The responses of isolated left atria and papillary muscles to isoprenaline, forskolin and calcium have been examined in 3 week streptozotocin-diabetic rats and the effects of oral ponalrestat administration (25 mg kg-1 daily) on diabetes-induced changes in cardiac responsiveness investigated. 2. Three weeks after animals were made diabetic, cardiac responses to isoprenaline were enhanced and this was accompanied by an increase in the density of ventricular [3H]dihydroalprenolol binding sites. Treatment of animals with ponalrestat prevented the increase in cardiac beta-adrenoceptor responsiveness and receptor number. 3. Diabetes also enhanced the sensitivity of cardiac tissues to forskolin, an effect that was not prevented by the treatment of animals with ponalrestat. 4. Ponalrestat treatment increased the resting and maximum tensions developed by cardiac tissues from diabetic animals and increased the maximum tensions developed by tissues from control animals. Diabetes alone had no effect on resting or maximum developed tensions. 5. Ponalrestat therefore prevents the changes in beta-adrenoceptor density and responsiveness induced by short-term diabetes in the rat and also increases the tension developed by cardiac muscle, an effect observed in diabetic and normal animals.
