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Inter‐relations between growth hormone, insulin, insulin‐like growth factor‐l (IGF‐I), IGF‐binding protein‐1 (IGFBP‐1) and sex hormone‐binding globulin in acromegaly
Author(s) -
Holly J. M. P.,
Cotterlll A. M.,
Jemmott R. C.,
Shears D.,
AlOthman S.,
Chard T.,
Wasa J. A. H.
Publication year - 1991
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1991.tb03766.x
Subject(s) - acromegaly , medicine , endocrinology , insulin , prolactin , somatomedin , hormone , insulin like growth factor , insulin like growth factor binding protein , growth factor , biology , growth hormone , receptor
Summary Acromegaly is characterized by a hypersecretion of GH, which in turn results in an excess of IGF‐I, an important mediator of its actions. IGF‐I itself is intimately related to insulin both in structure and function. IGF‐I circulates associated with specific binding proteins which appear to have Important effects on its activity. We have examined the inter‐relations between GH, prolactin, insulin, IGF‐I and one of the binding proteins, IGFBP‐1, in 62 patients with acromegaly of varying activity. Serum IGF‐I levels were closely related to the logarithm of mean GH levels (r = 0.76; n = 62; P < 0.001) but multiple regression analysis suggested that, after accounting for the variation due to GH, insulin accounted for some of the additional variation of IGF‐I. IGF‐I concentrations were independent of prolactin. Fasting Insulin levels were high and unrelated to mean GH levels but correlated with those of IGF‐I (r = 0.542; n = 57; P<0.001). This correlation coefficient was further improved by also accounting for variations in IGFBP‐1 (r = 0.684; n = 57; P< 0.001). Even In subjects whose acromegaly was well controlled or cured, as indicated by GH levels of <1 mU/l or IGF‐I levels of <2 U/ml, fasting insulin levels remained significantly elevated in some individuals. The reason for this persistent abnormality is not clear. Fasting IGFBP‐1 levels were low and unrelated to mean GH but were Inversely related to fasting insulin levels (r=−0.593; n = 57; P<0.001). We propose that a cascade of events occurs In acromegaly. GH hypersecretion causes chronic elevation of IGF‐I levels which In turn could lead to increased pancreatic insulin production. This raised insulin could then have additional effects, raising IGF‐I levels further and lowering IGFBP‐1; the latter could then result in accentuated IGF‐activity.