Ontogeny of somatostatin in the human gastro-intestinal tract, endocrine pancreas and hypothalamus.

The appearance, time and distribution of somatostatin in the pancreas, gastro-intestinal tract and hypothalamus were studied comparatively in human foetuses aged 6--32 weeks, by immuno-cytochemistry and radioimmunoassay. Somatostatin was detected by both methods in all segments including the colon. The first cells were observed, and somatostatin was present in measurable amounts at 8 weeks in pancreas, duodenum and intestine, while the peptide was detected at 12 weeks in antrum and colon, at 14 weeks in fundus, and at 16 weeks in hypothalamus. Subsequently, the largest cell population was located in the pancreas, where peptide concentration and age were positively correlated (P less than 0.01, r = 64). From 15 to 21 weeks of age, the mean somatostatin concentration in pancreas (12.4 +/- 1.84 ng/mg) was clearly higher than in hypothalamus (0.05 +/- 0.02 ng/mg) or in any segment of the gut, where values ranged from 0.36 +/- 0.06 (fundus) to 4.74 +/- 0.83 ng/mg (duodenum). The early appearance time of somatostatin, and its specific distribution with preferential location in the pancreas, suggest that the peptide may play a major role for the development of the foetal digestive tract, and that it may be involved in the regulation of other endocrine secretions, especially in the pancreas.