Selenium content of food consumed by Canadians

Four composite diets from three cities, each representing the daily per capita consumption of foods in Canada, contained on analysis 191, 220, 113, and 150 mug selenium. Cereals provided the most selenium (62-112 mug) followed by meat, poultry, and fish (25-90 mug) and dairy products (5-25 mug). The average daily intake of selenium in Canada was also calculated from published analytical data and the per capita disappearance of unprepared foods. The total intake was 197 mug/day, and the major sources were wheat flour (98 mug), pork (21 mug), poultry products (24 mug), and fish (17 mug). Because the average diet is rich in selenium, the possibility of a deficiency in the adult is considered to be remote. Milk is relatively low in selenium, and thus the greatest deprivation in humans would occur during infancy.

General and specific effects of modifiers of mutant expression

Strains homozygous for mutants affecting the length of the L4 vein in Drosophila melanogaster were selected for increased or decreased vein length. Substitution of chromosomes selected for their effect on one mutant into the genome of a non-homologous mutant has shown that many modifiers of mutant expression must be considered as acting generally on the character rather than affecting only a specific mutant.

N-acetyl-beta-hexosaminidase: role in the degradation of glycosaminoglycans

Extracts of cultured normal human skin fibroblasts released radioactivity from a (14)C-labeled heptasaccharide prepared by addition of [(14)C]N-acetylgalactosamine to the nonreducing terminus of a hexasaccharide derived from chondroitin 4-sulfate whereas fibroblast extracts from patients with Tay-Sachs and Sandhoff-Jatzkewitz diseases did not. The results suggest that N-acetyl-beta-hexosaminidase A is responsible for degradation of the oligosaccharide substrate.

The uptake and metabolism of retinol, retinoic acid and methyl retinoate by the early chick embryo

1. Fertile eggs deficient in vitamin A were obtained by feeding hens a diet deficient in retinol (vitamin A alcohol) but containing methyl retinoate.

2. Radioactive retinol was injected into the albumen of three of these eggs at a level of 2 μg [6,7-14C]retinol/egg. After 5 days' incubation, 4.6–8.3% of the injected material was recovered in the lipid of the embryo, representing a four- to nine-fold concentration into the embryo from the albumen. Approximately 40–50% of this was unchanged retinol, 15–20% retin-aldehyde and 20–30% probably a long-chain fatty acid retinyl ester. The early embryo can, therefore, metabolize vitamin A very effectively.

3. [6,7-14C]Retinoic acid (2 μg) was injected into normal fertile eggs, killing most of the embryos. The eggs with dead embryos were analysed; 0.24% and 0.33% of the injected material was recovered from the embryos. Two embryos which developed contained 0.51% and 0.53% of the injected dose. In no instance was any material identified other than retinoic acid. The extremely low amounts of retinoic acid absorbed by the embryos emphasize the very high toxicity of retinoic acid to the early chick embryo.

4. [6,7-14C]Methyl retinoate (0.5 μg) was injected into each of four normal eggs; 8.5–11.6% was isolated as unchanged methyl retinoate after 5 days; no other radioactive substance was detected.

The biological activity of retinoic acid in the domestic fowl and the effects of vitamin A deficiency on the chick embryo

1. Male and female chickens were reared from hatching on vitamin A-free diets, either unsupplemented or containing retinoic acid (vitamin A acid), methyl retinoate or retinyl acetate (vitamin A acetate). The birds given retinyl acetate grew well and had a normal appearance, but those given the unsupplemented diet died before 4 weeks of age after developing typical signs of avitaminosis A. The birds given retinoic acid or methyl retinoate did not show overt signs of vitamin A deficiency or other abnormalities except for a progressive failure of vision. Minimal histological changes were found in their retinas, and their vision was rapidly restored after feeding with retinyl acetate.

2. The cocks maintained with retinoic acid or methyl retinoate had normal testes and the hens laid eggs at a normal rate, but although their eggs could be obtained fertile the development of the embryo became abnormal after 2 days incubation and it always died. The development of the embryos could be stimulated and sometimes restored to normal by injection of various forms of vitamin A into the eggs before incubation, or by previous administration of retinyl acetate to the hens.

3. It is concluded that feeding retinoic acid as the sole source of vitamin A enables the hen to produce eggs that lack vitamin A but are otherwise normal, thus permitting the demonstration of a hitherto undescribed requirement of the early chick embryo for vitamin A.

4. The toxicity of vitamin A derivatives to chick embryos was investigated; injected retinoic acid was found to be extremely toxic.

The retinol requirements of rats for spermatogenesis and vision

1. Hooded rats were fed from weaning on a basal retinol-deficient diet containing retinoic acid. Such a diet maintains growth and general health but does not prevent the appearance of lesions associated with vitamin A deficiency in the retina and testis. Some animals were also given supplements of retinol averaging 0.1, 0.25, 1 or 5 μg retinyl acetate per day. Rats were killed at intervals up to 28 weeks after weaning. The weights of the testes and the histological appearance of the testes and epididymides indicated that 5 μg retinyl acetate per day had maintained spermatogenesis throughout the experimental period. Doses averaging 1 μg retinyl acetate per day were only partially effective and the two smaller doses had little beneficial effect.

2. In a second similar experiment rats were given doses of retinyl acetate averaging 0.25, 0.5, 1, 2 or 100 μg per day. Measurements of the electroretinogram thresholds of the rats indicated that a dose of 1 μg retinyl acetate per day maintained mainly normal vision until the end of the experiment 29 weeks after weaning. Additional histological observations made 21 weeks after weaning showed that this dose level had not maintained spermatogenesis but that doses of 2 μg retinyl acetate per day had been effective.

3. The experiments show that the differing functions of vitamin A in spermatogenesis and vision are reflected in the hooded rat in differences in the dietary retinol levels needed to maintain these processes.