases the proportion of chromosomal abnormalities in oocytes in rats and uterine horn is incapable of nourishing large number of blastocysts tyring to implant and also to develop in to a fetus [35]. However, there were no significant differences in the percentages of resorption, percentages of live fetus, and mean fetus weight between the F2 generation in ovarian stimulation group and naturally conceived group.…”

Rat embryo quality and production efficiency are dependent on gonadotrophin dose in superovulatory treatments

“…Production of ES cells in rats is somehow limited by the fact that superovulation protocols have not been optimized for the production of high-quality embryos. Although superovulation protocols for rat have already been published, they mainly focused on the production of either oocytes or zygotes (Mukumoto et al 1995, Tain et al 2000, Hirabayashi et al 2001, Corbin & McCabe 2002, Popova et al 2002, Krivokharchenko et al 2003, and the techniques for the production of morulae or blastocysts are still not well defined (Tain et al 2001, Ishigame et al 2004. Since both morulae and blastocysts are the source of ES cells (Evans & Kaufman 1981, Capecchi 1989, Iannaccone et al 1994, Ouhibi et al 1995, Thomson et al 1998, Vassilieva et al 2000, it would be useful to improve the superovulation protocols that allow obtaining embryos suitable for ES cell production.…”

Efecto De La Aplicación De Gonadotropinas Recombinantes Humanas Sobre La Producción Y Calidad De Ovocitos Y Embriones en Coneja

“…De hecho, se ha observado que el tratamiento con eCG puede resultar en una disminución de la tasa de ovocitos liberados en el estadio esperado (Chrenek et al, 1998;Tain et al, 2000), una alteración en la organización de determinados orgánulos ovocitarios (Lee et al, 2005;Lee et al, 2006a), en fallos de fertilización de los ovocitos (Lee et al, 2005), en una menor tasa de desarrollo de los embriones (Sengoku and Dukelow, 1988; anormalidades cromosómicas o en un aumento de la sensibilidad a la crioconservación . Además, parece que los efectos negativos de la administración de eCG son dependientes de la dosis (Lee et al, 2005;Mehaisen, 2005;Yu et al, 2010; sea constante.…”

“…La importancia de un cumulus en correcto estado, atendiendo tanto a su integridad como a su grado de compactación y al número de capas, ha sido señalada en númerosas ocasiones como indicador de calidad, ya que todas ellas son características necesarias para que el ovocito pueda adquirir la competencia que le permite ser fecundado de forma normal (Gilchrist and Thompson, 2007); de hecho, aunque son necesarias otras valoraciones complementarias, la del conjunto de cumulus y ovocito es una herramienta crucial para la selección de éstos últimos (Goovaerts et al, 2010). Por otra parte, para considerarlos normales, se atiende (en función de su estadio) a la homogenidad del citoplasma, a la presencia o ausencia de degeneración o fragmentación citoplasmática, a la presencia de picnosis en el núcleo, así como a las posibles fracturas de la zona pelúcida o la pérdida de forma esférica (Zanagnolo et al, 1996;Tain et al, 2000;Prentice and Anzar, 2011), resultando también interesante la valoración del diámetro del ovocito (Otoi et al., 1997).…”

“…Permite observar la cinética de la placa Indica una correcta disyunción de los cromosomas (Cooke et al, 2003;Mandelbaum et al, 2004) (Vincent et al, 1989;Tain et al, 2000); (Salvetti et al, 2010) Cromosomas Técnica TUNEL Permite la observación de la fragmentación de ADN (Van Blerkom and Davis, 2001;Contreras et al, 2008) *Estos autores realizaron esta valoración en embriones…”