1 This study examined the potential role of impaired nitric oxide production and response in the development of endoneurial ischaemia in experimental diabetes. Rats were anaesthetized (Na pentobarbitone 45 mg kg-', diazepam 2 mg kg-') for measurement of sciatic nerve laser Doppler flux and systemic arterial pressure. Drugs were administered into the sciatic endoneurium via a microinjector attached to a glass micropipette. 2 In two separate studies comparing diabetic rats (streptozotocin-induced; 8-10 wk duration) with controls, nerve Doppler flux in diabetic rats (Study 1, 116.6+40.4 and Study 2, 90.1+34.7 (s.d.) in arbitrary units) was about half that measured in controls (219.6+52.4 and 212.8+95.5 respectively; P<0.005 for both). There were no significant differences between the two in systemic arterial pressure. 3 Inhibition of nitric oxide production by microinjection of 1 nmol L-NAME into the endoneurium halved flux in controls (to 126.3+41.3 in Study 1 and 102.1+38.9 in Study 2; both P<0.001), with no significant effect in diabetic rats, indicating markedly diminished tonic nitric oxide production in the latter. D-NAME was without effect on nerve Doppler flux. 4 L-Arginine (100 nmol), injected after L-NAME, markedly increased flux in controls (by 65.8% (P<0.03) and 97.8% (P<0.01) in the two studies) and by proportionally similar amounts in diabetic rats [75.8% (P<0.001) and 60.2% (P<0.02)]. The nitro-donor, sodium nitroprusside (SNP; 10 nmol) had similar effects to L-arginine in both groups (increases of 66.0% in controls and 77.5% in diabetics; both P<0.002). 5 A second diabetic group, treated with evening primrose oil performed exactly like control rats in respect of responses to L-NAME, L-arginine and SNP. At the end of all measurements blood was collected for plasma glucose measurement by a glucose oxidase assay kit, as defined elsewhere (Stevens & Tomlinson, 1993;Karasu et al., 1995). Endoneurial drug administrationA glass micropipette (tip diameter 10-15 im) was advanced into the endoneurium of the sciatic nerve using a X-Y-Z micropositioner; this pipette was connected to a Drummond Microdispenser (Laser Labs, Southampton, U.K.). The sciatic nerve was impaled about 1-2 mm proximal to the site at which LDF was monitored. Resting cardiovascular parameters were then recorded in steady-state. In some rats, saline (1 ml) was injected to demonstrate that the physical effect of injection was insignificant and short-lasting (<5 min). Infusion of L-NAME (1 nmol in 1 Ml) was made over 5 min to inhibit the production of nitric oxide. Approximately 30 min later L-arginine (100 nmol in 1 Ml) was infused in some of the rats to reverse the effect of L-NAME. In the remaining animals, L-NAME was followed after about 30 min with sodium nitroprusside (10 nmol in 1 Ml) to examine the response of the guanyl cyclase system to a nitro-donor. Both of these infusions were also made over 5 min. Statistical analysisAll data are presented as means + 1 standard deviation. Acute drug effects were evaluated by comparison withi...

Decreased nerve blood flow may be a pathogenetic factor in diabetic neuropathy. Previously it was shown that insulin treatment, commenced at the onset of streptozotocin-diabetes, prevents the development of a nerve blood flow deficit in the diabetic rat. The present study sought to determine the effect of short-term (one month) and acute (one hour) insulin reversal treatment on nerve blood flow deficits in streptozotocin-diabetes. Sciatic nerve blood flow was assessed using laser Doppler flowmetry. Treatment was initiated after one month of diabetes. One month of reversal insulin treatment ameliorated nerve laser Doppler flux (NDF) deficits; in untreated diabetic rats NDF was 51% of that in control animals (P < 0.01) in insulin-treated diabetic rats NDF was 85% of control values (P < 0.01 vs. untreated diabetic, P < 0.05 vs. control). In association with blood flow increases, we found a significant amelioration of motor (P < 0.05 vs. untreated diabetic) and sensory (P < 0.01 vs. untreated diabetic) nerve conduction velocities but not of exaggerated resistance to hypoxic conduction block. Insulin partially reversed hyperglycaemia and sciatic nerve polyol and sugar levels. In a second experiment, in rats with one month of diabetes, acute infusion of insulin led to a 47% (P < 0.001 vs. pre-insulin values) reduction of plasma glucose. This fall in plasma glucose was accompanied by a 38% (P < 0.05 vs. pre-insulin values) increase in NDF. Sensory nerve conduction velocity was marginally increased (6%, P < 0.05 vs. pre-insulin values) after insulin infusion, but motor conduction velocity was not. The data indicate that insulin can partially reverse deficits in nerve blood flow and conduction in diabetic rats.