Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Steroid hormones membranes

Steroid hormones act in a different manner from most hormones we have considered. In many cases, they do not bind to plasma membrane receptors, but rather pass easily across the plasma membrane. Steroids may bind directly to receptors in the nucleus or may bind to cytosolic steroid hormone receptors, which then enter the nucleus. In the nucleus, the hormone-receptor complex binds directly to specific nucleotide sequences in DNA, increasing transcription of DNA to RNA (Chapters 31 and 34). [Pg.849]

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. [Pg.279]

Cholesterol is a widely distributed sterol found free or esterified to fatty acids. It is an important intermediate in the biosynthesis of steroid hormones and the principal component of cell plasma membranes and the membranes of intracellular organelles. [Pg.356]

LDL is the major carrier of cholesterol to the periphery and supplies the cholesterol essential for the integrity of nerve tissue, steroid hormone synthesis, and cell membranes. The association between elevated plasma cholesterol carried in LDL and the risk of coronary heart disease has been well established. LDL is also sometimes called the bad cholesterol. [Pg.704]

Steroid hormones are produced by the adrenal cortex, testes, ovaries, and placenta. Synthesized from cholesterol, these hormones are lipid soluble therefore, they cross cell membranes readily and bind to receptors found intracellularly. However, because their lipid solubility renders them insoluble in blood, these hormones are transported in the blood bound to proteins. Furthermore, steroid hormones are not typically preformed and stored for future use within the endocrine gland. Because they are lipid soluble, they could diffuse out of the cells and physiological regulation of their release would not be possible. Finally, steroid hormones are absorbed easily by the gastrointestinal tract and therefore may be administered orally. [Pg.112]

Amine hormones include the thyroid hormones and the catecholamines. The thyroid hormones tend to be biologically similar to the steroid hormones. They are mainly insoluble in the blood and are transported predominantly (>99%) bound to proteins. As such, these hormones have longer half-lives (triiodothyronine, t3, = 24 h thyroxine, T4, = 7 days). Furthermore, thyroid hormones cross cell membranes to bind with intracellular receptors and may be administered orally (e.g., synthryoid). In contrast to steroid hormones, however, thyroid hormones have the unique property of being stored extra-cellularly in the thyroid gland as part of the thyroglobulin molecule. [Pg.114]

The signal is what starts everything off. Signals take a variety of forms, but for our purposes there are only two. The first type are signals that go into the cell, bind to internal receptors, and exert their effects. Steroid hormones, vitamin D, thyroid hormone, and retinoids are the only members of this class. All of the intracellular receptors ultimately activate the transcription of regulated genes. The common feature of signals that enter the cell is that they are all small lipophilic molecules that can cross the cell membrane. [Pg.138]

The signal crosses the membrane and activates gene transcription. Signals for soluble receptors include steroid hormones, retinoic acid, thyroid hormone, and vitamin D. [Pg.139]

Hormonal actions on target neurons are classified in terms of cellular mechanisms of action. Hormones act either via cell-surface or intracellular receptors. Peptide hormones and amino-acid derivatives, such as epinephrine, act on cell-surface receptors that do such things as open ion-channels, cause rapid electrical responses and facilitate exocytosis of hormones or neurotransmitters. Alternatively, they activate second-messenger systems at the cell membrane, such as those involving cAMP, Ca2+/ calmodulin or phosphoinositides (see Chs 20 and 24), which leads to phosphorylation of proteins inside various parts of the target cell (Fig. 52-2A). Steroid hormones and thyroid hormone, on the other hand, act on intracellular receptors in cell nuclei to regulate gene expression and protein synthesis (Fig. 52-2B). Steroid hormones can also affect cell-surface events via receptors at or near the cell surface. [Pg.846]

Fig. 1.1. General mechanism of action of steroid hormones. Steroid hormones cross through the plasmatic membrane without apparent difficulty favored by gradient. Some, which can be considered prohormones, are metabolized and transformed into more active products. This is the case with testosterone, which becomes dihydrotestosterone (DHT) in the target tissues of androgens, through the 5-alfa-reductase enzyme. The hormone binds to the receptor, a soluble protein of the cellular cytosol that, in the absence of hormone, is found associated with other proteins (hsp90 and others) that maintain the receptor in an inactive state. The hormone-receptor bond causes the other proteins to separate and a homodimer to be formed. The homodimer is the activated form of the receptor since it is capable of recognizing the genes that depend on that steroid hormone as well as of activating its expression, which leads to the synthesis of specific proteins... Fig. 1.1. General mechanism of action of steroid hormones. Steroid hormones cross through the plasmatic membrane without apparent difficulty favored by gradient. Some, which can be considered prohormones, are metabolized and transformed into more active products. This is the case with testosterone, which becomes dihydrotestosterone (DHT) in the target tissues of androgens, through the 5-alfa-reductase enzyme. The hormone binds to the receptor, a soluble protein of the cellular cytosol that, in the absence of hormone, is found associated with other proteins (hsp90 and others) that maintain the receptor in an inactive state. The hormone-receptor bond causes the other proteins to separate and a homodimer to be formed. The homodimer is the activated form of the receptor since it is capable of recognizing the genes that depend on that steroid hormone as well as of activating its expression, which leads to the synthesis of specific proteins...
The entrance of steroid hormones into the cells has always been assumed to be a passive phenomenon, based on its solubility in the phospholipids of the cell membrane. Nevertheless, the existence of specific fixation of steroid hormones to cell membranes has opened the possibility of their entrance into the cells mediated by proteins of the membrane (Levin 2002). Nevertheless, it has not been possible to verify that they participate in some way in the transportation of steroids to the interior of the cell (Beato et al. 1996 Beato 1989). For them, other possible extragenomic actions have been postulated such as enzymes that participate in the metabolism of hormones or even membrane receptors (Beato et al. 1996 Chirino et al. 1991 Fernandez et al. 1994 Gruber et al. 2002 Revelli et al. 1998). [Pg.48]

There are also numerous enzymes anchored in membranes of the microsomal cell fraction that participate in the metabolism of steroid hormones. Thus, those of the p450 family, which carry out molecular oxidation, or the sulfatases and sulfotransferases, more or less specific to several hormones (Pasqualini et al. 1995). The affinity of steroid hormones for proteins of the membrane (Kd between 10 and 100 nM) is frequently greater than that which some of these enzymes present for their substrates (Luzardo et al. 2000). Therefore, it is unlikely that a part of the proteins of the membrane that bind steroids is in reality enzymes metabolizing these hormones. [Pg.49]

Photoaffinity Labeling of Steroid Hormone Receptors and Membrane Probes... [Pg.217]

A large and diverse group of proteins, including enzymes, cytoskeleton, contractile proteins, and receptors, have been shown to be modified by calpains. Thus, a number of enzymes such as tyrosine hydrolase, tryptophan hydrolase, transglutaminase, protein kinase C, and membrane Ca2+-ATPase are activated by calpain proteolysis [38]. Several receptor proteins, in particular receptors for steroid hormones, growth factors, and adrenaline, are modulated by calpains, which participate also in platelet activation, cell fusion, and mitosis [39], Although the physiological roles of calpains continue to be un-... [Pg.40]


See other pages where Steroid hormones membranes is mentioned: [Pg.108]    [Pg.271]    [Pg.387]    [Pg.705]    [Pg.168]    [Pg.172]    [Pg.223]    [Pg.438]    [Pg.458]    [Pg.17]    [Pg.60]    [Pg.118]    [Pg.268]    [Pg.10]    [Pg.140]    [Pg.47]    [Pg.261]    [Pg.33]    [Pg.297]    [Pg.18]    [Pg.48]    [Pg.51]    [Pg.170]    [Pg.217]    [Pg.110]    [Pg.407]    [Pg.142]    [Pg.88]    [Pg.382]    [Pg.79]    [Pg.127]    [Pg.29]    [Pg.584]    [Pg.270]   
See also in sourсe #XX -- [ Pg.852 ]




SEARCH



Hormones, steroidal

Steroids steroid hormones

© 2024 chempedia.info