A 31P NMR investigation into the effects of repeated vascular occlusion on uterine metabolites, intracellular pH and force, in vivo.

Little is known about the metabolic effects of ischaemia on high energy phosphates in vivo in smooth muscle. We have developed a method for reversibly occluding the uterine artery, which allows simultaneous measurement of uterine metabolites using 31P NMR spectroscopy, and intra-uterine pressure, in vivo during ischaemia. We have investigated the effects of repeated ischaemia on metabolites, intracellular pH and contractions in anaesthetized rats. Occlusion produced an immediate drop in uterine blood flow and decreased contractions. Although contractions recovered upon reperfusion after both occlusions, the contractile activity was less after the second period of occlusion, suggesting less resistance after a prior ischaemic period. Significant falls in [ATP] and [phosphocreatine] and an increase in [P(i)] occurred during both occlusions. These were all reversed within 30 min of reperfusion. There was a large drop in intracellular pH produced by occlusion, which was rapidly reversed upon reperfusion. The changes in metabolites and intracellular pH were similar during the repeated ischaemic period, to those occurring during the first ischaemic period suggesting no alteration in energy production or utilization had occurred, with prior exposure to ischaemia. The significance of these results to the functioning of the uterus in labour is briefly discussed.