Uptake, distribution and binding of vertebrate and invertebrate steroid hormones and time-dependence of ponasterone A binding in Calliphora vicina. Comparisons among cholesterol, corticosterone, cortisol, dexamethasone, 5 alpha-dihydrotestosterone, 1,25-dihydroxyvitamin D3, ecdysone, estradiol-17 beta, ponasterone A, progesterone, and testosterone

Immune-Neuroendocrine Interactions: Evolution, Ecology, and Susceptibility to Illness

The integration between immune and neuroendocrine systems is crucial for maintaining homeostasis from invertebrates to humans. In the first, the phagocytic cell, i.e., the immunocyte, is the main actor, while in the latter, the principle player is the lymphocyte. Immunocytes are characterized by the presence of pro-opiomelanocortin (POMC) peptides, CRH, and other molecules that display a significant similarity to their mammalian counterparts regarding their functions, as both are mainly involved in fundamental functions such as immune (chemotaxis, phagocytosis, cytotoxicity, etc.) and neuroendocrine (stress) responses. Furthermore, the immune-neuroendocrine system provides vital answers to ecological and immunological demands in terms of economy and efficiency. Finally, susceptibility to disease emerges as the result of a continuous dynamic interaction between the world within and the world outside. New fields such as ecological immunology study the susceptibility to pathogens in an evolutionary perspective while the field of neuro-endocrine-immunology studies the susceptibility from a more immediate perspective.

Estradiol-stimulated nitric oxide release in nervous tissue, vasculature, and gonads of the giant cockroach Blaberus craniifer

The vertebrate system of steroid hormones appears to have been conserved widely throughout the animal kingdom. The sex hormone estrogen, 17-beta-estradiol (E2), long considered to be exclusively a vertebrate hormone, is found also in invertebrates related to reproductive and developmental processes such as spawning, vitellogenesis and molting. These processes are affected by estrogen induced changes at the genomic level and take place at a large time scale. The discovery of surface membrane receptors for E2 has opened new possibilities for the involvement of estrogen in biological functions other than reproductive. These processes take place within a few seconds to minutes and involve sudden cytosolic calcium transients, activation of adenylate cyclase or activation of phospholipase C (PLC). E2 can modulate the production of nitric oxide (NO) in endotheliar and other cells. A similar mechanism linking estrogen to cNOS catalized nitric oxide (NO) release is reported herein for the first time in several tissues of the giant cockroach Blaberus craniifer. This process has been identified in the brain, nerve cord, vasculature and ovaries. This effect is concentration dependent and is inhibited by tamoxifen an estrogen receptor blocker.

The presence of estradiol-17beta and its specific binding sites in posterior silk gland of Bombyx mori

Although estradiol-17beta (E2) is known to be a vertebrate sex steroid, its presence in insects, particularly in Bombyx mori, has recently created considerable sensation regarding its significance in insect life. The specificity of estradiol action on the posterior silk gland (PSG) of B. mori has been previously assessed by the use of ICI-182780 as a specific receptor antagonist for estradiol. The present study provides evidence for systematic changes in the titer of estradiol-17beta in B. mori and its specific binding sites in the posterior silk gland according to the physiological age of fifth instar larvae. The changes in the estradiol level in the PSG after E2 treatment have also been determined to assess whether the administered estradiol has been taken up by the silk gland cells and whether the effect of exogenously administered E2 on the PSG is direct. The correlation in the profile of E2 binding sites with the endogenous estradiol level of PSG on different days of fifth instar larvae suggests that the level of binding sites in the PSG is regulated by the estradiol titer and that E2 may have some biological function in B. mori. Scatchard analysis of E2 binding sites in the PSG on 9th day of fifth instar larvae reveals that it consists of only one type of binding component. The dissociation constant (Kd) and maximum binding capacity (Bmax) of this putative E2 receptor have been found to be 8.98 +/- 0.744 nM and 55.8 +/- 5.53 fmol/mg cytosolic protein, respectively. The study thus indicates an involvement of the putative receptor in E2-mediated action on the silk gland of B. mori and paves a pathway for further evaluation of the physiological relevance of the presence of vertebrate steroids in insects.

Interaction of PAHs and PCBs with ecdysone-dependent gene expression and cell proliferation

This study was done to determine whether PAHs and PCBs can interact with the arthropod steroid hormone system. Ecdysteroid molting hormones control growth, molting, and reproduction in arthropods. A spike in 20-OH ecdysone (20 HE) triggers the molt cycle in crustaceans, and earlier studies have shown that PAHs can affect this molt cycle in several crab species. However, the mechanism of this molt cycle interaction is unknown. Both PAHs and PCBs interact with other nuclear receptors; however, nothing is known about their ability to interact with the invertebrate ecdysone receptor (EcR). Four PAHs, benzo[a]pyrene, benzo[b]fluoranthene, pyrene, and chrysene, and the commercial PCB mixture, Aroclor 1254, were used to determine the ability of these classes of compounds to induce ecdysone-dependent reporter gene expression and to modify the proliferation and differentiation response of the ecdysteroid-responsive Cl.8+ cell line. The four PAHs were each able to enhance the ecdysteroid response in both the reporter gene and the cell proliferation assays only when given in conjunction with ecdysteroids. Aroclor 1254 had no effect in either system, either alone or in conjunction with ecdysteroids. These studies show that although the PAHs alone do not activate ecdysteroid-dependent gene expression or cell differentiation, they are able to enhance the effect of ecdysteroids, presumably through a non-receptor-mediated process. This mechanism may explain the effects on molting which have been reported after low-level crude oil exposures in crustaceans.

Presence of immunoreactive corticotropin-releasing hormone and cortisol molecules in invertebrate haemocytes and lower and higher vertebrate thymus

Corticotropin-releasing hormone- and cortisol-like molecules are present in the haemocytes of different molluscan species and in the epithelial cells, interdigitating cells and macrophages - but not in the lymphocytes - of fish, frog, chicken and rat thymus. Taking into account the fact that other pro-opiomelanocortin-derived peptides, such as adrenocorticotropin hormone, are present in the haemocytes and thymus of the same species, these results complete the list of stress mediators present in molluscan haemocytes and further support the hypothesis that, although the prototype stress response we have demonstrated in invertebrates is concentrated in a single cell, i.e. the haemocyte, it is similar to the response seen in vertebrates. Moreover, the data presented here are compatible with the hypothesis that an evolutionary, conserved stress response can occur locally with a single organ, e.g. the thymus, in which all the main mediators of this biological response, such as corticotropin-releasing hormone, adrenocorticotropin hormone and glucocorticoids, are present. The implications of these findings for the physiology of thymus and stress response may be far reaching.

Progesterone in Periplaneta americana and Neobellieria bullata adults from the procuticle phase until first progeny production

A significant amount of progesterone-like immunoreactive material (150 ng/g) was measured by EIA in the procuticle phase of adult of both sexes of Periplaneta americana. This peak markedly decreased to 1-10 ng/g during sclerotization and was unlikely to be of dietary origin. In the case of 0-hr-old P. americana adults 96-98% of progesterone-like material was localized in the digestive tract and Malpighian tubules. In contrast, a relatively low level of progesterone-like immunoreactive material was measured in 0-hr-old Neobellieria bullata adults. Activity of 3beta-HSD/isomerase converting pregnenolone to progesterone was high (22-43 fmol/mg protein/20 min) in 0-hr-old P. americana adults and significantly fell during sclerotization. High progesterone levels (13-16 ng/g), measured by HPLC-RIA, coexist with high levels of 3beta-HSD/isomerase activity. Orally active human contraceptives (ethisterone, ethynodiol, ethynodiol diacetate, lynestrenol, mestranol, norgestrel, norethynodrel, tamoxifen citrate, and mifepristone) which act on mammalian steroid receptors had no significant effects on progeny production in either polytrophic or meroistic insect ovaries even at concentration of 5000 mg/kg.

Ecdysteroid binding sites in gastrolith forming tissue and stomach during the molting cycle of crayfish Procambarus clarkii

The distribution of ecdysteroid binding sites in the stomach and gastrolith disc tissue of crayfish (Procambarus clarkii) was examined in relation to the molting stage by thaw-mount autoradiography. The radiolabeled hormone analogue ponasterone A (25-deoxy-20-hydroxyecdysone) was used. Ecdysteroid binding sites were demonstrated only in certain molting stages, the small gastrolith period and the aftermolt stage. In gastrolith epithelium, ponasterone A binding sites first appeared in the cytoplasm, and then in the nuclei and cytoplasm. In the stomach epithelium, many nuclear binding sites were detectable during the period of gastrolith secretion. These periodical changes in specific ponasterone A binding when correlated with the molting stages clearly show that ecdysteroids may function as an initiator for gastrolith formation and reabsorption. The findings also suggest that ecdysteroids control calcium transport in the stomach epithelium. The time-related and functional differences of cytoplasmic and nuclear concentration of ecdysteroid receptors indicate the presence of cytoplasmic and nuclear receptors associated with specific actions.