(A) 2beta-hydroxylase
(B) 5alpha-reductase
(C) 6beta-hydroxylase
(D) 7alpha-hydroxylase

The correct response is Option B.
Finasteride is a competitive and specific inhibitor of type II 5alpha-reductase that converts testosterone into dihydroxytestosterone (DHT). Type I 5alpha-reductase is predominant in the sebaceous glands of the skin, scalp, and liver; type II 5alpha-reductase is also found within the liver, as well as in the prostate, seminal vesicles, epididymides, and hair follicles. The conversion of approximately one-third of circulating DHT is mediated by type I, and type II is responsible for the conversion of the remaining circulating DHT.

In men with androgenetic alopecia, hair follicles within the balding areas of scalp are miniaturized, and DHT levels are increased. The mechanism of action of finasteride involves preferential inhibition of the type II isozyme. Administration of finasteride rapidly decreases the concentrations of DHT within the scalp and serum, reaching a suppression percentage within the serum of 65% during the first 24 hours after oral administration of 1 mg.

The relative contributions of these decreases to the overall treatment effect of finasteride have not been defined. Finasteride appears to interrupt a key factor in the development of androgenetic alopecia in patients who are genetically predisposed to this condition.

2beta-hydroxylase converts testosterone to 2beta-hydroxytestosterone, 6beta-hydroxylase converts testosterone to 6beta-hydroxytestosterone, and 7alpha-hydroxylase converts testosterone to 7alpha-hydroxytestosterone.

Reference
1. Sifton DW, ed. Physicians' Desk Reference. Montvale, NJ: Medical Economics Co; 2002.