Effects of diet restriction on insulin-sensitive phosphodiesterase in rat fat cells

Effects of insulin on insulin-sensitive phosphodiesterase were investigated using fat cells from diet-restricted rats. The enzyme activities in diet-restricted rats were higher in case of 0 to 30 nmol/L insulin concentrations than in ad lib fed rats. In fat cells from the diet-restricted rats, the curves shifted to the left and half-maximum stimulation was obtained at 0.04 nmol/L, compared to that of 0.18 nmol/L in ad lib fed rats. Specific binding of insulin for fat cells from diet restricted and ad lib fed rats was 6.0% and 5.4%/2 X 10(5) cells, respectively. However when insulin binding was expressed per unit cell surface area, it was significantly increased in fat cells from diet-restricted rats compared with that from control rats. These results suggest that the insulin effector system related to the phosphodiesterase activation is improved in fat cells from diet-restricted rats, in particular, sensitivity to insulin. These increases in sensitivity to the phosphodiesterase are possibly due to improvements of insulin receptor binding.