TISSUE DISTRIBUTION OF SOMATOSTATIN RECEPTOR SUBTYPE MESSENGER-RIBONUCLEIC-ACID IN THE RAT

The tissue distribution of mRNA encoding five somatostatin receptor su btypes, SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5, was determined in adult rat tissues by solution hybridization/nuclease protection analysis us ing sequence-specific cRNA probes. In the central nervous system, SSTR 1 and SSTR2 mRNA were expressed widely, with highest levels in hippoca mpus, hypothalamus, cortex, and amygdala and expression of both isofor ms in cerebellum and spinal cord. Expression of SSTR3 was also widespr ead, occurring in all brain regions examined, with the highest level o f expression in the cerebellum. SSTR4 mRNA was detected in most brain regions, with highest levels occurring in the hippocampus, cortex, and olfactory bulb. No detectable levels were found in cerebellum. SSTR5 showed a unique pattern of expression in the central nervous system, b eing found primarily in the hypothalamus and preoptic area. In periphe ral tissues, high levels of SSTR1 and SSTR2 mRNA were found in pituita ry and spleen. SSTR1 mRNA was also found in the heart and intestine, S STR2 was detected in pancreas, and both isoforms were expressed in sto mach. Expression of SSTR3 was noted in heart, liver, stomach, intestin e, kidney, spleen, and pituitary. The patterns of expression were simi lar for SSTR4 and SSTR3 mRNA; however, SSTR4 was not expressed in live r. SSTR5 was expressed predominantly in the pituitary, but detectible levels were observed in spleen and intestine. Thus, the SSTR subtype m RNA showed both a tissue-specific and overlapping pattern of expressio n. Taken together with SSTR-specific signal transduction systems, this probably explains the diverse physiological actions of somatostatin.