Insulin stimulation of particulate, low Km adenosine 3',5'-monophosphate phosphodiesterase activity in fat cells of the obese-hyperglycemic (ob/ob) mouse.

Cyclic AMP phosphodiesterase activity was examined in particulate (30,000 X g for 30 min sediment) and supernatant subcellular fractions of epididymal fat cells isolated from obese-hyperglycemic (ob/ob) mice and their lean (+/?) LITTERMATES. The activity of the enzyme(s) was measured during both the early onset phase (5-6 weeks of age) and the static (5 months of age) of the obese-hyperglycemia syndrome. Fat cell particulate and supernate cyclic AMP phosphodiesterase activity of obese-hyperglycemic mice and their lean littermates at both ages displayed nonlinear Lineweaver-Burk kinetic plots. The maximum velocities of the fat cell particulate cyclic AMP phosphodiesterase activity of the obese mice were 67% and 84% lower than those of their lean littermates at 5-6 weeks and 5 months of age, respectively. Incubating fat cells obtained from either lean or obese mice of both age groups with 30 to 240 microunits of insulin per ml for 15 min increased the activity of the particulate, low Km cyclic AMP phosphodiesterase. This increase in activity was manifest as an increase in the maximum velocity of the enzyme(s) with no significant alteration of the affinity of the enzyme(s) for cyclic AMP.