During puberty, plasma insulin levels increase, and insulin sensitivity decreases along with multiple other physical and hormonal changes. To determine 1) the time course of the decrease in insulin sensitivity in relationship to Tanner stage of genital development, and 2) how this change relates to changes in GH secretion, insulin-like growth factor-I (IGF-I), IGF-binding protein-3, and gonadal steroid secretion, we studied 58 healthy children and adolescents (34 males and 24 females; age 7-15 yr) using overnight GH sampling and frequently sampled iv glucose tolerance tests. The insulin sensitivity index (ISI) was calculated using the program MINMOD. ISI differed significantly by Tanner stage (P < 0.05, by analysis of variance) with a decrease from Tanner stage 1 to 2 (P < 0.05). IGF-I and IGF-binding protein-3 followed opposite patterns to ISI, with lower levels in Tanner stage 1 than in stages 2-5 (P < 0.05). Mean GH levels did not increase until Tanner stage 4 (P < 0.05) and then fell during Tanner stage 5. Multiple linear regression analysis revealed negative relationships among ISI, IGF-I, and body mass index. No relationship was found with GH. We conclude that the pubertal change in ISI is not necessarily associated with increased GH secretion, but is associated with increased GH peripheral effect, as indicated by the relationship between ISI and IGF-I.

The exact mechanisms for the decrease in R-R interval (RRI) during acute physiological hyperinsulinemia with euglycemia are unknown. Power spectral analysis of RRI and microneurographic recordings of muscle sympathetic nerve activity (MSNA) in 16 normal subjects provided markers of autonomic control during 90-min hyperinsulinemic/euglycemic clamps. By infusing propranolol and insulin ( n = 6 subjects), we also explored the contribution of heightened cardiac sympathetic activity to the insulin-induced decrease in RRI. Slight decreases in RRI ( P < 0.001) induced by sevenfold increases in plasma insulin could not be suppressed by propranolol. Insulin increased MSNA by more than twofold ( P < 0.001), decreased the high-frequency variability of RRI ( P< 0.01), but did not affect the absolute low-frequency variability of RRI. These results suggest that reductions in cardiac vagal tone and modulation contribute at least in part to the reduction in RRI during hyperinsulinemia. Moreover, more than twofold increases in MSNA occurring concurrently with a slight and not purely sympathetically mediated tachycardia suggest regionally nonuniform increases in sympathetic activity during hyperinsulinemia in humans.

No abstract

Adolescents with Type 1 diabetes have poorer glycemic control and more hypoglycemia than do adults. While physiologic reasons for these problems exist, the most common problems are failure to administer insulin, monitor glucose levels, and maintain an appropriate meal plan.