RECOVERY OF C-13 IN BREATH FROM INFUSED (NAHCO3)-C-13 INCREASES DURING EUGLYCEMIC HYPERINSULINEMIA

1. The effect of euglycaemic hyperinsulinaemia on the recovery of C-13 in expired CO2 has been assessed in six normal subjects. Each was stu died on three occasions: once with a 6 h primed constant infusion of ( NaHCO3)-C-13 combined with a euglycaemic hyperinsulinaemic clamp for t he last 3 h (study 1) with a 6 h primed constant infusion of (NaHCO3)- C-13 alone (study 2) and once with a 6 h infusion of normal saline com bined with a hyperinsulinaemic clamp for the last 3 h (study 3). Measu rements of C-13 enrichment of expired CO2 were made in the third and s ixth hour of each infusion. 2. There was no significant increase in en richment during study 3 (3 h 0.00047+/-0.00016 versus 6 h 0.00069+/-0. 00028 atom per cent excess) with potato-starch-derived D-glucose used to maintain euglycaemia. C-13 recovery increased in the sixth hour of both study 1 and 2 (study 1: 3 h 74.4+/-2.0 versus 6 h 85.5+/-2.6%, P< 0.01; study 2: 3 h 72.1+/-2.4 versus 6 h 81.7+/-1.4%, P<0.01). There w as no significant difference in recovery between studies 1 and 2. 3. T hese results suggest that increased recovery during a sequential eugly caemic clamp is predominantly time-dependent. Studies which use this t echnique to examine the effect of insulin an substrate oxidation shoul d take this into account.