Expression of prostatic TRH-like peptides differs between species and between malignant and nonmalignant tissues

Thyrotropin-releasing hormone-immunoreactive peptides (iTRH) were analyzed in normal rat and rabbit prostates and in human benign prostatic hyperplasia (BPH) and prostate cancer. Peptides were extracted from tissues, fractionated by anion and cation exchange chromatography, and analyzed by TRH radioimmunoassay. pGlu-Glu-Pro-NH2 predominated in rabbit, but accounted for only 10-15% of iTRH in rat and human BPH. Uncharged peptides predominated in rat and human prostate. Authentic TRH (pGlu-His-Pro-NH2) is not present in rabbit prostate, but may account for up to 25% of iTRH in rat and human prostate. iTRH was virtually absent in prostate cancer. These results demonstrate considerable heterogeneity in the expression of TRH-like peptides in the prostates of various animal species, and suggest decreased expression of these peptides in prostate cancer.