Influence of lipid peroxidation on [H]ketanserin binding to 5-HT2 prefrontal cortex receptors

The influence of lipid peroxidation on 5-HT₂ receptor binding was examined in prefrontal cortex membranes from sheep brain. Lipid peroxidation was induced with ascorbic acid and ferrous sulphate and measured by the thiobarbituric acid method. In lipid-peroxidized membranes, ³H]ketanserin specific binding was inhibited. The B_max values decreased by 80%, from 50.1±3.5 fmol/mg protein in control membranes to 10.1±2.0 fmol/mg protein in peroxidized membranes, indicating a decrease in the number of 5-HT₂ binding sites. However, the K_D values for the ³H]ketanserin specific binding did not significantly change. In order to further characterize ³H]ketanserin binding, the inhibition potency (IC₅₀ values) of antagonists or agonists of serotonin and dopamine receptors for ³H]ketanserin specific binding was determined. In control membranes, the order of the inhibition potency of the drugs tested was the following: ketanserin (?log IC₅₀] = 8.56±0.70) ritanserin (?log IC₅₀] = 8.13±0.30) methysergide (?log IC₅₀] = 7.42±0.50) spiperone (?log IC₅₀] = 7.23±0.18) serotonin (?log IC₅₀] = 6.99±0.65) haloperidol (?log IC₅₀] = 6.95±0.65) dopamine (?log IC₅₀] = 5.82±0.76). After membrane lipid peroxidation, the IC₅₀ value for ritanserin was significantly increased, suggesting a decreased capacity for displacing ³H]ketanserin specific binding. Other antagonists of 5-HT₂ receptors showed apparent increases in IC₅₀ values upon peroxidation, whereas spiperone was shown to be the most potent drug (?log IC₅₀] = 7.19±1.06) in inhibiting ³H]ketanserin specific binding. A decrease in polyunsaturated fatty acids, namely docosahexaenoic acid (22:6) was also observed in peroxidized membranes. These results indicate a modulating role of the surrounding lipids and of the physical properties of the membranes on the binding activity of 5-HT₂ receptors upon the lipid peroxidation process, which can be involved in the tissue impairment that occurs during the aging process and in post-ischemic situations.