To determine whether 1)
insulin stimulates
pyruvate dehydrogenase (PDH) and
glycogen synthase (GS) in isolated human adipocytes and 2) adipocytes from subjects with
obesity or
noninsulin-dependent diabetes mellitus (
NIDDM) are resistant to the effects of
insulin, PDH and GS were assayed in adipocytes from 11 control, 8 obese, and 9
NIDDM subjects. Basal PDH activities were 123 +/- 20, 129 +/- 21, and 128 +/- 25 pmol
pyruvate oxidized/min per 2 X 10(5) adipocytes in these groups.
Insulin stimulated PDH activity to a maximum of 223 +/- 38 pmol/min per 2 X 10(5) in adipocytes from control subjects, but did not significantly increase values from obese subjects.
Insulin significantly decreased PDH activity in cells from
NIDDM subjects (99 +/- 20 pmol/min per 2 X 10(5) cells, P less than 0.05). PDH activity assayed with high
magnesium and
calcium concentrations was significantly stimulated by
insulin in adipocytes from control, but not obese or
NIDDM subjects. GS assayed with 1 mM
glucose 6-phosphate did not differ significantly among control, obese, or
NIDDM subjects (446 +/- 110, 451 +/- 156, and 291 +/- 35 pmol incorporated into
glycogen, respectively).
Insulin significantly stimulated
glycogen synthase in all three groups (827 +/- 179, 764 +/- 177, and 569 +/- 51 pmol incorporated) to a similar extent.
Glycogen synthase assayed with 10 mM
glucose 6-phosphate was decreased in
NIDDM (1,335 +/- 131 pmol incorporated) compared with obese or control subjects (2,512 +/- 451 and 2,239 +/- 230 pmol incorporated, respectively, P less than 0.01).