A reduced calorie-high fiber diet retards age-associated decreases in muscarinic receptor sensitivity

The effects of a reduced calorie-high fiber diet (RCHF) were examined on three cholinergic signal transduction (ST) parameters: (a) oxotremorine enhancement of K+-evoked dopamine release and (b) carbachol-stimulated low KM GTPase activity [an indicator of muscarinic receptor (mAChR)-G protein coupling/uncoupling], and (c) [3H]Quinuclidinyl benzilate (QNB) autoradiography. Comparisons were made among: young control (6 months), old normal control, old reduced calorie high fiber [both 24 months)]. The results indicated that old reduced calorie high fiber rats (1900 kcal/kg/day, 2.4010, lipids 2.4010, fiber 28010, carbohydrates 40.7010) as compared to the old normal control rats (3000 kcal/kg/day, 4.8010 lipids, 4.2010 fiber, carbohydrates 61.5010) showed a retardation of age-related deficits in dopamine release (a above) and GTPase activity (b above). These parameters were 25010 higher in the old reduced calorie high fiber rats as compared to old normal controls and did not differ from young controls, even though there was no increase in mAChR concentration in the restricted group. Thus, these results indicate that a reduced calorie high fiber diet as utilized in these experiments was effective in retarding the age-related decrements in two of three signal transduction parameters. They are discussed in terms of the induction of membrane changes (e.g., fluidity) or related decreases in oxidative stress by the restricted diet that may be involved in these signal transduction effects.