Vitamin A-active substances

Animals are not capable of de novo synthesis of vitamin A-active substances, neither preformed retinol and its derivatives nor the carotenoid precursor forms. The preformed retinoids are defined and their chemical and structural characteristics are given in other chapters in this volume and in the appendix. 

The dietary source of vitamin A-active substances for herbivores and carnivores is provided, respectively, by carotenoids and by retinol and its esters. But for omnivores such as man, the proportionate contribution of each to habitual diets varies widely, as does the absolute quantity. In the FAO/WHO report of 1967, the lowest intakes of foods with vitamin A activity were said to be in the Near East, Asia, and the Far East, intermediate intakes in Latin America and... 

It has been difficult to study in vivo the onset of deficiency signs in various organ systems because animals frequently succumb to infection secondary to the deficiency before signs appear. Among conventionally reared survivors, it is often difficult to separate the secondary physical signs of deterioration, such as the effects of infection, from those of vitamin A deficiency per se (Beaver, 1961). It is important to ascertain these differences in order to establish the quantitative and qualitative dietary requirement for various vitamin A-active substances for the prevention of specific deficiency signs. 

The reproductive system requires a vitamin A-active substance for maintaining a normally differentiated epithelium, for other functions supportive of spermatogenesis in males (Palludan, 1966 Ahluwalia and Bieri, 1971 Thompson et al, 1964 Coward et al, 1969 Mitranond et al, 1979 Sobhon et al, 1979), and of a full gestation, embryonic development, and delivery in females (Thompson et al, 1964 Takahashi et al, 1975) it is also required for hatch-ability of the fertile eggs of fowl (Thompson et al, 1969). Retinoic acid can fulfill the role of epithelial maintenance, but retinol is required for the other functions noted. An exception appears to occur in the cockerel, in which retinoic acid is reported to maintain spermatogenesis (Thompson et al, 1969). 

Leviton, A. 1956A. Process for the microbiological synthesis of vitamin Bi2 active substances. U.S. Patent 2,753,289. 

Labeling Indicate the form of the Vitamin A the presence of any preservative, dispersant, antioxidant, or other added substance and the Vitamin A activity in terms of the equivalent amount of retinol in milligrams per gram and in International Units. 

El 60(a) Solatene ) is a carotenoid and a vitamin substance widespread in plants and animals. In plants it is almost always associated with chlorophyll. It is a vitamin A precursor and exhibits strong vitamin A activity. It can be used in topical ultraviolet sunscreen preparations (but has not been shown to be effective). It can be given orally to reduce photosensitivity reactions in patients with erythro-poetic protoporphyria, and is sometimes tried as an adjunct in treating polymorphous light eruptions. It can be used orally as a dietary supplement also used as a yellow food colorant. 

The classical method for the biological testing of vitamin K-active substances is the measuring of their effect on the blood clotting time of the vitamin K-deficient chick. Dam et al. (1951) have described a modified method, by which a linear relationship between vitamin K dosage and clotting time was obtained. 

A group of substances with yellow, orange, and red colors. Many of the pigments have vitamin A activity. They are present in a wide variety of fruits and vegetables. 

Properties—Vitamin A (retinol) is an almost colorless (pale yellow) fat-soluble substance. It is insoluble in water hence, there is no loss by extraction from cooking. Although the esters of vitamin A are relatively stable compounds, the alcohol, aldehyde, and acid forms are rapidly destroyed by oxidation when they are exposed to air and light Since vitamin A occurs in the stable form (the ester) in most foods, normal preparation procedures do not destroy much vitamin A activity. However, fats that undergo oxidative rancidity, can lose their vitamin A rapidly. We depend mainly on storage in a cool, dark place (refrigeration) and on added antioxidants, such as vitamin E, to protect fats and oils from vitamin A loss. 

Phthiocol was isolated from tubercle bacilli (269a) and since the Johne factor was soluble in fat solvents and water, Woolley and McCarter tested phthiocol for activity. The vitamin K activity of phthiocol suggested a test of other vitamin-K-active substances, and a highly potent concentrate of vitamin K, and also the simple 2-methyl-l, 4-naphthoquinone were thus found to be active for Johne s bacillus. 

Thus vitamin-K-active substances, of which phthiocol is a natural... 

PRECURSOR. In biological systems, an intermediate compound or molecular complex present in a living organism which, when activated physiochemically, is converted to a specific functional substance. Sometimes the prefix pro is used to indicate that a compound in question plays the role of a precursor. Examples from the history of vitamin and other essential chemical developments include ergosterol (pro-vitamin D2), which is activated by ultraviolet radiation to form vitamin D carotene (provitamin A) is a precursor of vitamin A prothrombin forms thrombin upon activation in the blood-clotting mechanism. 

As a brief introductory summary, vitamin D substances perform the following fundamental physiological functions (1) promote normal growth (via bone growth) (2) enhance calcium and phosphorus absorption from the intestine (3) serve to prevent rickets (4) increase tubular phosphorus reabsorpiion (5) increase citrate blood levels (6) maintain and activate alkaline phosphatase m bone (7) maintain serum calcium and phosphorus levels. A deficiency of D substances may be manifested in the form of rickets, osteomalacia, and hypoparathyroidism. Vitamin D substances are required by vertebrates, who synthesize these substances in the skin when under ultraviolet radiation, Animals requiring exogenous sources include infant vertebrates and deficient adult vertebrates, Included there are vitamin D (calciferol ergocalciferol) and vitamin D< (activated 7-dehydrocholesterol cholecalciferol). 

It has been established that the above phenomenon is caused by the presence of certain flavonoid compounds in fruit juice that influence blood circulation, increasing the permeability and elasticity of capillaries. This action is known as vitamin P activity, but the flavonoids showing this property are not classified as vitamins, because there are several substances with this activity and no serious deficiency diseases occur if they are not consumed. There are indications that these flavonoids have a useful protective action, in particular against some respiratory diseases, but they are readily decomposed in the body and it is impossible to maintain an effective concentration in the blood. 

This is one vitamin that most laboratories can measure. There are a number of old-fashioned approaches that use 2,6-dichloroindophenol in a titrimetric method such as AOAC 985.33. This works well in some systems but can give rise to false positive results if there are other reducing substances present. It will not detect dehydroascorbic acid (DHA) and so it may well underestimate the actual vitamin C activity if a product contains a significant level of DHA. However, even with for these shortcomings, it is often used as a quick and rough method. In the AOAC there is also a fluorometric method (AOAC 984.26) where ascorbic acid is oxidised to DHA and this is reacted with o-phenylenediamine to give a fluorometric compound which can be detected. This is a robust method that has general applicability. 

Further studies have extended this promotion of auxin and gibberellin action to other fat-soluble substances, in particular some isoprenoid vitamins and related compounds (I). For instance, vitamin E, vitamin Kl9 and phytol are quite comparable in their growth-promoting ability to the fatty acid ester, methyl linoleate. But some fat-soluble vitamins are not active—for instance, vitamin A, -carotene, and vitamin D2. 

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