147 Characteristics of guinea pig oocytes (Cavia porcellus) at two stages of the oestrous cycle on glucose-6-phosphate dehydrogenase activity and oocyte diameter
J. X. Samaniego A , K. M. Castro A , E. F. Bravo A , D. A. Galarza A , L. E. Ayala A , P. Villamediana B , F. P. Perea A and S. Ruiz CA
B
C
Guinea pigs are regarded as excellent animal models within the scientific community, owing to their versatility for studying diseases that affect humans. However, their use has been restricted due to their limited litter size and the absence of an effective in vitro embryo production system (IVEP). For this reason, morphological and functional characterisation of guinea pig oocytes is necessary for further application of assisted reproduction techniques in this species. This study aimed to assess the effect of two stages of the oestrous cycle on glucose-6-phosphate dehydrogenase activity (G6PDa) and oocyte diameter in guinea pig oocytes. Both G6PDa and oocyte diameter assessment have allowed the identification of oocytes highly competent for IVEP. Animals (n = 40) were synchronized with oral progesterone (0.22 mg/kg/day) for 15 days. Cumulus–oocyte complexes (COCs; n = 946) were collected from the ovaries by slicing on Days 2 (periovulatory; n = 20) and 9 (diestrus; n = 20), after oral progesterone was suspended. According to the appearance of the cytoplasm and cumulus cells, COCs were classified as A, B, and C, which are associated with high, intermediate, and poor quality, respectively. Oocytes were stained with brilliant cresyl blue (BCB) and categorized into grown oocytes (BCB+) and growing oocytes (BCB−); oocyte diameter was then measured. Data were analysed by logistic regression and general linear model of SAS. There was an effect (P < 0.0001) of oestrous cycle stage and COC type on proportions of BCB+ oocytes (Table 1). Oocyte diameter was affected by oestrous cycle stage (P = 0.0126) and COC type (P < 0.0001). In conclusion, regardless of the stage of the oestrous cycle, oocyte diameter was greater in COC A and decreased as oocyte quality declined. A greater proportion of high-quality oocytes were observed in the periovulatory than in the diestrus stage. The periovulatory stage seems to be better for obtaining a greater number of good-quality oocytes.
| Variable | Oestrous cycle stage | ||||||
|---|---|---|---|---|---|---|---|
| Periovulatory | Diestrus | ||||||
| A | B | C | A | B | C | ||
| BCB+ % (n) | 73.0a,1 (65/89) | 59.1a,1 (84/142) | 13.6b,1 (11/81) | 50b,2 (24/48) | 36.0c,2 (58/161) | 2.0cd,2 (2/100) | |
| Oocyte diameter µm (n) | 90.6 ± 1.0a (155) | 85.2 ± 0.8b (238) | 82.6 ± 1.2b (98) | 91.2 ± 1.4a (78) | 89.9 ± 0.8a (218) | 83.8 ± 1.0b (159) | |
For each oestrous cycle stage, different letters in the same row differ: a–b, b–d, c–dP < 0.01; b–cP < 0.05.
Between the same COC category, different numbers in the same row differ: 1–2P < 0.01.
