[Protective effect of soy proteins under excessive amount of fats in the diet of rats].

Excessive fat intake causes the development of metabolic syndrome (MS). Our studies have shown that soy proteins in the diet improve vascular reactivity in rats with a high-salt dietary load and renal dysfunction. We hypothesized that the introduction of soy proteins into a high-fat diet (HFD) can prevent or reduce vascular dysfunction. The aim of the study was to test the hypothesis about the possible protective effect of soy protein isolate on endothelium-dependent dilation of the mesenteric arteries of male Wistar rats receiving an excess amount of fat in the diet. Material and methods. The study used 3 groups of 20 rats, weighing 220-240 g. The HFD group received a diet containing 50% fat (by calorie value) and 20% casein, HFD + Soy group received a diet containing 50% fat and 20% soy isolate SUPRO-760, the control group - a standard casein diet. After 8 weeks, the responses of mesenteric arteries precontracted with phenylephrine to acetylcholine (ACh) were studied in the absence and with the use of NO synthase (L-NAME), cyclooxygenase (indomethacin), BKCa and Kv channel (tetraethylammonium) blockers, using microphoto- and video recording of the vessel diameter in vivo. Results. Compared with the standard diet, visceral fat mass increased by 54.6% in rats fed HFD and by 25.9% in rats fed HFD + Soy (p<0.01). In the HFD + Soy group, the increase in blood pressure was less than in the HFD group (p<0.01). Consumption of HFD + Soy prevented disorders typical of HFD, reducing glycemia and insulin resistance, normalizing lipid metabolism (p<0.05). Evaluation of the functional state of the mesenteric arteries (in vivo) showed that in the HFD + Soy group the amplitude of dilation on ACh remained close to the control group, whereas in the HFD group the suppression of ACh-induced relaxation was observed (by 19.8% (p<0.01). After blockade of NO synthase by incubation with L-NAME the magnitude of vasodilation on ACh decreased (p<0.001) in the HFD group by 47.0±7.4%, in the HFD + Soy group - by 68.2±6.6% and in the control group - by 68.9±5.6%. After incubation with L-NAME, indomethacin and tetraethylammonium, the amplitude of dilation on ACh in rats of the HFD and HFD + Soy groups was 1.5 fold greater (p<0.05) than in the control. The relaxation amplitude to sodium nitroprusside did not differ between the groups. Conclusion. The introduction of soy proteins into a HFD prevents the development of impairs characteristic of MS: it reduces visceral obesity, improves the state of carbohydrate and lipid metabolism, and has a hypotensive effect. The protective effect of soy proteins on vascular reactivity in rats with excessive fat consumption was confirmed: the introduction of soy protein isolate into the diet leads to the prevention of endothelial dysfunction characteristic of HFD, preventing the disruption of NO-dependent vasodilation mechanisms. It is assumed that the positive effect of soy on vascular reactivity is mediated by maintaining NO synthesis by the endothelium, and may be associated with the anti-inflammatory and antioxidant properties of both proteins and isoflavonoids contained in soy.