Reduction of cyclic AMP in the sciatic nerve of rats made diabetic with streptozotocin and the mechanism involved

Abstract

ABSTRACT We have investigated the relationship between cyclic nucleotides and nerve function in the sciatic nerve of rats made diabetic with streptozotocin. Cyclic AMP (cAMP) content in the sciatic nerves of diabetic rats was significantly (P < 0·05) lower than in those of normal rats, while cyclic GMP content did not differ between the two groups. Administration of the stable prostacyclin analogue iloprost or dibutyryl cyclic AMP (dbcAMP) significantly (P<0·05) restored the cAMP content in the sciatic nerves and motor nerve conduction velocity, which reflects nerve function. There was a positive correlation between cAMP content in the sciatic nerves and motor nerve conduction velocity in both normal and diabetic rats. Endoneurial preparations of sciatic nerves obtained from normal rats were incubated in Krebs–Ringer bicarbonate buffer containing d-glucose (30 or 5·5 mmol/l). Cyclic AMP accumulation was significantly (P<0·05) suppressed in the buffer containing 30 mmol d-glucose/l compared with that containing 5·5 mmol/l. Iloprost (P<0·05) and dbcAMP (P<0·01) increased cAMP accumulations in the tissues incubated in buffer containing both 5·5 and 30 mmol d-glucose/l. When non-metabolizing hexoses, such as l-glucose or 3-O-methylglucose instead of d-glucose were used, cAMP accumulations at 30 mmol hexose/1 were not significantly different from those at 5·5 mmol/l. Cyclic AMP phosphodiesterase activity in the sciatic nerves of diabetic rats did not change compared with that in nerves from normal rats. Although not significant, mean ATP content in the sciatic nerves of diabetic rats was about 30% lower than that in nerves of normal rats. Basal, iloprost-stimulated and forskolin-stimulated adenylate cyclase activities in the sciatic nerves of diabetic rats were significantly (P<0·05) reduced when compared with those of control rats. We therefore conclude that reduction of cAMP content in peripheral nerves may be involved in the pathogenesis of diabetic neuropathy and is mainly caused by the impairment of adenylate cyclase activity in the diabetic state. Journal of Endocrinology (1993) 136, 431–438