The controversy of the treatment of critically ill patients with thyroid hormone

Serum total triiodothyronine (T3) as a predictor of mortality and morbidity in critically ill patients and its correlation of predictability with acute physiology and chronic health evaluation II score: A prospective observational study

Background:

The aim is to assess the prognostic value of total T3, total T4, and thyroid-stimulating hormone among critically ill patients admitted to the medical intensive care unit (ICU) in association with mortality and its correlation with the acute physiology and chronic health evaluation II (APACHE II) score.

METHODS

: Our prospective observational study consists of 257 patients without known thyroid diseases admitted to the medical ICU. The baseline characteristics of the patients were recorded, including the APACHE II score and thyroid hormone levels at ICU admission. Based on the primary outcome of mortality, we analyzed the data by appropriate statistical methods. A P < 0.05 was considered significant.

Results:

Of the 257 patients included in the study, 47 (18.28%) succumbed to their illnesses. A significant difference in T3 levels (P < 0.001), T4 levels (P < 0.001), and APACHE II score (P < 0.001) was found between the survivors and the nonsurvivors. There was negative correlation observed between T3 and APACHE II score (r = −0.448, P < 0.001) and T4 and APACHE II score (r = −0.221, P ≤ 0.001). Multivariate logistic regression analysis determined T3 to be the only independent predictor of ICU mortality among thyroid hormones. The area under the curve (AUC) for T3 (0.811 ± 0.04) was almost equal to that of the APACHE II score (0.858 ± 0.029). The duration of ICU stay and hospital stay in patients with low T3 was significantly higher compared to patients with normal T3.

Conclusion:

Serum T3 is a good indicator for predicting mortality and morbidity among critically ill patients.

Long non-coding RNA pairs to assist in diagnosing sepsis

Background

Sepsis is the major cause of death in Intensive Care Unit (ICU) globally. Molecular detection enables rapid diagnosis that allows early intervention to minimize the death rate. Recent studies showed that long non-coding RNAs (lncRNAs) regulate proinflammatory genes and are related to the dysfunction of organs in sepsis. Identifying lncRNA signature with absolute abundance is challenging because of the technical variation and the systematic experimental bias.

Results

Cohorts (n = 768) containing whole blood lncRNA profiling of sepsis patients in the Gene Expression Omnibus (GEO) database were included. We proposed a novel diagnostic strategy that made use of the relative expressions of lncRNA pairs, which are reversed between sepsis patients and normal controls (eg. lncRNA_i > lncRNA_j in sepsis patients and lncRNA_i < lncRNA_j in normal controls), to identify 14 lncRNA pairs as a sepsis diagnostic signature. The signature was then applied to independent cohorts (n = 644) to evaluate its predictive performance across different ages and normalization methods. Comparing to common machine learning models and existing signatures, SepSigLnc consistently attains better performance on the validation cohorts from the same age group (AUC = 0.990 & 0.995 in two cohorts) and across different groups (AUC = 0.878 on average), as well as cohorts processed by an alternative normalization method (AUC = 0.953 on average). Functional analysis demonstrates that the lncRNA pairs in SepsigLnc are functionally similar and tend to implicate in the same biological processes including cell fate commitment and cellular response to steroid hormone stimulus.

Conclusion

Our study identified 14 lncRNA pairs as signature that can facilitate the diagnosis of septic patients at an intervenable point when clinical manifestations are not dramatic. Also, the computational procedure can be generalized to a standard procedure for discovering diagnostic molecule signatures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07576-4.

Anabolic and anticatabolic agents used in burn care: What is known and what is yet to be learned

Major thermal injury induces profound metabolic derangements secondary to an inflammatory "stress-induced" hormonal environment. Several pharmacological interventions have been tested in an effort to halt the hypermetabolic response to severe burns. Insulin, insulin growth factor 1, insulin growth factor binding protein 3, metformin, human growth hormone, thyroid hormones, testosterone, oxandrolone, and propranolol, among others, have been proposed to have anabolic or anticatabolic effects. The aim of this broad analysis of pharmacological interventions was to raise awareness of treatment options and to help establishing directions for future clinical research efforts. A PubMed search was conducted on the anabolic and anticatabolic agents used in burn care. One hundred and thirty-five human studies published between 1999 and 2017 were included in this review. The pharmacological properties, rationale for the treatments, efficacy considerations and side effect profiles are summarized in the article. Many of the drugs tested for investigational purposes in the severely thermally injured are not yet gold-standard therapies in spite of their potential benefit. Propranolol and oxandrolone have shown great promise but further evidence is still needed to clarify their potential use for anabolic and anticatabolic purposes.

Thyroid Hormones in Critical Illness

Thyroid hormone is integral for normal function, yet during illness, circulating levels of the most active form (triiodothyronine [T3]) decline. Whether this is an adaptive response in critical illness or contributes to progressive disease has remained controversial. This review outlines the basis of thyroid hormone changes during critical illness and considers the evidence regarding T3 replacement.

Thyroid Function in the Neonatal Intensive Care Unit

Patients in the neonatal intensive care unit (NICU) are at high risk for abnormal thyroid function testing because of illness and preterm birth. Preterm infants are born before hypothalamic-pituitary-thyroid axis maturation and the normal feedback mechanisms that regulate thyroid hormone production remain immature. Preterm and sick infants may develop hypothyroidism even if routine thyroid screening tests collected in the first several days after birth are normal. This article reviews normal hypothalamic-pituitary-thyroid axis maturation, thyroid hormone testing and interpretation in the NICU, and the current evidence for and against levothyroxine treatment of NICU patients with borderline abnormal thyroid function testing.

Impact of Thyroid Hormone Levels on Functional Outcome in Neurological and Neurosurgical Early Rehabilitation Patients

Background

Neurological and neurosurgical early rehabilitation (NNER) is a specialized treatment option for patients with severe neurological disorders. The present study investigated whether thyroid hormone levels on admission have an impact on the outcome of NNER patients.

Method

The study included 500 NNER patients who were admitted to the BDH-Clinic Hessisch Oldendorf between 2009 and 2010. Data such as age, sex, diagnoses, comorbidities, Glasgow Coma Scale score, length of stay, and thyroid hormone levels (obtained as part of clinical routine care) were analyzed retrospectively. Improvement in the Early Rehabilitation Barthel Index (ERBI) at the end of the NNER treatment was defined as outcome parameter.

Results

Most patients made functional progress during treatment, as reflected in significant enhancements of the ERBI. Approximately half of the patients were transferred to further rehabilitation treatment. Young age, early onset of NNER treatment, low functional impairment on admission, and, in particular, low total T3 levels were independently associated with a good outcome.

Conclusion

Age, severity of disease, and time between injury and admission are known to predict outcome. The present study confirms the influence of these general factors. In addition, an association between thyroid hormones and functional outcome was demonstrated for NNER patients.

Thyroid Hormone Stimulation of Adult Brain Fatty Acid Oxidation

Thyroid hormone is a critical modulator of brain metabolism, and it is highly controlled in the central nervous system. Recent research has uncovered an important role of thyroid hormone in the regulation of fatty acid oxidation (FAO), an energetic process essential for neurodevelopment that continues to support brain metabolism during adulthood. Thyroid hormone stimulation of FAO has been shown to be protective in astrocytes and mouse models of brain injury, yet a clear mechanism of this relationship has not been elucidated. Thyroid hormone interacts with multiple receptors located in the nucleus and the mitochondria, initiating rapid and long-term effects via both genomic and nongenomic pathways. This has complicated efforts to isolate and study-specific interactions. This chapter presents the primary signaling pathways that have been identified to play a role in the thyroid hormone-mediated increase in FAO. Investigation of the impact of thyroid hormone on FAO in the adult brain has challenged classical models of brain metabolism and widened the window of potential neuroprotective strategies. A detailed understanding of these pathways is essential for any researchers aiming to expand the field of neuroenergetics.

Triiodothyronine Administration in a Model of Septic Shock: A Randomized Blinded Placebo-Controlled Trial

OBJECTIVES

Triiodothyronine concentration in plasma decreases during septic shock and may contribute to multiple organ dysfunction. We sought to determine the safety and efficacy of administering triiodothyronine, with and without hydrocortisone, in a model of septic shock.

DESIGN

Randomized blinded placebo-controlled trial.

SETTING

Preclinical research laboratory.

SUBJECTS

Thirty-two sheep rendered septic with IV Escherichia coli and receiving protocol-guided sedation, ventilation, IV fluids, and norepinephrine infusion.

INTERVENTIONS

Two hours following induction of sepsis, 32 sheep received a 24-hour IV infusion of 1) placebo + placebo, 2) triiodothyronine + placebo, 3) hydrocortisone + placebo, or 4) triiodothyronine + hydrocortisone.

MEASUREMENTS AND MAIN RESULTS

Primary outcome was the total amount of norepinephrine required to maintain a target mean arterial pressure; secondary outcomes included hemodynamic and metabolic indices. Plasma triiodothyronine levels increased to supraphysiological concentrations with hormonal therapy. Following 24 hours of study drug infusion, the amount of norepinephrine required was no different between the study groups (mean ± SD μg/kg; placebo + placebo group 208 ± 392; triiodothyronine + placebo group 501 ± 370; hydrocortisone + placebo group 167 ± 286; triiodothyronine + hydrocortisone group 466 ± 495; p = 0.20). There was no significant treatment effect on any hemodynamic variable, metabolic parameter, or measure of organ function.

CONCLUSIONS

A 24-hour infusion of triiodothyronine, with or without hydrocortisone, in an ovine model of septic shock did not markedly alter norepinephrine requirement or any other physiological parameter.

Age-dependent alterations in the inflammatory response to pulmonary challenge

The aging lung is increasingly susceptible to infectious disease. Changes in pulmonary physiology and function are common in older populations, and in those older than 60 years, pneumonia is the major cause of infectious death. Understanding age-related changes in the innate and adaptive immune systems, and how they affect both pulmonary and systemic responses to pulmonary challenge are critical to the development of novel therapeutic strategies for the treatment of the elderly patient. In this observational study, we examined age-associated differences in inflammatory responses to pulmonary challenge with cell wall components from Gram-positive bacteria. Thus, male Sprague–Dawley rats, aged 6 months or greater than 18 months (approximating humans of 20 and 55–65 years), were challenged, intratracheally, with lipoteichoic acid and peptidoglycan. Cellular and cytokine evaluations were performed on both bronchoalveolar lavage fluid (BAL) and plasma, 24 h post-challenge. The plasma concentration of free thyroxine, a marker of severity in non-thyroidal illness, was also evaluated. The older animals had an increased chemotactic gradient in favor of the airspaces, which was associated with a greater accumulation of neutrophils and protein. Furthermore, macrophage migration inhibitory factor (MIF), an inflammatory mediator and putative biomarker in acute lung injury, was increased in both the plasma and BAL of the older, but not young animals. Conversely, plasma free thyroxine, a natural inhibitor of MIF, was decreased in the older animals. These findings identify age-associated inflammatory/metabolic changes following pulmonary challenge that it may be possible to manipulate to improve outcome in the older, critically ill patient.

Low T3 levels as a predictor marker predict the prognosis of patients with acute ischemic stroke

BACKGROUND

Early and accurate prediction of outcome in acute stroke is important. The aim of this prospective study was to explore the correlation between serum triiodothyronine level and prognosis in acute ischemic stroke patients.

METHODS

A prospective observational study which included 359 consecutive patients with acute ischemic stroke from December 2014 to November 2015 was interrogated. Serum triiodothyronine (T₃) concentrations were measured on admission to understand their value in predicting functional outcome within 90 d using multivariable models adjusted for confounding factors. Receiver operating characteristic (ROC) curves were calculated to define the best cut-off value of triiodothyronine to predict outcome. The accuracy of the test was assessed measuring the area under the ROC curve (AUROC).

RESULTS

Triiodothyronine was significantly decreased in patients with an unfavorable functional outcome as compared to patients with a favorable functional outcome within 90 d (p = 0.01). Binary logistic regression analyses revealed that lower triiodothyronine concentrations on admission were associated with a risk for poor outcomes (OR 0.05, 95% CI 0.01-0.25; p < 0.01). In addition, in ROC curve analysis, triiodothyronine may improve the National Institutes of Health Stroke Scale (NIHSS) score in predicting functional outcome. The combined model AUROC was 0.84 for 30 d and 0.91 for 90 d, which were both significantly higher than the AUROCs of original NIHSS (0.83 and 0.87), triiodothyronine (0.64 and 0.69) and age (0.57 and 0.68) (all p < 0.05).

CONCLUSIONS

Low serum triiodothyronine levels can be a predictive marker of short-term outcome after ischemic stroke. A combined model (triiodothyronine, age and NIHSS score) can add significant additional predictive information to the clinical score of the NIHSS.

Cardiac organ donor management

There is a critical shortage of donor organs. According to the United Network for Organ Sharing (UNOS), 20% of organs are discarded after procurement. Many of these may be potentially salvageable. Brain death is particularly detrimental to cardiac function. The initial sympathetic storm can produce direct myocardial injury. The ensuing spinal shock reduces global oxygen delivery. There is a change to anaerobic metabolism due to global mitochondrial dysfunction. Diabetes insipidus worsens hypovolemia and thyroid deficiency impairs cardiac function. Inadequate replacement of blood loss from trauma and coagulopathy worsens anemia and oxygen delivery. In the mid-1990s, the Papworth Hospital group in the UK advocated early invasive hemodynamic monitoring and administration of a ‘hormonal cocktail’, consisting of triiodothyronine (T3), vasopressin, methylprednisolone and insulin. This has been widely accepted and is endorsed by UNOS. Ventricular function, volume status and adequacy of resuscitation should be guided by invasive monitoring and serial echocardiography. Dopamine or epinephrine is used for inotropic support. If hypotension persists, vasopressin should be added which may allow reduction of inotropes. Donor lung function and ventilation should be optimized. Recently, two large retrospective studies have shown that, with aggressive pharmacological and hormonal resuscitation, a significant increase in the number and quality of organs harvested can be achieved.

Anesthetic considerations in organ procurement surgery: a narrative review

PURPOSE

While a few publications specify the anesthetic implications of either brain or cardiac death, they lack detail on how to provide anesthesia during organ donation surgery. We provide a thorough description of important anesthetic considerations during organ donation surgery in patients with either brain or cardiac death.

SOURCE

A thorough literature review was undertaken to locate all relevant articles that describe systemic effects of brain and cardiac death and their anesthetic implications. We searched PubMed, Pubget, and EMBASE™ for relevant articles using the following search terms: anesthesia, management, donation cardiac death, donation brain death. In addition, we reviewed the relevant protocols at our own institution.

PRINCIPAL FINDINGS

Highly specific intraoperative management by an anesthesiologist is required during organ procurement after brain death. To manage the heart-beating brain-dead donor, the anesthesiologist must incorporate knowledge of the effects of brain death on each organ system as well as the effects of the preoperative measures that the donor required in the intensive care unit. It is also important to know which organs are going to be procured in order to establish specific goals and implement strategies (e.g., lung-protective ventilation or intraoperative glycemic control) to optimize donor outcome. During organ procurement after cardiac death, an anesthesiologist's direct involvement is particularly important for lung donors.

CONCLUSION

Anesthesiologist-guided physiological optimization of the brain-dead donor may be a factor in determining the outcome of the organ recipient. Additionally, anesthesiologists have an important role in helping to ensure that the highest quality and most appropriate care are rendered to non-heart-beating donors. This is achieved through establishing protocols in their hospitals for donation after cardiac death that maximize the number of available organs with the best chance for long-term graft viability.

Treatment of endocrine disorders in the neuroscience intensive care unit

OPINION STATEMENT

This review discusses concepts and treatments associated with the most clinically relevant areas of acute endocrine dysfunction amongst patients with common diseases in neuroscience intensive care units (Neuro ICUs). We highlight the following points:• While a thorough work-up for hyponatremia when it is present is always warranted, subarachnoid hemorrhage (SAH) patients who are in a time window concerning for cerebral vasospasm and who are hyponatremic with high urine output are generally thought to have cerebral salt wasting. These patients are typically treated with a combination of continuous hypertonic saline infusion and fludrocortisone.• Diabetes insipidus (DI) is often seen in patients fulfilling death by neurological criteria, as well as in patients with recent pituitary surgery and less often in SAH and traumatic brain injury patients who are not brain dead. Patients with DI in the Neuro ICU often cannot drink to thirst and may require a combination of desmopression/vasopressin administration, aggressive fluid repletion, and serum sodium monitoring.• Diagnosing adrenal insufficiency immediately following pituitary injury is complicated by the fact that the expected atrophy of the adrenal glands, due to lack of a stimulus from pituitary adrenocorticotropic hormone, may take up to 6 weeks to develop. Cosyntropin testing can be falsely normal during this period.• Both hyperglycemia (glucose >200 mg/dL) and hypoglycemia (glucose <50 mg/dL) are strongly associated with neurological morbidity and mortality in ICUs and should be avoided. Glucose concentrations between 120-160 mg/dL can serve as a reasonable target for insulin infusion protocols.• There is no data to suggest that treatment of abnormal thyroid function tests in nonthyroidal illness syndrome/sick euthyroid leads to benefits in either mortality or morbidity. True myxedema coma is a rare clinical diagnosis that is treated with intravenous levothyroxine accompanied by stress-dose steroids.

Thyroid function, cardiovascular events, and mortality in diabetic hemodialysis patients

BACKGROUND

In dialysis patients, the prevalence of thyroid disorders and their impact on specific cardiovascular (CV) events and mortality are largely unknown. The aim of the present study was to analyze whether subclinical thyroid disorders were associated with CV events and mortality.

STUDY DESIGN

Prospective multicenter cohort study.

SETTING & PARTICIPANTS

Thyroid status and clinical outcomes were explored in 1,000 diabetic hemodialysis patients from 178 centers in Germany.

PREDICTOR

Thyroid status, defined by the following cutoff values: euthyroidism (thyrotropin [TSH], 0.30-4.0 mIU/L; free triiodothyronine [T3], 2.7-7.6 pmol/L; and free thyroxine [T4], 11.0-24.0 pmol/L), subclinical hyperthyroidism (TSH<0.3 mIU/L and free T3/free T4 within reference ranges), subclinical hypothyroidism (TSH, 4.1-15.0 mIU/L and free T3/free T4 within reference ranges), euthyroid sick syndrome (free T3<2.7 pmol/L and TSH/free T4 low or within reference ranges).

OUTCOMES

During 4 years' follow-up, prespecified adjudicated end points were determined: sudden cardiac death, myocardial infarction, stroke, combined CV events, and overall mortality. Short-term effects within the first 12 months were contrasted to long-term effects (years 2-4).

MEASUREMENTS

TSH, free T3, and free T4 levels at baseline.

RESULTS

Euthyroidism was present in 78.1% of patients; subclinical hyperthyroidism, in 13.7%; and subclinical hypothyroidism, in 1.6%. Euthyroid sick syndrome was exhibited by 5.4% of patients. The adjusted short-term risk of sudden cardiac death was more than doubled (HR, 2.03; 95% CI, 0.94-4.36) in patients with subclinical hyperthyroidism, and similarly for patients with euthyroid sick syndrome (HR, 2.74; 95% CI, 0.94-7.98) compared with patients with euthyroidism. Short-term mortality was increased almost 3-fold for patients with euthyroid sick syndrome (HR, 2.97; 95% CI, 1.66-5.29), but this effect was not seen in the long term. Subclinical hypothyroidism was not associated with CV events or all-cause mortality. Risks of stroke and myocardial infarction were not affected meaningfully by thyroid disorders.

LIMITATIONS

Observational study design.

CONCLUSIONS

Sudden cardiac death may be influenced by subclinical hyperthyroidism and euthyroid sick syndrome in the short term. Furthermore, euthyroid sick syndrome is associated strongly with mortality in hemodialysis patients. Regular assessment of thyroid status may help estimate the cardiac risk of dialysis patients.

Hormonal synchronization of lipopolysaccharide-induced hypothermic response in rats

BACKGROUND

Recent experimental evidence suggests that lipopolysaccharide (LPS)-induced hypothermia is an adaptive thermoregulatory strategy against immunological challenge in rats. We hypothesized that the hormones which are predominantly responsible for energy homeostasis may have efferent signaling roles for development of the hypothermia.

AIM

The aim of the study was to evaluate the changes of hypothalamic-pituitary-thyroid (HPT) and hypothalamic- pituitary-adrenal (HPA) axis hormones, leptin and erythropoietin at various phases of LPS-induced hypothermia such as the initial phase, nadir and the end of the response in blood sampled rats.

MATERIAL AND METHODS

Body temperature of adult male albino Wistar rats was recorded by biotelemetry. E. coli O111:B4 LPS (250 μg/kg, ip) was injected alone or with SC-560, a cyclooxygenase-1 selective inhibitor (1 mg/kg, sc).

RESULTS

Serum FT4 levels elevated at the initial phase, but FT3 levels decreased at nadir and remained low at the end of the response. Meanwhile, no change was observed in TSH levels. Serum adrenocorticotropic hormone (ACTH) levels reduced at the initial phase and serum corticosterone levels decreased at nadir without any change in serum corticotropin-releasing hormone (CRH) levels throughout the hypothermia. Serum leptin levels increased only at the end of the response. No change was observed in the levels of serum erythropoietin. SC-560 treatment abolished both LPS-induced hypothermia and respective hormonal changes.

CONCLUSION

Data suggest that HPT axis hormones may contribute to development of LPS-induced hypothermia in rats. Data also support the view that leptin may have a role for the recovery of hypothermic response.

Stress response in critical illness

Sepsis brings about neuroendocrine dysfunction in children that differs significantly from that of adults and can thus be difficult to interpret and manage. Aggressive treatment of sepsis with appropriate and judicious use of antibiotics remains a top priority. Strict glycemic control in children has been associated with significant risk of hypoglycemia, which may independently contribute to morbidity and mortality. Timely initiation of hydrocortisone in persistently hypotensive children with fluid-refractory, catecholamine-resistant shock is controversial, but its use in children with suspected or proven adrenal insufficiency is suggested. Fluid and electrolyte abnormalities must be corrected. Treatment of thyroid dysfunction has been shown to be beneficial in certain specific populations but cannot be extrapolated to all septic patients with the current available data.

Thyroid hormone levels predict mortality in intensive care patients with cirrhosis

INTRODUCTION

Mortality rates of intensive care patients are quite high. The aim of this study was to determine the availability of thyroid function tests and predictive scoring systems on the outcome of cirrhotic patients admitted to the intensive care unit.

METHODS

A total of 106 patients were included in the final analysis, of which 32 were men (30.2%) and 74 were women (69.8%). Predictors of mortality that were investigated include acute physiology and chronic health evaluation (APACHE II), model for end-stage liver disease (MELD), Child-Turcotte-Pugh (CTP) and sequential organ failure assessment (SOFA) scores and thyroid function tests including free triiodo-L-thryronin (fT3), free tetraiodothyronine/thyroxine (fT4) and thyroid-stimulating hormone/thyrotropin (TSH) levels.

RESULTS

High APACHE II, MELD, CTP and SOFA score and suppression of fT3 were all found to be associated with higher mortality in our intensive care patients who have cirrhosis (P < 0.001). Suppression of fT3 was also found to be reciprocally correlated with high APACHE II, MELD, CTP and SOFA scores (P < 0.001). fT4 had also reciprocal correlation with APACHE II, MELD, CTP and mortality. There is no correlation between TSH levels and predictive scores or mortality.

CONCLUSIONS

Calculation of APACHE II, MELD, CTP and SOFA scores and measurement of fT3 and fT4 levels may all be useful as predictors of mortality in intensive care patients who have cirrhosis.

Thyroid hormone levels as a predictor of mortality in intensive care patients: A comparative prospective study

BACKGROUND

Mortality rates of intensive care patients are quite high. The aim of this study was to determine the role, as well as to compare the value of several markers in predicting mortality in intensive care patients. Patient-wise, this is the largest study of its kind and the first that attempts to correlate the degree of thyroid hormone suppression with elevations in procalcitonin (PCT) levels.

PATIENTS AND METHODS

In this study, a total of 417 patients were included in the final analysis, 235 of which were men (56%), and 182 were women (44%). Predictors of mortality that were investigated include age, APACHE II score, PCT, free triiodo-L-thyronine (fT3), free tetraiodothyronine/thyroxine (fT4) and thyroid stimulating hormone/thyrotropin (TSH).

RESULTS

High APACHE II score and low PCT levels, as well as suppression of fT3, fT4 and TSH levels were all found to be associated with higher mortality in our intensive care patients (p < 0.001). Suppression of thyroid hormones was also found to be reciprocally correlated with high APACHE II scores and PCT levels (p < 0.05).

CONCLUSION

Calculation of APACHE II score as well as measurement of PCT, fT3, fT4 and TSH levels may all be useful as predictors of mortality in intensive care patients.

Type 2 deiodinase and host responses of sepsis and acute lung injury

The role of thyroid hormone metabolism in clinical outcomes of the critically ill remains unclear. Using preclinical models of acute lung injury (ALI), we assessed the gene and protein expression of type 2 deiodinase (DIO2), a key driver for synthesis of biologically active triiodothyronine, and addressed potential association of DIO2 genetic variants with ALI in a multiethnic cohort. DIO2 gene and protein expression levels in murine lung were validated by microarrays and immunoblotting. Lung injury was assessed by levels of bronchoalveolar lavage protein and leukocytes. Single-nucleotide polymorphisms were genotyped and ALI susceptibility association assessed. Significant increases in both DIO2 gene and D2 protein expression were observed in lung tissues from murine ALI models (LPS- and ventilator-induced lung injury), with expression directly increasing with the extent of lung injury. Mice with reduced levels of DIO2 expression (by silencing RNA) demonstrated reduced thyroxine levels in plasma and increased lung injury (increased bronchoalveolar lavage protein and leukocytes), suggesting a protective role for DIO2 in ALI. The G (Ala) allele of the Thr92Ala coding single-nucleotide polymorphism (rs225014) was protective in severe sepsis and severe sepsis-associated ALI after adjustments for age, sex, and genetic ancestry in a logistic regression model in European Americans. Our studies indicate that DIO2 is a novel ALI candidate gene, the nonsynonymous Thr92Ala coding variant of which confers ALI protection. Increased DIO2 expression may dampen the ALI inflammatory response, thereby strengthening the premise that thyroid hormone metabolism is intimately linked to the integrated response to inflammatory injury in critically ill patients.

A systems approach to bone pathophysiology

With evolving interest in multiscalar biological systems one could assume that reductionist approaches may not fully describe biological complexity. Instead, tools such as mathematical modeling, network analysis, and other multiplexed clinical- and research-oriented tests enable rapid analyses of high-throughput data parsed at the genomic, proteomic, metabolomic, and physiomic levels. A physiomic-level approach allows for recursive horizontal and vertical integration of subsystem coupling across and within spatiotemporal scales. Additionally, this methodology recognizes previously ignored subsystems and the strong, nonintuitively obvious and indirect connections among physiological events that potentially account for the uncertainties in medicine. In this review, we flip the reductionist research paradigm and review the concept of systems biology and its applications to bone pathophysiology. Specifically, a bone-centric physiome model is presented that incorporates systemic-level processes with their respective therapeutic implications.

Thyroid hormone receptors are down-regulated in skeletal muscle of patients with non-thyroidal illness syndrome secondary to non-septic shock

AIM

Non-thyroidal illness syndrome (NTIS) is related to changes in thyroid hormone (TH) physiology. Skeletal muscle (SM) plays a major role in metabolism, and TH regulates SM phenotype and metabolism. We aimed to characterize the SM of non-septic shock NTIS patients in terms of: i) expression of genes and proteins involved in TH metabolism and actions; and ii) NFKB's pathway activation, a responsible factor for some of the phenotypic changes in NTIS. We also investigated whether the patient's serum can induce in vitro the effects observed in vivo.

METHODS

Serum samples and SM biopsies from 14 patients with non-septic shock NTIS and 11 controls. Gene and protein expression and NFKB1 activation were analyzed by quantitative PCR and immunoblotting. Human SM cell (HSkMC) cultures to investigate the effects of patient's serum on TH action mediators.

RESULTS

Patients with non-septic shock NTIS showed higher levels of pro-inflammatory cytokines than controls. Expression of TRβ (THRB), TRα1 (THRA), and retinoid X receptor γ (RXRG) was decreased in NTIS patients. RXRA gene expression was higher, but its protein was lower in NTIS than controls, suggesting the existence of a post-transcriptional mechanism that down-regulates protein levels. NFKB1 pathway activation was not different between NTIS and control patients. HSkMC incubated with patient's serum increased TH receptor and RXRG gene expression after 48  h.

CONCLUSIONS

Patients with non-septic shock NTIS showed decreased expression of TH receptors and RXRs, which were not related to increased activation of the NFKB1 pathway. These findings could not be replicated in cultures of HSkMCs incubated in the patient's serum.

Clinical analysis on alteration of thyroid hormones in the serum of patients with acute ischemic stroke

Low T3 has been associated with increased short-term mortality in intensive care unit and long-term mortality in cardiovascular disease. The objective of this retrospective study is to investigate associations of thyroid hormone status with clinical severity and outcome in acute ischemic stroke, and whether there is association between the pituitary axis abnormality and the anterior/posterior circulation involvement. Patients with no history of thyroid abnormality who presented first ever stroke were studied. Total T3, T4, TSH levels, basic and clinical characteristics were collected and categorized. Neurological impairment was assessed using NIHSS and modified Rankin Scale. Twenty-nine patients (61%) had T3 ≤ 75 ng/dL. Low T3 group had significant higher NIHSS compared to normal T3 group. There was a significant negative correlation between T3 levels and NIHSS scores on admission. A significantly smaller percentage of patients with low T3 showed favorable neurological function improvement by both NIHSS and mRS measures compared to those with normal T3. There was no significant difference for anterior or posterior circulation involvement between low T3 and normal T3 groups. It is suggested that low T3 is associated with worse neurological outcome. The severity of low T3 may be a predictor of functional improvement in acute ischemic stroke.

Nonthyroidal illness syndrome in children

Neuroendocrine changes in the hypothalamic-pituitary-thyroid axis during critical illness result in nonthyroidal illness syndrome (NTIS) characterized by abnormal thyrotropin (TSH) and thyroid hormone levels. Studies looking at the natural history of neuroendocrine changes during critical illness have revealed the presence of NTIS. NTIS has been described in a variety of patient settings. Many studies have tried to uncover the pathophysiology behind NTIS and several theories are proposed. Whether NTIS requires treatment or intervention is still controversial and the results of the treatment studies are arguably mixed. Whether implicitly stated or not, the underlying purpose of all the natural history, pathophysiology, or treatment studies is to determine whether NTIS is adaptive or maladaptive. Some studies have illustrated a correlation between illness severity and the degree of NTIS but a cause and effect relationship is still elusive. The human studies can be divided between those with either adult or pediatric subjects, with much less data available in the latter. This review examines the available literature on NTIS with an emphasis on the pediatric literature.

Hypothalamic-pituitary-thyroid axis changes in children after cardiac surgery

INTRODUCTION

Hypothalamic-pituitary-thyroid axis changes in critical illness result in nonthyroidal illness syndrome (NTIS) characterized by abnormal TSH and thyroid hormone levels. It is unclear whether NTIS is adaptive or maladaptive. Some have suggested that NTIS adversely affects outcome, but there are limited data in children.

OBJECTIVE

Our objective was to determine the natural history of NTIS in children undergoing cardiac bypass surgery and to correlate these changes with outcome and illness severity.

METHODS

Thyroid function was measured in 21 patients, aged 1-11 yr, preoperatively and postoperatively twice daily on postoperative days (POD) 0-3 and daily thereafter until POD 7. Pediatric Logistic Organ Dysfunction and inotrope scores and pediatric intensive care unit, hospital, and ventilation days were measured and statistically analyzed in relation to thyroid function.

RESULTS

All patients exhibited NTIS within the first day postoperatively. TSH recovered by POD 4. Total T(3), free T(3) index, and T(3) uptake were still below preoperative levels on POD 7. NTIS changes correlated to prolonged hospital stays with increased pediatric intensive care unit and mechanical ventilation days and also showed strong relations with Pediatric Logistic Organ Dysfunction and inotrope scores. The T(3) measures drawn within 6-14 h from surgery were predictive of clinical outcome. Alterations in illness severity preceded changes in thyroid function.

CONCLUSION

NTIS was present in this population of critically ill children with some of the biochemical changes not corrected by 8 d postoperatively. The degree of NTIS was related to and predictive of clinical outcome and illness severity.

Advance in the relationship between thyroid function and liver diseases

Numerous researches have showed that thyroid diseases affect liver function and progression of liver diseases; conversely, liver diseases, especially severe liver disease, can also affect thyroid function. Thyroid function may have changes in patients with chronic viral hepatitis treated with interferon. So physicians should pay more attention to the relationship between thyroid and liver diseases during the course of diagnosis and treatment.

Identification of molecular mechanisms related to nonthyroidal illness syndrome in skeletal muscle and adipose tissue from patients with septic shock

OBJECTIVE

Septic shock is one of various causes of nonthyroidal illness syndrome (NTIS). In humans, the molecular mechanisms involved in NTIS are mostly unknown. The aim of this study was to investigate, in patients with NTIS secondary to septic shock, changes in the expression of genes involved in the actions of thyroid hormones and in the activity of deiodinase enzymes, in two tissues important for protein and energy metabolism, skeletal muscle (SM) and subcutaneous adipose tissue (SAT).

DESIGN

Hospitalized patients were divided into a control and a septic shock NTIS group.

MEASUREMENT

Serum collection for biochemical measurements, and SM and SAT biopsies for mRNA expression analysis of thyroid hormone receptors (THRB1, THRA1), retinoid X receptors (RXRA, RXRB, RXRG), nuclear receptor corepressor (NCOR1), silencing mediator of retinoid and thyroid hormone receptor (SMRT), steroid receptor coactivator (SRC1), type 1 and 2 deiodinases (D1, D2), monocarboxylate transporter 8 (MCT8), SECIS binding protein 2 (SBP2) and uncoupling protein 3 (UCP3) as well as D1, D2 and D3 enzyme activity measurements.

RESULTS

The NTIS group had lower serum TSH, and free T3 and higher rT3 than controls. D1 and D3 were detected in SAT, with no differences found between the two groups; SM had very low D2 activity and again no differences were found between groups; D3 activity in SM was higher in NTIS than controls. SM expression of THRB1, RXRG and D2 was lower and RXRA higher in NTIS than controls. SAT from NTIS patients had lower MCT8, THRB1, THRA1, RXRG and SMRT, and higher UCP3 expression than controls.

CONCLUSIONS

In patients with septic shock NTIS tissue responses are orientated to decrease production and increase degradation (muscle) or decrease uptake (adipose tissue) of T3, as well as to decrease thyroid hormone actions.

Low triiodothyronine serum levels as a predictor of poor prognosis in burn patients

OBJECTIVE

Euthyroid sick syndrome is a common finding in critically ill patients with nonthyroidal illness, characterized by low serum levels of free triiodothyronine (fT3) with a peculiar increase in reverse T3 (rT3) and normal-to-low free thyroxine (fT4) as well as thyroid-stimulating hormone (TSH) levels. This condition has been proposed as a prognostic factor of worse outcome in critically ill patients, while no conclusive data are available in burns.

METHODS

Since thyroid function testing is contained in our baseline laboratory tests at admission, we retrospectively evaluated fT3, fT4 and TSH in 295 consecutive burn patients admitted to the Burn Center of Turin from January 2002 to December 2006, comparing hormone levels in survivors and non-survivors.

RESULTS

fT3 and TSH levels were significantly lower (p<or=0.0002) in non-survivors compared to survivors, while no significant difference between the two populations was found in fT4 concentrations. Excluding from the study 20 patients who received dopamine administration for more than 21h, serum fT3 levels fell further still (p=0.0003). In addition, fT3 concentrations showed a significant correlation with burn severity expressed by the Roi score (Spearman's correlation coefficient -0.37 with p<0.00001).

CONCLUSION

Low fT3 levels are associated with poor outcome in burn patients. Hence, fT3 measurement could be proposed as a strong and cost-effective tool of poor prognosis.

Metabolism modulators in sepsis: the abnormal pituitary response

OBJECTIVE

Summarize the current knowledge on the role of the hypothalamic pituitary axis in the development of sepsis.

DESIGN

Review article.

METHOD

We systematically searched for relevant articles in MEDLINE and Embase (up to December 2006) using the following search terms: sepsis or septic shock or septicemia or endotoxemia and pituitary gland or hypothalamus. We also retrieved relevant references from selected articles.

RESULTS

During sepsis, the pituitary gland is activated via blood-borne proinflammatory cytokines and through a complex interaction between the autonomic nervous system and the immune cells. Sepsis elicits a very reproducible pattern of pituitary hormone secretion, with plasma adrenocorticotropin and prolactin increasing within a few minutes following the insult, and with a rapid inhibition of secretion of luteinizing and thyroid-stimulatory hormone but not of follicle-stimulating hormone. Growth hormone secretion also is stimulated. Nitric oxide is a key mediator in the activation of the hypothalamic-pituitary axis and in excess nitric oxide is the main factor accounting for abnormal pituitary response. Low adrenocorticotropin and vasopressin levels are likely the most deleterious consequences of the abnormal pituitary response, because they will contribute to shock and progression of inflammation with subsequent multiple organ failure and death.

CONCLUSIONS

Sepsis is associated with major changes in the hypothalamic-pituitary axis. The manipulation of the pituitary function during sepsis is a major challenge for the next decade.

The nonthyroidal illness syndrome

This article briefly summarizes thyroid function alterations generally seen in the euthyroid sick syndrome, provides an overview of specific thyroidal adaptations during several clinical conditions and secondary to specific pharmacologic agents, and discusses the current controversy in thyroid hormone treatment of nonthyroidal illness.

Non thyroidal illness: to treat or not to treat?

In critically ill patients, pronounced alterations in the hypothalamic-pituitary-thyroid axis occur without any evidence for thyroid disease. T3 decreases and rT3 increases within a few hours of the onset of disease. Severity and duration of disease are related to the magnitude of these changes. This manuscript discusses whether these changes in thyroid hormone levels during critical illness should be treated, and was in part published elsewhere.

Low triiodothyronine: a strong predictor of outcome in acute stroke patients

BACKGROUND

Low triiodothyronine (T3) has been associated with increased short-term mortality in intensive care unit patients and long-term mortality in patients with heart disease. The objective of this study was to investigate possible associations of thyroid hormone status with clinical outcome in patients admitted for acute stroke.

MATERIALS AND METHODS

A total of 737 consecutive patients with acute first ever stroke who presented within 24 h from symptoms' onset were studied. Total T3, thyroxin (T4) and thyroid-stimulating hormone (TSH) levels were assessed in the morning following admission. Cases with T3 values < or = 78 ng dL(-1) (1.2 nmol L(-1)) (median) were characterized as 'low T3'. Cases with T4 values < or = 4.66 microg dL(-1) (60 nmol L(-1)) were characterized as 'low T4'. Basic and clinical characteristics, stroke risk factors, and brain imaging were evaluated. Neurological impairment was assessed using the Scandinavian Stroke Scale.

RESULTS

Four hundred and seventeen (56%) patients had T3 values < or = 78 ng dL(-1) and 320 had normal T3 values. The 1-year mortality was 27.34% for low T3 and 19.37% for normal T3 cases (P = 0.006). A smaller percentage of patients with low T3 values were independent at 1 year compared to those with normal T3 values [54.2% vs. 68.7%, chi(2) = 12.09, P < 0.001, odds ratio (OR) = 0.53, 95% confidence interval (CI) 0.37-0.76]. Cox regression analysis revealed that increased age, haemorrhagic stroke, low Scandinavian Stroke Scale score, increased glucose and low T3 values (hazards ratio 0.69, CI = 0.48-0.98, P = 0.041) were significant predictors of 1-year mortality.

CONCLUSIONS

A high proportion of patients with acute stroke were found soon after the event with low T3 values. The low-T3 syndrome is an independent predictor of early and late survival in patients with acute stroke, and predicts handicap at 1 year.

Toll-like receptor-MyD88 and Fc receptor pathways of mast cells mediate the thyroid dysfunctions observed during nonthyroidal illness

Bacterial infections and other pathologic conditions induce complex dysfunctions of the hypothalamic-pituitary-thyroid axis, collectively known as nonthyroidal illness (NTI). To explore the pathogenesis of bacterial NTI, we injected Mycobacterium tuberculosis extracts or Escherichia coli LPS in mice lacking key components of the Toll-like receptor or crystallizable fragment (Fc) receptor pathways. In wild-type mice, the bacterial components induced a hypothyroidism characterized by elements of both hypothalamic and thyroidal dysfunction. This NTI hypothyroidism did not develop in mice lacking the MyD88 adaptor or in those with a reduced number of mast cells. The hypothyroid responsiveness to LPS, however, was restored upon reconstitution with mast cells derived from the bone marrow of wild-type donors. In addition to bacterial components, whole immunoglobulins induced NTI hypothyroidism in wild-type mice, but not in those lacking activating Fc receptors or mast cells. The study demonstrates a link between Toll-like and Fc receptor signaling and thyroid gland function, uncovering a role of mast cells in murine NTI.

Endocrine modifications and interventions during critical illness

The ongoing hypermetabolic response in patients with prolonged critical illness leads to the loss of lean tissue mass. Since the cachexia of prolonged illness is usually associated with low concentrations of anabolic hormones, hormonal intervention has been thought to be beneficial. However, most interventions have been shown to be ineffective and their indiscriminate use even causes harm. Before considering endocrine intervention in these frail patients, a detailed understanding of the neuroendocrinology of the stress response is warranted. It is now clear that the acute phase and the later phase of critical illness behave differently from an endocrinological point of view. The acute stress reponse consists primarily of an actively-secreting pituitary in the presence of low circulating peripheral anabolic hormones, suggesting resistance of the peripheral tissues to the effects of anterior pituitary hormones. However, when the disease process becomes prolonged, there is a uniformly-reduced pulsatile secretion of anterior pituitary hormones with proportionally reduced concentrations of peripheral anabolic hormones. The origin of this suppressed pituitary secretion is located in the hypothalamus, as hypothalamic secretagogues can reactivate the anterior pituitary and restore pulsatile secretion. The reactivated pituitary secretion is accompanied by an increase in peripheral target hormones, indicating at least partial sensitivity of these tissues to anterior pituitary hormones in this chronic phase of illness. Thus, endocrine intervention with a combination of hypothalamic secretagogues that more completely reactivate the anterior pituitary could be a more physiological and effective strategy for inducing anabolism in patients with prolonged critical illness.

The dynamic neuroendocrine response to critical illness

The severity of striking alterations in the hypothalamic-anterior pituitary-peripheral hormone axes, which are the hallmark of severity of critical illness, is associated with a high risk for morbidity and mortality. Most attempts to correct the hormone balance are ineffective or harmful because of lack of pathophysiologic understanding. Extensive research has provided more insight in the biphasic neuroendocrine response to critical illness: the acute phase is characterized by an actively secreting pituitary but low peripheral effector hormone levels. In contrast, in prolonged critical illness, uniform suppression of the neuroendocrine axes, predominantly of hypothalamic origin, contributes to low serum levels of the respective target-organ hormones.

Endocrine aspects of acute and prolonged critical illness

Critical illness is characterized by striking alterations in the hypothalamic-anterior-pituitary-peripheral-hormone axes, the severity of which is associated with a high risk of morbidity and mortality. Most attempts to correct hormone balance have been shown ineffective or even harmful because of a lack of pathophysiologic insight. There is a biphasic (neuro)endocrine response to critical illness. The acute phase is characterized by an actively secreting pituitary, but the concentrations of most peripheral effector hormones are low, partly due to the development of target-organ resistance. In contrast, in prolonged critical illness, uniform (predominantly hypothalamic) suppression of the (neuro)endocrine axes contributes to the low serum levels of the respective target-organ hormones. The adaptations in the acute phase are considered to be beneficial for short-term survival. In the chronic phase, however, the observed (neuro)endocrine alterations appear to contribute to the general wasting syndrome. With the exception of intensive insulin therapy, and perhaps hydrocortisone administration for a subgroup of patients, no hormonal intervention has proven to beneficially affect outcome. The combined administration of hypothalamic releasing factors does, however, hold promise as a safe therapy to reverse the (neuro)endocrine and metabolic abnormalities of prolonged critical illness by concomitant reactivation of the different anterior-pituitary axes.

DHEAS levels and mortality in disabled older women: the Women's Health and Aging Study I

BACKGROUND

Dehydroepiandrosterone sulfate (DHEAS) is an endogenously produced sex steroid that has been hypothesized to have anti-aging effects. Low DHEAS levels are associated with mortality in older men, but the relationship between DHEAS levels and mortality in women is not clearly defined.

METHODS

The relationship between serum DHEAS level and 5-year mortality was analyzed in a cohort of 539 disabled women aged 65-100 years enrolled in the Women's Health and Aging Study I (WHAS I). Using Cox proportional hazard models, we calculated multivariate-adjusted mortality risks by DHEAS quartiles and by DHEAS continuously, allowing for a nonlinear relationship. We also examined cause-specific mortality.

RESULTS

We found a U-shaped relationship between DHEAS level and mortality. After adjusting for multiple covariates, women in the top and bottom DHEAS quartiles had a more than 2-fold higher 5-year mortality than did those in the middle quartiles (hazard ratio, 2.15; 95% confidence interval [CI], 1.17-3.98 for the top quartile and 2.05; 95% CI, 1.27-3.32 for the bottom quartile, each compared to the third quartile). Women with higher DHEAS levels tended to have greater cancer mortality, whereas those with lower DHEAS tended to have greater cardiovascular mortality.

CONCLUSION

Disabled older women with either low or high levels of DHEAS are at greater risk for death than are those with intermediate levels. More research is needed to determine if targeted dehydroepiandrosterone supplementation would provide clinical benefit to disabled older women.

The Neuroendocrine Response to Critical Illness is a Dynamic Process

Striking alterations in the hypothalamic-anterior pituitary-peripheral hormone axes hallmark the state of critical illness, their severity being associated with high risk for morbidity and mortality. Early endocrine intervention strategies aimed to correct the hormone balance have been shown ineffective or even harmful because of lack of thorough pathophysiologic understanding of these neuroendocrine changes. Extensive research, however, has provided crucial insights, with the demonstration of the biphasic response of the anterior pituitary to the severe stress of critical illness.

Hypothalamic-pituitary dysfunction in critically ill patients with traumatic and nontraumatic brain injury

BACKGROUND

A significant number of studies have shown that critically ill patients with brain injury (BI) frequently exhibit abnormal pituitary hormonal responses during the immediate postinjury period.

DISCUSSION

The elucidation of endocrine alterations depends on the criteria used, the diagnostic tests applied, and the timing of testing in relation to BI. The pattern of the detected hormonal abnormalities shows considerable variability. Altered endocrine responses are due mostly to hypothalamic changes rather than to pituitary dysfunction. Several studies have examined the correlation between hormonal alterations and BI severity, but the results are inconsistent. Furthermore, it remains currently unclear whether and how pituitary abnormalities adversely affect the clinical course of BI patients during the period of critical illness. On the basis of current knowledge, with the exception of clinically significant relative adrenal deficiency and diabetes insipidus, the other endocrine alterations do not seem to require any therapeutic intervention in severely ill BI patients. It is also uncertain whether hormonal abnormalities detected in the early post-BI period persist for the rest of these patients' lives.

CONCLUSIONS

In view of current evidence indicating a high incidence of pituitary dysfunction even years following BI it is recommended that repetition of endocrine evaluation should be performed during the rehabilitation phase in all patients.

Malnutrition and nonthyroidal illness syndrome after stroke

In the present study, nonthyroidal illness syndrome (NTIS), which is characterized by reduction of serum triiodothyronine (T3) without elevation of thyroid-stimulating hormone (TSH), was induced by protein-energy malnutrition (PCM). Protein-energy malnutrition is a common condition and is associated with worse clinical outcome in stroke patients admitted to a rehabilitation service. However, little is known about NTIS in stroke patients. Therefore, we studied the effects of PCM and NTIS on functional dependence in 51 stroke patients. We examined thyroid function by measuring serum free T3 (free T3), free thyroxine (free T4), and TSH. We estimated whether patients had mild NTIS (reduction of only free T3) or serious NTIS (reduction of both free T3 and free T4), examined PCM by measuring serum albumin, calculated body mass index (BMI) from weight and height on admission, and examined disability by obtaining the functional independence measurement (FIM). The 51 patients were divided into 2 groups according to FIM score on admission (low and high). The low-FIM group was divided into 2 subgroups according to the change in FIM score during hospitalization (improved or non-improved). Hypoalbuminemia was observed in 57% of patients, underweight in 22%, and mild NTIS in 82%; serious NTIS was not observed in any patients. Albumin and BMI were significantly higher in the high-FIM group than in the low-FIM group. Serum albumin concentration and BMI significantly positively correlated with free T3. Free T3 (but not albumin or BMI) was significantly higher in the improved subgroup than in the non-improved subgroup. Nonthyroidal illness syndrome after stroke was common and was provoked by PCM, which occurred in a high proportion of functionally dependent patients. It appears that, once stroke patients develop NTIS, it is difficult to achieve functional improvement. Therefore, during the recovery period after stroke, it is important to determine whether NTIS is present and ensure proper intensive rehabilitation and nutritional management.

PROLACTIN SECRETION IN HYPOTHYROID ENDOTOXEMIC RATS: INVOLVEMENT OF L-ARGININE AND NITRIC OXIDE SYNTHASE

The identification of nitric oxide (NO) within the hypothalamus and pituitary gland has suggested its role as modulator of the activity on hypothalamic-pituitary axis. Hypothalamic NO synthase (NOS) is known to be regulated by thyroid hormones. We investigated the effects of previous injection of N-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, and L-arginine (L-Arg), the substrate for NO synthesis, on prolactin (PRL) secretion, through the lipopolysaccharide (LPS)-induced inflammatory response in thyroidectomized (TX) rats. TX or sham-operated (N) rats were intraperitoneally (i.p.) injected with L-NAME (10 mg kg) or L-Arg (200 mg kg) or the same volume of vehicle (saline solution) 30 min before endotoxemia-induction with LPS at 250 mug (100 g body weight), i.p.. In N rats, NO increased PRL release in response to endotoxemia, whereas in hypothyroid rats, NO appeared to have the opposite effect. Our data support the hypothesis that NO exerts a modulatory influence on PRL secretion after LPS-induced inflammatory response.