Cephalic phase pancreatic polypeptide responses to liquid and solid stimuli in humans

Abstract

The hormone, pancreatic polypeptide (PP) is postulated to be involved in body weight regulation. PP release is dependent on vagal activation and is a marker of vagal efferent activity. Because vagal activity plays a role in glucose homeostasis, elucidating the conditions of activation has important implications for nutrient metabolism. In humans, modified sham-feeding is known to elicit vagally-mediated hormonal responses. We present results of 3 studies in which healthy human subjects tasted various stimuli including sweet and salty liquids, unflavored and flavored gum and mixed nutrient foods flavored with either sweet or salt and rendered palatable or unpalatable. We examined the effects of these stimuli on PP levels relative to fasting. We found that liquids flavored with either glucose or salt, did not elicit an increase in PP levels greater than fasting. Similarly, chewing gum, whether unflavored or flavored with a non-nutritive sweetener or the sweetener paired with a mint flavor, did not significantly increase PP levels. In contrast, when subjects tasted mixed nutrient foods, these reliably elicited increases in PP levels at 4 min post-stimulus (sweet palatable, p<0.002; sweet unpalatable, p<0.001; salty, palatable, p<0.05, salty unpalatable, p<0.05). The magnitude of release was influenced by the flavor, i.e. a sweet palatable stimulus (320.1+/-93.7 pg/ml/30 min) elicited the greatest increase in PP compared with a salty palatable stimulus (142.4+/-88.7 pg/ml/30 min; p<0.05). These data suggest that liquids and chewing gum do not provide adequate stimulation for vagal efferent activation in humans and that mixed nutrient foods are the optimal stimuli.

Figure 1

Left graph: Mean PP levels during fasting and in response to the taste of sweet and salty liquids in normal weight men and women (n=10, mean ± standard error). Right graph: PP area under curve (AUC) over a 30 min period for the three experimental conditions. No significant differences were found among treatments.

Figure 2

Left graph: Mean PP levels during fasting and in response to chewing an unflavored gum, sweet gum flavored with a non-nutritive stimulus and sweet gum flavored with mint (n=15, mean ± standard error). Right graph: PP area under curve (AUC) over a 30 min period for the four experimental conditions. . No significant differences were found among treatments.

Figure 3

Panel A: Mean PP levels during fasting and during sham-feeding of 4 mixed macronutrient stimuli rated as: 1) sweet palatable 2) sweet unpalatable, 3) salty palatable and 4) salty, unpalatable in normal weight mean and women (n=12, mean ± standard error). Time points significantly elevated over baseline are indicated by “*”. Panel B: PP area under curve (AUC) over a 30 min period for the five experimental conditions. The PP AUC in response to the sweet palatable mixed nutrient stimulus was significantly greater than salty palatable and salty unpalatable (P<0.05). No significant difference was found between the sweet palatable and sweet unpalatable food. P<0.05 indicated by *. Panel C: Ratings of liking, salty intensity and sweet intensity of the four stimuli.