IGF1R expression in alpaca (Vicugna pacos) ovaries: Preliminary results

Abstract

Alpacas are induced ovulators requiring a stimulus in presence of a mature follicle to trigger the ovulatory process. In this species, ovarian activity occurs in waves of follicular growth and regression. During each follicular wave, one follicle becomes dominant, grows to maturity and finally regresses. Folliculogenesis and ovulation are regulated by gonadotrophins and other factors such as Insulin like growth factor 1 (IGF1). In various species it has been described that IGF1 stimulates proliferation and differentiation of granulose cells. Also, in cows, IGF1 receptor (IGF1R) shows different expression according to the size of follicles. As there are no reports about IGF1R expression in alpacas ovaries, the aim of the study was to evaluate IGF1R expression in alpacas ovaries and analyze if this expression is related to the presence of corpus luteum (CL).The ovaries of 10 alpacas (without CL: n=6, with CL: n=4) were obtained from ?Estación Experimental de altura de Chuquibambilla (Universidad Nacional del Altiplano, Puno, Perú). An immunohistochemical technique was used to detect IGF1R immunostaining in primary and secondary follicles, in granulosa and theca interna cells of tertiary follicles, and in luteal cells. Staining was then evaluated by two independent observers. IGF1R was evaluated as percentage of positive area and analyzed by Student?s t-test. The level of significance was P < 0.05.IGF1R positive area in primary follicles was 82% and 89% in ovaries with and without CL, respectively (p=0.7). Few secondary follicles were observed, and their positive area was around 75% in both groups. Greater staining was observed in granulosa cells of tertiary follicles of ovaries without CL compared with ovaries with CL (94% and 64%, respectively, p=0.0007). No significant differences were found in theca interna cells between groups (22% and 14% with and without CL, respectively, p= 0.11). In both groups, the immunostaining of granulosa cells was greater than theca interna cells (p=0.0016). IGF1R staining was observed in most of luteal cells (89% of positive area).In conclusion, it was demonstrated that IGF1R is expressed in alpaca ovarian follicles and in CL, suggesting a possible role of IGF in follicular development and CL function. Furthermore, IGF1R could be regulated by ovarian steroid hormones, since IGF1R expression was greater in granulosa cells in ovaries without CL, thus with basal progesterone concentrations.