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Fell & Mellanby (1952) showed that in organ cultures the addition to the medium of excess of vitamin A (10-s15 i.u./ml.) severely affects cartilaginous limb-bone rudiments from 6-7-day chick embryos. During 7-10 days' cultivation, the vitanin A-treated rudiments cease to grow, begin to shrink and become soft and gelatinous; the matrix no longer stains metachromatically with toluidine blue and the intercellular partitions become narrow and eventually disappear. These effects on the matrix are accompanied by cytological changes; the cartilage cells become smaller and less vacuolated and lose most of their glycogen (Fell & Thomas, 1960). They remain viable, however, and continue to multiply by mitosis. In experiments on foetal-mouse cartilage, it was shown that if the cells are killed by heating to 45° for 15 min., vitamin A has no effect on the explants (Fell & Mellanby, 1952). In radioautographic experiments with labelled inorganic sulphate (35SO4), Fell, Mellanby & Pelc (1956) found that in the presence of the vitamin the explants first cease to take up sulphate and then lose that already incorporated; in the matrix the loss of 35SO4 is accompanied by the disappearance of metachromasia. They concluded that vitamin A first inhibits the synthesis of new chondroitin sulphate and then causes the dissolution of that already formed. That these effects of vitamin A on cartilage matrix and cells are not peculiar to organ cultures has recently been demonstrated by Thomas, McCluskey, Potter & Weissmann (1960), who observed similar changes in the cartilage of young rabbits dosed with excess of vitamin A. The object of the present investigation was to find what biochemical changes are associated with the morphological effects of excess of vitamin A on limb-bone rudiments in culture.

biochemical journal. cellular aspects

Studies on the mode of action of excess of vitamin A. 1. Effect of excess of vitamin A on the metabolism and composition of embryonic chick-limb cartilage grown in organ culture