Influence of oestrogens on formation of reactive oxygen species in liver microsomes of differently aged male Wistar rats.

Metabolic pathways of oestrogens are the formation of catechol oestrogens (CE; 2- and 4-hydroxy-oestrogens), redox cycling of CE and free radical generation, mediated through cytochrome P450 (P450) oxidase/reductase activity. We checked the oestrogens oestradiol (E2), oestradiol valerate (E2V) and ethinyloestradiol (EE2) for formation of reactive oxygen species in vitro and ex vivo in male Wistar rats in dependence on age. In liver microsomes of 10-, 30-, 60- and 270-day-old rats the influence of E2, E2V and EE2 (10(-7)-10(-3) M) on NADPH-Fe(++)-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) was investigated. The same parameters, additionally P450 content and monooxygenase activities were measured in liver 9000 x g supernatants after subchronic administration of the oestrogens (1, 10 mg/kg b. wt. orally). The most important results are the strong inhibitory capacities of the oestrogens in vitro on LPO in the order of E2V < E2 < EE2, most pronounced in 10-, 60- and 270-day-old animals. In microsomes of 30-day-old rats with the highest control LPO the antioxidative effect of the oestrogens was lower. Whereas the H2O2 generation was not changed by E2, enhanced by E2V, but diminished by EE2 in all age groups, CL(LUC) and CL(LUM) were inhibited in the order of E2 < E2V < EE2. Also after subchronical treatment of the rats the antioxidative action of the oestrogens was evident, microsomal LPO was inhibited in the order of E2 < E2V < EE2. All oestrogens inhibited ethylmorphine N-demethylation. But enhanced H2O2 generation and increased CL(LUC) also indicate a formation of reactive oxygen species by these oestrogens. Obviously in vitro the antioxidative phenolic structure of the oestrogens dominates, whereas after in vivo administration the dose- and age-dependent biotransformation produces prooxidative in addition to antioxidative structures.

The contrast characteristic of the pattern electroretinogram depends on temporal frequency.

BACKGROUND: The pattern electroretinogram (PERG) amplitude is believed to be linearly related to contrast. In the context of analyzing the effects of media opacities on the PERG, we measured its contrast-amplitude function at various temporal frequencies. METHODS: PERGs were recorded in nine subjects with a checksize of 0.8 degree and a mean luminance of 45 cd/m2. Experiment 1 covered six temporal frequencies [checkerboard pattern onset/offset in a transient (4 Hz) condition and checkerboard pattern reversal at 7, 10, 13, 16, 21 rev/s] at three contrast levels (25%, 50% and 100%). A second experiment covered two frequencies (7 and 21 rev/s) at five contrast levels from 25 to 100%, in a large field (27 degrees x 32 degrees) and a perifoveal condition (central mask of 7.5 degrees radius). RESULTS: Experiment 1: At all temporal frequencies the PERG amplitude increases with contrast, but the shape of the contrast-amplitude function varies markedly: Under transient conditions and at 7 rev/s, the PERG increases linearly with contrast, but this function displays a progressively positive curvature at higher frequencies (P < 0.001). At 21 rev/s a reduction of the contrast from 100% to 50% reduces the amplitude to 1/5. Experiment 2: Experiment 1 was replicated. The amplitude-contrast characteristic was found to be linear at 7 rev/s and smoothly accelerating at 21 rev/s; the same characteristics were found when stimulating the perifoveal area alone. CONCLUSION: This dependency of the contrast characteristic on temporal frequency is contrary to what would be expected from a magno/parvo model. Further, this contrast dependency needs to be taken into account when designing stimuli for use in patients that may have media opacities.