Direct vasodilative effect of FK506 on porcine mesenteric artery in small bowel transplantation

Inhibition of big-conductance Ca2+-activated K+ channels in cerebral artery (vascular) smooth muscle cells is a major novel mechanism for tacrolimus-induced hypertension

Tacrolimus (TAC, also called FK506), a common immunosuppressive drug used to prevent allograft rejection in transplant patients, is well known to alter the functions of blood vessels. In this study, we sought to determine whether chronic treatment of TAC could inhibit the activity of big-conductance Ca²⁺-activated K⁺ (BK) channels in vascular smooth muscle cells (SMCs), leading to hypertension. Our data reveal that the activity of BK channels was inhibited in cerebral artery SMCs (CASMCs) from mice after intraperitoneal injection of TAC once a day for 4 weeks. The voltage sensitivity, Ca²⁺ sensitivity, and open time of single BK channels were all decreased. In support, BK channel β1-, but not α-subunit protein expression was significantly decreased in cerebral arteries. In TAC-treated mice, application of norepinephrine induced stronger vasoconstriction in both cerebral and mesenteric arteries as well as a larger [Ca²⁺]_i in CASMCs. Chronic treatment of TAC, similar to BK channel β1-subunit knockout (KO), resulted in hypertension in mice, but did not cause a further increase in blood pressure in BK channel β1-subunit KO mice. Moreover, BK channel activity in CASMCs was negatively correlated with blood pressure. Our findings provide novel evidence that TAC inhibits BK channels by reducing the channel β1-subunit expression and functions in vascular SMCs, leading to enhanced vasoconstriction and hypertension.

The optimal intestinal segment length for experimental size-mismatched intestinal transplantation: Defining the maximum length with the lowest blood flow needs in a porcine model

Transplanted Intestinal Segments (IS) must match the perfusion capacities of the recipient. This can be challenging during a size-mismatched SBTX. In this study, we defined the maximum IS length with lowest blood flow needs in a porcine model by evaluating the physiological perfusion rates of different IS lengths. Blood flow in the SMA, aorta segment four, and general circulatory parameters were monitored before and after sequential intestinal resection. IS lengths of 30 cm, 60 cm, 120 cm, and 300 cm (n = 8 each) were compared. The IS blood flow requirements increased with IS length (30 cm: 19.5 ± 3.4 mL/min; 60 cm: 16.9 ± 6.7 mL/min; 120 cm: 34.9 ± 8.5 mL/min; 300 cm: 62.9 ± 11.6 mL/min). Absolute IS blood flow (P = .004), percentage IS blood flow uptake from the SMA (P = .001), and percentage IS blood flow uptake from the aorta (P = .005) increased significantly between 60 cm and 120 cm. We concluded that 60 cm was the maximum IS length before blood flow demands significantly increased in a porcine model.

Intestinal ischemia/reperfusion: microcirculatory pathology and functional consequences

BACKGROUND

Intestinal ischemia and reperfusion (I/R) is a challenging and life-threatening clinical problem with diverse causes. The delay in diagnosis and treatment contributes to the continued high in-hospital mortality rate.

RESULTS

Experimental research during the last decades could demonstrate that microcirculatory dysfunctions are determinants for the manifestation and propagation of intestinal I/R injury. Key features are nutritive perfusion failure, inflammatory cell response, mediator surge and breakdown of the epithelial barrier function with bacterial translocation, and development of a systemic inflammatory response. This review provides novel insight into the basic mechanisms of damaged intestinal microcirculation and covers therapeutic targets to attenuate intestinal I/R injury.

CONCLUSION

The opportunity now exists to apply this insight into the translation of experimental data to clinical trial-based research. Understanding the basic events triggered by intestinal I/R may offer new diagnostic and therapeutic options in order to achieve improved outcome of patients with intestinal I/R injury.