Different effect of serotonin on intracellular calcium ion dynamics in the smooth muscle cells between rat posterior ciliary artery and vorticose vein

Platelet Serotonin Aggravates Myocardial Ischemia/Reperfusion Injury via Neutrophil Degranulation

BACKGROUND

Platelets store large amounts of serotonin that they release during thrombus formation or acute inflammation. This facilitates hemostasis and modulates the inflammatory response.

METHODS

Infarct size, heart function, and inflammatory cell composition were analyzed in mouse models of myocardial reperfusion injury with genetic and pharmacological depletion of platelet serotonin. These studies were complemented by in vitro serotonin stimulation assays of platelets and leukocytes in mice and men, and by measuring plasma serotonin levels and leukocyte activation in patients with acute coronary syndrome.

RESULTS

Platelet-derived serotonin induced neutrophil degranulation with release of myeloperoxidase and hydrogen peroxide (H₂O₂) and increased expression of membrane-bound leukocyte adhesion molecule CD11b, leading to enhanced inflammation in the infarct area and reduced myocardial salvage. In patients hospitalized with acute coronary syndrome, plasmatic serotonin levels correlated with CD11b expression on neutrophils and myeloperoxidase plasma levels. Long-term serotonin reuptake inhibition-reported to protect patients with depression from cardiovascular events-resulted in the depletion of platelet serotonin stores in mice. These mice displayed a reduction in neutrophil degranulation and preserved cardiac function. In line, patients with depression using serotonin reuptake inhibition, presented with suppressed levels of CD11b surface expression on neutrophils and lower myeloperoxidase levels in blood.

CONCLUSIONS

Taken together, we identify serotonin as a potent therapeutic target in neutrophil-dependent thromboinflammation during myocardial reperfusion injury.

Pharmacology of Serotonin Receptors Causing Contraction of Isolated Bovine Posterior Ciliary Arteries: Role in Ocular Blood Flow

PURPOSE

To determine the serotonergic (5HT) receptor subtype mediating the contraction of bovine posterior ciliary arteries (BPCAs) in vitro.

METHODS

Longitudinal isometric tension was measured in BPCA strips (4-5 mm) mounted in 25 mL organ baths containing oxygenated Krebs solution at 37°C. Cumulative contractile concentration-response (C-R) curves were generated for various 5-HT agonists to assess their potencies and maximal degrees of contraction. Multiple agonist C-R curves were also constructed in the presence and absence of receptor-selective antagonists to determine antagonist potencies using Schild plots.

RESULTS

Selective and nonselective agonists for 5-HT receptors elicited concentration-dependent contractile responses in BPCAs with the following rank order of potency: MK-212 > BW723C86 > α-methyl-5-HT >5-methoxy-α-5-methyl-5-HT >> R-DO1 > >5-HT >> cabergoline >> 5-methoxy-dimethyl-tryptamine >> 2-methyl-5-HT >> tryptamine. Interestingly, both 8-OH-DPAT (5HT_1A agonist) and quipazine (5HT₃ agonist) did not elicit contractions in BPCAs. The contractions produced by BW723C86 (5-HT_2B agonist) were antagonized by 5-HT receptor blockers, RS-127445 (5-HT_2B antagonist), and M-100907 (5-HT_2A antagonist), yielding antagonist pA₂ values of 7.5 ± 0.12 (n = 4) and 6.2 ± 0.17 (n = 4), respectively. Furthermore, contractions elicited by MK-212 (5-HT_2C agonist) was blocked by RS-102221 (5-HT_2C antagonist), although noncompetitively.

CONCLUSIONS

On the basis of the pharmacological profile of selective agonists and antagonists, we conclude that serotonin-induced contractions of the BPCA are mediated primarily by a combination of 5HT_2C and/or 5HT_2B receptors. It appears that 5-HT_1A and 5-HT₃ receptors are not involved in the contractile action of BPCAs to serotonin.