Regulation, hormone synthesis

Many hormones influence the above processes only indirectly by regulating the synthesis and release of other hormones (hormonal hierarchy see p.372). 

A topical application of 10Q g of geranylbenzoquinone on pupae of Tenebrlo caused severe abnormalities and death. Although the exact mechanism of toxicity for (II) is not known, its similarity to the juvenile hormones suggests that (II) might be a powerful alkylator of enzymes regulating juvenile hormone synthesis. Compound (VI) was not as potent as (II), but previous reports of (VI) in Cordla alllodora (Boraglnaceae) indicate that... 

The thyroid gland also regulates its uptake of iodide and thyroid hormone synthesis by intrathyroidal mechanisms that are independent of TSH. These mechanisms are primarily related to the level of iodine in the blood. Large doses of iodine inhibit iodide organification (Wolff-Chaikoff block, see Figure 38-1). In certain disease states (eg, Hashimoto s thyroiditis), this can inhibit thyroid hormone synthesis and result in hypothyroidism. Hyperthyroidism can result from the loss of the Wolff-Chaikoff block in susceptible individuals (eg, multinodular goiter). 

TEicosanoids are paracrine hormones, substances that act only on cells near the point of hormone synthesis instead of being transported in the blood to act on cells in other tissues or organs. These fatty acid derivatives have a variety of dramatic effects on vertebrate tissues. They are known to be involved in reproductive function in the inflammation, fever, and pain associated with injury or disease in the formation of blood clots and the regulation of blood pressure in gastric acid secretion and in a variety of other processes important in human health or disease. 

Several other mechanisms also regulate cholesterol synthesis (Fig. 21-44). Hormonal control is mediated... 

In the animal body three important groups of hormones are formed by the metabolism of cholesterol the progestins, the sex hormones, and the adrenal cortical hormones 249 Their synthesis occurs principally in mitochondria of the adrenal cortex and the gonads. Steroid hormone synthesis is regulated by hormones, such as corticotropin (ACTH), from the anterior pituitary250 (see Chapter 30) and is also dependent upon the recently discovered steroidogenic acute regulatory protein, which in some way promotes the movement of stored cholesterol into mitochondrial membranes.251 252 Some major pathways of... 

The synthesis of many hormones is regulated by a cascade of hormones (fig. 24.20). Frequently, a hypothalamic hormone impinges on the pituitary to stimulate synthesis of a hormone that activates hormone synthesis in yet another organ. The end products of these cascades generally feed-back-inhibit the production of hormones at the beginning of the cascade (fig. 24.21). 

Mitochondria play a central role in a variety of biological processes, including ATP synthesis, steroid hormone synthesis, the urea cycle, lipid and amino acid metabolism, and cellular Ca2+ homeostasis. Ca2+ is an essential regulator of vital processes, such as secretion, motility, metabolic control, synaptic plasticity, proliferation, gene expression and apoptosis. Therefore, the location, amplitude,... 

Regulation and Effects of Hormonal Synthesis During the Menstrual Cycle... 

Chiang A.-S., Gadot M., Burns E. L. and Schal C. (1991) Developmental regulation of juvenile hormone synthesis ovarian synchronization of volumetric changes in corpus allatum cells in cockroaches. Molec. Cell. Endocrinol. 75, 141-147. 

Hormones are proteins responsible for regulating molecular synthesis in vivo. The most well known therapeutic hormones are insulin, glucagon, growth hormones, and gonadotropins. 

Regulation of synthesis Thyroid function is controlled by a tropic hormone, thyroid-stimulating hormone (TSH, thyrotropin), a glycoprotein synthesized by the anterior pituitary (see Figure 25.2). TSH generation is governed by the hypothalamic thyrotropin-... 

It should be noted that in addition to the GABA(A)-R benzodiazepine-binding sites or central benzodiazepine Rs (CBZ-Rs) there are peripheral benzodiazepine Rs (PBZ-Rs) associated with the outer membrane of mitochondria in glial cells and cells of peripheral tissue and which are involved in cholesterol transport and hence in regulation of steroid hormone synthesis. The GABA(B)-Rs are metabotropic and coupled via heterotrimeric G proteins to Ca2+ and K+ channels (Chapter 5). The psychotropic GABA breakdown product y-hydroxybutyrate (GHB) also acts via heterodimeric G protein-linked receptors (see Chapter 5). 

Endocrine disruption which is independent of interactions between xenobiotics and endogenous hormone receptors can occur in a variety of different ways, including alterations in the number of hormone receptor sites (up- or down-regulation) or direct or indirect hormone modifications which alter hormonal function (Evans, 2007 Keith, 1997). Xenobiotics can change the rate of synthesis or destruction of endogenous hormones and can alter how hormones are stored, how they are released into and/or transported within the circulation, or even how they are eventually cleared from the body (Capen, 2008 Evans, 2007 Keith, 1997 Sikka et al, 2005). Any xenobiotic toxic to hormone-producing organs or tissues (e.g. testis and ovary) also has the potential to decrease hormone synthesis and thereby indirectly cause endocrine disruption (Devine and Hoyer, 2005 Evans, 2007). 

Vitamin D, apart from its availability in the diet, is produced in the body, in response to sunlight striking the skin, and really acts like a hormone. It helps to raise the blood levels of calcium and phosphorus in several ways. It stimulates calcium and phosphorus absorption in the gastrointestinal tract promotes transfer of calcium and phosphorus from bone to blood promotes calcium retention by the kidney. As a hormone it acts 1 entering the cell nucleus and interacting with DNA to regulate protein synthesis. 

Peptide-hormones like hypothalamus-pituitary, gastrointestinal, parathyroid, neurohormones, Gfs related peptide-hormones cannot penetrate the plasma membrane and their receptors are located on the cell surface and the signal transport to the nucleus is becoming via a second messenger. The main hormone action seems to be DNA synthesis whereas other including mediation of neurotransmission, enzyme synthesis, regulation and synthesis of structural proteins are responsible for the specific characteristics of differentiated cell. 

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