Coronary microvascular dysfunction in diabetes mellitus.

The significance, mechanisms and consequences of coronary microvascular dysfunction associated with diabetes mellitus are topics into which we have insufficient insight at this time. It is widely recognized that endothelial dysfunction that is caused by diabetes in various vascular beds contributes to a wide range of complications and exerts unfavorable effects on microcirculatory regulation. The coronary microcirculation is precisely regulated through a number of interconnected physiological processes with the purpose of matching local blood flow to myocardial metabolic demands. Dysregulation of this network might contribute to varying degrees of pathological consequences. This review discusses the most important findings regarding coronary microvascular dysfunction in diabetes from pre-clinical and clinical perspectives.

Hyperbaric oxygenation affects the mechanisms of acetylcholine-induced relaxation in diabetic rats.

The effects of hyperbaric oxygenation (HBO2) on acetylcholine-induced vasorelaxation (AChIR) were evaluated in male Sprague-Dawley (SD) rats randomized into four groups: healthy controls (Ctrl), diabetic rats (DM), and control and diabetic rats that underwent hyperbaric oxygenation (Ctrl+HBO2 and DM+HBO2). AChIR was measured in aortic rings, with L-NAME, indomethacin, or MS-PPOH and a combination of inhibitors. mRNA expression of eNOS, iNOS, COX-1 and COX-2 was assessed by qPCR, and protein expression of CYP4A(1-3) by Western blot. Plasma antioxidative capacity and systemic oxidative stress were determined with the ferric reducing ability of plasma (FRAP) and thiobarbituric acid-reactive substances (TBARS) assays, respectively. AChIR was preserved in all groups of rats, but mediated with different mechanisms. In all experimental groups of rats, AChIR was mediated mainly by NO, with the contribution of CYP450 vasodilator metabolites. This effect was the most prominent in the DM+HBO2 group of rats. The TBARS was significantly higher in both DM and DM+HBO2 groups compared to respective controls. eNOS expression was upregulated in the DM+HBO2 group compared to other groups, COX-1 expression was upregulated in the DM+HBO2 group compared to the control. CYP450-4A1 / A2/A3protein expression was significantly higher expressed in both hyperbaric groups compared to their respective controls. In conclusion, HBO2 affected all three vasodilator pathways and shifted AChIR to CYP450 enzymes pathway.

Influence of hyperbaric oxygen on blood vessel reactivity: concept of changes in conducted vasomotor response.

The actions of oxygen in the body are extremely complex, and are also involved in various signalling pathways. Hyperbaric oxygen is known to contribute to the improvement of conditions where tissue circulation is suboptimal, and has considerable usage in different treatment protocols and experimental investigations. However, the precise mechanism by which hyperbaric oxygen changes the functioning of coordinated blood vessel systems and microcirculation is still unknown. Taking into account the known facts, we suggest that hyperbaric oxygen induces changes in conducted vasomotor responses, and in that way influences vascular sensitivity and reactivity to vasodilators and vasoconstrictors. Conducted vasomotor responses are constrictions and dilations that are propagated along the vessel, leading to changes in vessel diameter on a certain distance of the initial site of vasoactive substance activity. Because these vascular responses are of substantial significance in physiological processes, their modification would subsequently cause alterations of blood vessel function and tissue perfusion that could explain observed effects of hyperbaric oxygen. We also discuss potential molecular targets of hyperbaric oxygen, investigation of which could presumably help in the eventual clarification of hyperbaric oxygen action.

Do Thebesian veins and arterioluminal vessels protect against myocardial edema occurrence?

Thebesian veins, arteriosinusoidal and arterioluminal vessels drain blood from heart muscle into the chambers. Thebesian veins are reported common in atria and right ventricle, but scarce in the left ventricle. Since the left ventricle may be less prone to edema due to its intermittent cycle of perfusion, it is here proposed that Thebesian veins prevent myocardial edema. This is in concordance with reports that Thebesian veins are common at the ventricle apex and at papillary muscles base, regions prone to edema due to distance to the coronary sinus. Thebesian veins can act as local reducers of venous hydrostatic pressure that correct small differences in fluid filtration and maintain contractility. By analogy, arterioluminal and arteriosinusoidal vessels might act as regulators of local arteriolar pressure. All these vessels reduce capillary fluid filtration in otherwise healthy tissue surrounding ischemic lesions in coronary patients and other situations that lead to edema.