Adipocyte glycogen synthase and pyruvate dehydrogenase in obese and type II diabetic subjects

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 10⁵ adipocytes in these groups. Insulin stimulated PDH activity to a maximum of 223 ± 38 pmol/min per 2 x 10⁵ 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 10⁵ cells, P < 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 incoporated 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 < 0.01).