Infusion of 5-HT caused 5-HT7 receptor-dependent splanchnic venous dilation and decreased arterial pressure by ~13 mmHg in male rats.
5-HT causes 5-HT7 receptor-dependent splanchnic venous dilation associated with a fall in blood pressure, suggesting splanchnic venodilation plays a role in blood pressure regulation.
Serotonin 5-hydroxytryptamine (5-HT) causes relaxation of the isolated superior mesenteric vein, a splanchnic blood vessel, through activation of the 5-HT7receptor. 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-HT7receptor dependent. In tissue baths for measurement of isometric contraction, the portal vein and abdominal inferior vena cava relaxed to 5-HT and the 5-HT1/7receptor agonist 5-carboxamidotryptamine; relaxation was abolished by the 5-HT7receptor antagonist SB-269970. Western blot analyses showed that the abdominal inferior vena cava and portal vein express 5-HT7receptor protein. In contrast, the thoracic vena cava, outside the splanchnic circulation, did not relax to serotonergic agonists and exhibited minimal expression of the 5-HT7receptor. 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 decreased (~13 mmHg). Measures returned to baseline after infusion termination. In a separate group of animals, treatment with SB-269970 (3 mg/kg iv) prevented the splanchnic venodilation and fall in blood pressure during 24 h of 5-HT infusion. Thus, 5-HT causes 5-HT7receptor-dependent splanchnic venous dilation associated with a fall in blood pressure. NEW & NOTEWORTHY This research is noteworthy because it combines and links, through the 5-HT7receptor, an in vitro observation (venorelaxation) with in vivo events (venodilation and fall in blood pressure). This supports the idea that splanchnic venodilation plays a role in blood pressure regulation.
Seitz et al. (2017) studied this question. 5-HT vs. vehicle (saline) was evaluated on Venous diameters and arterial pressure. Infusion of 5-HT caused 5-HT7 receptor-dependent splanchnic venous dilation and decreased arterial pressure by ~13 mmHg in male rats.