Effect of angiotensin II with follicle cells and insulin-like growth factor-I or insulin on bovine oocyte maturation and embryo development

Abstract

The objective was to evaluate the effects of angiotensin II (Ang II), insulin-like growth factor-I (IGF-I) and insulin on the nuclear and cytoplasmic maturation of bovine oocytes in the presence of follicular cells. Cumulus-oocyte complexes (COCs) were cultured for 22 h in the presence of follicular cells (control with cells) and Ang II, IGF-I or insulin (treatments), or in the absence of follicular cells (control without cells). Using these five groups, Experiment 1 was conducted with and without the addition of gonadotrophins. Only oocytes in the Ang II group resumed meiosis at rates (88.2 ± 1.8% and 90.7 ± 4.3% for oocytes cultured in the absence or presence of LH/FSH, respectively) similar to those observed for oocytes cultured in the absence of follicular cells (89.7 ± 0.3% and 92.6 ± 2.6%; P < 0.01). In Experiment 2, the effect of Ang II alone and in combination with IGF-I or insulin on oocyte maturation for 7 h (germinal vesicle breakdown), 12 h (metaphase I) and 22 h (metaphase II) was evaluated in a design similar to that of the first experiment. Ang II plus IGF-I or insulin induced the resumption of meiosis, irrespective of the presence of gonadotrophins ( P < 0.01). Experiment 3 used groups similar Experiment 2 to determine the rate of subsequent embryo development, using fetal calf serum (FCS) in the culture medium. The COCs were cultured in maturation medium for 1 h (1 + 23 h), 12 h (12 + 12 h) or 24 h in the presence of follicular cells and the respective treatments and for the remaining period in the absence of follicular cells to complete 24 h. In Experiment 4, BSA was used in lieu of serum in the maturation medium in a 12 + 12 h maturation system. Oocytes matured using the 12 + 12 h system with BSA or FCS in the presence of Ang II + IGF-I had higher rates of blastocyst formation than the other treatments ( P < 0.05). In conclusion, Ang II reversed the inhibitory effect of follicular cells on nuclear maturation of bovine oocytes, irrespective of the presence of gonadotrophins, IGF-I and insulin. However, oocyte cytoplasmatic maturation (i.e., subsequent embryo development), was higher when Ang II and IGF-I were present in the maturation medium containing follicular cells cultured for 12 + 12 h.