Immunomodulation by bromocriptine

Bone turnover in rats treated with 1,25-dihydroxyvitamin D3, 25-hydroxyvitamin D3 or 24,25-dihydroxyvitamin D3

Female rats were given 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), 0.25 microgram per 100 g body weight (bw), 25-hydroxyvitamin D3 (25(OH)D3), 1.7 micrograms/100 g bw or 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) 1.7 micrograms/100 g bw, subcutaneously three times a week for 12 weeks. Traditional variables pertaining to calcium homeostasis and growth, i.e. blood and urine calcium (Ca) and phosphate (P), serum levels of vitamin D3 metabolites parathyroid hormone, (PTH), calcitonin (CT), prolactin (PRL) and growth hormone (GH) were measured every four weeks. This data pool was correlated with bone matrix turnover parameters, i.e. serum levels of alkaline phosphatase (ALP) and urinary hydroxyproline (u-HYP) excretion. After 12 weeks of treatment, 1,25(OH)2D3 significantly enhanced serum total and ionized Ca, urine Ca and urine P, and also diminished urine cAMP due to reduced renal function (creatinine clearance). However, 25(OH)D3 administration had no such impact. 24,25(OH)2D3 opposed the effect of 1,25(OH)2D3 after 12 weeks by significantly augmenting serum P and diminishing serum levels of total Ca and ionized Ca. Cross sectional group analyses showed that circulating levels of ALP were directly related with serum 1,25(OH)2D3 and inversely related to serum 24,25(OH)2D3 and CT. Total u-HYP and per cent non-dialysable HYP (ndHYP) were reciprocally and positively correlated with serum PRL, respectively. However, no such relations were observed with serum GH. It appears that rats with elevated circulating levels of 1,25(OH)2D3 exhibit increased bone resorption, while augmented 24,25(OH)2D3 is associated with the opposite. Apparently, high bone turnover (i.e. reduced total urinary HYP and enhanced ndHYP) is associated with high serum PRL.

Prolactin and prolactin secretagogues reverse immunosuppression in mice treated with cysteamine, glucocorticoids, or cyclosporin-A

Suppression of prolactin (PRL) secretion with the dopamine agonist, bromocriptine, has been shown in rodents to diminish a variety of immunologic responses, including delayed type hypersensitivity, primary antibody response, T-cell dependent macrophage activation, and ex vivo T- and B-lymphocyte proliferation in response to mitogens. These same responses can be suppressed by endogenous or exogenous glucocorticosteroids and, in large measure, the immunosuppressant peptide cyclosporin A. The sulfhydryl reducing agent cysteamine (2-aminoethanethiol) is known to reduce pituitary and plasma prolactin levels. Treatment of mice with cysteamine at doses which suppressed circulating PRL levels resulted in suppression of ex vivo blastogenic responses of lymphocytes from treated mice. The T-cell-dependent primary IgM response to immunization with sheep red blood cells was also suppressed by cysteamine treatment. Treatment of mice with drugs stimulating the release of endogenous PRL, or with exogenous ovine PRL, was found to antagonize the suppression of lymphocyte proliferative responses to mitogens induced in mice by glucocorticoid or cyclosporin treatment. These data suggest that many drugs in common clinical use could have potential immunomodulatory actions due to suppression or stimulation of pituitary PRL secretion. Furthermore, lactogenic hormones appear to exert counterregulatory actions which may modify glucocorticosteroid actions on immune and other target issues.

Activation of the prolactin receptor gene by promoter insertion in a Moloney murine leukemia virus-induced rat thymoma

The prolactin receptor (Prlr) and growth hormone receptor (Ghr) genes and the Moloney murine leukemia virus integration-2 (Mlvi-2) locus were mapped to mouse chromosome 15 and human chromosome 5 bands p12-p14. To examine the potential relationship between Mlvi-2 and the genes encoding the growth hormone receptor and the prolactin receptor, we determined the chromosomal location of all three loci in the rat, using a panel of rat-mouse somatic cell hybrids, and in the mouse, using a panel of (C57BL/6J x Mus spretus)F1 x C57BL/6J interspecific backcross mice. These analyses revealed that Ghr, Prlr, and Mlvi-2 map to chromosome 2 in the rat and to chromosome 15 in the mouse, in close proximity with each other. Pulsed-field gel electrophoresis of rat genomic DNA showed no overlaps between the gene encoding the prolactin receptor and the remaining loci. Moreover, expression of the prolactin receptor was not affected by provirus insertion in Mlvi-2. During these studies, however, we detected one T-cell lymphoma line (2779) in which the prolactin receptor gene was activated by provirus integration. Sequence analysis of polymerase chain reaction-derived cDNA clones showed that the prolactin receptor RNA message initiates at the 5' long terminal repeat and utilizes the splice donor site 5' of the gag gene to splice the viral sequences onto exon 1 of the prolactin receptor. This message is predicted to encode the intact prolactin receptor protein product. Exposure of the T-cell lymphoma line 2779 to prolactin promoted cellular proliferation.

Prolactin as an immunoregulatory hormone in mammals and birds

The immunoregulatory function of prolactin (PRL) and the mechanism of its action in mammals seem to be well documented. Reciprocal interdependence between PRL secretion and immune system function is essential for normal ontogeny, development and aging. PRL receptors in lymphocytes participate in the transduction of its regulatory signal into the intracellular enzymatic machinery including that of the nucleus, leading to the expression of some genes and to the synthesis of new proteins. Activation of phosphoinositide turnover and subsequent increase in protein kinase-C activity seems to be a possible mechanism acting in the regulatory influence of PRL on mammalian immune cells. These cells in turn, under mitogen or antigen stimulation, secrete a substance with PRL-like activity. The regulatory function of PRL within the avian immune system is less well known, but it seems to have some features in common with those in mammals. Direct mitogenic action on thymocytes and splenocytes in the chicken might indicate the existence of PRL receptors in these cells and could explain the immunostimulatory effect of PRL observed in vivo, which is dependent on the time of hormone administration. As the avian PRL stimulates mitogenesis of rat Nb2 lymphoma cells, the mechanism of direct PRL action on immune cells in mammals and birds seems to be similar. PRL in chickens also modifies the level and the diurnal rhythm of corticosterone which, in turn, influences the immunoregulatory effect exerted by PRL. Thus, PRL seems to be an important factor, influencing directly or indirectly the avian immune system.

Effects of prolactin on rat paw oedema induced by different irritants

Evidence suggests that prolactin (PRL) may have a role in immune function, but no data exist on the possible interference between PRL and inflammatory processes, in spite of the known correlation between inflammatory and immune reactions. In the present study the activity of prolactin on rat paw oedema was investigated. Repeated administrations of ovine PRL or a hyperprolactinaemia induced by pituitary gland graft provoked an evident increase of the inflammatory response induced by carrageenan. This effect was also present when adrenalectomised animals were used. Indomethacin completely suppressed the pro-inflammatory effect of ovine PRL; bromocriptine reduced the paw oedema, but when both bromocriptine and PRL were administered the two opposite effects seem to annual each other. Also phospholipase A2-induced paw oedema was potentiated by PRL pretreatment and inhibited by bromocriptine, whereas in dextran or serotonin-induced paw oedema both PRL and bromocriptine were ineffective. A possible involvement of prostaglandins and/or of phospholipase A2 in the pro-oedemigenic activity of PRL is suggested.

Hyperprolactinemia inhibits natural killer (NK) cell function in vivo and its bromocriptine treatment not only corrects it but makes it more efficient

We studied NK cell function in eight patients with pathological hyperprolactinemia by measuring 51Cr release by K562 cells exposed to their mononuclear cells and found it decreased compared to normal controls (P less than 0.01). Bromocriptine (BrC) treatment corrected NK function but also made it more efficient at 12:1 than at 25:1 or 50:1 effector:target ratios (ANOVA; P = 0.01). The study of NK cell function in agarose revealed that its decrease in hyperprolactinemia is due to their low active binding to target cells, active killing, and recycling capacity. BrC tended to correct them but also increased recycling capacity to levels higher than those of controls (P less than 0.05). Sequential studies in three hyperprolactinemic patients before and after BrC showed correction of NK function within 1 week but its increased efficiency at the 12:1 effector:target ratio required 8 weeks. We conclude that hyperprolactinemia decreases NK cell function. BrC corrects this by decreasing prolactin levels but also makes NK function more efficient by increasing the capacity of NK cells to recycle after killing.

Hyperprolactinemia in systemic lupus erythematosus: association with disease activity

This study was designed to determine the prevalence and clinical significance of hyperprolactinemia in systemic lupus erythematosus (SLE) and other rheumatic diseases. Basal levels of prolactin were determined in 130 nonselected sera from patients with rheumatic diseases including 45 with SLE, 31 with rheumatoid arthritis, 23 with osteoarthritis, 18 with fibromyalgia, and 13 with polymyalgia rheumatica. Serum samples of 28 healthy subjects were used as normal controls. Serum prolactin was measured by radioimmunoassay. ANA, anti-DNA, RNP, Sm, Ro, La, and anticardiolipin antibodies were determined by standard techniques. Elevated serum levels of prolactin (PRL greater than 20 ng/ml) were found in a subset of SLE patients. In addition, a direct correlation with clinical disease and serological (ANA) activity was also found. These findings suggest a potential role for this immunoregulatory hormone in SLE pathogenesis.

Altered prolactin response of the lymphocytes of tumor-bearing mice

Interaction of prolactin and glucocorticoid on thymocytes and splenocytes of normal and tumor-bearing mice with reference to their mitogen-responsive blastogenesis has been studied. Prolactin alone had little or no mitogenic effect on thymocytes and splenocytes of normal mice but it was co-stimulatory, with ConA, in inducing blastogenesis in normal splenocytes. Thymocytes and splenocytes of tumor-bearing mice responded differently to prolactin. Hormone alone inhibited growth of thymocytes but at certain concentrations stimulated splenocytes. When cultured with prolactin and ConA, the thymocytes of tumor hosts responded with increased proliferation compared to that induced by ConA alone. Glucocorticoid suppressed ConA-induced lymphocyte proliferation in both normal and tumor-bearing mice. Prolactin reversed the inhibitory effect of glucocorticoid in normal mice but failed to abrogate inhibition in tumor hosts. Altered responsiveness of lymphocytes of tumor hosts to prolactin was not a function of circulating prolactin, as the serum prolactin level was similar in normal and tumor-bearing mice. Prolactin, however, could not reverse estradiol-induced suppression of lymphocyte proliferation. The lactogenic hormone, but not somatogenic hormones, altered the glucocorticoid inhibition of lymphocyte growth.

Reproductive hormone levels after pituitary allograft in cyclosporin-treated monkeys

OBJECTIVE

To determine the course of events during the onset of hyperprolactinemic amenorrhea, a nonhuman primate model was sought that did not require suckling or interference with the in situ hypothalamic-pituitary axis.

DESIGN

Because removal of the adenohypophysis from hypothalamic influence results in secretion of large quantities of prolactin (PRL) but little of the other adenohypophyseal hormones, we explored the possibility of establishing pituitary allografts in monkeys. Normally cycling female rhesus monkeys were immunosuppressed with a daily regimen of cyclosporin A (CyA; 10 to 15 mg/kg per day) and then subcutaneously grafted with a pituitary from another animal (allograft). Blood samples were obtained daily via saphenous vein puncture during control, only CyA-treatment, and allografted-plus CyA- menstrual cycles.

SETTING

Oregon Regional Primate Research Center, Beaverton, Oregon.

PARTICIPANTS

Female Macaca mulatta exhibiting regular menstruation.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Prolactin, luteinizing hormone (LH), estradiol (E2), and progesterone (P) levels were determined in harvested serum.

RESULTS

Temporary survival of 5 of 11 (45%) allografts was assumed based on elevations in serum PRL. Of the viable grafts, 4 of 5 (80%) resulted in reproductive dysfunction, as first evidenced by delay or loss of the preovulatory rise in E2. When the peak of follicular E2 was delayed, then the LH surge occurred, but it was also delayed. If follicular E2 levels did not peak, then the LH surge was absent as was luteal P production.

CONCLUSION

These data suggest that in the etiology of PRL-induced infertility in women, the first event is a suppression of follicular E2 production. In addition, the hypothalamus probably remains responsive to the positive feedback of E2 during early or moderate hyperprolactinemia.

Does prolactin play a role in skin biology and pathology?

Despite its extensive repertoire of biological activities, which include the growth- and osmoregulation of epithelial tissues as well as immunoregulatory properties, the potential significance of the pituitary hormone prolactin (PRL) for human skin biology and pathology has yet to be fully appreciated. In this essay, the hypothesis is presented that PRL acts as a neuroendocrine modulator of skin epithelial cell proliferation and of the skin immune system by forming a 'prolactin-circuit' between the central nervous system and the skin. Binding to specific skin receptors, modulation of cytokine release in the skin, and stimulation of somatomedin release by mesenchymal cells are among the suggested pathways by which PRL could affect epithelial cell growth in the skin. Potential feedback signals, arising from the skin and modifying pituitary PRL release, are briefly outlined. Centering on the role of PRL in both psoriasis and hair growth as models for studying the proposed PRL-skin connection, clinical and experimental evidence in support of this theory is discussed in the context of a 'neuroimmune-dermatological' perspective.

Elevated prolactin levels in human aqueous humor of patients with anterior uveitis

Evidence is accumulating that prolactin (PRL) may play a physiological role in the regulation of humoral and cell-mediated immune responses. On the basis of these observations, we measured levels in the serum and aqueous humor of 28 patients with cataract or anterior uveitis with concomitant cataract. Intraocular concentrations were measured in a range from 0.1 to 3.4 ng/ml. Whereas serum PRL levels failed to show significant differences between the two groups (P = 0.39), intraocular concentrations were significantly higher in uveitis patients (P less than 0.001). The level in aqueous humor did not reflect the serum concentration in either group. To the best of our knowledge, this is the first study measuring PRL concentrations in human aqueous humor.

Requirement of nuclear prolactin for interleukin-2--stimulated proliferation of T lymphocytes

Prolactin (PRL) is necessary for the proliferation of cloned T lymphocytes in response to interleukin-2 (IL-2). Translocation of PRL into the nucleus occurs during IL-2--stimulated mitogenesis. Therefore, the function of intranuclear PRL in T cell proliferation was tested. Eukaryotic expression vectors were prepared to express wild-type PRL [PRL(WT)], PRL that lacks the signal sequence for translocation into the endoplasmic reticulum [PRL(ER-)], and chimeric PRL in which the signal peptide was replaced with the sequence that directs the nuclear translocation of the SV40 large T antigen [PRL(NT+)]. Expression of these constructs in a T cell line (Nb2) responsive to PRL and IL-2 resulted in localization of PRL in the extracellular milieu, cytoplasm, or nucleus, respectively. Stimulation with IL-2 alone resulted in a five- to tenfold increase in the incorporation of [3H]thymidine by cells expressing PRL(NT+) or PRL(WT) as compared to PRL(ER-) or the parental Nb2 cells. Only the PRL(NT+) clone proliferated continuously with IL-2 stimulation in the presence of antiserum to PRL. These results demonstrate that nuclear PRL is necessary for IL-2--stimulated proliferation and suggest that a peptide hormone can function in the nucleus without binding to its cell surface receptor.

The role of prolactin in autoimmune demyelination: suppression of experimental allergic encephalomyelitis by bromocriptine

Several lines of evidence suggest that the anterior pituitary hormone prolactin has a stimulatory role on immune function and that pharmacological suppression of prolactin secretion with the dopamine-agonist bromocriptine suppresses both humoral and cellular immunity. Here, we describe the effects of prolactin-suppression on the course of experimental allergic encephalomyelitis in female Lewis rats. Initiation of continuous bromocriptine treatment before immunization reduced both the severity and incidence of clinical signs of acute experimental allergic encephalomyelitis. Experimental allergic encephalomyelitis-immunized rats experienced a threefold rise in basal prolactin levels on day 4 after immunization and maintained elevated prolactin levels on day 10, before the onset of neurological signs of experimental allergic encephalomyelitis. Bromocriptine treatment reduced prolactin levels to those of sham-immunized rats. In vivo bromocriptine pretreatment inhibited splenic lymphocyte proliferative responses in vitro to the immunizing antigen and to concanavalin A. Moreover, bromocriptine therapy was protective when initiated 1 week after the initial immunization and was also effective in suppression of late disease. These results indicate that (1) prolactin levels are elevated after immunization and before the onset of experimental allergic encephalomyelitis, (2) bromocriptine inhibits both prolactin secretion and the severity of acute experimental allergic encephalomyelitis, and (3) inhibition is also present when treatment is begun after sensitization, suggesting an effect of prolactin on the effector limb of the immune response during experimental allergic encephalomyelitis.

Prolactin, immunoregulation, and autoimmune diseases

Cells of the immune system synthesize prolactin and express mRNA and receptors for that hormone. Interleukin 1, interleukin 6, gamma interferon, tumor necrosis factor, platelet activator factor, and substance P participate in the release of prolactin. This hormone is involved in the pathogenesis of adjuvant arthritis and restores immunocompetence in experimental models. In vitro studies suggest that lymphocytes are an important target tissue for circulating prolactin. Prolactin antibodies inhibit lymphocyte proliferation. Prolactin is comitogenic with concanavalin A and induces interleukin 2 receptors on the surface of lymphocytes. Prolactin stimulates ornithine decarboxylase and activates protein kinase C, which are pivotal enzymes in the differentiation, proliferation, and function of lymphocytes. Cyclosporine A interferes with prolactin binding to its receptors on lymphocytes. Hyperprolactinemia has been found in patients with systemic lupus erythematosus. Fibromyalgia, rheumatoid arthritis, and low back pain patients present a hyperprolactinemic response to thyrotropin-releasing hormone. Experimental autoimmune uveitis, as well as patients with uveitis whether or not associated with spondyloarthropathies, and patients with psoriatic arthritis may respond to bromocriptine treatment. Suppression of circulating prolactin by bromocriptine appears to improve the immunosuppressive effect of cyclosporine A with significantly less toxicity. Prolactin may also be a new marker of rejection in heart-transplant patients. This body of evidence may have an impact in the study of rheumatic disorders, especially connective tissue diseases. A role for prolactin in autoimmune diseases remains to be demonstrated.

Immunosuppressive drugs in immune and inflammatory ocular disease

Advances in immunology, particularly ocular immunology, have been accompanied by the emergence of safer, more specific immunosuppressive drugs, notably, cyclophosphamide, chlorambucil, methotrexate, azathioprine, cyclosporine A, bromocriptine, dapsone, and colchicine. These drugs have become an important, and often essential, part of the ophthalmologist's armamentarium against inflammatory and immune-mediated ocular diseases. In order to better acquaint the ophthalmologist with the properties of the most commonly used immunosuppressive drugs, we review the literature and relate our own experience with these agents.

Effects of bromocriptine treatment on immune responses and 3-methylcholanthrene-induced tumorigenesis in rats

Seven-week-old male Sprague-Dawley rats were given a single injection of 1.5 mg of 3-methylcholanthrene (3MC) to induce in situ fibrosarcomas. The rats were also treated with the dopamine agonist bromocriptine (BCR) from two days prior to 14 days after 3MC treatment and again for 14 consecutive days beginning at week 5. Tumor incidence was markedly increased and latency decreased in BCR-3MC rats compared to 3MC controls. Natural killer (NK) cell cytotoxicity responses and production of interleukin 2 (IL2) was enhanced at two weeks in rats treated with only BCR. Natural killer cell activity was suppressed at two weeks in rats treated with only 3MC. This effect was reversed by BCR treatment. Rats treated with 3MC and BCR had suppressed NK cell responses and production of IL2 and interferon-gamma (IFN) at 12 weeks. In another study, rats injected with 1, 3 or 5 mg/kg BCR for 14 consecutive days had increased NK cell activity and IL2 production at all doses and increased IFN production at the two high doses. Antibody (IgG) responses to an injected antigen and delayed-type hypersensitivity reactions were not affected by BCR treatment. Animals treated with the two high doses of BCR had decreased serum prolactin (PRL) levels. Serum growth hormone (GH) concentrations were markedly increased in the group treated with 3 mg/kg BCR. These data suggest that BCR enhances 3MC-induced tumorigenesis. The mechanism of this effect is apparently not mediated by suppression of the immune system since BCR-treated rats had selectively enhanced immune function. Enhancement of immune responses by BCR has not been previously reported.

Neurohormonal immunoregulation

The immune system may be divided into primary lymphoid organs (bone marrow, bursa of Fabricius, and thymus), which produce mature leukocytes and secondary organs (spleen, lymph nodes, tonsils, Peyer's patches, etc.), which are concerned with specific immune responses. In the primary organs, stem cells proliferate and differentiate into various subsets of polymorphonuclear and mononuclear cells. Evidence is increasing that cell proliferation in the primary lymphoid organs is dependent on pituitary growth hormone (GH) and prolactin (PRL), which control the expression of growth regulatory genes (protooncogenes) such as c-myc and also induce essential growth factors (insulinlike growth factor, thymic and bursal hormones, etc.) and, possibly, their receptors. The adrenocorticotropic hormone-adrenal axis serves as an inhibitory pathway, antagonizing the action of PRL and GH on primary lymphoid tissue. The effect of glucocorticoids is especially forceful on thymocytes through the activation of the genetically programmed suicide pathway. Sex hormones also regulate the primary lymphoid organs, but their mechanism of action remains to be clarified. Thymus-derived feedback signals toward the pituitary gland have already been described. The pituitary gland exerts a similar regulatory influence on mature lymphocytes during their antigen-driven differentiation. PRL or GH is required for primary immune reactions; however, the secondary immune response may be less dependent on these hormones. Once the immune system is primed, antigen itself becomes a primary regulator. Exposure of memory cells to antigen leads to the production of growth factors (interleukins) and to the expression of their receptors. Therefore, antigen appears to fulfill, at this stage, a role that is originally played by GH or PRL in the primary lymphoid organs and, to some extent, also during antigen-driven differentiation. During immune reactions, interleukin-1 and tumor necrosis factor activate the adrenocorticotropic hormoneadrenal axis, which plays an important role in setting upper limits to and terminating responses. Lymphocytes have receptors for and react to numerous hormones, neurotransmitters, and mediators derived from a number of organs and tissues. Therefore, ultimately the reaction of a lymphocyte will be the vector of all positive and negative signals received. A hierarchy and sequential system of signals exists. Primary regulatory signals (competence signals) represent the most powerful regulators (e.g., PRL, GH or antigen) of lymphoid cells. The delivery of a competence signal is the prerequisite for subsequent lymphoproliferation, which is regulated by growth factors that are specific for a certain developmental stage of the lymphoid cell and act sequentially. Hormonal factors that promote growth and differentiation deliver the second regulatory signals. Competence factors and growth and differentiation hormones regulate gene expression in lymphocytes. The third class of signals modulate the function of mature effector cells (e.g., locomotion, secretion, phagocytosis, cytotoxicity). Neuro-transmitters appear to function as secondary signal modulators and tertiary functional regulators.

Effects of metoclopramide on rat spleen lymphocyte proliferation

The effect of metoclopramide on proliferation of spleen lymphocytes in rats was examined. The rate of [3H]thymidine incorporation into DNA was used as an index of lymphocytes proliferation. It was shown that the incorporation of [3H]thymidine into DNA of spleen lymphocytes in the rats treated with metoclopramide was significantly higher than that in the control group. The effects of various concentrations of prolactin and metoclopramide on [3H]thymidine uptake by DNA of spleen lymphocytes was also studied in vitro. It was shown that: 1, Prolactin, at the concentration of 1 and 0.1 ng/ml significantly increased [3H]thymidine incorporation into DNA of spleen lymphocytes. Metoclopramide in all the examined concentrations also caused a significant proliferogenic effect on lymphocytes.

Neuroimmunomodulation of in vivo anti-rotavirus humoral immune response

Neuropeptides and neurohormones (neurotransmitters) have been shown to modulate immune responses in vitro and in vivo. Since reproduction and lactation are regulated by neurohormones, we investigated whether neurohormones could enhance anti-rotavirus immunity in milk. Rotavirus-free mice were immunized orally with killed bovine rotavirus (BRV) and bred 6 weeks post-immunization. Post-whelping, each group of dams (ten mice/group) was given a single injection of prolactin (PRL), estrogen, PRL and estrogen or testosterone. The effects of neuropeptides, substance P (SP) and somatostatin (SS) on serum and lactogenic anti-rotavirus humoral immune responses were also investigated. The results revealed that in the groups given PRL or estrogen, anti-rotavirus antibody titers in milk and serum were enhanced. In contrast, testosterone had a negative effect on antibody titers. The administration of neuropeptide SP resulted in some enhancement of the lactogenic anti-rotavirus antibody titer at day 9 post-whelping whereas the opposite effect was observed following administration of SS. Prolactin given at 100 micrograms/mouse, on the day after whelping, gave optimum milk and serum antibody responses. Neurotransmitters potentiated immune responses to the weaker immunogenic proteins, VP4 and VP7 as well as to the strongly immunogenic VP6. In order to verify that the enhancement of anti-rotavirus antibody production was due to PRL and not to other factor(s), bromocriptine (BCR), a selective PRL inhibitor, was used as a control. Mice given BCR exhibited a drastic reduction in anti-rotavirus antibody in serum and milk. The role of neurotransmitters in the modulation of the lactogenic immune response and its significance in protection of neonates from enteric infections is discussed.

Down-regulation of autoantibody levels of cyclosporine and bromocriptine treatment in patients with uveitis

The administration of cyclosporine A, cyclosporine A plus bromocriptine, or bromocriptine results in down-regulation of antinuclear autoantibody levels in the sera of patients with uveitis. Decreased levels of autoantibodies against DNA, histones, cardiolipin, RNP, Sm, Ro (SS-A), and La (SS-B) were detected in the sera of patients with uveitis receiving cyclosporine A or cyclosporine A plus bromocriptine following 3 months of treatment. In contrast to the decreased antibody titers obtained following the treatment, the total immunoglobulin levels remained within the normal range. The results indicate that cyclosporine may affect B cell function, thereby yielding the observed decrease in autoantibody levels. This phenomenon might have clinical importance as a serological indicator of the efficiency of the patients to respond to the drug.

Bromocriptine as an adjuvant to cyclosporine immunosuppression after heart transplantation

Prolactin, a pituitary hormone, has been shown to have an active role in the regulation of the immune system. Prolactin receptors have been described on the membrane of lymphocyte cells, and competitive binding to these receptors by cyclosporine and circulating prolactin has been demonstrated. Experimental evidence suggests a synergistic effect of cyclosporine and bromocriptine, an inhibitor of pituitary release of prolactin, on immunosuppression. Between July 1986 and January 1988, 54 patients were randomly assigned to two groups of immunosuppression treatment. Thirty patients (group 1) were administered cyclosporine, azathioprine, and prednisone and 24 patients (group 2), a modified protocol aimed at decreasing the level of circulating prolactin by adding bromocriptine to the immunosuppression regimen. The two groups were similar in regard to age, preoperative diagnosis, and duration of follow-up. Minimal side effects related to bromocriptine were observed. The overall incidences of rejection and infection were similar, although actuarial analysis showed that freedom from these complications among patients treated with bromocriptine was significantly higher throughout the first 2 months after heart transplantation compared with that of patients in the control group. Other variables such as serum cyclosporine levels and lymphocyte counts were similar in both groups. In conclusion, suppression of circulating prolactin by bromocriptine appears to improve the immunosuppressive effect of cyclosporine, at least during the early postoperative period when the risk of rejection and infection is higher, and could be a promising avenue to successful hormonal manipulations of the immune process after organ transplantation.

Natural killer activity in hyperprolactinemic patients

Several pieces of evidence suggest the existence of a relationship between neuroendocrine and immune systems. Prolactin (PRL) has been demonstrated to modulate some immune responses and its influence seems to be permissive or inhibitory depending on its concentration. Previous studies have reported a reduced natural killer (NK) cell function in patients with hyperprolactinemia. In 36 patients (34 females and 2 males, aged 14-46 years) with hyperprolactinemia (mean +/- SEM PRL 142.2 +/- 42.1 micrograms/l) of tumorous (19 patients) and functional (17 patients) origins, NK activity of peripheral blood lymphocytes (PBL) was studied. Patients had NK cell activity against the K562 cell line which did not differ from that of lymphocytes from 36 age- and sex-matched healthy donors (mean +/- SEM lytic units (LU) 619.0 +/- 103.0 and 531.9 +/- 52.6 respectively). No correlation between PRL levels and LU values was found (r = 0.28). When patients with tumors or functional hyperprolactinemia were separately analysed no difference was found between these two groups (mean +/- SEM LU 690.0 +/- 117.7 vs. 606.0 +/- 148.8). In conclusion, our data demonstrate that neither the elevated PRL levels nor the PRL-secreting tumor per se interfere with the NK system of hyperprolactinemic patients.

Oestrogen induced suppression of collagen arthritis. IV: Progesterone alone does not affect the course of arthritis but enhances the oestrogen-mediated therapeutic effect

The effects of 17 beta-oestradiol and progesterone on the development of type II collagen-induced arthritis (CIA) and the anti-type II collagen (CII) autoantibody response were investigated. Treatment with physiological doses of 17 beta-oestradiol, inducing serum levels below the estradiol peak at the end of pregnancy, abrogated the development of arthritis and suppressed the anti-CII autoantibody response. Treatment with progesterone alone did not have significant effects on the development of arthritis or on the anti-CII autoantibody response. However, a combined treatment with both progesterone and oestrogen in physiological doses induced a more pronounced suppression of CIA than the suppression induced with oestrogen treatment alone. These findings suggest that oestrogen, but not progesterone, may be the critical factor to explain the pregnancy-related down-regulation of CIA.

Pituitary dependence of bone marrow function

The anaemia, leucopenia, thrombocytopenia and impaired DNA and RNA synthesis in the bone marrow of hypophysectomized rats could be restored by syngeneic pituitary grafts placed under the kidney capsule, or by treatments with ovine or bovine prolactin or growth hormone. Treatment with ACTH, FSH, LH and TSH had no effect in this respect. These results indicate that bone marrow function is regulated by the pituitary gland.

Inhibition of lipopolysaccharide-induced alpha/beta-interferon synthesis by dopamine and the dopamine-1 agonist fenoldopam

In vitro incubation of Listeria monocytogenes-immune spleen cells in the presence of dopamine or fenoldopam, a dopamine-1 (D1) agonist, inhibited alpha/beta-interferon (IFN) synthesis induced by the mitogen lipopolysaccharide (LPS), in a manner that appeared to be concentration dependent. In addition, the inhibitory effect of dopamine and fenoldopam on the synthesis of IFN was prevented by incubating immune spleen cells in the presence of haloperidol, a D1 antagonist.

Rapid activation of protein kinase C in isolated rat liver nuclei by prolactin, a known hepatic mitogen

Rat liver nuclei pure by enzymatic and electron microscope criteria contain protein kinase C (PKC) that can be activated several hundredfold within 3 min of addition of prolactin or phorbol 12-tetradecanoate 13-acetate. Rat prolactin stimulated PKC maximally at 10(-12) M, whereas ovine prolactin was maximally stimulatory at 10(-10) M. Activation was time and dose dependent, exhibited a biphasic pattern, and was blocked by anti-prolactin antiserum, by PKC inhibitors such as 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) and sphingosine, and by cyclosporine. Moreover, the ability of prolactin to activate nuclear PKC was inhibited totally by a monoclonal antibody to the rat liver prolactin receptor, implicating a prolactin receptor-mediated activation process. Epidermal growth factor (EGF), a liver mitogen, caused a lesser but significant activation of nuclear PKC. However, EGF and suboptimal prolactin were synergistic. Human growth hormone, which has lactogenic properties, stimulated PKC activity, whereas nonlactogenic substances such as ovine growth hormone, insulin, dexamethasone, and 8-bromo-cAMP were inactive. That this may be a general mechanism for prolactin is suggested by the ability of prolactin to stimulate PKC 140-fold in rat splenocyte nuclei. Prolactin has comitogenic properties in lymphocytes.

Neonatal administration of prolactin antiserum alters the developmental pattern of T- and B-lymphocytes in the thymus and spleen of BALB/c female mice

We have evaluated the effect of neonatal administration of mouse prolactin (PRL) antiserum on the developmental expression of T- and B-lymphocytes in the thymus and spleen of female BALB/c mice. Newborn female mice were injected subcutaneously with a 50-microliters aliquot of PRL antiserum or normal rabbit serum on days 1, 2, and 3. On neonatal day 5, the PRL antiserum-treated group had a significantly (P less than 0.05) increased population of cells in the thymus and the spleen that were positive for Thy-1.2 and for L3T4. Increases in Thy-1.2- and L3T4-positive cells in the thymus were detectable also on days 8 and 14 in mice that received the PRL antiserum and in mice injected with bromocriptine, a dopamine agonist that inhibits PRL release from the anterior pituitary. On neonatal days 21, 28, and 32, there were no significant differences in the percentage of cells positive for Thy-1.2, Ly-2 (formerly Lyt-2), or L3T4 antigens in the thymus. However, there were significant increases in the percentage of Thy-1.2- and L3T4-positive spleen cells in the bromocriptine-treated group at all times monitored and in the PRL antiserum-treated group except on day 14. In addition, the percentage of splenocytes that were positive for IgG was significantly increased in the PRL antiserum-treatment group on days 8-28, although not on neonatal day 32. Of tissues known to contain PRL receptors, neonatal administration of PRL antiserum or bromocriptine resulted in a significant alteration in the wet weight of spleen and liver, with no significant effect in thymus, heart, and kidney. Pituitary implants also resulted in a significant increase in both concanavalin A- and lipopolysaccharide-stimulated thymidine incorporation into murine splenic lymphocytes prepared from 45-day-old female mice. These data extend the role of PRL as an immunomodulator of adult lymphocyte function to a role in the developmental expression of T- and B-lymphocyte populations in the thymus and spleen of mice.

Hypothalamic site of action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Administration of TCDD produced a significant decrease in the serum concentration of prolactin (PRL) detected in rats after 4 hr compared to pair-fed vehicle controls and noninjected controls. This effect of TCDD was reversed by pimozide, a dopamine receptor antagonist. These data suggest that TCDD decreased the release of PRL from the adenohypophysis either by a direct effect on the gland or by altering the dopamine concentration in the median eminence (ME). Concentrations of TCDD from 5 to 500 ng/ml had no direct effect on the ability of the adenohypophysis to secrete PRL in vitro. However, the dopamine concentration increased to 3.24 +/- 0.07 ng per ME in TCDD-treated rats compared to 2.81 +/- 0.08 ng in vehicle controls. This is a dramatic alteration in the dopamine concentration, since the dopamine is being measured in the portal circulation which exhibits a rapid turnover. The rate constant of dopamine depletion after alpha-methyl-p-tyrosine and the turnover rate were also significantly elevated in the ME of TCDD-treated rats. These data provide the first biochemical evidence for a hypothalamic site of action of TCDD. Since dopamine is inhibitory to PRL release from the adenohypophysis, increased ME steady-state concentrations and turnover of this catecholamine may be responsible for the decreased concentration of serum PRL detected within 4 hr of TCDD injection. Thus, one of the early modes and sites of action of TCDD is to elevate the dopaminergic activity of the tuberoinfundibular nucleus. A hypothalamic site of action for TCDD may result in a number of the endocrinological effects known to be produced by exposure to TCDD.

Prolactin receptors on large granular lymphocytes: dual regulation by cyclosporin A

Although evidence has been provided for a modulatory role of prolactin (PRL) on humoral and cell-mediated immune responses and PRL receptors have been found on T and B lymphocytes, no indications exist concerning the influence of PRL on natural killer (NK) activity nor has a structural basis for interaction been found on the NK effector cells (large granular lymphocytes, LGL). We show here that highly purified LGL express binding sites for PRL. The calculated receptor number was 660 per cell and the dissociation constant (Kd) was 3.0 X 10(-10) M. Since previous studies have reported that cyclosporin (CsA), an immunosuppressive agent used in organ transplant patients, affects the binding of PRL to T and B lymphocytes, but not to rabbit mammary gland cells, we investigated whether this compound could alter the binding of the hormone to LGL. At concentrations from 10(-7) to 10(-6), corresponding to the therapeutical range, CsA induced a complete inhibition of the PRL binding. By contrast, concentrations of CsA ranging from 10(-11) to 10(-9) increased the PRL binding to more than 100% of control levels. In addition to their antitumor role, LGL have been proposed to participate in graft versus host disease and in transplant rejection. The finding that CsA can differently affect PRL-receptor expression on LGL points to an involvement of CsA--PRL interactions in determining the output of these immune responses. In addition, these data strongly support the idea of a close relationship between the neuroendocrine and immune systems.

Suppression of macrophage activation and T-lymphocyte function in hypoprolactinemic mice

The effects of prolactin on lactation and reproductive organs are well known. However, the other possible target organs and physiological consequences of altered levels of circulating prolactin remain poorly understood. In this study, mice were treated with bromocryptine, a dopamine receptor agonist that inhibits pituitary prolactin secretion. Bromocryptine treatment prevented T-cell-dependent induction of macrophage tumoricidal activity after the intraperitoneal injection of Listeria monocytogenes or Mycobacterium bovis. Coincident treatment with ovine prolactin reversed this effect. Of the multiple events leading to macrophage activation in vivo, the production by T-lymphocytes of gamma-interferon was the most impaired in bromocryptine-treated mice. Lymphocyte proliferation after stimulation with mitogens in vitro was also depressed in spleens of bromocryptine-treated mice, and coadministration of prolactin also reversed this effect. Bromocryptine treatment also reduced the number of deaths resulting from inoculation of mice with Listeria; exogenous prolactin significantly reversed this effect. The critical influence of pituitary prolactin release on maintenance of lymphocyte function and on lymphokine-dependent macrophage activation suggests that, in mice, lymphocytes are an important target tissue for circulating prolactin.

Interleukin 2 and a lactogen regulate proliferation and protein phosphorylation in Nb2 cells

Cell proliferation and protein phosphorylation in response to activation of lactogenic and interleukin 2 (IL-2) receptors were studied in Nb2 cells, a rat T-lymphocyte cell line. Human growth hormone (hGH) and rat IL-2 stimulated Nb2-cell proliferation to approximately the same degree, and the actions of both mitogens were potentiated by phorbol 12-myristate 13-acetate (PMA). A monoclonal antibody specific for the rat IL-2 receptor inhibited the mitogenic actions of rat IL-2, but not those of hGH. Exposure of Nb2 cells to either mitogen for 2-3 h increased phosphorylation of an 18,600-Da protein and decreased phosphorylation of a 15,600-Da protein. PMA also inhibited phosphorylation of the latter protein, but, by itself, PMA did not stimulate phosphorylation of the 18,600-Da protein. Overall, the results suggest that hGH and IL-2 act through separate receptors to stimulate proliferation of Nb2 cells, and that some of the actions of both mitogens may be mediated, in part, through regulation of protein phosphorylation.

Release of multiple hormones by a direct action of interleukin-1 on pituitary cells

Exposure to bacterial endotoxins has long been known to stimulate the release of anterior pituitary hormones; administration of endotoxin was at one time a common clinical test of anterior pituitary function. Endotoxin is a potent stimulus for production of the endogenous pyrogenic protein, interleukin-1 (IL-1), by macrophages and monocytes. The possibility that IL-1 has a direct effect on the secretion of hormones by rat pituitary cells in a monolayer culture was investigated. Recombinant human IL-1 beta stimulated the secretion of adrenocorticotropic hormone, luteinizing hormone, growth hormone, and thyroid-stimulating hormone. Increased hormone secretion into culture supernatants was found with IL-1 concentrations ranging from 10(-9) M to 10(-12) M. Prolactin secretion by the monolayers was inhibited by similar doses. These concentrations of IL-1 are within the range reported for IL-1 in serum, suggesting that IL-1 generated peripherally by mononuclear immune cells may act directly on anterior pituitary cells to modulate hormone secretion in vivo. Incubation of IL-1 solutions with antibody to IL-1 neutralized these actions. These pituitary effects of IL-1 suggest that this monokine may be an important regulator of the metabolic adaptations to infectious stressors.

Hepatic prolactin binding is rapidly altered by endotoxin in lactating mice

Endotoxin or lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, produces profound physiologic changes in most mammals. The effects of LPS on ovine prolactin (oPRL) binding by hepatic membranes of lactating mice is explored in this report. Specific 125I-oPRL binding by liver membranes from LPS-responder C3HfB/HeN mice increased two-fold within fifteen minutes of the injection of LPS, while no change was observed in the non-responder C3H/HeJ mice. Specific 125I-insulin binding did not change. Scatchard analysis of equilibrium binding of oPRL to C3HfB/HeN liver membranes indicated that within fifteen minutes of LPS injection, a receptor of differing binding affinity appears and then disappears by one hour post-injection. We propose that these rapid alterations in the specific binding of oPRL by liver membranes from LPS-injected, lactating C3HfB/HeN mice are due to the transient creation or unmasking of a novel class of PRL receptor.

Stimulation of in vivo antibody production and concanavalin-A-induced mouse spleen cell mitogenesis by prolactin

Regulation of the immune system by neuroendocrine hormones is receiving increased attention. Prolactin, a hormone normally associated with lactation, has been shown recently to reconstitute immunosuppressed hypophysectomized rats. The present studies demonstrate that prolactin administration to normal mice results in a biphasic stimulation of antibody production to sheep red blood cells. While 100 and 200 micrograms bovine prolactin/animal stimulated antibody production, 400 micrograms had no effect. Potentiation of lectin-induced T-cell mitogenesis by prolactin was also biphasic. As the concentration of prolactin increased the incorporation of [3H]thymidine into the cells first increased and then decreased. Decreasing serum prolactin levels with the dopaminergic agonist bromocriptine resulted in a reduction of antibody titers to sheep erythrocytes and a modulation of thymic weight. These data show that prolactin can stimulate the immune system in a biphasic manner and that a reduction in the basal levels of this hormone results in an attenuated immune response.

Prolactin binding sites in human erythrocytes and lymphocytes

Specific binding sites for prolactin (PRL) have been studied in human peripheral lymphocytes and erythrocytes of normal adult volunteers and of term cord bloods. In erythrocytes from healthy adult subjects of both sexes a very low specific binding of 125I-human PRL was found (0.24%), whereas a higher binding was found in term cord blood (1.1%). The binding was hormone specific, the binding capacity was 2.6 fmol/4 X 10(9) cells and the Kd was 3.4 X 10(-10) M. In lymphocytes of both adults and term cord bloods an evident specific binding was observed (male adults: 1.6%; female adults: 1.7%; cord blood: 1.8%). The binding was specific for lactogenic hormones and the binding capacity was 3.7 fmol/2 X 10(6) cells and the Kd was 3.9 X 10(-10) M. The presence of specific binding sites for PRL on human erythrocytes and lymphocytes could be used to study PRL binding on blood cells of patients in different physiological or pathological situations.

Bromocriptine and low dose cyclosporine in the treatment of experimental autoimmune uveitis in the rat

The immunologic effects of bromocriptine and low dose cyclosporine on experimental autoimmune uveitis (EAU) induced in Lewis rats by S-antigen immunization were studied. Rats treated with a sub-optimal dose (low dose) of cyclosporine (2 mg/kg per d), bromocriptine (1.8 mg/kg per d), or both drugs were compared with untreated rats in regard to the development of EAU, lymphocyte proliferative responses, and anti-S-antigen serum antibodies. Bromocriptine alone decreased the incidence of EAU only in female rats (P less than 0.01), did not effect the lymphocyte proliferative response, but did significantly decrease antibody titers in both males (P less than 0.004) and females (P less than 0.0005). Low dose cyclosporine also partially decreased the incidence of EAU in female rats, but did not decrease antibody titers or lymphocyte proliferative responses. Bromocriptine plus low-dose cyclosporine led to more marked decreases in the incidence of EAU and anti-S-antigen antibody titers as well as in the lymphocyte proliferative assay (P less than 0.01 for males, P less than 0.0005 for females). This study suggests that bromocriptine can enhance the immunosuppression of low dose cyclosporine.

Circadian alterations in prolactin, corticosterone, and thyroid hormone levels and down-regulation of prolactin receptor activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Studies were initiated to determine whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affects circadian rhythms of serum prolactin (PRL), corticosterone, thyroxine (T4), and triiodothyronine (T3) in male Sprague-Dawley rats. In addition, the effects of TCDD on PRL receptor activity, as assessed by the ability of PRL to induce ornithine decarboxylase (ODC), were determined. The earliest effect detected following TCDD administration was a significant decrease in the serum PRL concentration compared with that of pair-fed controls within 4 hr (p less than 0.05). This was followed by a significant decrease in serum T4 by 6 hr (p less than 0.05). By 8 hr the serum peak of corticosterone was shifted to 2 hr later in the TCDD-treated rats. This temporal sequence of hormonal changes suggests that the earlier alteration in PRL may be involved in the later alterations in the concentrations of serum T4 and corticosterone. The serum PRL concentration 7 days after TCDD administration was significantly higher (p less than 0.05) in TCDD-treated animals compared with that in pair-fed controls (mean of 20.5 +/- 3.7 vs 13.6 +/- 1.8 ng/ml serum, p less than 0.05, respectively). The elevation of ODC activity in response to PRL, 2 days after TCDD, was decreased in the order of thymus greater than adrenal greater than spleen greater than heart greater than kidney greater than liver. By 7 days, liver ODC activity in response to PRL was only 12% that detected in pair-fed controls. Liver ODC activity in response to dexamethasone and aminophylline was decreased to 25 and 22% of pair-fed controls, respectively, by 7 days after TCDD administration. However, in kidney, TCDD-treated rats had an increased ODC response to aminophylline to 191% of pair-fed controls by Day 7. These results suggest that the ability of TCDD to alter receptor coupling or the receptor number for diverse hormones may play a role in TCDD toxicity.

Selective T cell defects induced by dopamine administration in mice

Dopamine administration in BALB/c mice depressed the overall delayed-type hypersensitivity reaction to sheep red blood cells, the mixed-lymphocyte culture responses, the generation of cytotoxic T cells, and the number of spleen T cell populations. Conversely, dopamine enhanced concanavalin A stimulation of spleen cells, and had no effect on stimulation by PHA, on total spleen and thymus cell number, and on distribution of thymus Ly-t1+ or Ly-t2+ cell subsets. These results indicate that dopamine produces selective T cell defects probably mediated by a direct peripheral action of the drug on subsets of T lymphocytes.

Immunomodulation by tamoxifen and pergolide

Treatment of rats with tamoxifen citrate or pergolide mesylate was as effective in inhibiting antibody formation and contact sensitivity skin reactions as was hypophysectomy. The immunocompetence of tamoxifen citrate- and pergolide mesylate-suppressed animals could be fully restored by additional treatment with prolactin or growth hormone.

GH3 pituitary adenoma cells can reverse thymic aging in rats

Thymic size and T-cell function decrease with age, and it has not yet been possible to totally reverse this thymic atrophy and completely restore T-cell-dependent immune functions. In this study, GH3 pituitary adenoma cells, which secrete growth hormone and prolactin, were implanted subcutaneously into 16- and 22-month-old female Wistar-Furth rats and the rats were sacrificed approximately 2 months later. Only thymic remnants were detected in aged, non-implanted rats, but thymus glands were found in both the 18- and the 24-month-old rats that had been implanted with GH3 cells. Thymus glands from the GH3-implanted 18-month-old rats contained distinct cortical thymocytes and medullary epithelial cells. Depending on the concentration of phytohemagglutinin or concanavalin A, T-cell proliferative responses of splenocytes from these implanted rats were 2- to 5-fold greater than those of 18-month-old controls. At the optimal concentration of mitogen, proliferative responses to either lectin could be restored to those levels observed in splenocytes from 3-month-old Wistar-Furth females. Thymus glands from 24-month-old GH3-implanted rats contained more cortical thymocytes and fewer fat vacuoles than controls, but they were not totally reconstituted. No significant lectin-induced T-cell proliferative responses or IL-2 secretion were detected in 24-month-old control rats, but splenocytes from GH3-implanted rats showed augmented T-cell proliferative responses and increased synthesis of IL-2. Fluorescence-activated cell-sorter analysis of thymocytes revealed that 24-month-old rats implanted with GH3 cells had a higher proportion of lymphocytes with the Thy-1.1 and helper-T-cell phenotypes. These data show that it is possible to regenerate normal thymic tissue in situ and reverse the natural loss in cell-mediated immunity that occurs with aging.

Prolactin as a modulator of lymphocyte responsiveness provides a possible mechanism of action for cyclosporine

Lymphocyte responsiveness in rats was found to depend on serum prolactin levels. Blocking pituitary prolactin release with bromocriptine severely reduces lymphocyte reactivity in vitro (mixed lymphocyte reaction) as well as in vivo (graft-versus-host reaction). In addition, evidence for a prolactin/growth hormone-related mRNA species produced in mitogen- and antigen-stimulated lymphocytes has been obtained. Prolactin was shown to compete in a dose-dependent fashion with the immunosuppressant cyclosporine (cyclosporin A) for a common binding site on the surface of T lymphocytes. Further, stimulation of prolactin secretion reversed the immunosuppression induced by cyclosporine. We conclude that prolactin is involved in the maintenance of T-cell immunocompetence and that the immunosuppressive effects of cyclosporine may be mediated by the displacement of prolactin from binding sites on lymphocytes.

T-cell dysregulation in patients with hyperprolactinemia: effect of bromocriptine treatment

We studied four patients with tumoral hyperprolactinemia and normal ovarian function before and after prolactine levels had become normal with treatment with bromocriptine (BrC), a dopamine agonist that inhibits prolactin release. Their proliferative responses to concanavalin A, pokeweed mitogen, and, to a lesser extent, phytohemagglutinin, their spontaneous and concanavalin A-induced suppression, and their production of interleukin 2 were found to be decreased and to correct partially or completely after bromocriptine treatment. The T-cell response to interleukin 2 was low in two patients in whom it increased after BrC treatment. These findings give insight on the immunomodulatory role of prolactin in vivo.