A comparison of the relative photosensitizing potential of 15 methyl- or methoxy-substituted psoralens with that of psoralen (I) itself was carried out by placing each compound in acetone solution on the abdominal skin of guinea-pigs in a concentration of 2.5 tzg/cm 2 and strongly irradiating at 3655 A. Erythema usually appeared after 24 hr, though sometimes only after 48 hr. The highest photosensitizing activity was found in 8-methyl-l, followed in descending order by 5-methyl-I, 5',8-dimethyl-I, 4,8-dimethyl-I, 4,5',8-trimethyl-I, 4,4',8-trimethyl-l, 4',8-dimethyl-I and 4-methyl-I. The highest activity found was more than five times that of I. It was concluded that the introduction of one methyl group into the molecule of I in positions 4, 5 or 8 leads to an increase in activity. In contrast, methylation in position 4' tends to depress activity, while I-derivatives with a methyl group in position 3 are very weak photosensitizers or virtually inactive. It was not possible to relate these results to an earlier test in which 4,5',8- and 4,4',8trimethyl-I were found to be highly photosensitizing to human skin because of the different test conditions and the apparently lower sensitivity of guinea-pig skin. The latter replaced human skin in the later tests because of the very high activity of some of the derivatives tested. The authors attribute the varying effects of different methyl derivatives to the influence of the site of substitution on photoreactions shown to take place between the pyrimidine bases of nucleic acids and the 4',5' or 3,4 double bonds of furocoumarins. 1619. Fish-induced allergy
Aas, K. (1967). Studies of hypersensitivity to fish. Studies of different fractions of extracts from cod muscle tissue. Int. Archs. Allergy appl. Dnmun. 31, 239. We recently reviewed a variety of substances emanating from marine animals that had proved toxic to man (see p. 530 of this issue) but the question of allergic reactions was not considered. Although fish is said to be a frequent cause of hypersensitivity, comparatively little attempt has apparently been made to isolate the allergens responsible. In the present study, fractionation experiments on DEAE-cellulose were undertaken to separate allergenic and non-allergenic constituents of extracts of cod white muscle and the fractions obtained were subjected to scratch tests on children known to react with asthma or urticaria to ingestion of cod and to give positive skin reactions to cod extracts and on others who were not sensitive to fish in any form. The original allergen extract was separated into an allergenically-active group of proteins and a protein group which had minimal allergenic activity but which was nevertheless obviously antigenic to rabbits. On further separation of the allergenically-active material by polyacrylamide-gel disc electrophoresis, the major allergenic activity was located in two fast-moving protein zones. Both of these protein zones appeared to contain the same major allergens. Some evidence was obtained in support of the theory that the major allergenic activity is associated with an 'albuminous' protein. Immunodiffusion experiments demonstrated four distinct antigens in one of the active eluates from the polyacrylamide gel, so the isolation of 'pure' allergen is likely to meet with considerable difficulty. 1620. Join the tea set and avoid atherosclerosis?
Young, W., Hotovec, R. L. & Romero, A. G. (1967). Tea and atherosclerosis. Nature,
Lond., 216, 1015. We have previously reported the detection of a positive correlation between the intake of coffee and the incidence of coronary heart disease (Citedin F.C.T. 1966, 4, 348). In pursuance