Increased expression of insulin-like growth factor in intestinal lengthening by mechanical force in rats

IntroductionA segment of the jejunum could double its length by the application of an axial mechanical force. We hypothesize that this growth is correlated with an increased expression of insulin-like growth factor (IGF-I) in the jejunum.MethodsAdult Sprague-Dawley rats underwent the isolation of a 1.5-cm segment of the jejunum. The isolated jejunal segment was either lengthened using mechanical force or left alone for 3 weeks. The jejunal segments were analyzed by quantitative polymerase chain reaction and immunofluorescence for the expression of IGF-I.ResultsWhereas jejunal segments that underwent isolation alone did not change their length, isolated jejunal segments that were stretched by applying a gradual mechanical force doubled their initial length. Both groups increased their muscular thickness 5 folds as compared to the normal jejunum. The mRNA level of IGF-I in the lengthened jejunum was 6 folds higher than that in the normal jejunum, but the IGF-I mRNA level in the isolated jejunum without mechanical lengthening was unchanged. By immunofluorescence, the increased IGF-I expression in the lengthened jejunum was localized to the intestinal smooth muscle cells.ConclusionsInsulin-like growth factor I may be an important signal induced by the applied axial force that mediates longitudinal intestinal growth.