Thyroid hormones greatly impact energy homeostasis in the heart, and excess thyroid hormone leads to a hypermetabolic state. The thyroid gland produces two hormones, thyroxine (T4) and triiodothyronine (T3). The major form of thyroid hormone is thyroxine, which acts mostly as a prohormone. 1 The set point for thyroid hormone production and secretion by the thyroid gland is regulated by the hypothalamic thyrotropin-releasing hormone (TRH), which stimulates the production and secretion of thyroid stimulating hormone (TSH) that, in turn, controls thyroid hormone concentrations. Most of T4 is converted to biologically active T3 through the removal of an iodide by deiodinases. While there are three types of deiodinases, most of the circulating T3 is derived from Type 1; Type 1 activates thyroid hormone by converting T4 to active T3, and it deactivates thyroid hormone by converting T4 to inactive reverse T3 (rT3) or to T2.2 It is important to note that there is no significant intracellular deiodinase activity in cardiac cells; therefore, the heart relies mainly on the action of T3 since that is the hormone transported into the myocyte.3 Both T4 and T3 circulate in the blood almost entirely (> 95%) bound to thyroxine-binding globulin and a family of other hormone-binding proteins. The remaining unbound T3 is transported through a variety of membrane transport proteins and subsequently to the cell nucleus to regulate expression of selected genes. 4 Molecular Mechanisms of Thyroid Hormone ActionThe intracellular cardiac effects of thyroid hormone are exerted by two mechanisms: genomic and nongenomic. Several of the main effects are exerted through genomic actions, which consist of T3 linking to nuclear receptors that bind to thyroid-responsive elements (TREs) in the promoter of target genes. 5 There are several key myocyte-specific genes regulated by this mechanism (Table 1). 3 Binding of thyroid hormone to these TREs can either activate or repress gene expression, thereby regulating the expression of specific messenger RNA and translated proteins and producing different tissue-specific responses. Importantly, thyroid hormone-regulated genes are also involved in structural and regulatory proteins, and long-term exposure to high T3 levels can increase the synthesis of cardiac proteins, leading to cardiac hypertrophy and dysfunction. Extranuclear nongenomic activities provoke rapid changes in the cardiac myocyte plasma membrane and cytoplasmic organelles. These include changes in sodium, potassium, and calcium ion channels; changes in actin cytoskeleton polymerization; and changes to the intracellular signaling pathways in the heart and smooth muscle cells.Both genomic and nongenomic mechanisms act together to regulate cardiac function and cardiovascular hemodynamics.2 For example, they upregulate expression of the sarcoplasmic reticulum calcium-activated ATPase and downregulate phospholamban expression, thereby enhancing myocardial relaxation. They also increase expression of the more rapid contractile isoforms of the myo...

Human immunodeficiency virus (HIV)-lipodystrophy syndrome (HLS) is characterized by hypertriglyceridemia, low high-density lipoprotein-cholesterol, lipoatrophy, and central adiposity. We investigated fasting lipid metabolism in six men with HLS and six non-HIV-infected controls. Compared with controls, HLS patients had lower fat mass (15.9 +/- 1.3 vs. 22.3 +/- 1.7 kg, P < 0.05) but higher plasma glycerol rate of appearance (R(a)), an index of total lipolysis (964.71 +/- 103.33 vs. 611.08 +/- 63.38 micromol x kg fat(-1) x h(-1), P < 0.05), R(a) palmitate, an index of net lipolysis (731.49 +/- 72.36 vs. 419.72 +/- 33.78 micromol x kg fat(-1) x h(-1), P < 0.01), R(a) free fatty acids (2,094.74 +/- 182.18 vs. 1,470.87 +/- 202.80 micromol x kg fat(-1) x h(-1), P < 0.05), and rates of intra-adipocyte (799.40 +/- 157.69 vs. 362.36 +/- 74.87 micromol x kg fat(-1) x h(-1), P < 0.01) and intrahepatic fatty acid reesterification (1,352.08 +/- 123.90 vs. 955.56 +/- 124.09 micromol x kg fat(-1) x h(-1), P < 0.05). Resting energy expenditure was increased in HLS patients (30.51 +/- 2.53 vs. 25.34 +/- 1.04 kcal x kg lean body mass(-1) x day(-1), P < 0.05), associated with increased non-plasma-derived fatty acid oxidation (139.04 +/- 24.17 vs. 47.87 +/- 18.81 micromol x kg lean body mass(-1) x min(-1), P < 0.02). The lipoatrophy observed in HIV lipodystrophy is associated with accelerated lipolysis. Increased hepatic reesterification promotes the hypertriglyceridemia observed in this syndrome.

Although evidence has emerged regarding functional neural impairment of all four limbs with a diagnosis of type II diabetes (T2D), there is conflicting evidence regarding impairment in manual function with the disease. The purpose of the current study was to evaluate hand/fingertip function in T2D as compared to healthy age- and gender-matched controls. Ten adults with T2D and ten healthy age- and gender-matched control subjects underwent a battery of clinically validated and laboratory-based evaluations of sensory function, motor function, and quality of life evaluation. The T2D group exhibited sensory dysfunction and altered kinetic output and inconsistent differences in clinically-validated timed performance tasks as compared to age-matched controls. No difference in quality of life was found between the two groups. Sensory dysfunction and some timed evaluations correlated with disease severity. Linear kinetic features did not covary with diminished sensation; however, nonlinear measures did covary with sensation changes. None of the recorded measures were related to clinical diagnosis of peripheral neuropathy. The relationship among exhibited behavioral changes is discussed in terms of small fiber neuropathy, micro-vascular adaptations, and endothelial dysfunction co-occurring with T2D.

In patients with acromegaly, chronic excess of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) leads to the development of acromegalic cardiomyopathy. Its main features are biventricular hypertrophy, diastolic dysfunction, and in later stages, systolic dysfunction and congestive heart failure. Surgical and/or pharmacological treatment of acromegaly and control of cardiovascular risk factors help reverse some of these pathophysiologic changes and decrease the high risk of cardiovascular complications.

In individuals with advanced type 2 diabetes (T2DM), combination therapy is often unavoidable to maintain glycaemic control. Currently metformin is considered the first line of defence, but many patients experience gastrointestinal adverse events, necessitating an alternative treatment approach. Established therapeutic classes, such as sulphonylureas and thiazolidinediones, have some properties undesirable in individuals with T2DM, such as hypoglycaemia risk, weight gain and fluid retention, highlighting the need for newer agents with more favourable safety profiles that can be combined and used at all stages of T2DM. New treatment strategies have focused on both dipeptidyl peptidase (DPP)-4 inhibitors, which improve hyperglycaemia by stimulating insulin secretion in a glucose-dependent fashion and suppressing glucagon secretion, and sodium-glucose co-transporter-2 (SGLT2) inhibitors, which reduce renal glucose reabsorption and induce urinary glucose excretion, thereby lowering plasma glucose. The potential complimentary mechanism of action and good tolerance profile of these two classes of agents make them attractive treatment options for combination therapy with any of the existing glucose-lowering agents, including insulin. Together, the DPP-4 and SGLT2 inhibitors fulfill a need for treatments with mechanisms of action that can be used in combination with a low risk of adverse events, such as hypoglycaemia or weight gain.