Seasonal effects on the response of ovarian follicles to IGF1 in mares

Abstract

The response of follicles to IGF1 was compared between the transition into the ovulatory season (transitional period) and the ovulatory season (ovulatory period) in eight mares using a cross-over experimental design within periods. Granulosa cells were collected from follicles 15-24 or 25-34 mm and expression of IGF1R, IGF2R, FSHR, LHCGR and PAPPA was determined by qPCR. In addition, 10 mg IGF1 or vehicle were injected into the largest follicle (transitional period) or the second largest follicle (ovulatory period) of a follicular wave before the beginning of diameter deviation between the two largest follicles (mean diameters at injection 19.2 and 20.0 mm during transitional and ovulatory periods respectively). Follicular fluid was collected 24 h after injection for determination of free IGF1, IGFBP, inhibin A and oestradiol levels. Granulosa cells from follicles 25-34 mm, but not follicles 15-24 mm, expressed higher levels of IGF1R (PZ0.01), FSHR (P!0.007) and LHCGR (PZ0.09) during the ovulatory period than during the transitional period, whereas IGF2R expression was higher in transitional than ovulatory follicles (PZ0.06). Follicular IGFBP2 levels were not different (PO0.1) between periods and treatments, whereas IGFBP5 levels were higher (P!0.05) during the ovulatory period. Finally, IGF1 injection before the beginning of deviation induced an approximately twofold increase (PZ0.01) in follicular inhibin A levels during each period and did not affect oestradiol (PO0.1). These results suggest that, as during ovulatory waves, equine follicles during transitional waves are responsive to IGF1 before the beginning of deviation and that, therefore, inadequate IGF1 responsiveness before deviation may not underlie the deficient development of dominant follicles during transition. Reproduction (2008) 136 589-598

Involvement of miRNAs in equine follicle development

“…Follicular aspiration was performed by trans-vaginal ultrasound-guided follicle puncture using a 17 gauge, 55 cm long ovum pickup needle (Popper & Sons, Inc., New Hyde Park, NY, USA) and an Aloka 500V ultrasound scanner (BCF Technology, Rochester, MN, USA) equipped with a 5 mHz curved array transducer, as described in Doyle et al (2008). Antral fluid was completely aspirated from each follicle and aspirates were centrifuged at 700 g for 10 min to separate granulosa cell pellets from fluid supernatant.…”

Hemodynamic, endocrine, and gene expression mechanisms regulating equine ovarian follicular and cellular development

“…Other studies reported no relationship between the granulosa IGF1R mRNA expression and follicle development in cattle (Armstrong et al, 2000), sheep (Hastie & Haresign, 2006), and pigs (Liu et al, 2000). In this regard, it is worth noting that mRNA expression may not precisely reflect the actual abundance of the functional protein (Doyle et al, 2008); therefore, more in‐depth studies are required to characterize the functional IGF1R protein in the follicle wall in relation to follicle development.…”

Artificial photoperiod: it’s influence on mare’s autumn transition period and seasonal anestrus

“…In mares fed with a low energy diet or protein during the winter, Sticker et al (1995a) observed diminished IGF-1 secretion, an important factor for follicular development. In mares, IGF-1 and its receptors increase specifically in the dominant follicle before divergence (Doyle et al 2008), making it possible to attribute a special role to IGF-1 in the selection and subsequent development of ovulatory follicles (Ginther et al 2004).…”