THE DETECTION OF THYROTROPIN-RELEASING-HORMONE (TRH) AND TRH RECEPTORGENE-EXPRESSION IN SIBERIAN HAMSTER TESTES

Thyrotropin-releasing hormone (TRH) from the hypothalamus is the major regulator of TSH synthesis and secretion. Most recently, TRI I and TR H receptors (TRH-R), as well as their mRNAs, have been identified in r at testis. To expand our knowledge on the testicular TRH and TRH recep tor gene expression in different species, in the present study the mRN A levels of testicular TRH and TRH-R were investigated in Siberian ham sters. To further localize the cellular sites of the gene expression, the animal model was treated with a single injection of ethylene dimet hane sulfonate (EDS) (TP, 80 mg/kg body weight), a compound known as t o specifically eliminate testicular Leydig cells. The elimination of L eydig cells induced by EDS treatment was confirmed by histological stu dies of the testis sections and by serum hormonal analyses, which show ed a dramatic reduction of serum testosterone (T) levels and significa ntly elevated serum LH concentrations. Messenger RNA levels of TRH and TRH-R in the testes were determined by Northern blot analyses quantit ated with densitometry scanning. The results showed that specific TRH- R mRNA, 3.8 kb in size, was identified in Siberian hamster testes and the mRNA levels were significantly elevated in the EDS-treated testes compared to the controls (p < 0.01). Testicular TRH mRNA was also dete cted; however, no significant differences in TRH mRNA levels were foun d between EDS-treated and control groups. The size of TRH mRNA was cha racterized as about 1.2 kb in hamster testes, which was smaller than t hat observed in the rat hypothalamus (1.6 kb) and in the rat testis (2 .0 kb). Further studies by RNase H digestion revealed the presence of smaller TRH transcripts in the hamster testes than those in the rat te stis. No hybridization signal for TRW mRNA was detected by RNase prote ction assay, when a rat TRH riboprobe was applied to hamster testis RN A, suggesting the limited homology of TRH gene sequences between these two species. Our results demonstrate that both TRH and TRH-R genes ar e expressed in Siberian hamster testes, and a significant increase of TRH-R mRNA levels occurs in the Leydig cell eliminated hamster testes. Unlike the rat testicular TRH mRNA mainly detected in Leydig cells, i n hamster TRH mRNA could also be detected in other testicular compartm ent. (C) 1997 Elsevier Science Inc.