Role of monoamine oxidases in the exaggerated 5-hydroxytryptamine-induced tension development of human isolated preeclamptic umbilical artery

The Serotonin-Immune Axis in Preeclampsia

PURPOSE OF REVIEW

To review the literature and detail the potential immune mechanisms by which hyperserotonemia may drive pro-inflammation in preeclampsia and to provide insights into potential avenues for therapeutic discovery.

RECENT FINDINGS

Preeclampsia is a severe hypertensive complication of pregnancy associated with significant maternal and fetal risk. Though it lacks any effective treatment aside from delivery of the fetus and placenta, recent work suggests that targeting serotonin systems may be one effective therapeutic avenue. Serotonin dysregulation underlies multiple domains of physiologic dysfunction in preeclampsia, including vascular hyporeactivity and excess platelet aggregation. Broadly, serotonin is increased across maternal and placental domains, driven by decreased catabolism and increased availability of tryptophan precursor. Pro-inflammation, another hallmark of the disease, may drive hyperserotonemia in preeclampsia. Interactions between immunologic dysfunction and hyperserotonemia in preeclampsia depend on multiple mechanisms, which we discuss in the present review. These include altered immune cell, kynurenine pathway metabolism, and aberrant cytokine production mechanisms, which we detail. Future work may leverage animal and in vitro models to reveal serotonin targets in the context of preeclampsia's immune biology, and ultimately to mitigate vascular and platelet dysfunction in the disease. Hyperserotonemia in preeclampsia drives pro-inflammation via metabolic, immune cell, and cytokine-based mechanisms. These immune mechanisms may be targeted to treat vascular and platelet endophenotypes in preeclampsia.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Endothelium-Independent Vasodilatory Effect of Sailuotong (SLT) on Rat Isolated Tail Artery

Background

Sailuotong (SLT) is a standardized three-herb formulation consisting of extracts of Panax ginseng, Ginkgo biloba, and Crocus sativus for the treatment of vascular dementia (VaD). Although SLT has been shown to increase cerebral blood flow, the direct effects of SLT on vascular reactivity have not been explored. This study aims to examine the vasodilatory effects of SLT and the underlying mechanisms in rat isolated tail artery.

Methods

Male (250-300 g) Wistar Kyoto (WKY) rat tail artery was isolated for isometric tension measurement. The effects of SLT on the influx of calcium through the cell membrane calcium channels were determined in Ca²⁺-free solution experiments.

Results

SLT (0.1-5,000 μg/ml) caused a concentration-dependent relaxation in rat isolated tail artery precontracted by phenylephrine. In the contraction experiments, SLT (500, 1,000, and 5,000 μg/mL) significantly inhibited phenylephrine (0.001 to 10 μM)- and KCl (10-80 mM)-induced contraction, in a concentration-dependent manner. In Ca²⁺-free solution, SLT (500, 1,000, and 5,000 μg/mL) markedly suppressed Ca²⁺-induced (0.001-3 mM) vasoconstriction in a concentration-dependent manner in both phenylephrine (10 μM) or KCl (80 mM) stimulated tail arteries. L-type calcium channel blocker nifedipine (10 μM) inhibited PE-induced contraction. Furthermore, SLT significantly reduced phenylephrine-induced transient vasoconstriction in the rat isolated tail artery.

Conclusion

SLT induces relaxation of rat isolated tail artery through endothelium-independent mechanisms. The SLT-induced vasodilatation appeared to be jointly meditated by blockages of extracellular Ca²⁺ influx via receptor-gated and voltage-gated Ca²⁺ channels and inhibition of the release of Ca²⁺ from the sarcoplasmic reticulum.

Mechanisms underlying increased serotonin-induced contraction in carotid arteries from chronic type 2 diabetic Goto-Kakizaki rats

Serotonin (5-hydroxytryptamine; 5-HT) plays important roles in the cardiovascular system; however, the relationship between 5-HT-induced vasocontraction and the arterial 5-HT system including metabolism and signal transduction, in the presence of chronic type 2 diabetes (T2D) remains unclear. Therefore, we investigated 5-HT-induced contraction and associated mechanisms in carotid arteries from chronic T2D Goto-Kakizaki (GK) rats. Contractions in response to 5-HT were examined in carotid arteries from GK rats (42-46 weeks old). To investigate the response mechanisms of arterial smooth muscle, we constructed concentration-response curves for TCB2 (5-HT2A-receptor agonist), BW723C86 (5-HT2B-receptor agonist), and 5-HT in the presence of various inhibitors using endothelium-denuded preparations. Carotid arterial expressions of monoamine oxidase-A (MAO-A), serotonin transporter (SERT), and 5-HT2A were detected by immunoblotting. 5-HT-induced contraction was increased in carotid arteries from GK compared to control Wistar rats in both endothelium-intact and -denuded preparations. In denuded preparations, we found that: (1) TCB2-induced contraction was increased in GK rat arteries (vs. Wistar); (2) MAO-A inhibitor did not affect 5-HT-induced contraction, whereas SERT inhibitor augmented such contractions in both groups; and (3) differences in 5-HT-induced contractions were abolished by p38 MAPK, PI3K, and Rho kinase inhibitors. Carotid arterial expressions of MAO-A, SERT, and 5-HT2A remained unchanged in the groups. The results suggest that 5-HT-induced contraction is augmented in T2D GK rat carotid arteries. This augmentation is due to smooth muscle activation partly mediated by p38 MAPK, PI3K, and Rho kinases, and may also be partly due to arterial SERT activity.

Intrapulmonary arteries respond to serotonin and adenosine triphosphate in broiler chickens susceptible to idiopathic pulmonary arterial hypertension

This study examined factors contributing to increased vascular resistance and plexiform lesion formation in broiler chickens susceptible to idiopathic pulmonary arterial hypertension (IPAH). A diet supplemented with excess tryptophan (high-Trp diet), the precursor for serotonin, was used to accelerate the development of IPAH. Broilers fed the high-Trp diet had higher pulmonary arterial pressures than broilers fed the control diet, and plexiform lesion incidences tended to be higher (P = 0.11) in the high-Trp group than in the control group at 30 d of age. The intrapulmonary arteries were assessed for vasoconstriction in response to serotonin and adenosine triphosphate (ATP) and for activities of key metabolic enzymes for serotonin and ATP. The pulmonary artery (defined as the first major branch of the pulmonary artery inside the lung) and the primary pulmonary arterial rami (defined as the second major branch of the pulmonary artery inside the lung) both exhibited vasoconstriction in response to serotonin and ATP. This is the first study to demonstrate purinergic-mediated vasoconstriction in intrapulmonary arteries from broilers. Arteriole responsiveness did not differ between broilers fed the control diet or the high-Trp diet. Therefore, the high-Trp diet enhanced the development of IPAH but did not affect the artery's sensitivity to serotonin or ATP. Monoamine oxidase activity, responsible for the breakdown of serotonin, was severely impaired in pulmonary arteries from broilers in the high-Trp group. Accordingly, serotonin may persist longer and elicit an amplified response in broilers fed the high-Trp diet.