ABSTRACT
The production of tumor necrosis factor (TNF)-alpha is a key step in the response to sepsis and has powerful local and systemic effects on the host. These systemic responses include a complex cascade of centrally mediated endocrine and neural responses. An integrative model of these regulatory cytokine-neuroendocrine interactions in humans is presented. The rapid kinetics of these responses are illustrated by data showing the response of normal human subjects to experimental endotoxemia. Appreciation of the integrative biology of the in vivo response to experimental endotoxemia can provide a framework for the design of experiments aimed at examining the effects of physical training paradigms on particular cytokine and neuroendocrine pathways.
Subject(s)
Cytokines/metabolism , Hormones/metabolism , Lipopolysaccharides/pharmacology , Sepsis/physiopathology , Tumor Necrosis Factor-alpha/physiology , Adrenocorticotropic Hormone/drug effects , Adrenocorticotropic Hormone/metabolism , Dehydroepiandrosterone/metabolism , Humans , Hydrocortisone/metabolism , Infusions, Intravenous , Models, Biological , Norepinephrine/metabolism , Receptors, Cytokine/metabolism , Receptors, Tumor Necrosis Factor/metabolism , Time Factors , Tumor Necrosis Factor-alpha/drug effectsABSTRACT
Normal human blood BFU-E are believed to be in a quiescent state with respect to DNA synthesis, since few or none of these progenitors can be killed by cycle-active agents. Using Percoll discontinuous density gradient centrifugation of normal human blood mononuclear cells, we have separated two subpopulations of BFU-E with different proportions in DNA synthesis. Mononuclear cells were obtained with Ficoll-Isopaque from 24 samples of normal blood. BFU-E were assayed with the methylcellulose technique, and their proliferative state was studied with the hydroxyurea (HU) suicide method. The results obtained with a five-step gradient of density range 1.060-1.068 g/ml showed that the vast majority of BFU-E were distributed approximately equally between pooled fractions with rho = 1.060 + 1.062 g/ml and those with rho = 1.064 + 1.066 g/ml. Among nonseparated cells or cells in the fraction of rho = 1.060 + 1.062 g/ml, we failed to detect a significant proportion of DNA-synthesizing BFU-E in the great majority of samples. In contrast, in the pooled fractions with rho = 1.064 + 1.066 g/ml, 14 of 24 samples showed significant kill, and among these 14, a highly significant proportion of BFU-E were killed by HU (39.3% +/- 3.4%). Therefore, the separation of mononuclear cells on the basis of their different buoyant densities revealed the presence of DNA-synthesizing BFU-E in normal human blood. Either DNA-synthesizing BFU-E have a higher buoyant density than non-DNA-synthesizing BFU-E, or else cells of lower buoyant density normally inhibit DNA synthesis in BFU-E.
