Sex Difference in the Kinetics of Triglyceride Metabolism in Normal and Hypertriglyceridaemic Human Subjects

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Abstract
Several years ago we demonstrated in man that increasing plasma very low density lipoprotein (VLDL) triglyceride (TG) concentrations were associated with increasing VLDL‐TG production rates, and that this relationship described a rectangular hyperbola which could be characterized in terms of enzyme kinetics. Utilizing this approach Nikkilä and Kekki confirmed these observations in a large group of normal subjects. Moreover, after analyzing the Km and Vmax values of their subjects they noted a striking and important sex difference: females were found to have significantly lower Km values than men, whereas the Vmax values for the two groups were the same. This indicates that for a given VLDL‐TG production rate, females will have lower plasma TG concentrations. We have now studied 53 subjects with widely varying plasma TG concentrations, and have been able to detect a similar sex difference in subjects with hypertriglyceridaemia. Furthermore, we have noted a highly significant direct relationship between TG concentration and production in both sexes, and have found no relationship between an individual's Km value and his coexisting plasma TG level. These results allow us to conclude that: 1) the sex difference in TG kinetics which Nikkilä and Kekki originally note in normals can now be extended to include hypertriglyceridaemic subjects, and 2) in general, overproduction, and not underutilization, is the initiating event in most cases of hypertriglyceridaemia.