36 EFFECT OF cAMP MODULATORS DURING OOCYTE IN VITRO MATURATION ON GAP JUNCTIONAL ACTIVITY OF VITRIFIED BOVINE OOCYTES

Abstract

Oocyte cryopreservation is a strategic tool for in vitro embryo production, but low rates of cryosurvival are reported for bovine oocytes. Simulated physiological oocyte maturation system (Albuz et al. 2010 Hum. Reprod. 25, 12) uses cAMP modulators to increase oocyte competence by the extension of meiosis block and gap junctional communications activity. The aim of this study was to investigate the effect of simulated physiological oocyte maturation system on gap junctional activity of vitrified bovine oocytes. Oocytes from slaughterhouse ovaries were divided into 4 groups: C (control: fresh immature oocytes); V (vitrified immature oocytes); PM-V (vitrified oocytes after a 2-h pre-in vitro maturation phase – in the presence of AMPc modulators, 100 μM Forskolin, and 500 μM IBMX); and PM (fresh immature oocytes subjected to pre-in vitro maturation). Viable oocytes (n = 404 obtained from 4 replicates) were stained with Calcein-AM using the protocol of Thomas et al. (2004 Biol. Reprod. 71(4), 1142–1149) in order to measure gap junctions activity. Images were captured in fluorescence microscope, and fluorescence intensity was analysed with ImageJ software. Mean fluorescence intensity of each group was normalized to control group to obtain relative intensity value. Means were compared by Kruskal-Wallis test and Dunn post-test. A second analysis was performed considering the percentage of each staining pattern (low, middle, and high intensity) for each group. Results were analysed using Fisher exact test. All statistical analysis were performed in GraphPad Instat program with 5% significance level. Results demonstrated that all treatments induced an increase (P < 0.05) in fluorescence intensity (V: 1.76 ± 1.13; PM-V: 1.58 ± 0.98; PM: 1.38 ± 0.94) compared with control (C: 1.00 ± 0.48). Regarding the staining patterns analyses, immature vitrified oocytes (V group) differed from control group in middle and low patterns (G1, calibrator – high: 11.2%ab, middle: 43.8%a, low: 44.9%a; G2 – high: 8.2%ab, middle: 63.9%b, low: 27.9%b; G3 – high: 16.3%a, middle: 42.3%a, low: 41.3%a; G4 – high: 6.7%b, middle: 53.9%ab, low: 39.3a). In conclusion, unexpectedly, vitrification also increased gap junctional activity, as was found for pre-in vitro maturation group. However, staining pattern analysis results showed only vitrified group was different from control, suggesting vitrified and pre-in vitro maturation groups could have gap activity affected by different ways. This research was supported by FAPERJ (E26/111.61/2013) and CAPES.