ABSTRACT
Intestinal tract, which produces more than fifty kinds of gut peptides, is regarded as the largest endocrine organ. With regard to the gut peptides, a number of studies were focused on their structure, function and the roles in some diseases. The changes in output or distribution of gut peptides in the intestinal tract during development have been largely unknown. This study was aimed to investigate the changes of somatostatin (SST) and somatostatin receptor 2 (SSTR2) in small intestinal and hepatic tissues during the development of macaque. The tissue samples of small intestine, liver or blood samples from peripheral and portal vein of 4 macaques in 6-month fetus, 2-day neonate, 45-day neonate and adult were obtained after anesthetization. The concentrations of SST in blood or tissues of macaques were measured by radioimmunoassay. The distributions of SST in small intestinal or hepatic tissues were visualized by immunohistochemical staining. The expression of SSTR2 was detected by in situ hybridization. SST concentration of intestinal tissue in 6-month-old macaque was (27.3+/-16.6) ng /mg protein and light positive staining of SST was localized in mucosal crypts but negative in muscle layer. The intestinal concentration of SST increased gradually with macaque development and reached to the peak [(120.1+/-35.3) ng /mg protein] in adult. It was significantly higher than that in fetus (P<0.01). Strong positive staining of SST was found in both mucosal crypts and myenteric nerve plexus of adult animal. SSTR2 was obviously expressed in intestinal epithelium of fetus but its expression was greatly reduced in epithelium and was shifted to mucosal crypts when grown to adult. Negative staining of SSTR2 in muscle layer of fetal or neonatal macaque turned to be positive in myenteric nerve plexus of adult. The levels of SST or SSTR2 in liver decreased gradually during development. SST concentrations of small intestinal tissue kept significantly higher than those of hepatic tissues in the macaque developing stages. SST levels of portal vein were also maintained significantly higher than those of peripheral blood in the macaque developing stages. In conclusion, the level of SST and expression of SSTR2 in mucosal crypt increased gradually with macaque development. SST from intestinal tract was quickly degraded in portal vein before entering into liver. SST positive myenteric nerve plexus was visualized only in mature macaque.