SEXUAL DIFFERENCES IN 5'-DEIODINASE ACTIVITY IN THE HARDERIAN-GLAND OF SYRIAN-HAMSTERS AND THE EFFECT OF PINEALECTOMY - REGULATION BY ANDROGENS

Sexual differences on thyroxine 5'-deiodinase (5'-D) in the Harderian gland of Syrian hamsters were investigated. We compared the 24-h profi le of 5'-D activity in male and female hamsters, observing a clear rhy thm in males but not in females. Female values were always significant ly higher than male ones. After pinealectomy day/night variations in m ale 5'-D activity at the time points studied were abolished, results t hat are in correlation with serum thyroid hormones. We also studied th e regulation by androgen of the enzyme activity. Basal 5'-D activity i ncreased in castrated males and levels fell when animals were implante d with testosterone or its product 5 alpha-dihydrotestosterone (DHT). Female 5'-D activity was also inhibited by androgens. As only the addi tion of DHT in the presence of epitestosterone, an inhibitor of the co nversion of testosterone on DHT, in castrated males was able to decrea se 5'-D activity to the control animal levels, we suggest a probable d irect effect of DHT by itself. (C) 1996 Wiley-Liss, Inc.