Fig. 4. Oocyte wet mass (WM)/`initial control' wet mass (WM₀) ratio after a 60-h in vitro incubation. Follicle-enclosed oocytes were incubated in the presence of different steroids: 11-deoxycorticosterone (DOC, 5 ng ml^–1); 17,20ß-dihydroxy-4-pregnen-3-one (MIS, 40 ng ml^–1); cortisol (12 ng ml^–1); cortisol (12 ng ml^–1) plus 17,20ß-dihydroxy-4-pregnen-3-one (40 ng ml^–1). IC, initial control; ethanol vehicle was used as the negative control (NC). Values are mean ± s.d. (N=7). Different letters indicate significant differences between treatments (P<0.05). The percentage of germinal vesicle breakdown (GVBD) after a 60 h incubation is shown below for each group.