The inductive effect of rickets on glycolytic enzymes of rat epiphyseal cartilage and its reversal by vitamin D and phosphate

In rickets produced in rats by low phosphate, vitamin D-free diets, epiphyseal cartilage increases in wet weight, and in deoxyribonucleic acid, glycogen, and protein content. Dietary phosphate reverses all of these effects. Vitamin D reverses all of these rachitic changes with the exception of that in deoxyribonucleic acid content. The effectiveness of vitamin D in reducing cartilage cell hypertrophy without decreasing cell numbers differentiates the mechanism of vitamin D action from that of phosphate. Glycolysis is doubled per cell in rachitic cartilage and there is a corresponding coordinate increase in specific activities (EU/mg protein) of phosphofructokinase, aldolase, pyruvate kinase, and lactate dehydrogenase. Both effects are reversed by dietary phosphate or vitamin D. It is suggested that increased glycolysis may be due to a specific increment in glycolytic enzyme levels supplemented by a general increase in tissue protein. A proportional relationship between cellular lactate production and glycolytic enzyme activity is demonstrated in nine different physiological states. The hypothesis is advanced that a regulatory mechanism operates in cartilage to coordinately control the levels of glycolytic enzymes and cellular metabolism.