Vitamin D3 Enhances Endothelial Function and Improves Vascular Reactivity in an Experimental Model of Type 2 Diabetes...

Background/Objectives: Type 2 Diabetes Mellitus (T2DM) is characterized by insulin resistance and chronic hyperglycemia, which significantly impair vascular function. In experimental T2DM models, the vascular endothelium is compromised, showing decreased vasodilator responses. Vitamin D3 has emerged as a promising intervention for improving glycemic parameters and restoring endothelial function. This study evaluated the effects of vitamin D3 (0.25 and 0.50 µg/kg/day) administered for 4 and 8 weeks on the ex vivo aortic vascular reactivity of T2DM rats. Methods: T2DM was induced in male Wistar rats via a high-fat, normoprotein diet and streptozotocin (30 mg/kg, i.p.). Groups included normal control, diabetic control, metformin, and vitamin D3 (0.25 or 0.50 µg/kg/day). Following 4 or 8 weeks of treatment, thoracic aortic segments were isolated for ex vivo vascular reactivity studies to assess responses to vasoconstrictor and vasorelaxant agents. Results: Vitamin D3 treatment improved glycemic profiles; the 0.25 µg/kg dose reduced fasting glucose, while the 0.50 µg/kg dose lowered glycated hemoglobin at 8 weeks. Endothelium-dependent relaxation induced by acetylcholine was significantly increased in diabetic rats treated with vitamin D3 at both doses over 4 weeks compared to diabetic controls. Moreover, vitamin D3 prevented the attenuation of maximal contractile responses to phenylephrine observed in untreated diabetic rats at 8 weeks. Conclusions: Vitamin D3 supplementation restores endothelial function and improves vascular reactivity in an experimental T2DM model. These findings suggest that vitamin D3 may mitigate vascular complications by enhancing vasorelaxation and maintaining contractile integrity.