The present studies were designed to monitor metabolic perturbations following changes in contractile activity and ion transport in rat and rabbit myometrium by simultaneous measurement of NADH fluorescence, lactate production and isometric force. Stimulation (127 mM K+) and inhibition (Ca2+-deficient solution) of isometric force development induced a decrease/increase of fluorescence intensity corresponding to a more oxidized/reduced state of tissue pyridine nucleotides, respectively. If tension development was abolished by EGTA, fluorescence changes due to altered ion transport could be monitored. Slow progressive stimulation of the sodium pump by Ca2++-deficient solution resulted in an ouabain (10(-3) M) sensitive monophasic NADH oxidation, which was reversed by inhibition of the pump by isotonic K+ solution. If, however, stimulation of the pump was rapid and maximal (addition of 30 mM KCl to Na+-loaded tissues) the fluorescence response was triphasic and ouabain sensitive: it consisted of an initial NAD reduction followed by a transient NADH oxidation and a second slow NAD reduction. These fluorescence changes are interpreted in terms of separate redox changes in the cytoplasm and mitochondria. The ouabain sensitive stimulation or inhibition of Na/K transport was always accompanied by parallel changes in uterine lactate production irrespective of the actual contractile state of the myometrium. The present results show that 1 fluorescence technique can be applied to monitor metabolic perturbations in the uterus evoked by changes in contractility or ion transport; and 2 aerobic glycolysis and Na/K transport are tightly coupled in the myometrium.