246IMPROVEMENT OF THE DEVELOPMENTAL CAPACITY OF OOCYTES FROM PREPUBERTAL CATTLE BY INTRAOVARIAN IGF-I APPLICATION

Abstract

The developmental potential of oocytes from prepubertal cattle is lower compared to their adult counterparts. Differences between oocytes from calves and cows have been found with regard to size, ultrastructural characteristics and metabolism. GH and IGF-I receptor mRNA have been identified in the cumulus cells and in oocytes (Izadyar F et al. 1997 Mol. Reprod. Dev. 47, 175–180; Armstrong D. et al., 2002 Reproduction 123 (6), 789–797). It is known that IGF-I and GH affect mRNA expression of glucose transporter 1 (Glut1) as well as glucose uptake by embryos. The goal of this study was to improve the developmental capacity of oocytes from prepubertal cattle and to determine whether an induced increase of GH and IGF-I levels affects the mRNA expression pattern of Glut1, UBF and eIF1A. Holstein calves (n=30), 6–7 months old, were randomly divided into three groups. One group received a single s.c. injection of 500mg of somatotrophin (rbST Posilac, Monsanto Company, St. Louis, MO, USA) and during the subsequent 2 weeks their follicles were aspirated 4 times via transvaginal ultrasound-guided ovum pick-up (OPU). The second group received an intraovarian injection of 6μg rhIGF-I (R&D Systems, Wiesbaden-Nordenstadt, Germany). The third group served as control and received an intraovarian injection of 0.6mL of 10mM acetic acid. All animals were i.m. injected with 60mg FSH (Folltropin®; Vetrepharm Inc., Ontario, Canada) 48h prior to aspiration. The treatments were repeated with the same animal groups at the ages of 9–10, 11–12 and 14–15 months. Five adult cows were i.m. injected each with 100mg FSH. For mRNA expression analysis (RT-PCR), embryos were collected with 2–4 cells, 8–16 cells and as blastocysts. The relative abundance of mRNA for Glut 1 and eIF1A was higher (P<0.05) in 8–16 cell embryos from IGF-I-treated calves and cows than in control and rbST treated calves. The in vitro embryo production (IVP) results are shown in the Table 1. Our data show that IGF-I increased mRNA expression of Glut1 and eIF1A which may improve the developmental capacity of embryos produced from calves. Table 1 OPU/IVP-Results for calves (6–15 months old) in comparison with cows