The effect of thionaphthene-2-carboxylic acid (TNCA) on bone structure in the rat: a histomorphometric study.

Thionaphthene-2-carboxylic acid (TNCA) has been shown to decrease osteoclast-mediated bone resorption in vitro and has shown efficacy in animal models of hypercalcaemia of malignancy. In this study, the effects of TNCA on the tibial proximal epiphysis and the sternum have been quantified by image analysis in rats administered the drug orally for 90 days at 75, 125 or 250 mg/kg/day. The amount of bone in the subepiphyseal area and sternum was increased in a dose-related manner. TNCA exerted a biphasic effect on the height of the epiphyseal plate. It was stimulatory at the low dosage and inhibitory at the high dose. This study constitutes the first of its kind to demonstrate the in-vivo effect of TNCA on the bones of rats.