Reproduction of postprandial neurotensin plasma levels by intravenous neurotensin and the effect of neurotensin on exocrine pancreatic secretion in humans.

A fatty meal releases neurotensin immunoreactivity from the small bowel in humans and dogs, and an infusion of synthetic neurotensin elicits exocrine pancreatic secretion in these species. It is not clear, however, which amount of exogenous neurotensin will reproduce endogenous neurotensin plasma levels as postprandial neurotensin immunoreactivity is composed of several fragments of neurotensin without biologic activity in addition to intact neurotensin. In order to clarify this question, we infused 1.25, 2.5, 5.0 and 7.5 pmol/kg/min synthetic Gln4-neurotensin in four volunteers, determined neurotensin plasma levels with a radioimmunoassay recognizing only intact neurotensin, and collected duodenal contents for estimation of pancreatic secretion. On another day, we determined neurotensin plasma levels after a fatty meal. Reverse-phase high-pressure liquid chromatography (HPLC) was performed on postprandial plasma samples. We found a stimulatory action of neurotensin on pancreatic secretion of volume enzymes and bicarbonate beginning with 1.25 pmol/kg/min neurotensin. The neurotensin plasma level after infusion of this dose of synthetic neurotensin was 69 pg/ml; after the meal, maximal neurotensin plasma concentration was 50 pg/ml (basal neurotensin plasma levels in both investigations were subtracted). HPLC indicated the presence of the tridecapeptide known to be the active molecular form of neurotensin in postprandial plasma. These results suggested that neurotensin plays a role as an endocrine hormone in the postprandial regulation of exocrine pancreatic secretion in humans.