Effectiveness of natural oils as sources of gamma-linolenic acid to correct peripheral nerve conduction velocity abnormalities in diabetic rats: modulation by thromboxane A2 inhibition.

Reduced nerve conduction velocity (NCV) in experimental diabetes can be prevented by evening primrose oil (EP), which is rich in gamma-linolenic acid (GLA). This study examined the efficacy of natural GLA sources, blackcurrant (BC), borage (BO) and fungal (FU) oils, compared with EP, in correcting motor and sensory NCV deficits in streptozotocin-diabetic rats, and any potential contribution of thromboxane (TX) A2 synthesis using the TX antagonist, ZD1542, alone and jointly with GLA-rich oils. Sciatic motor NCV, 20% reduced by 8 weeks of diabetes, was partially (16%) corrected by 2 weeks ZD1542 treatment. 1% BC, BO, FU and EP dietary supplementation caused 11%, 32%, 41% and 53% NCV ameliorations, respectively. A 2% EP diet, more closely matching the GLA intake from the other oils, caused 67% correction. Joint oil/ZD1542 treatment produced further motor NCV improvements for BC and, particularly, BO. A 13% sensory saphenous NCV deficit in diabetic rats was ameliorated by 31%, 24%, 49%, 81%, 70% and 94% for ZD1542, BC, BO, FU, EP and 2% EP, respectively. Joint ZD1542-oil treatment further improved NCV, particularly for BO. Therefore, efficacy against experimental diabetic neuropathy is not predictable from the GLA content of natural oils, EP consistently outperforming BC, BO and FU. Increased TXA2 with diabetes made a minor contribution to NCV deficits, but blockade improved the response to BO.