Vitamin physiological effects

FIGURE 18.30 The physiological effects of ascorbic acid (vitamin C) are the result of its action as a reducing agent. A two-electron oxidation of ascorbic acid yields dehy-droascorbic acid. 

PTH is the most important regulator of bone remodelling and calcium homeostasis. PTH is an 84-amino acid polypeptide and is secreted by the parathyroid glands in response to reductions in blood levels of ionised calcium. The primary physiological effect of PTH is to increase serum calcium. To this aim, PTH acts on the kidney to decrease urine calcium, increase mine phosphate, and increase the conversion of 25-OH-vitamin D to l,25-(OH)2-vitamin D. PTH acts on bone acutely to increase bone resorption and thus release skeletal calcium into the circulation. However, due to the coupling of bone resorption and bone formation, the longer-term effect of increased PTH secretion is to increase both bone resorption and bone formation. 

Steroid hormones are divided into six classes, based on physiological effects estrogens, androgens, progestins, glucocorticoids, mineralocorticoids and vitamin D 847... 

There is reasonable hope that in the vitamin field interrelations and antagonisms may not prove to be unduly disturbing. These substances in general do not interfere with each other seriously they are usually inert unless built into enzyme systems. The concentrations which have to be administered to be physiologically effective are so low that they are not likely to affect adversely or otherwise any process except the ones which they affect enzymatically. 

Retinoids are a family of naturally occurring and synthetic analogues of vitamin A. The skin of subjects deficient in vitamin A becomes hyperplastic and keratotic (phrynoderma, or toad skin). While natural vitamin A is occasionally employed therapeutically, synthetic retinoids are more effective and represent a major advance in dermatological pharmacotherapy. Retinoids have myriad effects on cellular differentiation and proliferation it is likely that nuclear retinoic acid receptors mediate these effects by activating gene expression in a manner analogous to receptors for steroid hormones and thyroid hormones. Despite a common mechanism of action, however, retinoids vary widely in their physiological effects. 

Continuing in the tradition of the acclaimed first edition. Pharmacodynamic Basis of Herbal Medicine, Second Edition examines in extensive detail the physiologic effects of complementary and alternative therapies, foods, supplements, vitamins, and traditional herbal remedies. This encyclopedic volume considers the site, mode, and mechanism of action to explain the desired and adverse effects and interactions of each herb, drug, and food. 

These receptors are chiefly responsible for the physiological effects of steroid hormones such as cortisol as well as thyroid hormone and vitamin A. They are proteins that share a common basic structure consisting of a ligand binding domain and a DNA binding domain (comprised of zinc finger motifs). They operate as ligand-responsive transcription factors (see Chap. 17 for further discussion). 

A primer of the physiologic effects of the vitamins and inorganic essentials can be found in Tables 17-1 and 17-2. Vitamins are named alphabetically in the order in which they were discovered or first reported.Therefore the listing intersperses fat- and water-soluble members. Food sources and deficiency states of vitamins are listed in Tables 17-3 and 17-4. 

Other adverse physiological effects may show up, e.g. natural oils of plant origin contain a lot of lipid soluble vitamins. Replacement of natural oils by synthetic fats exempt of vitamins may influence the uptake of other lipids and lead to a plentitude of physiological disturbances due to lack of essential lipids and vitamins. 

Some of these substances are fundamental building blocks of animal tissue, and minute amounts of others have dramatic physiological effects, both harmful and beneficial. Countless other biologically important substances, including many vitamins, antibiotics, and other drugs, contain amino groups, —NR2 (where R can represent an H, alkyl, or aryl group). 

Although the allograft is able to remove uremic toxins from the body, it may take several weeks for other physiologic complications of chronic renal failure, such as anemia, calcium and phosphate imbalance, and altered lipid profiles, to resolve. The renal production of erythropoietin and 1-hydroxylation of vitamin D may return toward normal early in the postoperative period. Because the onset of physiologic effects may be delayed, continuation of pretransplant calcitriol, calcium supplementation, and/or phosphate binders may be warranted in some patients. 

Major Nutritional Sources of Water-Soluble Vitamins Required by Humans and Some Physiological Effects of Deficiencies... 

Throughout this book we have encountered many drugs, vitamins, and hormones, and in many cases we have discussed the mechanism by which each compound produces its physiological effect. Table 30.2 lists some of these compounds, their uses, and where in the text they are discussed. Now we will take a look at how drugs are discovered and how they are named, and we will examine some of the techniques currently used by scientists in their search for new drugs. 

In experiments performed to elucidate the action of the vitamin, it is important to distinguish clearly between the physiological and the pharmacodynamic dose of the vitamin. In the gut the action of the large dose is only an enhancement of the physiological effect. In the bones the net result of the pharmacodynamic effect is the opposite of the physiological. 

Vitamin Be, see also under Pyridoxine deficiency, manifestations, VIII, 56 fat metabolism and, VIII, 56 physiological effects, VIII, 56 terminology, VIII, 56 Vitamin Bio, activity, VIII, 11 nature of, VI, 20 Vitamin Bn, activity, VIII, 11 nature of, VI, 20... 

The lipid fractions obtained from plants and animals contain another important group of compounds known as steroids. Steroids are important biological regulators that nearly always show dramatic physiological effects when they are administered to living organisms. Among these important compounds are male and female sex hormones, adrenocortical hormones, D vitamins, the bile acids, and certain cardiac poisons. 

As is the case with most vitamins, it is not the vitamin but one of its metabolites that is responsible for the physiological effect. DeLuca [11] discovered a vitamin metabolite that is highly active on the intestine. The metabolite has been identified as 25-hydroxycholecal-ciferol (see Fig. 5-5) it is produced in liver exclusively. The hydroxylation of vitamin D appears to occur in liver by the catalytic effect of a hydroxylase that requires NADPH but is insensitive to traditional inhibitors of lipid peroxidases (N,N -diphenyl, p-pheny-lenediamine) [12]. 

We have come to realize that vitamin D is actually a prehormone, serving as the parent compound for the production of three active metabolites 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, and 24,25-dihydroxyvitamin D3. This chapter summarizes evidence that all three metabolites produce physiological effects in vitro and in vivo, and where possible, discusses what is known about their receptors. 

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