Insulin Pulse Characteristics and Insulin Action in Non-Diabetic Humans.

OBJECTIVE Pulsatile insulin secretion is impaired in diseases such as type 2 diabetes that are characterized by insulin resistance. This has led to the suggestion that changes in insulin pulsatility directly impair insulin signaling. We sought to examine the effects of pulse characteristics on insulin action in humans, hypothesizing that a decrease in pulse amplitude or frequency is associated with impaired hepatic insulin action. METHODS We studied 29 nondiabetic subjects on two occasions. On one occasion, hepatic and peripheral insulin action was measured using a euglycemic clamp. The deuterated water method was used to estimate the contribution of gluconeogenesis to endogenous glucose production. On a separate study day we utilized nonparametric stochastic deconvolution of frequently sampled peripheral C-peptide concentrations during fasting to reconstruct portal insulin secretion. In addition to measuring basal and pulsatile insulin secretion, we used Approximate Entropy (ApEn) to measure orderliness and Fourier transform to measure the average, and the dispersion of, insulin pulse frequencies. RESULTS In univariate analysis, basal insulin secretion (R 2 = 0.16) and insulin pulse amplitude (R 2 = 0.09), correlated weakly with insulin-induced suppression of gluconeogenesis. However, after adjustment for age, sex and weight these associations were no longer significant. The other pulse characteristics also did not correlate with the ability of insulin to suppress endogenous glucose production (and gluconeogenesis), or to stimulate glucose disappearance. CONCLUSIONS Overall, our data demonstrate that insulin pulse characteristics, considered independently of other factors, do not correlate with measures of hepatic and peripheral insulin sensitivity in non-diabetic humans.