The effect of retinoids on DNA synthesis was studied in the female Sprague-Dawley rat. Animals were treated with either solvent, 7,12-dimethylbenz(a)anthracene, or 1-methyl-1-nitro-sourea at 50 days of age and were placed on either placebo or retinyl acetate diet at 57 days of age. [3H]Thymidine incorporation into purified DNA isolated from mammary parenchymal cells was determined. Retinyl acet...

Retinol and retinyl esters are measured in serum or plasma samples by gradient, normal-phase, adsorption "high-performance" liquid chromatography, with ultraviolet detection at 325 nm. The four major circulating retinyl esters in humans (esters of palmitate, stearate, oleate, and linoleate) are coeluted as a single peak. Retinyl acetate is included as an internal standard, to correct for variab...

Acetate, by condensation and decarboxylation reactions, is converted to isopentenyl pyrophosphate, which condenses to form Cm terpenol pyrophosphates. These latter compounds condense to yield the initial Ca carotenoid precursor which is presumably phytoene. By a series of dehydrogenation, cyclization, isomerization, and hydration reactions, various acyclic and alicyclic carotenoids are formed. ...

Acetate, by condensation and decarboxylation reactions, is converted to isopentenyl pyrophosphate, which condenses to form Cm terpenol pyrophosphates. These latter compounds condense to yield the initial Ca carotenoid precursor which is presumably phytoene. By a series of dehydrogenation, cyclization, isomerization, and hydration reactions, various acyclic and alicyclic carotenoids are formed. ...

This paper proposes a simple HPLC method for the identification of vitamin A in dietary supplements, which does not imply thout saponification of the samples in order to preventing their degradation. The method was applied to the determination of the retinol concentration in five commercial products containing known amounts of vitamin A, under the following chromatographic conditions: werw used...

BACKGROUND Genetically engineered "Golden Rice" contains up to 35 microg beta-carotene per gram of rice. It is important to determine the vitamin A equivalency of Golden Rice beta-carotene to project the potential effect of this biofortified grain in rice-consuming populations that commonly exhibit low vitamin A status. OBJECTIVE The objective was to determine the vitamin A value of intrinsic...

Skin aging is a slow multifactorial process influenced by both internal as well as external factors. Ultra-violet radiations (UV), diet, smoking and personal habits are the most common environmental factors that affect skin aging. Fat contents and fibrous proteins as collagen and elastin are core internal structural components. The direct influence of UV on elastin integrity and health is centr...

A reversed-phase high-performance liquid-chromatographic method for the simultaneous determination of retinol, alpha-tocopherol, alpha-carotene, beta-carotene, cryptoxanthin, lutein/zeaxanthin, and lycopene is described. This method was applied to plasma measurements in healthy young and elderly subjects. The plasma, deproteinized with ethanol, is extracted twice with n-hexane. After evaporatio...

1. The synthesis, both in vivo and in vitro, of various steroid hormones in the adrenals, testes and ovaries of rats was compared at various stages of vitamin A deficiency with the corresponding pair-fed controls. 2. The enzymic conversion of the Delta(5)-3beta-hydroxy steroids into the corresponding Delta(4)-3-oxo steroids was significantly decreased in these tissues even at the mild-deficienc...

with oral conitraceptives. Without being able categorically to deny this possibility I think it unlikely for the following reasons. Retinol in human blood is predominantly bound to a specific transport-protedin known as the retinol-binding protein (RBP). Under physiological conditions RBP ibinds to prealbumin.4 The amount of free retinol is very small, indeed. Using a fluorescence assay5 measur...