Objective Pancreatic polypeptide (PP) is a 36-amino acid peptide produced by the F-cells of the pancreas, the plasma concentration of which has been used as a marker of parasympathetic activity. Recent work in rodents suggests that both sympathetic and parasympathetic input to adipose tissue may regulate its endocrine function and play a role in intra-abdominal fat (IAF) accumulation. We hypothesized that in humans parasympathetic activity mediates IAF accumulation and thereby insulin resistance.
Research Design and Methods To test this hypothesis, we measured PP levels in 177 non-diabetic, healthy subjects (75 M/102 F; age 32-75 y). IAF and subcutaneous fat (SCF) areas were measured by CT scan. The insulin sensitivity index (SI) was quantified using Bergman's minimal model from the results of a tolbutamide-modified frequently sampled intravenous glucose tolerance test.
Results PP levels were higher in men than in women (96.2 ± 72.2 vs 76.1 ± 55.0 pg/mL, mean ± SD, p = .037), as was IAF area (124.7 ± 67.4 vs 83.0 ± 57.7 cm2, p < .001). However, SCF was higher in women than in men (243.0 ± 133.1 vs 184.0 ± 87.8 cm2, p = .001). PP levels were positively associated with age (β = 0.03, p < .01). While PP levels were significantly associated with IAF (β = 0.01, p = .031), they were not associated with SCF (β = 0.001, p = .829). The association between PP and IAF disappeared after adjusting for age or gender. SI was negatively associated with PP levels (β = -0.002, p = .026) and IAF area (β = -0.006, p < .001). The association between SI and PP disappeared after adjusting for IAF.
Conclusion In humans, parasympathetic innervation may be mediating the effect of age and gender on IAF accumulation, but not SCF accumulation.