Glycolytic Control Mechanisms in Myometrium from Pregnant Rhesus Monkeys1

Biopsies of myometrium from pregnant rhesus monkeys and taenia coli from nonpregnant monkeys were rapidly excised and freeze-clamped. Tissue levels of all the metabolic intermediates and cofactors of the glycolytic pathway were determined and the mass-action ratios for each reaction calculated. The apparent equilibrium constants were over 1000 times larger than the mass-action ratios for hexokinase, phosphofructokinase. and pyruvic kinase; this is evidence that these three enzymes are rate-limiting for glycolysis in both types of smooth muscle. The apparent equilibrium constants of the combined reaction for glyceraldehyde-P dehydrogenase plus P-glycerate kinase were 30 and 50 times greater than the mass-action ratios for myometrium and taenia coli respectively: thus it is possible that this step is also rate-limiting. The remaining reactions in glycolysis are either at equilibrium or fairly close to equilibrium and therefore cannot be rate-limiting. The conversion of [‘4CJ fructose-6-P to [‘4C] lactate by cell-free extracts of myometrium and taenia coli was studied. Without added ATP, no [‘4C] lactate was produced, increasing the level of ATP increased and then decreased lactate production. This biphasic response to increasing levels of ATP is also found in semipurified preparations of cardiac and skeletal muscle phosphofructokinase. As in cardiac and skeletal muscle, the ATP inhibition of [‘4C] lactate production by myometrium was relieved by inorganic phosphate. The amount of data on the metabolism and biochemistry of mammalian skeletal muscle published during the last 15 years contrasts sharply with the paucity of information on smooth muscle, especially on primate myometrium. Studies on myometrium from the pregnant rhesus monkey (Macaca mu!atla), which is biologically similar to the human primate, are therefore of particular interest. Numerous publications are available on the identification of rate-limiting or regulatory reactions for the glycolytic pathway in voluntary skeletal and cardiac muscle (Newsholme and Start 1973; Mansour 1972), but similar data on smooth muscle appear to be lacking.