泌乳素与自身免疫性疾病的研究进展

泌乳素(PRL)具有300多种独立的生物活性。其生理功能包括生殖、内分泌与代谢、维持水电解质平衡、促进生长发育,以及免疫调节和免疫保护功能等。近10年来,PRL与免疫系统之间的相互关系得到了阐述。PRL不仅能由垂体前叶分泌,而且垂体前叶以外的免疫细胞等也能够分泌PRL。内分泌、旁分泌和自分泌的PRL通过与泌乳素受体(PRL-R)结合,影响着靶细胞的生长、增殖和分化。自身免疫性疾病常伴有高泌乳素血症,推测PRL对人类的免疫调节起着重要的作用。     

Prolactin and Autoimmunity

The interrelationship between prolactin (PRL) and the immune system have been elucitaded in the last decade, opening new important horizons in the field of the immunoendocrinology. PRL is secreted not only by anterior pituitary gland but also by many extrapituitary sites including the immune cells. The endocrine/paracrine PRL has been shown to stimulate the immune cells by binding to PRL receptors. Increased PRL levels, frequently described in autoimmune diseases, could depend on the enhancement of coordinated bi-directional communications between PRL and the immune system observed in these diseases. Hyperprolactinemia has been described in the active phase of some non organ-specific autoimmune diseases, as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) and organ-specific autoimmune diseases, as celiac disease, type 1 diabetes mellitus, Addison's disease, autoimmune thyroid diseases. In these diseases PRL increases the syntesis of IFNγ and IL-2 by Th1 lymphocytes. Moreover, PRL activates Th2 lymphocytes with autoantibody production. Of particular interest is the association between hyperprolactinemia and levels of anti DNA antibodies, islet cell antibodies (ICA), thyreoglobulin antibodies (TgAb), thyroperoxidase antibodies (TPOAb), adrenocortical antibodies (ACA), transglutaminase antibodies (tTGAb) in SLE, in type 1 diabetes mellitus, in Hashimoto's thyroiditis, in Addison's disease and in celiac disease, respectively. High levels of PRL have been also frequently detected in patients with lymphocytic hypophysitis (LYH). Several mechanisms have been invoked to explain the hyperprolactinemia in LYH. The PRL increase could be secondary to the inflammatory process of the pituitary gland but, on the other hand, this increase could have a role in enhancing the activity of the immune process in LYH. Moreover, the detection of antipituitary antibodies targeting PRL-secreting cells in some patients with idiopathic hyperprolactinemia suggests the occurrence of a possible silent LYH in these patients. Finally, the role of anti-prolactinemic drugs to inactivate the immune process in LYH is still discussed.     

Prolactin gene expression in human thymocytes.

Recent evidence suggests that lymphocytes produce prolactin (PRL). Here, we report the cDNA cloning and expression of PRL from normal human thymocytes. Sequence analysis showed that the thymocyte cDNA encodes a 23 kDa protein which is identical to pituitary PRL. RNA blot analysis showed that the thymocyte PRL mRNA is approximately 170 nucleotides larger than the pituitary PRL message. PRL message was also detected in several non-pituitary human cell lines including Jurkat T, HeLa, and JEG cells. Furthermore, PRL gene expression in JEG cells was inhibited by glucocorticoid treatment. Our data support the hypothesis that PRL is a T cell-derived cytokine.     

Prolactin (PRL)-releasing peptide stimulates PRL secretion from human fetal pituitary cultures and growth hormone release from cultured pituitary adenomas

The hypothalamic peptide PRL-releasing peptide (PrRP) has recently been cloned and identified as a ligand of an orphan pituitary receptor that stimulates in vitro PRL secretion. PrRP also induces PRL release in rats in vivo, especially in normal cycling females. However, no information on the effects of PrRP in the human is available. To elucidate the role of PrRP in regulating human anterior pituitary hormones, we used human PrRP-31 in primary cultures of human pituitary tissues, including fetal (20--27 weeks gestation) and normal adult pituitaries, as well as PRL- and GH-secreting adenomas. PrRP increased PRL secretion from human fetal pituitary cultures in a dose-dependent manner by up to 35% (maximal effect achieved with 10 nM), whereas TRH was slightly more potent for PRL release. Coincubation with estradiol resulted in enhanced fetal PRL response to PrRP, and GH release was only increased in the presence of estradiol. Although PRL secretion from PRL-cell adenomas was not affected by PrRP, PrRP induced PRL release from cultures of a GH-cell adenoma that cosecreted PRL. PrRP enhanced GH release in several GH-secreting adenomas studied by 25--27%, including GH stimulation in a mixed PRL-GH-cell tumor. These results show for the first time direct in vitro effects of PrRP-31 on human pituitary cells. PrRP is less potent than TRH in releasing PRL from human fetal lactotrophs and is unable to release PRL from PRL-cell adenomas in culture, but stimulated GH from several somatotroph adenomas. Thus, PrRP may participate in regulating GH, in addition to PRL, in the human pituitary.     

Prolactin in human systemic lupus erythematosus.

In the last decade, evidence has accumulated to support the hypothesis that both mild and moderate elevations of serum prolactin (PRL) participate in the clinical expression and pathogenesis of systemic lupus erythematosus (SLE). Hyperprolactinemia (HPRL) has been found in 20-30% of patients with SLE. HPRL seems to be associated with clinical activity of SLE during pregnancy. Although the relationship between HPRL and active SLE in non-pregnant patients is controversial, recent clinical and experimental studies support the potential role of prolactin (PRL) as a promoter of clinical activity and severity of SLE. Mild elevations of serum PRL secondary to microadenoma could trigger the onset of SLE in a subset of patients. Elevated PRL and interleukin (IL)-6 have been found in the urine of patients with active lupus nephritis and in cerebrospinal fluid (CSF) of patients with active central nervous system (CNS) SLE. PRL may therefore participate in the pathogenesis of lupus nephritis and cerebritis, and the presence of PRL may reflect an abnormal communication between the immune system and the neuroendocrine system in active SLE. Lymphocytes from patients with active SLE produce increased amounts of PRL, and this extrapituitary PRL may participate in aberrant immune processes in SLE. There is exciting new evidence that HPRL in SLE may be explained by stimulation of pituitary PRL secretion by cytokines. In addition, defects in peptidergic modulators and dopamine metabolism have been described in patients with SLE. The interactions between PRL, cytoquines, autoantibodies and organ involvement suggest that PRL participates in local and generalized immune and inflammatory processes and acts as a bridge between the neuroendocrine and immune systems in SLE. Understanding the interactions between these systems in SLE will help us to understand and treat this important autoimmune disease.     

Human thymocytes express a prolactin-like messenger ribonucleic acid and synthesize bioactive prolactin-like proteins.

Recent evidence has demonstrated an important immunoregulatory role for pituitary PRL. Moreover, PRLs have been identified as products of transformed human lymphocyte cell lines and normal murine lymphocytes, and implicated as regulators of their proliferative responses. However, PRL synthesis by normal human lymphocytes has not yet been reported. Here we demonstrate that human thymocytes and peripheral blood lymphocytes (PBL) synthesize PRL in primary culture. The principal form produced by thymocytes is 24 kilodaltons (kDa), essentially the same size as pituitary PRL, while PBL produced a 27-kDa variant. Size heterogeneity was evident, with products detected ranging from 21-29 kDa in various tissue samples, a phenomenon also found to occur in human pituitary and decidual PRL. Thymocytes and PBLs also synthesized a low mol wt form (11 kDa) that was released into culture supernatants concurrently with the larger PRL. The 24- and 11-kDa forms expressed PRL-like bioactivity in the Nb2 node lymphoma bioassay, further supporting their PRL-like nature. Expression of these PRLs was regulated by mitogen stimulation in thymocytes, but was constitutively produced in PBL. Northern blot analysis of thymocyte RNA using a human PRL cDNA probe detected a single PRL-like mRNA, which was significantly larger than human pituitary PRL mRNA. This was constitutively present in unstimulated thymocytes. Taken together, these data demonstrate that normal human lymphocytes synthesize bioactive PRLs similar in size to those produced by the pituitary. The presence of a single PRL mRNA suggests that the size variation observed in these proteins is probably due to posttranslational modification, such as proteolysis and glycosylation.     

催乳素和免疫系统

催乳素 (PRL)是一种具有多种功能的垂体激素 ,其受体广泛存在于免疫系统各个组织和器官中 ,参与调节细胞和组织的免疫活性 ,介导各类生理或病理的免疫反应 ,对自身免疫性疾病、器官移植和肿瘤的发生都有一定影响。本文介绍了近年来PRL在免疫领域中相关的研究进展。     

Peritonitis activates transcription of the human prolactin locus in myeloid cells in a humanized transgenic rat model

Prolactin (PRL) is mainly expressed in the pituitary in rodents, whereas in humans, expression is observed in many extrapituitary sites, including lymphocytes. Due to the lack of adequate experimental models, the function of locally produced PRL in the immune system is largely unknown. Using transgenic rats that express luciferase under the control of extensive human PRL regulatory regions, we characterized immune cell responses to thioglycollate (TG)-induced peritonitis. Resident populations of myeloid cells in the peritoneal cavity of untreated rats expressed barely detectable levels of luciferase. In contrast, during TG-induced peritonitis, cell-specific expression in both neutrophils and monocytes/macrophages in peritoneal exudates increased dramatically. Elevated luciferase expression was also detectable in peripheral blood and bone marrow CD11b(+) cells. Ex vivo stimulation of primary myeloid cells showed activation of the human extrapituitary promoter by TNF-α, lipopolysaccharide, or TG. These findings were confirmed in human peripheral blood monocytes, showing that the transgenic rat provided a faithful model for the human gene. Thus, the resolution of an inflammatory response is associated with dramatic activation of the PRL gene promoter in the myeloid lineage.     

Morphological studies of prolactin-secreting cells in estrogen receptor alpha and estrogen receptor beta knockout mice

Estrogens play a major role in the regulation of prolactin (PRL) secretion through activation of pituitary and hypothalamic estrogen receptors (ERs). In order to evaluate the relative role of ERalpha and ERbeta in the control of PRL density in the pituitary gland, we performed immunocytochemical localization of PRL and ERs in pituitaries of wild-type (WT), ERalpha knockout (KO) and ERbetaKO mice. In WT and ERbetaKO anterior pituitaries, the vast majority of secretory cells contained ERalpha immunoreactivity, while no ERalpha immunostaining could be found in ERalphaKO pituitaries. No ERbeta immunoreactivity could be detected in pituitaries of WT, ERalphaKO or ERbetaKO mice. At the light microscopic level, a large number of cells staining for PRL were present in pituitaries of female WT, while in female ERalphaKO pituitaries, the density of PRL cells was much lower. In WT male pituitaries, the density of PRL cells was lower than observed in female WT, while PRL staining was markedly decreased in male ERalphaKO as compared to male WT. In ERbetaKO mice of both sexes, the results were identical to those observed in WT animals. At the electron microscopic level, in WT mice of both sexes, type 1 PRL cells exhibited a well-developed Golgi apparatus and a large number of strongly stained large mature and immature secretory granules. Type 2 PRL cells were also present in the pituitary. Type 2 PRL cells contain small poorly labelled granules. In ERalphaKO mice of both sexes, type 1 PRL cells were atrophied with poorly developed Golgi apparatus, and no type 2 PRL cells could be observed. In ERalphaKO pituitaries, typical gonadectomy cells were found. No ultrastructural changes were observed in PRL cells of ERbetaKO mice. The present data strongly suggest that the positive regulation of PRL expression at the pituitary level by estrogens is mediated by ERalpha and does not involve ERbeta activation.     

The human placental growth hormone variant is mitogenic for rat lymphoma Nb2 cells

Although there is evidence that human (h) placental GH variant (hGH-V) possesses a growth-promoting function, lactogenic activity by the hormone has not been demonstrated. Rat anterior pituitary tumor (GC) cells stably transfected with the hGH-V gene (GC [hGH-V] cells) synthesize and secrete hGH-V. This hormone shares considerable structural similarity with pituitary growth hormone (hGH-N) and chorionic somatomammotropin (hCS) at the nucleotide (greater than 90%) and amino acid (greater than 80%) levels. As expected, both hGH-N and hCS antibodies detect hGH-V by immunoblotting. However, hGH-V, but not hGH-N or hCS, cross-reacts with human or rat pituitary prolactin (PRL) antibodies. These data indicate that structural features shared by hGH-V and pituitary PRL are not present in hGH-N or hCS. Comparison of amino acid sequences implicates two regions that may account for a common epitope between hGH-V and hPRL, and structural difference from hGH-N and hCS. The possible lactogenic activity by hGH-V was assessed in a rat lymphoma Nb2 cell bioassay. Conditioned medium from GC[hGH-V] cells permitted growth of lactogen-dependent Nb2 lymphoma cells in culture. This activity was blocked by antibodies raised to rat PRL but not hPRL or hGH-N. Comparison of the hGH-V amino acid sequence with those from 14 other lactogenic hormones, including hPRL, hCS and hGH-N, reveals 6 conserved amino acids. These data indicate a lactogenic as well as growth-promoting function for the secreted hGH-V protein in vivo.     

Endothelin-induced biphasic response of lactotrophs cultured under different conditions.

Endothelin (ET), a recently discovered vasoconstrictor peptide, is widely distributed in different tissues including brain and pituitary. Although evidence regarding the role of ET in neuroendocrine processes is still fragmentary, it appears that the release of several anterior pituitary (AP) hormones can be modulated by peptides of the ET family. In the present study, we compared the effects of ET-1 and ET-3 on the release of PRL from AP cells cultured in serum-free (SFM) or serum-containing (SCM) medium. AP obtained from adult male rats were enzymatically dispersed, and the cells were plated in either SFM or SCM. After 4 days, cells were incubated with ET-1 or ET-3 for designated periods of time, and PRL levels in the incubation media were measured by RIA. When AP cells maintained in SCM were exposed to ET for 20 min, both peptides inhibited PRL release, with ET-1 being a more potent inhibitor than ET-3. In contrast, a biphasic response was observed in cultures grown in SFM: low concentrations of ET peptides inhibited the secretion of PRL, while high concentrations caused a significant stimulation. Further characterization of the effects of ET-1 revealed that the stimulatory phase was relatively short (15-30 min) and was followed by inhibition of PRL release. The addition of either horse serum or fetal bovine serum to SFM on the day of plating resulted in a dose-dependent reduction in the ET-induced stimulation of lactotrophs. These findings indicate that the presence of serum in culture medium alters the expression of cell properties underlying inhibitory and stimulatory responses to ET in terms of PRL secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification and functional activity of prolactin receptors in thymic epithelial cells.

Thymic epithelial cells (TECs), the major component of the thymic microenvironment, can be modulated by pituitary hormones. We have shown previously that prolactin (PRL) can influence the endocrine activity of TECs and stimulate TEC proliferation as well as cytokeratin expression, suggesting the existence of PRL receptors on TECs. Using a series of monoclonal antibodies (mAbs) to the extracellular domain of the rat liver PRL receptor, we have demonstrate that rat TECs bear specific receptors for PRL, as assessed by immunoblotting as well as by immunocytochemistry experiments. Using a probe specific for the long form of PRL receptor, mRNAs of 6.7 and 10.1 kilobases were detected, although by immunoblot the major protein in TECs had a molecular mass of 43 kDa. Functionally, these mAbs were able to modulate thymulin secretion, as well as TEC proliferation. Moreover, the mAbs cross-reacted with human TECs and were able to mimic the action of PRL on these cells. These data bring further support for the general concept of the neuroendocrine immune circuit and extend the notion for a pleiotropic role of PRL as an immunomodulatory hormone.     

Interleukin-6 stimulates anterior pituitary hormone release in vitro

Interleukin-6 (IL-6), a cytokine produced by inflammatory reactions, was found to stimulate PRL, GH and LH release from anterior pituitary cells at concentrations similar to those which affected lymphocyte mitogenesis. Perifused pituitary cells responded to IL-6 with prompt increases in hormone release that declined rapidly following cessation of exposure. Dopamine (DA) attenuated IL6-induced PRL release. In addition, IL-6 potentiated both GHRF- and TRH-induced hormone release without an affect on intracellular cAMP. These data demonstrate a new biological activity for IL-6 and provide evidence for immune system regulation of anterior pituitary hormone release.     

Interleukin-2 inhibits the synthesis and release of prolactin from human decidual cells

PRL is synthesized and released by several extrapituitary tissues, including decidualized endometrial stromal cells. As interleukin-2 (IL-2) stimulates the synthesis and release of pituitary PRL, and decidual stromal cells have receptors for IL-2, we examined whether IL-2 also regulates the release of decidual PRL. Exposure of primary cultures of human decidual cells (10(6) cells/well) from term pregnancies to IL-2 (50 ng/mL) inhibited PRL release beginning 48 h after exposure. The inhibition by IL-2 was dose dependent, and the maximal inhibition of PRL release after 5 days of exposure to IL-2 was 71.0 +/- 0.9% (mean +/- SE). IL-2, however, had no effect on decidual cell viability. The inhibitory effect of IL-2 on PRL release was secondary to inhibition of PRL synthesis. Decidualized human endometrial stromal cells transfected with 3 kb of the extrapituitary PRL (exon 1a) promoter coupled to a luciferase expression vector responded to IL-2 (10 ng/mL) with a significant decrease in luciferase activity. These findings strongly suggest that IL-2 inhibits the synthesis and release of decidual PRL and provide further support for a critical role of cytokines in the regulation of decidual PRL gene expression.     

Prolactin receptors in human pituitary adenomas

OBJECTIVE In the rat, prolactin receptors (PRL-R) have been identified In normal pituitary cells and In anterior pituitary tumours induced by oestradiol. No published data are available concerning PRL-R in the human pituitary. The aim of our study was therefore to detect the presence of PRL-R in the normal human pituitary gland and human pituitary adenomas. DESIGN Evaluation of free and total PRL-R In the normal pituitary gland and different pituitary tumours characterized by Immunocytochemical analysis. PATIENTS Twenty-six unselected patients (14 M, 12 F) who underwent surgery for pituitary adenoma (3 prolactinomas, 4 GH-PRL adenomas, 5 GH adenomas, 1 ACTH adenoma, 9 glycoprotein and/or α-subunlt adenomas, 4 null ceils adenomas) were studied. Nine pltultaries from subjects whose death was unrelated to brain and endocrine diseases, were also studied as a control group in the PRL binding studies. MEASUREMENTS Free PRL-R in microsomal membranes were determined by in-vitro radioreceptor assay using ¹²⁵l-labelled human PRL as llgand. Total PRL-R were also measured In the same membrane fractions by removing endogenous PRL bound to its receptors using 4 m MgCl². Serum PRL levels were also evaluated in all patients before surgery using an IRMA method. RESULTS Specific binding values for PRL (free PRL-R) were 0.39±0.03% (range 0–1.96%) In the pituitary adenomas. These binding values were Identical to those observed in normal pltultaries (0.38±0.07%, range 0.1–0.78%). Elevated PRL binding (1.25% and 1.96%) was found in two patients with PRL secreting adenomas and very high serum PRL levels (5768 and 11240 mU/l. No PRL binding was shown In 4 patients. Treatment of membranes with 4 M MgCl² increased the specific binding (total PRL-R) In both pituitary tumours (0.5±0.11%; P<0.001) and normal pituHarles (0.47±0.07%; P<0.02). CONCLUSIONS Our data have demonstrated the presence of prolactin receptors in normal cadaveric pituitary and in most pituitary adenomas, Irrespective of histological classification. In particular, elevated prolactin receptor levels were shown In PRL-secreting tumours from patients with markedly increased serum PRL levels. Our study may support several lines of experimental evidence for a specific functional role for PRL in the growth of some pituitary adenomas.     

Somatomammotrophic cells in GH-secreting and PRL-secreting human pituitary adenomas

A morphological study has been carried out on 20 GH-secreting adenomas removed from acromegalic normoprolactinemic patients, on 29 PRL-secreting adenomas removed from hyperprolactinemic patients without signs of acromegaly and on one normal human anterior pituitary gland collected at autopsy. The protein A-gold immunoelectron microscopic technique has been utilized in order to verify the presence of mixed cells producing both GH and PRL (somatomammotrophs) in these pituitary tissues. In the normal pituitary a considerable number of somatomammotrophs (15-20%) was found, thus supporting the idea that these cells are normal components of the human anterior pituitary gland. In 10 GH-secreting adenomas and in 10 PRL-secreting adenomas somatomammotrophs were present in a variable number (from 4 to 20% of the whole cell population in GH adenomas and from 1 to 47% in PRL tumors). It can be concluded therefore that these cells, largely present in all GH/PRL-secreting adenomas, can also be found in GH-secreting and PRL-secreting tumors without clinical evidence of a mixed secretion. Adenomatous somatomammotrophs displayed ultrastructural features of adenomatous somatotrophs and mammotrophs (prominent Golgi complexes, abundant rough endoplasmic reticulum, irregular nuclei). The size and the number of granules were variable. In some cells GH and PRL were stored in distinct secretory granules, in others in mixed granules or both in mixed and distinct granules, thus suggesting that in adenomatous somatomammotrophs the efficiency of the mechanisms of sorting of the two hormones varies from one cell to another.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction by tumor necrosis factor-alpha of rapid release of immunoreactive and bioactive luteinizing hormone from rat pituitary cells in vitro

Tumor necrosis factor-alpha (TNF-alpha) is secreted by activated monocytes and other immune cells. This paper reports studies on the effects of TNF-alpha on the releases of pituitary hormones such as luteinizing hormone (LH), follicle-stimulating hormone, prolactin (PRL) and adrenocorticotropic hormone (ACTH). The addition of recombinant human TNF-alpha (rTNF-alpha) to cultures of pituitary cells resulted in significantly increased releases of gonadotropins, PRL, and ACTH for up to 30 min, but not later. rTNF-alpha, like GnRH, also stimulated the release of bioactive LH. In addition, rTNF-alpha induced production of an interleukin-6 (IL-6)-like molecule by pituitary cells. As IL-6 induces the releases of multiple hormones from pituitary cells, our data suggest that rTNF-alpha may stimulate the releases of multiple pituitary hormones through IL-6 production as well as by its direct action on pituitary cells.     

Expression of prolactin-releasing peptide and its receptor messenger ribonucleic acid in normal human pituitary and pituitary adenomas

The recently identified PRL-releasing peptide (PrRP) is the first hypothalamic peptide hormone that specifically stimulates PRL production from the pituitary gland. Similar to other hypothalamic regulatory hormones, it acts through its specific seven-transmembrane domain, G protein-coupled receptor. Using RT-PCR, we examined messenger ribonucleic acid (mRNA) expression of PrRP and its receptor in normal human pituitary tissue and in pituitary tumors. PrRP mRNA was expressed in all five normal pituitary glands examined. In contrast, PrRP mRNA was detected in only 5 of 11 of the human prolactinomas. All 5 prolactinomas expressing PrRP were responsive to dopamine agonist treatment, whereas PrRP-negative prolactinomas were non- or partially responsive. PrRP mRNA was also detected in 6 of 13 GH-secreting tumors and 5 of 10 clinically nonfunctioning tumors investigated. PrRP receptor mRNA was found in all the normal and neoplastic human pituitary samples studied. The production of PrRP and its receptor by normal and neoplastic pituitary tissue raises the question of whether it may regulate PRL production in an autocrine/paracrine manner in pituitary tissue. Further investigation of PrRP and its receptor expression and function will be needed to clarify its potential role in regulating PRL secretion in normal human lactotrophs and pituitary tumors.     

Leptin and leptin receptor expression in normal and neoplastic human pituitary: evidence of a regulatory role for leptin on pituitary cell proliferation.

Leptin is a circulating hormone secreted by adipose and a few other tissues. The leptin receptor consists of a single transmembrane-spanning polypeptide that is present as a long physiologically important form as well as in several short isoforms. Recent studies have suggested that the anterior pituitary may have a role in the regulatory effects of leptin in animal models. To test this possibility in human pituitaries, we examined the expression of leptin and OB-R in normal and neoplastic pituitaries, and the possible functions of leptin in the pituitary were also analyzed. Leptin was present in 20-25% of anterior pituitary cells and was expressed in most normal anterior pituitary cells, including ACTH (70% of ACTH cells), GH (21%), FSH (33%), LH (29%), TSH (32%), and folliculo-stellate cells (64%), but was colocalized with very few PRL cells (3%), as detected by double labeling immunohistochemistry with two different antileptin antibodies. In addition, leptin expression was detected by RT-PCR in some pituitary tumors, including ACTH (three of four), GH (one of four), null cells (two of four), and gonadotroph (one of four) tumors as well as in normal pituitary. Immunohistochemical staining showed greater immunoreactivity for leptin in normal pituitaries compared to adenomas. Treatment of an immortalized cultured anterior pituitary cell line, HP75, with leptin stimulated pancreastatin secretion in vitro. Leptin also inhibited cell growth in the human HP75 and in the rat pituitary GH3 cell lines. Both long (OB-Rb) and common (OB-Ra) forms of the leptin receptor messenger ribonucleic acid and leptin receptor protein were expressed in normal and neoplastic anterior pituitary cells. These findings show for the first time that leptin is expressed by most human anterior pituitary cell types and that there is decreased leptin protein immunoreactivity in pituitary adenomas compared to that in normal pituitary tissues. We also show that OB-Rb is widely expressed by normal and neoplastic anterior pituitary cells, implicating an autocrine/paracrine loop in the production and regulation of leptin in the pituitary.