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PubMed2004

Cyclic adenosine 3',5'-monosphosphate mediate prolactin regulation of mitochondrial aconitase in human prostate carcinoma cells.

Mitochondrial aconitase (mACON) is regarded as the key enzyme for citrate oxidation in human prostatic epithelial cells. The results of RT-PCR and immunoblot assays indicated that human prostatic carcinoma cells (PC-3 cells) express the long-form of the prolactin receptor. In vitro studies determined that prolactin upregulates mACON enzymatic activity and cell proliferation of PC-3 cells. Immunoblot assay revealed that prolactin treatments increase the gene expression of mACON. Transient gene expression assay indicated that the regulation by prolactin of mACON gene expression depends on the presence of the cyclic adenosine 3',5'-monosphosphate (cAMP) response element on the promoter of the mACON gene. Both prolactin and dibutyryl-cAMP doubled the promoter activity of the mACON gene; however, adding H-89, a specific protein kinase A inhibitor, suppressed the prolactin response. The intracellular cAMP levels, but not the cGMP levels, increased after treatment with prolactin. This study showed that prolactin regulates the expression of the mACON gene via the cAMP signal pathway in human prostatic carcinoma cells.

Aconitate Hydratase↗
PubMed2000

Prolactin signaling in erythrophores and xanthophores of teleost fish.

Prolactin directly affects erythrophores and xanthophores of teleost fish, resulting in pigment dispersion. In the present study, signal transduction elicited by prolactin was examined using split-tail fin preparations of the rose bitterling and Nile tilapia, and cultured erythrophores and xanthophores from the paradise goby and rose bitterling. When antibodies to the prolactin receptor were added to an ovine prolactin (oPRL) solution, pigment dispersion within cultured cells was significantly inhibited, suggesting the existence of a prolactin receptor in the cell membrane. In mammals and birds, prolactin receptors belong to a cytokine receptor superfamily and signal through a tyrosine kinase-mediated pathway. Therefore, we examined the effects of three kinds of protein tyrosine kinase inhibitors on pigment dispersion elicited by oPRL. None of those inhibitors depressed the response. On the other hand, lithium ions (an inhibitor of adenylate cyclase) and H-88 and H-89 (inhibitors of protein kinase A) decreased the levels of oPRL-induced pigment dispersion in a dose-dependent manner. In cultured cells treated with cholera toxin for 3 hrs, the effect of oPRL was irreversible, indicating the possible involvement of Gs protein in the prolactin action. From these results, we conclude that cAMP may be a second messenger in the dispersion of pigment induced by prolactin and that a novel protein receptor coupled with a Gs protein may be present in the membrane of erythrophores and xanthophores of teleost fish.

Animals↗
PubMed2003

Prolactin receptor signaling during platelet activation.

Prolactin is a newly recognized platelet coactivator that functions through potentiation of ADP-induced platelet activation. However, the possible association between hyperprolactinemia and venous thromboembolism (VTE) has not been systematically investigated up to now; prolactin signaling mechanisms in platelets still need to be elucidated. In this study, plasma prolactin levels in healthy subjects and patients with VTE were determined, demonstrating that patients with VTE and no other congenital risk factors had significantly increased plasma prolactin levels. Moreover, prolactinoma patients demonstrated a higher incidence of VTE than the general population. To elucidate the molecular mechanisms for the development of venous thrombosis, prolactin receptor signaling during platelet activation was investigated with a focus on ADP-stimulated G-protein-regulated signaling pathways. The short isoform of prolactin receptors was detected on platelets. Signaling through this receptor, although not directly linked to Gq-proteins, substitutes for Gq-protein regulated signaling pathways involved in platelet activation. We identified protein kinase C, a well-established signaling molecule in platelet activation, as a target molecule for prolactin signaling pathways in human platelets. Our findings indicate that hyperprolactinemia may be an important novel risk factor for VTE, suggesting that its thrombogenic effect may be mediated through enhanced platelet reactivity. Revealing the molecular mechanisms of prolactin signaling will allow the design of new antithrombotic therapies.

Adult↗
PubMed2002

Exercise increases prolactin-receptor expression on human lymphocytes.

Plasma prolactin has been shown to increase during stress; the immune system is responsive to prolactin and affected by stress. Therefore, this study was undertaken to investigate the effects of acute graded, maximal treadmill exercise on prolactin-receptor expression by lymphocytes. Eight healthy men underwent one exercise and one nonexercise session. Blood was sampled immediately before and after the exercise. On the day of the nonexercise session, two resting blood samples were obtained at the same times as the exercise session samples to act as baseline data. Plasma prolactin concentrations were significantly elevated in response to exercise and correlated positively with total prolactin-receptor expression per B lymphocyte. An increase in total prolactin-receptor expression per B lymphocyte in response to exercise also was observed. In addition, exercise significantly increased the total number of circulating B lymphocytes expressing prolactin receptor as well as the total number of circulating B lymphocytes. These data support the idea that exercise may enhance the interaction between immune target cells and prolactin, a stress hormone capable of enhancing immune function.

Adult↗
PubMed2006

Socs2 and elf5 mediate prolactin-induced mammary gland development.

The proliferative phase of mammary alveolar morphogenesis is initiated during early pregnancy by rising levels of serum prolactin and progesterone, establishing a program of gene expression that is ultimately responsible for the development of the lobuloalveoli and the onset of lactation. To explore this largely unknown genetic program, we constructed transcript profiles derived from transplanted mammary glands formed by recombination of prolactin receptor (Prlr) knockout or wild-type mammary epithelium with wild-type mammary stroma. Comparison with profiles derived from prolactin-treated Scp2 mammary epithelial cells produced a small set of commonly prolactin-regulated genes that included the negative regulator of cytokine signaling, Socs2 (suppressor of cytokine signaling 2), and the ets transcription factor, E74-like factor 5 (Elf5). Homozygous null mutation of Socs2 rescued the failure of lactation and reduction of mammary signal transducer and activator of transcription 5 phosphorylation that characterizes Prlr heterozygous mice, demonstrating that mammary Socs2 is a key regulator of the prolactin-signaling pathway. Reexpression of Elf5 in Prlr nullizygous mammary epithelium restored lobuloalveolar development and milk production, demonstrating that Elf5 is a transcription factor capable of substituting for prolactin signaling. Thus, Socs2 and Elf5 are key members of the set of prolactin-regulated genes that mediate prolactin-driven mammary development.

Animals↗
PubMed1987

Further observations on the autoregulation of the prolactin receptor in rat ventral prostate explants.

In confirmation and extension of an earlier preliminary communication, ovine prolactin was found to elevate prolactin binding by approximately 100% in rat ventral prostate explants incubated for 20 h in vitro. A stimulation was observed with low doses of ovine hormone (150 micrograms/l) which, from available data on the relative biological potencies, could be considered equivalent to the upper limit of the physiological range of endogenous rat prolactin. The response was associated with a lag period of 3-6 h. The effect could be obtained with other lactogenic hormones, including human and rat prolactin and human growth hormone, but not with non-lactogenic hormones such as insulin, hCG, corticosterone, testosterone or oestradiol. The prostaglandin synthesis inhibitor, indomethacin, and the Ca2+-antagonist, verapamil, could not counteract the increase in prolactin binding induced by prolactin treatment, nor could dibutyryl cyclic AMP alone mimic the response. These data suggest that prostaglandins, Ca2+ or cAMP do not mediate the alteration in receptor binding. Furthermore, inhibition of lysosome activity by chloroquine could not alone increase the prolactin binding in the control tissues, suggesting that up-regulation does not simply reflect a protective action of prolactin on receptor degradation.

Animals↗
PubMed1981

Effects of bromocriptine and occlusion of nipples on prolactin receptor and lactose synthetase activity in the mammary gland of the lactating rat.

The response of prolactin receptor and lactose synthetase to suppression of plasma concentrations of prolactin was examined in normal and occluded (teat-sealed) mammary glands of Sprague-Dawley rats, Rats, with mammary glands unilaterally occluded, were given bromocriptine (2.5 mg/kg per 12 h) between 5 and 8 post partum. Bromocriptine reduced plasma prolactin concentrations from 460.4 +/- 120.8 (mean +/- s.e.m.) to 2.56 +/- 0.89 ng/ml within 12h whilst concentrations in control rats were 553.4 +/- 110.25 ng/ml. Lactose synthetase activity declined rapidly, within 24h, in occluded glands of both groups but was maintained for 24 h in normal glands of bromocriptine-treated rats and decreased thereafter. Prolactin receptors also declined significantly within 24h in occluded glands. Desaturation of the prolactin receptor by bromocriptine treatment in vivo was compared with desaturation by exposure of membranes to MgCl2 in vitro. Both treatments enhanced prolactin binding but the increase after treatment with MgCl2 may have been partly artefactual since there was a selective loss of protein from the membranes. These results indicate that the prolactin receptor in rat mammary gland may be maintained after acute suppression of prolactin secretion.

Animals↗
PubMed1985

Correlation between mammary prolactin receptors of lactating mice and litter weight.

Correlations between numbers and dissociation constants of mammary prolactin receptors of lactating mice and litter weight were examined. The apparent numbers and dissociation constants of mammary prolactin receptors were obtained from Scatchard plots with inhibition of iodine-125 prolactin binding by various concentrations of unlabeled prolactin. Litter weight measured 5 h after separation from the mother showed a nearly quadruple, almost linear increase during the first 15 d after birth. The dissociation constant for prolactin binding was fairly constant through lactation and did not correlate with either number of prolactin receptors or litter weight. The number of prolactin receptors in mammary cells increased rapidly in early lactation, reached a maximum at mid-lactation, began to decrease thereafter, and was correlated closely with litter weights on d 5 (.70) and 10 (.64) postpartum, suggesting that number of prolactin receptors represents the lactational potential of the lactating mouse.

Animal Population Groups↗
PubMed1997

Molecular actions of prolactin in the immune system.

The immunoregulatory properties of prolactin, a pituitary peptide hormone, have received renewed attention. The prolactin receptor, a member of the hematopoietin/cytokine receptor superfamily, is ubiquitously expressed by cells in the immune system. Certain subpopulations of lymphocytes synthesize and secrete biologically active prolactin, which suggests that prolactin can act as an autocrine and/or paracrine factor to modulate the activities of cells of the immune system. This review focuses on the molecular actions of prolactin in the immune system. Emphasis is given to recent information about the molecular mechanisms of prolactin receptor signal transduction, and the signaling molecules and prolactin-inducible target genes that participate in these responses. In particular, the prolactin-inducible interferon regulatory factor-1 gene and its roles in mediating diverse immune responses are highlighted.

Animals↗
PubMedDate not supplied

[Relation of prolactin with nodular hyperplasia and carcinoma of the prostate].

The relationship between prolactin in NH and prostate carcinoma has several aspects: under normal conditions, prolactin enhances androgens output, increasing the Leydig cell susceptibility to LH. At the prostate level, it increases testosterone binding to the prostate epithelium and stimulates the conversion of testosterone to dihydrotestosterone. On its own, it decreases prostatic protein degradation and increases the DNA synthesis index. With regard to Nodular Hyperplasia, once its hormone dependency is rated, it also appears to be stimulated by high levels of prolactin. The NH cell cultures with human prostate increase their growth, cell division, as well as the DNA synthesis. The aspects of the prolactin-prostate carcinoma interaction involve considering this hormone as a possible carcinogenic agent, emphasizing the existence of high plasma levels of this hormone in individuals with prostate carcinoma, where any androgen excess is considered a major factor at the genesis of this tumour, and prolactin increases indirectly its testicular synthesis. Also, prolactin itself stimulates the growth and development of carcinomatous human cell lines, increasing its effect in the presence of testosterone. For this reason, controlling this hormone levels becomes an element to have into consideration in the treatment and follow-up of these patients; also, the reevaluation of any drug therapy that, besides the initial goal pursued, does not maintain baseline prolactin levels. The association of anti-prolactin drugs has to be understood as a co-adjuvant therapy when there is androgenic deprivation, never as a single treatment.

Animals↗
PubMedDate not supplied

[Recent data on the mechanism of action of prolactin].

Prolactin is a hormone involved in the control of many functions, from osmoregulation in fishes to lactation in mammals. For that reason, the control of its secretion by hypophysis is particularly complex. Multiple factors of hypothalamic origin (dopamine, GABA, VIP, etc . . .) and hormones (oestrogens, TRH, thyroxine, . . .) are involved in this control. Prolactin molecule contains about 200 aminoacids. It has three disulfide bridges, of which one, at the center of the molecule, is required for the lactogenic activity. The expression of prolactin gene is dependent upon oestrogens, TRH, Ca++ ion and cAMP which favour its transcription. In contrast, dopaminergics such as CB 154 lower the expression rate of this gene. Prolactin receptor is located essentially on the plasma and intracellular membranes of target cells. Its essential binding part has a molecular weight of about 40,000. In mammary gland and liver prolactin receptor is up-regulated following a slow process. It is also down-regulated following a rapid and reversible process. In mammary gland, prolactin controls the expression of milk protein genes by enhancing their transcription rate and also by increasing the stability and the translation rate of the mRNAs. The transfer of the prolactin information to genes takes place through a relay which is released from plasma membrane when the receptor is occupied by the hormone or by anti-prolactin receptor antibodies. This relay which seems to be a small peptide (less than 1000 daltons and inactivated by trypsin) acts directly and specifically on isolated mammary nuclei via a dephosphorylation of nuclear proteins.

Animals↗
PubMed1975

[The pulsatile LH fluctuation (spiking) dependent on the circulating prolactin. Studies during physiological (puerperium), functional pathological and TRH induced hyperprolactinemia].

The magnitude and frequency of episodic LH-fluctuations have been observed to change during the different phases of the menstrual cycle. A hypothalamic control center appears to be responsible for these variations. Disturbances of the hypothalamus often make themselves known through a lack of LH-episodes. Ahypothalamic derangement in women with functional amenorrhoea can result in a disregulation of gonadotropins as well as prolactin, thereby leading to hyperprolactinemia. One finds an inverse relationship between high prolactin secretion and cessation of or decreased pulsatile LH-secretion (spiking). LH-spiking was tested in physiological post partum, functional pathological and TRH-induced hyperprolactinemias. No LH-episodes were observed post partum after the end of HCG clearance although prolactin had returned to normal levels at 12 days p.p. The mode of LH-secretion in a group of functionally amenorrhoic patients was changed by a TRH-induced prolactin increase: the previously observed LH-spikes in these women could no longer be seen. Normal cycling women, however, were not affected. In patients with hyperprolactinemic anovulatory syndromes, prolactin suppressed LH-fluctuations reappeared after administration of 2-Bromo-alpha-ergocryptin. The inhibitory influence of hyperprolactinemia on the function of the gonadostat will be discussed. High plasma prolactin levels influence the cyclic and tonic hypothalamic function. Furthermore, prolactin appears to have a peripheral inhibitory influence on ovarian gonadotropin stimulation. Post partum anovulation and amenorrhoea can be caused by an antigonadotropic and antigonadic effect of prolactin.

Amenorrhea↗
PubMed1976

The effect of neuroleptics on serum prolactin in schizophrenic patients.

Serum prolactin levels were studied before and during long-term administration of phenothiazines on a twice daily schedule to 27 newly admitted schizophrenic patients. An increase in serum prolactin is believed to be a reflection of inhibition of dopamine receptors in the hypothalamopituitary axis. By 72 hours after the initiation of treatment, all 27 patients had persistently elevated serum prolactin levels averaging 3.2-fold and 3.8-fold in men and women, respectively. There was a lag between clinical response and dopamine blockade, as indicated by serum prolactin levels in most patients. Serum prolactin levels remained elevated during the one- to three-month period subjects were studied, suggesting there was no tolerance to this effect of phenothiazines. Serum prolactin levels tended to be higher with thioridazine than on equivalent doses of chlorpromazine or trifluoperazine hydrochloride. There was some evidence that the magnitude of the serum prolactin elevation correlated with clinical response. After cessation of phenothiazines, serum prolactin levels rapidly reverted to normal within 48 to 96 hours.

Acute Disease↗
PubMed1977

Prolactin dynamics following transphenoidal hypophysectomy for metastatic carcinoma of the breast.

In nine patients who had undergone trans-sphenoidal hypophysectomy, prolactin dynamics were studied with intravenous thyrotropin releasing hormone (TRH). Residual prolactin secretory reserve was demonstrated in seven. Five patients were TRH tested both before and after trans-sphenoidal hypophysectomy. Hypophysectomy did not alter base line prolactin concentration but did decrease prolactin response to TRH from 55 ng/ml to 21 ng/ml (p less than 0.001). Post-hypophysectomy L-Dopa suppressed baseline prolactin concentrations to undetectable levels. There was no correlation between alterations in prolactin dynamics and tumor response to hypophysectomy. Trans-sphenoidal hypophysectomy is not effective in ablating prolactin secretion and serious doubts are raised about the role of altered prolactin dynamics in inducing breast cancer remission.

Breast Neoplasms↗
PubMed1992

Regulation of prolactin transformation in the rat pituitary.

We have investigated the mechanisms involved in the inhibition by dopamine of the transformation of prolactin within the anterior pituitary of the lactating rat. The degree of inhibition depends on the intracellular age of prolactin, being greater in newly synthesized (<1 hour) and in older (>12 hours since biosynthesis) hormone and lesser in prolactin synthesized 4-8 hours earlier. Transformation occurs in prolactin granules and involves an increase in oligomeric forms of prolactin at the expense of the monomeric form. A reversible disulphide-linked mechanism may be involved in dopamine inhibition of prolactin transformation; it is dependent upon the intracellular and/or intragranular pH via a Na+/H+ exchange mechanism. Transient suppression of dopamine inhibition may lower the intracellular/intragranular pH and subsequently cause transformation of the hormone. Developmentally, dopamine secretion by tuberoinfundibular neurons is seriously impaired and the response of pituitary lactotrophs to dopamine is reduced in adult rats deprived of milk prolactin during Days 2-5 post partum. These results suggest milk prolactin ingested during a critical post partum period may exert an organizational effect upon dopamine secretion and its function on the pituitary lactotroph during adulthood.

Animals↗
PubMed1980

Immunocytochemistry of prolactin-producing human pituitary adenomas.

Among 92 surgically removed pituitary adenomas immunostained for prolactin and growth hormone, 70 showed positive staining for prolactin. The majority of these (54) was associated with hyperprolactinemia leading to amenorrhea (and often galactorrhea) in women of reproductive age. Similar tumors, asymptomatic or conducive to disturbances of sexual function, were found in six hyperprolactinemic men. Among nine acromegalics, seven had immunostained lactotrophs associated with the somatotrophic adenomas cells, but only two of these had hyperprolactinemia. In all of the remaining tumors that had at least some immunoreactive lactotrophs, mild hyperprolactinemia had been present This indicates that immunostaining of pituitary tumors for prolactin correlated well with elevated plasma prolactin levels, except in the case of mixed somatolactotrophic adenomas. The patterns of distribution of immunoreactive prolactin in adenoma cells are illustrated. Since only some of the prolactin-producing adenomas stained with carmoisine--a dye that has been suggested as a marker for prolactin cells--immunocytochemistry is the method of choice for the identification of prolactin-secreting adenomas.

Adenoma↗
PubMed1986

Prolactin in partial epilepsy: an indicator of limbic seizures.

A study was performed to evaluate changes in serum prolactin levels after simple and complex partial seizures, and to identify which specific anatomical structures must be involved in seizures for postictal elevation of prolactin levels to occur. Seventy-eight seizures were studied in patients with electrodes implanted bilaterally into amygdala, hippocampus, hippocampal gyrus, and frontal sites. All 38 complex partial seizures had bilateral limbic ictal discharges, and each was followed by a significant increase in prolactin concentration (mean peak, 50.8 ng/ml; range, 16.0 to 150.0 ng/ml). Eight of 10 simple partial seizures with unilateral high-frequency regional limbic discharges were followed by prolactin elevation (mean peak, 28.2 ng/ml; range, 13.4 to 44 ng/ml). Thirty simple partial seizures with other ictal limbic discharges or without limbic discharges were not followed by an elevated prolactin level. The data indicate that serum prolactin levels always rise after complex partial seizures involving the temporal lobes, and rise after certain simple partial seizures involving limbic structures. Thus, measurement of the prolactin level can help identify which simple partial seizures involve mesial temporal lobe structures. Limbic structures serve to trigger prolactin release, which may depend upon spread of the seizure to subcortical structures.

Electroencephalography↗
PubMed1992

Human prolactin regulates transfected MMTV LTR-directed gene expression in a human breast-carcinoma cell line through synergistic interaction with steroid hormones.

Prolactin plays a key role in the regulation and growth of mammary cells, and influences tumor promotion. We have shown that chronic energy restriction intake depresses prolactin levels, inhibits production of MMTV proviral DNA and proto-oncogene expression in mammary glands and prevents development of mammary tumors. Since the expression and proto-oncogene activation of MMTV are regulated by promoter/enhancer elements within its long terminal repeat (LTR), in the present study we used a chloramphenicol acetyl transferase (CAT) reporter gene system and gene transfection methods to study the effect of prolactin on MMTV LTR using a human ductal carcinoma cell line T47D stably or transiently transfected with a plasmid consisting of the LTR upstream of CAT gene. Human prolactin or dexamethasone induced, respectively, a 2-fold or 6-fold increase in CAT activity compared with background CAT activity in the absence of hormones. However, the combination of human prolactin and dexamethasone strongly enhanced (20-fold) induction of the LTR compared with the control. Human prolactin also showed a synergistic effect with progesterone on LTR induction. Both LTR and CAT genes needed to be linked for induction of CAT activity by prolactin and dexamethasone. Our results indicate that human prolactin can act synergistically with steroid hormones to regulate MMTV LTR-directed gene expression in transfected T47D cells.

Breast Neoplasms↗