Hyperprolactinemia Induced by Pituitary Isografts Suppresses the Priming Effect of LH-Releasing Hormone in Normal and Hypogonadal Mice

Lewis, Claire E.; Fink, George; Dow, R. C.; Morris, John F.

doi:10.1159/000124585

Cited by 11 publications

(5 citation statements)

References 22 publications

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“…In rodent models, the effect of prolactin on gonadotrophin secretion is varied but generally supports an inhibitory role for prolactin on GnRH/gonadotrophin secretion. In normal and hypogonadal mice, an increased level of serum prolactin, using pituitary isografts, suppresses LH release (63). In OVX oestrogen‐treated mice, a 7‐day icv infusion of prolactin markedly suppressed serum LH levels (64).…”

Section: Discussionmentioning

confidence: 99%

Kisspeptin Cells in the Ovine Arcuate Nucleus Express Prolactin Receptor but not Melatonin Receptor

Rao

Pereira

et al. 2011

Journal of Neuroendocrinology

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Melatonin is secreted at night by the pineal gland and governs the reproductive system in seasonal breeders, such as sheep. The mechanism by which melatonin regulates reproduction is not known. The circannual rhythmicity of other factors, including prolactin, is also regulated by photoperiod via changes in melatonin secretion. In sheep, plasma prolactin levels are higher in the nonbreeding season than the breeding season. Kisspeptin, synthesised by neurones in the ovine arcuate nucleus (ARC) and preoptic area, is a key regulator of reproduction through stimulation of gonadotrophin-releasing hormone secretion and its expression in the ARC is reduced during the nonbreeding season. We hypothesised that kisspeptin expression is directly, or indirectly, regulated by melatonin and/or prolactin. We first examined the expression of melatonin receptor (MTNR1A) in kisspeptin (Kiss1 mRNA) neurones in the ARC of ovariectomised (OVX) sheep using double-label in situ hybridisation. MTNR1A mRNA was not expressed by kisspeptin neurones, whereas strong expression was detected in the pars tuberalis. We then examined the expression of the long-form prolactin receptor (PRLR-L) in ARC kisspeptin neurones. In OVX ewes, approximately 60% of kisspeptin neurones expressed PRLR-L mRNA at similar levels in the breeding and nonbreeding seasons. We then aimed to determine whether prolactin treatment during the breeding season regulates kisspeptin expression in the ARC. Continuous central infusion of prolactin (20 μg/h for 7 days) in oestradiol-treated OVX sheep did not alter Kiss1 mRNA expression or luteinising hormone secretion, although it induced substantial phosphorylated signal transducer and activator of transcription 5-immunoreactive nuclei staining in the mediobasal hypothalamus. We conclude that the seasonal change in kisspeptin neurones cannot be regulated directly by melatonin, although it may be a result of changes in prolactin levels. Despite this, kisspeptin expression was unchanged after exogenous prolactin treatment in breeding season ewes.

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Section: Discussionmentioning

confidence: 99%

Kisspeptin Cells in the Ovine Arcuate Nucleus Express Prolactin Receptor but not Melatonin Receptor

Rao

Pereira

et al. 2011

Journal of Neuroendocrinology

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“…Physiologically, the rapid effect of E on type II lactotrophs may contribute to the regulation of the reproductive axis. Testosterone and E, by rapidly facilitating PRL release, may contribute to the negative feedback effects of these steroids on gonadotrophin release as stimulation of lactotrophs is known to inhibit gonadotrophins (Lewis et al 1986; Makino et al 1987).…”

Section: Discussionmentioning

confidence: 99%

Rapid actions of 17β‐oestradiol on a subset of lactotrophs in the rat pituitary

Christian

Morris

2002

The Journal of Physiology

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Increasingly the role of rapid mechanisms of steroid action in physiological regulation are being recognised. We have investigated rapid effects of 17β‐oestradiol (E) on prolactin (PRL) release in vitro. Pituitary segments from male rats were incubated for 5, 10 or 20 min in Earle's balanced salt solution containing 1.2 mm tannic acid (to enable visualisation of exocytosed secretory granules by electron microscopy) either alone (control) or containing 10−10‐10−8m E conjugated to bovine serum albumin (E‐BSA). PRL and leuteinising hormone (LH) release from pituitary segments were also determined in response to E and E‐BSA by radioimmunoassay. Within 10 min E‐BSA and E (10−12‐10−6m) stimulated a significant (P < 0.05) concentration‐dependent release of PRL but not LH. After exposure to experimental media for 5 min, only occasional exocytosis from type I lactotrophs (characterised by large polymorphic secretory granules) was observed in either control or E‐BSA treated tissue. In contrast, E‐BSA (10−10‐10−8m) induced a significant (P < 0.05) increase in the number of exocytotic profiles from type II lactotrophs (characterized by smaller, spherical granules). This effect was not inhibited by removal of extracellular calcium, or by pre‐treatment of cells with the RNA synthesis inhibitor actinomycin‐D (0.5 μg ml−1), the protein synthesis inhibitor cycloheximide (1 μg ml−1) or the anti‐oestrogen ICI 182,780 (1 μm). FACS analysis demonstrated binding of E‐BSA‐fluorescein isothiocyanate (FITC) (10−10‐10−7m) to a subpopulation of anterior pituitary cells. The E‐BSA‐FITC binding sites assumed a patchy distribution across the cell surface. In conclusion, we report for the first time a rapid, non‐genomic effect of E on PRL secretion in normal pituitary tissue.

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“…As mentioned before, our results demonstrate that the effect of the ovarian factor can be overridden by a sufficiently high LHRH stimulus. Recently, it was shown that hyperprolac¬ tinaemia induced by pituitary isografts suppressed the magnitude of the priming effect of LHRH in intact female mice (Lewis, Fink, Dow & Morris, 1986). These results also suggest that prolactin, with or without FSH, may play an important role in regulating the pituitary responsiveness to LHRH through the ovaries.…”

Section: Discussionmentioning

confidence: 90%

The self-priming action of LHRH increases the low pituitary LH and FSH response caused by ovarian factors: observations in vitro

Koning

Tijssen²,

Rees³

1989

Journal of Endocrinology

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Pituitary glands taken from intact rats on day 2 of dioestrus and incubated with LHRH show a biphasic pattern of LH and FSH release. Initially the release of the gonadotrophins is low (first-phase or lag-phase response), but increases during further incubation with LHRH (second-phase or primed-state response). Removal of the influence of an unidentified ovarian factor either by ovariectomy or prolonged incubation in medium only leads to an increased (lag-phase) response to LHRH. The development of the increased response after prolonged incubation was prevented by the addition of cycloheximide to the media, implicating that this process is dependent upon the synthesis of protein. Steroid-free material (bovine follicular fluid or rat ovarian extracts) prevented the development of this process. In addition, it was shown that steroid-free rat ovarian extracts were also able to induce the development of a lag phase in pituitary glands from ovariectomized rats. Finally, it was found that steroid-free ovarian extracts reversed the self-priming effect of LHRH. The biological activity which reduced the responsiveness of the pituitary gland towards stimulation by LHRH was eliminated after the use of protein-denaturating techniques such as increased temperature or addition of methanol. The presence of this activity in ovaries, did not vary during the oestrous cycle, contrary to inhibin-like activity. Hence the ovarian factor responsible for the low lag-phase response is a protein which is probably not identical to inhibin. It is concluded that a non-steroidal ovarian factor reduces the responsiveness of the anterior pituitary gland to LHRH.(ABSTRACT TRUNCATED AT 250 WORDS)

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Hyperprolactinemia Induced by Pituitary Isografts Suppresses the Priming Effect of LH-Releasing Hormone in Normal and Hypogonadal Mice

Cited by 11 publications

References 22 publications

Kisspeptin Cells in the Ovine Arcuate Nucleus Express Prolactin Receptor but not Melatonin Receptor

Kisspeptin Cells in the Ovine Arcuate Nucleus Express Prolactin Receptor but not Melatonin Receptor

Rapid actions of 17β‐oestradiol on a subset of lactotrophs in the rat pituitary

The self-priming action of LHRH increases the low pituitary LH and FSH response caused by ovarian factors: observations in vitro

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