Absence of hepatic extraction of pancreatic polypeptide in conscious dogs

In 15 conscious dogs basal portal vein pancreatic polypeptide (PP) (306 +/- 8 pg/ml) exceeded both hepatic vein PP (255 +/- 8 pg/ml) and arterial PP (244 +/- 9 pg/ml) and increased rapidly 10 min after oral glucose administration. In contrast to oral glucose, intraportal glucose infusion decreased PP levels from 45 min until the end of the infusion. Meat ingestion rapidly and promptly increased PP. During the basal state, hepatic extraction of total immunoreactive PP was 10 +/- 4%, not significantly different from zero, of the 150 +/- 14 ng/min presented to the liver. Fractional hepatic extraction of PP did not change after oral glucose, meat ingestion, or intraportal glucose infusion. Chromatographic analysis showed at least four different components of immunoreactive PP. The first peak eluted with the void volume, the second peak between the void volume and authentic PP, and the third peak coincided with authentic PP. When present, the fourth peak eluted after authentic PP. More than half of the immunoreactive PP in the basal state eluted with authentic PP, whereas about one-third was found in the second peak. The marked alterations in PP after meat, oral glucose, or intraportal glucose and atropine reflected primarily changes in the third peak. The fractional hepatic extraction of all the components was very similar.