Lists
Lists
Garside, Deborah A. (1983) Evidence for the formation of supplementary corpora lutea in the pregnant and pseudopregnant rat. Doctoral thesis, City of London Polytechnic.
In a series of experiments investigating a possible post-coitum contraceptive, it was observed that the numbers of corpora lutea (CL) of pregnant Sprague-Dawley (CD) rats were greater than in cyclic, unmated control females (p<0.001).
The ontogeny of these supplementary CL (SCL) was established by the recording the mean number of CL in pregnant Sprague-Dawley rats on days 1 to 9 post-coitum (day 1 being the first day post-coitum) using the gross phological dissection of the ovary.
Compared to cyclic controls, an initial significant increase in mean CL numbers was recorded on day 1 post-coitum (p<0.05) with a further significant increase between days 5 and 7 (p<0.001). This phenomena was neither Sprague-Dawley strain, nor pregnancy specific, as a similar increase was also recorded for Wistar rats between days 4 and 7 postcoitum and identical increases in mean CL numbers were recorded in pseudopregnant rats of both strains.
Histological studies of ovarian tissue confirmed the presence of newly formed CL on day 5 and 6 post-coitum and an absence of entrapped ova; follicular development was also present in early pregnancy with Graafian follicles evident on day 4 post-coitum.
Plasma progesterone determinations revealed no increase in circulating progesterone as a result of SCL formation in either pregnant or pseudopregnant rats.
Supplementary ovulations may be initiated by the preimplantation surge of oestrogen, on day 4 post-coitum, as treatment with the anti-oestrogen. Tamoxifen, inhibits their formation. Investigations into the presence of an appropriately-timed preovulatory surge of gonadotrophins in the early stages of pregnancy however, proved inconclusive.
Supplementary ovulation occurs therefore between day 4 and 7 post-coitum in both pregnant and pseudopregnant Wistar and Sprague-Dawley rats, probably initiated by a consistent physiological event. This phenomena therefore obviously has an impact on the estimation of embryo mortality studies in this species.
 |
View Item |