Cell hormones, definition

Lipids are naturally occurring organic molecules that have limited solubility in water and can be isolated from organisms by extraction with nonpolar organic solvents. Fats, oils, waxes, many vitamins and hormones, and most nonprotein cell-meznbrane components are examples. Note that this definition differs from the sort used for carbohydrates and proteins in that lipids are defined by a physical property (solubility) rather than by structure. Of the many kinds of lipids, we ll be concerned in this chapter only with a few triacvlglycerols, eicosanoids, terpenoids, and steroids. 

An important observation linking Ca + to hormone action involved the definition of the intracellular targets of Ca action. The discovery of a Ca -dependent regulator of phosphodiesterase activity provided the basis for a broad understanding of how Ca and cAMP interact within cells. 

By definition all hormones affect the behavior of their target cells. Examples of the interplay between endocrine disturbances and their biochemical consequences are provided by some of the diseases of the thyroid, which directly affects basal metabolic rate, and diabetes mellitus, where glucose metabolism is deranged. 

Interestingly, the antiproliferative effects of the hydroxyferrocifens lb (n = 3) and Id (n = 5) are definitely superior to OH-Tam at 1 pM at this concentration, the contribution of a non-receptor-mediated and a dose-dependent cytotoxic component, which is not reversed upon the addition of oestradiol, begins to appear [64], On MDA-MB-231 cells, possessing undetectable amounts of ERa and low amounts of ERp, and thus classified as hormone-independent, these compounds have IC50 values as low as 0.5 pM (Table 1), while OH-Tam was completely inactive on these cells. Consequently, two kinds of behaviour can be observed one which is similar to the anti-oestrogenic role of OH-Tam on the ER, and a cytotoxic effect that involves the ferrocene moiety. 

Less well-defined but particularly important in terms of the function of non-neuronal cells are so-called receptor-operated channels [6,7]. By definition these are channels in the plasma membrane which open in response to hormone-receptor interaction without a change in membrane potential. The mechanism of their opening may either be by a direct coupling of receptor (possibly via a G protein) with the channel, or by an indirect coupling via the generation of an intracellular messenger such as cAMP or the putative messenger, inositol 1,3,4,5-tetrakisphosphate. 

All enzymes are in fact labeled, at least by their active binding ate for substrates, and by coenzymes (catalytic sites) which both together enable them to fulfil their very specific catalytic function. The same can be said about hormones and antibodies which are adapted for a specific interaction with a target cell or antigen by some definite mode of labeling. 

It proved difficult to definitively demonstrate CRH synthesis from immune cells, although numerous studies provided evidence this does happen (Aird et al., 1993 Ekman et al., 1993). Eventually it became clear that regulation of CRH synthesis and release in immune cells differs from that in hypothalamic neurons. While immune cells may synthesize and release much smaller concentrations of CRH and other neuroimmune peptides, and although their release may require de novo synthesis, an inherently slow process, the fact that immune cells release these hormones locally in the target area compensates for both of these factors to some extent. These data indicating site and tissue specific effects of CRH, sometimes even contradictory effects, point to the complex interrelationship betw een the nervous, endocrine and immune systems, an interaction that has yet to be deciphered completely. 

In summary, advances in our understanding of the nutritional and hormonal requirements of cells in culture and of the role played by attachment factors and transport proteins have led to the possibility that any cell can be cultured in the absence of serum. The type of serum substitute used and the means of achieving a serum-free culture system should be determined by the ultimate purpose that the culture system is to serve. The advantages of serum-free culture are manifest both in the practical realm of providing an inexpensive and simple starting material for the purification of cell-secreted proteins, such as antibodies, and for providing a more precise definition of the in vitro environment in order to model more... 

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