INCREASE OF SERUM-INSULIN AND STABLE C-PEPTIDE CONCENTRATIONS WITH EXHAUSTIVE INCREMENTAL GRADED-EXERCISE DURING ACUTE-HYPOXIA IN SEDENTARYSUBJECTS

Hypoxia was shown to reduce insulin concentrations at rest and during exercise. However, some studies have also demonstrated increases in th e hormone associated with arterial desaturation. This study was conduc ted in order to decide [1] whether acute alveolar hypoxia increased or decreased the circulating insulin levels, and [2] to elucidate whethe r interactions of insulin with other hormones were of relevance in thi s respect. Glucose (GLU), insulin (INS), c-peptide (CP), adrenaline an d noradrenaline (CATs), atrial natriuretic peptide (ANP) and cortisol (CORT) as well as the capillary blood gases were determined in 15 heal thy fasting male volunteers (age: 26.2 +/- 2.8 years, body mass index: 22.4 +/- 2.7 kg . m(-2)). On two separate test days the subjects brea thed, in random order, either normal air (N) or a gas mixture with red uced oxygen content (H; F102: 0.14). Measurements were made at rest as well as during an incremental cycle exercise in a supine position (in crements of 6 min and 50 W) at 100 W and 150 W, at volitional exhausti on (N: 227 +/- 36 W; H: 200 +/- 32 W) as well as in the 5th min of rec overy. Arterial desaturation was seen throughout on H-day. At rest all hormones and GLU were normal and showed no influence of H. During exe rcise INS remained constant on N-day, increased on H-day and was signi ficantly higher with H than with N, most pronounced at 150 W and at vo litional exhaustion with 20%, respectively. For CP and GLU no signific ant exercise-induced changes were seen on either test day and no influ ence of H was detected. During exercise the CATs, CORT and ANP behaved normally on both test days and showed no significant influence of H. When acute hypoxia is present, incremental exhaustive exercise on high er workloads can be associated with slightly augmented INS levels and with a temporary dissociation of INS and CP. Since INS and CP are rele ased in equimolar amounts, we conclude [1] that this suggests a tempor ary diminution of the clearance of circulating INS. [2] No influence o f H was detected on the interactions of INS with other hormones.