Effect of dietary phytosterols on 5α-reductase and aromatase activity in the rat

Studies of populations consuming high levels of plant foods demonstrated a lower incidence of several forms of cancer. The objective of the present study was to examine the effect of dietary plant sterols (PS), on the activities of 5α-reductase and aromatase. These enzymes catalyze the metabolism of testosterone to the active form of the hormone (dihydrotestosterone, DHT) and to estrogen, respectively. Thus, these enzymes may play a role in the development of prostate cancer. Male Sprague-Dawley rats were fed either a control diet, AIN-93, containing 0.2% cholic acid or the control diet plus 2% PS for 22 days. Cholic acid was added to increase the absorption of dietary PS. The enzyme activities were examined in microsomes prepared from the liver, testis and the ventral prostate. 5α-Reductase activity was measured by analyzing the conversion of testosterone to DHT. Aromatase activity was assessed by the production of [³H] water released from [³H] androstenedione. Enzyme activities were the highest in the liver as compared to testis and prostate. Dietary PS reduced the activity of 5α-reductase by 45% in the liver (from 1163.4 ± 198.8 to 640.4 ± 58.8 pmol/mg/hr) and aromatase activity by 60% in the prostate (from 10.1 ± 2.4 to 4.3 ± 1.0 pmol/mg/hr). No effect was observed in the testis. These results suggest that dietary PS have differential effects on liver, prostate and testis.