Summary Heat shock may disrupt oocyte function by increasing the generation of reactive oxygen species (ROS). We evaluated the capacity of the antioxidant melatonin to protect oocytes using two models of oxidative stress - heat shock and the pro-oxidant menadione. Bovine cumulus-oocyte complexes (COC) were exposed in the presence or absence of 1 M melatonin to the following treatments during maturation: 38.5°C, 41°C and 38.5°C+5 M menadione. In the first experiment, COC were matured for 3 h with 5 M CellROX® and analyzed by epifluorescence microscopy to quantify production of ROS. The intensity of ROS was greater for oocytes exposed to heat shock and menadione than for control oocytes. Melatonin reduced ROS intensity for heat-shocked oocytes and oocytes exposed to menadione, but not for control oocytes. In the second experiment, COC were matured for 22 h. After maturation, oocytes were fertilized and the embryos cultured for 7.5 days. The proportion of oocytes that cleaved after fertilization was lower for oocytes exposed to heat shock and menadione than for control oocytes. Melatonin increased cleavage for heat-shocked oocytes and oocytes exposed to menadione, but not for control oocytes. Melatonin tended to increase the developmental competence of embryos from heat-shocked oocytes but not for embryos from oocytes exposed to menadione or from control oocytes. In conclusion, melatonin reduced production of ROS of maturing oocytes and protected oocytes from deleterious effects of both stresses on competence of the oocyte to cleave after coincubation with sperm. These results suggest that excessive production of ROS compromises oocyte function.
Bibliographical noteFunding Information:
Financial support. This research was supported by Research Grant Award No. US-4719-14 from BARD (the United States - Israel Binational Agricultural Research and Development Fund) to PJ Hansen and Z Roth, by Fundação de Amparo à Pesquisa do Estado de São Paulo (grant no. 2015/ 20379-0 to Cláudia Lima Verde Leal and PhD scholarship no. 2017/04376-6 to Fernanda Cavallari de Castro) and by funds from the L.E. 'Red' Larson Endowment. The authors thank Florida Beef, Wauchula, Florida, for allowing us to procure ovaries and Eddie Cummings and Dr Paula Tribulo for technical assistance.
© Cambridge University Press 2019.
- Heat shock
- Reactive oxygen species.