EFFECTS OF MATURATIONAL STAGE ON INSULIN SENSITIVITY DURING PUBERTY

During puberty, plasma insulin levels increase, and insulin sensitivit y decreases along with multiple other physical and hormonal changes. T o determine 1) the time course of the decrease in insulin sensitivity in relationship to Tanner stage of genital development, and 2) how thi s change relates to changes in GH secretion, insulin-like growth facto r-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 glu cose tolerance tests. The insulin sensitivity index (ISI) was calculat ed using the program MINMOD. ISI differed significantly by Tanner stag e (P < 0.05, analysis of variance) with a decease from Tanner stage 1 to 2 (P < 0.05). IGF-I and IGF-binding protein-3 followed opposite pat terns 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 a nalysis revealed negative relationships among ISI, IGF-I, and body mas s index. No relationship was found with GH. We conclude that the puber tal change in ISI is not necessarily associated with increased GH secr etion, but is associated with increased GH peripheral effect, as indic ated by the relationship between ISI and IGF-I.