Vascular Resistance in Transplanted Kidneys

Chronic allograft failure of transplanted kidneys is often related to hemodynamics rather than immunological rejection, which usually occurs more acutely. Therefore the vascular compliance of transplanted kidneys is now being considered as another predictive parameter in long-term survival of renal transplants. Using an animal model to assess the role of changes in vascular resistance in transplanted kidneys, Gabriels et al. [9] measured the responses of excised small renal arteries to a series of vasoactive agents. Small arteries (200 to 270 mm) were obtained from kidneys donated from Fischer rats (Fl) transplanted into nephrec-tomized Lewis rats. Several control animals were also studied: rats with syngeneic transplants, uninephrectomized, uninephrectomized with denervated kidneys, and kidneys made ischemic, as well as native kidneys. All animals were treated with cyclosporine. After 18 weeks, the coronary, femoral, and mesenteric arteries and small arteries from the kidney were excised and placed in a myograph. The reactivity was assessed by the responses to constrictors (norepi-nephrine, epinephrine, Ang II, vasopressin) and dilators (Ach, sodium nitroprusside). Histology showed that only the kidneys from FL rats had glomerular lesions and vasculo-pathy. However, renal vessels from both allogeneic and syngeneic transplants were more sensitive to all

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Figure 4 Sequential images obtained from a representative field of superficial peritubular capillaries before renal artery occlusion and after release of the clamp. Note the initially interrupted blood flow abated after the renal artery was clamped and 1 to 2 minutes after release of the clamp (frame 46'). Of note, not all capillaries seen at the initial image remain perfused on the subsequent postischemia images.

Figure 4 Sequential images obtained from a representative field of superficial peritubular capillaries before renal artery occlusion and after release of the clamp. Note the initially interrupted blood flow abated after the renal artery was clamped and 1 to 2 minutes after release of the clamp (frame 46'). Of note, not all capillaries seen at the initial image remain perfused on the subsequent postischemia images.

Figure 5 Time course of changes in red blood cell (RBC) velocity in postischemic peritubular capillaries. Shaded area, means SE. Individual experimental sequences are represented by different symbols. Inset: Proportion of nonfunctional peritubular capillaries in the postischemic kidney.

vasoconstrictors, compared to the control groups. Similarly, the vessels from transplanted kidneys were less responsive to the vasodilators than was the control tissue. There were no vessel reactivity differences in nonrenal arteries. This study demonstrates that small-artery reactivity is reduced in transplanted kidneys, regardless of their source. Further, the small arteries in all the transplanted kidneys appeared more constricted, which may contribute to reduced function and survival in transplanted kidneys.

A recent clinical study used a similar hypothesis to identify the predictive value of vascular resistance on allograft survival. In a prospective study of 601 transplanted patients, renal segmental arterial index (RI) was measured at least 3 months after surgery in order to exclude acute rejection causes [10]. RI was determined by the percent reduction of the end-diastolic flow compared with the systolic flow in renal segmental arteries, measured by Doppler ultra-sonography. This value reflects primarily renal cortical vascular resistance. They divided the subjects into RI of greater than 80 (122 patients) and less than 80 (479 patients) and tested the hypothesis that lower renal resistances (an RI of less than 80) predicted long-term allograft survival. The combined end point that defined survival was a reduction in creatinine clearance of 50 percent. Patients were followed for up to 3 years. Sixty-nine percent of the high-RI patients showed a 50 percent reduction in creatinine clearance compared to only 12 percent of the low-RI patients. In addition, 47 percent of the high-RI patients and only 9 percent of the low-RI patients required dialysis. Though this study did not evaluate nonresistance issues in rejection, it confirmed that high vascular resistance predicted poor allograft performance.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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