Project Title: 16. Exposure to External and Internal Radiation in Vivo Measurement of Radionuclides in Man; Body Burden and Kinetic Factors, Computer Applications BX-01-01-(b) Technical Progress in FY 1973: (Cont'd.) TBNAA reveals a decrease in total body calcium in subjects exhibiting the condition of hyperthyroidism, With respect to an estimated normal total body calcium (Cap) for the individual based on height, sex, and potassium level, a mean decrease to 90.6% was observed. The empirical value of Cag uses body potassium as a parameter, as it is an index of lean body mass, The relationship derived empirically from a study of 9 normal males is Cag = 54. 5/K H and from a study of 5 normal females is Cag = 57.0 /K H; where Ca and K are expressed in grams and height (H) in centimeters. The P/Ca ratio in hyperthyroid patients was slightly higher than the 0.55 value observed in normals. Treatment of thyrotoxicosis by drug therapy, by surgery or by administration of I-131 leads to an increase in the mean Ca level at nine months following therapy. A concomitant decrease in the mean P/Ca ratio was observed in these patients, Loss of bone mass in thyrotoxicosis has generally been associated with increased bone resorption and a negative calcium balance. Changes in bone are most probably not mediated via alterations of parathormone (PTH) or calcitonin but rather are the result of the action of the thyroid hormone on the osteoclasts. Similar analysis of hypothyroid patients indicated a mean calcium value of 93.5% of their expected value, than in normal subjects. The mean P/Ca ratio was also lower At nine months following the institution of maintenance therapy in three patients, the mean calcium decreased to 88% of the total body calcium. The therapy also resulted in an increase in the mean P/Ca ratio. Decreased urinary calcium excretion and variable phosphorus excretion has been reported for hypothyroid patients. studies have revealed a decrease in bone turnover, Additionally, kinetic In parathyroid studies, hyperparathyroid patients exhibit a uecrease in calcium to 89% of the expected value. A low mean P/Ca ratio was observed, consistent with evidence of a loss of phosphorus, This condition may result from the inhibition of proximal tubular resorption responding to an increase in the PTH level. Nine months following the initiation of a course of treatment, a further decrease in total calcium was observed in two of PTH acts directly on bone as well as affecting the three patients treated. the functioning of the kidneys and the absorption in the gastrointestinal The finding of decreased total calcium is consistent with densitometric tract. ographic evidence of demineralization in hyperparathyroid patients. and A decfitgse in bone mass often precipitates, via the body's homeostatic mechanism, &compensatory increase in the bone accretion rate. Hence, the metabolic picture may vary considerably in the course of this disorder. Hypoparathyroid patients exhibited an increased body calcium, in For example, one patient with idiopathic terms of the expected value. hypoparathyroidism showed an increase to 170% of the total-body calcium. (See Continuation Sheet) peagid RX-17