Rate of Initial Entry of Ca 47 and Sr 85 from the Intestine into the Vascular Space. ∗

Summary

The rate of initial entry of both radioactive calcium and strontium from the gastrointestinal tract into the vascular system has been determined in man by adapting an integral equation approach for use with a digital computer. A single tracer dose of Ca⁴⁷ and of Sr⁸⁵ was given both by the oral and intravenous route in separate studies and serial samples of plasma were obtained for radioassay. The maximal rate of initial entry of Ca⁴⁷ per 15-minute interval ranged from 2.2% to 3.8% of the dose and was reached within 1 1/2 hours. This rate was sustained for about one hour and decreased thereafter with time. The rate of initial entry for Sr⁸⁵ was less than that for Ca⁴⁷, not exceeding 1.5% of the dose in any 15-minute interval, but was relatively more sustained from the first to the fourth hour After the fourth hour, the rates of initial entry of Sr⁸⁵ and Ca⁴⁷ were almost proportional.