Translocatable estrogen receptors in rat splenocytes

Effect of 17beta-estradiol and voluntary exercise on lymphocyte apoptosis in mice

During the perimenopause, women may begin estrogen replacement therapy (ERT) and physical activity programs to reduce the symptoms of the climacteric. High-intensity exercise increases lymphocyte apoptosis, and estrogen is also known to have immune modulatory effects. The present study determined whether (1) estrogen exposure in vivo, and (2) low-intensity, voluntary exercise affect thymic and splenic lymphocyte apoptosis in adult female mice. 'Middle-aged' (>1 year), ovarian-intact female B6D2F(1) mice were implanted with 17beta-estradiol (E) pellets (L: 3 microg/day or H: 12 microg/day) or placebo (P: 0 microg/day). Mice were given 1 week to recover from implantation surgery after which they were randomized to wheel-running or no-wheel-running conditions. Twenty one days later, mice were sacrificed and thymus and spleen removed for determination of percent apoptosis and percent necrosis by flow cytometry, serum E levels by RIA, and tissue and body weights. Estrogen-treated, ovarian-intact mice accumulated less cumulative wheel-running activity than mice implanted with placebo (P<.001). E exposure was associated with lighter thymuses (P<.05), higher thymocyte apoptosis (P<.001), and higher serum E levels (P<.001), effects which were not modified by voluntary exercise. In contrast, splenocyte apoptosis and spleen weights did not differ by estrogen treatment or exercise. The results suggest that in vivo exposure to supplemental estrogen is associated with greater spontaneous apoptosis of thymocytes and reduced thymus weights in older ovarian-intact mice. The clinical significance for thymic (cellular) immunity in perimenopausal women given HRT remains to be determined.

In vivo regulation of syndecan-3 expression in the rat uterus by 17 beta-estradiol

The immature rat uterus has been extensively used as an in vivo model system to study the molecular mechanisms of steroid hormone actions. In this study, we demonstrated the regulated expression of syndecan-3 in the rat uterus by the steroid hormone 17 beta-estradiol. Administration of a single physiological dose of 17 beta-estradiol (40 microg/kg) to ovariectomized immature animals induced a rapid and transient increase in uterine syndecan-3 mRNA. Transcript levels reached a peak elevation of 3-fold above saline control tissues 4 h after hormone administration. Inhibition of message up-regulation by actinomycin D but not cycloheximide indicated a hormone response dependent on RNA transcription but not new protein synthesis. The estrogenic ligands estriol and tamoxifen were also effective at raising syndecan-3 mRNA levels; however, nonestrogenic ligands, including progesterone, 5 alpha-dihydrotestosterone, and dexamethasone, failed to stimulate a change in mRNA levels. Hormone-induced changes in mRNA led to transient changes in syndecan-3 protein content and significant alteration in the temporal and spatial expression in endometrial epithelial cells. Collectively, these data show that the steroid hormone 17 beta-estradiol, regulates transcription of the syndecan-3 gene in the uterus via an estrogen receptor-dependent mechanism. This estrogen-regulated expression of syndecan-3 may play an important role in changes in tissue ultrastructure crucial for proper uterine growth.

Hormones and mating system affect sex and species differences in immune function among vertebrates

Males generally exhibit reduced immune responses as well as increased intensity and prevalence of infections compared to female conspecifics. Physiologically, these sex differences may reflect the immunosuppressive effects of androgens. In addition to suppressing immune function, androgens maintain several characteristics important for reproductive success. Thus, a dynamic relationship is assumed to exist among hormones, secondary sex traits, and the immune system. Ultimately, the extent to which this relationship exists may be related to the mating system. Because polygynous males generally have higher circulating testosterone concentrations and rely more heavily on testosterone-dependent traits for reproductive success than monogamous males, sex differences in immune function are hypothesised to be more pronounced among polygynous as compared to monogamous species. Additionally, if secondary sex traits are used to advertise infection status, then females should be able to use the condition of male secondary sex traits to discern the immune/infection status of males during mate selection. The purpose of this review is to survey current studies that examine both the proximate mechanisms and ultimate function of variation in immune function and susceptibility to infection and determine whether immunological variation influences mate preference and possibly reproductive success.

The effects of hormones on sex differences in infection: from genes to behavior

Males of many species are more susceptible than females to infections caused by parasites, fungi, bacteria, and viruses. One proximate cause of sex differences in infection is differences in endocrine-immune interactions. Specifically, males may be more susceptible to infection than females because sex steroids, specifically androgens in males and estrogens in females, modulate several aspects of host immunity. It is, however, becoming increasingly more apparent that in addition to affecting host immunity, sex steroid hormones alter genes and behaviors that influence susceptibility and resistance to infection. Thus, males may be more susceptible to infection than females not only because androgens reduce immunocompetence, but because sex steroid hormones affect disease resistance genes and behaviors that make males more susceptible to infection. Consideration of the cumulative effects of sex steroid hormones on susceptibility to infection may serve to clarify current discrepancies in the literature and offer alternative hypotheses to the view that sex steroid hormones only alter susceptibility to infection via changes in host immune function.

Effect of chronic or cyclic exposure to estradiol on the humoral immune response and the thymus

Estradiol (E2) is known to enhance humoral immunity. Previous studies examining serum immunoglobulin levels on days within the estrous cycle or in the ovariectomized, chronically E2-implanted rat have determined a positive correlation between serum E2 concentrations and antibody responsiveness. No previous study has investigated the effect of fluctuating E2 concentrations, as during the estrous cycle, throughout the course of a specific humoral immune response. Therefore, in the present study we addressed the influences of cyclic and tonic E2 exposure on the anti-fluorescein response in the rat. Ovariectomized rats were submitted to a 2 x 2 factorial design of chronic E2 implants and 4-day E2 injection (and vehicle control) regimens. Anti-fluorescein antibody production and thymic weights were measured. Animals given a 4-day cycle of E2 showed significantly (p less than 0.001) greater anti-fluorescein responses than did animals given tonic or no E2 replacement. Animals which were given implants, with or without cyclic E2 injections, experienced significant (p less than 0.001) thymic involution relative to those without implants. The 4-day E2 injections alone did not lead to thymic atrophy. These results indicate that while chronic E2 treatment induced thymic atrophy, cyclic exposure to E2 exerted a greater immunoenhancing influence than did tonic E2 exposure.