Enhancement of muscarinic receptor-coupled phosphatidyl inositol hydrolysis in diabetic bladder

We previously have shown an increase in muscarinic receptor density in streptozotocin (STZ)-induced diabetic and sucrosefed diuretic rat detrusor that correlates with an increase in the contractile response to muscarinic agonist (J Pharmacol Exp Ther 248: 81, 1989; Diabetes 40: 265, 1991). To investigate the signal transduction pathway involved in this altered functional response, we examined muscarinic receptor-coupled phosphatidylinositol metabolism in STZ-diabetic, sucrose-fed diuretic and age-matched control rat bladders. [³H]myo-inositol uptake was similar in all groups, but incorporation of myo-inositol into phosphatidylinositol (PI) was significantly increased in the diabetic bladder compared to the sucrose-fed and control rat bladders. Carbachol-induced increase in inositol phosphate (IPs) production was higher in the diabetic bladder than in bladders from control and sucrose-fed animals although the EC₅₀ values were similar for all groups. Enhanced inositol phosphate production after muscarinic agonist stimulation may be due not only to the upregulation of muscarinic receptors but also to the increased incorporation of myo-inositol into PI in the STZ-induced diabetic bladder.