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Kevin Yuen, Jan Frystyk, Margot Umpleby, Linda Fryklund, David Dunger, Changes in Free Rather Than Total Insulin-Like Growth Factor-I Enhance Insulin Sensitivity and Suppress Endogenous Peak Growth Hormone (GH) Release following Short-Term Low-Dose GH Administration in Young Healthy Adults, The Journal of Clinical Endocrinology & Metabolism, Volume 89, Issue 8, 1 August 2004, Pages 3956–3964, https://doi.org/10.1210/jc.2004-0300
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High-dose GH administration is commonly associated with impaired insulin sensitivity (SI) in humans. Paradoxically we have shown that low-dose GH (1.7 μg/kg·d) administration enhances β-cell function in young healthy adults. In the present double-blind, placebo-controlled, cross-over study, we explored the physiological effects of this low GH dose on glucose metabolism in 12 young healthy adults (seven males, 19–29 yr). At pretreatment and after each 14-d treatment block, overnight metabolic profiles were assessed followed by a hyperinsulinemic euglycemic clamp, whereas fasting blood samples were collected weekly.
In subjects treated with GH first (group A, n = 6), GH treatment increased total IGF-I (P < 0.05) and IGF binding protein-3 (P < 0.01) after 7 d, but these levels subsequently returned to pretreatment levels after 14 d. In contrast, free IGF-I increased (P < 0.05), and overnight GH pulse peak amplitude decreased (P < 0.01) after 14 d. In subjects treated with placebo first (group B, n = 6), all biochemical parameters were unchanged after placebo treatment, whereas the changes in free and total IGF-I were similar to those of group A after GH treatment. Combined clamp data from both groups A and B (n = 12) showed that 14-d GH treatment decreased overnight plasma insulin levels (P < 0.02) and hepatic glucose appearance (P < 0.05) and increased SI (P < 0.01). Of note, the GH-induced changes in SI positively correlated with the changes in free IGF-I (r = 0.72, P < 0.01).
In conclusion, low-dose GH administration enhanced SI and suppressed endogenous peak GH release, and we hypothesize that these effects are the direct result of increased serum levels of free IGF-I.
