Growth hormone/insulin-like growth factor I axis, glucose metabolism, and lypolisis but not leptin show some degree of refractoriness to short-term fasting in acromegaly

Starvation exerts critical influence on somatotroph and leptin secretion. Fasting enhances GH levels in normal subjects, but not in GH hyposecretory states, while it always inhibits leptin secretion. We aimed to clarify the GH/IGF-I and metabolic response to short-term fasting in a GH hypersecretory state such as acromegaly. To this goal, in 8 active acromegalic (ACRO) and in 7 normal women (NS) we evaluated mean GH (mGHc), leptin (mLEPc), insulin (mIN-Sc), glucose (mGLUc) concentrations as well as IGF-I, IGF binding protein (IGFBP)-3, IGFBP-1, and free fatty acid (FFA) levels before and after 36-h fasting. Before fasting, mGHc, IGF-I, mINSc, mGLUc, and FFA levels in ACRO were higher (p<0.01) than in NS. IGFBP-3, IGFBP-1, and mLEPc were similar in ACRO and in NS only. Fasting clearly (p<0.02) increased mGHc in NS only. After 36-h fasting, significant IGF-I reduction was recorded in NS only (p<0.03). IGFBP-3 did not change both in ACRO and NS. IGFBP-1 significantly increased (p<0.05) after fasting in both groups but in ACRO were lower (p<0.03) than in NS. Fasting decreased (p<0.03) mLEPc, mGLUc, and mINSc in ACRO as well as in NS; mINSc and mGLUc after fasting in ACRO persisted higher (p<0.005) than in NS. FFA levels were increased by fasting in NS (p<0.02), but not in ACRO. This study shows that GH/ IGF-I axis, glucose metabolism, and lypolisis but not leptin display some degree of refractoriness to short-term fasting in acromegaly. The lack of any GH response to fasting in acromegaly would likely reflect neuroendocrine alterations secondary to the GH hypersecretory state. On the other hand, the lack of somatotropic response and the peculiarly blunted metabolic reaction to short-term fasting would partially reflect the delayed adaptation of insulin resistance to starvation.