THE LOCALIZATION OF MESSENGER RIBONUCLEIC-ACIDS FOR SOMATOSTATIN RECEPTOR-1, RECEPTOR-2, AND RECEPTOR-3 IN RAT TESTIS

Somatostatin (SRIF) exerts multiple inhibitory actions throughout the body by binding to specific SRIF receptors (sst). In recent years, fiv e subtypes of SRIF receptors (sst1-5) have been cloned. In this study, S-35-labeled complementary RNA probes were used for in situ hybridiza tion to localize the sst1-5 messenger RNAs (mRNAs) in the rat testis a nd examine the changes in their distribution during the cycle of the s eminiferous epithelium. We found that sst 1-3 mRNAs were visualized in rat testes and were mainly localized within the seminiferous tubules. The signal for sst3 mRNA was also found in interstitial cells. sst4 a nd 5 mRNAs were not detected in rat testes with the method used in thi s study. In Sertoli cells, the most intense labeling for sst1 and 3 mR NAs was in stages IV-VII of the cycle of the seminiferous epithelium, which coincided with the lowest labeling intensity for sst2. In germ c ells, sst1-3 mRNAs showed similar patterns of distribution. In these c ells, sst1-3 mRNA was not observed at the early steps of spermatogenes is. Positive signals for sst1-3 mRNAs were first apparent in the pachy tene spermatocytes at stage VII and last until stage XII and in the di plotene spermatocyte at stage XIII. Positive signals for sst1-3 were a lso detected in round spermatids at stages I-VIII. Labeling of spermat ids dramatically decreased at stage IX, when these cells began their e longating changes. The presence of three sst in testis suggests that S RIF may play an essential role in testicular function.