The fundamental function of the parathyroid glands is the homeostatic regulation of the ionized calcium in body fluids. It has been conclusively demonstrated that parathyroid hormone causes mobilization of calcium from the skeleton and an increase in renal clearance of phosphorus. Recent studies strongly suggest that this hormone enhances both the intestinal absorption( 1,2) and the renal tubular reabsorption (3,4,5,6) of calcium.Earlier reports from this laboratory(4,S) demonstrated that there was a direct relationship between the filtered load and the renal clearance of calcium. For any given filtered load of this ion an increase in the circulating level of parathyroid hormone lowers renal clearance of calcium expressed as per cent of the filtered load excreted. These studies suggested that the increase in renal clearance of calcium in the hypoparathyroid human receiving Vit. D(7) was not due to a direct effect of the vitamin on the renal tubule but to the increase in serum calcium and filtered load which followed administration of the vitamin. The present experiments were undertaken to compare the effects of calcium infusions, parathyroid extract, and Vit. D2 on renal clearance of calcium over a comparable range of serum calcium or filtered load.Methods. The studies were performed in 2 post-surgical-hypoparathyroid females with normal renal function. Patient R.R., age 34, was hypoparathyroid 13 years and had never received supplemental Vit. D. Patient B.W., age 29, was hypoparathyroid 10 years and discontinued the daily dose of 4 cc of AT-10 four weeks prior to these studies.The patients were placed on a constant calcium and phosphorus intake and experiments were carried out in the following order : Approximately one-half hour clearance periods were obtained during an infusion of 1.7 g of calcium ion as calcium chloride over * Supported by USPHS grant. a 6-hour period. Three days later, after the serum calcium returned to the previous baseline levels, they were given progressively increasing doses of parathyroid extract (Parathyroid, Eli Lilly) up to a maximum of 350 units every 8 hours intramuscularly. Approximately one-half hour clearance periods were obtained twice daily over a range of serum calcium comparable to those achieved during the calcium infusion. After the parathyroid extract was discontinued and serum calcium once again returned to the baseline levels, the patients were placed on 1.5 g of oral calcium daily, and progressively increasing doses of Vit. D2 up to 150,oO units, for patient R.R. and 400,0001 units for patient B.W. Clearances were obtained as described above during administration of parathyroid extract.Calcium clearance was determined by dividing quantity of calcium excreted per minute in the urine by the serum diffusible calcium(8). The latter figure was determined separately for the calcium infusion, the parathyroid extract and the Vit. D administration by calculating the mean diffusible serum calcium from blood samples obtained during each experimental condition. The calcium clearan...
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