Vitamin tissue sensitivity

Anand et al. 1987). The authors hypothesized that the ocular effects associated with endosulfan may be a result of prolonged hypertension (although no data on blood pressure were presented, and there is no other information to indicate that chronically administered endosulfan induces hypertension) or an endosulfan-induced vitamin A deficiency (which was observed in this study). Although the rabbit may represent a uniquely sensitive species, the possibility that long-term exposure of persons at hazardous waste sites to endosulfan may result in adverse effects on ocular tissues cannot be eliminated. 

Ascorbic acid [71] and vitamin E [72] are powerful scavengers of reactive oxygen species and are known to enhance the sensitivity of vascular tissue to organic nitrates. Also the local concentration of NO due to administration of GTN is greatly enhanced by hypoxia [73]. 

The recognition of their structure permits the determination of vitamins by the tools of analytical chemistry, but while such methods are widely used in industrial production, the minute quantities in body fluids and tissues limit the purely chemical approach to a few members of this group present in relatively high concentration, e.g., vitamin C (K5). Microchemical methods are in use for the determination of thiamine, riboflavin, and some of the fat-soluble vitamins, based on the most sensitive colorimetric and, in particular, fluorometric techniques. Vitamin D, on the other hand, is determined by animal assay. 

A rapid electrophoretic method for the simultaneous separation and estimation of vitamin Bg and derivatives from various tissues has been described (105). The method is based on high voltage electrophoresis of small aliquots of tissue extracts, applied on cellulose-coated plates. The method is sensitive upto 1 yg of vitamin Bg. 

Alteration of serum enzyme activity has been shown to be a sensitive parameter of tissue injury (20). While the activities of such enzymes as pyruvate kinase, lactate dehydrogenase, glutamate oxaloacetate transaminase, alkaline phosphatase, and creatine phosphokinase in rat serum were significantly altered by the deprivation of dietary vitamin E, the activities of these enzymes were not influenced by smoking exposure under the experimental conditions (Table I). 

Increased uptake of calcium by arterial smooth muscle, leading to increased muscle tone, and hence increased circulatory resistance and blood pressure. This could reflect increased sensitivity of vascular smooth muscle to calcitriol (vitamin D) action in vitamin Bg deficiency the membrane calcium-binding protein is regulated by vitamin D, and vascular tissue has calcitriol receptors. 

Flavins are lost from the body as intael riboflavin, rather than as a breakdown product of riboflavin. Hence, vitamin status may be assessed by measuring the level of urinary riboflavin. Generally, the loss of 30 ig of riboflavin/g creatinine or less per day indicates a deficiency. This metht>d of assessment is not preferred because it is influenced by a number of factors unrelated to vitamin status. Another problem with this method is its great sensitivity to a short-term deficiency thus, it does not necessarily reflect the true concentrations of FAD and FMN in tissues. The most reliable way to assess riboflavin status is by a functional test. The test involves the assay of glutathione reductase, using red blood cells as the source of... 

Factor VII is the most sensitive of the vitamin K-dependent clotting factors. The mode of action is tissue factor-dependent activation of factors Xa and IXa on the surfaces of activated platelets (1). Factor Xa leads to thrombin generation and hemostasis, by converting fibrinogen to fibrin. This process is limited to the site of injury, since exposure of tissue factor from the subendothelial matrix has a role in the action of recombinant factor Vila, thereby reducing the risk of thromboembohc events (2). 

Research Needs. Over the years L-ascorbic acid has been shown to be an essential nutrient for many insects including species of Lepidoptera, Orthoptera, Coleoptera, and Diptera. Others such as cockroaches, houseflies, and mealworms are reared on simple diets without added ascorbic acid. Perhaps those insects require very low levels of vitamin C in their diets. A sensitive analytical method is needed to measure levels of L-ascorbic acid and dehydroascorbic acid in insect tissue and food. Such a method, which is likely to be developed using HPLC with electrochemical detection, could be used to monitor vitamin C levels in feed ingredients as well as in tissues during an insect s life cycle. This information is needed to determine whether ascorbic acid is used to... 

The oxidative product of ascorbic acid, dehydroascorbic acid, is the preferred form of the vitamin for uptake by neutrophils, erythrocytes, and lymphocytes (27). Once within the erythrocyte, dehydroascorbic acid is reduced to ascorbic acid by a glutathione-dependent, dehydro-ascorbic-acid-reducing enzyme (20,28). However, the reduced form of ascorbic acid is found in most other tissues, that is, liver, lungs, kidneys, skin, and pituitary and adrenal glands (20,29). From these studies, ascorbic acid is taken up by several tissues by an energy-dependent and Na -sensitive process, but the transport of the oxidized vitamin form follows the principles of diflFusion. 

Within metabohcally active and vitamin K using tissue, especially liver, a microsomal vitamin K cycle exists (Figure 30-7). The vitamin (quinone) is normafty reduced by a thiol-sensitive flavoprotein system to the hydroquinone, which then can couple to the oxygen- and carbon dioxideusing y-carboxyiation of glutamyl residues in specific pro-... 

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