Mediation by an androgen receptor of the stimulatory effect of testosterone on the growth of a fibrosarcoma in the rat

We studied the effect of testosterone on the growth of a 20-methylcholanthrene-induced transplanted fibrosarcoma and assayed androgen receptors in this tumor. The effect of an antiandrogen in male rats and the comparative tumor growth in females confirmed the androgen sensitivity. A synthetic androgen that strongly binds to the androgen receptor was used to characterize the binding activity in nuclear extracts of tumor. Scatchard analysis showed that the dissociation constant of the hormone receptor complexes (K d ) was 26±2 nmol/l and the number of binding sites was about 95±12 fmol/mg of protein. The hormone-receptor complexes sedimented in the region of 3.7 S