Type 1 deiodinase activity and generation of triiodothyronine (T3 ) in prostate of sexually active rats

BACKGROUND Thyroxine (T4) and triiodothyronine (T3) are involved in the development and function of the male reproductive system. The type 1 deiodinase enzyme (D1) plays a major role in the intracellular conversion of T4 to the active form, T3. D1 is expressed in the prostate of pubescent rats, but it is unknown whether locally generated T3 is involved in the development and function of this gland. METHODS D1 activity was analyzed in prostates from neonatal to old rats. Local T3 generation (D1 and T3 levels) was evaluated in adult animals with 1–5 months of continuous sexual activity. D1 activity was measured by the radiolabeled-iodide-release method and T3 concentration by radioimmunoassay. Secretory activity of the prostate was evaluated by a morphological analysis of epithelium (hematoxilin-eosin stain) and by measuring the activity of acid phosphatase as a marker enzyme for secretion. RESULTS The highest prostate D1 activity was expressed around puberty, and it was almost undetectable during the neonatal period and with aging. Interestingly, 1 and 4 months of sexual activity avoided the decrease of D1 activity associated with aging. Sexual activity provoked a hypertrophy and functional hyperplasia in all lobes, but D1 and acid phosphatase activity increased only in the ventral lobe. D1 activity correlated with an increase in the prostatic T3 concentration. CONCLUSIONS The increased local generation of T3 in prostate might be related to: (1) the differentiation/maturation that occurs at puberty and (2) the energy expenditure associated with maintaining the secretory activity of the glandular epithelium. Prostate 69: 1651–1659, 2009. © 2009 Wiley-Liss, Inc.