Pharmacokinetic parameters and mechanisms of inhibition of rat type 1 and 2 steroid 5α-reductases: determinants for different in vivo activities of GI198745 and finasteride in the rat 3 3Abbreviations: r5AR1, rat 5α-reductase 1; r5AR2, rat 5α-reductase 2; and DHT, dihydrotestosterone.