The effect of retinol and of retinol-binding protein on embryonic skeletal tissue in organ culture.

Retinol, bound non-specifically to serum proteins in organ culture medium, caused the degradation of the extracellular matrix of chick limb-bone rudiments. The loss of polymeric material was demonstrated histologically and measured chemically. Retinol, at the same concentration, bound specifically to retinol-binding protein, produced no significant effect. The addition of prealbumin to this system was also without discernible effect. The addition of apo-RBP to medium containing free retinol prevented the normal hypervitaminous A effects. The results indicate that the retinol-RBP complex has a high stability, sufficient to prevent the uptake, by the plasma or lysosomal membranes, of the amount of retinol needed for physical changes to occur. It is suggested that retinol-binding protein may serve to transport retinol to selected sites, whilst protecting biological membranes against a general non-specific effect of the vitamin's surface active properties.