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Summary. High levels of progesterone were found in the blastocysts, uterine fluid and sera of normal pregnant rabbits on Days 6 and 7 of pregnancy. Very little progesterone (< 2% of control) was present in bilaterally ovariectomized rabbits in which pregnancy was maintained by the administration of medroxyprogesterone acetate. The results demonstrate that the rabbit blastocyst is provided with large amounts of progesterone derived from the maternal ovaries.

While there are undoubtedly multiple causes of spontaneous abortion and congenital birth defects, high incidences of chromosomal abnormalities in human abortuses (Carr, 1965; Geneva Conference, 1966; Makino & co-authors, 1967; Ikeuchi, Sasaki, Kohno, Hayata & Fujimoto, 1972), and in early embryos of the pig (McFeely, 1967) suggest that chromosomal imbalance may be one of the primary causes of early embryonic death.

Excessive administration of HCG has been reported to affect sperm capacitation in rabbits (Soupart, 1967; Wettemann & Hafs, 1970), and the development of the zona pellucida in baboons (Katzberg & Hendrickx, 1966). Recently, a high incidence of triploid embryos has been associated with PMSG-HCG-induced superovulation in mice (N. Takagi, personal communication).

The present investigation was conducted to study the effect of superovulation on the karyological constitution of preimplantation rabbit blastocysts.

Nine mature nulliparous female

Summary.

The technique of laparoscopy was modified for use in the rabbit and was found to facilitate continuous observation of follicular development and ovulation. The timing of ovulation was studied and suggests that 100 i.u. HCG, whether used in a superovulation regimen or solely as an ovulatory stimulus, causes a greater ovulation rate than does a mating stimulus. Follicular rupture was observed and frequently occurred in the smaller follicles first. Laparoscopy in pregnant rabbits suggests that quantification of preimplantation blastocysts is not only possible but also very accurate and is without deleterious effects on the developing embryos. These results suggest that the laparoscopic technique may be a valuable asset to the study of reproductive phenomena in the rabbit.

Summary.

The development of a laparoscopy technique in the gilt which allows repeated direct observation of ovarian cyclicity with minimal surgical stress and trauma is described. Follicular activity before, during and after ovulation can be observed as well as corpus luteum development, especially during critical periods, such as oestrus. This technique may have application in studies of early embryonic growth and as a tool for investigating the cause of early embryonic death.