Effect of estradiol on endotoxin-induced changes in steroid hormone levels and lethality in male rats

We examined the effect of exogenous estradiol on the changes in serum steroid hormone levels induced by a nonlethal dose of Escherichia coli endotoxin in male rats and the deaths due to nonlethal and lethal doses of endotoxin. Injection of estradiol 5 min before a nonlethal dose of endotoxin changed the serum sex steroid hormone response of male rats to endotoxin. The serum estrogen concentrations of estradiol + endotoxin-treated rats decreased by 50% (P < 0.001), while those of the endotoxin-treated rats increased (2- to 5-fold). The serum androgen concentrations of estradiol + endotoxin-treated rats did not change significantly, while those of endotoxin-treated rats dropped to 30-40%, P < 0.001. Exogenous estradiol also appeared to influence the percentage of endotoxin-induced deaths in a dose-dependent manner. It reduced the number of deaths induced by nonlethal (2 mg/kg) dose of endotoxin but increased the number of deaths induced by a highly lethal dose (8 mg/kg). These results, together with the known relationships between estrogen and the immune response, suggest that estrogens affect the course of septic shock in a complex fashion and may have either protective or deleterious effect.

Secretogogue-induced gating of chloride channels in the secretory vesicles of parafollicular cells

Thyroid parafollicular (PF) cells are neural crest-derived endocrine cells that secrete serotonin and calcitonin. The secretory vesicles of PF cells acidify when secretion is induced by increased extracellular Ca2+ or TSH. We tested the hypothesis that acidification is regulated by secretogogue-gated Cl- channels in vesicular membranes. Cl- channel (p64) immunoreactivity was enriched in purified PF vesicles. X-Ray microanalysis showed a change in chlorine level in PF vesicles in response to secretogogue-stimulation of isolated cells. Secretogogue stimulation also altered the degree of p64 channel phosphorylation. Protein kinase and phosphatase inhibitors antagonized secretogogue-induced vesicle acidification and secretion; however, secretion could occur even when acidification was blocked. We conclude that acidification of PF vesicles is regulated by a gatable Cl- channel in vesicle membranes and that protein phosphorylation and dephosphorylation are involved in channel activation. Acidification of vesicles is not required for exocytosis.

Free fatty acid profiles in the non-obese diabetic (NOD) mouse: basal serum levels and effects of endocrine manipulation

The non-obese diabetic mouse (NOD) is one of the few available models of spontaneous autoimmune insulin-dependent diabetes mellitus (IDDM). The authors determined the free fatty acid (FFA) levels and the concentrations and relative percentages of the various classes of FFA before the onset of diabetes in both sexes at 2 and 4 months of age and in diabetic females. A circadian rhythm of FFA concentrations was found in prediabetic mice, with lower values in the evening. Moreover, there was a sex difference in FFA concentrations in the morning, with 2-month-old females having higher concentrations than males. Sex and age-related differences were also observed in the concentrations of the various classes of FFA, with higher polyunsaturated fatty acid concentrations in 2-month-old females and increases in di- and tri-unsaturated fatty acids concentrations in both sexes with age. Hormonal manipulation such as adrenalectomy and/or castration modulated total FFA and the concentrations of the various classes of FFA in 2-month-old mice. These FFA differences between males and females should be taken into account in the onset of type I diabetes.

Regulation of rat thyroxine-binding globulin and transthyretin: studies in thyroidectomized and hypophysectomized rats given tri-iodothyronine or/and growth hormone

We have investigated the role of the thyroid compared with the hypophysis in the regulation of the two saturable thyroid hormone carriers of rat serum, thyroxine-binding globulin (TBG) and transthyretin (TTR). We examined, at serum and hepatic mRNA level, the responses of TBG and TTR to thyroidectomy (Tx), hypophysectomy (Hx) and replacement treatments with tri-iodothyronine (T3) or/and GH, both hormones which are depleted when the thyroid or hypophysis are removed. The studies were performed on male rats at the age of 8 weeks, when the developmentally regulated TBG becomes undetectable after its transient postnatal rise, while the nondevelopmentally regulated TTR presents its normal, age-independent level of expression. Tx-induced TBG re-expression was completely reversed by T3 replacement and unresponsive to GH replacement. TTR in the serum, on the other hand, was not affected by Tx or T3 replacement, moderately reduced by Tx in terms of the amount of mRNA, and markedly reduced by GH replacement. GH treatment, moreover, inhibited the expression of TTR in euthyroid controls. Hx, like Tx, induced TBG re-expression, an effect efficiently antagonized by T3 replacement. However, TBG synthesis was higher in Hx than in Tx rats and less effectively antagonized by T3 replacement. Most unexpectedly, GH induced a dramatic further increase in TBG synthesis, and the TBG synthesized in the GH-replaced Hx rats was entirely resistant to down-regulation by T3 replacement. TTR was markedly decreased at both serum and hepatic levels by Hx, unaffected by T3 and further decreased by GH replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acids and cell signal transduction

Fatty acids released from membrane phospholipids by cellular phospholipases or available to the cell from the extracellular environment are important cell signalling molecules. Fatty acids can act as second messengers involved in the transduction of external signals because their concentrations are rapidly and transiently altered in response to the binding of specific agonists to plasma membrane receptors, and they substitute for the classical second messengers of the inositide phospholipid and the cyclic AMP signal transduction pathways. Fatty acids are also modulators because they act in a reversible manner at a precise intracellular location for a very short time to amplify, attenuate or deviate a signal. Fatty acids modify the activities of phospholipases, protein kinases, G-proteins, adenylate and guanylate cyclases as well as ion channels and other biochemical events involved in stimulus-response coupling mechanisms. The action of fatty acids on signal transduction pathways can be direct and/or indirect (by catabolic conversion of arachidonic acid to eicosanoids). However, a number of studies clearly show that fatty acids per se are messenger and modulator molecules mediating responses of the cell to extracellular signals.

Biological role of alpha-fetoprotein in the endocrinological field: data and hypotheses

alpha-Fetoprotein (AFP), depending on the surrounding conditions, exerts different functions by different mechanisms. (1) A regulatory effect on the concentration of the unbound form of its various ligands (e.g. fatty acids, estrogens, phytosteroids). Thus, numerous studies have demonstrated that fatty acids, particularly the polyunsaturated fatty acids, modulate positively or negatively many steps of the action of various steroids and many enzymes involved in the transduction of membrane-triggered signals. (2) Different conformations (holoforms) of AFP, depending on the nature and concentration of the ligand(s) bound, might influence the binding of the protein to specific receptor(s) and as a consequence its biological properties (internalization, action on the membrane signal transduction pathway). (3) Regardless of the mechanisms, proposed in points 1 and 2, the protein can exert effects associated with other signals such as growth factors. The nature of the associated growth factor(s) and AFP ligand(s) can orient cells towards multiplication or differentiation.

In vivo effect of free fatty acids on the specific binding of glucocorticosteroids to corticosteroid binding globulin and liver receptors in immature rats

Stimulating lipase activity with heparin (200 IU/kg b.w.) increased the plasma free fatty acid (FFA) concentration of immature rats (15 days). The effect of this elevated FFA concentration on glucocorticoid binding to corticosteroid binding globulin (CBG), and liver cytosol glucocorticoid receptor (GR), was analyzed. The plasma FFA concentration increased 2-fold, 10 minutes (P < 0.001), 20 minutes (P < 0.01), and 60 minutes (P < 0.01) post-heparin. The corticosterone (B) and progesterone concentrations were unchanged 60 minutes post-injection. The binding activity of immature rat CBG for B dropped 50% (P < 0.001) 60 minutes post-heparin injection, decreased B binding and increased plasma FFA were correlated (r = -0.8). The decreased B binding resulted from a 2-fold decrease in the apparent number of CBG binding sites; the affinity constant (Ka) remained unchanged. The liver cytosol endogenous FFA content of immature rats was also increased 2-fold, 60 minutes after heparin-induced lipolysis. The increased cytosol FFA, with no significant change in glucocorticoid, was accompanied by a significant decrease in dexamethasone binding to liver cytosol glucocorticoid receptor. The decrease resulted from a significantly lower apparent Ka for dexamethasone and fewer receptor binding sites (n). There was a good inverse correlation between Ka (r = -0.93) and n (r = -0.90) and the increased liver cytosol FFA content. Thus the higher plasma FFA induced in vivo by lipase activation or a standard FFA mixture probably causes conformational changes in CBG and GR, reducing glucocorticoid binding to immature rat CBG and liver GR.

Interaction of unsaturated fatty acids with rat liver glucocorticoid receptors: studies to localize the site of interaction

Polyunsaturated fatty acids have been shown to decrease the binding of [3H]dexamethasone to rat liver glucocorticoid receptors by mixed non-competitive inhibition, suggesting that these fatty acids interact at a site on the receptor different from the hormone binding site. The present study was undertaken to localize the site of interaction of polyunsaturated fatty acids on the receptor by comparing the differential effects of docosahexaenoic acid (a 22-carbon polyunsaturated fatty acid of the series n-3) on antagonist (RU486) and agonist binding, by covalent cross-linking of the hsp 90 and other proteins to the receptor to attempt to mask the site of interaction, by limited trypsinization to cleave the site and by using antibodies against specific epitopes to prevent fatty acid access by steric hindrance. Binding [3H]RU486 was not inhibited by docosahexaenoic acid at a concentration (60 mumol/l) that increases the dissociation constant of [3H]dexamethasone eightfold. Covalent stabilization of the hetero-oligomeric glucocorticoid receptor structure did not keep the fatty acid from inhibiting [3H]dexamethasone binding. The binding to the receptor of monoclonal and polyclonal antibodies against different domains of the receptor did not sterically hinder the fatty acid interaction with the receptor. After limited trypsinization of the receptor, the fatty acid still increased the dissociation rate constant of [3H]dexamethasone binding, indicating that the site of interaction of polyunsaturated fatty acids is on a fragment of the receptor containing the hormone-binding domain and some sequences C-terminal of the DNA-binding domain.

Perturbation of the immunosuppressive action of glucocorticoids in rat thymocytes by liposoluble extracts of serum from AIDS patients

Liposoluble extracts of serum from healthy men and AIDS patients (stages IVC1 and IVD by CDC criteria) inhibited the incorporation of [3H]thymidine into isolated rat thymocytes, but AIDS extracts were less inhibitory, requiring 1.8 times more cortisol in the AIDS extracts than in the healthy extracts to inhibit [3H]thymidine incorporation by 50%. Although the total serum extracts from AIDS patients contained 1.7 times more cortisol than the extracts from healthy controls, the AIDS extracts decreased the binding affinity (Ka) of [3H]dexamethasone to rat thymus glucocorticoid receptors by 50% less than the healthy control extracts. The present study seems to indicate that a substance(s) can be extracted from the serum of AIDS patients that attenuates the inhibitory effect of cortisol on thymocyte proliferation and interferes with the binding of cortisol to the glucocorticoid receptor.

Stimulation of the binding properties of adult rat corticosteroid-binding globulin by a lipolysis-induced rise in plasma free fatty acids

In vitro studies have shown that FFA induce conformational changes in human corticosteroid-binding globulin (CBG). We increased the plasma FFA concentrations of adult male rats by injecting heparin to determine whether such changes in CBG binding and immunological properties also occur in vivo. The in vivo transient activation of lipase by heparin produced a large increase in plasma FFA at 10 and 20 min (P < 0.01), which was maximal at 60 min (P < 0.005) and remained elevated at 120 min (P < 0.01) postinjection. This rise in FFA was associated with a 2- to 3-fold increase in the binding indices (C values; liters per g) of corticosterone (B) and progesterone to CBG 60-120 min postinjection (P < 0.001). There was a good positive correlation (r = 0.85) between the increase in B binding and the rise in plasma FFA in heparin-treated rats. The enhanced B binding to CBG resulted from a 2-fold increase in the apparent number of binding sites, without any significant change in the affinity constant (Ka). FFA extracted from postheparin plasma and a standard FFA mixture induced similar changes in B binding to purified mature rat CBG. The immunological behavior of CBG was not significantly changed after heparin-induced lipolysis, but the immunoreactivity of CBG from heparin-treated rats was more reduced by incubation with exogenous FFA than that from controls. FFA extracted from the plasma of heparin-treated rats and a standard FFA mixture both produced a dose-dependent drop in the immunodetection of pure CBG. These binding and immunological studies indicate that FFA mediate conformational changes in rat CBG in vivo. Thus, FFA, in addition to their roles as metabolic energy sources and components of complex lipids, can be rapid potent endogenous modulators of steroid-protein interactions.

Rapid and long-term effects of 17 beta-estradiol on PIP2-phospholipase C-specific activity of MCF-7 cells

Activity of the enzyme phosphatidylinositol 4,5-bisphosphate phospholipase C (PIP2-PLC) was demonstrated in MCF-7 human breast cancer cell homogenate. The addition of 10(-9) M 17 beta-estradiol to the culture medium elicited in the cells two types of responses depending on the period of exposure. Enzyme activity was rapidly activated at 15 s of incubation. After 5 min, PIP2-PLC activity was inhibited, and this effect continued at least until 24 h of exposure to the hormone. When 17 beta-estradiol was added in vitro to the total homogenate of untreated cells, enzyme activity was stimulated in a dose-dependent manner. These findings indicate that 17 beta-estradiol induces early and long-term modifications of the phosphoinositide signal pathway in intact MCF-7 cells as well as in vitro. The rapidity of the early effect suggests a non-genomic action of estradiol.

Free fatty acid-induced alterations in the steroid-binding properties of rat androgen-binding protein

The free fatty acid (FFA) concentration in the epididymal cytosol of the adult rat was found to be 20-fold higher than in the serum. The binding of [3H] dihydrotestosterone to epididymal rat androgen binding protein (rABP) was modified by physiological concentrations of saturated and unsaturated fatty acids. Polyunsaturated fatty acids inhibited the binding more efficiently than monounsaturated or saturated fatty acids. Scatchard analysis and Dixon plots indicated that the number of binding sites decreased in presence of unsaturated fatty acids with an inhibition constant (Ki) of 4 microM for arachidonic acid (C20:4) and 20 microM for oleic acid (C18:1). These results indicate that unsaturated fatty acids induce alterations in rABP steroid-binding properties that could modulate the endocrine function of rABP.

Re-expression of thyroxine-binding globulin in post-weaning rats during protein or energy malnutrition

Thyroxine-binding globulin, the highest affinity thyroid hormone binder of rat serum, was studied during 28 days of dietary protein restriction (6% protein vs 18% protein in isocaloric control diet) or energy restriction (60% intake of control diet). Studies were performed on male rats aged four weeks at the beginning of experiments: the animals had reached the ontogenic stage when the thyroxine-binding globulin had declined, after its high postnatal surge, to undetectable levels. Short-term administration (seven days) of one or the other restricted diet similarly induced resynthesis of the protein. Its serum concentrations reached 26-46% of those measured in eight-day pups (peak of the neonatal surge) and its liver mRNAs showed corresponding enhanced signals. Serum T4 binding activities were increased, although concomitantly transthyretin, second specific T4 carrier of the rat serum, decreased markedly (65-75% of controls) in response to the dietary restrictions. Longer-term diet administration (14 or 28 days) resulted in the further increase of the thyroxine-binding globulin in the protein-restricted rats, in contrast to its decline and eventual disappearance in the energy-restricted animals. Protein restriction was associated with increased total and free T3 serum concentrations, in contrast to energy restriction which little affected these parameters. These studies reveal rat thyroxine-binding globulin as a positive (increasing), highly sensitive reactant of malnutrition, able to discriminate between energy deficiency and composition dysequilibrium of diets. They suggest that up-regulation of its synthesis in the two dietary models involves differential mechanisms.

Serotonergic signalling between thyroid cells: protein kinase C and 5-HT2 receptors in the secretion and action of serotonin

Parafollicular (PF) cells of the thyroid gland are neural crest derivatives, which costore the neurotransmitter, 5-hydroxytryptamine (5-HT) with calcitonin. PF cells are located adjacent to follicular (F) cells within the basement membrane of thyroid follicles. It has been proposed that 5-HT serves an intercellular signalling function in the thyroid and that F cells are its target. This proposal was tested by using cell lines derived from PF (medullary thyroid carcinoma [MTC]) and F (FRTL-5) cells to study the mechanisms that mediate the secretion and action of 5-HT. Secretion of 5-HT by MTC cells was evoked by thyroid stimulating hormone, thyrotropin (TSH), elevated extracellular calcium (increases [Ca2+]e), or by agents that increase intracellular cAMP (increases [cAMP]i). When protein kinase C (PKC) was down-regulated by prolonged treatment of MTC cells with phorbol 12-myristate 13-acetate (PMA), or PKC was inhibited by staurosporin, the TSH- or PMA-evoked secretion of 5-HT was blocked; however, interference with PKC function did not affect 5-HT secretion evoked by increases [Ca2+]e or increases [cAMP]i. In the putative targets, FRTL-5 cells, 5-HT increased the turnover of phosphoinositides (PI), cytosolic calcium (increases [Ca2+]i), increases [cAMP]i, and biphasically modified the effect of TSH on cAMP. All of these 5-HT effects were inhibited by 5-HT2 receptor antagonists (spiperone and ketanserin) and by pertussis toxin (PTx), suggesting that the actions of 5-HT are mediated by 5-HT2 receptors, which are coupled to a G protein. This suggestion was supported by the following additional observations: FRTL-5 membranes bound the 5-HT2 agonist, [125I]2,5-dimethoxy-4-iodophenylisopropylamine ([125I]-DOI), and anti-idiotypic antibodies, which recognize 5-HT2 receptors. [125I]-DOI binding was inhibited by guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S) and the antibodies were displaced by spiperone. Data are consistent with the hypothesis that 5-HT serves as a PF to F cell messenger.

Modulation of glucocorticoid binding to rat liver cytosol receptor by lipid-soluble extracts from the serum of AIDS patients

The total liposoluble extract of sera from AIDS patients, IVC1 and IVD stages, containing cortisol and free fatty acids (FFA) inhibited [3H]dexamethasone binding to a lesser extent than did the same quantity of total liposoluble extract of sera from healthy men. FFA isolated from extracts of AIDS sera by Sephadex LH20 chromatography had less effect on [3H]dexamethasone binding to rat liver glucocorticoid receptor than those extracted from sera of healthy men. These results suggest the presence in sera of AIDS patients of a liposoluble substance which could be limiting the inhibitory effect of FFA on [3H]dexamethasone binding to glucocorticoid receptor by inducing a conformational change in glucocorticoid receptor that could alter the biological action of glucocorticoids. The pathological consequence could be the apparent contradiction of high cortisolemia and clinical symptoms of adrenal insufficiency that have been observed in AIDS patients.

Alterations in the concentrations and binding properties of sex steroid binding protein and corticosteroid-binding globulin in HIV+patients

The abnormal concentrations of steroid hormones and free fatty acids in the plasma of HIV-infected subjects are associated with qualitative and quantitative alterations in two of the major steroid hormones carrier proteins, sex steroid-binding protein (SBP) and corticosteroid-binding globulin (CBG). The properties of SBP and CBG in the sera of two age-matched groups of 67 men healthy blood donors (controls) and 64 HIV+subjects: 11 CDC group II and III (ASY), 6 CDC group IVA and 47 groups IV C1+D (AIDS) were analyzed. The HIV+patients had SBP concentrations 39-51% above those of controls. The sera of AIDS patients had higher SBP association constants (Ka) for testosterone than did those of the II, III and IVA groups and controls. In contrast, the CBG concentrations in all the HIV+subjects were similar to those of the controls. However, the binding properties of HIV+CBG were abnormal: the Ka's for cortisol and 17 alpha hydroxyprogesterone binding were 50% below normal, while the number of binding sites was significantly higher. Such changes in these carrier proteins could result from conformational transitions; they may cause abnormal transfer of hormonal information and/or steroid hormones metabolism, thus modifying the impact of steroids on the immune response in HIV+subjects.

Structural and functional microheterogeneity of rat thyroxine-binding globulin during ontogenesis

Thyroxine-binding globulin (TBG), the major carrier of thyroid hormones in human and murine sera, is in the rat a developmentally regulated protein, showing a large surge during post-natal growth followed by virtual disappearance in adults. Here we study as a function of age, from the 19-day embryo to 60 days after birth, the structural and binding characteristics of rat TBG microheterogeneity. Serum obtained throughout development, when pre-incubated with 125I-thyroxine (T4), was shown by isoelectric focusing (IEF; pH range 4-5) to contain six labelled isoforms of TBG, with isoelectric points between 4.25 and 4.55. These isoforms differ in their sialic acid content. The relative labelling densities of the isoforms show age-related changes: in neonates, the bulk of T4 is bound to the most alkaline (least sialylated) TBG isoforms; then, with advancing age, it shifts to the most acidic isoforms. To understand whether this progressive transfer of ligand reflects developmental changes in the relative abundance of isoforms, we submitted sera from rats of different ages to crossed immunoelectrofocusing analysis. We demonstrate that the relative proportions of the TBG isoforms remain fairly constant, independent of the level of total TBG. The most acidic forms always represented the majority (approximately 50%), with the most alkaline ones only representing 15% of total TBG. Experiments based on IEF of charcoal-treated sera, supplemented or not with lipidic serum extracts, further demonstrate that the paradoxical low labelling seen in the neonates for the most abundant highly sialylated isoforms is due to inhibition of their binding abilities by liposoluble components, which are particularly concentrated in the sera at the earlier post-natal ages. These studies represent the first analysis of concentration versus binding functions of rat TBG isoforms in the physiological conditions of normal ontogeny. Our results point to an important influence for the serum environment on the binding properties of TBG isoforms. The physiological significance of such interactions remains to be clarified.

In vivo transient rise in plasma free fatty acids alters the functional properties of alpha-fetoprotein

Previous in vitro studies have shown that unsaturated fatty acids (UFA) induce conformational changes in rodent and human alpha-fetoprotein (AFP). To determine whether such changes in the binding and immunological properties of rat AFP also occur in vivo, plasma free fatty acid (FFA) concentrations were increased in young male rats (15, 21 and 28 days old) by acute i.v. injection of heparin (200 IU/kg). Plasma estrogens (estrone and estradiol) did not change after injection of heparin. There was a large increase in plasma FFA 10-20 min post-heparin injection, with a return to normal 60 min later. This transient rise in FFA plasma was associated with a 50% drop (P less than 0.001) in the binding of estradiol to rat AFP of 15-, 21- and 28-day-old rats by reducing the number of binding sites (P less than 0.001), leaving the affinity constant (Ka) unchanged. FFA extracts from post-heparin plasma induced similar changes in estradiol binding to purified rat AFP. The rise in plasma FFA induced a loss of AFP immunoreactivity, in 21- (P less than 0.001) and 28-day-old rats (P less than 0.001), but not in 15-day-old rats. This age-dependent response correlated with the FFA/AFP molar ratio (38 in 15-day-old rats, 388 in 21-day-old rats, and 5600 in 28-day-old rats). These results indicate that an in vivo rise in FFA induces rapid and reversible conformational changes in AFP which may modulate the endocrine and immune function of this oncofetal protein.

Relationship between changes in serum estrone levels and outcome in human males with septic shock

The effect of septic shock on the production of estrogens, other steroid hormones, and gonadotropins in men was investigated. Two groups of male patients in the early septic shock were studied over 3 days following their admission to the Intensive Care Unit. Group I (n = 9) patients recovered and group II (n = 6) patients died. The simplified acute physiological score was 13.5 +/- 1.5 for group I and 21.2 +/- 2.3 for group II (P less than .05). In group I patients, estrogen levels (particularly E1) were high on day 1 and decreased progressively (day 1: 3,515 +/- 884 pmol/L, day 2: 2,450 +/- 292 pmol/L, and day 3: 1,043 +/- 255 pmol/L). In group II patients, estrone levels were as high as in group I on day 1, but increased throughout the 3 days (day 1: 3,250 +/- 1,200 pmol/L, day 2: 4,495 +/- 930 pmol/L, and day 3: 6,123 +/- 966 pmol/L). There were few changes in gonadotropins and other steroid hormones, except that the testosterone levels were below normal in both patient groups, while cortisol was elevated in group II. The changes in serum E1 may provide an accurate marker of individual outcome.

Glucocorticoids in the nonobese diabetic (NOD) mouse: basal serum levels, effect of endocrine manipulation and immobilization stress

The NOD mouse is a recognized model for studying immunologically mediated insulin-dependent diabetes mellitus (IDDM). In most colonies, the disease appears with a greater preponderance in females than in males and castration alters the expression of the disease. The prevalence of diabetes may also vary depending upon environmental factors such as stress. Therefore, we measured in the NOD mouse serum glucocorticoid concentrations in basal and stress conditions. We observed in NOD as well as in C57BL/6 mice, taken as controls, a circadian rhythm of corticosterone, with females having higher values than males. After a single restraint stress, female and male NOD mice exhibit a comparable response, whereas after repeated stress, males respond significantly less than females, suggesting an adaptation phenomenon. In contrast, there is no difference in the pattern of corticosterone response of C57BL/6 females and males to both types of stress, but females always respond better than males. Moreover, whatever the stress considered, NOD mice generally exhibit a higher corticosterone response than C57BL/6 mice. The sexual dimorphism in diabetes expression in NOD mice may be related to the levels of corticosterone, a hyperglycemic hormone, in both basal and stress conditions. However, the understanding of corticosteroid effects in this model of type I IDDM is rather complex given their well known anti-inflammatory and immunosuppressive effects in other models of autoimmune diseases.

Effect of the aromatase inhibitor, 4 hydroxyandrostenedione, on the endotoxin-induced changes in steroid hormones in male rats

The increase in circulating estrogen concentrations that follows injection of Escherichia coli endotoxin (Endo) may be due to increased aromatase activity. We have therefore analysed the effect of the aromatase inhibitor, 4 hydroxyandrostenedione (4OHA) on the steroid hormone response of male rats, particularly the dramatic increase in estrogens and decrease in androgens, induced by Endo. The concentrations of corticosterone (B), progesterone (P4), 17 alpha hydroxyprogesterone (17 alpha OHP4), androstenedione (delta 4), testosterone (T), estrone (E1) and estradiol (E2) were determined 2 hours after injection of increasing doses of 4OHA with and without Endo. The increase in serum estrogen concentrations and drop in serum androgen levels in response to Endo were blocked by a single dose of 4OHA. The effect of 4OHA appeared to be dose dependent. Low doses (30 mg/kg and 50 mg/kg) induced significant changes in the estrogen and androgen responses, but the high dose (100 mg/kg) blocked all changes in sex steroids induced by Endo. 4OHA did not alter the Endo-induced changes in other steroids.

Phytoestrogens: new ligands for rat and human alpha-fetoprotein

The binding of the lignans, enterolactone, enterodiol, nordihydroguaiaretic acid (NDGA), and the isoflavonic phytoestrogen equol, to human and rat alpha-fetoprotein (AFP) was studied. They had differential inhibitory effects (NDGA greater than equol greater than enterolactone greater than enterodiol) on the binding of estrone and estradiol to rat AFP and the binding of unsaturated fatty acid to both rat and human AFP. Inhibition was dose-dependent. The apparent dissociation constants (Kd) for phytoestrogens binding to AFP were: Kd NDGA = 5 +/- 1.2.10(-7) M, Kd equol = 6.7 +/- 0.8.10(-6) M, Kd enterolactone = 1.7 +/- 0.4.10(-5) M and Kd enterodiol = 2.2 +/- 0.6.10(-5) M. The Kd for estrone binding to rat AFP was increased by increasing concentrations of equol, but the number of esterone binding sites remained unchanged. This, plus the results of double-reciprocal plots, suggests that they compete for the same site(s). NDGA also competitively inhibited estrone binding at low NDGA concentrations (increased Kd), but high concentrations induced conformational changes in rat AFP, as both Kd and the number of binding sites (n) were altered. Both rat and human AFPs underwent changes in electrophoretic behaviour and loss of immunoreactivity with increasing NDGA, suggesting that NDGA binding induces conformational changes in the AFPs. However, equol did not alter the electrophoretic or immunological properties of either rat or human AFP, providing further evidence for qualitative differences in the effects of these diphenols. These findings indicate that phytoestrogens could play a role in AFP-dependent normal and pathological growth and development.