Luteinizing Hormone Response to Oxytocin Is Steroid-Dependent

Evans, John J.; Robinson, G.; Catt, Kevin J.

doi:10.1159/000126167

Cited by 18 publications

(9 citation statements)

References 21 publications

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“…At this time, medium, oxytocin (100 n M ) [5]or NPY (1 µ M ) [4], alone or in combination, were perifused for 2 h. Samples of 20 min in duration were collected for measurement of LH by radioimmunoassay. For the study of tissue stimulated with GnRH, after the 2-hour pre-exposure, a 4-min pulse of GnRH (10 n M ) was delivered and delivery of oxytocin and/or NPY continued as in the prior treatment.…”

Section: Methodsmentioning

confidence: 99%

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Release of Luteinizing Hormone from the Anterior Pituitary Gland in vitro Can Be Concurrently Regulated by at Least Three Peptides: Gonadotropin-Releasing Hormone, Oxytocin and Neuropeptide Y

2001

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Normal action of the female ovulatory cycle is dependent on a surge of luteinizing hormone (LH) from the pituitary. Regulation of the levels of LH is therefore vital to reproductive function. It has long been established that gonadotropin-releasing hormone (GnRH) is an important component of the regulatory processes. Other peptides, including oxytocin and neuropeptide Y (NPY), have also been observed to affect LH activities. However, the possibility of the concurrent actions of these peptides has rarely been considered despite their documented presence in the hypophyseal blood during pro-oestrus. In this study, the direct effects of oxytocin and NPY on LH release were studied, as well as the effects of both peptides simultaneously. Also, pituitaries were stimulated with GnRH, and the effects of pre-exposure of the pituitary tissue to oxytocin or NPY were investigated. Further, the effect of oxytocin and NPY together on GnRH stimulation of LH release was determined. Anterior pituitaries were collected from adult female rats on the morning of pro-oestrus. Hemipituitaries were cut in two and placed in a chamber of a perifusion system. The pituitary tissue was perifused with medium alone, oxytocin and NPY, separately or in combination, for 2 h after an initial 100-min equilibration period with no peptide present. Fractions of eluate were collected and LH was measured by radioimmunoassay. LH output was stimulated by both oxytocin (p < 0.01) and NPY (p < 0.02). Furthermore, the addition of NPY to oxytocin during the perifusion elicited a further increase in LH release (p < 0.05). The pituitary tissue was exposed to a 4-min pulse of GnRH after 220 min. Stimulation of LH release by GnRH was synergistically augmented by exposure of the tissue to either oxytocin (p < 0.01) or NPY (p < 0.05) for the immediately preceding 2 h. When NPY was added to oxytocin in the perifusion medium, stimulation of LH release by GnRH was increased even further (p < 0.05). Oxytocin also synergistically enhanced the effect of a second, primed GnRH pulse, whereas the effect of NPY was less robust. This study therefore demonstrated that LH release is modified in the presence of oxytocin, NPY or GnRH alone, and also that combinations of the peptides produce further variations in LH output. Therefore, the concentrations of LH that are present in vivo are likely to be at least partly the result of the co-ordinated effects of combinations of peptides acting on the pituitary.

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Section: Methodsmentioning

confidence: 99%

“…Oxytocin has been demonstrated to increase the secretion of LH from pituitary cells in static culture [5, 6], but there are no reports of its effects in dynamic perifusion conditions. The situation with regard to the direct action of NPY on gonadotropes is controversial.…”

Section: Introductionmentioning

confidence: 99%

Release of Luteinizing Hormone from the Anterior Pituitary Gland in vitro Can Be Concurrently Regulated by at Least Three Peptides: Gonadotropin-Releasing Hormone, Oxytocin and Neuropeptide Y

2001

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“…It is known that oxytocin increases release of LH from dispersed anterior pituitary cells [17, 33]and from tissue pieces [34], and thus effects on stores may have taken place. This study noted that oxytocin stimulated c-fos and LH expression within cells as detected by immunocytochemistry.…”

Section: Discussionmentioning

confidence: 99%

Regulation of C-fos Protein in Gonadotrope Cells by Oxytocin and Gonadotropin-Releasing Hormone

Abbas¹,

Evans²

2000

Neuroendocrinology

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The integrated regulation of luteinizing hormone (LH) from the anterior pituitary gland is vital to the functioning of the ovulatory cycle in the female and consists of several components acting at different time points. The best-studied is the rapid release of LH elicited by gonadotropin-releasing hormone (GnRH). The so-called primary (immediate early) response genes (PRGs), including c-fos, regulate relatively long-term activities, such as mitosis, protein synthesis, protein release and cell differentiation. Regular ovulatory cycles occur as a result of interaction of several peptide factors including the primary factor, GnRH and oxytocin, although GnRH and oxytocin do not have identical activities. We wished to determine whether oxytocin could mediate changes in expression of c-fos protein and compare its effects with those of GnRH. Anterior pituitary glands were collected from female rats at proestrus and a single-cell suspension prepared. Cells were incubated with oxytocin or GnRH at selected concentrations for various times. C-fos protein was extracted and submitted to Western blot analysis. Other cells were stained immunohistochemically for c-fos and LH following incubation with the peptides and fixation. There was an increase in c-fos protein from 15 to 60 min in Western blots of cells from all incubations. After immunohistochemistry, it was observed that both oxytocin (100 nM) and GnRH (100 nM) increased the percentage of cells that expressed c-fos protein (p < 0.001) and of cells that expressed LH (p < 0.001). The responses to the peptides were concentration dependent. We found that neither all LH-containing cells expressed c-fos, nor all c-fos-containing cells immunostained for LH. The effects of the peptides were not the same. High concentrations of GnRH (1 µM) induced the appearance of a higher percent of LH-containing cells having c-fos than did 10 nM GnRH (p < 0.01), whereas a lower percent of LH-containing cells with c-fos were observed when the oxytocin concentration was raised from 10 nM to 1 µM (p < 0.02). It appears, therefore, that the two peptides have different regulatory effects on LH-containing cells, indicating the possibility of specialized function. The results emphasize the suggestion that stimulation of LH secretion is not the sole index of gonadotrope-directed activity by a peptide. Collectively, these results indicate that the peptides oxytocin and GnRH are able to modulate processes that are associated with longer-term activities of gonadotropes and also demonstrate that specific subpopulations of LH-containing gonadotropes are stimulated to express c-fos.

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“…In addition, other investigations have revealed that peptides act at the pituitary to directly elicit LH release and/or to alter the effect of GnRH on the level of LH release [13]. It is believed that the steroidal milieu of the pituitary also has a significant effect on peptide activity [13, 14]. …”

Section: Introductionmentioning

confidence: 99%

Effects of Galanin and Leptin on Gonadotropin-Releasing Hormone-Stimulated Luteinizing Hormone Release from the Pituitary

Peters

Towler²,

Mason³

et al. 2008

Neuroendocrinology

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Background: A number of peptides regulate luteinizing hormone (LH) release. In some cases, these peptides exert an effect at the pituitary, to directly regulate LH release and/or to modulate the effects of gonadotropin-releasing hormone (GnRH). A link between nutrition and reproductive function is well established. In this study we investigated the effects of two peptides associated with appetite control, galanin and leptin, on the regulation of LH release from the pituitary. Methods: Using perifused anterior pituitary tissue from freely fed rats, we investigated the effect of galanin on basal LH release and GnRH-stimulated LH release from pituitaries in a high-estrogen (proestrus) and a low-estrogen (metestrus) environment. In addition, we examined the effect of galanin on LH release following GnRH self-priming. The effect of inhibiting protein synthesis, with cycloheximide, was also studied under these conditions. Finally, the effects of leptin alone and on a galanin-modulated LH response were investigated. Results: There was no detectable effect of leptin, either alone or in conjunction with galanin. We observed that galanin enhanced GnRH stimulation of LH secretion, an effect that was dependent on protein synthesis and on an estrogenized environment. In addition, importantly, galanin also enhanced the LH response in GnRH self-primed pulses. Conclusion: Our results provide further details on the effect of galanin on the LH surge, particularly the effect on the response to pulsatile GnRH and the effect of protein production, and thereby indicate a means by which appetite- and nutrition-related peptides may act on the ovulatory cycle at the pituitary.

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Luteinizing Hormone Response to Oxytocin Is Steroid-Dependent

Cited by 18 publications

References 21 publications

Release of Luteinizing Hormone from the Anterior Pituitary Gland in vitro Can Be Concurrently Regulated by at Least Three Peptides: Gonadotropin-Releasing Hormone, Oxytocin and Neuropeptide Y

Release of Luteinizing Hormone from the Anterior Pituitary Gland in vitro Can Be Concurrently Regulated by at Least Three Peptides: Gonadotropin-Releasing Hormone, Oxytocin and Neuropeptide Y

Regulation of C-fos Protein in Gonadotrope Cells by Oxytocin and Gonadotropin-Releasing Hormone

Effects of Galanin and Leptin on Gonadotropin-Releasing Hormone-Stimulated Luteinizing Hormone Release from the Pituitary

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