Retinol improves development of heat-stressed oocytes during maturation

Addition of retinol may improve development of maturing oocytes stressed by culture. Objective was to evaluate retinol for improving development of heat-stressed oocytes. Cumulus oocyte complexes (COC) were matured for 24 h at 38.5 or 41.0°C (first 12 h) in 0 or 5 μM all trans-retinol. Ability of putative zygotes (268-297/treatment) to cleave and develop to blastocyst was assessed on days 3 and 8 after fertilization, respectively. Fixed effects in statistical model included temperature, retinol, and the interaction. Data were tested to ensure normality. Culture of COC at 4l.0°C did not affect lysis (1.6 and 2.1% for 38.5 and 41.0°C; SEM=0.8) or cleavage after fertilization (75.4 and 72.2% for 38.5 and 41.0°C; SEM=3.8). Within cleaved embryos however, culture of COC at 41.0°C increased 2-cell (10.6 versus 6.2% for 41.0 and 38.5°C; SEM= 1.3; P< 0.04) but decreased 8-16 cell (41.4 versus 51.1% for 41.0 and 38.5°C, SEM=4.7; P< 0.05) embryos and development to blastocyst (20.0 vs 27.5% for 41.0 and 38.5°C, SEM= 2.2; P<0.007). Blastocysts derived from heat-stressed COC had fewer nuclei (85.3 versus 94.0 for 41.0 and 38.5°C; SEM=6.7; P < 0.005; Hoechst staining). Addition of retinol during maturation did not improve development of COC regardless of culture temperature. In three replicates, effects of 41.0°C for reducing development of COC to blastocyst were minimal. When these replicates were deleted from analysis, a significant temperature x retinol interaction was observed (n= 4 reps; 189-197 COC/treatment) for development to blastocyst (P<0.01) and number of nuclei (P<0.004). Addition of retinol to COC compromised by heat stress during maturation prevented heat-induced reductions in development to blastocyst (24.6 versus 14.7% for 38.5 and 41.0°C; and 23.2 and 22.0% for 38.5 and 41.0°C cultured in presence of 5 μM retinol; SEM = 2.4). Also, culture of COC at 38.5°C in 5 μM retinol increased number of nuclei in blastocysts (102.6 versus 98.7 for 38.5 C and 41.0° C; and 120.5 versus 95.1 for 38.5 and 41.0°C cultured in 5 μM retinol; SEM= 5.0). Retinol may protect oocytes that are heat-stressed during maturation from the deleterious effects of elevated temperature.