HETEROTOPIC HEART-TRANSPLANTATION ALTERS HIGH-ENERGY PHOSPHATE-METABOLISM IRRESPECTIVE OF CARDIAC ALLOGRAFT-REJECTION

This study was undertaken to validate the potential of P-31 magnetic r esonance spectroscopy (MRS) as a noninvasive alternative for transveno us endomyocardial biopsy in detecting cardiac allograft rejection. Don or hearts from either Lewis rats (L) or Brown-Norway rats (BN) were tr ansplanted into the neck of L rats resulting in a non-rejecting group L-L and a rejecting group L-BN. L-L and L-BN rats were serially studie d by means of P-31 MRS from postoperatine day 1-8. In addition, reject ion was confirmed by histology. A similar, marked decrease in phosphoc reative/beta-adenosinetriphosphate (PCr/ATP) ratio from day 1-3 was ob served in both L-L and L-BN hearts. This ratio levelled off on postope rative day 3 and remained depressed on subsequent postoperative days i n both groups, although histology showed an increase in the severity o f rejection in L-BN. However, the PCr signal/noise ratio in L-BN start ed to decrease after day 4, coinciding with the histologic evidence of severe rejection (score IV), whereas in L-L hearts (score 0) this rat io remained unaltered until day 8. Since high-energy phosphate metabol ism is affected by the unloaded status of the heterotopically transpla nted heart, irrespective of rejection, the PCr/ATP ratio appears not t o be a specific marker for the detection of acute rejection in this mo del. In contrast, the PCr S/N ratio appears to be a specific and sensi tive marker of acute rejection, but only in a late, severe stage.