Effect of human chorionic gonadotropin on oocyte maturation and developmental competence in buffalo

Abstract

We hypothesized that human chorionic gonadotropic (hCG) could replace LH in the maturation media for buffalo oocytes, and hCG administration before ovum pick-up (OPU) enhances in-vitro development of buffalo oocytes. Objectives were 1) to investigate the effect of hCG supplementation on nuclear maturation, oocyte development, and granulosa cell mRNA abundance of genes related to growth and antioxidant pathways and 2) to determine the effect of hCG administration before OPU on in-vitro oocyte development. In Experiment 1, buffalo oocytes retrieved from slaughterhouse ovaries were maturated in the media supplemented with 0.5 μg of LH or 2 IU of hCG. After fertilization, cleavage and embryo were assessed on 48 h and 7 d of the culture, respectively. The nuclear maturation of the oocytes and granulosa cells mRNA abundance of genes (AREG, EREG, NRG1, CYP19A1, GDF9, CASP9, SOD1) were assessed after maturation. In Experiment 2, buffaloes were synchronized and superstimulated with FSH and 6 h before OPU, randomly assigned to either receive saline (CON, n = 4) or 1500 IU of hCG (hCG, n = 6). Four OPU sessions per buffalo were conducted at weekly intervals and retrieved oocytes were maturated and fertilized in-vitro. In Experiment 1, nuclear maturation, cleavage, embryo production, and mRNA abundance of the genes related to growth and steroidogenesis did not differ between treatments but SOD1 gene expression tended (P = 0.10) to lower in hCG treatment as compared with LH. In Experiment 2, oocytes retrieved from hCG-treated buffaloes resulted in a higher proportion of cleavage (84.0 vs. 42.5 ± 8.9 %, P = 0.02) and embryo (84.0 vs 24.0 ± 7.3, P < 0.01) than CON. In conclusion, hCG supplementation in the maturation media yielded comparable outcomes to that of LH, and hCG administration 6 h before OPU enhanced the in-vitro developmental competency of the buffalo oocytes.