Vitamin A and Mucopolysaccharide Biosynthesis

Vitamin A administration in lizards during tail regeneration determines epithelial mucogenesis and delays muscle and cartilage differentiation

Regenerating epidermis and spinal cord is essential to maintain tail regeneration in lizards. The effects of vitamin A, an inhibitor of epithelial cornification, have been studied in lizards during tail regeneration. The injection of high doses of vitamin A induces regeneration of a thinner tail with gummy consistency and suppression of the formation of a normal cartilaginous axial skeleton. Microscopic analysis reveals that all epithelia increase the secretion of glycoprotein-mucus. During the analyzed period the epidermis does not form scales and keratinocytes limit or stop the production of bundles of intermediate filament keratins and packets of corneous beta-proteins (β-keratins). Differentiation of oberhautchen and β-layers is much reduced or inhibited while α-keratinization and the formation of a corneous layer are affected as well. The effects of vitamin A are dramatic also on mesoderm cells since the treatment stimulates an invasion of blood cells likely due to the disruption of the wall of blood vessels, mesenchymal cell death (pycnosis), and diffuse phagocytosis by immune cells. A delay of cartilage differentiation and cartilage degradation due to an increase of lysosomes in these cells or released by white blood cells explains the lack of stiffness of the regenerating tail after vitamin A treatment. Regenerating muscles are variably affected, ranging from a variable necrotic effect with partial degradation of internal organelles and myofilaments to a massive or complete loss of myofibrils that do not organize in sarcomeres. In general hypervitaminosis A appears to delay epithelial but also mesodermal cell differentiation and maintains the regenerating tail in an immature condition.

The effect of vitamin A deficiency and fluoride on glycosaminoglycan metabolism in bone

The effects of fluoride intake and vitamin A deficiency on glycosaminoglycan metabolism in vivo were investigated. Weanling female rats were fed either a vitamin A deficient diet ad libitum, a vitamin A supplemented diet pair-fed to the deficient animals, or the vitamin A supplemented diet ad libitum. Additionally, each vitamin A dietary group was divided into three subgroups with the animals receiving water containing 0, 10 or 50 ppm fluoride. The results showed that the groups receiving 10 and 50 ppm fluoride at all dietary levels of vitamin A had significantly higher in vivo 35SO4 incorporation in both the epiphyseal and diaphyseal regions of the bone than the animals receiving 0 ppm fluoride. The vitamin A deficient animals incorporated significantly less 35SO4 into glycosaminoglycans in the epiphyseal and diaphyseal regions of the bone compared to the pair-fed, vitamin A sufficient animals for all three fluoride receiving groups. There was no interaction between fluoride intake and dietary vitamin A levels on 35SO4 incorporation into glycosaminoglycans. Fluoride either increased sulfation or turnover of glycosaminoglycans.

Plasma somatomedin activity in vitamin A deficient children

A role for vitamin A in the sulphation of mucopolysaccharides has been suggested. Somatomedin, a growth hormone dependent serum factor, has also been shown to stimulate the uptake of sulphate by cartilage. Therefore studies were undertaken on vitamin A deficient children to examine the possible interrelationship between vitamin A and somatomedin activity. Plasma somatomedin activity was markedly lowered in vitamin A deficient children and plasma HGH levels were in the normal range. The data suggest that vitamin A and somatomedin may be interrelated and also that plasma somatomedin activity may not always be determined by plasma growth hormone levels.

Teratogenic action of bis(dichloroacetyl)diamine on rats: patterns of malformations produced in high incidence at time-limited periods of development

Win 18,446, a bis(dichloroacetyl)diamine, is a drug that was previously shown to suppress spermatogenesis and to be an effective oral abortifacient in rats. The present study shows that the drug is capable of producing characteristic congenital malformations in high incidence, by a single treatment, and with high survival of fetuses to day 21. Gestation day 11 is the most sensitive time. The teratologies obtained after various schedules of treatment include malformations of the snout (100%), septal heart defects (100%) diaphragmatic hernias (100%), cryptorchism (100%), cervical pockets (100%) and absent or small irregular thymus (92%). Some of these data, namely of the heart, face and thymus, cluster in patterns that indicate that the action of the drug is upon a time-resistricted developmental process. These periods of sensitivity are subsiding or have ended before primordia of these structures appear, but they coincide with the proliferation and migration of those mesenchyme cells that will eventually form or contribute to the structures affected. It is postulated that the drug acts on these mesenchyme cells, or on the extracellular matrix that provides the necessary framework for their dispersal.

Vitamin A and the biosynthesis of sulphated mucopolysaccharides. Experiments with rats and cultured neoplastic mast cells

1. The uptake and incorporation of [(35)S]sulphate into mucopolysaccharides by colon and duodenum in vitro are unaffected by the vitamin A status of the animals. 2. Uptake and incorporation in vivo are unaffected at 4hr. after injection of [(35)S]sulphate, but at later times are decreased in some tissues of vitamin A-deficient animals. 3. The rate of removal of (35)S from blood, its rate of appearance in urine, the plasma concentration of sulphate and the uronic acid content of several tissues are not significantly altered in vitamin A deficiency. 4. These results, and direct measurement of (35)S in mucopolysaccharides at various times after injection of [(35)S]sulphate, suggest that the synthesis of mucopolysaccharides is unaffected but that their turnover is increased in vitamin A deficiency. 5. Neither the growth rate of, nor the incorporation of [(35)S]sulphate into heparin by, P815Y and HC cultured neoplastic mast cells is decreased when the horse serum necessary for growth is treated with ultraviolet light or is replaced by serum from vitamin A-deficient rats. 6. The addition of citral is no more toxic to growth rate or to incorporation of (35)S than is the addition of vitamin A itself. 7. It is concluded that neoplastic mast cells in culture do not require vitamin A for growth or for the synthesis of heparin. 8. None of these results is compatible with the view that vitamin A or a derivative is directly involved in the biosynthesis of sulphated mucopolysaccharides.

Taste changes in vitamin A deficiency

Taste preferences were studied in two groups of rats depleted of vitamin A by dietary restriction. One group received sufficient vitamin A acid supplement to maintain normal growth. The other group was repleted with vitamin A alcohol after the classical deficiency symptoms had appeared; this group gradually lost normal preferences for NaCl and aversion to quinine solutions during depletion. Vitamin A alcohol repletion tended to restore taste preferences to normal. In contrast, the group receiving vitamin A acid showed normal taste preferences throughout the depletion period. When the vitamin A acid supplement was removed taste preferences became abnormal and returned to normal when vitamin A acid was restored. Peripheral gustatory neural activity of depleted rats without any form of vitamin A was less than normal both at rest and when the tongue was stimulated with NaCl solutions. Histological examination showed keratin infiltrating the pores of the taste buds. Accessory glandular tissues were atrophied and debris filled the trenches of the papillae. It is concluded that vitamin A acid can provide the vitamin A required for normal taste, as contrasted with its inability to maintain visual function. It is suggested that the effect of vitamin A is exerted at the receptor level, as a result of its role in the biosynthesis of mucopolysaccharides, which have been recently identified in the pore area of taste buds, as well as being present in the various secretions of the oral cavity.

The regulatory function of the fat-soluble vitamins

The regulation of cell metabolism involves controls imposed at three general levels: (a) modification of the activity of existing enzymes, (b) modification of the permeability and function of cell and organelle membranes, and (c) the control of the synthesis of enzymes and other proteins of biological significance mediated by genetic mechanisms. Attempts to explain the action of the fat-soluble vitamins in terms of the first two mechanisms cited above have not been successful. In view of the fact, however, that the fat-soluble vitamins, as a class, do influence the concentrations of enzymes and other proteins in various organisms, it appeared possible that these changes reflected an action at the genetic level.It has been shown that actinomycin D inhibits vitamin K induced prothrombin formation in chicks deficient in vitamin K. Doses of actinomycin which inhibited the normal response to vitamin K inhibited incorporation of adenine-8-C14into hepatic RNA. These results were consistent with the hypothesis that vitamin K acts by stimulating messenger RNA formation for the synthesis of clotting proteins. Since the coumarin drugs antagonize vitamin K, it seemed possible that the site of antagonism was a molecule which regulates this expression of genetic information. To test this hypothesis, rats were fed a diet containing 0.05% dicumarol for 48 hours, at which time they showed prolonged clotting and one-stage prothrombin times. This clotting defect could be corrected in 6 hours by the administration of 1 mg of vitamin K1to each rat by mouth. The administration of actinomycin D in closes from 30 to 240 μg per 100 g body weight 4 hours before vitamin K1either modified or prevented the action of the vitamin. If actinomycin was given after the vitamin, or given to normal rats, no anticoagulant effect was noted. These data are consistent with the view that the site of antagonism between vitamin K and the coumarin drugs is a molecule which controls DNA-dependent RNA replication.