Steroids signaling

Hormonal actions occur during sensitive periods in development, in adult life during natural endocrine cycles and in response to experience as well as during the aging process (see Ch. 30). As a result of their fundamental actions on cellular processes and genomic activity and of the control of their secretion by environmental signals, steroid and thyroid hormone actions on the brain provide unique insights into the plasticity of the brain and behavior (see also Ch. 50). 

Regioselective acylations of polyhydroxylated compounds such as carbohydrates, glycerols, steroids, or alkaloids have been carried out with lipases, esterases, and proteases [13, 20]. One example is the Candida antartica lipase (immobilized on acrylic resin) catalyzed monoacylation of the signalling steroid ectysone (1) giving selectively the 2-C)-acetate 2 (eq. (1)). Using vinyl acetate for this transesterification the reaction was irreversibly pushed to the product side, since the liberated enol instantaneously isomerizes to acetaldehyde [21]. The sometimes unfavorable aldehyde is avoided when 1-ethoxyvinyl acetates [22], trichloro- or -fluoroethyl esters [23 a, b], oxime esters [23 c] or thioesters [23 d] are employed for the quasi-irreversible reaction courses. 

The chemical natures of hormones play a predictably important role in their roles in cell signaling. Steroid hormones, for example, can enter the cell directly through the plasma membrane or can bind to plasma membrane receptors. Nonsteroid hormones enter the cell exclusively as a result of binding to plasma membrane receptors (Figure 24.8). 

When an ovum implants into the uterine lining, a placenta—da intricate capillary network—begins to develop between the mother and the embryo. Capillaries from the mother and fetus anastomose, or mingle, closely together. While the mother s blood does not come into direct contact with the fetus s, oxygen, nutrients, and other chemicals, such as cell signaling steroids can be passed from the mother s system to the developing fetus. 

In nuclear magnetic resonance (NMR) spectra the protons of the oxirane ring are usually shifted out of the steroid methylene envelope. Tori et al have tabulated the relationships of the angular methyl proton resonances and the oxirane proton signals with respect to location and configuration of the oxirane group. 

Steroid hormones are crucial signal molecules in mammals. (The details of their physiological effects are described in Chapter 34.) Their biosynthesis begins with the desmolase reaction, which converts cholesterol to preg-... 

Cato AC, Nestl A, Mink S (2002) Rapid actions of steroid receptors in cellular signaling pathways. Sci STKE 2002 RE9. 

Cellular functions are controlled by extracellular signals such as hormones, neurotransmitters, odorants, light and other chemical or physical stimuli. Only a few of these signal molecules, e.g., the highly lipid-soluble steroids or thyroid hormones, can diffiise across the... 

Kliewer SA, Moore JT, Wade L, Staudinger JL, Watson MA, Jones SA, et al. An orphan nnclear receptor activated by pregnanes defines a novel steroid signalling pathway. Cell 1998 92 73-82. 

Signals that enter the cell (steroids, vitamin D, thyroid hormone, and retinoids)... 

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. 

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