Human Semen Contains Thyrotropin Releasing Hormone (TRH), a TRH‐homologous Peptide, and TRH‐binding Substances

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Abstract
High levels of thyrotropin releasing hormone (TRH) and TRH-homologous peptide, with the general structure pGlu-X-Pro-NH2 where X is either Histidine (His) or a neutral amino acid residue, have been identified in rat and human prostate (Pekary et al, 1980, 1981a, 1982c). Because of the secretory nature of prostatic tissue, it was considered likely that these peptides would be measurable in human semen. The mean (± SD) TRH immunoreactivity (TRH IR) in semen from 26 normal donors, aged 26 to 41 years, was found to be 12.2 ± 5.2 ng/ml. TRH and TRH-homologous peptide, which constitute most of the TRH IR of human semen, were undetectable in unconcentrated human serum. TRH IR levels in semen from azoospermic donors were in the normal range. The level of TRH IR in semen from vasectomized donors was significantly less (P < 0.01) than in semen from normal subjects. Evidence for at least two TRH-binding substances, which coextract and bind to added synthetic TRH, was obtained by exclusion and cation exchange chromatography. Purification of extracts of human semen by TRH affinity chromatography or gradient, reversed phase high pressure liquid chromatography (HPLC) revealed two major TRH immunoreactive peptides, one corresponding to the TRH-homologous peptide previously reported in rat and human prostate and one cochromatographing with synthetic TRH.