Thyroid hormone-catecholamine interrelationship during cold acclimation in rats. Compensatory role of catecholamine for altered thyroid states

Adipose-targeted triiodothyronine therapy counteracts obesity-related metabolic complications and atherosclerosis with negligible side effects

Thyroid hormone (TH) is a thermogenic activator with anti-obesity potential. However, systemic TH administration has no obvious clinical benefits on weight reduction. Herein we selectively delivered triiodothyronine (T3) to adipose tissues by encapsulating T3 in liposomes modified with an adipose homing peptide (PLT3). Systemic T3 administration failed to promote thermogenesis in brown and white adipose tissues (WAT) due to a feedback suppression of sympathetic innervation. PLT3 therapy effectively obviated this feedback suppression on adrenergic inputs, and potently induced browning and thermogenesis of WAT, leading to alleviation of obesity, glucose intolerance, insulin resistance, and fatty liver in obese mice. Furthermore, PLT3 was much more effective than systemic T3 therapy in reducing hypercholesterolemia and atherosclerosis in apoE-deficient mice. These findings uncover WAT as a viable target mediating the therapeutic benefits of TH and provide a safe and efficient therapeutic strategy for obesity and its complications by delivering TH to adipose tissue.

Thyroid hormones and the mechanisms of adaptation to cold

The thyroid gland plays a crucial role in the regulation of metabolism, oxygen consumption, and the release of energy in the form of heat to maintain the body. Even at rest, these processes are sensitive to changes in thyroid function. This means that along with the adrenergic system, thyroid function determines the organism's ability to adapt to cold. Cold adaptation causes deiodination of thyroxine (T₄) and thus promotes an increase in blood triiodothyronine (T₃) levels in humans and animals. Triiodothyronine is an inductor of iodothyronine deiodinase expression in brown fat, liver, and kidney. Iodothyronine deiodinase plays an important role in adaptation of the organism to cold by contributing to high adrenergic reactivity of brown fat. T₃ also leads to an increase in expression of uncoupling proteins and uncoupling oxidative phosphorylation and an increase in heat production. The aim of this article is to review the available literature regarding the role of thyroid hormones in adaptation to cold and to present the current knowledge of the understanding of the molecular mechanism underlying their action during cold adaptation.

Risperidone and Levothyroxine for Managing "Myxedema Madness"

Hypothyroidism is one of the common comorbidities seen in patients with psychiatric conditions. Sometimes few patients may present with neuropsychiatric symptoms such as cognitive slowing, depression, or psychosis (“myxedema madness”). These patients are managed with antipsychotic medications while admitting laboratory works are processed. It has been found that antipsychotic use is associated with lower free thyroxine levels, so untreated hypothyroid patients may experience worsening of symptoms with antipsychotic use. It is recommended that hypothyroid patients with psychosis be treated for the underlying hypothyroidism with thyroid hormone replacement. In this article, we are presenting a case of a hypothyroid patient presenting to a psychiatric facility for worsening psychosis and persecutory delusions, and medication non-compliance to levothyroxine. We also discuss the management of psychosis in a patient with worsening hypothyroidism with a combination regimen: levothyroxine and risperidone.

Thermogenesis in Adipose Tissue Activated by Thyroid Hormone

Thermogenesis is the production of heat that occurs in all warm-blooded animals. During cold exposure, there is obligatory thermogenesis derived from body metabolism as well as adaptive thermogenesis through shivering and non-shivering mechanisms. The latter mainly occurs in brown adipose tissue (BAT) and muscle; however, white adipose tissue (WAT) also can undergo browning via adrenergic stimulation to acquire thermogenic potential. Thyroid hormone (TH) also exerts profound effects on thermoregulation, as decreased body temperature and increased body temperature occur during hypothyroidism and hyperthyroidism, respectively. We have termed the TH-mediated thermogenesis under thermoneutral conditions “activated” thermogenesis. TH acts on the brown and/or white adipose tissues to induce uncoupled respiration through the induction of the uncoupling protein (Ucp1) to generate heat. TH acts centrally to activate the BAT and browning through the sympathetic nervous system. However, recent studies also show that TH acts peripherally on the BAT to directly stimulate Ucp1 expression and thermogenesis through an autophagy-dependent mechanism. Additionally, THs can exert Ucp1-independent effects on thermogenesis, most likely through activation of exothermic metabolic pathways. This review summarizes thermogenic effects of THs on adipose tissues.

Acute psychosis and concurrent rhabdomyolysis unveiling diagnosis of hypothyroidism

Neuropsychiatric and muscular symptoms can develop as part of hypothyroidism. However, frank psychosis or rhabdomyolysis due to hypothyroidism are uncommon and have been reported rarely as the first presenting features of hypothyroidism. We report a case of a 44-year-old man who presented with a 2-week history of delusions, hallucinations and mild bilateral leg pain, without apparent signs of myxedema. Investigations revealed raised thyroid stimulation hormone >100 mIU/L and high creatine kinase >21 000 U/L. Diagnosis of hypothyroidism-induced psychosis and rhabdomyolysis was made. He received thyroxine, olanzapine and a short course of steroids. His symptoms improved after 2 weeks of treatment and he remained free of symptoms at 6 months of follow-up. To the best of our knowledge, this is the first case of concomitant psychosis and rhabdomyolysis leading to hypothyroidism diagnosis. This case highlights the importance of hypothyroidism screening when faced with unexplained psychosis or rhabdomyolysis, especially if combined.

Pharmacological Activation of Thyroid Hormone Receptors Elicits a Functional Conversion of White to Brown Fat

The functional conversion of white adipose tissue (WAT) into a tissue with brown adipose tissue (BAT)-like activity, often referred to as "browning," represents an intriguing strategy for combating obesity and metabolic disease. We demonstrate that thyroid hormone receptor (TR) activation by a synthetic agonist markedly induces a program of adaptive thermogenesis in subcutaneous WAT that coincides with a restoration of cold tolerance to cold-intolerant mice. Distinct from most other browning agents, pharmacological TR activation dissociates the browning of WAT from activation of classical BAT. TR agonism also induces the browning of white adipocytes in vitro, indicating that TR-mediated browning is cell autonomous. These data establish TR agonists as a class of browning agents, implicate the TRs in the browning of WAT, and suggest a profound pharmacological potential of this action.

Myxedema madness complicating postoperative follow-up of thyroid cancer

Although hypothyroidism is associated with an increased prevalence of psychiatric manifestations, myxedema madness is rarely observed. We report the case of a 62-year-old woman with no prior history of psychiatric disorders, who presented to the emergency department with psychomotor agitation 6 weeks after total thyroidectomy for papillary thyroid cancer. Serum thyroid stimulating hormone (TSH) on admission was 62.9 mIU/L and free T4 was < 0.35 ng/dL, indicating severe hypothyroidism. After ruling out other possible causes, the diagnosis of myxedema madness was considered; hence, antipsychotic drug treatment and intravenous levothyroxine were prescribed. Behavioral symptoms returned to normal within 4 days of presentation, while levels of thyroid hormones attained normal values 1 week after admission. Recombinant TSH (Thyrogen®) was used successfully to prevent new episodes of mania due to thyroid hormone withdrawal in further controls for her thyroid cancer. This case illustrates that myxedema madness can occur in the setting of acute hypothyroidism, completely reverting with levothyroxine and antipsychotic treatment. Recombinant TSH may be a useful tool to prevent myxedema madness or any severe manifestation of levothyroxine withdrawal for the follow-up of thyroid cancer.

Thermogenic mechanisms and their hormonal regulation

Increased heat generation from biological processes is inherent to homeothermy. Homeothermic species produce more heat from sustaining a more active metabolism as well as from reducing fuel efficiency. This article reviews the mechanisms used by homeothermic species to generate more heat and their regulation largely by thyroid hormone (TH) and the sympathetic nervous system (SNS). Thermogenic mechanisms antecede homeothermy, but in homeothermic species they are activated and regulated. Some of these mechanisms increase ATP utilization (same amount of heat per ATP), whereas others increase the heat resulting from aerobic ATP synthesis (more heat per ATP). Among the former, ATP utilization in the maintenance of ionic gradient through membranes seems quantitatively more important, particularly in birds. Regulated reduction of the proton-motive force to produce heat, originally believed specific to brown adipose tissue, is indeed an ancient thermogenic mechanism. A regulated proton leak has been described in the mitochondria of several tissues, but its precise mechanism remains undefined. This leak is more active in homeothermic species and is regulated by TH, explaining a significant fraction of its thermogenic effect. Homeothermic species generate additional heat, in a facultative manner, when obligatory thermogenesis and heat-saving mechanisms become limiting. Facultative thermogenesis is activated by the SNS but is modulated by TH. The type II iodothyronine deiodinase plays a critical role in modulating the amount of the active TH, T(3), in BAT, thereby modulating the responses to SNS. Other hormones affect thermogenesis in an indirect or permissive manner, providing fuel and modulating thermogenesis depending on food availability, but they do not seem to have a primary role in temperature homeostasis. Thermogenesis has a very high energy cost. Cold adaptation and food availability may have been conflicting selection pressures accounting for the variability of thermogenesis in humans.

Brown adipose tissue: function and physiological significance

The function of brown adipose tissue is to transfer energy from food into heat; physiologically, both the heat produced and the resulting decrease in metabolic efficiency can be of significance. Both the acute activity of the tissue, i.e., the heat production, and the recruitment process in the tissue (that results in a higher thermogenic capacity) are under the control of norepinephrine released from sympathetic nerves. In thermoregulatory thermogenesis, brown adipose tissue is essential for classical nonshivering thermogenesis (this phenomenon does not exist in the absence of functional brown adipose tissue), as well as for the cold acclimation-recruited norepinephrine-induced thermogenesis. Heat production from brown adipose tissue is activated whenever the organism is in need of extra heat, e.g., postnatally, during entry into a febrile state, and during arousal from hibernation, and the rate of thermogenesis is centrally controlled via a pathway initiated in the hypothalamus. Feeding as such also results in activation of brown adipose tissue; a series of diets, apparently all characterized by being low in protein, result in a leptin-dependent recruitment of the tissue; this metaboloregulatory thermogenesis is also under hypothalamic control. When the tissue is active, high amounts of lipids and glucose are combusted in the tissue. The development of brown adipose tissue with its characteristic protein, uncoupling protein-1 (UCP1), was probably determinative for the evolutionary success of mammals, as its thermogenesis enhances neonatal survival and allows for active life even in cold surroundings.

Hypothyroidism Presenting as Psychosis: Myxedema Madness Revisited

Hypothyroidism is a medical condition commonly encountered in a variety of clinical settings. The clinical presentations of thyroid hormone deficiency are diverse, complicated, and often overlooked. Hypothyroidism is a potential etiology for multiple somatic complaints and a variety of psychological disturbances. The physical complaints are primarily related to metabolic slowing secondary to lack of thyroid hormone. Psychiatric presentations include cognitive dysfunction, affective disorders, and psychosis. The realization that hypothyroidism might be the potential etiology of an assortment of symptoms is critical in the identification and treatment of the hypothyroid patient. Once hypothyroidism is identified, symptoms usually respond to appropriate thyroid hormone supplementation. This article presents a case of clinical hypothyroidism that came to clinical attention due to psychotic symptoms consisting of auditory and visual hallucinations. The case is followed by a brief discussion of the literature describing the relationship of hypothyroidism and psychiatric symptomatology. References were identified with an English language-based MEDLINE search (1966-2003) using the terms thyroid, hypothyroid, depression, dementia, delirium, mania, bipolar disorder, psychosis, and myxedema and utilization of referenced articles.

Iron and thermoregulation: a review

Poor temperature regulation in both human and animal models has been associated with iron deficiency anemia. The review examines the evidence for causality in both animals and humans, as well as provides an overview of temperature regulation in homeotherms. A number of investigations conclude that anemia is a central component of the inability of iron-deficient individuals to temperature regulate when they are cold stressed. This is apparently due to effects both on heat production and heat loss rates. The former is related to poor thyroid function in iron deficiency and the latter to the competing demands for tissue oxygenation vs. decreased flood flow to minimize heat losses to the environment. Future research needs are outlined that require integration of endocrinology, physiology, and nutrition disciplines.

Thyroid hormone control of thermogenesis and energy balance

The mechanisms whereby thyroid hormone increases heat production have been analyzed with emphasis in more recent developments. Thyroid hormone increases obligatory thermogenesis as a result of the stimulation of numerous metabolic pathways involved in development, remodeling, and delivery of energy to the tissues. In addition, thyroid hormone may specifically stimulate some thermogenic mechanisms selected during evolution of homeotherms (e.g., Na/K-ATPase, Ca2+ cycling in muscle). Thyroid hormone also plays an essential role in facultative thermogenesis interacting with the sympathetic nervous system (SNS) at various levels. Peripherally, thyroid hormone potentiates the effects of the SNS at the level of the adrenergic receptor and adenylyl cyclase complex as well as distal from this point. Synergistic interactions between T3 and cAMP on the regulation of gene expression have been described. Brown adipose tissue (BAT) T4-5'-deiodinase plays a central role in controlling heat production. When this enzyme is stimulated by norepinephrine in the euthyroid and hypothyroid condition, it provides high concentrations of T3 to BAT; inhibition by T4 in hyperthyroidism may limit brown fat thermogenic responses. Also, thyrotoxicosis uniquely reduces the expression of beta 3-adrenergic receptors in brown adipose tissue, and the increased obligatory thermogenesis of this condition, via afferent neural pathways, may reduce the hypothalamic stimulation of brown fat, providing additional mechanisms to limit brown adipose tissue thermogenesis in hyperthyroidism.

Functional consequences of sustained sleep deprivation in the rat

Sleep deprivation disrupts vital biological processes that are necessary for cognitive ability and physical health, but the physiological changes that underlie these outward effects are largely unknown. The purpose of the present studies in the laboratory rat is to prolong sleep deprivation to delineate the pathophysiology and to determine its mediation. In the rat, the course of prolonged sleep deprivation has a syndromic nature and eventuates in a life-threatening state. An early and central symptom of sleep deprivation is a progressive increase in peripheral energy expenditure to nearly double normal levels. An attempt to alleviate this negative energy balance by feeding rats a balanced diet that is high in its efficiency of utilization prolongs survival and attenuates or delays development of malnutrition-like symptoms, indicating that several symptoms can be manipulated to some extent by energy and nutrient consumption. Most changes in neuroendocrine parameters appear to be responses to metabolic demands, such as increased plasma catecholamines indicating sympathetic activation. Plasma total thyroid hormones, however, decline to severely low levels; a metabolic complication that is associated with other sleep deprivation-induced symptoms, such as a decline in body temperature to hypothermic levels despite increased energy expenditure. Metabolic mapping of the brain revealed a dissociation between the energy metabolism of the brain and that of the body. Sleep deprivation's effects on cerebral structures are heterogeneous and unidirectional toward decreased functional activity. The hypometabolic brain structures are concentrated in the hypothalamus, thalamus and limbic systems, whereas few regions in the rest of the brain and none in the medulla, are affected. Correspondence can be found between some of the affected cerebral structures and several of the peripheral symptoms, such as hyperphagia and possible heat retention problems. The factor predisposing to mortality is a decreased resistance to infection. Lethal opportunistic organisms are permitted to infect the bloodstream, which presumably results in a cascade of toxic-like reactions. Host defense is thus the first system to fail. There is neither fever nor marked tissue inflammatory reactions typical of infectious disease states, suggesting that sleep deprivation is immunosuppressive. Each of the four abnormalities identified--(1) a deep negative energy balance and associated malnutrition; (2) heterogeneous decreases in cerebral function; (3) low thyroid hormone concentrations; and (4) decrease resistance to infection--can be viewed as having an early origin during the sleep deprivation process to signify the foremost pathogenic situation to which the other abnormalities might be secondarily related.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of cerebrocortical type II 5'-deiodinase activity in Syrian hamsters kept under short photoperiod and reduced ambient temperature

Cerebrocortical type II thyroxine 5'-deiodinase (5'-D II) was studied in the Syrian hamster. Animals maintained in 14 hr light/day and 20 degrees C ambient temperature and then subjected to acute cold exposure (4 degrees C) for 4 hours did not exhibit changes in cortical 5'-D II activity. Prolonged exposure of hamsters to natural autumnal short photoperiods and reduced ambient temperatures for 8 weeks increased cortical 5'-D II activity compared to hamsters maintained inside under controlled long photoperiod (14:10 LD) and temperature (20 +/- 2 degrees C) conditions. Animal given subcutaneous implants of melatonin and exposed to the natural autumnal condition for 8 weeks exhibited a greater increase in the cortical 5'-D II activity than that in hamsters with blank pellets kept under the same conditions of reduced photoperiod and temperature. Type II 5'-deiodinase activity was not affected by treatment with 6-methoxy-2-benzoxazolinone (6-MBOA), a compound with a chemical structure related to melatonin. All animals maintained outdoors in the natural photoperiod and temperature conditions had depressed circulating thyroxine (T4) and elevated triiodothyronine (T3) concentrations; neither implants of melatonin nor 6-MBOA affected these thyroid hormone levels. It is concluded that serum T4 is depressed and cerebrocortical 5'-D II activity is stimulated despite the elevation of T3 levels in this autumnal condition. These responses, unlike classic pineal-mediated responses to environmental changes, are not blocked by subcutaneous implants of melatonin. However, chronic administration of melatonin might augment the cortical 5'-D II response to low serum T4 or some other component of the autumnal condition.