Increased glucose production following neurotensin administration

Neurotensin (NT), a recently isolated extract from bovine hypothalami, has been shown to have a hyperglycemic effect when injected into fed rats. This hyperglycemia has been attributed entirely to glycogenolysis, but no evidence is available regarding the effect of NT on the rate of glucose production and uptake. We have therefore used the primed-constant infusion of 6-³H-glucose technique to evaluate the effect of an intravenous injection of NT (1.2 nmole/kg) on glucose production $\text{in vivo}$ in 48-h starvèd, conscious rats (n=10). NT induced a progressive rise in plasma glucose concentration from the control value of 101 ± 2.3 to 162.2 ± 10.8 mg/dl at 30 min. Glucose production was significantly (p<.05) elevated 35–40% throughout the first 30 minutes after NT, while the rate of disappearance of glucose was slightly, but not significantly, elevated. An average of 38.2 mg/animal of glucose was required to account for the average increase in glucose production above the basal rate during the 30 minutes following NT. This requirement exceeded the total amount of glycogen (27.9 mg.) found in the livers of 48 hour starved rats. We therefore concluded that the rise in blood glucose concentration after NT injection was entirely due to an increased rate of glucose production, and that at least part of the increased glucose production represented an elevated rate of gluconeogenesis.