Lipid peroxidation in rat liver microsomes. I. Stimulation of the NADPH-cytochrome P-450 reductase-dependent process in hyperthyroid state.

The effect of hyper- and hypothyroidism on lipid peroxidation has been studied in rat liver microsomes under three different experimental conditions. Under none of these conditions was the formation of TBA-reactive substances affected by either of these two pathological states. On the contrary, with NADPH as the only peroxidation inducer, hydroperoxide concentration increased some three fold in microsomes from hyperthyroid rats, while a small decrease was measured in those from hypothyroid animals. Similarly, the activity of NADPH-cytochrome P-450 reductase was found to be 45.1% higher in hyperthyroid and 40.3% lower in hypothyroid microsomes. The possibility discussed here is that two distinct peroxidative mechanisms (of which one, NADPH-cytochrome P-450 reductase-dependent, is influenced by the thyroid hormone) can compete with each other for the substrate polyunsaturated fatty acids.