Jejunal Calcium Transport in Health and Metabolic Bone Disease: Effect of Vitamin D

Abstract

Net absorption (JnetCa) and unidirectional fluxes (JMSCa, JSMCa) of calcium were determined by continuous intestinal perfusion of a 30-cm segment of proximal jejunum on 24 occasions in 12 children. The test solution contained calcium gluconate, 2.5 mmoles per liter, and radioactive 47Ca. The results were compared with those of preceding metabolic balance studies in 22 instances. The subjects included 5 patients with sporadic vitamin D-resistant rickets, and 1 each with florid nutritional rickets and with acute disuse osteoporosis. In controls, the bidirectional calcium flux across the luminal cell wall of the absorbing epithelium, as measured by JSMCa, is small in magnitude. Jejunal calcium absorption was decreased in all untreated patients; in 5 of these, this was attributable to a reduction in mucosal calcium uptake (JMSCa) but 2 patients with vitamin D-resistant rickets demonstrated an unexpected increase in calcium flux in the reverse direction (JSMCa). Therapy with vitamin D2 invariably resulted in accelerated net calcium absorption without changes in net transport of water, sodium, chloride, and potassium, and in flow rate and calcium content of fasting intestinal contents. A linear correlation (r = 0.87) existed between JnetCa and net calcium absorption determined by metabolic balance study. JnetCa of less than 3 μ moles per hr-cm correctly separated patients with untreated metabolic bone disease from treated patients and control subjects on 22 of 23 occasions. Jejunal calcium absorption, determined by steady state intestinal perfusion, proved to be a reliable and convenient indicator of total calcium balance in this group of subjects.