Testosterone and Dihydrotestosterone, but Not Estradiol, Selectively Maintain Pituitary and Serum Follicle-Stimulating Hormone in Gonadotropin-Releasing Hormone Antagonist Treated Male Rats

Arslan, Mohammed; Weinbauer, Gerhard F.; Khan, Shafiq A.; Nieschlag, Eberhard

doi:10.1159/000125144

Cited by 24 publications

(16 citation statements)

References 22 publications

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“…When male rats were administered GnRH antiserum and/or GnRH antagonists, pulsatile FSH release was maintained but that of LH was abolished, giving further credence to the view that reproductive function may be regulated by more that one GnRH neuronal system [50]. Additionally, testosterone supplementation of intact rats can maintain the FSH content of the pituitary in GnRH antagonist-suppressed males [51]. A possible autocrine-paracrine regulation of FSH release at the pituitary level by activins, inhibins, and follistatins also cannot be overlooked [52][53][54].…”

Section: Discussionmentioning

confidence: 94%

Episodic Gonadotropin Secretion in the Mature Fowl: Serial Blood Sampling from Unrestrained Male Broiler Breeders (Gallus domesticus)1

Vizcarra

Kreider

Kirby

2004

Biology of Reproduction

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Forty-week-old male broiler breeders were used in two experiments. Males were reared as recommended by the breeder, housed in individual cages, and cannulated to facilitate blood sampling. In experiment 1, blood samples were collected at 10- min intervals for 4 h commencing the day of cannulation (Day 0) and for 12 h on each of Days 1 and 2. In experiment 2, blood samples were collected at 10-min intervals for 8 h on Day 1. After centrifugation, plasma was stored at -20 degrees C until LH, FSH (experiment 1 and 2), testosterone, and corticosterone (experiment 1) concentrations were determined by RIA. Different statistical methods used to identify hormone secretion profiles revealed a characteristic pulsatile pattern of LH and FSH in plasma. However, LH pulses were more frequent and had greater amplitude than FSH pulses. Less than 32% of the FSH pulses were associated with LH episodes. Conversely, the association between LH and testosterone pulses averaged 83% in birds with testis weight greater than 10 g. Concentrations of corticosterone tended to increase after cannulation and remained elevated for only 3-4 h. Our data indicate that LH, FSH, and testosterone secretion is pulsatile in male broiler breeders. Additionally, LH pulses are associated with testosterone episodes but not with FSH pulses. The pulsatile pattern of FSH secretion, which is unique from those of LH, in adult males suggests that FSH secretion is independently regulated in the adult male fowl.

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Section: Discussionmentioning

confidence: 94%

Episodic Gonadotropin Secretion in the Mature Fowl: Serial Blood Sampling from Unrestrained Male Broiler Breeders (Gallus domesticus)1

Vizcarra

Kreider

Kirby

2004

Biology of Reproduction

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“…This finding might be explained by the decreased serum testosterone levels observed in this study. In fact, earlier reports have shown that testosterone directly increased FSH secretion on cultured pituitary cells [29, 33]and also in male rats when the action of GnRH was blocked [34, 35]. Furthermore, the effects of testosterone on inhibin, activin and follistatin, which may differentially regulate FSH production and secretion, have been implicated in the testosterone stimulation on FSH secretion [36, 37].…”

Section: Discussionmentioning

confidence: 99%

Regulation of Gonadal and Somatotropic Axis by Chronic Intraventricular Infusion of Insulin-Like Growth Factor 1 Antibody at the Initiation of Puberty in Male Rats

Pazos

Sánchez‐Franco²,

Balsa³

et al. 1999

Neuroendocrinology

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There has been increasing experimental evidence to suggest that insulin-like growth factor 1 (IGF-I) may be one of the essential regulators in the reproductive system of the rat. IGF-I is synthesized in the hypothalamus and IGF-I immunoreactivity increases during puberty. Consequently we hypothesized that centrally located IGF-I might contribute to the initiation of puberty. Centrally located IGF-I was immunoneutralized to assess this hypothesis. Male Wistar rats, 28 days old, were infused intracerebroventricularly with specific purified IgGs from rabbit IGF-I antiserum (IGF-I-Ab). The intracerebroventricular administration of IGF-I-Ab resulted in a reduction in testicular weight and consequently in delayed pubertal development. There was also a reduction in serum testosterone, pituitary immunoreactive (IR) luteinizing hormone (LH) and serum IR follicle-stimulating hormone (FSH). The accumulation of βLH mRNA was not modified, whereas βFSH mRNA was increased. An increment in the serum growth hormone (GH) levels was also observed. There were no significant alterations in hypothalamic IR growth hormone releasing factor content, although IR somatostatin (SRIH) content was increased by IGF-I-Ab. The body weight gain remained unaltered. As a whole, our study suggests that centrally located IGF-I influences pubertal development, production and release of gonadotropins and supports the finding that endogenous centrally located IGF-I plays a role at the initiation of puberty in the male rat. It also gives support to the physiological role of centrally located IGF-I in the release of GH mediated by hypothalamic SRIH at the initiation of puberty.

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“…Recent studies have shown that in the male rat in which GnRH stimulation of the anterior pituitary is prevented with a GnRH antagonist, androgens will potently and selectively stim ulate the release of FSH [6][7][8], In females, it is known that the estrous increase in FSH is independent of GnRH stimulation [39] , Consequently, rising T titers on proestrous evening [9,40] coupled with an increased numbers of AR might initiate the selective release of FSH from the AP on estrous morning. This hypothesis is consistent with previous studies by Gay and Tomacari [9] concerning the effect of passive immunoneutralization o fT o n FSH secretion in the female.…”

Section: Discussionmentioning

confidence: 99%

“…Received: March 26, 1990 Accepted after revision: June 8, 1990 anterior pituitary gland [4] and occurs in both male and female rats [5], Several studies have also suggested that T may play a role in the selective release of follicle-stimulating hormone (FSH) by the anterior pituitary gland of rats of both sexes [6][7][8][9],…”

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confidence: 99%

A Characterization of Estrogen’s Influence on Anterior Pituitary Androgen Receptor: Effect of Bromocriptine Treatment

Rodriguez

1991

Neuroendocrinology

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The action of gonadal steroids are mediated through the binding to specific intracellular receptors. Our recent studies have demonstrated that estrogen (E) treatment will increase the concentration of cytosolic androgen receptor (AR) in the anterior pituitary (AP) gland perhaps reflecting in increased sensitivity of this tissue circulating androgen. However, chronic E treatment also increases AP weight and cell number. Consequently, the following studies were performed to determine the relationship between increases in AP cytosolic AR and increases in AP weight following chronic E treatment. Gonadectomized male and female Fischer 344 (F344) rats were implanted with a 5-mm Silastic capsule of 17β-estradiol. Control animals were sham implanted. Animals were sacrificed at 1 3, 7 and 21 days after the commencement of E treatment and AP glands were weighed and processed for cytosolic AR and nuclear estrogen receptor (ER) content. AR and ER were determined by in vitro binding assays using ³H-dihydrotestosterone and ³H-estradiol, respectively. AP weight increased significantly by 3 days of E treatment in females and by 7 days in males (p < 0.05). However, AP weight of E-treated males was significantly less than females throughout (p < 0.05). Significant increases in AP cytosolic AR content (fmol bound/gland) were detected within 1 day of E treatment to female rats but not until 7 days in male rats. AP cytosolic AR content peaked at 7 days of E treatment in females and 21 days in males. AP cytosolic AR concentration (expressed as per milligram cytosol protein) peaked 3 days after E at which time there were significant E effects in both males and females. AR concentration was not elevated following 21 days of E treatment to female rats. These data suggested that the increases in AP weight following 21 days of E treatment were masking the effects of E on AP cytosolic AR when expressed on a per milligram protein basis. Consequently, we inhibited E-induced AP growth by the simultaneous administration of bromocriptine (BR). BR was administered concurrently with E to female F344 rats by the implantation of a constant release pellet of BR (25 mg/animal/21 days). Animals were sacrificed 21 days following E treatment. Concurrent BR treatment significantly reduced AP weight and plasma prolactin levels following E treatment and increased the concentration but not the content of AR (p < 0.05). These data demonstrate that increases in AR number in the AP as a result of E exposure is not a consequence of AP growth. This suggests that E-induced increases in AR are not related to lactotroph proliferation.

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Testosterone and Dihydrotestosterone, but Not Estradiol, Selectively Maintain Pituitary and Serum Follicle-Stimulating Hormone in Gonadotropin-Releasing Hormone Antagonist Treated Male Rats

Cited by 24 publications

References 22 publications

Episodic Gonadotropin Secretion in the Mature Fowl: Serial Blood Sampling from Unrestrained Male Broiler Breeders (Gallus domesticus)1

Episodic Gonadotropin Secretion in the Mature Fowl: Serial Blood Sampling from Unrestrained Male Broiler Breeders (Gallus domesticus)1

Regulation of Gonadal and Somatotropic Axis by Chronic Intraventricular Infusion of Insulin-Like Growth Factor 1 Antibody at the Initiation of Puberty in Male Rats

A Characterization of Estrogen’s Influence on Anterior Pituitary Androgen Receptor: Effect of Bromocriptine Treatment

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