(a) Effect of 6-thioguanine on blood ionized-calcium concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanine was begun on the following day. Vertical arrows indicate the days of treatment. We administered 6-thioguanine (10 mg/kg/day subcutaneously) for the first 10 days of the experiment. Final blood samples were obtained 1–2 hours after 6-thioguanine was given. (b) Effect of 6-thioguanine on serum PTHrP concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanine was begun on the following day. Vertical arrows indicate the days of treatment. We administered 6-thioguanine (10 mg/kg/day subcutaneously) for the first 10 days of the experiment. Final blood samples were obtained 1–2 hours after 6-thioguanine was given. (c) Effect of 6-thioguanosine on blood ionized-calcium concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanosine was begun on the following day. Vertical arrows indicate the days of treatment. We administered 6-thioguanosine (10 mg/kg/day subcutaneously) for the first 10 days of the experiment. Final blood samples were obtained 1–2 hours after 6-thioguanosine was given. (d) Effect of 6-thioguanosine on serum PTHrP concentrations in male athymic nude mice bearing RWGT2 cells. Treatment with 6-thioguanosine was begun on the following day. Vertical arrows indicate the days of treatment. We administered 6-thioguanosine (10 mg/kg/day subcutaneously) for the first 10 days of the experiment. Final blood samples were obtained 1–2 hours after 6-thioguanosine was given. Values in all panels represent means ± SEM (n = 5 per group). *P < 0.05.