Increase in hepatic microsomal lipid peroxidation mediated by alpha-adrenergic system under cold stress and noradrenaline treatment.

Lipid peroxidation measured both by the formation of malondialdehyde and by oxygen uptake in presence of NADPH, Fe2+ and ADP in hepatic microsomes increased on cold exposure and decreased on heat exposure of rats. Malondialdehyde content of isolated microsomes also showed similar changes. Treatment of animals with noradrenaline or a alpha-adrenergic agonist, phenylephrine, increased lipid peroxidation which was prevented by simultaneous treatment with cycloheximide, a protein synthesis inhibitor. Cold- and noradrenaline-induced increases were not found in animals pretreated with alpha-adrenergic receptor antagonist, phenoxybenzamine, but not with propranolol, a beta-adrenergic blocking agent. The concentration of the microsomal cytochromes P-450 and b5 remained unaffected under these conditions but the activity of NADPH-cytochrome c reductase showed parallel changes. These observations suggest a role for lipid peroxidation in cellular thermogenesis in liver tissue.