In vitro maturation of ovarian oocytes from unstimulated rhesus monkeys: assessment of cytoplasmic maturity by embryonic development after in vitro fertilization

One-hundred and sixty-six cumulus-enclosed oocytes, obtained from ovaries of unstimulated rhesus monkeys, were subjected to six different treatments in vitro--two types of media (simple = TALP; complex = CMRL) x three levels of gonadotropins (none, FSH, FSH + hCG)--to assess their ability to undergo maturation, fertilization, and embryo development. A summary of development in culture for all experimental treatments is as follows: 58% of oocytes underwent germinal vesicle breakdown; 37% extruded a first polar body; 17% had more than one pronucleus and/or two polar bodies after insemination (i.e., were activated/fertilized); and 12% cleaved (i.e., developed) to at least the 2-cell stage in vitro. Of 45 oocytes incubated only in medium (either simple or complex) without gonadotropins, only 3 were activated/fertilized (6.7%), and only one embryo developed to at least the 2-4-cell stage (2.2%). There were no differences between oocytes incubated with only FSH and oocytes incubated with FSH + hCG. Activation/fertilization (20.7% vs. 6.7%) and embryo development (greater than or equal to 2 cells; 15.7% vs. 2.2%) were significantly higher in treatments with than without gonadotropin supplementation. There were no statistically significant differences attributable to incubation in different media during oocyte maturation. Cumulus-enclosed oocytes recovered from unstimulated ovaries of rhesus monkeys can resume maturation during culture in vitro, as shown by their ability to be fertilized and by the cleavage in vitro of the resultant zygotes.