A binding protein for retinol may mediate the effects of vitamin A on the osteoclast

Excess vitamin A (retinol) can stimulate bone resorption, yet the mechanism of vitamin A action on the skeleton remains obscure. Here the authors report investigations of the actions of retinol and retinoic acid on the cellular biochemistry of the isolated osteoclast, a possible target cell for vitamin A. Osteoclasts, isolated from medullary bone of laying hens fed a hypocalcaemic diet, were pretreated with 10 super(-8) - w x 10 super(-5) M retinol and retinoic acid for 3 days. Histochemical studies showed an increase in acid phosphatase activity and in the proportion of acid phosphatase-positive osteoclasts. Fluorescence spectroscopy demonstrated a dose-dependent increase in acid phosphatase levels to 1.5-4 times that of control cultures (0.01) with 10 super(-8) 2 x 10 super(-5) retinol and retinoic acid.