Effect of a new 5α-reductase inhibitor on size, histologic characteristics, and androgen concentrations of the canine prostate

Mature male beagles were used in studies designed to determine the effect of the steroidal 5α‐reductase inhibitor 17β‐N,N‐diethylcarbamoyl‐4‐aza‐4‐methyl‐5α‐androstan‐3‐one (4‐MA) on size, histology, and androgen concentration of the prostate. Subcutaneous administration of 3 or 15 mg/kg/day for 43 days caused a sharp decline in prostate volume, flattening of prostatic epithelial cells, vacuolization of the cytoplasm and pycnosis of the nuclei. Whereas serum testosterone levels remained normal in dogs injected with 3 mg/kg/day, they were lower in those that received 15 mg/kg/day. Concentrations of both testosterone and 5α‐dihydrotestosterone were reduced in the prostates of dogs that had received either 3 or 15 mg/kg/day of 4‐MA. The 15 mg/kg/day level also appeared to adversely affect spermatogenesis. In a 43‐day study, 4‐MA given orally once each day at levels of 0.1, 0.3, or 1 mg/kg failed to cause a significant decrease in prostate volume. However, daily divided oral doses totaling 1 or 3 mg/kg were given in a 42‐day test and both treatment levels produced significant reductions in prostate size.