Marongiu, Maria Laura and Gulinati, Alessandro (2008) Ultrasound evaluation of ovarian follicular dynamics during early pseudopregnancy as a tool to inquire into the high progesterone (P+) syndrome of rabbit does. In: 9th World rabbit congress: proceedings, June 10-13, 2008, Verona, Italy. Brescia, Fondazione iniziative zooprofilattiche. p. 393-397. (Fondazione iniziative zooprofilattiche e zootecniche, 72). ISBN 9788890281464. Conference or Workshop Item.
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The investigation of the underlying causes for the high progesterone (P+) syndrome should presuppose further studies to more precisely characterise pseudopregnant rabbit does. The purpose of the present research was to examine follicular dynamics in the postovulatory rabbit ovary by means of real-time B-mode ultrasound scanning. A particular attention was focused upon the population of large-sized follicles present through the first 6 days after induced pseudopregnancy, since this follicular category, being steroidogenically active, may be crucial to the survival of the developing CL. Pseudopregnancy was induced in twenty-four hybrid rabbit does caged individually by injection of 100 IU human chorionic gonadotropin (hCG). Sequential monitoring of dynamic changes in the follicular population was performed by ultrasonography on day 0, 2 and 6 of pseudopregnancy (day 0 being the day of hCG injection). The follicle distribution in ovaries of untreated does (day 0) was marked by approximately equal number of small follicles (46.1%±6.7 <2.0 mm) and large follicles (54.4%±6.1 ≥2.0 mm). However, at 2 days after injection of an ovulatory dose of hCG, the large follicles population was markedly depleted with only 10.2%±0.9 of the follicles present classified as large. The ovulation rate averaged 10.8±0.7 per rabbit. By day 6 of pseudopregnancy the size distribution showed that a repopulation of the ovary with large follicles occurred with 71.3%±6.8 in this category. The large follicles lost at ovulation had apparently been replaced by the time of luteal estrogen dependence at day 6 of pseudopregnancy. The results presented in this report, demonstrating that the rabbit ovary is depleted of large follicles following ovulation but that large, steroidogenically active follicles are again present by day 6, could be considered as a preliminary step to understand what mechanisms protect the CL from luteolysis until day 6 of pseudopregnancy, when CL shift from complete refractoriness to partial and complete responsiveness to PGF2α treatment. Since little is known about what factors effectively trigger luteolysis in normal, physiological conditions as well as what mechanisms protect CL from luteolysis in the first days of pseudopregnancy, the innovative and noninvasive approach supplied by the real-time ultrasonography could represent an additional tool for investigation.
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