PARENT SESSION

(M703) DIFFERENCES IN PRE-PUBERTAL AND ADULT OOCYTE DEVELOPMENTAL COMPETENCE IS CORRELATED WITH OOCYTE cAMP CONTENT IN THE PIG.

Bagg, Melanie¹, Nottle, Mark¹, Armstrong, David¹, Grupen, Christopher¹, ¹ The University of Adelaide, Adelaide, SA, Australia

ABSTRACT- IVM pre-pubertal oocytes display lower developmental competence (DC) than adult oocytes. In previous studies, dibutyryl cAMP (dcAMP) treatment reversibly inhibited meiotic progression and increased DC of pre-pubertal oocytes. This improved DC may result from increasing the intra-oocyte cAMP content. The aim of this study was to compare, in the presence and absence of dcAMP, the cAMP content, meiotic progression and subsequent DC of pre-pubertal versus adult IVM oocytes. Cumulus-oocyte complexes (COCs) aspirated from 3-8 mm follicles of pre-pubertal and adult ovaries underwent 46 h IVM in modified medium 199, with or without 1mM dcAMP for the first 22h. First, oocytes were stained to assess meiotic stage at 0, 16, 22, 40 and 44h IVM. At least 40 oocytes were assessed in each group at each time point over 6 replicates. Second, the intra-oocyte cAMP concentration of zona-free oocytes was determined at 0h and 22h IVM and the remaining oocytes were artificially activated with calcium ionophore at 46h IVM to assess oocyte DC. At least 80 oocytes for cAMP and 120 for DC were assessed in each group at each time point over 3 replicates. There were no meiotic progression differences between pre-pubertal and adult oocytes, with or without dcAMP, at 0 and 44h. In the absence of dcAMP a greater proportion of pre-pubertal oocytes reached MI by 22h compared with adult (69 ± 2% vs. 49 ± 2%, P < 0.03). The presence of dcAMP reduced the proportion of oocytes in MI at 22h for both groups, yet the proportion of pre-pubertal oocytes that progressed to MI was greater than adult (60 ± 2% vs. 26 ± 2%, P < 0.002). At 22h IVM in the absence of dcAMP, adult but not pre-pubertal oocyte cAMP levels increased two-fold compared with 0h (P < 0.04). At 22h of IVM with dcAMP, cAMP content increased two-fold in pre-pubertal oocytes (P < 0.02) and five fold in adult oocytes (P < 0.04) compared with 0h. Under control conditions adult oocytes demonstrated higher DC than pre-pubertal oocytes (59 ± 2% vs. 25 ± 5%, P < 0.0001). IVM with dcAMP improved DC of pre-pubertal (25 ± 5% to 35 ± 6%, P < 0.002) but not adult oocytes (59 ± 2% to 57 ± 11%, P > 0.7). In conclusion, pre-pubertal oocytes accumulate less cAMP than adult during IVM. The presence of dcAMP increases accumulation of cAMP in pre-pubertal oocytes. Processes responsible for controlling oocyte cAMP acquisition require more investigation.

KEY WORDS: Oocyte donor age, oocyte cAMP content, in vitro embryo production, oocyte developmental competence