Early alterations in thyroid hormone physiology during acute infection in man

Human Dose-Response Data for Francisella tularensis and a Dose- and Time-Dependent Mathematical Model of Early-Phase Fever Associated with Tularemia After Inhalation Exposure

Military health risk assessors, medical planners, operational planners, and defense system developers require knowledge of human responses to doses of biothreat agents to support force health protection and chemical, biological, radiological, nuclear (CBRN) defense missions. This article reviews extensive data from 118 human volunteers administered aerosols of the bacterial agent Francisella tularensis, strain Schu S4, which causes tularemia. The data set includes incidence of early-phase febrile illness following administration of well-characterized inhaled doses of F. tularensis. Supplemental data on human body temperature profiles over time available from de-identified case reports is also presented. A unified, logically consistent model of early-phase febrile illness is described as a lognormal dose-response function for febrile illness linked with a stochastic time profile of fever. Three parameters are estimated from the human data to describe the time profile: incubation period or onset time for fever; rise time of fever; and near-maximum body temperature. Inhaled dose-dependence and variability are characterized for each of the three parameters. These parameters enable a stochastic model for the response of an exposed population through incorporation of individual-by-individual variability by drawing random samples from the statistical distributions of these three parameters for each individual. This model provides risk assessors and medical decisionmakers reliable representations of the predicted health impacts of early-phase febrile illness for as long as one week after aerosol exposures of human populations to F. tularensis.

The interpretation of the serum protein-bound iodine: A review

The effects of physiological and environmental factors, of thyroid and non-thyroid diseases, and of drugs on the serum protein-bound iodine are described and discussed.

Endocrine regulation of the immune system

Immunoregulation, the major process of self-defence, appears to be more complex than has been previously thought, involving the central nervous and endocrine systems. This review demonstrates growing evidence for the hypothesis that endocrine factors from the pituitary and hypothalamus directly influence the development and function of the immune system. Both pituitary and hypothalamic hormones interfere with lymphocyte proliferation and function. Proliferation of T-lymphocytes as well as production of immunoglobulins by plasma cells seem to be hormone dependent. Clinical observations suggest that hematological, oncological, and immunological disorders known for their immune pathogenesis are associated with alterations of the endocrine homeostasis. Recently, human peripheral mononuclear cells have been shown to possess specific receptors for pituitary hormones. It is hypothesized that proteohormones act directly on lymphocytes via specific membrane receptors. Thus, the endocrine system, closely related to cortical and subcortical centers in the central nervous system, is one of the body's instruments to regulate and modulate its immune response. This hypothesized immunoregulatory pathway via the central nervous system and endocrine glands may well be of importance for the body's defence against infectious and malignant diseases. In addition, a new picture of the complex immunoregulatory mechanisms emerges for a better understanding of the function of the immune system. However, there is no single hormone which has yet been identified as being crucial for development and/or function of the immune system. It appears from the literature that a number of various proteohormones rather than a single hormone acts on immunocompetent cells.

The inter-relationship of thyroid hormones, vitamin A and their binding proteins following acute stress

The effects of surgical stress on the metabolism of the retinol-binding-protein-thyroxine-binding-prealbumin complex were investigated. The immediate postsurgical period was characterized by a rapid decline in the serum concentration of retinol, retinol binding protein and triiodothyronine and an increase in the 24 h urinary excretion of retinol, retinol-binding-protein and thyroxine. Similar, but less pronounced, changes were seen in other subjects suffering acute myocardial infarction but were not observed in normal healthy euthyroid males or in pre-operative euthyroid patients. The preparation of specific anti-retinol binding protein anti-serum and the use of this in 'monorocket' immunoelectrophoresis are also described.

Accelerated cellular uptake and metabolism of L-thyroxine during acute Salmonella typhimurium sepsis

The effects of acute Salmonella typhimurium sepsis on the kinetics of peripheral L-thyroxine (T(4)) distribution and metabolism and on serum total and free T(4) concentrations were studied in rhesus monkeys inoculated i.v. with either heat-killed or viable organisms. The rate of disappearance of labeled T(4) from serum was increased within 8 h after inoculation of monkeys with either heat-killed or viable Salmonella. The effects of the heat-killed organisms were transient and no longer evident by 16 h postinoculation. The monkeys inoculated with the viable Salmonella experienced a 2-3 day febrile, septic illness that was accompanied by an increase in the absolute rate of T(4) disposal. In the infected monkeys, serum total T(4) and endogenously labeled protein-bound iodine concentrations fell significantly during the period of acute sepsis and then rose during convalescence to values that exceeded the preinoculation values, suggesting that thyroidal secretion of hormone had increased in response to a primary depletion of the peripheral hormonal pool. Total cellular and hepatic uptakes of T(4) were enhanced by 4 h after inoculation of monkeys with either heat-killed or viable Salmonella, but the increase in total cellular uptake persisted for 24 h only in the monkeys inoculated with the viable organisms. These alterations in T(4) kinetics could neither be correlated with changes in the binding of T(4) in plasma nor attributed to an increase in vascular permeability. Moreover, they could not be ascribed to an in vitro product of bacterial growth, suggesting that the presence of the organisms themselves was required. An acceleration of T(4) disappearance was also observed during Escherichia coli and Diplococcus pucumoniae bacteremias. Our findings are consistent with a primary increase in the cellular uptake and metabolism of T(4) during bacterial sepsis, possibly related to phagocytic cell function in the host.

Alterations in thyroid iodine release and the peripheral metabolism of thyroxine during acute falciparum malaria in man

Previous studies of thyroid function during various infections have yielded conflicting results, but most have suggested an acceleration of peripheral thyroxine (T(4)) turnover during the acute infectious illness. In the present studies, thyroid function was examined by a method allowing simultaneous analysis of both endogenous thyroidal release and peripheral T(4) disposal in normal volunteers after induction of acute falciparum malaria. Subjects received iodide-(125)I, followed in 5-7 days by (131)I-T(4) intravenously. 4 days later, infection was induced by the injection of parasitized red blood cells. Bidaily measurements of serum protein-bound (125)I and protein-bound (131)I, and urinary (125)I and (131)I, together with frequent estimates of serum (127)I-T(4) (Murphy-Pattee) and free T(4) (FT(4)), were made during a control period, during acute illness, and during convalescence. Alterations in the peripheral metabolism of (131)I-T(4) during infection included significant decreases in the fractional disappearance rate for T(4) [(k)], and in the clearance and daily disposal of T(4), all of which returned to control values during convalescence. Total serum (127)I-T(4) increased late in the infected period to become greater during convalescence than either before or during infection, while FT(4) did not increase significantly until convalescence. An analysis of serum (131)I-T(4)/(127)I-T(4) and (131)I-T(4)/PB(125)I ratios confirmed these observations. The slope with time of ratios for urinary (125)I/(131)I, a reflection of thyroidal iodine release, was decreased during infection, but rebounded to control values during the convalescent period. The observed increments in serum (127)I-T(4) concentration in the convalescent phase may reflect in part the slowing of (k), but together with the rising ratios of urine (125)I/(131)I suggests enhanced thyroidal T(4) secretion immediately after the acute illness. Thus, with malarial infection, there appears to be an initial depression followed by a rebound in rates of thyroidal iodine release. In contradistinction to other infections, fractional turnover and daily disposal of hormone is decreased in malaria, perhaps due to hepatic dysfunction and the consequent impairment in cellular deiodinative processes.