The dynamics of systolic and diastolic BP and vasodilatory activity of the endothelium in SHR and Wistar-Kyoto rats was studied from the 5th to the 12th week of life. Systolic and diastolic BP did not differ in 5-week-old SHR and Wistar-Kyoto rats. After the 6th week of life, two stages of arterial hypertension development were observed in SHR. Stage 1 (weeks 6-8) was characterized by a significant increase in systolic and diastolic BP that exceeded the corresponding parameters in Wistar-Kyoto rats by 26-32%. Vasodilatory activity of the endothelium was similar in rats of both strains at the age of 5-7 weeks. Stage 2 (weeks 9-12) in SHR rats was characterized by further increase in systolic and diastolic BP that exceeded the corresponding parameters in Wistar-Kyoto rats by 54-89%. The increase in BP during this period was accompanied by a significant decrease in endothelium-dependent relaxation (by 14-16% compared to that in Wistar-Kyoto rats of the same age).

We studied the effect of dihydroquercetin (20 mg/kg/day intragastrically for 6 weeks) on mean BP and macro- and microrheological blood parameters in hypertensive SHR rats; in vitro effect of dihydroquercetin on the tone in thoracic aorta rings isolated from hypertensive SHR rats were also examined. At the end of the treatment course, the mean BP in the experimental rats decreased by 11%; the left ventricular mass index by 2%, and whole blood viscosity by 7-10% in comparison with control SHR rats; erythrocyte aggregation half-time increased by 15%; plasma viscosity, hematocrit, and erythrocyte deformability did not change. In in vitro experiments, dihydroquercetin (10-10M) induced relaxation of the isolated thoracic aorta rings in a dose-dependent manner. Hence, the antihypertensive effect of dihydroquercetin results from the decrease in blood viscosity and vasodilation.

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The effects of dihydroquercetin (50 mg/kg intragastrically daily for 6 weeks) on the density of capillary network (mean number of capillaries per mm), mean capillary diameter, structure of capillary network, capillary diameter distribution (<3, 3-5, 5-7, and 7-9 μ), and local cerebral blood flow (by laser Doppler) in the visual cortex were studied in SHR rats during the development of arterial hypertension (from the 6th to the 12th week of life). Normally, the systolic and diastolic BP progressively increased in SHR rats during this period. Dihydroquercetin did not affect the development of arterial hypertension. At the same time, the drug significantly increased the mean diameter of capillaries (by 11%), capillary network density (by 23%), and in the percentage of capillaries with a diameter of 3-9 μ (passable for erythrocytes; by 42%). Positive effects of dihydroquercetin on the structure of microcirculatory bed improved microcirculation: local cerebral blood flow in the visual cortex of SHR rats was significantly higher (by 36%) than in rats receiving no flavonoid and close to the value in Wistar-Kyoto rats. Dihydroquercetin improved microvascularization and microcirculation in the cerebral cortex of SHR rats during the formation of arterial hypertension.