Heterogeneous Metabolic Changes in the Calf Muscle of the Rat during Ischaemia-reperfusion: in Vivo Analysis by 31 P Nuclear Magnetic Resonance Chemical Shift Imaging and 1 H Magnetic Resonance Imaging

Abstract

Non-localized and localized ³¹P nuclear magnetic resonance (NMR) spectra of rat calf muscle during arterial occlusion and after reperfusion were concurrently observed using chemical shift imaging and ‘H magnetic resonance imaging (MRI). During ischaemia. the levels of high-energy phosphates (phosphocreatine and adenosine 5′-triphosphate) were depleted and that of inorganic phosphate was increased. In addition, the signal intensity on ¹H MRI was increased. These changes were observed to be relatively homogeneous throughout the calf. In contrast, the changes during reperfusion were heterogeneous. In the central part of the calf, inorganic phosphate disappeared, phosphocreatine was restored immediately on reperfusion and the ‘H signal was decreased. However, in the regions of the tibialis anterior muscle and the superficial part of the gastrocnemius muscle, inorganic phosphate persisted for several hours, phosphocreatine was not restored and the signal intensity on T2-weighted ¹H MRI was increased further. The heterogeneous changes detected by ³¹P NMR spectroscopy and ¹H MRI showed close agreement. The susceptibility of different calf muscles to ischaemia and reperfusion seems to depend on their predominant muscle fibre type (i.e. fast-twitch or slow-twitch fibres). Reversible and irreversible ischaemic changes could be non-invasively distinguished by in vivo ³¹P NMR spectroscopy and ¹H MRI.