A new microvascular model for noninvasive nuclear magnetic resonance spectroscopy of the transplanted kidney.

The cellular biology of graft rejection is not well understood. Phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy is a new noninvasive technique for the measurement of intracellular pH and relative amounts of phosphorus-containing compounds, such as adenosine triphosphate (ATP), inorganic phosphate, phosphocreatine, and sugar phosphates, in any tissue from which a clear signal can be obtained. Biochemical analysis of such precision, without the need for tissue destruction, represents an unusual opportunity for analysis of in vivo cellular metabolism under varying conditions, including graft rejection. 31P NMR study of intra-abdominal viscera has not been feasible in most laboratories without laparotomy because of signal interference from abdominal wall muscle. In this study, to eliminate this interference, a rat kidney was transplanted to the groin, where it could be serially studied without overlying skeletal muscle. This new vascular technique was successful in 11 of 11 attempts and maintained normal serum creatinines in 10 chronic survivors after removal of both native kidneys. The 31P NMR spectroscopic signal from the groin kidney is clear and highly reproducible. This new microvascular model will make it possible to carry out noninvasive long-term spectroscopic studies that could potentially identify a reliable marker for allograft rejection.