Thyrotropin-releasing hormone (TRH)-Gly conversion to TRH in rat ventral prostate is inhibited by castration and...

TRH levels in rat prostate are very high in the 2-month-old rat and decline at least 90% during the next 2 yr. This decline in prostatic TRH levels with aging may be a significant factor in benign prostatic hypertrophy in man and other animals. Because prostatic TRH correlates positively with serum testosterone and negatively with serum thyroid hormone levels, we have examined the possibility that the age-related decline in prostatic TRH is hormonally regulated. TRH and a TRH precursor peptide, TRH-Gly (pGlu-His-Pro-Gly), were measured in ventral prostates from 2-, 5-, and 18-month-old Fisher 344 male rats using a combination of HPLC and specific RIAs for TRH and TRH-Gly. Similar measurements were made in a group of 2-month-old Sprague-Dawley rats which were castrated, sham castrated, or left untreated for 3 or 7 days before death. Aging and castration resulted in a significant decrease in the absolute TRH concentration as well as the TRH/TRH-Gly ratio, but no significant change was observed in TRH-Gly levels. The serum testosterone concentration did not change with aging, but serum T4 levels fell significantly. Because testosterone levels do not change during the first 18 months of life in most rat strains, and hypothyroidism in young animals is associated with a significant increase in prostate TRH and TRH-Gly levels, we conclude that the aging-related decline in prostate TRH biosynthesis is not the result of a hypogonadal state.