Role of Prolactin in the Gonadotroph Responsiveness to Gonadotrophin‐Releasing Hormone During the Equine Annual Reproductive Cycle

Hodson, David J.; Townsend, Julie; Gregory, SJ; Walters, Clifford A.; Tortonese, Domingo J.

doi:10.1111/j.1365-2826.2010.01986.x

Cited by 21 publications

(22 citation statements)

References 49 publications

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“…During the non-breeding season, all steroids were at the basal level, and in next breeding season after 47 weeks of age, remarkable increments were observed. The reduction in gonadotropins and in turn steroids in the non-breeding winter months could be due to the modulatory role of decreased photoperiod and low hypothalamic GnRH output [29]. The HPG axis is regulated by the negative feedback of steroids on gonadotropins [7], which is difficult to appreciate in this study due to the long interval sampling procedure.…”

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confidence: 76%

“…The prolactin hormone profiles of the colts and fillies in this study reflected seasonality without any direct possibility of modulation of other hormones, at least in the breeding season of birth as there was no overall significant correlation of prolactin with gonadal hormones and gonadotropins. The prolactin action on gonadotrophs during the breeding season has recently been shown to be tightly regulated by dopamine [29]. Profiling of dopamine can thus give better understanding of the relationship between prolactin and other hormones.…”

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confidence: 99%

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Circulating Pituitary and Gonadal Hormones in Spring-born Thoroughbred Fillies and Colts from Birth to Puberty

et al. 2012

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Abstract. The present study was conducted to elucidate the profile of circulating gonadotropins and gonadal hormones from birth to puberty and relationship between gonadal seasonality and hormonal secretion in both sexes of Thoroughbred horses. Spring-born colts (n=6) and fillies (n=9) were blood sampled weekly from jugular vein from birth to 60 weeks of age. Circulating FSH, LH, prolactin, testosterone, progesterone, estradiol-17β, and immunoreactive (ir)-inhibin were measured by radioimmunoassay. In both sexes, the steroid hormones levels were remarkably high at birth, rapidly dropped within a week and remained at the lower levels until the start of second spring after birth. Ir-inhibin was also high during the birth, remaining lowest during winter and again increasing towards the second summer. There was an increase in FSH concentration in foals during the first summer months after birth and in the next summer, the FSH concentration along with that of LH increased significantly. The seasonal increase in circulating prolactin was remarkable even in the first year, and no differences were noted between the two summers. These results clearly demonstrated that the hypothalamo-pituitary axis is already responsive to changes in photoperiod and secrete prolactin similar to adult horses, but pituitary gonadotrophs for FSH and LH secretion is less sensitive. When the values of these hormones in the second breeding season after birth were compared with adult values of the respective sex in the breeding season, no significant differences were observed, indicating that spring-born fillies and colts have already attained the stage of puberty at the second breeding season after birth. Key words: Prolactin, Puberty, Seasonality, Thoroughbred (J. Reprod. Dev. 58: [522][523][524][525][526][527][528][529][530] 2012) E quines are seasonal breeders with activity being highest as days grow longer [1]. There is no univocal reporting of the age of puberty in horses, which has been reported to vary in the range of 7.8-37 months [2]. This variation can be attributed to differences in breeds [3][4][5], locales, management and puberty definition [6,7]. Furthermore, there have been few studies on Thoroughbreds [7][8][9], and most of them were conducted in southern hemisphere. Geographical location influences the season, and there have been fewer reports regarding puberty in horses from the northern hemisphere.There is a dearth of information on the characteristics of circulating gonadotropins and gonadal hormones in Thoroughbred foals immediately after birth through pre-pubertal age until puberty. Previous studies provided information on relatively shorter periods [10,11] of developmental periods after birth, and those studies focused on certain hormones [3,4,6] only. In seasonal breeders, there is evidence for the involvement of both photoperiodic cues and degree of maturity in the onset of puberty [8]. The photoperiodic information is thought to be conveyed to the reproductive and prolactin axis via changes in circulating concentra...

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confidence: 76%

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Circulating Pituitary and Gonadal Hormones in Spring-born Thoroughbred Fillies and Colts from Birth to Puberty

et al. 2012

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“…An apparent connectivity exists between gonadotrophs and lactotroph cells, exhibited by the presence of adherent and gap junctions (Horvath et al 1977, Morand et al 1996. Prolactin (PRL), the hormone product of lactotroph cells, acts on gonadotrophs cells to modulate the secretion of LH (Cheung 1983, Hodson et al 2010a. Lactotrophs are also estrogen sensitive, and gonadotrophs express PRL receptors (Henderson et al 2008).…”

Section: Discussionmentioning

confidence: 99%

Identification of estradiol/ERα-regulated genes in the mouse pituitary

Kim¹,

Gieske²,

Trudgen³

et al. 2011

Journal of Endocrinology

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Estrogen acts to prime the pituitary prior to the GnRHinduced LH surge by undiscovered mechanisms. This study aimed to identify the key components that mediate estrogen action in priming the pituitary. RNA extracted from the pituitaries of metestrous (low estrogen) and proestrus (high estrogen) stage mice, as well as from ovariectomized wildtype and estrogen receptor a (ERa) knockout mice treated with 17b-estradiol (E 2 ) or vehicle, was used for gene expression microarray. Microarray data were then aggregated, built into a functional electronic database, and used for further characterization of E 2 /ERa-regulated genes. These data were used to compile a list of genes representing diverse biological pathways that are regulated by E 2 via an ERa-mediated pathway in the pituitary. This approach substantiates ERa regulation of membrane potential regulators and intracellular vesicle transporters, among others, but not the basic components of secretory machinery. Subsequent characterization of six selected genes (Cacna1a, Cacna1g, Cited1, Abep1, Opn3, and Kcne2) confirmed not only ERa dependency for their pituitary expression but also the significance of their expression in regulating GnRH-induced LH secretion. In conclusion, findings from this study suggest that estrogen primes the pituitary via ERa by equipping pituitary cells with critical cellular components that potentiate LH release on subsequent GnRH stimulations.

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“…Moreover, the seasonal changes in PRL secretion are unlikely to be directly responsible for the seasonal change in reproduction [57], further emphasising this dual site of action for melatonin in regulating photoperiodic physiology. The effect on the hypothalamus to regulate reproduction has been reviewed elsewhere [6], here is summarised the current knowledge on the seasonal regulation of the pituitary hormone PRL (fig.…”

Section: Pt a Melatonin Target Tissue To Control Photoperiodic Respomentioning

confidence: 99%

Encoding and Decoding Photoperiod in the Mammalian Pars Tuberalis

Dupré¹

2011

Neuroendocrinology

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In mammals, the nocturnal melatonin signal is well established as a key hormonal indicator of seasonal changes in day-length, providing the brain with an internal representation of the external photoperiod. The pars tuberalis (PT) of the pituitary gland is the major site of expression of the G-coupled receptor MT1 in the brain and is considered as the main site of integration of the photoperiodic melatonin signal. Recent studies have revealed how the photoperiodic melatonin signal is encoded and conveyed by the PT to the brain and the pituitary, but much remains to be resolved. The development of new animal models and techniques such as cDNA arrays or high throughput sequencing has recently shed the light onto the regulatory networks that might be involved. This review considers the current understanding of the mechanisms driving photoperiodism in the mammalian PT with a particular focus on the seasonal prolactin secretion.

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Role of Prolactin in the Gonadotroph Responsiveness to Gonadotrophin‐Releasing Hormone During the Equine Annual Reproductive Cycle

Cited by 21 publications

References 49 publications

Circulating Pituitary and Gonadal Hormones in Spring-born Thoroughbred Fillies and Colts from Birth to Puberty

Circulating Pituitary and Gonadal Hormones in Spring-born Thoroughbred Fillies and Colts from Birth to Puberty

Identification of estradiol/ERα-regulated genes in the mouse pituitary

Encoding and Decoding Photoperiod in the Mammalian Pars Tuberalis

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