This study examined the effects of insulin (INS) and growth hormone (GH) on mRNA and functional expression of somatostatin receptors (SSTR). Rainbow trout liver was used as a model system to evaluate the direct effects of INS and GH on the mRNA expression of three SSTR subtypes characterized previously from this species: SSTR1A, SSTR1B, and SSTR2. INS and GH directly stimulated steady-state levels of all SSTR mRNAs in a concentration- and timedependent manner; however, the pattern of expression was hormone- and SSTR subtypespecific. INS stimulated the expression of SSTR2 expression to a greater extent than either that of SSTR1A or SSTR1B, whereas GH stimulated the expression of SSTR2 and SSTR1B to a similar extent, with both SSTR2 and SSTR1B expression being more responsive to GH than SSTR1A. Whether INS- or GH-stimulated SSTR expression resulted from altered rates of transcription and/or changes in mRNA stability also was investigated. The formation of nascent SSTR transcripts in nuclei isolated from rainbow trout hepatocytes was significantly stimulated by INS and GH. Neither INS nor GH, however, affected the stability of SSTR mRNAs. The functional expression of SSTRs was studied in Chinese hamster ovarian (CHO-K1) cells stably transfected with either SSTR1A or SSTR1B. Surface expression of functional SSTRs was stimulated by both INS and GH. These findings indicate that INS and GH stimulate SSTR expression by regulating transcription of SSTR mRNAs and by increasing functional SSTRs on the cell surface, and they suggest that the regulation of SSTRs may be important for the coordination of growth, development, and metabolism of vertebrates.