Parathyroid activity in hyperthyroidism

Abstract

Even in the absence of PTH, serum P levels rose in response to thyroxine. Thus, PTH secretion is not suppressed in hyperthyroidism as assumed hitherto. In contrast, the findings suggest an activation of endogenous PTH secretion in thyrotoxic animals. These results agree with the finding of increased serum PTH levels in thyrotoxic patients (radioimmunoassay*), reported elsewhere (3). After parathyroidectomy TRP of hyperthyroid animals was not different from that of euthyroid animals, although the serum P levels were elevated. At high serum P levels, TRP was higher in hyperthyroid PTX animals, pointing to a raised renal “threshold”. In view of the contracted extracellular space in hyperthyroid animals, this effect of thyroxine might be mediated by changes of extracellular volume, although alternative mechanisms are not excluded.