The in vivo relationship between blood flow, contractions, pH and metabolites in the rat uterus.

Little is known about the relationship between smooth muscle contractile activity and its blood supply. We have therefore investigated this in the rat uterus, using laser-Doppler flow measurement and intra-uterine pressure recordings. We found an inverse linear relationship between flow and contractile activity. There was no evidence for a critical level of flow, above which function is maintained and below which it declines; even small reductions in blood flow decreased uterine force. Force was rapidly restored upon reperfusion. Reactive hyperaemia was absent from all but 6 of the 41 preparations studied. We used 31P nuclear magnetic resonance (NMR) spectroscopy to measure concentrations of adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi) and intracellular pH (pHi) simultaneously with force and flow. Reductions in flow were associated with significant reductions in [ATP], [PCr] and pHi, and an increase in [Pi]. These changes were related to flow significantly and linearly and their effects on force may be additive. These data show that uterine smooth muscle is closely dependent upon its blood supply for maintaining both normal force production and metabolite levels. Consequently, even small decrements in flow may have deleterious functional effects.