Parenteral nutrients in rat suppresses hepatic vagal afferent signals from portal vein to hypothalamus.

BACKGROUND

Parenteral nutrition (PN) suppresses spontaneous food intake in rats by stimulating dopamine in lateral hypothalamic area (LHA), which is attenuated by vagotomy. Sensors for glucose and for some individual amino acids exist in hepatoportal areas sending signals via hepatic vagal afferents to LHA. Hypothesizing that the decrease in spontaneous food intake occurs because a PN amino acid solution is recognized by portal vein sensors, we measured afferent nerve discharges in hepatic vagus in response to PN.

METHODS

Hepatic vagus was divided in 11 rats, and an isolated nerve filament was placed on recording electrodes. Afferent firing rate was recorded before and after injecting during 1 minute a well-balanced crystalline amino acid mixture into either the portal or peripheral vein. Isotonic glucose was used as standard solution.

RESULTS

A significant decrease in hepatic vagal afferent discharge rate was recorded after both intraportal and intravenous injection of the PN amino acid mixture. The mean discharge rate was inversely related to the concentration of the solution. Successive injections produced further decreases in discharge rate, and the effect was more sustained.

CONCLUSIONS

The observed decrease in discharge rates suggests that the crystalline amino acid PN solution is sensed in hepatoportal areas informing LHA via hepatic afferents. This effect may play a role in regulating food intake during PN.