Effects of Bromocriptine and Ectopic Pituitary Transplants on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

Prins, Gail S.; Bartke, Andrzej; Chandrashekar, Varadaraj; Reiher, Jill; Hodges, Sherie; Meyers, Rita

doi:10.1159/000124917

Cited by 7 publications

(5 citation statements)

References 27 publications

(37 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast, others have measured bound nuclear androgen receptors and observed a significant decrease in their number following SD treatment, an effect found to be secondary to the suppression of plasma T levels [10]. We have also found that bromocriptine treatment mark edly reduced total pituitary nuclear androgen receptors in adult hamsters exposed to LD [11]; however, this effect was indepen dent of serum T.It is currently believed that androgen receptors are primarily nuclear proteins which can differ in activational status. In the unoccupied form, the receptor possesses weak affinity for chro matin and is readily displaced into the cytosol (or supernatant) following cell disruption and fractionation by centrifugation.…”

contrasting

confidence: 51%

“…Seminal vesicles were weighed together with coagulat ing glands and their respective secretions. Plasma T, PRL, LH and FSH levels were measured by radioimmunoassays as described pre viously |6, 7,11,15]. The results were expressed in terms of NIH rat LH-RP3 and rat FSF1 RP2 reference preparations and a purified hamster PRL preparation.…”

Section: Animals and Hormone Assaysmentioning

confidence: 99%

“…In the male Syrian (golden) hamster, short photoperiods (SD) suppress gonadotropin re lease and testicular function and increase sensitivity to testoster one (T) feedback. Accordingly, spontaneous or long-photoperiod (LD)-induced recovery of pituitary and gonadal function is associated with reduced plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) responses to inhibition by T [1, 2, 4], In addition, prolactin (PRL) is involved in mediating the effects of photoperiods on testicular function in this species [4,5] and can modulate the sensitivity of the hypothalamic-pitu itary system to T feedback [6,7], To understand the intracellular mechanism of this altered T sensitivity, several laboratories have examined the effects of the photoperiod, melatonin an d /o r PRL on the pituitary and hypo thalamic androgen receptors [8][9][10][11]. However, the results are Received: March 2, 1990 Accepted after revision: April 30, 1990 inconsistent, a finding which may be explained in part by tech nical differences.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Influence of Photoinhibition, Photostimulation and Prolactin on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

1990

Self Cite

View full text Add to dashboard Cite

Testosterone (T) feedback sensitivity is markedly altered in adult male golden hamsters following exposure to short photoperiods (SD). Using a technique which measures total androgen receptors within the cell nucleus, the present study examined pituitary and hypothalamic nuclear androgen receptor levels in animals exposed to (1) long days (LD) or SD in the presence and absence of a constant T level supplied via a Silastic implant, (2) photostimulation following SD-induced testicular regression and (3) short-term prolactin injections following SD-induced testicular regression. Short photoperiods were associated with a drop in nuclear androgen receptor levels which was correlated with a decline in circulating T. When constant T was supplied to gonadectomized hamsters, those exposed to SD possessed higher pituitary and similar hypothalamic nuclear androgen receptor levels than those exposed to LD. As expected, plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were greatly reduced in SD-exposed, castrated, T-treated hamsters as compared to LD-exposed, castrated, T-treated animals. Photostimulation of intact SD-exposed hamsters for 5 or 10 days was associated with a decline in pituitary nuclear androgen receptors. Prolactin treatment caused no noticeable change in pituitary or hypothalamic androgen receptors even though plasma LH and FSH levels were significantly increased. These results support the hypothesis that altered T feedback mechanisms controlling LH and FSH release following chronic exposure to SD may be related to an alteration in the amount of androgen receptors present in the anterior pituitary.

show abstract

contrasting

confidence: 51%

Section: Animals and Hormone Assaysmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Influence of Photoinhibition, Photostimulation and Prolactin on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

1990

Self Cite

View full text Add to dashboard Cite

show abstract

“…Under long daylength, treatment with bromocriptine at doses that suppress prolactin to concentrations measured under short daylength does not lead to gonadal atrophy (Prins et al 1988). Much higher doses of bromocriptine do cause testicular regression (Bex et al 1978) although this has not been a consistent finding (Klemcke et al 1984).…”

Section: Role Of Prolactin In Species With Photoperiodic Inhibition Omentioning

confidence: 98%

Seasonal prolactin secretion and its role in seasonal reproduction: a review

Jd¹

1992

Reprod. Fertil. Dev.

130

View full text Add to dashboard Cite

The majority of seasonally breeding mammals show a seasonal pattern of prolactin secretion with peak concentrations in spring or summer and a nadir in autumn or winter. Photoperiod influences prolactin secretion via its effects on the secretion of the pineal hormone melatonin. Preliminary evidence suggests that the effects of melatonin on both prolactin and gonadotrophin secretion are via a common target area, possibly within the anterior hypothalamus, and that differences in response to photoperiod may be due to differences in the processing and/or interpretation of the melatonin signal. In contrast to seasonal gonadotrophin secretion, the seasonal changes in prolactin are not due to changes in the sensitivity of a feedback loop and so must be due to direct effects on the hypothalamic pathways that control prolactin secretion. Little else can be said with confidence about the neuroendocrine mechanisms that lead to the seasonal changes in prolactin secretion. Dopamine and noradrenaline turnover in the arcuate nucleus and median eminence decrease under short daylength. If catecholamine turnover in these structures is positively correlated with catecholamine concentrations in the long or short hypophysial portal vessels, it is unlikely that the decrease in prolactin concentration in winter is due to the effects of increased concentrations of dopamine or noradrenaline in the portal vessels. There is, however, evidence for increased pituitary sensitivity to dopamine under short daylength, so increased dopamine concentrations may not be required for suppression of prolactin secretion at this time. In addition to the diminished secretion of prolactin under short daylength, rate of prolactin synthesis and pituitary content of prolactin also decline although the mechanisms that regulate these changes are poorly understood.Although all seasonal breeders show a seasonal change in prolactin secretion, there are continuously breeding species in which prolactin secretion is also under photoperiodic control. It is likely therefore that a seasonal pattern of prolactin secretion is only evidence of neuroendocrine sensitivity to changing photoperiod. Depending upon the species, this sensitivity to the seasonal changes in daylength may or may not be accompanied by seasonal changes in a biological endpoint such as seasonal reproduction or indeed other adaptations. Whether the seasonal change in prolactin secretion is an endocrine mediator of such adaptations remains in contention. Certainly in some species this signal does have a role in reproduction. For example, in species with an obligate seasonal embryonic diapause, the seasonal increase in prolactin can act as a luteotrophin (mink and western spotted skunk) or luteostatin (Bennett's and tammar wallabies). In species where seasonal anoestrus or oligo-or azoospermia are due to a direct effect of photoperiod on gonadotrophin secretion, the seasonal changes in prolactin levels may also have been used by some species to influence seasonal reproduction. For example, the increase in ...

show abstract

“…In the hypothalamus, it modifies the turnover of neurotransmitters involved in the control of the pituitary (Steger et al, 1982, 1984, 1986). In the pituitary, it influences the number of androgen receptors (Prins et al, 1988). Actions of PRL on the hypothalamic‐adenohypophyseal system result in the stimulation of follicle‐stimulating hormone (FSH) synthesis and release (Bartke et al, 1981; Steger et al, 1983; Carrillo et al, 1984) and reduction of the sensitivity of gonadotropin release to negative testosterone feedback (Bartke et al, 1984; Matt et al, 1984).…”

Section: Role Of Prl In the Control Of Seasonal Breeding In The Male mentioning

confidence: 99%

Prolactin in the Male: 25 Years Later

Bartke

2004

Journal of Andrology

Self Cite

View full text Add to dashboard Cite

In an article published 25 years ago in the first volume of the Journal of Andrology (Bartke et al, 1980), we reported evidence of involvement of prolactin (PRL) in the control of testicular growth in the golden hamster. In this seasonally breeding species, testes undergo regression in the fall and recover their size and activity the following spring. PRL-secreting transplants of anterior pituitaries augmented the stimulatory effect of treatment with human chorionic gonadotropin on the recrudescence of the regressed testes, while treatment with an inhibitor of PRL release, bromocriptine, delayed recrudescence of the testes and the seminal vesicles induced by exposure to long photoperiods. Role of PRL in the Control of Seasonal Breeding in the Male HamsterStudies conducted in our laboratory following the abovereferenced report of the effects of bromocriptine (Bartke et al, 1980) reaffirmed the role of photoperiod-induced alterations in plasma PRL levels in the control of seasonal transitions between periods of full testicular activity and testicular quiescence in the golden hamster and identified a number of mechanisms involved in the actions of PRL. In the male golden hamster, PRL acts at multiple levels of the hypothalamic-pituitary-testicular axis. In the hypothalamus, it modifies the turnover of neurotransmitters involved in the control of the pituitary (Steger et al, , 1984. In the pituitary, it influences the number of androgen receptors (Prins et al, 1988). Actions of PRL on the hypothalamic-adenohypophyseal system result in the stimulation of follicle-stimulating hormone (FSH) synthesis and release Steger et al, 1983;Carrillo et al, 1984) and reduction of the sensitivity of gonadotropin release to negative testosterone feedback Our studies of the role of PRL in seasonal breeders were supported by NICHD.Correspondence to: Dr Andrzej Bartke, Departments of Physiology and Internal Medicine, Southern Illinois University School of Medicine, 801 N Rutledge, Springfield, IL 62794-9628 (e-mail: abartke@siumed.edu).Received for publication May 7, 2004; accepted for publication May 8, 2004. ( Bartke et al, 1984;Matt et al, 1984). This latter effect is of particular interest, because the major shifts observed in the sensitivity of luteinizing hormone (LH) and FSH release to feedback control by gonadal steroids accompany annual cycles of reproductive activity in both sexes of many (presumably all) seasonal breeders and are critically important for transitions between reproductive activity and quiescence. Reduced sensitivity of the hypothalamus and the pituitary to negative feedback of sex steroids during annual reactivation of the gonads resembles the endocrine changes that take place during puberty in both seasonal and nonseasonal breeders, including humans.In the hamster testis, PRL, along with the gonadotropins, regulates the expression of its own receptors (Klemcke et al, 1984(Klemcke et al, , 1986Amador et al, 1985) and LH receptors (Bex et al, 1978; and enhances the responsiveness of Leydig cells to LH stim...

show abstract

Effects of Bromocriptine and Ectopic Pituitary Transplants on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

Cited by 7 publications

References 27 publications

Influence of Photoinhibition, Photostimulation and Prolactin on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

Influence of Photoinhibition, Photostimulation and Prolactin on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

Seasonal prolactin secretion and its role in seasonal reproduction: a review

Prolactin in the Male: 25 Years Later

Contact Info

Product

Resources

About