Effects of recombinant murine leptin[1-147] and leptin fragment 116-130 on steroid secretion and proliferative activity of the regenerating rat adrenal cortex

Leptin, the product of the ob gene, is a hormone mainly secreted by the adipose tissue, which acts through specific receptors (Ob-R) widely distributed in the body tissues. Ob-Rs are present in the mammalian hypothalamo-pituitary-adrenal axis, and evidence indicates that leptin regulates adrenocortical secretion. Moreover, leptin is known to act as a growth promoting factor in some tissues, including the endocrine ovary. We have investigated the effects of three subcutaneous injections of 2 nmol/100 g of native murine leptin[1-147] and of its biologically active fragment 116-130 on the secretory and proliferative activity of the regenerating rat adrenal cortex. Leptin[1-147] increased plasma aldosterone concentration at day 8 and plasma corticosterone concentration (PBC) at day 5 of regeneration, without affecting mitotic index. In contrast, leptin[116-130] lowered PBC and mitotic index at both times of adrenal regeneration. In light of the fact that adrenal regeneration is at least in part dependent on the pituitary ACTH, we conclude that: (i) native leptin moderately stimulates steroid secretion, acting directly on the adrenal cortex, through signaling mechanisms other than those involved in the ACTH action; (ii) native leptin is unable to enhance the proliferative activity of regenerating adrenals, which conceivably is maximally stimulated by ACTH; (iii)leptin[1-147] and leptin[116-130] differently interact with Ob-Rs or interact with different receptors; and (iv) leptin[116-130] inhibits the signaling pathways mediating both the secretagogue effect of native leptin and the proliferogenic effect of ACTH.     

Effects of leptin on the response of rat pituitary-adrenocortical axis to ether and cold stresses

Leptin is a hormone mainly secreted by the adipose tissue, which acts through specific receptors widely distributed in the body tissues, including hypothalamopituitary-adrenal axis. We have investigated the effects of a subcutaneous bolus injection of 5 nmol/kg leptin on the pituitary-adrenocortical function in both normal and ether- or cold-stressed rats. Blood concentrations of ACTH, aldosterone and corticosterone were measured by specific RIA 2 or 4 h after the leptin injection. Leptin administration to normal rats resulted in significant rises in the blood levels of ACTH, aldosterone and corticosterone at 2 h, but not at 4 h. Ether and cold stresses markedly increased hormonal blood concentrations at both 2 and 4 h. Leptin magnified ACTH response to ether stress at 2 h, but depressed it at 4 h, and enhanced aldosterone response at 2 h, without affecting corticosterone response. Leptin increased ACTH response to cold stress at both 2 and 4 h, without altering aldosterone and corticosterone responses. In light of these findings, we conclude that: (i) leptin evokes a middle transient activation of the pituitary-adrenocortical axis of rats under basal conditions; (ii) leptin inhibits the ACTH response to ether stress, but magnifies that to cold stress; and (iii) the leptin-evoked changes in the blood level of ACTH are not paralleled by significant modifications in the secretory activity of the adrenal cortex, which probably undergoes a maximal stimulation under stressful conditions.     

Homologous and heterologous down-regulation of leptin receptor messenger ribonucleic acid in rat adrenal gland

Leptin, the adipocyte-produced hormone that plays a key role in body weight homeostasis, has recently been found to be involved in the regulation of the hypothalamic-pituitary-adrenal axis. Moreover, reciprocal interactions between leptin and glucocorticoids have been described. In the present communication, two different strategies were undertaken to explore the mode of action of leptin in the direct control of rat adrenal function. First, a synthetic peptide approach demonstrated that the inhibitory effect of leptin on basal and ACTH-stimulated corticosterone secretion in vitro is, at least partially, mapped to a domain of the native protein between amino acids 116 and 130, i.e. an area of the molecule also relevant in terms of regulation of food intake and endocrine control. Secondly, semi-quantitative RT-PCR analysis indicated a complex pattern of adrenal leptin receptor (Ob-R) mRNA expression, with predominant expression of the Ob-Ra and Ob-Rb isoforms, as well as moderate levels of the Ob-Rc and Ob-Rf variants, whereas negligible signals for the Ob-Re isoform were detected. Interestingly, such an expression pattern appeared hormonally regulated as exposure to human recombinant leptin (10(-7 )M) or ACTH (10(-7 )M) significantly decreased Ob-R isoform mRNA expression. Indeed, dose-dependent ligand-induced Ob-Ra and Ob-Rb mRNA down-regulation was further confirmed by adrenal stimulation with increasing concentrations (10(-9)-10(-5 )M) of the active leptin fragment, leptin 116-130 amide. Overall, our results provide evidence for a novel regulatory step at the level of Ob-R mRNA expression in the interplay between ACTH and leptin for the tuning of rat adrenal corticosterone secretion. Furthermore, our data showing down-regulation of Ob-R mRNA expression by its cognate ligand may well be relevant to leptin physiology and its alteration in various disease states.     

Centrally administered murine-leptin stimulates the hypothalamus-pituitary- adrenal axis through arginine-vasopressin

Starvation induces a decrease in circulating leptin levels and activation of the hypothalamus-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis in unfed rodents or genetically leptin-deficient ob/ob mice, whereas it stimulates corticotropin-releasing hormone (CRH) gene expression in the paraventricular nucleus (PVN). However, the interactions between leptin, CRH and the HPA axis are poorly understood and are likely to be complex. We recently demonstrated that central leptin administration caused increases in plasma arginine-vasopressin (AVP) and AVP gene expression of the PVN in nonstressful rats. AVP stimulates the release of adrenocorticotropic hormone (ACTH), but it also potentiates the action of CRH on ACTH release. In this study, we investigated the effects of leptin on plasma ACTH and corticosterone levels, CRH mRNA of the PVN and proopiomelanocortin (POMC) mRNA of the pituitary in nonstrained rats. Intracerebroventricularly administered leptin caused increases in plasma ACTH and corticosterone levels in dose-dependent manners. In Northern blot analyses, the leptin injection induced significant increases in the expression of CRH mRNA in the PVN and POMC mRNA in the pituitary. The increased plasma ACTH and corticosterone levels by leptin were attenuated with intracerebroventricular pretreatment of a V(1a) receptor antagonist (OPC-21268) or a V(1a)/V(1b) receptor antagonist (dP[Tyr(Me)(2)]AVP), but not with that of a V(2) receptor antagonist (OPC-31260). The leptin-induced CRH mRNA expression in the PVN and POMC mRNA expression in the pituitary were also reduced by the pretreatment with OPC-21268 and dP[Tyr(Me)(2)]AVP. These results suggest that intracerebroventricular leptin administration activates the HPA axis by AVP receptor activation through V(1a) receptors in the PVN which in turn activates CRH neurons to drive ACTH and corticosterone secretion in concert with AVP in nonstrained rats.     

Neuromedin U partially mediates leptin-induced hypothalamo-pituitary adrenal (HPA) stimulation and has a physiological role in the regulation of the HPA axis in the rat

Intracerebroventricular (ICV) administration of the hypothalamic neuropeptide neuromedin U (NMU) or the adipostat hormone leptin increases plasma ACTH and corticosterone. The relationship between leptin and NMU in the regulation of the hypothalamo-pituitary adrenal (HPA) axis is currently unknown. In this study, leptin (1 nm) significantly increased the release of CRH from ex vivo hypothalamic explants by 207 +/- 8.4% (P < 0.05 vs. basal), an effect blocked by the administration of anti-NMU IgG. The ICV administration of leptin (10 mug, 0.625 nmol) increased plasma ACTH and corticosterone 20 min after injection [plasma ACTH (picograms per milliliter): vehicle, 63 +/- 20, leptin, 135 +/- 36, P < 0.05; plasma corticosterone (nanograms per milliliter): vehicle, 285 +/- 39, leptin, 452 +/- 44, P < 0.01]. These effects were partially attenuated by the prior administration of anti-NMU IgG. Peripheral leptin also stimulated ACTH release, an effect attenuated by prior ICV administration of anti-NMU IgG. We examined the diurnal pattern of hypothalamic NMU mRNA expression and peptide content, plasma leptin, and plasma corticosterone. The diurnal changes in hypothalamic NMU mRNA expression were positively correlated with hypothalamic NMU peptide content, plasma corticosterone, and plasma leptin. The ICV administration of anti-NMU IgG significantly attenuated the dark phase rise in corticosterone [corticosterone (nanograms per milliliter): vehicle, 493 +/- 38; NMU IgG, 342 +/- 47 (P < 0.05)]. These studies suggest that NMU may play a role in the regulation of the HPA axis and partially mediate leptin-induced HPA stimulation.     

Homer 1 - a new player linking the hypothalamic-pituitary-adrenal axis activity to depression and anxiety

Homer 1 gene products are involved in the regulation of synaptic transmission and plasticity. Beside other deficits, the Homer 1 knockout (KO) mice show distinct behavioural abnormalities, such as anxiety and depression-like behaviours. In addition, we recently reported that the global deletion of the Homer 1 proteins in mice leads to a?conspicuous endocrine phenotype linked to hypertrophy of the adrenal cortex, elevated basal and/or adrenocorticotropic hormone-induced corticosterone and aldosterone release in vitro and in vivo, as well as a?drastic increase in the adrenocorticotropic hormone receptor mRNA in the adrenocortical cells. Interestingly, the basal secretion of adrenocorticotropic hormone was not changed in these mutants, which is in line with our recent observations, suggesting that the central limb of the hypothalamic-pituitary-adrenal axis (namely hypothalamic corticotropin-releasing hormone levels and the activation of its neurons in response to restraint stress) is not affected in the Homer 1 KO mice. On the contrary, the elevation of both plasma and intra-adrenal corticosterone and aldosterone concentrations in these mutants clearly indicates that the alteration primarily occurred in the adrenal cortex. We propose that excessive steroid release may contribute to depression- and anxiety-like behaviours and that the Homer 1 gene products may be involved in the pathogenesis of these stress-related mood disorders. Keywords: Homer 1, HPA axis, CRH, ACTH, adrenal cortex, corticosterone, aldosterone.     

Inhibition of steroidogenic response to adrenocorticotropin by leptin: implications for the adrenal response to maternal separation in neonatal rats

Previous studies have shown that leptin can regulate the adrenocortical axis. Neonatal rodents exhibit a period of adrenal hyporesponsiveness to stress in the first 2 wk of life, and we determined the role of leptin as a mediator of this process. We examined the direct effects of leptin on neonatal adrenal steroidogenic responses to ACTH under basal conditions and after 24-h maternal separation. In isolated adrenocortical cells from as early as postnatal d 5 (PND5) and throughout the neonatal period, acute (2.5 h) incubation with leptin significantly inhibited ACTH-stimulated corticosterone and aldosterone secretion without affecting cAMP production. In PND10 pups, 24-h maternal separation and the resulting rapid decline in plasma leptin levels increased basal corticosterone and aldosterone secretion in vivo and in isolated cells, but did not modify the ability of leptin to inhibit stimulated steroid production in vitro. Maternal separation in PND10 pups increased adrenal expression of steroidogenic acute regulatory protein (StAR) and peripheral-type benzodiazepine receptor (PBR) proteins as well as all steroidogenic enzymes measured (3beta-hydroxysteroid dehydrogenase, P450C11B1, and P450C11B2). Leptin (1 mg/kg body weight, i.p.) replacement during maternal separation did not affect basal corticosterone output, but reduced corticosterone secretion and StAR and PBR protein expression induced by exogenous ACTH challenge (20 or 80 microg/kg body weight, i.p.). These results indicate that leptin inhibits ACTH-stimulated secretion of corticosterone and aldosterone, at least through a rapid reduction in the expression of StAR and PBR protein in the neonatal adrenal gland. As leptin concentrations in pups are controlled to a large extent by the maternal diet, these results emphasize the key role of leptin to mediate the maternal influence on the adrenocortical axis of the infant.     

Leptin and the hypothalamic-pituitary-adrenal axis activity in women with different obesity phenotypes

OBJECTIVE: Women with visceral obesity may have hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Since glucocorticoids are involved in the expression of the ob gene, this study was carried out to investigate the relationship between serum leptin and the activity of the HPA axis in women with different obesity phenotypes. DESIGN: Cross sectional clinical study. SUBJECTS: Fifteen obese (Body Mass Index BM128 kg/m2) women and ten normal weight control women (BM126 kg/m2) were included in the study. MEASUREMENTS: Body fat distribution was defined by CT scan at the L4-L5 level. Baseline blood samples were obtained for hormone concentrations. The activity of the HPA axis was evaluated by measuring ACTH and cortisol blood levels after combined iv administration of corticotropin releasing factor (100 microg) + arginine-vasopressin (0.3 IU). RESULTS: Baseline cortisol, ACTH, and androgen levels were similar in all groups, whereas leptin levels were significantly higher in the obese groups than in normal weight controls, without any significant difference between women with different obesity phenotypes. Incremental areas of ACTH and cortisol were significantly higher in women with visceral obesity than in those with subcutaneous obesity and controls. No significant correlation was found between the activity of the HPA axis and leptin concentrations. Leptin showed a highly significant correlation with BMI and subcutaneous fat and a weak but significant correlation with visceral fat and the visceral-to-subcutaneous fat ratio. CONCLUSION: Women with different obesity phenotypes had similar serum leptin concentrations but different HPA axis activity, and there was no correlation between them.     

Adrenocortical insufficiency in Otsuka Long-Evans Tokushima Fatty rats, a type 2 diabetes mellitus model

In diabetes, dysregulation of the hypothalamic-pituitary-adrenocortical (HPA) axis causes effects such as elevation of corticotropin (ACTH) and glucocorticoids. Cholecystokinin and its receptors are involved in the HPA axis and influence the regulation of the HPA axis. We examined adrenocortical function in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes mellitus, that lack the cholecystokinin A receptor. We measured adrenal weight, plasma ACTH, serum and urinary corticosterone, and serum leptin in OLETF rats at 5 to 36 weeks of age. Messenger RNA (mRNA) expression of 11beta-hydroxysteroid dehydrogenase and 5alpha-reductase type 1 in adrenal glands of the rats were examined. Long-Evans Tokushima Otsuka (LETO) rats were used as controls. In OLETF rats at 32 to 36 weeks of age, plasma ACTH was significantly higher (P < .001); serum corticosterone and 24-hour urinary corticosterone were significantly lower (P < .005); and adrenal weight was significantly lower (P < .005) than those in LETO rats. At the same ages, serum leptin in OLETF rats was significantly higher (P < .001) than that in LETO rats. In the younger OLETF rats, these changes were not observed. Overall, there was an inverse correlation between serum corticosterone and serum leptin (r = -0.374, P < .0005), whereas there was a positive correlation between plasma ACTH and serum leptin (r = 0.654, P < .0001). At 5 and 36 weeks of age, mRNA expression of 5alpha-reductase type 1 in the adrenal gland of OLETF rats was significantly higher (P < .05) than that of LETO rats, whereas there was no significant difference in mRNA expressions of 11beta-hydroxysteroid dehydrogenase types 1 and 2. We showed that adrenocortical insufficiency and adrenal atrophy were acquired in OLETF rats, and the possibility of elevated serum leptin relates to this phenomenon.     

Effect of maternal nutrient restriction in early gestation on development of the hypothalamic-pituitary-adrenal axis in fetal sheep at 0.8-0.9 of gestation

The fetal hypothalamic-pituitary-adrenal (HPA) axis has numerous key roles in development. Epidemiological data have linked adverse prenatal nutrition with altered organ development and increased incidence of disease in adult life. We studied HPA axis development in resting and stimulated states in late gestation fetal sheep, following 15% reduction in maternal nutritional intake over the first 70 days of gestation (dGA). Fetuses from control (C) and nutrient-restricted (R) ewes were chronically catheterised and response profiles for ACTH and cortisol were determined at 113-116 and 125-127 dGA after administration of corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP). At 126-128 dGA cortisol profiles were also determined following ACTH administration. Basal ACTH and cortisol concentrations were not different between C and R fetuses. In R fetuses, ACTH response to CRH+AVP was significantly smaller at 113-116 dGA (P<0.01), and cortisol responses were smaller at both 113-116 dGA (P<0.01) and 125-127 dGA (P<0.0001). Cortisol response to ACTH was also smaller in R fetuses (P<0.001). We conclude that, in late gestation fetal sheep, pituitary and adrenal responsiveness is reduced following modest maternal nutrient restriction in early gestation.     

Expression of CRHR1 and CRHR2 in mouse pituitary and adrenal gland: implications for HPA system regulation

Deficiency of corticotropin-releasing hormone receptor I (CRHR1) reduces anxiety-related behavior in mice and severely impairs the stress response of the hypothalamic-pituitary-adrenocortical (HPA) system. Most recently, we could show that severe emotional stressors induce a significant rise in plasma ACTH even in mice deficient for the CRHR1 (Crhr1-1-) which is, however, not accompanied by an increase in plasma corticosterone concentration, suggesting that CRHR1 might be directly involved in the regulation of adrenal corticosterone release. We therefore used the Crhr1-1- mouse model to clarify the potential role of adrenal CRHR1 in the regulation of the HPA system and, in particular, of corticosterone secretion. In Crhr1-/- mice, intravenous ACTH administration failed to stimulate corticosterone secretion despite a significant upregulation of ACTH receptor mRNA levels in the adrenal cortex of these mutants. Further, by means of RT-PCR and in situ hybridization analyses, we could provide first evidence that both CRHR1 and CRHR2 are expressed in the mouse pituitary and adrenal cortex. Stimulation of pituitary CRHR2 does not induce ACTH secretion either in vitro or in vivo. Our data strongly suggest that CRHR1 plays a crucial role in the release of corticosterone from the adrenal cortex, independently of pituitary function. The existence of an intra-adrenal CRH/CRHR1 regulatory system which contributes to the corticosteroid secretory activity adds to the complexity of HPA system regulation and stress hormone homeostasis.     

Regulation of the Mineralocorticoid Hormones in Adrenocortical Disorders with Adrenocorticotropin Excess

Chronic stimulation by adrenocorticotropin (ACTH) of the adrenal cortex produces different plasma mineralocorticoid hormone (MCH) patterns, depending on the amount of glucocorticoid hormones (cortisol) concurrently generated and the degree of activation of the renin-angiotensin system (RAS). Patients with Cushing's disease or the ectopic ACTH-excess syndrome have normal or low production of the MCHs, aldosterone and 18-hydroxycorticosterone (18-OHB), by the zona glomerulosa (ZG), elevated cortisol and deoxycorticosterone (DOC) levels, and high-normal to elevated production of the MCHs cortico-sterone (B) and 18-hydroxydeoxycorticosterone (18-OHDOC) by the zona fasciculata (ZF). Prolonged administration of superphysiologic doses of ACTH to normal subjects yields similar patterns. Patients with simple virilizing 21–hydroxylase deficiency (21–OHD) have impaired ZF production of B and 18-OHDOC and elevated DOC, 18-OHB, and aldosterone secretion secondary to the superimposed RAS stimulation of the ZG. Patients with 17α-hydroxylase deficiency (17α-OHD) have elevated levels of the ZF MCHs DOC, B, 18-OHDOC, and 18-OHB and a functionally suppressed ZG. Patients with 11β–hydroxylase deficiency (11β–OHD) have only elevated production of DOC by the ZF and suppressed RAS and aldosterone. A significant negative correlation between cortisol and aldosterone concentrations suggests that cortisol is involved in the ACTH-mediated inhibition of aldosterone formation.     

Leptin(116-130) stimulates prolactin and luteinizing hormone secretion in fasted adult male rats.

Leptin is a hormone secreted by adipocytes with an important role in the control of feeding behavior and neuroendocrine function. Leptin stimulates in vivo LH secretion in fasted female rats and in vitro PRL secretion. Recent data indicate that leptin(116-130), an active fragment of the native molecule, exerts effects similar to those of the native peptide on body weight and food intake. The present study was carried out to determine whether this fragment is also able to stimulate LH and PRL secretion. Adult male rats fasted for 5 days were injected with saline or leptin(116-130) (15 microgram i.c.v.) and LH and PRL concentrations were measured thereafter at 15-min intervals during a 150-min period. Administration of leptin(116-130) increased the frequency of LH pulses (2.0 +/- 0.26 vs. 1.20 +/- 0. 37/150 min; p 相似文献   

Experimentally-induced hyperthyroidism is associated with activation of the rat hypothalamic-pituitary-adrenal axis

OBJECTIVE: Previous studies on the effects of altered thyroid function on the secretion and metabolism of adrenocortical hormones suggest a degree of adrenocortical hyperactivity in hyperthyroidism. We have previously shown that experimentally-induced hyperthyroidism is associated with significant alterations in pituitary-adrenal responsiveness to synthetic ovine corticotropin-releasing hormone (oCRH) that are contingent upon the duration of the altered thyroid function. The purpose of this study was to assess the time-dependent effects of hyperthyroidism on the functional integrity of the hypothalamic-pituitary-adrenal (HPA) axis by in vivo stimulation of the hypothalamic CRH neuron and adrenal cortex. METHODS: The functional integrity of the HPA axis was examined in vivo in sham-thyroidectomized male Sprague-Dawley rats given placebo or in thyroidectomized rats given 50 mug of thyroxine every day for 7 or 60 days. Responses to insulin-induced hypoglycemia and IL-1alpha stimulation were used to assess the hypothalamic CRH neuron. Adrenocortical reserve was assessed in response to low-dose adrenocorticotropic hormone (ACTH), following suppression of the HPA axis with dexamethasone. Adrenal and thymus tissue weight, in addition to basal plasma ACTH, corticosterone and thyroid indices were also determined. RESULTS: Basal plasma corticosterone and corticosterone binding globulin (CBG) concentrations were significantly increased in short- and long-term hyperthyroid rats, and by 60 days, cerebrospinal fluid (CSF) corticosterone levels were significantly increased. Basal plasma ACTH levels were similar to controls. Although plasma ACTH responses to hypoglycemic stress and IL-1alpha administration in both short- and long-term hyperthyroidism were normal, corticosterone responses to the ACTH release during the administration of these stimuli were significantly increased. The adrenal reserve was significantly elevated in short-term hyperthyroidsim. Long-term hyperthyroidism, however, was associated with a significant reduction in adrenocortical reserve. A significant increase in adrenal weights and a decrease in thymus weights were observed in both short- and long-term hyperthyroidism. CONCLUSIONS: The available data confirms that hyperthyroidism is associated with hypercorticosteronemia, although the locus that is principally affected still remains unclear. Despite the sustained hyperactivity of the HPA axis, long-term experimentally-induced hyperthyroidism is associated with diminished adrenal functional reserve. The alterations in HPA function in states of disturbed thyroid function were found to be somewhat more pronounced as the duration of thyroid dysfunction increased.     

Leptin interferes with adrenocorticotropin/3',5'-cyclic adenosine monophosphate (cAMP) signaling, possibly through a Janus kinase 2-phosphatidylinositol 3-kinase/Akt-phosphodiesterase 3-cAMP pathway, to down-regulate cholesterol side-chain cleavage cytochrome P450 enzyme in human adrenocortical NCI-H295 cell line

CONTEXT: Obesity has adverse effects on adrenocortical functions. Adipocyte-derived leptin, a biomarker molecule of obesity, may directly control adrenal steroidogenesis via an unclear mechanism. OBJECTIVE: We studied the mechanism underlying leptin action on adrenal steroidogenesis in human adrenocortical NCI-H295 tumor cell line. METHODS: Levels of progesterone, cortisol, and cAMP were determined by ELISA. Western blotting was used to detect protein amounts of P450 side-chain cleavage (P450scc), Janus kinase 2 (JAK2), Akt, and their phosphorylated forms. The mRNA expressions of P450scc and leptin receptors were measured by RT-PCR and real-time PCR. P450scc promoter activity was analyzed with a luciferase reporter system. RESULTS: Cholera toxin mimicked ACTH action by increasing adrenal cAMP levels and steroid secretion. Leptin did not affect basal release but significantly inhibited ACTH/cholera toxin-induced steroid secretion. The concomitant inhibitions by leptin on cholera toxin-induced protein and ACTH/cholera toxin-induced mRNA expression of P450scc were confirmed. Leptin inhibited ACTH/cholera toxin-induced CYP11A1 promoter activity via a known cAMP-responsive region located between -1.7 and -1.5 kb. Leptin activated phosphorylations of JAK2 and Akt. Inhibitory effects of leptin on ACTH/cholera toxin-induced cAMP levels, CYP11A1 promoter activity, and steroid secretion were blunted by either inhibitor of JAK2 (AG490) or phosphatidylinositol 3-kinase/Akt (wortmannin) as well as inhibitors of cAMP-degrading phosphodiesterases (PDEs), including nonspecific 3-isobutyl-1-methylxanthine and PDE3-specific SKF94836. Leptin failed to affect the inductions of CYP11A1 promoter activity and steroid secretion by PDE-nonhydrolyzable N(6)-monobutyryl-cAMP. CONCLUSIONS: Leptin interferes with ACTH/cAMP signaling, possibly through a cAMP-degrading mechanism involving activation of JAK2, phosphatidylinositol 3-kinase, and PDE3, to down-regulate P450scc expression and consequent adrenal steroidogenesis.     

Maternal undernutrition throughout pregnancy increases adrenocorticotrophin receptor and steroidogenic acute regulatory protein gene expression in the adrenal gland of twin fetal sheep during late gestation

We have previously demonstrated that maternal undernutrition during either the 'periconceptional' (i.e. from 60 days (d) before until 7 d after mating) or 'gestational' periods (i.e. from 8 d after mating until the end of pregnancy) have differential effects on the subsequent development of the hypothalamo-pituitary-adrenocortical (HPA) axis and on adrenal growth and steroidogenesis in the sheep fetus during late gestation (term=147+/-3 d gestation). The specific mechanisms by which periconceptional or gestational undernutrition result in activation of the fetal HPA axis in late gestation are unclear. We have therefore investigated the impact of maternal nutrient restriction imposed either during the periconceptional period, or between 8 and 147 d gestation on the expression of specific genes in the fetal pituitary and adrenal which regulate adrenal steroidogenesis in late gestation. Ewes were maintained on either a Control (C) or Restricted (R, 70% of C) diet from 60 d before until 7 d after mating (periconceptional period) and then maintained on either a Control or Restricted diet from 8 d after mating for the remainder of pregnancy (gestational period). Four nutritional treatment groups were therefore generated (C-C, C-R, R-R and R-C). Whilst periconceptional undernutrition (R-R and R-C groups) resulted in higher fetal plasma adrenocorticotrophic hormone (ACTH) at 135-146 d gestation, there was no change in the relative level of expression of the ACTH receptor (MC2R), steroidogenic acute regulatory protein (StAR) or steroidogenic enzyme mRNAs in the fetal adrenal in late gestation. Exposure to gestational undernutrition (R-R and C-R groups), however, resulted in a stimulation in the relative level of expression of MC2R mRNA (P=0.001) and StAR mRNA (P=0.007) in the fetal adrenal during late gestation. This study provides new insights into the potential mechanisms by which alterations of the nutrient environment of the fetus at different stages of gestation may result in differential activation of the fetal HPA axis.     

The late gestation increase in circulating ACTH and cortisol in the fetal sheep is suppressed by intracerebroventricular infusion of recombinant ovine leptin

The obese gene product leptin, originally characterised as an adipocyte hormone coordinating the behavioural and neuroendocrine responses to starvation, is expressed in fetal adipocytes and placental trophoblast cells and is present in the fetal circulation. Concentrations of leptin in fetal blood correlate with fetal bodyweight and fat mass. In post-natal life, leptin conveys information about calorie intake and the state of adipose tissue energy stores, and plasma leptin levels are generally inversely correlated with hypothalamo-pituitary adrenal (HPA) activity. Late fetal life is characterised by increasing HPA activity that prepares the fetus for extrauterine life and initiates the endocrine cascade leading to parturition. We have investigated the hypothesis that leptin in the fetal circulation can inhibit the fetal HPA axis, thereby providing a mechanism by which the fetus can determine the fine timing of parturition as long as it is adequately nourished and growing appropriately. Here we show that a 5-day intracerebroventricular infusion of leptin to the sheep fetus in late gestation inhibits the pre-parturient rise in ACTH and cortisol concentrations, and that this seems to be a centrally mediated effect.     

Effect of leptin on ACTH-stimulated secretion of cortisol in rhesus macaques and on human adrenal carcinoma cells

OBJECTIVE: Because glucocorticoids stimulate leptin release and, at least in vitro, leptin inhibits cortisol secretion, a feedback system between glucocorticoids and leptin has been proposed. However, in humans and non-human primates there are no in vivo studies to support any role for leptin in the control of the hypothalamic-pituitary-adrenal axis. In this study, we investigated the effect of leptin on (i) ACTH-stimulated secretion of cortisol in six male rhesus monkeys and (ii) basal and forskolin (FSK)-stimulated cortisol secretion by the human adrenal carcinoma cell H295R in vitro. DESIGN AND METHODS: In vivo studies: after suppression of endogenous ACTH with either dexamethasone (n=6) or a corticotropin-releasing factor (CRF) antagonist (d-Phe CRF(12-41)) (n=3), 1 microg bolus of human ACTH(1-24) was administered to stimulate adrenal cortisol release. Blood samples were collected every 15 min for 3 h. Leptin (1 mg) was infused over 4 h, starting 1 h before ACTH bolus. In vitro studies: NCI-H295R cells were incubated for 6, 12, 24 and 48 h in the absence or presence of 20 micromol/l FSK in combination with leptin (100 ng/ml medium). Cortisol levels in serum and medium were measured by solid phase radioimmunoassay. RESULTS: Acute leptin infusion to rhesus monkeys did not change basal cortisol levels, peak cortisol levels after ACTH(1-24) or the area under the curve when compared with studies in which leptin was not given. FSK increased cortisol levels in medium at 24 and 48 h, but leptin did not change cortisol release in either control or FSK-stimulated cells. CONCLUSIONS: Short-term leptin infusion affected neither the cortisol response to ACTH in non-human primates in vivo nor cortisol release (basal or FSK stimulated) by H295R cells, in vitro. These data suggest that leptin may not be an acute regulator of primate adrenal cortisol secretion.     

Fetal programming of the hypothalamic-pituitary-adrenal (HPA) axis: low birth weight and central HPA regulation

Fetal programming of the hypothalamic-pituitary-adrenal (HPA) axis has been proposed as an intermediary in the association between reduced fetal growth and adult cardiovascular and metabolic diseases. Previous studies have shown that small size at birth is associated with increased fasting plasma cortisol and adrenal responsiveness to ACTH stimulation. We have extended these studies by evaluating the salivary cortisol response to awakening and plasma ACTH and cortisol responses to CRH stimulation and a dexamethasone-suppressed CRH (DEX/CRH) test in a group of low birth weight [LBW; <3.18 kg (7 lb), n = 58] and high birth weight [>3.86 kg (8.5 lb), n = 65] men aged 60-69 yr. Despite no difference in basal pituitary-adrenal activity or in their ACTH and cortisol responses to CRH, LBW men had significantly lower pituitary-adrenal responses in the DEX/CRH test. Although these findings do not explain the HPA abnormalities associated with LBW in previous studies, they provide further evidence of dysregulation of the HPA axis in people who were small at birth.     

Bovine adrenal cells secrete interleukin-6 and tumor necrosis factor in vitro

Interleukin-6 (IL-6) and tumor necrosis factor (TNF) are secreted and/or synthesized by the rat and human adrenal cortex. In this study, the release of IL-6 and TNF from bovine adrenal cells was determined. Bovine adrenal glands were collected from an abattoir and dissected into the zona glomerulosa (ZG), zona fasciculata (ZF), zona reticularis (ZR), and medulla. The tissues were enzymatically dispersed to single cells and cultured for 4-6 days. The cells were then exposed (4 h) to angiotensin II (AII), adrenocorticotrophic hormone (ACTH), phorbol dibutyrate (PDB), interleukin-1beta (IL-1beta), interleukin-1alpha (IL-1alpha), and endotoxin (LPS). The IL-6 and TNF content of the incubation medium was determined by bioassays. The release of IL-6 and TNF from the ZG, ZF, ZR, and medulla was increased by PDB, IL-1alpha, IL-1beta, and LPS. In contrast, ACTH and AII increased IL-6 release from the ZG, ZF, and ZR but had no effect on IL-6 release from the medulla. ACTH decreased TNF release from all adrenal cortical zones but had no effect on TNF release from the medulla. Immunohistochemistry utilizing antibodies against TNFalpha demonstrated TNFalpha-containing cells throughout the adrenal gland. The majority of the cells of the ZG, ZF, and ZR contained TNFalpha. However, the cells of the ZG contained more TNFalpha than the cells of the ZR or ZF. Small patches of TNFalpha-containing cells were also found in the adrenal medulla and capsule. These findings support the hypothesis that IL-6 and TNF may have autocrine/paracrine effects on the adrenal gland.