Bauer & Fung: J. Pharmacol. Exp. Ther., 256, 249 (1991), Gibson, A., et al.: Brit. J. Pharm., 107, 715 (1992), Shaffer, et al.: J. Pharm. Exper. Ther., 260, 286 (1992), Jansen, A., et al.: J. Pharmacol. Exp. Ther., 261, 154 (1992), Lander, H.M. et al.: J. Immunol., 150, 1509 (1993)