Effects of intravenous calcium on release of serotonin into jejunal lumen and portal circulation.

The effect of intravenous calcium bolus (180 mg in 10 ml normal saline over 25-30 sec) on the release of serotonin into the jejunal lumen and the portal and peripheral venous circulation was studied. Proximal jejunal 25-cm cannulated Thiry-Vella loops were perfused with a neutral physiological buffer in an isoperistaltic direction at 2 ml/min. One minute after the calcium bolus, serum calcium levels increased from 8.7 +/- 0.3 to 14.2 +/- 0.8 mg/dl. Jejunal luminal concentrations of 5HT increased from 135 +/- 21 to 208 +/- 44 ng/ml at the same time; luminal levels peaked at 236 +/- 27 ng/ml at 7 min and slowly returned to baseline. In contrast, portal and systemic venous concentrations did not change after intravenous calcium bolus. The data support the contention that there are independent mechanisms for the release of serotonin into the bowel lumen and the blood stream.