System hormonal regulation

Among vertebrate species, the neuro-endocrine-immime system is responsible for many complex, inter-related physiological processes including neuronal, homeostatic, reproductive and immune functions. There are four main types of hormone polypeptides, eicosanoids, steroids and thyroid hormones. Reflecting the inter-dependency of the neiiro-endocrine and immune systems, hormones, neuropeptides and other neiirotransmitters are known to be produced by some immune cells and play a role in the regulation of the immune system, while endocrine and nervous tissues express receptors for many substances produced by the immune system. The major focus of interest in endocrine disruption has... 

Aldosterone A hormone produced in and secreted by the zona glomerulosa of the adrenal cortex. Aldosterone acts on the kidneys to reabsorb sodium and excrete potassium. It is also a part of the renin-angiotensin-aldosterone system, which regulates blood pressure and blood volume. 

Abstract Pheromones are utilized by many insects in a complex chemical communication system. This review will look at the biosynthesis of sex and aggregation pheromones in the model insects, moths, flies, cockroaches, and beetles. The biosynthetic pathways involve altered pathways of normal metabolism of fatty acids and isoprenoids. Endocrine regulation of the biosynthetic pathways will also be reviewed for the model insects. A neuropeptide named pheromone biosynthesis activating neuropeptide regulates sex pheromone biosynthesis in moths. Juvenile hormone regulates pheromone production in the beetles and cockroaches, while 20-hydroxyecdysone regulates pheromone production in the flies. 

Independently, if these cytokines can exert their bone resorption functions without RANKL, they all stimulate the production of RANKL for stromal/OB cells, and conversely RANKL is able to increase IL-1 and TNF-a synthesis in vitro. To complicate this scenario, these systems of cytokines connect with the network of systemic hormones, such as PTH, PTH-related protein (PTHrP), vitamin D3, estrogens, androgens, glucocorticoids, and T4, since the hormones regulate the production of many of these cytokines by stromal/OB cells (Manolagas et al. 1995 Bellido et al. 1995 Lakatos et al. 1997). 

Each hormone is the center of a hormonal regulation system. Specialized glandular cells synthesize the hormone from precursors, store it in many cases, and release it into the bloodstream when needed (biosynthesis). For transport, the poorly water-soluble lipophilic hormones are bound to plasma proteins known as hormone carriers. To stop the effects of the hormone again, it is inactivated by enzymatic reactions, most of which take place in the liver (metabolism). Finally, the hormone and its metabolites are expelled via the excretory system, usually in the kidney (excretion). All of these processes affect the concentration of the hormone and thus contribute to regulation of the hormonal signal. 

Ubiquitin System-Dependent Regulation of Growth Hormone Receptor Signal Transduction and Effects of Oxidative Stress... 

Figure 8-6. Hormonal regulation of cholesterol synthesis by reversible phosphorylation of HMG CoA reductase. Availability of mevalonic acid as the fundamental building block of the sterol ring system controls flux through the pathway that follows. cAMP, cyclic adenosine monophosphate HMG CoA, hydroxymethylglutary I CoA.

Current theories suggest that hypersecretion of cortisol during stress may damage the hippocampus. Studies have demonstrated reduced hippocampal volume in trauma survivors with PTSD, compared to nontrauma tized individuals (Sapolsky, 2000 Bremner, 2001). However, hormonally regulated plasticity in the hippocampus involves multiple influences, and glucocorticoid hormones work in concert with excitatory amino acids and N-methyl-D-aspartate (NMDA) receptors, as well as other neurotransmitters and the GABA-benzodiazepine system (see McEwen, 2000a,b, for review). 

The biosynthesis and secretion of a hormone is regulated by a number of mechanisms and they themselves are involved in complex regulatory schemes. An informative example is the hierarchically ordered hypothalamus-hypophysis system which regulates the biosynthesis and secretion of many hormones of the nuclear receptors. 

The chaperones are used as tools in this system for regulation of activity of the steroid hormone receptors. The function of the chaperones is obviously to fix the receptor in a conformation which allows high affinity binding to the hormone and the subsequent steps of specific DNA binding and transactivation. For the steroid hormone receptors this means that they must exist in functionally different conformations. It may be a function of the chaperones to stabilize the particular conformation optimal for hormone binding. 

Yamada, K. Noguchi, T. (1999) Nutrient and hormonal regulation of pyruvate kinase gene expression. Biochem J. 337, 1—11. Detailed review of recent work on the genes and proteins of this system and their regulation. 

Mammals are hardly unique in possessing hormonal signaling systems. Insects and nematode worms have highly developed systems for hormonal regulation, with fundamental mechanisms similar to those in mammals. Plants, too, use hormonal signals to coordinate the activities of their various tissues (Chapter 12). The study of hormone action is not as advanced in plants as in animals, but we do know that some mechanisms are shared. To illustrate the structural diversity and range of action of mammalian hormones, we consider representative examples of each major class listed in Table 23-1. 

Vitamin D. The term vitamin D refers to a group of seco-steroids that possess a common conjugated triene system of double bonds. Vitamin I), (10a) and vitamin D, (10b) are the best-known examples (Fig. 2). Vitamin D (10a) is found primarily in vertebrates, whereas vitamin 11 (10b) is found primarily in plants. The term vitamin is a misnomer. Vitamin I) is a prohormonc that is converted into physiologically active form, primarily 1.25-dihydroxy vitamin D3 (11), by successive hydroxylalions in the liver and kidney. This active form is part of a hormonal system that regulates calcium and phosphate metabolism in the target tissues. 

Fig. 1. Integrated scheme showing the metabolic systems of regulation operating in eu-ryhaline Crustacea (after ref. 9). Broken lines indicate an inhibitory action of the effector and the heavy lines indicate activation. Notice the key role played by glutamic dehydrogenase as well as the controls exerted on the reactions utilizing reducing equivalents. The cAMP concentration is higher in concentrated medium than in dilute medium. The hormone responsible for this effect is not yet identified. HMPS, hexoses monophosphate shunt.

Consequently, bone is a rather dynamic tissue that is constantly undergoing changes in mineral content and internal structure. The balance between bone resorption and formation is controlled by the complex interaction of local and systemic factors. In particular, several hormones regulate bone formation and help maintain adequate plasma calcium levels. The primary hormones involved in regulating bone mineral homeostasis are described below. 

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