Pancreatic endocrine responses to physiological changes in plasma neurotensin concentration in the calf.

1. Plasma neurotensin concentration was found to increase by between 3 and 18 pmol/l 20 min after feeding in conscious 2-6 week old calves. 2. Synthetic bovine neurotensin was infused I.V. at a dose which reproduced the rise in the plasma concentration (1 pmol. kg-1 min-1), in calves of the same age, which were also receiving a continuous I.V. infusion of glucose (0.03 mmol. kg-1. min-1) to mimic alimentary hyperglycaemia. Under these conditions neurotensin caused a significant rise in the mean concentration of both insulin and pancreatic polypeptide (PP), but not that of glucagon, in the arterial plasma. 3. The rise of plasma insulin concentration, but not that of PP, in response to the same dose of neurotensin was strongly potentiated during infusions of exogenous amino acids. There was also a significant rise in plasma glucagon concentration in response to neurotensin in the calves given amino acids. 4. It is concluded that neurotensin is a physiological incretin in the calf.