Lactation increases prolactin receptor expression in spleen and thymus of rats

Hormonal control of T-cell development in health and disease

The physiology of the thymus, the primary lymphoid organ in which T cells are generated, is controlled by hormones. Data from animal models indicate that several peptide and nonpeptide hormones act pleiotropically within the thymus to modulate the proliferation, differentiation, migration and death by apoptosis of developing thymocytes. For example, growth hormone and prolactin can enhance thymocyte proliferation and migration, whereas glucocorticoids lead to the apoptosis of these developing cells. The thymus undergoes progressive age-dependent atrophy with a loss of cells being generated and exported, therefore, hormone-based therapies are being developed as an alternative strategy to rejuvenate the organ, as well as to augment thymocyte proliferation and the export of mature T cells to peripheral lymphoid organs. Some hormones (such as growth hormone and progonadoliberin-1) are also being used as therapeutic agents to treat immunodeficiency disorders associated with thymic atrophy, such as HIV infection. In this Review, we discuss the accumulating data that shows the thymus gland is under complex and multifaceted hormonal control that affects the process of T-cell development in health and disease.

Lactation modifies stress-induced immune changes in laboratory rats

Lactation and stressor exposure both influence the activity of the immune system, but the interaction of both factors on the immune defense is poorly understood. The aim was therefore to investigate in lactating Long-Evans rats the effect of social stress on aspects of cellular immunity in the blood and mesenteric lymph nodes (MLN). Acute social stress (2h) was induced in lactating and non-lactating female intruders using a confrontation model that yielded into social defeat and increased plasma corticosterone concentrations. Stress as well as lactation had marked effects on the immune system. Acute social stress caused granulocytosis, reduced lymphocyte proliferation, and cytokine production in the blood, but had no significant effects in MLN. In the blood of lactating rats, increased numbers of granulocytes and enhanced phagocytosis, but decreased B cell numbers and reduced IL-2 production was observed. However, in MLN both lymphocyte proliferation and monocyte numbers were increased in lactating rats. The effect of stress on the immune measures was often similar in lactating and non-lactating females, but a few important differences were evident: Only non-lactating animals showed an increase in blood granulocyte numbers and a decrease in IL-2 production in response to stressor exposure. Thus, during lactation, a neuroendocrine status may exist which impedes stress-induced modulations at least of some immune parameters.

Effects of photoperiod during the dry period on prolactin, prolactin receptor, and milk production of dairy cows

Cows exposed to short day photoperiod during the dry period produce significantly more milk in their subsequent lactation than cows exposed to long days. The mechanism(s) underlying this effect are unknown. Because concentrations of prolactin (PRL) in circulation are consistently affected by changes in photoperiod, we hypothesized that alterations in the prolactin axis and sensitivity of the mammary gland to prolactin signaling may mediate photoperiodic effects in dry cows. The objective of this study was to determine the effects of exposure to different lengths of daylight during the dry period on circulating PRL and PRL receptor (PRL-R) mRNA expression in lymphocytes and mammary tissue during the transition to lactation. Multiparous Holstein cows were dried off 62 d before calving and assigned to long day (16 h light: 8 h dark) or short day photoperiod (8 h light: 16 h dark). During the dry period, PRL and PRL-R mRNA were analyzed biweekly in plasma and lymphocytes, respectively. Expression of PRL-R mRNA was assessed in mammary biopsies during the dry and periparturient periods. Dry matter intake (DMI) was recorded through 21 d of lactation, and milk yield was recorded until 120 d in milk. Short day photoperiod was associated with reduced PRL, whereas milk yield and expression of PRL-R mRNA in lymphocytes and mammary tissue were increased. Cows on short days had higher DMI during the dry period but did not differ in DMI after parturition. These data support the concept that greater responsiveness and sensitivity to PRL during transition to lactation may be associated with an increase in subsequent milk yield.

Evaluation of the immune response following exposure of mice to bisphenol A: induction of Th1 cytokine and prolactin by BPA exposure in the mouse spleen cells

Bisphenol A [2, 2 bis (4-hydoxyphenyl) propane; BPA] is a widely used endocrine disruptors and has estrogenic activities. Although interests on biological effect of BPA are rising, evidences of its effect on immune system are lacking. We investigated that the effect of BPA on immune parameters to postulate the mechanism, and BPA interruptions between neuroendocrine and immune system. BPA was administrated to mice by p.o. (as a drinking water) dose on 0.015, 1.5 and 30 mg/ml for 4 weeks. The BPA treatment did not result in any change in body weight, spleen weight and distribution of lymphocyte subpopulation collected from spleen. BPA induced prolactin production in spleen, and exposure of BPA increased the activity of splenocyte proliferation in response to Con A (p<0.001). The production of a strong Th-1 type cytokine (IFN-gamma) was induced while Th-2 type (IL-4) was suppressed by BPA treatment. These were consistent with RT-PCR results of transcription factor GATA-3 and IRF-1. These findings suggested that stimulation of prolactin production by estrogenic effects of BPA would affect cytokine profiles, and lead to imbalanced cellular immune response. In addition, we could speculate that prolactin and cytokine is important mediator involved in network between neuroendocrine and immune system by BPA.

Prolactin receptor gene expression in the forebrain of pregnant and lactating rats

Prolactin plays a large role in the onset of maternal behavior at parturition. Knowledge of the change in expression of the prolactin receptor in the brain across pregnancy and lactation, however, is limited. Prolactin receptor gene expression was determined by in situ hybridization histochemistry during pregnancy and lactation in rats. Expression of the mRNA for the longform of the prolactin receptor (PRL-R-L) was measured in various forebrain structures in primigravid rats at different stages of pregnancy, in primiparous rats during early, mid-, and late lactation, and in age-matched, nulliparous females in diestrus. Hybridizations were performed using a [33P]-labeled riboprobe specific for the long form of the prolactin receptor mRNA complimentary to 290 bp of the prolactin receptor gene. The following areas of the forebrain were examined: medial preoptic area (MPOA), median preoptic nucleus both dorsal (MePOd) and ventral (MePOv) to the anterior commissure, ventral lateral septum (LSv), and the ventral and principal parts of the bed nucleus of the stria terminalis (BnSTv and BnSTpr, respectively). Overall, the number of cells expressing PRL-R-L mRNA was significantly higher at 2 h postpartum compared to diestrus in all areas examined except the LSv. In addition, there were lower numbers of PRL-R-L cells during all stages of lactation compared to pregnancy. The number of grains per cell in the MPOA and LSv did not change as dramatically as the number of cells expressing PRL-R-L mRNA in those brain regions. These data contribute to the growing body of evidence that the neural lactogenic system changes as a function of female reproductive state. Changes in PRL-R-L mRNA in terms of behavior and endocrine functions are discussed.

Lipopolysaccharide-induced tumor necrosis factor-alpha release is controlled by the central nervous system

OBJECTIVE

Lipopolysaccharide (LPS) injection in mammals orchestrates the release of many proinflammatory and anti-inflammatory cytokines. Intravenous administration of 0.2 mg/kg of LPS into unanesthetized rats with indwelling jugular catheters provoked a rapid, 50-fold increase in plasma tumor necrosis factor (TNF)-alpha within 30 min, which declined by 60% by 120 min. To test our hypothesis that such a rapid increase of TNF-alpha would be either neurally or hormonally controlled, the effect on TNF-alpha release of anesthesia (ketamine/acepromazine/xylazine) and catecholaminergic agonists and antagonists, either alone or in the presence of LPS, was determined.

METHODS

Rats bearing indwelling external jugular catheters were injected with the test drug or saline after removal of 0.6 ml of blood (-10 min). At time zero, LPS or saline was administered. Thereafter, blood samples were drawn at 15, 30, 120, 240 and 360 min. TNF-alpha was measured by immunoassay.

RESULTS

Among all the drugs tested, only propranolol increased plasma TNF-alpha. Anesthesia significantly blunted the LPS-induced TNF-alpha peak by 50%. Isoproterenol, a beta-adrenergic agonist, also blocked LPS-induced TNF-alpha release by 70% at 30 min and 90% at 120 min. On the contrary, propranolol, a beta-receptor blocker, induced a highly significant 3-fold increase in plasma TNF-alpha concentrations at 30 min and augmented the response to LPS 2-fold after endotoxin injection. Phentolamine, an alpha-receptor blocker, decreased the LPS-induced TNF-alpha release by 57% at 30 min. Similarly, alpha-bromoergocryptine, a dopamine D2 receptor agonist, decreased the LPS-induced TNF-alpha peak by 70% at 30 min and 50% at 120 min.

CONCLUSIONS

We conclude that TNF-alpha is at least in part neurally controlled since the anesthetic blocked its response to LPS. The fact that isoproterenol decreased the LPS-induced TNF-alpha release, whereas propranolol augmented basal and LPS-induced release suggests that the sympathetic nervous system inhibits basal and LPS-stimulated TNF-alpha release via beta-adrenergic receptors. Since phentolamine blocked LPS-induced release, this release may be induced, in part at least, by LPS-stimulated adrenergic drive acting on alpha-adrenergic receptors. The suppressive action of bromoergocryptine, a dopamine D2 receptor agonist, on LPS-induced TNF-alpha release may be mediated in part by suppression of prolactin release, which triggers TNF-alpha release.

Neuroendocrine control of thymus physiology

The thymus gland is a central lymphoid organ in which bone marrow-derived T cell precursors undergo differentiation, eventually leading to migration of positively selected thymocytes to the peripheral lymphoid organs. This differentiation occurs along with cell migration in the context of the thymic microenvironment, formed of epithelial cells, macrophages, dendritic cells, fibroblasts, and extracellular matrix components. Various interactions occurring between microenvironmental cells and differentiating thymocytes are under neuroendocrine control. In this review, we summarize data showing that thymus physiology is pleiotropically influenced by hormones and neuropeptides. These molecules modulate the expression of major histocompatibility complex gene products by microenvironmental cells and the extracellular matrix-mediated interactions, leading to enhanced thymocyte adhesion to thymic epithelial cells. Cytokine production and thymic endocrine function (herein exemplified by thymulin production) are also hormonally controlled, and, interestingly in this latter case, a bidirectional circuitry seems to exist since thymic-derived peptides also modulate hormonal production. In addition to their role in thymic cell proliferation and apoptosis, hormones and neuropeptides also modulate intrathymic T cell differentiation, influencing the generation of the T cell repertoire. Finally, neuroendocrine control of the thymus appears extremely complex, with possible influence of biological circuitry involving the intrathymic production of a variety of hormones and neuropeptides and the expression of their respective receptors by thymic cells.

Novel mechanisms linking angiotensin II and early atherogenesis

We propose that Ang II exerts an as yet uncharacterized immunomodulatory effect on monocyte maturation, differentiation, or extravasation, which may depend on the myelomonocytic phenotype. Since the myelopoietic process originating at stem cells and culminating in release to the blood is at least 6 days, it is conceivable that the observation of reduced monocyte CD11b expression two weeks after completion of losartan treatment indicates a suppression of the CD11b phenotype in newly released CD14(+)/CD45(+) monocytes. Other studies employing suppression of AT(1)-receptors with deoxy-oligonucleotides have reported effects on blood pressure that surpass those predicted by the duration of the treatment.(87) These data would suggest that it is possible to interrupt a stimulatory signal by Ang II through a gene-related mechanism that in our experiments may reside in the mechanisms that regulate myelopoiesis. While our knowledge of the role of Ang II in the regulation of monocyte formation and function is incomplete, we have taken a first step in attempting to synthesize the data described above into a comprehensive hypothesis for further evaluation of the factors that initiate atherogenesis. Such effects may crucially contribute to the clinical benefit of AT(1)-receptor antagonists, independent of depressor effects, and may represent a paradigm for novel, anti-inflammatory actions by this class of drugs.