1. Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan, Faculty of Pharmaceutical Sciences, Kyushu University, Higashi-ku, Fukuoka 812, Japan, Faculty of Pharmaceutical Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan, and National Institute of Radiological Sciences, Inage-ku, Chiba 263, Japan