A longitudinal study of calcium regulation in a nonhuman primate model of parenteral nutrition

The question of whether parenteral nutrition adversely affects calcium regulation remains unclear. Human studies of this question have been confounded by uncontrolled variables including the degree to which food is ingested orally; gut absorption: underlying disease; medication adversely affecting bone, including steroids; and aluminum contamination of parenteral nutrients. The present study was undertaken to examine whether parenteral nutrition adversely affects calcium regulation in a nonhuman primate model that allows for control of underlying clinical variables and mobility. With use of this model, it was possible to show weight maintenance and positive nitrogen and calcium balances with parenteral nutrition. There was no demonstrable effect of the animals' wearing a jacket and tether system or of catheterization on calcium regulation. Calciuria in response to parenteral nutrition was elevated initially but diminished by 2 wk of therapy. The calciuria observed resulted from an increased urine-filtered calcium load. Calcium balance with parenteral nutrition was preserved by a diminished fraction of calcium filtered by the kidney being excreted in the urine. The present study suggests that negative calcium balance produced by parenteral nutrition may result from abnormal renal tubular function or disruption of normal parathyroid hormone regulation.