Homeostatic regulation

Bde salts, cholesterol, phosphoHpids, and other minor components are secreted by the Hver. Bile salts serve three significant physiological functions. The hydrophilic carboxylate group, which is attached via an alkyl chain to the hydrophobic steroid skeleton, allows the bile salts to form water-soluble micelles with cholesterol and phosphoHpids in the bile. These micelles assist in the solvation of cholesterol. By solvating cholesterol, bile salts contribute to the homeostatic regulation of the amount of cholesterol in the whole body. Bile salts are also necessary for the intestinal absorption of dietary fats and fat-soluble vitamins (24—26). 

Homeostatic regulation of metabolic efficiency (i.e., caloric intake required to maintain body weight constant to maintain constant ratios of energy expenditure/ conservation). 

Gvilia, I., Turner, A., McGinty, D Szymusiak, R. (2006). Preoptic area neurons and the homeostatic regulation of rapid eye movement sleep. J. Neurosci. 26, 3037-44. 

Subsequent work by our laboratory and others has shown that adenosine accumulation in the basal forebrain is particularly important in this homeostatic regulation (Strecker et ah, 2000 Basheer et ah, 2004). 

After a careful review of the literature, we found evidence that the PH also plays a role in PS regulation. First, despite the fact that a PS-like state still occurred in pontine cats , showing that the brainstem was sufficient to produce PS, PS recovery following PS deprivation was abolished in these animals (Jouvet, 1988). These results suggest that the brainstem contains the structures responsible for PS but not those responsible for its homeostatic regulation. In support of these observations, several studies reported that a small proportion of the neurons recorded in the PH are specifically active during PS (Alam et al., 2002 Koyama et al., 2003 Steininger et al., 1999). Recent data summarized below confirm that the PH contains populations of neurons involved in PS control. 

Thakkar, M. M., Winston, S. McCarley, R. W. (2003b). Al receptor and adenosinergic homeostatic regulation of sleep-wakefulness effects of antisense to the Al receptor in the cholinergic basal forebrain. J. Neurosci. 23, 4278-87. 

Franken, P., Chollet, D. Tafti, M. (2001). The homeostatic regulation of sleep need is under genetic control. J. Neurosci 21 (8), 2610-21. 

Hayaishi, O., et al. (2004). Genes for prostaglandin D synthase and receptor as well as adenosine A2A receptor are involved in the homeostatic regulation of mem sleep. Arch. Ital. Biol 142, 533-9. 

Fabre, V., Boutrel, B., Hanoun, N. el al. (2000). Homeostatic regulation of serotonergic function by the serotonin transporter as revealed by nonviral gene transfer. J. Neurosci 20, 5065-75. 

The second constellation of narcoleptic symptoms can be summarized under the rubric of excessive daytime sleepiness, or an inability to regulate wakefulness. As recently reviewed by Mochizuki et al. (2004), at least four explanations have to date been proposed for this sleepiness a deficit in arousal, an impaired circadian alertness signal, abnormal homeostatic regulation of non-REM sleep, and excessive vigilance state fragmentation. These mechanisms are not mutually exclusive, and there are possible roles for orexin signaling in each of them, as we review in the following sections. 

Nickel is considered essential to animals because it is present in the fetus or newborn, is homeostatically regulated, the metabolic pool of nickel is specifically influenced by hormonal substances or pathologic processes, certain metalloproteins contain nickel, and because nickel deficiency has been induced experimentally in certain species of birds and animals (NAS 1975 USPHS 1977 Kirchgessner and Schnegg 1980). In general, the nickel deficiency syndrome can be cured or prevented by trace amounts of nickel (NAS 1975). However, nickel administration may not be successful in reversing all abnormalities produced by nickel deprivation (USPHS 1977). 

Dysregulation hypothesis. This theory emphasizes a failure of homeostatic regulation of neurotransmitter systems, rather than absolute increases or decreases in their activities. Effective antidepressants are theorized to restore efficient regulation to these systems. 

Gonzalez-Flecha, B. Demple, B. Homeostatic regulation of intracellular hydrogen peroxide concentration in aerobically growing Escherichia coli. J. Bacteriol. 1997, 179, 382-388. 

More research is needed on the accurate measurement of boron in biological materials when the concentrations are <1.0 mg B/kg (Sullivan and Culver 1998). Standard biological reference materials with low boron levels need to be produced for use in interlaboratory comparisons. This becomes especially important in studies on boron-deficiency states and the ability of the organism to conserve boron at very low intakes (Sullivan and Culver 1998). More research is needed on homeostatic regulation of boron and functional markers of boron metabolism (Sutherland et al. 1998). Sullivan and Culver (1998) recommend additional studies to establish ... 

Homeostatic regulation of body temperature is mediated in part by the action of endogenous opioid peptides in the brain. This has been supported by experiments demonstrating that administration of -opioid receptor agonists such as morphine administered to the anterior hypothalamus produces hyperthermia, whereas administration of agonists induces hypothermia. 

Fridlyand, L.E. Scheibe R. (1999) Homeostatic regulation upon changes of enzyme activities in the Calvin cycle as an example for general mechanisms of flux control what can we expect from transgenic plants Photosynth. Res. 61, 227-239. 

When one refers to biological regulations, one usually thinks of homeostatic regulations, that is, regulations that tend to maintain the level of variables in the vicinity of a supposedly optimal value, usually well below the level that would be reached if the system operated at its maximal rate. I shall discuss these mechanisms in Section I.D. Note that this homeostatic type of regulation operates essentially like a thermostat in practice, even where the objective is constancy, the system usually oscillates around the chosen value because this regulation proceeds by alternate upward and downward corrections. 

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