5-HT causes splanchnic venodilation

Serotonin [5-hydroxytryptamine (5-HT)] causes relaxation of the isolated superior mesenteric vein, a splanchnic blood vessel, through activation of the 5-HT7 receptor. As part of studies designed to identify the mechanism(s) through which chronic (≥24 h) infusion of 5-HT lowers blood pressure, we tested the hypothesis that 5-HT causes in vitro and in vivo splanchnic venodilation that is 5-HT7 receptor dependent. In tissue baths for measurement of isometric contraction, the portal vein and abdominal inferior vena cava relaxed to 5-HT and the 5-HT1/7 receptor agonist 5-carboxamidotryptamine; relaxation was abolished by the 5-HT7 receptor antagonist SB-269970. Western blot analyses showed that the abdominal inferior vena cava and portal vein express 5-HT7 receptor protein. In contrast, the thoracic vena cava, outside the splanchnic circulation, did not relax to serotonergic agonists and exhibited minimal expression of the 5-HT7 receptor. Male Sprague-Dawley rats with chronically implanted radiotelemetry transmitters underwent repeated ultrasound imaging of abdominal vessels. After baseline imaging, minipumps containing vehicle (saline) or 5-HT (25 μg·kg–1·min–1) were implanted. Twenty-four hours later, venous diameters were increased in rats with 5-HT-infusion (percent increase from baseline: superior mesenteric vein, 17.5 ± 1.9; portal vein, 17.7 ± 1.8; and abdominal inferior vena cava, 46.9 ± 8.0) while arterial pressure was...
Source: AJP: Heart and Circulatory Physiology - Category: Cardiology Authors: Tags: RESEARCH ARTICLE Source Type: research