Vitamin A status and the metabolism of cholesterol in the rat

1. The interrelationship between cholesterol and vitamin A metabolism has been studied in rats.

2. The effect of cholesterol feeding in increasing the liver storage of cholesterol w-as enhanced during vitamin A deficiency.

3. This effect was due to an increased rate of absorption of cholesterol and not due to a decreased turnover rate.

4. Feeding of high levels of vitamin A markedly depressed the cholesterol absorption; however, its turnover was unaffected.

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.

Studies on metabolism of vitamin A. The effect of hormones on gestation in retinoate-fed female rats

1. Female rats, raised to maturity on a vitamin A-deficient diet supplemented with retinoate as the sole source of vitamin A, conceived when allowed to mate with normal males, but the conception resulted in foetal resorption, beginning from day 14 or 15 of pregnancy. 2. Daily injections of pregnenolone or oestradiol-17beta, but not of progesterone, were fully effective, and transplantation of pituitary homografts under kidney capsules was 80% effective, in preventing resorption. 3. Unilateral ovariectomy, leading to compensatory hypertrophy of the remaining ovary, resulted in significantly fewer corpora lutea and in lower weight of the hypertrophied ovary of the retinoate-treated rats, as compared with the corresponding retinyl acetate-fed ones. 4. The activity of the enzyme system Delta(5)-3beta-hydroxy steroid dehydrogenase was significantly less in the ovaries of the retinoate-fed rats that were subjected to unilateral ovariectomy or were made pregnant, when compared with that of the corresponding controls. Also, the ovaries of the retinoate-treated rats were insensitive to both exogenous and endogenous gonadotrophin stimulus. 5. These results indicate that one of the reasons for foetal resorption in the retinoate-fed rats might be inadequate synthesis of steroid hormones such as pregnenolone and oestrogen.

Preparation, properties and metabolism of 5,6-monoepoxy-3-dehydroretinal

1. 5,6-Monoepoxy-3-dehydroretinal was synthesized from 3-dehydroretinyl acetate and characterized. 2. When fed to vitamin A-deficient rats, 5,6-monoepoxy-3-dehydroretinal was converted into 5,6-monoepoxy-3-dehydrovitamin A and stored in the liver. 3. It was demonstrated that the rat possesses the necessary enzymes for the reduction and oxidation of 5,6-monoepoxy-3-dehydroretinal to the corresponding alcohol and acid respectively. 4. The biological potency of the epoxy-3-dehydroretinal by the rat-growth assay (determined by USP XIV procedure) was 1.07% of that of vitamin A.

Preparation, properties and metabolism of retro-3-dehydroretinyl acetate

1. Treatment of 3-dehydroretinyl acetate with aqueous hydrobromic acid resulted in the formation of retro-3-dehydroretinyl acetate, which, on alkaline hydrolysis, gave the corresponding alcohol. 2. retro-3-Dehydroretinyl acetate was isomerized to 3-dehydrovitamin A when fed to vitamin A-deficient rats. 3. When retro-3-dehydroretinyl acetate was administered orally, it was hydrolysed to retro-3-dehydroretinol in the rat intestine, isomerized to 3-dehydroretinol and esterified before being transported to the liver for storage. 4. When administered intraperitoneally, both 3-dehydrovitamin A and retro-3-dehydrovitamin A were accumulated in liver and other tissues, whereas after enterectomy 3-dehydrovitamin A was not detected anywhere in the body. 5. The small intestine was shown to be the major site of conversion of retro-3-dehydrovitamin A into 3-dehydrovitamin A. 6. The extent of conversion of retro-3-dehydroretinyl acetate into 3-dehydrovitamin A was much smaller than that of the conversion of retro-retinyl acetate into vitamin A. 7. The biological potency of retro-3-dehydroretinyl acetate, determined by the rat-growth assay, was 2.6% of that all-trans-retinyl acetate, when given orally.