Posttranscriptional regulation of neurotensin in the gut

Previous studies have suggested an important role for neurotensin as an enterotrophic factor in the adaptive response of the gut. The purpose of this study was to determine the specific tissue distribution of neurotensin messenger RNA (mRNA) and to examine the molecular mechanisms that regulate intestinal neurotensin gene expression and content. In the first experiment, various segments of gut tissue from three Sprague-Dawley rats were harvested, and polyadenylated RNA was extracted for Northern hybridization with a rat neurotensin probe. In the second experiment, 32 Sprague-Dawley rats were fasted for 72 hours and then killed at 0, 3, 12, and 24 hours after refeeding (n = 8 rats/group). Rats fed ad libitum were killed before fasting (control, n = 8). Distal ileal segments (30 cm) were resected for measurement of neurotensin tissue concentration by radioimmunoassay and extraction of poly (A)⁺ RNA for Northern hybridization with a rat neurotensin complementary DNA probe. Blots were stripped and reprobed for β-actin as a control for RNA loading. A nuclear run-on transcription assay was performed to determine the relative rate of neurotensin transcription. In the first experiment, neurotensin messenger RNA transcripts of 1.0 and 1.5 Kb sizes were found throughout the small intestine and proximal colon; the greatest abundance was found in the distal small intestine. In the second experiment, neurotensin tissue concentration was significantly reduced with fasting. Refeeding a diet for 24 hours returned neurotensin concentration to control levels. However, neither the amount of neurotensin messenger RNA nor its rate of transcription were altered by fasting and refeeding. These findings suggest that a posttranscriptional mechanism is responsible for regulation of neurotensin synthesis in gut mucosa.