Effect of luminally administered serotonin and substance P on jejunal handling of water and electrolytes

This study was initiated to evaluate the effect of luminally administered serotonin (5-hydroxytryptamine) and substance P on jejunal handling of water and electrolytes. Five dogs with chronic cannulated jejunal Thiry-Vella loops were studied. The isolated jejunal segments were perfused at 2 ml/min for 2 hours with an isosmotic, isothermic perfusate containing labeled polyethylene glycol for recovery calculation. Fluxes of water and sodium, chloride, and potassium were calculated during 30 minute baseline, 60 minute study, and 30 minute recovery periods. Substance P was administered intraluminally at 25 pg/ml, whereas serotonin was perfused at 600 ng/ml. Neither hormone was absorbed into the portal circulation. Intraluminal serotonin converted absorption to secretion of water from 43 ± 23 to -105 ± 25 μl/min, sodium from 7.3 ± 3.1 to -15.7 ± 4.1 μEq/min, chloride from 4.4 ± 3.4 to -16.4 ± 3 μEq/min, and potassium from 0.16 ± 0.20 to -0.86 ± 0.17 gmEq/min. Secretion ceased on cessation of serotonin perfusion. Substance P perfusion induced secretion of chloride (3.6 ± 1.9 to -9.2 ± 2.9 μEq/ min) but only significantly decreased absorption of water (73 ± 13 to 13 ± 21 μl/min) and sodium (8.1 ± 1.9 to 0.2 ± 3.1 μEq/min); in contrast, there was no significant change in jejunal handling of potassium.