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Objective: To study the effects of 12 weeks of cotherapy with recombinant human IGF-I (rhIGF-I) and insulin on glycemic control in patients with type 1 diabetes., Research Design and Methods: The study population consisted of 223 patients who ranged in age from 11-66 years and were randomized in a double-blind study to receive 12 weeks of treatment with twice-daily subcutaneous injections of placebo (n = 54), or rhIGF-I at a dose (A.M/P.M) of 40/40 micrograms/kg (n = 56), 80/40 micrograms/kg (n = 57), or 80/60 micrograms/kg (n = 56), while continuing to receive standard insulin therapy. Patients were instructed to test blood glucose levels four times daily and adjust insulin doses to optimize blood glucose control. HbAlc, insulin requirements, body weight, and parameters of the IGF-IGF-binding protein axis were assessed before and during treatment., Results: All groups were comparable at baseline with respect to mean age, gender distribution, duration of diabetes, HbAlc, and BMI. Cotherapy with rhIGF-I/insulin produced a mean decrease in HbAlc of 1.2%, compared with a 0.7% decrease in HbAlc for patients receiving intensified insulin therapy alone (P < or = 0.01). Subjects receiving rhIGF-I/insulin cotherapy also decreased their daily insulin usage by 11-19%, compared with a 7% increase in insulin usage reported by the placebo group. Moreover, the incidence of hypoglycemia was similar in subjects treated with rhIGF-I/Insulin cotherapy compared with those treated with insulin alone, despite the better glycemic control of the former group. The 40/40 dose of rhIGF-I was well tolerated. Higher doses of rhIGF-I did not further improve efficacy yet were associated with unacceptable levels of adverse events, including edema, jaw pain, and early worsening of retinopathy., Conclusions: These results demonstrate that rhIGF/insulin cotherapy improves glycemic control in patients with type 1 diabetes better than optimized insulin management alone; longer-term trials would be required to determine an acceptable benefit-risk profile.

Activation of the gonadotropic and somatotropic axes in puberty is marked by striking amplification of pulsatile neurohormone secretion. In addition, each axis, as a whole, constitutes a regulated network whose feedback relationships are likely to manifest important changes at the time of puberty. Here, we use the regularity statistic, approximate entropy (ApEn), to assess feedback activity within the somatotropic (hypothalamo-pituitary/GH-insulin-like growth factor I) axis indirectly. To this end, we studied pubertal boys and prepubertal girls or boys with sex-steroid hormone deficiency treated short-term with estrogen, testosterone, or a nonaromatizable androgen in a total of 3 paradigms. First, our cross-sectional analysis of 53 boys at various stages of puberty or young adulthood revealed that mean ApEn, taken as a measure of feedback complexity, of 24-h serum GH concentration profiles is maximal in pre- and mid-late puberty, followed by a significant decline in postpubertal adolescence and young adulthood (P = 0.0008 by ANOVA). This indicates that marked disorderliness of the GH release process occurs in mid-late puberty at or near the time of peak growth velocity, with a return to maximal orderliness thereafter at reproductive maturity. Second, oral administration of ethinyl estradiol for 5 weeks to 7 prepubertal girls with Turner's syndrome also augmented ApEn significantly (P = 0.018), thus showing that estrogen per se can induce greater irregularity of GH secretion. Third, in 5 boys with constitutionally delayed puberty, im testosterone administration also significantly increased ApEn of 24-h GH time series (P = 0.0045). In counterpoint, 5 alpha-dihydrotestosterone, a nonaromatizable androgen, failed to produce a significant ApEn increase (P > 0.43). We conclude from these three distinct experimental contexts that aromatization of testosterone to estrogen in boys, or estrogen itself in girls, is likely the proximate sex-steroid stimulus amplifying secretory activity of the GH axis in puberty. In addition, based on inferences derived from mathematical models that mechanistically link increased disorderliness (higher ApEn) to network changes, we suggest that sex-steroid hormones in normal puberty modulate feedback within, and hence network function of, the hypothalamo-pituitary/GH-insulin-like growth factor I axis.

The metabolic effects of recombinant human insulin-like growth factor I (rhIGF-I) were compared using bolus vs. continuous subcutaneous infusions. Subjects (n = 5, 29 +/- 3 yr) received rhIGF-I as subcutaneous infusions by a Minimed pump (200 microg x kg(-1) x day(-1) over 16 h/day), and their data were compared with those of subjects (n = 6, 24 +/- 2 yr) who received subcutaneous 200 microg x kg(-1) x day(-1) injections twice a day. L-[1-14C]leucine and [6,6-2H2]glucose infusion studies and indirect calorimetry were performed, and total and free IGF-I, insulin, and glucose concentrations were measured before and after 5-7 days of rhIGF-I. Estimates of protein breakdown, oxidation, and synthesis did not change after pump therapy; in contrast, after bolus doses, protein oxidation decreased (P = 0.001) and whole body protein synthesis increased (P = 0.04). There was no change in lipid oxidation after pump treatment, whereas the bolus group had lower lipid oxidation (P = 0.035). Both treatment modalities increased glucose oxidation (P < 0.02) and glucose production rates (P < 0.03). Overnight fasting insulin concentrations decreased in both groups, whereas plasma glucose remained invariant in the bolus group and decreased modestly in the pump group. Total IGF-I concentrations increased comparably in both groups, but the increase in free IGF-I was greater in the bolus-treated group (P = 0.001). We conclude that, in GH-sufficient postabsorptive individuals, the metabolic effects of rhIGF-I are in part dependent on the mode of administration, with a robust protein-anabolic effect when rhIGF-I is given as twice daily bolus injections but no detectable effect on protein turnover after a continuous mode of delivery. There were higher free IGF-I levels in the bolus-treated subjects, suggesting that this form of the molecule may be important for mediating IGF-I's protein-anabolic effects at the tissue level. The data also suggest that carbohydrate metabolism is more responsive than protein metabolism to the continuous subcutaneous modality of rhIGF-I administration. Even though the mechanism of these differences in metabolic effects is not entirely clear, it should be taken into account when patients are given rhIGF-I as prolonged treatment.