A mathematical model of the hypothalamic-pituitary-adrenal (HPA) axis of the human endocrine system is proposed. This new model provides an improvement over previous models by introducing two nonlinear factors with physiological relevance: 1) a limit to gland size; 2) rejection of negative hormone concentrations. The result is that the new model is by far the most robust; e.g., it can tolerate at least -50% and +100% perturbations to any of its parameters. This high degree of robustness allows one, for the first time, to model features of the system such as circadian rhythm and response to hormone injections. In addition, relative to its closest predecessor, the model is simpler; it contains only about half of the parameters, and yet achieves more functions. The new model provides opportunities for teaching endocrinology within a biological or medical school context; it may also have applications in modeling and studying HPA axis disorders, for example, related to gland size dynamics, abnormal hormone levels, or stress influences.
Lysine-rich proteins are some of the most important proteins of neurons and it has become necessary to investigate the possible role of L-lysine as a brain functioning regulator. The purpose of our study is to identify the characteristics and the mechanisms of L-lysine effects on the different types of pain-induced behavior in the stimulation of tail and foot-shock models in 210 adult male Wistar rats. L-lysine was administered in intraperitoneal or intracerebroventricular injections in doses of 0.15–50.0 µg/kg. When a tail is irritated, L-lysine was found to enhance pain sensitivity and affective defense after both intraperitoneal and intracerebroventricular administration. In the case of unavoidable painful irritation of a pair of rats with both types of L-lysine administration, there was no direct correlation of the severity of pain with defensive reactions and outbursts of aggression. This indicates a more complex integration of the activity of brain structures in this situation of animal interaction, which was confirmed by the results of the direct amino acid action on the periventricular brain structures. Our findings show that L-lysine influences the selective brain activity in dependence on the biological significance of pain-induced behavior.
Surfagon, a synthetic analog of gonadotropin-releasing hormone injected before emotional painful stress dose-dependently changed the number of antibody-producing cells in rats and phagocytic and functional activities of neutrophils in mice. In castrated animals this peptide increased all studied parameters. This suggests that sex steroids are not involved in the realization of these effects.
We studied the effect of Gly-His -Lys tripeptide administered intraperitoneally in doses of 5, 15, 50 and 150 μg/kg on pain-induced aggressive-defensive behavior. A foot-shock model of aggression in rats grouped in pairs in an electrified chamber was used. Analgesic and antiaggresiogenic effects of the peptide were demonstrated. It was found the L-lysine residue plays the key role in these effects, because they were observed under the influence of L-lysine administration in doses close to its equimolar content in the studied tripeptide.
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