Kinetic analysis of rat steroid 5α-reductase activity in prostate and epididymis homogenates at neutral pH: Evidence for type I activity in epididymis

Abstract

Im m unocytochem ical studies and m R N A m easu rem en ts have show n th at the rat ep id id ym is-like the rat prostate-expresses both rat steroid 5a-reductase isozym es, i.e. type I and IL So far, enzym e activity m easurem ents in rat epididym is hom ogenates, how ever, do not support the presence o f type I 5a-reductase activity. Incubating hom ogenates o f both tissues w ith a wide range o f substrate concentrations, we were able to detect activity o f both isozym es in rat p rostate and ep id id ym is tissues at neutral pH. In rat prostate the am ount o f type I activity, as m easu red by the J/max at pH 7,0, exceeds that of type II 5a-reductase 50-fold. The efficiency ratio, VmaJ K my o f the type I isozym e accounts for 25% of the total in vivo potential activity. A possible anabolic role for the type I iso zy m e in rat prostate was thus surm ised. In rat epidid ym is the Fmax o f type I and type II 5a-reductase at pH 7.0 were sim ilar. C om parison of the efficiency ratio VmaJ K m o f either iso zy m e in the rat epididym is, however, suggested that the type II isozym e would play the m ajor role in the 5a-re duction o f testosterone at physiological concentrations and at n eu tral pH. The specific localization of the isozym es should be considered to allow for correct quantification o f their in vivo contribution to dihydrotestosterone form ation . C opyright © 1996 E lsevier Science Ltd.

Z-350, a new chimera compound possessing α1-adrenoceptor antagonistic and steroid 5α-reductase inhibitory actions

“…Isozyme selectivity was examined in the rat liver at pH 7.0 and epididymis at pH 5.0. These organs express predominantly types 1 and 2 isozymes, respectively (Levy et al 1990;Normington and Russell 1992;Thigpen et al 1993;Span et al 1996). Z-350 inhibited both isozymes at the same concentration range with pIC 50 values of 8.44 and 8.86, respectively (Table 4).…”

“…Z-350 inhibited rat prostatic steroid 5α-reductase noncompetitively and inhibited steroid 5α-reductase in hepatic and epididymal tissue, which expresses predominantly types 1 and 2 isozymes, respectively (Levy et al 1990;Normington and Russell 1992;Thigpen et al 1993;Span et al 1996), with the same potency as in the prostate. These potencies of Z-350 were greater than that of finasteride, a subtype non-selective inhibitor for rat enzymes (Normington and Russell 1992), indicating that Z-350 was a potent and isozyme non-selective inhibitor of rat steroid 5α-reductase.…”

Identification and partial characterization of two steroid 5α-reductase isozymes in the canine prostate

“…Moore and Wilson were the first to postulate the existence of two isozymes of 5␣-reductase, based on the presence of two distinct pH optima in 5␣reductase activity in human fibroblasts [27]. The acidic pH optimum of the type II isozyme is one of its most striking characteristics, which has been conserved in mouse, rat, monkey, and human [3,20,21,[26][27][28][29][30]. In this article, contrary to previously reported data by Liang et al [31], two pH optima of 5␣-reductase activity were found in the dog prostate.…”

“…The assay has been described and validated in detail in earlier papers [20,21]. In short, radiolabeled T was isotopically diluted to a range of 1.8 nM to 2.4 M (final concentration), dissolved in incubation buffer (400 l) in Pyrex culture tubes (borosilicate glass, 12 × 75 mm, Corning Inc., Corning, NY) and subsequently preheated at 37°C.…”

“…Thus, we set out to investigate the kinetic characteristics of canine prostatic 5␣-reductase, applying a previously reported and validated assay [20,21]. Furthermore, the effects of three different human isozyme-specific inhibitors on enzymatic activity in vitro were evaluated in dog prostatic homogenates.…”