Plasma FSH, inhibin A and inhibin isoforms containing pro- and -alphaC during winter anoestrus, spring transition and the breeding season in mares

Watson, E.

doi:10.1530/reprod/123.4.535

Cited by 6 publications

(9 citation statements)

References 6 publications

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“…This has been confirmed by a later paper (Donadeu and Ginther 2002). In the presence of anovulatory follicle waves in spring, circulating concentrations of inhibin A were higher than in anoestrus, but were significantly lower than during the same period of growth of an ovulatory follicle (Watson et al 2002a). Furthermore, in contrast to preovulatory follicles which contained high concentrations of circulating inhibin A, large anovulatory transitional follicles in our mares contained significantly lower concentrations of inhibin A (Watson et al 2002b).…”

Section: Discussioncontrasting

confidence: 50%

“…In cyclic mares, mean concentration of oestradiol during growth of an ovulatory follicle was significantly higher (P < 0.001) than during the growth of an anovulatory follicle. Plasma concentrations of inhibin A were significantly higher (P < 0.05) during growth of a preovulatory follicle than during growth of an anovulatory follicle in spring transition (see Watson et al 2002a). Concentrations of oestradiol, progesterone and inhibin A were significantly lower in fluid collected from dominant, anovulatory transitional follicles than from preovulatory follicles.…”

Section: Resultsmentioning

confidence: 92%

“…Histological sections were subsequently stained with haematoxylin and eosin. Hormone assays, immunostaining, in situ hybridization, and Western ligand blots were carried out as described previously (Xu et al 1995, Armstrong et al 1998, Nicholas et al 2002, Watson et al 2002a.…”

Section: Methodsmentioning

confidence: 99%

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Molecular and functional characteristics of dominant follicles during spring transition in mares: a review

Watson¹,

Bae²,

Armstrong³

2003

PHK

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Many mares enter a period of spring transition between winter anoestrus and cyclicity when follicles may reach preovulatory size, yet fail to ovulate. The aim of the present study was to determine the morphological, functional and molecular characteristics of large dominant transitional follicles. Follicle growth was monitored regularly from February through July in 25 pony mares. In some of the mares, one of the ovaries was removed on the day after an anovulatory follicle reached 30 mm, and the contralateral ovary was removed during cyclicity on the day after the preovulatory follicle reached 30 mm. Samples of the large follicle were processed for immunohistochemistry and in situ hybridisation, and follicular fluid was frozen. Hormonal control of growth of the large transitional follicles was similar to that seen during cyclicity. However concentrations of oestradiol were significantly lower than during growth of the preovulatory follicle and LH remained low until ovulation. During growth of anovulatory follicles, uterine oedema was sometimes present along with low, but significant, elevations in oestradiol. Transitional follicles had poorly developed theca that received a scant blood supply and there was little VEGF, the main ovarian angiogenic factor, in these follicles. Transitional follicles contained only low concentrations of oestradiol and progesterone and there was low expression of mRNA encoding StAR, the steroidogenic enzymes, and LHr in the follicle walls. Our results show that the poor steroidogenic capacity of transitional follicles is directly related to low gene expression of the steroidogenic enzymes, possibly caused by the low levels of LHr and IGF mRNAs. The scant blood supply and poor development of the theca would also contribute to the steroidogenic incompetence of these follicles. Expression of IGF-I and-II mRNAs were lower in transitional anovulatory follicles than in preovulatory follicles and intrafollicular concentrations of IGFBP-2 were significantly higher in transitional than in preovulatory follicles. These results suggest that the bioavailability of intrafollicular IGF is enhanced in large preovulatory follicles during the breeding season and suggests that intrafollicular IGF bioavailability must exceed a threshold level before an ovulation can occur.

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Section: Discussioncontrasting

confidence: 50%

Section: Resultsmentioning

confidence: 92%

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Molecular and functional characteristics of dominant follicles during spring transition in mares: a review

Watson¹,

Bae²,

Armstrong³

2003

PHK

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“…2003b). Only minor waves (largest follicle <21 mm) occurred during the middle of the anovulatory season or deep anoestrus, whereas major waves were often detected during the first 2 months (fall transition) and the last 2 months (spring transition) of the anovulatory season, in agreement with previous studies (Ginther 1990; Watson et al. 2002).…”

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confidence: 60%

Follicle Development in Mares

Donadeu

Pedersen

2008

Reprod Domestic Animals

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The mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or to regress) at any given stage of follicular wave development. Periodic development of follicular waves continuously occurs during most of post-natal life in the mare and is influenced by factors such as stage of oestrous cycle, season, pregnancy, age, breed and individual so that different types of follicular waves (minor or major, ovulatory or anovulatory) and different levels of activity within waves may develop under different physiological conditions. Changes in gonadotropin levels and/or in the sensitivity of follicles to circulating gonadotropins seem to account largely for these physiological variations in follicle development.

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“…In early spring, the period of transition between anoestrus and cyclicity is characterized by a resurgence of follicular activity, irregular exhibition of oestrous behaviour and resumption of secretion of gonadotrophins and ovarian steroids (Ginther 1990, Davis & Sharp 1991. 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%

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

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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.

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Plasma FSH, inhibin A and inhibin isoforms containing pro- and -alphaC during winter anoestrus, spring transition and the breeding season in mares

Cited by 6 publications

References 6 publications

Molecular and functional characteristics of dominant follicles during spring transition in mares: a review

Molecular and functional characteristics of dominant follicles during spring transition in mares: a review

Follicle Development in Mares

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

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