The involvement of the stimulatory G protein in sexual dimorphism of beta-adrenergic receptor-mediated functions in rat liver

17beta-estradiol enhances vascular endothelial growth factor production and dihydrotestosterone antagonizes the enhancement via the regulation of adenylate cyclase in differentiated THP-1 cells

We studied the in vitro effects of sex hormones on vascular endothelial growth factor (VEGF) production in differentiated THP-1 monocytic cells. Phorbol-12-myristate-13-acetate differentiated THP-1 into macrophage-like cells. 17beta-estradiol (10 (-9) M) increased VEGF secretion of controls 3.1-fold in differentiated THP-1 and this effect of 17beta-estradiol was antagonized by dihydrotestosterone, although dihydrotestosterone alone did not alter VEGF secretion. 17beta-estradiol increased steady-state mRNA level of VEGF and the increase was counteracted by dihydrotestosterone in differentiated THP-1, although dihydrotestosterone alone did not alter the VEGF mRNA level. Progesterone did not affect the constitutive and 17beta-estradiol-induced VEGF secretion and mRNA level. Transient transfection revealed that 17beta-estradiol enhanced chloramphenicol acetyl transferase expression driven by VEGF promoter and the enhancement was antagonized by dihydrotestosterone. Adenylate cyclase inhibitor suppressed 17beta-estradiol-induced enhancement of VEGF secretion, mRNA level, and promoter activity, whereas dihydrotestosterone-induced suppression on the effects of 17beta-estradiol was counteracted by 3',5'-adenosine cyclic monophosphate (cAMP) analog. 17beta-estradiol increased intracellular cAMP level by activating adenylate cyclase, while dihydrotestosterone reduced the basal and 17beta-estradiol-increased cAMP level by inhibiting adenylate cyclase. Transfection with 5'-deleted VEGF promoters demonstrated that the region between -88 and -66 bp may be involved in the transcriptional regulation by each hormone. The mutation within activator protein-2 element in this region abrogated the transcriptional stimulation and repression by the respective hormones. 17beta-estradiol activated transcription from activator protein-2-responsive reporter plasmid while dihydrotestosterone antagonized the effect of 17beta-estradiol. These results suggest that 17beta-estradiol enhances VEGF production while dihydrotestosterone antagonizes the effect of 17beta-estradiol via up- or downregulation of adenylate cyclase in differentiated THP-1.

Sex hormones regulate the contribution of PKCepsilon and PKA signalling in inflammatory pain in the rat

We have evaluated the contribution of differences in second messenger signalling to sex differences in inflammatory pain and its control by sex hormones. In normal male but not female rats, epinephrine-induced mechanical hyperalgesia was antagonized by inhibitors of protein kinase Cepsilon (PKCepsilon), protein kinase A (PKA) and nitric oxide synthetase (NOS). Similarly, in PKCepsilon knockout mice, a contribution of PKCepsilon to epinephrine-dependent mechanical hyperalgesia occurred in males only. In contrast, hyperalgesia induced by prostaglandin E2, in both females and males, was dependent on PKA and NO. In both sexes, inhibitors of mitogen-activated protein kinase/extracellular-signal related kinase kinase (MEK) inhibited epinephrine hyperalgesia. In gonadectomized females, the second messenger contributions to epinephrine hyperalgesia demonstrated the pattern seen in males. Administration of oestrogen to gonadectomized females fully reconstituted the phenotype of the normal female. These data demonstrate gender differences in PKCepsilon, PKA and NO signalling in epinephrine-induced hyperalgesia which are oestrogen dependent and appear to be exerted at the level of the beta-adrenergic receptor or the G-protein to which it is coupled.

Gonadotropin-releasing hormone and G proteins: potential roles in autoimmunity

The hypothalamic homone gonadotropin-releasing hormone (GnRH) displays gender-specific actions. Pituitary responsiveness to GnRH is generally increased by estrogens and decreased by androgens. GnRH is now known to be produced by the immune system and to exert potent immunologic actions. Our central hypothesis is that gender differences in responsiveness to GnRH in the immune system play a pivotal role in the gender differences in immunity and autoimmunity. Studies in lupus-prone mice demonstrate that GnRH exacerbates murine lupus in a gender-specific fashion. Subsequent studies from our laboratory suggest that the gender differences in immunologic responsiveness to GnRH may relate to differences in the expression of the signal transducers through which GnRH acts, namely, the G proteins, Gs, and Gq/11. We have further demonstrated gender differences in second messengers for GnRH, IP3, and cAMF in immune cells. We have also demonstrated that GnRH agonist increases the quantities and/or activity of G proteins in immune cells in a gender-specific fashion. We speculate that gender differences in GnRH production and action, and in G protein expression play a role in a variety of autoimmune diseases that affect females predominantly.

Roles of prolactin and gonadotropin-releasing hormone in rheumatic diseases

PRL is capable of influencing immune responses and is a cytokine in all likelihood. Circulating PRL is elevated in a number of autoimmune diseases, and about 20% of SLE patients are hyperprolactinemic. The serum PRL concentration often does not reflect disease activity in SLE. The PRL-suppressing drug bromocriptine has been reported to benefit small numbers of patients with reactive arthritis and inflammatory eye disease, and bromocriptine may be beneficial in treating SLE. In NZB/NZW mice, bromocriptine was beneficial and prolonged life. Bromocriptine therapy favorably modified disease in human SLE. In a preliminary open-label study, SLE patients treated with bromocriptine for 6 months had significant improvement in disease activity. These responses were corroborated by masted therapeutic studies. Daily treatment with low-dose bromocriptine prevented lupus flares, and bromocriptine was as effective as hydroxychloroquine in treating active nonorgan-threatening disease. The reports of the efficacy of bromocriptine treatment of SLE are encouraging. Additional studies may confirm the findings reported in this review and may lead to further use of hormonal modification to treat lupus and other autoimmune diseases. For the present, it is important to understand that treatment with dopamine agonists such as bromocriptine is experimental and best confined to therapeutic trials. In the experience of the authors, bromocriptine should not be relied on to treat severe life-threatening autoimmune disease. If bromocriptine is used to treat SLE and is then discontinued, the patient should be observed carefully for rebound hyperprolactinemia and the development of a lupus flare. GnRH is produced by lymphocytes and exerts immunomodulatory actions. Thus, GnRH resembles a cytokine. GnRH can be shown to exert gender-restricted immune actions in vitro and in vivo. The authors' preliminary observations are consistent with the possibility that gender-related differences in expression of the GnRH receptor or in GnRH signal transducers may contribute to gender-related differences in immune responsiveness to GnRH. These differences in G proteins may contribute to the gender-related differences in immunity and expression of autoimmune disease.

Effects of cafeteria diet feeding on beta3-adrenoceptor expression and lipolytic activity in white adipose tissue of male and female rats

OBJECTIVE

To investigate the effects of short term (15 days) cafeteria diet feeding on the expression of beta3-AR in vivo and its association with lipolytic stimulation induced by beta3-AR agonist CGP12177A in isolated white adipocytes.

ANIMALS

Six female and 6 male Wistar rats (at 4 weeks of age) were fed on a cafeteria diet plus standard diet for 15 days. The remaining 12 age- and sex-matched rats always received standard diet only.

MEASUREMENTS

White gonadal adipose tissue was isolated and used for the determination of beta3-AR and leptin expression, and for in vitro studies of lipolytic activity.

RESULTS

Control male rats had higher levels of both beta3-AR and leptin mRNA in white adipose tissue than their female counterparts. Both male and female rats up-regulated the levels of both beta3-AR and leptin mRNA in response to 15 day cafeteria diet feeding. Noradrenaline- and isoprenaline-induced lipolysis were significantly increased in fat cells from control females compared to their male counterparts. CGP12177A stimulation resulted in significantly higher glycerol release in fat cells from cafeteria diet-fed female rats, whereas there were no differences due to dietary treatment in male rats. The maximal lipolytic response of forskolin (stimulating adenylyl cyclase) and dibutyryl cyclic AMP (cyclic AMP analogous) was not affected by sex or cafeteria diet feeding.

CONCLUSION

Cafeteria diet feeding brings about higher excess body weight and impaired adipose tissue lipolytic activity in female rats compared to male rats. Thus, the higher levels of beta3-AR mRNA induced by cafeteria feeding are not indicative per se of an increase of the lipolytic response of the adipocytes. The changes seen in other adrenoceptor subtypes (beta1 and beta2) may be more determinant of the overall lipolytic response of adipocytes.