Somatostatin and regulation of prolactin secretion

Enjalbert, A; Bertrand, P.; Dafniet, M. Le; Epelbaum, Jacques; Hugues, Jean‐Noël; Kordon, C.; Moyse, Emmanuel; Peillon, F; Shu, Christine

doi:10.1016/0306-4530(86)90050-8

Cited by 26 publications

(21 citation statements)

References 37 publications

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“…Hence, the use of less-sensitive methodologies to measure changes in mRNA may explain the inability of previous studies to detect changes. Somatostatin has been shown previously to modulate PRL synthesis [24] and the results reported here confirm and extend this knowledge. Similar to what occurred with Pit-1, SS had no effect on basal PRL mRNA levels.…”

Section: Discussionsupporting

confidence: 81%

“…In addition, estra diol is involved in the mechanisms determining the size and number of lactotrophs [20][21][22] in the anterior pitu itary. The effects of estrogens on PRL are most likely both indirect, through modulation of hypothalamic factors [17,19,23,24] and posterior pituitary hormone release [18-20. 25], and direct at the level of the lactotroph [14-16, 26, 27], Indeed, these effects can be mediated directly at the level of the PRL gene since it contains an estrogen response element (ERE) [28].…”

Section: Introductionmentioning

confidence: 99%

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In vivo and in vitro Regulation of Pituitary Transcription Factor-1 (Pit-1) by Changes in the Hormone Environment

et al. 1996

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Pituitary transcription factor-1 (Pit-1 or GHF-1) is a transcription factor specific to the anterior pituitary and is involved in the expression and regulation of the growth hormone (GH), prolactin (PRL) and thyroid-stimulating hormone (TSH) β-subunit genes. The expression of these three genes can be modulated by changes in the hormone environment and it is thought that some of these effects are mediated through Pit-1, but little is known about the physiological regulation of this transcription factor. Therefore, we first asked whether Pit-1 gene expression is modified as a result of changes in the in vivo gonadal steroid environment and if this could be correlated with changes in GH and/or PRL mRNA levels. Secondly, we sought to determine if sex steroids affect the mRNA levels of these three peptides by acting at the level of the pituitary and whether these effects are androgen or estrogen mediated. Finally, how sex steroids modulate the response of these three genes to the hypothalamic neuropeptides growth hormone-releasing hormone (GHRH) and somatostatin (SS) was analyzed. To this end, we compared Pit-1 GH and PRL mRNA levels in the anterior pituitary of intact, castrated, and castrated testosterone-replaced adult male rats. In addition, primary cultures of adult male pituitaries were used to study the direct effects of both androgens and estrogens on Pit-1 GH, and PRL mRNA levels. In situ hybridization histochemistry was used to compare relative levels of Pit-1 GH and PRL mRNA. Densitometric analysis of the in vivo studies showed that castration resulted in a 57, 40 and 55% decline in Pit-1 GH and PRL mRNA signal levels, respectively. Furthermore, replacement with testosterone (T) at the time of castration completely prevented the decline in all three mRNA species (ANOVA: Pit-1 mRNA, p < 0.0001; GH mRNA, p < 0.0001; PRL mRNA, p < 0.0001). In vivo, both T (10^–7M) and estradiol (10^–9 M) were capable of stimulating Pit-1 mRNA and PRL mRNA levels, while dihydrotestosterone (DHT; 10^–7M) had no effect. There was no effect of any of these steroid treatments on GH mRNA levels in vitro. Addition of GHRH to the cultures increased GH mRNA levels, as well as those of Pit-1 and PRL, and SS had the opposite effect on GH mRNA levels. Whereas the GH response to GHRH was not significantly modified by exposure to sex steroids, the effect of SS was. The presence of sex steroids was capable of modifying the Pit-1 and PRL responses to both GHRH and SS. These results clearly indicate that changes in circulating levels of sex steroids modulate the expression of Pit-1 in the anterior pituitary and that these changes can be correlated with commensurate modifications in GH and PRL mRNA levels. Furthermore, the effect on both Pit-1 and PRL mRNA levels occurs, at least in part, at the level of the anterior pituitary and is an estrogen-receptor-mediated event. In contrast, the effects of gonadal steroids on GH mRNA levels are less direct and are most likely mediated at the level of the hypothalamus, as w...

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Section: Discussionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

In vivo and in vitro Regulation of Pituitary Transcription Factor-1 (Pit-1) by Changes in the Hormone Environment

et al. 1996

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“…Anterior pituitary glands were removed and dispersed as previously described (38,39). Briefly, the anterior pituitaries were cut into small cubes and, after enzymatic digestion (consecutive incubation with trypsin (Sigma, St. Louis, MO, USA; 5 mg/ml for 15 min) and DNase (Sigma; 2 pg/ml for 1 min)), were washed in a CaZf/MgZ'-free medium and mechanically dispersed with a Pasteur Pipette.…”

Section: Cell Preparation and Culturesmentioning

confidence: 99%

Temperature and Protein Kinase C Modulation of Gonadotropin‐Releasing Hormone Receptors in Pituitary Cells from Intact or Castrated Male Rats

Leblanc

I’Heritier

Mounier

et al. 1990

J Neuroendocrinology

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Unite de recherches sur la dynamique des ensembles neuroendocriniens, U 159 INSERM, 2ter rue d'AIesia, 75014 Paris, France.t Pharmacologie Neuro-lmmuno-Endocrinienne (CNRS UA 11 13), lnstitut Pasteur, 28 rue du Dr Roux, 75015 Paris, France.Key words: gonadotropin-releasing hormone receptors, protein kinase C, pituitary cell culture, castration. AbstractBinding constants of ['251]Des-Gly,0-(D-Ala,)-gonadotropin-releasing hormone-ethylamide (GnRHa) to dispersed pituitary cells were evaluated in a 4-day culture. Cells were sampled either from intact or from castrated male rats and binding was measured at various temperatures before or after treatment with phorbol-12-myristate-13-acetate (PMA) or l-5-(isoquinolinyl-sulfc.xyl) 2-methylpiperazine (H7), which activate or inhibit, respectively, protein kinase C (PKC). In cells from intact rats incubated with increasing concentrations of ligand at 21 "C for 25 rnin, the Scatchard plot was not linear and calculation of the Hill coefficient (NH) was indicative of positive cooperativity (NH= 1.26_+0.02). Such non-linearity was not observed when cells were incubated at 0.5 "C for 3 h. In that condition the maximal number of binding sites measured at equilibrium (Bmax) increased (15.1 t0.05 versus 9.3k0.5 fmoles x mg-' proteins at 21 "C). Two control experiments permitted us to rule out the possibility that lower B , , , at 21 "C might reflect internalization: 1) Cells were first incubated with the ligand at 21 "C for 25 min and subsequently for 3 additional hours at 0.5 "C. Preincubation did not affect the B , , , obtained at 0.5 "C; 2) when the radioligand bound to the cell surface was washed out with an acidic buffer, only 13% of the specific radioactivity was retained irrespective of the ligand concentration applied, a much lower value than the 40% binding difference observed between 05°C and 21°C. When the cells were incubated with PMA, the Scatchard plot was linearized and the B, , , recorded at 21 "C increased by 50% over control cells (13k0.7 fmolesxrng-' proteins). Conversely, inhibition of PKC by H7, a preferential PKC inhibitor, was ineffective. In contrast, cells sampled from castrates exhibited linear and comparable Scatchard plots at either 0.5 or 21 "C, with B , , , values of 14.4k0.3 and 15k0.34 fmoles x mg-' proteins, respectively. PKC activation did not affect binding in that model, but H7 decreased the number of sites (B,,,= 10.7t0.9) and induced appearance of positive cooperativity (NH= 1.36k0.07). Taken together, these experiments reveal a pool of GnRH receptors in the pituitary of intact rats that recognizes the ligand in a phosphorylation-dependent manner. These binding sites also became evident when biological properties of the membrane were modified by temperature or cell homogenization. After castration, PKC activation was no longer a prerequisite for recruitment of the total population of receptors whereas protein kinase inhibition resulted in a reduction of maximal binding. Finally, our observations demonstrate that GnRH binding can exhibit positiv...

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“…In order to prevent pressure artefacts, we also used large diameter micropipettes (5 to 10 pm) which permit receptors appear t o be coupled to various transduction mechanisms. They are negatively coupled with adenylate cyclase (19, 20, 38, 39) and could be directly o r indirectly negatively coupled with phospholipase C (24)(25)(26). I n addition, they could also be coupled with calcium and/or potassium channels (17,18,40).…”

Section: Electrophysiolo~icul Experimmlsmentioning

confidence: 99%

“…DA was also shown to affect calcium and potassium fluxes in those cells (18). These phenomena are likely to be implicated in the mechanism o f action of DA on PRL release since, in addition to cyclic AMP (CAMP) production (19)(20)(21)(22) and modulation of phosphatidylinositol phosphate breakdown (23)(24)(25)(26), regulation of PRL secretion is dependent on calcium entry into lactotrophs (27,28).…”

mentioning

confidence: 99%

Interaction of Opiate Peptides with Dopamine Effects on Prolactin Secretion and Membrane Electrical Properties in Anterior Pituitary Cells from Lactating Rats

Enjalbert

Israël

Zhang

et al. 1990

J Neuroendocrinology

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Met-enkephalin and b-endorphin induced a partial reversion of the dopamine inhibition of prolactin release from pituitary cells of lactating rats in primary culture. This effect of opiate peptides was dose-dependent with an EC50 of 40f8 nM and 4 5 + 7 nM and maximal blockade of dopamine inhibition of 60% and 68% for Met-enkephalin and /]-endorphin, respectively. Naloxone antagonized the effect of Met-enkephalin with an EC50 of 22_$12 nM. Furthermore, this Met-enkephalin effect on dopamine inhibition of prolactin secretion appeared non-competitive since it reduced maximal inhibition without affecting the apparent affinity of dopamine. Finally, it should be noted that the two opiate peptides had no effect on spontaneous prolactin release.In electrophysiological experiments, local ejection of dopamine on tested cells induced an hyperpolarization concomitant with an increase of the membrane conductance. Ejection of Met-enkephalin or /&endorphin alone did not modify the electrical properties of the cells (resting potential, membrane conductance and excitability). In contrast, both peptides blocked in a reversible manner the dopamine-induced electrical responses. These effects were antagonized by naloxone. However, this interaction of opiate peptides with dopamine electrical response was not observed on all cells tested. We conclude that the blocking effect of opiates on dopamine-induced hyperpolarization may account, at least in part, for the ability of these peptides to interact with dopamine inhibition of prolactin release.Prolactin (PRL) release is under a tonic inhibitory control by dopamine (DA) (1). Opiates have been shown to interact with DA inhibition of PRL secretion both at the hypothalamic (2-4) and pituitary level (5 -8). I n the anterior pituitary, morphine and opiate peptides had no effect on the spontaneous PRL release (9, 10) but reversed inhibition of secretion induced by DA. Although this was not observed under all experimental conditions (1 l), this effect seems to involve a specific opiate receptor since it has been shown to be blocked by opiate antagonists ( 5 , 6, 8). In addition, spccific opiate binding sites have been described in anterior pituitary membranes (12, 13), although they could not be fully characterized because of the important contamination of endogenous B-endorphin-like peptides (14).Recently, it has been shown that DA induced a hyperpolarizing response due to a n increased potassium conductance on human (1 S), bovine (16) and rat lactotrophs ( I 7). During this response spontaneous calcium action potentials were suppressed (17). DA was also shown to affect calcium and potassium fluxes in those cells (18). These phenomena are likely to be implicated in the mechanism o f action of DA on PRL release since, in addition to cyclic AMP (CAMP) production (19-22) and modulation of phosphatidylinositol phosphate breakdown (23-26), regulation of PRL secretion is dependent on calcium entry into lactotrophs (27,28).An effect of morphinomimetic peptides on the DA hyperpolarization of ...

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Somatostatin and regulation of prolactin secretion

Cited by 26 publications

References 37 publications

In vivo and in vitro Regulation of Pituitary Transcription Factor-1 (Pit-1) by Changes in the Hormone Environment

In vivo and in vitro Regulation of Pituitary Transcription Factor-1 (Pit-1) by Changes in the Hormone Environment

Temperature and Protein Kinase C Modulation of Gonadotropin‐Releasing Hormone Receptors in Pituitary Cells from Intact or Castrated Male Rats

Interaction of Opiate Peptides with Dopamine Effects on Prolactin Secretion and Membrane Electrical Properties in Anterior Pituitary Cells from Lactating Rats

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