title: Effects of insulin-like growth factor-I on glucose tolerance, insulin levels, and insulin secretion.
abstract: Insulin-like growth factor-I (IGF-I) and insulin interact with related receptors to lower plasma glucose and to exert mitogenic effects. Recombinant human IGF-I (rhIGF-I) was recently shown to decrease serum levels of insulin and C-peptide in fasted normal subjects without affecting plasma glucose levels. In this study we have investigated in six healthy volunteers the responses of glucose, insulin, and C-peptide levels to intravenous rhIGF-I infusions (7 and 14 micrograms/kg.h) during standard oral glucose tolerance tests (oGTT) and meal tolerance tests (MTT), respectively. Glucose tolerance remained unchanged during the rhIGF-I infusions in the face of lowered insulin and C-peptide levels. The decreased insulin/glucose-ratio presumably is caused by an enhanced tissue sensitivity to insulin. The lowered area under the insulin curve during oGTT and MTT as a result of the administration of rhIGF-I were related to the fasting insulin levels during saline infusion (oGTT: r = 0.825, P less than 0.05; MTT: r = 0.895, P less than 0.02). RhIGF-I, however, did not alter the ratio between C-peptide and insulin, suggesting that the metabolic clearance of endogenous insulin remained unchanged. In conclusion, rhIGF-I increased glucose disposal and directly suppressed insulin secretion. RhIGF-I probably increased insulin sensitivity as a result of decreased insulin levels and suppressed growth hormone secretion. RhIGF-I, therefore, may be therapeutically useful in insulin resistance of type 2 diabetes, obesity, and hyperlipidemia.
authors.affiliation: Department of Internal Medicine, University Hospital, Zurich, Switzerland.
authors.forename: P D
authors.initials: PD
authors.lastname: Zenobi
authors.forename: S
authors.initials: S
authors.lastname: Graf
authors.forename: H
authors.initials: H
authors.lastname: Ursprung
authors.forename: E R
authors.initials: ER
authors.lastname: Froesch
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D002096:C-Peptide / Q000097:blood; D005502:Food; D005951:Glucose Tolerance Test; D013006:Growth Hormone / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood* / Q000378:metabolism; D000078790:Insulin Secretion; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000502:physiology*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008297:Male; D011994:Recombinant Proteins
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone