Relationship between steroidogenesis and oocyte maturation in rat graafian follicles cultured in vitro

Some studies on the morphological aspects of buffalo oocytes in relation to the ovarian morphology and culture condition

The present study was conducted to establish the effects of ovarian morphology on oocyte quantity and quality, as well as the effect of preincubated granulosa cells (PGCs) on in vitro maturation of buffalo oocytes and steroid hormones production. A total of 52 ovarian pairs were grouped into three types: type I (with functional corpus luteum), type II (with regressed corpus luteum), and type III (without corpus luteum). The number of follicles and oocytes/ovary were documented. The follicles were classified into three groups (<2, 2-6, and >6 mm Ø). Oocytes were classified according to their morphology into four grades (grades A, B, C, and D), or according to their cumulus compactness into four groups (more than three layers, one to three layers of cumulus cells, partial remnants of cumulus cells, and no cumulus cells). A PGCs was used to investigate their steroidogenic potential on the in vitro maturation. The highest number of follicles and oocytes was found in type III than types II and I. Grades A and B oocytes were significantly higher (P < 0.01) in number in type III ovaries. Oocytes with more than three layers of cumulus cells showed higher maturation rate than oocytes with partial remnants or no cumulus cells but with small difference from oocytes having one to three layers of cumulus cells. Beside the higher maturation rate in compact than denuded oocytes, a significantly higher (P < 0.01) rates obtained in compact or denuded oocytes when cultured in vitro with PGCs than the corresponding oocytes with no PGCs. These maturation rates coincided with higher level (P < 0.05) of estradiol-17ss when compact oocytes cultured with or without PGCs than denuded oocytes and higher level (P < 0.05) of progesterone after culture with PGCs for both compact and denuded oocytes than the corresponding oocytes with no PGCs. In summary, buffalo ovaries with no corpus luteum may be suggested for obtaining high number of follicles and good oocytes than the others. Oocytes with intact cumulus showed better maturation than those with partial or denuded cumulus, although the denuded oocytes improved their meiotic competence to a less or greater extent when cultured in vitro with PGCs.