Patricia M. Morgan

Evaluation of ultrasonography for monitoring follicular growth in rhesus monkeys

The purpose of this study was to determine if the ovaries and uterus of rhesus monkeys could be visualized by ultrasonography and to detect changes associated with follicular growth and ovulation. Animals were examined during 15 menstrual cycles, for an average of nine consecutive days. Ultrasonic recordings were correlated with hormonal parameters (estradiol 17beta, E(2); luteinizing hormone, LH; and progesterone, P) and laparoscopic findings. The uterus and both ovaries were observed in more than 90% of the examinations. A dominant follicle (DF) was identified during all ovulatory cycles, on average 1 d preceding the E(2) peak. The maximal diameter of the DF ranged from 3 to 7 mm. Laparoscopic examinations to determine the site of the DF confirmed ultrasonic findings in 10 of 14 cycles (P < 0.1). There was no significant difference in the size of the dominant and contralateral ovaries; however, more follicles with a diameter of 2 to 7 mm were found on the dominant ovary (P < 0.05). Two animals stimulated with exogenous gonadotropins showed a linear increase in ovarian size for 6 d prior to oocyte recovery (P < 0.05), reflecting an increase in the number of developing follicles. Ultrasonography can be used to identify the DF during spontaneous cycles in rhesus monkeys and to monitor the response of monkeys to exogenous gonadotropins.

Fertilization in the Rhesus Monkey

The nonhuman primates occupy a unique niche among species suitable for experimental studies on fertilization and early development. Studies with nonhuman primates provide an important link between the huge literature derived from work on rodents and other common laboratory species and the relatively small amount of data on humans. Research with rodent species continues to provide the bulk of basic information on early development, in large part because of the ready availability of oocytes and embryos, but it is difficult to know to what extent information can be extrapolated to primate species, including humans. Information is increasingly available from the numerous human in vitro fertilization (IVF) programs now in operation. However, the amount and quality of basic scientific data on early development that can be obtained from this source are restricted, in part by ethical constraints (Austin, 1990) and in part by conflicting priorities between research and clinical needs for the supply of oocytes and embryos. For example, most “excess” human IVF embryos in the U.S.A. are destined for cryopreservation or for use in a donor program and are thus unsuitable for any research protocol that might compromise their viability. In contrast, there are no prohibitions on the use of fertilized eggs or embryos of nonhuman primates for research, while the reproductive physiology and embryology of the Old-World nonhuman primates are sufficiently similar to humans that direct extrapolation of concepts is possible.