Experimental allergic encephalomyelitis in pituitary-grafted Lewis rats
© Esquifino et al; licensee BioMed Central Ltd. 2006
Received: 01 June 2006
Accepted: 23 August 2006
Published: 23 August 2006
Treatment of susceptible rats with dopaminergic agonists that reduce prolactin release decreases both severity and duration of clinical signs of experimental allergic encephalomyelitis (EAE). To assess to what extent the presence of an ectopic pituitary (that produces an increase in plasma prolactin levels mainly derived from the ectopic gland) affects EAE, 39 male Lewis rats were submitted to pituitary grafting from littermate donors. Another group of 38 rats was sham-operated by implanting a muscle fragment similar in size to the pituitary graft. All rats received subcutaneous (s.c.) injections of complete Freund's adjuvant (CFA) plus spinal cord homogenate (SCH) and were monitored daily for clinical signs of EAE. Animals were killed by decapitation on days 1, 4, 7, 11 or 15 after immunization and plasma was collected for prolactin RIA. In a second experiment, 48 rats were immunized by s.c. injection of a mixture of SCH and CFA, and then received daily s.c. injections of bromocriptine (1 mg/kg) or saline. Groups of 8 animals were killed on days 8, 11 or 15 after immunization and plasma prolactin was measured. Only sham-operated rats exhibited clinical signs of the disease when assessed on day 15 after immunization. A progressive decrease in plasma prolactin levels was observed in pituitary-grafted rats, attaining a minimum 15 days after immunization, whereas plasma prolactin levels were increased during the course of the disease in sham-operated rats. Plasma prolactin levels were higher in pituitary-grafted rats than in sham-operated rats 1 day after immunization, but lower on days 7, 11 and 15 after immunogen injection. Further supporting a correlation of suppressed prolactin levels with absence of clinical signs of EAE, rats that were administered the dopaminergic agonist bromocriptine showed very low plasma prolactin levels and did not exhibit any clinical sign of EAE. These results indicate that low circulating prolactin levels coincide with absence of clinical signs of EAE in Lewis rats.
Experimental allergic encephalomyelitis (EAE) is one of best-studied models of autoimmune disease, and is characterized by an autoimmune attack on CNS myelin mediated by neural autoantigen-specific T helper cells . EAE is currently the best available animal model of human multiple sclerosis. During induction of EAE, autoreactive T-cells are activated in the periphery by subcutaneous injection of either spinal cord homogenate (SCH) or CNS antigens, which may include myelin basic protein, myelin oligodendrocyte glycoprotein, or proteolipid protein or their peptides . About 10 days after the combined injection of complete Freund adjuvant (CFA) and spinal cord homogenate (SCH), susceptible rats (e.g., Lewis rats) develop a progressive paralysis associated with CNS demyelinization. Activated, autoreactive T-cells access the CNS and, in the presence of competent antigen presenting cells, are further activated and induce a local inflammatory response. In most such models, the T helper 1 (Th1) subset of T-cells has been implicated in the induction phase of EAE.
It is well established that prolactin is an important modulator of the immune system through an effect that is exerted in part on the cellular arm of immune defense involving Th1 cytokines [3, 4]. Factors that cause hypoprolactinemia are generally associated with reduced immunocompetence, whereas prolactin administration restores immunocompetence in hypophysectomized rats or bromocriptine-treated rats [5–7]. On the other hand, significant immune-suppressive effects of prolactin have been noticed: several investigators have reported that prolactin decreases natural killer cell migration and activity and reduces lymphocyte proliferative capacity and cytokine release in rodents [7–9]. Of relevance to EAE is the observation that treatment of animals with dopaminergic agonists which reduce prolactin release decreases both severity and duration of clinical signs of the disease [10, 11].
Since changes in prolactin secretion could modulate EAE symptomatology, we wished to assess to what extent the presence of an ectopic pituitary, producing an increase in plasma prolactin levels mainly derived from the ectopic gland , would affect EAE. The consequence of inhibiting prolactin secretion by injecting the dopaminergic agonist bromocriptine was also assessed.
Male Lewis rats (6 weeks old, 140–170 g) were purchased from Charles River S.A., Spain, and were housed under standard conditions of controlled light (12:12 h light/dark schedule, light on at 0800 h) and temperature (22 ± 2°C). All experiments were conducted in accordance with the guidelines of the International Council for Laboratory Animal Science (ICLAS). Protocols were approved by the Institutional Animals Ethics Committee. Spinal cord, obtained from adult Wistar rats, was homogenized in PBS buffer at a concentration of 1 mg/ml to serve as an immunogen (SCH).
Two experiments were performed. In experiment 1, 39 rats were subjected to pituitary grafting from littermate donors. Animals were anesthetized with 2.5% tribromoethanol in saline (1 ml/100 g body weight). Another group of 38 rats of the same age was sham-operated (by implanting a muscle fragment of a size similar to the pituitary graft) to be used as a control group. Rats were left undisturbed for 4 weeks – i.e., until the time at which increased prolactin levels in pituitary grafted animals attains a plateau  – at the end of which time all animals were immunized by subcutaneous (s.c.) injection of a mixture of SCH and CFA containing Mycobacterium tuberculosis H37Ra (5 mg/ml; Difco Laboratories, Detroit, Michigan) (v/v) in a final volume of 200 μl. Animals were monitored daily for clinical signs of EAE using the following assessment scale: 0, normal; 0.5, loss of tonicity in distal half of tail; 1, piloerection; 2, total loss of tail tonicity; 3, hind leg paralysis; 4, paraplegia; and 5, moribund . The rats were killed by decapitation on days 1, 4, 7, 11 or 15 after immunization (7–8 animals per group) and blood was collected from a trunk wound into heparinized tubes and was centrifuged. Plasma was collected and stored at -20°C until further analysis. Visual assessment of the grafts at the time of sacrifice did not show any gross differences between groups.
In experiment 2, 48 male Lewis rats were immunized with SCH plus CFA mixture, and then received daily s.c. injections of bromocriptine (1 mg/kg) or saline (n = 24 each). Animals were monitored daily for clinical signs of EAE and were killed by decapitation on day 8, 11 or 15 after immunization (8 animals per group), and blood was collected from a trunk wound.
Plasma prolactin levels were measured by a homologous specific double antibody RIA , using materials kindly supplied by the NIDDK's National Hormone and Pituitary Program and Dr. A. Parlow (Harbor UCLA Medical Center, Torrance CA 90509). The intra- and interassay coefficients were 6–8%. Sensitivity of the RIA was 40 pg/ml using the NIDDK rat prolactin RP-3 standard. Results were expressed as pg/ml of plasma. Statistical analysis of results was performed by employing either Student's t test, a factorial analysis of variance (ANOVA), or a one-way ANOVA followed by a Student-Newman-Keuls test.
Mild hyperprolactinemia has been found to enhance several autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis and autoimmune thyroiditis [6, 7, 20]. In studies of EAE, prolactin levels have been found to be elevated before the onset and during the disease , as observed in sham-operated animals in the present study. Therefore, a feasible explanation for the lack of clinical signs of EAE on day 15 after immunization in pituitary-grafted rats is a relative lack of prolactin.
Further supporting the correlation of suppressed prolactin levels with absence of clinical signs of EAE is the observation that rats administered the dopaminergic agonist bromocriptine did not exhibit any clinical sign of disease (Fig. 1, upper right panel). Bromocriptine treatment was very effective in preventing prolactin release at all examined time points (p < 0.001) (Fig. 1, lower right panel).
In summary, these results indicate that low circulating prolactin levels coincide with absence of clinical signs of EAE in Lewis rats. Since the presence of an ectopic pituitary would normally be expected to lead to increased plasma prolactin levels, further studies are needed to unravel why prolactin production by renal pituitary grafts is suppressed during EAE development. These results also confirm previous findings that treatment with dopaminergic agonists induces a reduction of prolactin levels accompanied by amelioration of the neurological signs of EAE [10, 11]. The effects of dopaminergic agents could be related to their ability to lower prolactin concentrations and/or to a neuroprotective action of the drugs.
Caution should be taken in extrapolating these results to human disease as monophasic EAE, particularly in the Lewis rat model, shares only some aspects of human multiple sclerosis. Indeed, contradictory results have been published on the occurrence of hyperprolactinemia in multiple sclerosis patients, with some studies finding increased prolactin levels [22–24] while others do not [25–27].
This work was supported by grants from FISS Madrid, Spain, Agencia Nacional de Promoción Científica y Tecnológica, Argentina (PICT 14087) and the Universidad de Buenos Aires (ME 075). DPC is a Research Career Awarded from the Argentine Research Council (CONICET).
- Wekerle H, Kojima K, Lannes-Vieira J, Lassmann H, Linington C: Animal models. Ann Neurol. 1994, 36 (Suppl): S47-S53. 10.1002/ana.410360714.View ArticlePubMedGoogle Scholar
- Coyle PK: The neuroimmunology of multiple sclerosis. Adv Neuroimmunol. 1996, 6: 143-154. 10.1016/0960-5428(96)00013-7.View ArticlePubMedGoogle Scholar
- Takagi K, Suzuki F, Barrow RE, Wolf SE, Herndon DN: Recombinant human growth hormone modulates Th1 and Th2 cytokine response in burned mice. Ann Surg. 1998, 228: 106-111. 10.1097/00000658-199807000-00016.PubMed CentralView ArticlePubMedGoogle Scholar
- Majumder B, Biswas R, Chattopadhyay U: Prolactin regulates antitumor immune response through induction of tumoricidal macrophages and release of IL-12. Int J Cancer. 2002, 97: 493-500. 10.1002/ijc.1624.View ArticlePubMedGoogle Scholar
- Nagy E, Berczi I, Wren GE, Asa SL, Kovacs K: Immunomodulation by bromocriptine. Immunopharmacology. 1983, 6: 231-243. 10.1016/0162-3109(83)90023-1.View ArticlePubMedGoogle Scholar
- Vera-Lastra O, Jara LJ, Espinoza LR: Prolactin and autoimmunity. Autoimmun Rev. 2002, 1: 360-364. 10.1016/S1568-9972(02)00081-2.View ArticlePubMedGoogle Scholar
- Yu-Lee LY: Prolactin modulation of immune and inflammatory responses. Recent Prog Horm Res. 2002, 57: 435-455. 10.1210/rp.57.1.435.View ArticlePubMedGoogle Scholar
- Arce A, Castrillon P, Della Maggiore V, Cardinali DP, Esquifino AI: Effect of cyclosporine on immune responses in submaxillary lymph nodes of pituitary-grafted rats. Biol Signals. 1996, 5: 334-342.View ArticlePubMedGoogle Scholar
- Matera L, Mori M, Geuna M, Buttiglieri S, Palestro G: Prolactin in autoimmunity and antitumor defence. J Neuroimmunol. 2000, 109: 47-55. 10.1016/S0165-5728(00)00302-7.View ArticlePubMedGoogle Scholar
- Canonico PL, Sortino MA, Favit A, Aleppo G, Scapagnini U: Dihydroergocryptine protects from acute experimental allergic encephalomyelitis in the rat. Funct Neurol. 1993, 8: 183-188.PubMedGoogle Scholar
- Dijkstra CD, van der Voort ER, De Groot CJ, Huitinga I, Uitdehaag BM, Polman CH, Berkenbosch F: Therapeutic effect of the D2-dopamine agonist bromocriptine on acute and relapsing experimental allergic encephalomyelitis. Psychoneuroendocrinology. 1994, 19: 135-142. 10.1016/0306-4530(94)90003-5.View ArticlePubMedGoogle Scholar
- Bartke A, Shrenker P: Effect of experimentally-induced chronic hyperprolactinemia on testosterone and gonadotropin levels in male rats and mice. Critical Rev Anat Sci. 1987, 1: 37-62.Google Scholar
- Tresguerres JA, Esquifino AI: Dissociation in the regulation of luteinizing hormone and follicle-stimulating hormone in a hyperprolactinaemic rat model: interrelationships between gonadotrophin and prolactin control. J Endocrinol. 1981, 90: 41-51.View ArticlePubMedGoogle Scholar
- Esquifino AI, Cano P, Jimenez V, Cutrera RA, Cardinali DP: Experimental allergic encephalomyelitis in male Lewis rats subjected to calorie restriction. J Physiol Biochem. 2004, 60: 245-252.View ArticlePubMedGoogle Scholar
- Castrillón P, Cardinali DP, Pazo D, Cutrera RA, Esquifino AI: Effect of superior cervical ganglionectomy on 24-h variations in hormone secretion from anterior hypophysis and in hypothalamic monoamine turnover, during the preclinical phase of Freund's adjuvant arthritis in rats. J Neuroendocrinol. 2001, 13: 288-295. 10.1046/j.1365-2826.2001.00627.x.View ArticlePubMedGoogle Scholar
- Stefferl A, Linington C, Holsboer F, Reul JM: Susceptibility and resistance to experimental allergic encephalomyelitis: relationship with hypothalamic-pituitary-adrenocortical axis responsiveness in the rat. Endocrinology. 1999, 140: 4932-4938. 10.1210/en.140.11.4932.PubMedGoogle Scholar
- Meehan TF, DeLuca HF: CD8+ T cells are not necessary for 1 alpha,25-dihydroxyvitamin D3 to suppress experimental autoimmune encephalomyelitis in mice. Proc Natl Acad Sci U S A. 2002, 99: 5557-5560.PubMed CentralView ArticlePubMedGoogle Scholar
- Neidhart M, Fluckiger EW: Hyperprolactinaemia in hypophysectomized or intact male rats and the development of adjuvant arthritis. Immunology. 1992, 77: 449-455.PubMed CentralPubMedGoogle Scholar
- Selgas L, Arce A, Esquifino AI, Cardinali DP: Twenty-hour hour rhythms of serum ACTH, prolactin, growth hormone and thyroid-stimulating hormone, and of median eminence norepinephrine, dopamine and serotonin, in rats injected with Freund's adjuvant. Chronobiol Int. 1997, 14: 253-265.View ArticlePubMedGoogle Scholar
- Chikanza IC: Prolactin and neuroimmunomodulation: in vitro and in vivo observations. Ann N Y Acad Sci. 1999, 876: 119-130. 10.1111/j.1749-6632.1999.tb07629.x.View ArticlePubMedGoogle Scholar
- Riskind PN, Massacesi L, Doolittle TH, Hauser SL: The role of prolactin in autoimmune demyelination: suppression of experimental allergic encephalomyelitis by bromocriptine. Ann Neurol. 1991, 29: 542-547. 10.1002/ana.410290514.View ArticlePubMedGoogle Scholar
- Kira J, Harada M, Yamaguchi Y, Shida N, Goto I: Hyperprolactinemia in multiple sclerosis. J Neurol Sci. 1991, 102: 61-66. 10.1016/0022-510X(91)90094-N.View ArticlePubMedGoogle Scholar
- Azar ST, Yamout B: Prolactin secretion is increased in patients with multiple sclerosis. Endocr Res. 1999, 25: 207-214.View ArticlePubMedGoogle Scholar
- Yamasaki K, Horiuchi I, Minohara M, Osoegawa M, Kawano Y, Ohyagi Y, Yamada T, Kira J: Hyperprolactinemia in optico-spinal multiple sclerosis. Intern Med. 2000, 39: 296-299.View ArticlePubMedGoogle Scholar
- Wei T, Lightman SL: The neuroendocrine axis in patients with multiple sclerosis. Brain. 1997, 120: 1067-1076. 10.1093/brain/120.6.1067.View ArticlePubMedGoogle Scholar
- Heesen C, Gold SM, Bruhn M, Monch A, Schulz KH: Prolactin stimulation in multiple sclerosis – an indicator of disease subtypes and activity?. Endocr Res. 2002, 28: 9-18. 10.1081/ERC-120004533.View ArticlePubMedGoogle Scholar
- Harirchian MH, Sahraian MA, Shirani A: Serum prolactin level in patients with multiple sclerosis: a case control study. Med Sci Monit. 2006, 12: CR177-CR180.PubMedGoogle Scholar
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