RESETTING OF PARATHYROID-HORMONE SECRETION AFTER VITAMIN-D-3 TREATMENT IN HYPOPARATHYROIDISM AND AFTER PARATHYROID ADENECTOMY IN PRIMARY HYPERPARATHYROIDISM

The relationship between parathyroid hormone (PTH) secretion and extra cellular calcium (Ca) level is reciprocal causality. The equilibrium o perating point determines basal PTH secretion rate and basal extracell ular Ca level. We studied how this equilibrium was achieved in the sub jects with decreased PTH secretion or decreased parathyroid glands num ber. Basal/maximum ratio of serum PTH, which reflects the basal secret ory state of parathyroid glands, was increased in 9 hypoparathyroid pa tients treated with vitamin D-3 (VD3) [7 patients with idiopathic hypo parathyroidism (IHP), and two patients with postsurgical hypoparathyro idism] and in seven of nine parathyroid adenectomized patients. There was a negative correlation between the ratio and basal serum Ca level in the patients with IHP after VD3 treatment (r = 0.7167, P < 0.05) an d in the patients after parathyroid adenectomy (r = 0.7760, P < 0.05). The regression curves in these two groups coincided regardless of the difference in maximum PTH secretion rate, which suggested that the ba sal secretory state of parathyroid glands was determined by extracellu lar Ca level in a similar manner in these subjects. There was a sigmoi dal relationship between basal/maximum ratio of serum PTH and basal se rum Ca level, when the data were collected from 15 hypoparathyroid pat ients before or after VD3 treatment, 9 parathyroid adenectomized patie nts, and 10 normal subjects (r = 0.9057, P < 0.001). This sigmoidal cu rve is thought to represent the fundamental relationship between the b asal secretory state of parathyroid glands and extracellular Ca level.