Anti-Mullerian hormone: expression and possible roles in the porcine ovary

Anti-Mullerian Hormone (AMH) is expressed by the granulosa cells of early developing follicles and plays an inhibiting role on the initial and cyclic processes of follicular recruitment in some species. We investigated the expression of AMH in the ovary of pre-pubertal and adult female pigs. Ovaries of 80-days old gilts (n = 12) and multiparous sows (n = 4) where collected and fixed in a 4% paraformaldehyde in 0.2 M phosphate buffer solution (pH 7.2–7.4) at 4 C for 24 h and embedded in paraffin. Immunohistochemistry analysis was performed using the peroxidase block and avidine-biotine complex with a primary polyclonal antibody. The ovarian sections were scored semi quantitatively for extent of AMH expression by two independent observers. Arbitrary scores were given as follows: 0, no expression; 1, mild expression; 2, moderate expression; 3, strong expression. The final score was the average values between the two observers. AMH expression was observed in the pre-granulosa cells of primordial follicles and in the granulosa cells of follicles of different stages of development (primary, pre-antral and pre-ovulatory follicles) as well as in the oocyte. In pre-pubertal gilts, primordial follicles showed the weakest pattern of staining (mean score: 1.1 ± 0.01; 1.7 ± 0.01 and 1.6 ± 0.01, respectively for primordial, primary and pre-antral follicles; p £ 0.01), but no difference in staining was observed between primary and pre-antral follicles. Additionally, the pattern of AMH expression was similar among primordial, primary and pre-antral follicles in multiparous sows, however pre-ovulatory follicles showed the strongest staining (mean score: 2.2 ± 0.2; 2.5 ± 0.2; 2.4 ± 0.2 and 3.6 ± 0.2, respectively for primordial, primary, pre-antral and pre-ovulatory follicles; p £ 0.01). The corpora lutea also expressed AMH, and no staining was observed in atretic follicles. In general, follicles in sow ovaries showed stronger AMH expression than in gilts (primordial: 1.1 ± 0.1 vs. 2.2 ± 0.1; primary: 1.7 ± 0.1 vs. 2.5 ± 0.1, and pre-antral: 1.6 ± 0.1 vs. .4 ± 0.1, respectively for gilts and sows; p £ 0.01). These results show, for the first time, that AMH expression in the porcine ovary is different from other species, like rodents and human. This suggests that AMH might play a different role in folliculogenesis, and may not be a follicular recruitment inhibitor, as in other species.