Absorption of Calcium Measured by Intubation and Perfusion of the Intact Human Small Intestine

direct intubation and perfusion of the small intestine in 10 volunteer normal adult subjects, two adults with celiac-sprue, and one with a parathyroid adenoma. A total of 60 studies were completed using one of two dif-ferent levels, duodenojejunum or ileum. Solutions con-taining stable calcium, radiocalcium47, and a nonabsorb-able dilution-concentration marker, polyethylene glycol, were infused at a uniform rate via the proximal lumen of a triple-lumen polyvinyl tube. The mixed intraluminal contents were continuously sampled by siphonage from two distal sites, 10 and 60 cm below the point of infusion. Unidirectional flux rates, lumen to blood and blood to lumen, and net absorption of calcium for the 50 cm seg-ment of small intestine between the two collection sites were calculated from the measured changes in concentra-tion of stable calcium, calcium-47, and polyethylene glycol. Flux of calcium from lumen to blood in the duodenoje-junum of normal subjects was appreciable even when the concentration of calcium in the perfusate was below that of extracellular fluid and, as the intraluminal concentra-tion of calcium was increased through a range of 0.5-3.5 Amoles/ml, was positively correlated, ranging from 1.9 to 7.0.moles/min per 50 cm. Repeated studies of in-dividual subjects demonstrated a consistent pattern of absorptive efficiency in each, but significant variability from person to person. Flux from lumen to blood in the ileal segment occurred at a much lower rate than that found in the proximal intestine, and there was not a sig-nificant dependence upon intraluminal calcium concentra