In this work we have evaluated the effects of blood sugar changes on human pancreatic polypeptide (hPP) secretion in young, healthy subjects. Mean fasting hPP level was 74 +/- 5 (SEM) pg/ml (n = 53). Insulin-induced as well as tolbutamide-induced hypoglycemia clearly provoked hPP secretion (peaks: 1201 +/- 370 pg/ml, P = 0.03, and 520 +/- 112 pg/ml, P = 0.005, respectively). In contrast, the induction of hyperglycemia by intravenous glucose infusion (0.6 g/min) elicited a significant depression of circulating hPP (37-49% of basal values); discontinuing the infusion resulted in an increase of hPP concentrations (peak: 519 +/- 141 pg/ml, P = 0.018), which coincided with the decline of blood sugar to sub-baseline levels. Glucose as an intravenous bolus (0.33 g/kg) also induced a fall in plasma hPP. Glucose ingestion (1.75 g/kg) was followed by a small and short lived elevation of hPP (154 +/- 34 pg/ml at 15 min, P = 0.04) and by a marked rise during the late hypoglycemic phase of the test (538 +/- 168 pg/ml at 120 min, P = 0.028). Finally, after intravenous arginine, a delayed increase of hPP values was observed, occurring subsequently to the plasma glucose drop. The foregoing data indicate that experimental fluctuations in glycemia inversely affect hPP secretion. Nevertheless, this relationship does not necessarily mean that hPP should be directly implicated in glucose homeostasis.