Expression of messenger ribonucleic acid encoding for steroidogenic acute regulatory protein and enzymes, and luteinizing hormone receptor during the spring transitional season in equine follicles

Watson, E.D.; Bae, Sung-Eun; Steele, M G; Thomassen, Ragnar; Pedersen, Hanne Gervi; Bramley, T. A.; Hogg, Charis; Armstrong, David G.

doi:10.1016/j.domaniend.2003.10.006

Cited by 21 publications

(23 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The mares in the present study were hemi-ovariectomized prior to onset of ovarian cyclicity. In a previous study, we confirmed that removal of one ovary during transition did not affect circulating concentrations of luteinizing hormone, follicle-stimulating hormone or oestradiol, or follicle growth during the ovulatory season compared with mares with two ovaries (Watson et al 2004). Therefore, it is unlikely that removal of one ovary in the present study had any influence on follicular function in the remaining ovary.…”

Section: Discussionsupporting

confidence: 67%

“…During spring transition, in many mares, large follicles grow sequentially in the ovaries to a size similar to preovulatory follicles and then regress without ovulating (Ginther 1990, Watson et al 2002a. These large follicles are steroidogenically incompetent, produce significantly lower concentrations of oestradiol and progesterone than preovulatory follicles within the natural breeding season, and have significantly lower expression of mRNA encoding key steroidogenic enzymes (Davis & Sharp 1991, Watson et al 2002b, 2004.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Insulin-like growth factors-I and -II and insulin-like growth factor-binding protein-2 in dominant equine follicles during spring transition and the ovulatory season

Watson

Bae²,

Thomassen³

et al. 2004

Reproduction

View full text Add to dashboard Cite

The period between seasonal anoestrus and cyclicity is characterized in many mares by cyclical growth and regression of large dominant follicles. The insulin-like growth factor (IGF) system plays a key role in follicular growth and regression; therefore, we hypothesized that changes in the IGF system and its binding proteins would modulate onset of cyclicity in mares. Ovaries were obtained from pony mares on the day after detection of an actively growing 30 mm transitional anovulatory follicle, and also at the second or third oestrus of the breeding season on the day after the preovulatory follicle reached 30 mm in diameter. Size of dominant follicles at the time of removal was similar in transition (32 6 0.8 mm) and at oestrus (34 6 0.6 mm). IGF-I mRNA was present in granulosa cells, with low thecal expression, whereas IGF-II mRNA was confined to the theca layer. Expression of IGF-I and -II mRNAs, and intrafollicular concentrations of oestradiol, were lower (P < 0.01; paired t test) in transitional anovulatory follicles than in preovulatory follicles. Messenger RNA encoding IGFBP-2 was present in both theca and granulosa layers. Steady-state concentrations of mRNA encoding IGFBP-2 mRNA increased (P < 0.001) in theca in preovulatory follicles. Intrafollicular concentrations of IGFBP-2 were higher (P < 0.001) in transitional than in preovulatory follicles. The similarity in circulating concentrations of IGF-I in transitional and cyclic mares, suggested that the somatotrophic axis is not involved in transition from anovulatory to ovulatory cycles. The results suggest that the increased expression of IGF-I and -II mRNAs in preovulatory follicles, along with the decrease in IGFBP-2 concentrations, could increase the bioavailability of intrafollicular IGF in large follicles during the breeding season, and support our hypothesis that intrafollicular IGF bioavailability must exceed a threshold level before ovulation can occur.

show abstract

Section: Discussionsupporting

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Insulin-like growth factors-I and -II and insulin-like growth factor-binding protein-2 in dominant equine follicles during spring transition and the ovulatory season

Watson

Bae²,

Thomassen³

et al. 2004

Reproduction

View full text Add to dashboard Cite

show abstract

“…The reason for this is not known but it does bring the possibility that a reduced responsiveness not only to LH but also to FSH may be involved in the failure of these follicles to acquire ovulatory capacity. The higher LHCGR expression in dominant-size follicles during the ovulatory period than during the transitional period is consistent with previous results (Watson et al 2004b). Although not critically tested in the present study, reduced LHCGR expression in transitional follicles is likely mediated, at least in part, by low levels of IGF1 in these follicles (Hirakawa et al 1999).…”

Section: Discussionsupporting

confidence: 82%

“…The largest follicle thus continues growing and becomes dominant whereas smaller follicles (subordinate follicles) cease growing and regress. However, although transitional dominant follicles can reach final diameters similar to their ovulatory counterparts, they have an underdeveloped theca, are poorly vascularised, express low levels of receptors for luteinising hormone (LHCGR) and have reduced capacity to produce steroids (Watson & Al-zi'abi 2002, Acosta et al 2004, Watson et al 2004b. These features critically determine the anovulatory fate of these follicles.…”

Section: Introductionmentioning

confidence: 99%

“…Low circulating LH levels and low follicular expression of LH receptor likely play a role (Donadeu & Ginther 2002a, Watson et al 2004b. In addition, follicular responsiveness to circulating follicle-stimulating hormone (FSH) may be altered during the anovulatory season (Donadeu & Ginther 2002a, King et al 2008, although seasonal changes in FSH receptor (FSHR) expression in follicles have not been determined.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Doyle

Hogg²,

Watson³

et al. 2008

Reproduction

View full text Add to dashboard Cite

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

show abstract