Acute effects of thyroid hormones on the production of adrenal cAMP and corticosterone in male rats

Sex Differences in Adrenal Bmal1 Deletion-Induced Augmentation of Glucocorticoid Responses to Stress and ACTH in Mice

The circadian glucocorticoid (GC) rhythm is dependent on a molecular clock in the suprachiasmatic nucleus (SCN) and an adrenal clock that is synchronized by the SCN. To determine whether the adrenal clock modulates GC responses to stress, experiments used female and male Cyp11A1Cre/+::Bmal1Fl/Fl knockout [side-chain cleavage (SCC)-KO] mice, in which the core clock gene, Bmal1, is deleted in all steroidogenic tissues, including the adrenal cortex. Following restraint stress, female and male SCC-KO mice demonstrate augmented plasma corticosterone but not plasma ACTH. In contrast, following submaximal scruff stress, plasma corticosterone was elevated only in female SCC-KO mice. Adrenal sensitivity to ACTH was measured in vitro using acutely dispersed adrenocortical cells. Maximal corticosterone responses to ACTH were elevated in cells from female KO mice without affecting the EC50 response. Neither the maximum nor the EC50 response to ACTH was affected in male cells, indicating that female SCC-KO mice show a stronger adrenal phenotype. Parallel experiments were conducted using female Cyp11B2 (Aldosterone Synthase)Cre/+::Bmal1Fl/Fl mice and adrenal cortex-specific Bmal1-null (Ad-KO) mice. Plasma corticosterone was increased in Ad-KO mice following restraint or scruff stress, and in vitro responses to ACTH were elevated in adrenal cells from Ad-KO mice, replicating data from female SCC-KO mice. Gene analysis showed increased expression of adrenal genes in female SCC-KO mice involved in cell cycle control, cell adhesion-extracellular matrix interaction, and ligand receptor activity that could promote steroid production. These observations underscore a role for adrenal Bmal1 as an attenuator of steroid secretion that is most prominent in female mice.

An inhibitor of 11-β hydroxysteroid dehydrogenase type 1 (PF915275) alleviates nonylphenol-induced hyperadrenalism and adiposity in rat and human cells

Background

Nonylphenol (NP) is an environmental endocrine-disrupting chemical (EDC) detected in human cord blood and milk. NP exposure in developmental periods results in hyperadrenalism and increasing 11β-hydroxysteroid dehydrogenase I (11β-HSD1) activity in an adult rat model. Alleviating 11β-HSD1 activity is therefore a logical and common way to treat hyperadrenalism. PF915275 (PF; 4′-cyano-biphenyl-4-sulfonic acid (6-amino-pyridin-2-yl)-amide) is a selective inhibitor for 11β-HSD1. This study aimed to determine whether PF915275 could alleviate the hyperadrenalism induced by NP. In addition to a rat model, the effects of NP and PF915275 were measured in human preadipocytes.

Methods

For the in vivo rat model, female adult rats exposed to NP during the developmental period were divided into two treatment groups, with one receiving oral DMSO solution and the other receiving PF915275 once per day for 4 weeks. After the final treatment, the rats from each group were sacrificed for analysis. For the in vitro human model, human preadipocytes received 2 regimens of NP treatment. One treatment regimen occurred before differentiation (to mimic the sensitive developmental period; P exposure), and the other included continuous exposure from preadipocytes to fully differentiated adipocytes (to mimic the growing and adult periods, respectively; C exposure). Protein and RNA were extracted from rat tissues and the preadipocytes for western blot and real-time PCR analysis.

Results

In the rat model, PF915275 alleviated NP-induced effects by interfering with adipogenesis pathways, including enhancing PPARα expression, decreasing PPARγ expression, and reducing both 11β-HSD1 protein and mRNA expression levels. Additionally, PF915275 reduced the effects of the adrenal corticoid synthesis pathway by reducing StAR expression and 11β-hydroxylase and aldosterone synthase activities. With short-term exposure, NP enhanced PPARγ and FASN mRNA expression levels and reduced PPARα expression, whereas PF915275 alleviated these effects. With C exposure, the NP-induced accumulation of intracellular lipids was reduced by PF915275 treatment, which was mediated by decreased PPARγ mRNA and protein expression levels and increased PPARα protein expression.

Conclusions

The effects of NP and PF915275 treatment in both rat and human cell models are similar. Rats may be an appropriate model to study the effects of NP in humans, especially during the developmental period.

A Novel Population of Inner Cortical Cells in the Adrenal Gland That Displays Sexually Dimorphic Expression of Thyroid Hormone Receptor-β1

The development of the adrenal cortex involves the formation and then subsequent regression of immature or fetal inner cell layers as the mature steroidogenic outer layers expand. However, controls over this remodeling, especially in the immature inner layer, are incompletely understood. Here we identify an inner cortical cell population that expresses thyroid hormone receptor-β1 (TRβ1), one of two receptor isoforms encoded by the Thrb gene. Using mice with a Thrb(b1) reporter allele that expresses lacZ instead of TRβ1, β-galactosidase was detected in the inner cortex from early stages. Expression peaked at juvenile ages in an inner zone that included cells expressing 20-α-hydroxysteroid dehydrogenase, a marker of the transient, so-called X-zone in mice. The β-galactosidase-positive zone displayed sexually dimorphic regression in males after approximately 4 weeks of age but persisted in females into adulthood in either nulliparous or parous states. T3 treatment promoted hypertrophy of inner cortical cells, induced some markers of mature cortical cells, and, in males, delayed the regression of the TRβ1-positive zone, suggesting that TRβ1 could partly divert the differentiation fate and counteract male-specific regression of inner zone cells. TRβ1-deficient mice were resistant to these actions of T3, supporting a functional role for TRβ1 in the inner cortex.

Effect of swimming on the production of aldosterone in rats

It has been demonstrated that exercise is one of the stresses known to increase the aldosterone secretion. Both potassium and angiotensin II (Ang II) levels are shown to be correlated with aldosterone production during exercise, but the mechanism is still unclear. In an in vivo study, male rats were catheterized via right jugular vein (RJV), and divided into four groups namely water immersion, swimming, lactate infusion (13 mg/kg/min) and pyruvate infusion (13 mg/kg/min) groups. Each group was treated for 10 min. Blood samples were collected at 0, 10, 15, 30, 60 and 120 min from RJV after administration. In an in vitro study, rat zona glomerulosa (ZG) cells were challenged by lactate (1–10 mM) in the presence or absence of Ang II (10⁻⁸ M) for 60 min. The levels of aldosterone in plasma and medium were measured by radioimmunoassay. Cell lysates were analyzed by immunoblotting assay. After exercise and lactate infusion, plasma levels of aldosterone and lactate were significantly higher than those in the control group. Swimming for 10 min significantly increased the plasma Ang II levels in male rats. Administration of lactate plus Ang II significantly increased aldosterone production and enhanced protein expression of steroidogenic acute regulatory protein (StAR) in ZG cells. These results demonstrated that acute exercise led to the increase of both aldosterone and Ang II secretion, which is associated with lactate action on ZG cells and might be dependent on the activity of renin-angiotensin system.

Effects of thyroid status on arginine vasotocin receptor VT2R expression and adrenal function in osmotically stimulated domestic fowl

The role of thyroid hormones in the regulation of adrenal function during stress has been documented in mammals, but only limited reports are available in avian species. The present study was undertaken to analyze the effect of hyper- or hypothyroidism on the adrenal activity under control (hydrated) and osmotically stressed (water deprived, WD) conditions, with special emphasis on the expression of arginine vasotocin receptor VT2 (VT2R) in pituitary corticotrophs. Chickens were made hyper- or hypothyroidic by injecting thyroxine (T4) and 2-thiouracil (TU), respectively for 14 days. After 10 days of injections, one sub-group of both, T4- or TU-treated chickens were subjected to osmotic stress by water deprivation. Hyperthyroidism stimulated adrenal steroidogenic activity compared to euthyroid control birds, but no change was observed in the expression of VT2R. On the other hand, TU-induced hypothyroidism however showed no effect on adrenal gland, but a significant increase in the expression of VT2R was observed. Neither hyper- nor hypothyroidism altered pro-opiomelanocortin (POMC) mRNA levels. Following osmotic stress, no effect was observed either on the adrenal gland or on the VT2R expression in hyperthyroidic birds, but in hypothyroidic birds, osmotic stress stimulated adrenal steroidogenic activity and decreased VT2R expression in comparison to its respective controls (T4 or TU). Expression of POMC mRNA was again unaltered following osmotic stress. Although exact mechanism is not clear, the data indicate that high plasma T4 level stimulates adrenal activity and may also modulate function of the pituitary-adrenal axis during dehydration.

Direct Effects of Prolactin on Adrenal Steroid Release in Male Hatano High-Avoidance (HAA) Rats May be Mediated Through Janus Kinase 2 (Jak2) Activity

Prolactin (PRL) has been proposed to directly stimulate corticosterone release. However, the role of PRL on adrenocortical function in male HAA rats has not been fully clarified. The aim of this study was to investigate the effect of PRL on the secretion of corticosterone and progesterone using an in vitro cell culture system in male rats. Administration of PRL (10(-7) and 10(-6) M) resulted in dose-dependent increases in corticosterone and progesterone release. Cotreatment with PRL produced an increase in the stimulatory effects of ACTH-induced corticosterone and progesterone secretion. However, the PRL-induced corticosterone and progesterone releases were significantly reduced by treatment with AG490, a specific Janus kinase 2 (Jak2) inhibitor. In addition, administration of AG490 blunted the significant inhibition of ACTH-induced corticosterone and progesterone secretion by PRL. These results demonstrated that PRL could act directly on the adrenal gland to drive corticosterone and progesterone secretion in male rats. Additionally, the results emphasize that PRL stimulation of adrenal steroid release may be mediated through Jak2 activity.

Effects of crude adlay hull acetone extract on corticosterone release from rat zona fasciculata-reticularis cells

Adlay is a grass crop which has been used in traditional Chinese medicine and also as a nourishing food. It has been shown to posses anti-allergic, antimutagenic and hypolipemic effects. However, the effects and action mechanisms of crude adlay hull acetone extract (AHA) on adrenal zona fasciculata-reticularis (ZFR) cells are still unclear. This study explored the effects of AHA on corticosterone release. ZFR cells were incubated with AHA in the presence or absence of adrenocorticotropin (ACTH), 8-bromo-cyclic 3': 5'- adenosine monophosphate (8-Br-cAMP), forskolin (FSK), 25-hydroxy cholesterol (25-OH-cholesterol), pregnenolone, progesterone or deoxycorticosterone. The concentrations of corticosterone or pregnenolone in the media were measured by radioimmunoassay (RIA). The cells were used to measure the expression of steroidogenic acute regulatory (StAR) protein by Western blot. The present data demonstrated that: (1) AHA inhibited ACTH-, 8-Br-cAMP-, forskolin-, 25-OH-cholesterol-, pregnenolone-, progesterone- or deoxycorticosterone-stimulated corticosterone release; (2) AHA (800 microg/ml) caused more pregnenolone release in control group, but not in 25-OH-cholesterol, trilostane or 25-OH-cholesterol+trilostane group; (3) kinetic study showed an uncompetitive inhibition model of AHA to P450 side chain cleavage enzyme (P450scc); (4) kinetic study showed a noncompetitive inhibition model of AHA to 11beta-hydroxylase; and (5) AHA inhibited the expression of StAR protein. These results suggest that AHA acts directly upon rat ZFR cells to diminish corticosterone release. These results indicate the inhibitory mechanism of AHA mediates through an inhibition of the activities of the post-cAMP corticosterone synthesis enzymes, i.e. 3beta-HSD, 21-hydroxylase, 11beta-hydroxylase, and inhibition of StAR protein expression.

Direct effects of IL-15 on corticosterone secretion by rat adrenocortical cells

Cytokines might regulate the function of the hypothalamic-pituitary-adrenal axis. IL-15 is a potent non-T-cell-derived cytokine with IL-2-like activities. It has been shown that IL-15 can reverse the inhibition of glucocorticoids on PBMC. In vitro experiments were designed to assess the direct effect of IL-15 on corticosterone (CORT) secretion in the adrenal zona fasciculata-reticularis (ZFR) cells of male rats. Administration of IL-15 dose dependently decreased the basal and adrenocorticotropin-stimulated release of CORT and production of cAMP in ZFR cells. The stimulatory effect of forskolin (an adenylate cyclase activator) on CORT secretion and accumulation of cAMP in ZFR cells was attenuated by the administration of IL-15. However, 8-Br-cAMP (a cAMP analogue)-stimulated release of CORT was not affected by IL-15. Exogenous administration of IL-15 (10(-7) mol/L) significantly attenuated the pregnenolone (the substrate of 3beta-hydroxysteroid dehydrogenase)- or deoxycorticosterone (the substrate of 11beta-hydroxylase)-induced release of CORT. The results indicate that decrease of CORT secretion by IL-15 is in part because of (i) the decrease of adenylate cyclase activity and cAMP production and (ii) the inhibition of 3beta-hydroxysteroid dehydrogenase and 11beta-hydroxylase activities in rat ZFR cells.

Inhibitory effects of digoxin and digitoxin on corticosterone production in rat zona fasciculata-reticularis cells

The aim of the present study was to investigate the direct effects and action mechanisms of digitalis on the production of corticosterone in rat adrenocortical cells. Male rats were challenged with digoxin (1 microg ml(-1) kg(-1)) in the presence or absence of adrenocorticotropin (ACTH, 5 microg ml(-1) kg(-1)) administered by intravenous injection to the right jugular vein. Blood samples were collected at 0, 30, 60, and 120 min following the challenge. The concentration of corticosterone in the rat plasma samples was measured by radioimmunoassay. Zona fasciculata-reticularis (ZFR) cells in male rats were prepared and then incubated with or without digoxin or digitoxin in the presence or absence of ACTH (10(-9) m), forskolin (10(-7) m), 8-bromo-cyclic 3' : 5'-adenosine monophosphate (10(-4) m), cyclopiazonic acid (CPA, 10(-5) m), trilostane (10(-6) m), 25-OH-cholesterol (10(-5) m), pregnenolone (10(-5) m), progesterone (10(-5) m), or deoxycorticosterone (10(-5) m) at 37 degrees C for 1 h before collection of the media. Corticosterone or pregnenolone levels were measured by radioimmunoassay. A single injection of digoxin did not alter the basal level of plasma corticosterone, but did inhibit the level of plasma corticosterone released in response to ACTH in vivo. Administration of digoxin or digitoxin decreased both spontaneous and ACTH-stimulated release of corticosterone in vitro. Digoxin (10(-7)-10(-5) m) and digitoxin (10(-7)-10(-5) m), but not ouabain (10(-7)-10(-5) m), dose-dependently inhibited corticosterone production in response to forskolin and 8-Br-cyclic AMP in rat ZFR cells. Both digoxin (10(-6)-10(-5) m) and digitoxin (10(-6)-10(-5) m) attenuated corticosterone production in response to CPA. Digoxin (10(-5) m) or digitoxin (10(-5) m) inhibited cytochrome P450 side-chain cleavage enzyme (cytochrome P450scc) activity (catalyses conversion of cholesterol to pregnenolone in the presence of trilostane) in rat ZFR cells. The enzyme activity of 11 beta-hydroxylase (catalyses conversion of deoxycorticosterone to corticosterone) in ZFR cells was also inhibited by the administration of digoxin (10(-5) m) or digitoxin (10(-5) m).10 These results together suggest that digoxin and digitoxin decrease the release of corticosterone by acting directly on ZFR cells via a Na+, K+-ATPase-independent mechanism involving the inhibition of the activities of adenylyl cyclase, cytochrome P450scc and 11 beta-hydroxylase, as well as the functioning of cyclic AMP and intracellular calcium.

Effects of dehydroepiandrosterone on corticosterone release in rat zona fasciculata-reticularis cells

The decline of plasma dehydroepiandrosterone (DHEA) and maintenance of glucocorticoid levels with increasing age contribute to excess body fat accumulation, hyperglycaemia, hyperlipidaemia, hyperinsulinaemia and cancer. Although opposing actions of DHEA and corticosterone have been proposed in a rat model, the effects and action mechanisms of DHEA on rat adrenal zona fasciculata-reticularis (ZFR) cells are still unclear. This study addressed the effects of DHEA on corticosterone release, cellular cAMP production, the functions of steroidogenic enzymes and the expression levels of steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage enzyme (P450scc). ZFR cells were incubated with DHEA in the presence or absence of adrenocorticotropin (ACTH), 8-Br-cAMP, forskolin, 25-OH-cholesterol, pregnenolone, progesterone or deoxycorticosterone at 37 degrees C for 30 min, 1 h or 5 h and the concentration of corticosterone or pregnenolone measured subsequently in the media by RIA. The cells were used to measure the content of cAMP by RIA and to extract protein for Western blot or mRNA for RT-PCR analysis. The data demonstrated that (1) DHEA inhibited ACTH-, 8-Br-cAMP-, 25-OH-cholesterol-, pregnenolone-, progesterone- or deoxycorticosterone-stimulated corticosterone release; (2) DHEA increased 25-OH-cholesterol-stimulated pregnenolone release but not when 25-OH-cholesterol was combined with trilostane; (3) DHEA increased the K(m) of 11beta-hydroxylase but not P450scc; (4) DHEA affected the expression levels of StAR protein but not of P450scc. These results suggest that DHEA acts directly on rat ZFR cells to diminish corticosterone secretion by inhibition within the post-cAMP pathway, by inhibiting steroidogenic enzymes downstream from P450scc and by inhibiting StAR expression.