Reduced basal ATP synthetic flux of skeletal muscle in patients with previous acromegaly

Abstract

Background: Impaired mitochondrial function and ectopic lipid deposition in skeletal muscle and liver have been linked to decreased insulin sensitivity. As growth hormone (GH) excess can reduce insulin sensitivity, we examined the impact of previous acromegaly (AM) on glucose metabolism, lipid storage and muscular ATP turnover. Participants and Methods: Seven AM (4f/3 m, age: 46±4 years, BMI: 28±1 kg/m2) and healthy volunteers (CON: 3f/4 m, 43±4 years, 26±2 kg/m2) matched for age and body mass underwent oral glucose testing for assessment of insulin sensitivity (OGIS) and β-cell function (adaptation index, ADAP). Whole body oxidative capacity was measured with indirect calorimetry and spiroergometry. Unidirectional ATP synthetic flux (fATP) was assessed from 31P magnetic resonance spectroscopy (MRS) of calf muscle. Lipid contents of tibialis anterior (IMCLt) and soleus muscles (IMCLs) and liver (HCL) were measured with 1H MRS. Results: Despite comparable GH, insulin-like growth factor-1 (IGF-I) and insulin sensitivity, AM had ∼85% lower ADAP (p<0.01) and ∼21% reduced VO2max (p<0.05). fATP was similarly ∼25% lower in AM (p<0.05) and related positively to ADAP (r = 0.744, p<0.01), but negatively to BMI (r =-0.582, p<0.05). AM had ∼3fold higher HCL (p<0.05) while IMCLt and IMCLs did not differ between the groups. Conclusions: Humans with a history of acromegaly exhibit reduced insulin secretion, muscular ATP synthesis and oxidative capacity but elevated liver fat content. This suggests that alterations in β-cell function and myocellular ATP production may persist despite normalization of GH secretion after successful treatment of acromegaly. © 2008 Szendroedi et al.