| The isolation and characterization of the cDNAs that encode for somatostatin receptors as well as selected factors that serve to regulate their expression were studied in rainbow trout, Oncorhynchus mykiss. Two unique cDNAs encoding for somatostatin receptors were cloned and sequenced. The two cDNAs share 63.6% identity in nucleotide sequence and 94.1% identity in deduced amino acid sequence and presumably arose through gene duplication. Each cDNA encodes for a putative 371-amino acid somatostatin receptor (one designated sst1A and the other sst1B) containing seven transmembrane domains. Trout sst1 mRNAs are differentially expressed, both in terms of distribution among tissues as well as in terms of abundance within selected tissues. Sst1B mRNAs were present in all tissues tested. Sst1A mRNA was found in all tissues, as well, except esophagus. Sst1A mRNA was more abundant than sst1B in optic tectum, whereas sst1 B mRNA was more abundant than sst1A in liver. Sst1A and sst1B were equally abundant in pancreas. Regulation of sst1A and sst1B mRNA expression is controlled by nutritional state as well as treatment with growth hormone (GH), insulin (INS), and insulin-like growth factor-I (IGF-I). Fasting, which occurs naturally in the life history of many fish species, reduced the mRNA levels of sst1A and sst1B in optic tectum over a 6-week period. In contrast, during the same 6-week period, fasting increased mRNA levels of sst1A and sst1B in the pancreas and the liver. Adaptive changes in sst1 mRNA expression levels appear to be important in metabolic changes associated with food deprivation in fish to regulate growth and metabolism. Growth hormone regulated sst1 mRNA in a tissue specific manner. Insulin regulated sst1 mRNA expression in a subtype- and tissue-specific manner. IGF-I generally reduced the expression of sst1 mRNAs in all tissues examined. The results of this dissertation help to explain the multifunctional nature of somatostatins and provide insight into the physiological processes that control the areas of growth, metabolism and regulation associated with somatostatins. |
