Comparison of short-term effects of insulin and essential fatty acids on the slowed nerve conduction of streptozotocin diabetes in rats

Abstract

Early effects of insulin and essential fatty acids on nerve conduction were studied. Insulin-dependent diabetes was induced in rats using streptozotocin (65 mg/kg, i.p.); control rats were treated with buffer. Five weeks later, diabetic rats were divided into 5 groups. Two groups were given oral essential fatty acids (75% linoleic and 9% γ-linolenic acids) for a further 3 and 5 days, respectively. Two other groups received subcutaneous insulin for a further 3 or 5 days. A group of diabetic rats were left without further treatment. Motor nerve conduction velocity was measured terminally in all rats by stimulating the sciatic nerve and recording EMGs in the gastroenemius muscle under urethane anaesthesia. Sensory nerve conduction velocity was measured by stimulating and recording from the saphenous nerve trunk. Diabetic rats had significantly slowed motor and sensory nerve conduction velocities after 5 weeks (16.7%, P < 0.001). Three days treatment with either insulin or fatty acids corrected the slowed motor nerve conduction velocity to a normal level. Conduction velocity in myclinated sensory nerves was still 10% slower in diabetic rats treated with insulin for 3 days ( P < 0.01). It was above the control level by 11% in diabetic rats treated with fatty acids for the same period ( P < 0.01). Conduction velocities in both sensory and motor nerves were normal in diabetic rats treated with either insulin or fatty acids for 5 days. It was concluded that both insulin and essential fatty acids had early effects on nerve conduction in diabetic rats. The speed of their actions, and the magnitudes of the responses were different in sensory and motor nerves.