INHIBITION OF MUSCLE GLYCOGEN-SYNTHASE ACTIVITY AND NONOXIDATIVE GLUCOSE DISPOSAL DURING HYPOGLYCEMIA IN NORMAL MAN

The purpose of the present study was to evaluate the role of muscle gl ycogen synthase activity in the reduction of glucose uptake during hyp oglycaemia. Six healthy young men were examined twice; during 120 min of hyperinsulinaemic (1.5 mU . kg(-1) . min(-1)) euglycaemia followed by: 1) 240 min of graded hypoglycaemia (plasma glucose nadir 2.8 mmol/ l) or 2) 240 min of euglycaemia. At 350-360 min a muscle biopsy was ta ken and indirect calorimetry was performed at 210-240 and 330-350 min. Hypoglycaemia was associated with markedly increased levels of adrena line, growth hormone and glucagon and also with less hyperinsulinaemia . During hypoglycaemia the fractional velocity for glycogen synthase w as markedly reduced; from 29.8 +/- 2.3 to 6.4 +/- 0.9%, p < 0.05. Tota l glucose disposal was decreased during hypoglycaemia (5.58 +/- 0.55 v s 11.01 +/- 0.75 mg . kg(-1) . min(-1) (euglycaemia); p < 0.05); this was primarily due to a reduction of non-oxidative glucose disposal (2. 43 +/- 0.41 vs 7.15 +/- 0.7 mg . kg(-1) . min(-1) (euglycaemia); p < 0 .05), whereas oxidative glucose disposal was only suppressed to a mino r degree, In conclusion hypoglycaemia virtually abolishes the effect o f insulin on muscle glycogen synthase activity. This is in keeping wit h the finding of a marked reduction of non-oxidative glucose metabolis m.