Measurements of Calcium-47 and Strontium-85 in Human Subjects

Tracer kinetics and actions of oral and intraperitoneal 1,25-dihydroxyvitamin D3 administration in rats

Tracer kinetic parameters of [3H]-1,25(OH)2D3 were calculated from data obtained following its acute oral (p.o.) or intraperitoneal (i.p.) administration. In normal rats studied after the tracer had distributed into the body, the slope and intercept of the log-serum [3H]-1,25(OH)2D3 versus time relationship were not significantly influenced by the route of administration. Pretreatment with 1,25(OH)2D3 (0.2 micrograms/100 g/day) by the same route as the tracer resulted in the following changes: in p.o. rats the serum [3H]-1,25(OH)2D3 intercept was much lower but the slope was not changed; in i.p. rats the intercept was not changed but the slope was increased. Both p.o. and i.p. treatment with 1,25(OH)2D3 lowered the weight gain and diet consumption, and increased serum calcium, kidney tissue calcium and urinary excretion of orally administered 45Ca. All the measures of bioactivity were greater in the i.p. dosed rats than in the p.o. dosed rats. We conclude that the p.o. 1,25(OH)2D3 was less potent because of diminished bioavailability due to self induction of its presystemic metabolism and inactivation.

Measurement of 47calcium retention with a whole-body counter

A method for measuring the retention of orally administered 47Ca using a whole-body counter (WBC) is described. One microcurie 47Ca in 90 ml of lowfat milk was given along with 5 microCi 51Cr as a stool marker. The retention of 47Ca was determined at 7 days if less than 2% of the administered 51Cr was present in the body. Correlation between calcium retention by the whole-body-counting and the excreta-recovery methods was highly significant (r = 0.835, P less than 0.0001; N = 17). In 5 subjects, each studied twice while on constant self-selected diets, calcium retention was measured by the WBC method with a precision (standard deviation) of +/- 2.6% of the administered dose or +/- 13.9% of the mean retained fraction. Whole-body measurement of 47Ca retention has the advantages over other techniques that no collections of blood or stool are needed, no residency on a metabolic ward is required, and the radiation exposure (13 mrem) is so low that multiple studies may be performed in the same subject.

Whole-body and part-body turnover of 85Sr in Paget's disease

The whole-body and part-body retention of 85Sr has been measured over a period of 150 days in 12 patients with Paget's disease, seven of whom were treated with calcitonin, starting 60 days after the 85Sr administration. Retentions were compared with those in a group of seven control subjects. The retention data were analysed using multiple exponential, single and double power-law and combined power law and exponential functions. The mean retention of 85Sr over a long period was greater in the Paget's patients than in the controls, 1.9 times at two months. No significant effect of calcitonin treatment was demonstrated. Part-body measurements based on profile scanning demonstrated a significantly increased uptake of 85Sr in sites where disease was present. The longer-term rate of disappearance from such sites was faster than from unaffected bones.