EFFECT OF CHANGES IN PARATHYROID ACTIVITY ON BONE METABOLISMIN VITRO

Abstract

The effects of alterations in parathyroid activity in vivo on the mineral equilibrium between surviving bone and its bathing fluid have been examined in vitro. Weanling rats treated with parathyroid extract (PTE) or parathyroid-ectomized (PTX) during the week prior to sacrifice were compared with untreated controls. Thin fragments of freshly excised skull were incubated in bicarbonate buffer under 95%O₂, 5%CO₂. After 8 hours of incubation the mean calcium concentrations in buffer were 5.2 ± .1 mg.% for PTE skulls, 3.8 ± .1for control skulls and 3.2 ± .1 for PTX skulls. The phosphorus concentrations were 4.2 ± .1, 3.8 ± .1 and 5.1 ±.1 mg.% respectively. Buffer citrate, lactate and pH did not differ significantly in the three treatment groups. The effects of prior treatment on buffer calcium concentration were similar after anaerobic incubation. Incubation of heat-inactivated bone resulted in a smaller final buffer calcium concentration. Addition of fluoroacetate to the buffer enhanced citric acid accumulation but buffer calcium concentration did not increase. Addition of iodoacetate inhibited lactate production and caused a marked decrease in buffer calcium concentration. These data indicate that the mineral equilibrium between surviving bone and its bathing fluid depends on metabolic activity and can be modified by prior changes in parathyroid function. Increased citrate production does not appear to be the mechanism of parathyroid hormone action. Glycolysis is active in bone tissue and appears to be required for calcium mobilization.