Fetal rat intestinal cells in monolayer culture: a new in vitro system to study the glucagon-like immunoreactive peptides.

To establish an in vitro model to investigate the glucagon-related peptides, fetal rat intestinal cells were enzymatically dispersed and placed into culture for up to 7 days. After 1 day in culture, the presence of epithelial-like cells containing glucagon-like immunoreactivity (GLI) was demonstrated using immunocytochemical techniques. The cell peptides were extracted by passage through a cartridge of octadecylsilyl silica and characterized by gel filtration and RIA. Two GLI moieties were detected with apparent mol wts of 11,000-12,000 and 5,000-6,000. The immunoreactive profile obtained for the cells in culture was identical to that of both whole fetal rat intestine and adult rat ileum. The presence of glucagon could not be demonstrated in any of the extracts. The basal levels of GLI and apparent immunoreactive glucagon (IRGa) were 1,457 +/- 381 and 198 +/- 57 pg/dish, respectively, on day 1 of culture. The GLI content of the cells, but not the IRGa, declined with time in culture for up to 5-7 days (P less than 0.03). Addition of insulin to the culture medium (10 or 100 mU/ml) did not influence the decrease in GLI content of the cells, but did inhibit the production of IRGa (P less than 0.05). Addition of 500 mg/dl glucose to the cells in the presence of 20 microU/ml insulin increased the secretion of GLI by 42 +/- 7% over 2 h (P less than 0.05). The stimulation by glucose was not seen in the absence of insulin or with higher insulin concentrations (100 microU/ml), nor did insulin alone (100 microU/ml) have any effect on the release of GLI. Thus, fetal rat intestinal cells in culture produce the GLI peptides, and secrete them in response to glucose. This system may provide a means by which the synthesis and control of secretion of the glucagon-related peptides can be investigated.