Effects of α-MSH on ischemia/reperfusion injury in the rat sciatic nerve

Abstract

Background: Ischemia/reperfusion (I/R) causes the production of toxic free radicals and leads to pathological changes in nerve tissue. We investigated the effect of alpha-melanocyte stimulating hormone (α-MSH) in a rat model for sciatic nerve I/R and discuss the possible cytoprotective and antioxidant mechanism of α-MSH against ischemic fiber degeneration.

Methods: Experiments were performed using 42 adult male Wistar rats. Rats were divided into six experimental groups: control group, ischemia group, I/R groups, and α-MSH treated groups. Ischemia was produced by clamping of the femoral vessels. Immediately after ischemia that lasted 3 h, 75 μg/kg of α-MSH was administered subcutaneously before reperfusion and the tissue malondialdehyde (MDA) level was evaluated as an indicator of lipid peroxidation in groups with different reperfusion periods.

Results: The reperfusion injury did not begin in the first hour of reperfusion after 3 h of ischemia, and MDA levels increased on the first day of reperfusion. During the first day, blood MDA levels were decreased in the α-MSH group compared to the control group. The tissue from animals pre-treated with α-MSH showed fewer morphological alterations. Myelin breakdown was significantly diminished after treatment with α-MSH, and the ultrastructural features of axons showed remarkable improvement. Two-way analysis of variance was used for comparing three or more groups. When a significant difference existed, the post-hoc multiple-comparison test was applied to demonstrate the differences.

Conclusions: The results confirm that pre-treatment with α-MSH after ischemia protected the peripheral nerves against I/R injury.

Keywords: ischemia/reperfusion injury; lipid peroxidation; peripheral nerve; rat sciatic nerve; α-MSH.

Figure 1

MDA levels for experimental groups. After 1 day of reperfusion, MDA levels in the α-MSH treated group were significantly decreased (P < 0.005)

Figure 2

(a) A micrograph demonstrating fine structural features of a sciatic nerve from a control rat (Group 1). Myelinated and unmyelinated fibers show normal ultrastructural features. The cytoplasm of the axon appears unremarkable and demonstrates no morphological abnormality. Schwann cells also show normal ultrastructure (uranyl acetate and lead citrate, 2000×). (b) An electron micrograph from a rat sciatic nerve after ischemia/reperfusion (Group 5). There are many vacuoles on the myelin sheath of axons. Axonal shrinkage (arrows) is seen in some axons. Vacuolization in the cytoplasm of some Schwann cells is clear. There is vacuolization and degeneration on the unmyelinated fiber (arrow head) (uranyl acetate and lead citrate, 2000×). (c) An ultrastructural picture showing a section from the sciatic nerve of a rat that was treated with α-MSH before reperfusion (Group 6). Vacuolization on the myelin sheath decreased remarkably. Axonal shrinkage and vacuolization of Schwann cells are evident only in a few fibers. Unmyelinated fibers seem to be normal (uranyl acetate and lead citrate, 2000×)