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Dimitri Novitzky and David K C Cooper

Acute critically ill patients experience a rapid decline in plasma free thyroid hormone levels (free triiodothyronine (FT3) and free levothyroxine (FT4)), with a marked elevation of reverse T3, recognized as the euthyroid sick syndrome (ESS) or low-T3 syndrome. The ESS is also often associated with depressed myocardial function, sometimes referred to as the ‘stunned myocardium’. Its clinical effects may vary from minimal hemodynamic impairment to cardiogenic shock. Medical management may range from aspirin alone to placement of a left ventricular assist device. With adequate supportive therapy, recovery usually occurs within days or weeks. The effect of T3/T4 therapy has been studied in three conditions in which the ESS and myocardial functional depression have been documented – i) transient regional myocardial ischemia and reperfusion, ii) transient global myocardial ischemia in patients undergoing cardiac surgery on cardiopulmonary bypass, and iii) transient inadequate global myocardial perfusion in brain-dead potential organ donors. Under all three conditions, myocardial ischemia leads to rapid loss of high-energy phosphates, accumulation of myocardial tissue lactate, and probably loss of homeostasis of cytosolic calcium, which may further increase cell injury. There is an inability to generate ATP through the Krebs cycle, which reduces the high-energy phosphate pool essential for all cell ATPases. Under all three conditions, following administration of T3/T4, the myocardial dysfunction was rapidly reversed. We, therefore, cautiously advocate the use of thyroid hormonal therapy to any patient with the ESS and/or a stunned myocardium.

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Tony K S Ku and David L Crowe

Steroid hormones such as 17β-estradiol (E2) are critical to diverse cellular processes including tumorigenesis. A number of cofactors such as nuclear receptor corepressor (NCoR), CREB-binding protein (CBP), and steroid receptor coactivator 1 (SRC-1) interact with estrogen receptors (ERs) to regulate transcriptional repression or activation of target genes. Estrogen signaling in non-reproductive tract tissues such as skin is less well characterized and the effectiveness of anti-estrogen therapy for cancer arising from these tissues is unknown. We show that tamoxifen (TAM) treatment inhibited cell cycle progression and proliferation of human cancer lines derived from stratified squamous epithelium squamous cell carcinoma (SCC). E2 had no effect on proliferation of these lines despite low levels of ERα expression. The E2 treatment promoted displacement of the NCoR from ERα and recruitment of CBP to the receptor. SRC-1 expression was not detected in these SCC lines; however, transient transfection of SRC-1, CBP, or both coactivators enhanced transactivation of an estrogen responsive promoter in cancer cells treated with E2 or TAM. In stable clones expressing SRC-1, the coactivator was recruited to ERα along with CBP in E2 but not in TAM-treated cells. SRC-1 expression restored the E2-mediated proliferative response to human SCC lines. This increased proliferation correlated with increased extracellular signal regulated kinase 1 (ERK1) expression. SRC-1 and CBP were recruited to the proximal ERK1 promoter region in E2 but not in TAM-treated cells. We concluded that SRC-1 was a key molecular determinant of estrogen-mediated proliferation in human SCC lines.

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Lesions were made in the pituitary stalk of rats, and the functional capacity of the hypophysial-adrenocortical axis of animals suffering from diabetes insipidus was studied. Eight days after the operation the weight, histological structure and histologically demonstrated lipid content of the adrenals had not changed. Whereas operative stress and unilateral adrenalectomy caused no ascorbic acid depletion in the contralateral adrenals, administration of adrenocorticotrophic hormone induced a significant decrease. The corticosterone content of the adrenal venous blood decreased moderately, whilst in vitro the adrenal slices secreted less corticosterone than normally. Secretion of aldosterone by the adrenals of animals with lesions was not different from that of controls. When large doses of corticosterone were administered adrenal atrophy occurred in both operated and control rats.

It is concluded that the functional capacity of the hypophysial—adrenocortical axis is decreased 8 days after the destruction of the pituitary stalk, although the production of hormones by the adrenal cortex does not cease completely; one must be cautious in assessing the functional state of the adrenal glands since the methods used for their evaluation do not always give comparable results.

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David R Broom, Masashi Miyashita, Lucy K Wasse, Richard Pulsford, James A King, Alice E Thackray, and David J Stensel

Acute exercise transiently suppresses the orexigenic gut hormone acylated ghrelin, but the extent to which exercise intensity and duration determine this response is not fully understood. The effects of manipulating exercise intensity and duration on acylated ghrelin concentrations and hunger were examined in two experiments. In experiment one, nine healthy males completed three, 4-h conditions (control, moderate-intensity running (MOD) and vigorous-intensity running (VIG)), with an energy expenditure of ~2.5 MJ induced in both MOD (55-min running at 52% peak oxygen uptake (V.O2peak)) and VIG (36-min running at 75% V.O2peak). In experiment two, nine healthy males completed three, 9-h conditions (control, 45-min running (EX45) and 90-min running (EX90)). Exercise was performed at 70% V.O2peak. In both experiments, participants consumed standardised meals, and acylated ghrelin concentrations and hunger were quantified at predetermined intervals. In experiment one, delta acylated ghrelin concentrations were lower than control in MOD (ES = 0.44, P = 0.01) and VIG (ES = 0.98, P < 0.001); VIG was lower than MOD (ES = 0.54, P = 0.003). Hunger ratings were similar across the conditions (P = 0.35). In experiment two, delta acylated ghrelin concentrations were lower than control in EX45 (ES = 0.77, P < 0.001) and EX90 (ES = 0.68, P < 0.001); EX45 and EX90 were similar (ES = 0.09, P = 0.55). Hunger ratings were lower than control in EX45 (ES = 0.20, P = 0.01) and EX90 (ES = 0.27, P = 0.001); EX45 and EX90 were similar (ES = 0.07, P = 0.34). Hunger and delta acylated ghrelin concentrations remained suppressed at 1.5 h in EX90 but not EX45. In conclusion, exercise intensity, and to a lesser extent duration, are determinants of the acylated ghrelin response to acute exercise.

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Meredith A Kelleher, Hannah K Palliser, David W Walker, and Jonathan J Hirst

Progesterone and its neuroactive metabolite, allopregnanolone, are present in high concentrations during pregnancy, but drop significantly following birth. Allopregnanolone influences foetal arousal and enhances cognitive and behavioural recovery following traumatic brain injury. Inhibition of allopregnanolone synthesis increases cell death in foetal animal brains with experimental hypoxia. We hypothesised that complications during pregnancy, such as early or preterm loss of placental steroids and intrauterine growth restriction (IUGR), would disrupt the foetal neurosteroid system, contributing to poor neurodevelopmental outcomes. This study aimed to investigate the effects of chronic inhibition of allopregnanolone synthesis before term and IUGR on developmental processes in the foetal brain. Guinea pig foetuses were experimentally growth restricted at mid-gestation and treated with finasteride, an inhibitor of allopregnanolone synthesis. Finasteride treatment reduced foetal brain allopregnanolone concentrations by up to 75% and was associated with a reduction in myelin basic protein (MBP) (P=0.001) and an increase in glial fibrillary acidic protein expression in the subcortical white matter brain region (P<0.001). IUGR resulted in decreased MBP expression (P<0.01) and was associated with a reduction in the expression of steroidogenic enzyme 5α-reductase (5αR) type 2 in the foetal brain (P=0.061). Brain levels of 5αR1 were higher in male foetuses (P=0.008). Both IUGR and reduced foetal brain concentrations of allopregnanolone were associated with altered expression of myelination and glial cell markers within the developing foetal brain. The potential role of neurosteroids in protecting and regulating neurodevelopmental processes in the foetal brain may provide new directions for treatment of neurodevelopmental disorders in infants who are exposed to perinatal insults and pathologies.

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Elizabeth K Fletcher, Monica Kanki, James Morgan, David W Ray, Lea M Delbridge, Peter J Fuller, Colin D Clyne, and Morag J Young

We previously identified a critical pathogenic role for mineralocorticoid receptor (MR) activation in cardiomyocytes that included a potential interaction between the MR and the molecular circadian clock. While glucocorticoid regulation of the circadian clock is undisputed, studies on MR interactions with circadian clock signalling are limited. We hypothesised that the MR influences cardiac circadian clock signalling, and vice versa. Aldosterone or corticosterone (10 nM) regulated Cry1, Per1, Per2 and ReverbA (Nr1d1) gene expression patterns in H9c2 cells over 24 h. MR-dependent regulation of circadian gene promoters containing GREs and E-box sequences was established for CLOCK, Bmal, CRY1 and CRY2, PER1 and PER2 and transcriptional activators CLOCK and Bmal modulated MR-dependent transcription of a subset of these promoters. We also demonstrated differential regulation of MR target gene expression in hearts of mice 4 h after administration of aldosterone at 08:00 h vs 20:00 h. Our data support MR regulation of a subset of circadian genes, with endogenous circadian transcription factors CLOCK and BMAL modulating the response. This unsuspected relationship links MR in the heart to circadian rhythmicity at the molecular level and has important implications for the biology of MR signalling in response to aldosterone as well as cortisol. These data are consistent with MR signalling in the brain where, like the heart, it preferentially responds to cortisol. Given the undisputed requirement for diurnal cortisol release in the entrainment of peripheral clocks, the present study highlights the MR as an important mechanism for transducing the circadian actions of cortisol in addition to glucocorticoid receptor (GR) in the heart.

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Hamzeh Karimkhanloo, Stacey N Keenan, Emily W Sun, David A Wattchow, Damien J Keating, Magdalene K Montgomery, and Matthew J Watt

Cathepsin S (CTSS) is a cysteine protease that regulates many physiological processes and is increased in obesity and type 2 diabetes. While previous studies show that deletion of CTSS improves glycaemic control through suppression of hepatic glucose output, little is known about the role of circulating CTSS in regulating glucose and energy metabolism. We assessed the effects of recombinant CTSS on metabolism in cultured hepatocytes, myotubes and adipocytes, and in mice following acute CTSS administration. CTSS improved glucose tolerance in lean mice and this coincided with increased plasma insulin. CTSS reduced G6pc and Pck1 mRNA expression and glucose output from hepatocytes but did not affect glucose metabolism in myotubes or adipocytes. CTSS did not affect insulin secretion from pancreatic β-cells, rather CTSS stimulated glucagon-like peptide (GLP)-1 secretion from intestinal mucosal tissues. CTSS retained its positive effects on glycaemic control in mice injected with the GLP1 receptor antagonist Exendin (9–39) amide. The effects of CTSS on glycaemic control were not retained in high-fat-fed mice or db/db mice, despite the preservation of CTSS’ inhibitory actions on hepatic glucose output in isolated primary hepatocytes. In conclusion, we unveil a role for CTSS in the regulation of glycaemic control via direct effects on hepatocytes, and that these effects on glycaemic control are abrogated in insulin resistant states.

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Paul G Farnworth, Yao Wang, Pauline Leembruggen, Guck T Ooi, Craig Harrison, David M Robertson, and Jock K Findlay

Inhibins are expressed in the adrenal cortex, but little is known of their binding or role in the adrenal. The aims of the present study were, first, to establish whether a mouse adrenocortical (AC) cell line expresses inhibins/activins and bone morphogenetic proteins (BMP), along with proteins required for inhibin to antagonise activin and BMP actions and, secondly, to characterise and compare inhibin binding sites and proteins in the rat adrenal gland and AC cells. AC cells were found to: (1) express mRNA for multiple BMPs (BMP-2, -3, -4, -6, -8a), growth/differentiation factors (GDF-1, -3, -5, -9), Lefty A and B, and the inhibin α, βA and βB subunits (2) secrete inhibin A and inhibin B and (3) express mRNA encoding the inhibin co-receptor, betaglycan, along with activin and BMP type I (ALK2–7) and type II (ActRII, ActRIIB, BMPRII) receptors, and binding proteins (follistatin, BAMBI, gremlin). When applied to sections of rat adrenal glands, [125I]inhibin A specifically bound to cells of the adrenal cortex, mainly in the zona reticularis. Scatchard analyses of in vitro [125I]inhibin A binding to dispersed rat adrenal cells and AC cells revealed sites of high affinity (Kd(1) of 0.18 and 0.15 nM, respectively) and low affinity (Kd(2) of 2.6 and 1.3 nM, respectively. Competition for [125I]inhibin A binding by activin A or B (30 nM) was negligible, whereas BMP-2, -6 and -7 competed for between 21 and 33% of specific inhibin A binding (IC50 between 0.2 and 0.3 nM). Inhibin B crossreaction with inhibin A binding sites was < 8%. Multiple binding protein complexes (molecular weight ranging from 35 to > 220 kDa) were affinity labelled by [125I]inhibin A on both the primary rat adrenal and AC cells. The species of > 220 kDa were shown by immunoprecipitation to include betaglycan, the species of 105 kDa is consistent in size with type II receptors for activin/BMP, and that of 62 kDa co-migrates with the inhibin-follistatin complex.

In summary, the results show that inhibin A binds selectively and with both high and low affinity to AC cells via multiple binding proteins, including a single betaglycan-like species. The results support the role of glycosylated betaglycan in the high affinity binding of inhibin A, but provide consistent evidence from two independent sources of adrenal cells that inhibin A interacts with several membrane proteins in addition to those currently understood to mediate the anti-activin/BMP actions of inhibin.

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Preston R Buff, Nat T Messer IV, Andria M Cogswell, David A Wilson, Philip J Johnson, Duane H Keisler, and Venkataseshu K Ganjam

Endocrine characteristics of Quarter Horse-type mares were determined during a 68 h feed deprivation and again in the same mares following surgical thyroidectomy (THX). A crossover experimental design was implemented, in which mares received brome hay available ad libitum (FED) or were food deprived (RES) for 68 h. Blood samples were collected every 20 min for 48 h, beginning 20 h after the onset of food deprivation. Concentrations of triiodothyronine and thyroxine were undetectable post-THX. Plasma concentrations of thyrotropin were greater post-THX versus pre-THX (P<0.001). Plasma concentrations of leptin were greater in the THX FED group than in the THX RES group (P< 0.01). The existence of leptin pulse secretion was found only in post-THX compared with the same horses pre-THX (P = 0.02). We theorize that non-pulsatile secretion of leptin may have contributed to the survival of this species, as it evolved in the regions of seasonal availability of food. Lack of pulsatile secretion of leptin may contribute to the accumulation of energy stores by modulating leptin sensitivity.

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Lars P Klieverik, Ewout Foppen, Mariëtte T Ackermans, Mireille J Serlie, Hans P Sauerwein, Thomas S Scanlan, David K Grandy, Eric Fliers, and Andries Kalsbeek

Thyronamines are naturally occurring, chemical relatives of thyroid hormone. Systemic administration of synthetic 3-iodothyronamine (T1AM) and – to a lesser extent – thyronamine (T0AM), leads to acute bradycardia, hypothermia, decreased metabolic rate, and hyperglycemia. This profile led us to hypothesize that the central nervous system is among the principal targets of thyronamines. We investigated whether a low dose i.c.v. infusion of synthetic thyronamines recapitulates the changes in glucose metabolism that occur following i.p. thyronamine administration. Plasma glucose, glucoregulatory hormones, and endogenous glucose production (EGP) using stable isotope dilution were monitored in rats before and 120 min after an i.p. (50 mg/kg) or i.c.v. (0.5 mg/kg) bolus infusion of T1AM, T0AM, or vehicle. To identify the peripheral effects of centrally administered thyronamines, drug-naive rats were also infused intravenously with low dose (0.5 mg/kg) thyronamines. Systemic T1AM rapidly increased EGP and plasma glucose, increased plasma glucagon, and corticosterone, but failed to change plasma insulin. Compared with i.p.-administered T1AM, a 100-fold lower dose administered centrally induced a more pronounced acute EGP increase and hyperglucagonemia while plasma insulin tended to decrease. Both systemic and central infusions of T0AM caused smaller increases in EGP, plasma glucose, and glucagon compared with T1AM. Neither T1AM nor T0AM influenced any of these parameters upon low dose i.v. administration. We conclude that central administration of low-dose thyronamines suffices to induce the acute alterations in glucoregulatory hormones and glucose metabolism following systemic thyronamine infusion. Our data indicate that thyronamines can act centrally to modulate glucose metabolism.