Patterns of expression of steroidogenic enzymes during the first wave of the ovine estrous cycle as compared to the preovulatory follicle

The expression patterns of steroidogenic enzymes in ovarian antral follicles at various stages of growth in a follicular wave have not been reported for sheep. Ovaries were collected from ewes (n = 4–5 per group) when the largest follicle(s) of the first wave of the cycle, as determined by ultrasonography, reached (i) 3 mm, (ii) 4 mm, (iii) ≥5 mm in diameter or when there was a single (iv) preovulatory follicle in the last wave of the cycle, 12 h after estrus detection. The expression pattern of steroidogenic enzymes was quantified using immunohistochemistry and grey-scale densitometry. The expression of CYP19 in the granulosa and 3β-HSD and CYP17 in the theca increased (P < 0.01) progressively from 3 to ≥5 mm follicles in the first wave of the cycle and was lower (P < 0.01) in the preovulatory follicle compared to ≥5 mm follicles. However, the expression of 3β-HSD in the granulosa increased (P < 0.05) from 3 to ≥5 mm follicles and was maintained (P < 0.05) at a high level in the preovulatory follicles. The amount of CYP19 in the granulosa of the growing follicles correlated positively (r = 0.5; P < 0.03) with the concurrent serum estradiol concentrations. We concluded that the expression pattern of steroidogenic enzymes in theca and granulosa of follicles growing in each wave in the ewe, paralleled with serum estradiol concentrations, with the exception that concentrations of 3β-HSD in granulosa increased continuously from follicles 3 mm in diameter to the preovulatory follicle.