Abstract
Summary
In this work we have examined the daily fluctuations of circulating hPP in normal individuals subjected to a conventional meal schedule (breakfast, lunch, and dinner) as well as during food deprivation for 84 hr. In addition, we have tested the effect of ingestion of a low-calorie, fiber-rich salad as well as 500 ml of tap water on hPP secretion.
Ingestion of each meal was followed by a sustained hPP elevation. Between meals, circulating hPP did not return to basal values. Both the vegetable meal and the water load evoked hPP release, suggesting that the hPP response to food intake is partially a nonspecific effect. In the fasted group, plasma hPP rose significantly 24 hr after the last meal and persisted elevated for the remainder of the experimental period. Moreover, in this condition hPP showed circadian variations, with higher values in the late evening than in the preceding and subsequent morning.
Since pancreatic polypeptide is suspected to possess gastrointestinal functions, its elevation in plasma throughout the daytime in conditions of normal feeding may be thought to exert a tonic influence on some digestive process. On this basis, the increase of hPP during prolonged fasting appears paradoxical and, indeed, the explanation of this phenomenon awaits a better knowledge of the biological activity of this peptide.
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