IDENTIFICATION AND CELLULAR-LOCALIZATION OF THYROTROPIN-RELEASING HORMONE-RELATED PEPTIDES IN RAT TESTIS

Endogenous TRH-like products were analyzed in rat testis using a TRH e nzyme immunoassay coupled to molecular sieve filtration and HPLC ident ification. Of the three immunoreactive peptides detected, the two majo r forms exhibited the same chromatographic properties as synthetic TRH and pGlu-Phe-Pro-NH2. These peptides accounted respectively for 33% a nd 54% of the total TRH immunoreactivity in the testis. In rat serum, HPLC analysis showed the presence of only one immunoreactive peak with a retention time similar to that of authentic TRH. Ethylene dimethane sulfonate treatment of adult rat was used to assess the effect of Leyd ig cell destruction on the TRH immunoreactivity content. The concentra tion of the three TRH immunoreactive peptides fell gradually after tre atment and reached a minimum at day 21, where a marked decrease (98%) was observed. At day 41, the regeneration of Leydig cells was achieved , as shown by histochemistry and measurements of serum testosterone an d testicular weight. However, no restoration of the TRH immunoreactive content was achieved, the three TRH-related peptides being only detec table in trace amount. On the other hand, no significant change in hyp othalamic levels of TRH was observed at any treatment time, indicating that hypothalamic TRH biosynthesis was not influenced by testosterone . By using the indirect immunofluorescence technique, TRH immunoreacti ve cells were found in the interstitial space of the testis. These res ults suggest that Leydig cells are the only source of authentic TRH an d TRH-like peptides in the rat testis. A paracrine, or autocrine role for these products is suggested.