Retinol improves development of bovine oocytes compromised by heat stress during maturation

The objectives of this study were to evaluate: 1) effects of a physiologically relevant elevated temperature on in vitro development of maturing oocytes, 2) effects of retinol on in vitro development of maturing oocytes, and 3) effects of retinol to improve development of oocytes compromised by an elevated temperature. Bovine oocytes were matured for 24 h at 38.5 or 41.0 degrees C (first 12 h) in 0 or 5 microM retinol. After insemination, cleavage and blastocyst development were assessed on d 3 and 8, respectively. Temperature, retinol, and their interaction were included in the statistical model. Culture of oocytes at 41.0 degrees C decreased the proportion of 8- to 16-cell embryos and increased that of 2-cell embryos. In addition, culture at 41.0 degrees C decreased the ability of oocytes to develop to the blastocyst stage. Blastocysts derived from oocytes cultured at 41.0 degrees C had fewer total nuclei. In 3 of the 7 experimental replicates, effects of 41.0 degrees C to reduce blastocyst development were minimal (difference in the development of the control vs. heat stress group was <20%). To provide a more precise test of our hypothesis (retinol administration may improve development of oocytes compromised by heat stress), data were analyzed, including only those replicates (n = 4) in which heat stress reduced development to blastocyst >20%. When this was done, a significant temperature x retinol interaction was noted. The addition of retinol to the maturation medium prevented heat-induced reductions in development of oocytes to blastocyst stage. Results indicate that retinol may protect oocytes from some of the deleterious effects of heat stress.