Role of insulin-like growth factor-I and follicular fluid from ovarian follicles with different diameters on porcine oocyte maturation and fertilization in vitro

Abstract

The objective of this study was to determine the effects of insulin-like growth factor-I (IGF-I) (0, 60, 120, 180, and 240 ng/mL) and follicular fluid (FF) derived from 2 to 5 and 6 to 10 mm diameter follicles (SpFFs and LpFFs, respectively) added during in vitro maturation (IVM) of porcine oocytes on nuclear maturation and IVF. Cumulus-oocyte complexes (COCs) were matured in NCSU-37 medium supplemented with SpFFs or LpFFs and various IGF-I concentrations. The COCs were cultured for 44 hours, and then fertilized in vitro. Maturation and IVF results were recorded 18 hours after insemination. The IVM (%) was higher (P < 0.05) in the COCs matured in LpFFs than with SpFFs when 0 (90.0 ± 6.9 vs. 76.3 ± 10.7) or 60 ng/mL IGF-I (92.0 ± 8.1 vs. 81.8 ± 10.2) was added. In SpFFs media, there was a quadratic relationship (P < 0.01) between IGF-I concentration and IVM (peak results at IGF-I = 129 ng/mL). However, when the COCs were matured with LpFFs, there was a decreasing linear effect between IGF-I concentration and IVM. At all concentrations of IGF-I, the percentage of degenerated oocytes was higher in COCs matured in SpFFs than in LpFFs. Penetration (%) did not differ (P > 0.05) between COCs matured with SpFFs or LpFFs when 60 (66.8 ± 9.4 vs. 72.7 ± 11.3) or 180 ng/mL of IGF-I (75.7 ± 10.4 vs. 73.8 ± 13.2) were used. Monospermy (%) was similar between SpFFs and LpFFs only with addition of 120 ng/mL IGF-I. The IVF performance (%) did not differ between COCs matured with SpFFs or LpFFs when IGF-I concentrations of 120 (28.5 ± 8.8 vs. 38.5 ± 8.3) and 180 ng/mL (24.3 ± 10.2 vs. 30.12 ± 8.2) were used. There was no effect of IGF-I concentration or of FF type on the number of penetrated sperm per oocyte and on male pronuclear formation. For COCs matured with SpFFs, there was a quadratic relationship between IGF-I concentration and penetration, monospermy, and IVF performance (peak results at IGF-I = 179, 122, and 135 ng/mL, respectively). Thus, on the basis of the observed quadratic relationships, we inferred that when using SpFFs, the addition of IGF-I (122–179 ng/mL) to the IVM medium produced results similar to those obtained with LpFFs without adding IGF-I. In conclusion, the addition of IGF-I to the IVM medium supplemented with SpFFs increased maturation and improved IVF results. Alternatively, IGF-I had no effect on IVM or IVF when used with LpFFs.