Biliary calcium and bile acid secretion in intact and TPTX rats with varying plasma calcium concentration

Investigations of the effects of plasma calcium concentration on the relationship between biliary secretion of bile acid and calcium were performed in normocalcemic, calcium gluconate-induced hypercalcemic, thyroparathyroidectomy-induced hypocalcemic (TPTX) rats, and TPTX rats that received calcium gluconate to maintain normocalcemia. Studies were done at normal bile flow and at sodium taurocholate-stimulated bile flow. The results showed that biliary calcium secretion, which could occur in the absence of parathyroid hormone and calcitonin, was dependent mainly on plasma calcium concentration and was only partly influenced by bile acid secretion. Concerning the route of biliary calcium secretion, 80% was by the transcellular pathway and 20% was by the paracellular pathway. During theophylline-stimulated bile-acid-independent bile flow, the increase in bile-acid-independent calcium was found to be secreted by both pathways.