5-hydroxytryptamine evokes endothelial nitric oxide synthase activation in bovine aortic endothelial cell cultures

Characterization of endothelium-dependent and -independent processes in occipital artery of the rat: Relevance to control of blood flow to nodose sensory cells

Circulating factors access cell bodies of vagal afferents in nodose ganglia (NG) via the occipital artery (OA). Constrictor responses of OA segments closer in origin from the external carotid artery (ECA) differ from segments closer to NG. Our objective was to determine the role of endothelium in this differential vasoreactivity in rat OA segments. Vasoreactivity of OA segments (proximal segments closer to ECA, distal segments closer to NG) were examined in wire myographs. We evaluated (a) vasoconstrictor effects of 5-hydroxytryptamine (5-HT) in intact and endothelium-denuded OA segments in absence/presence of soluble guanylate cyclase (SGC) inhibitor ODQ, (b) vasodilator responses elicited by NO-donor MAHMA NONOate in intact or endothelium-denuded OA segments in absence/presence of ODQ, and (c) vasodilator responses elicited by endothelium-dependent vasodilator, acetylcholine (ACh), in intact OA segments in absence/presence of ODQ. Intact distal OA responded more to 5-HT than intact proximal OA. Endothelium denudation increased 5-HT potency in both OA segments, especially proximal OA. ODQ increased maximal responses of 5HT in both segments, particularly proximal OA. ACh similarly relaxed both OA segments, effects abolished by endothelial denudation and attenuated by ODQ. MAHMA NONOate elicited transient vasodilation in both segments. Effects of ODQ against ACh were segment-dependent whereas those against MAHMA NONOate were not. The endothelium regulates OA responsiveness in a segment-dependently fashion. Endothelial cells at the OA-ECA junction more strongly influence vascular tone than those closer to NG. Differential endothelial regulation of OA tone may play a role in controlling blood flow and access of circulating factors to NG.

Molecular profiling of reticular gigantocellularis neurons indicates that eNOS modulates environmentally dependent levels of arousal

Neurons of the medullary reticular nucleus gigantocellularis (NGC) and their targets have recently been a focus of research on mechanisms supporting generalized CNS arousal (GA) required for proper cognitive functions. Using the retro-TRAP method, we characterized transcripts enriched in NGC neurons which have projections to the thalamus. The unique expression and activation of the endothelial nitric oxide (eNOS) signaling pathway in these cells and their intimate connections with blood vessels indicate that these neurons exert direct neurovascular coupling. Production of nitric oxide (NO) within eNOS-positive NGC neurons increases after environmental perturbations, indicating a role for eNOS/NO in modulating environmentally appropriate levels of GA. Inhibition of NO production causes dysregulated behavioral arousal after exposure to environmental perturbation. Further, our findings suggest interpretations for associations between psychiatric disorders and mutations in the eNOS locus.

Contemporary Approaches to Modulating the Nitric Oxide-cGMP Pathway in Cardiovascular Disease

Endothelial cells lining the vessel wall control important aspects of vascular homeostasis. In particular, the production of endothelium-derived nitric oxide and activation of soluble guanylate cyclase promotes endothelial quiescence and governs vasomotor function and proportional remodeling of blood vessels. Here, we discuss novel approaches to improve endothelial nitric oxide generation and preserve its bioavailability. We also discuss therapeutic opportunities aimed at activation of soluble guanylate cyclase for multiple cardiovascular indications.

Oh, the places you'll go! My many colored serotonin (apologies to Dr. Seuss)

Serotonin [5-hydroxytryptamine (5-HT)] has a truly fascinating history in the cardiovascular world. Discovered in the blood, 5-HT has long been appropriately regarded as a vasoconstrictor. A multitude of in vitro studies of isolated vessels support that addition of 5-HT causes vascular contraction. In only a few cases was 5-HT a vasodilator. Moreover, the potency and threshold of 5-HT causing contraction is increased in arteries from hypertensive vs. normotensive subjects, both animal and human. As such, we and others have hypothesized that 5-HT would contribute to hypertension by elevating arterial tone. In stark contrast to these decades of findings, we observed that a chronic infusion of 5-HT into conscious rats caused a reduction in blood pressure and nearly normalized blood pressure of experimentally hypertensive rats. Going back to the early work of Irvine Page, one of the scientists who discovered 5-HT, reveals an early recognized but never understood ability of 5-HT to reduce systemic blood pressure. Our laboratory, in collaboration with colleagues around the world, has dedicated itself to understanding the mechanisms of 5-HT-induced reduction in blood pressure. This manuscript takes you through a brief history of the discovery of 5-HT, in vitro serotonergic pharmacology of blood vessels, in vivo work with 5-HT and our studies that suggests the venous vasculature, potentially in combination with small arterioles, may be important to the actions of 5-HT in reducing blood pressure. 5-HT has certainly ended up in a place I never expected it to go.

Role of serotonin in angiogenesis: induction of angiogenesis by sarpogrelate via endothelial 5-HT1B/Akt/eNOS pathway in diabetic mice

Serotonin (5-hydroxytryptamine, 5-HT) plays a crucial role in peripheral artery disease (PAD) and diabetes mellitus (DM). In these conditions, the balance between the 5-HT2A receptor in smooth muscle cells and the 5-HT1B receptor in endothelial cells (ECs) regulates vascular tonus. In the present study, we focused on the role of 5-HT in endothelial dysfunction using a selective 5-HT2A receptor blocker, sarpogrelate. In human EC, 5-HT markedly stimulated eNOS expression and the phosphorylation of eNOS, Akt and ERK1/2. In addition, a dose-dependent increase in tubule-formation on Matrigel was observed after 5-HT treatment. In contrast, high glucose significantly inhibited tubule formation and eNOS expression through inactivation of Akt, while 5-HT significantly attenuated these actions of high glucose (P<0.01). These results indicate that 5-HT stimulated angiogenesis through activation of Akt in ECs. However, in clinical situations, 5-HT seems to act as the "devil". To examine the role of 5-HT in diabetic PAD, a hindlimb ischemia model was created in diabetic mice. The blood flow ratio of the ischemic to non-ischemic limb was significantly lower in DM mice than in normal mice, while sarpogrelate significantly attenuated the decrease in the blood flow ratio compared to control (P<0.01). Consistently, the decrease in eNOS expression and Akt activity in DM mice was significantly attenuated by sarpogrelate. Overall, the present study demonstrated that selective inhibition of 5-HT2A by sarpogrelate significantly restored ischemic limb blood perfusion in a severe diabetic mouse model through stimulation of the eNOS/Akt pathway via the endothelial 5-HT1B receptor. Enhancement of vasodilation and angiogenesis by sarpogrelate might provide a unique treatment for PAD and DM patients.

Depletion of serotonin and selective inhibition of 2B receptor suppressed tumor angiogenesis by inhibiting endothelial nitric oxide synthase and extracellular signal-regulated kinase 1/2 phosphorylation

The effects of serotonin (5-HT) on tumor growth are inconsistent. We investigated whether a decreased level of 5-HT affected tumor growth using 5-HT transporter knockout (5-HTT(-/-)) mice, which showed 5-HT depletion. When cancer cells were injected subcutaneously into both 5-HTT(-/-) and 5-HTT(+/+) mice, the tumor growth was markedly attenuated in 5-HTT(-/-) mice. Serotonin levels in the blood, forebrain, and tumors of 5-HTT(-/-) mice bearing tumors were significantly smaller than those of their 5-HTT(+/+) littermates. However, 5-HT did not increase cancer cells' proliferation in vitro. When we applied 5-HTT inhibitors to the wild mice bearing tumors, they did not inhibit tumor growth. The endothelial nitric oxide synthase (eNOS) expressions in tumors were reduced in 5-HTT(-/-) mice compared with 5-HTT(+/+) mice. Stimulations with 5-HT (1-50 microM) induced eNOS expressions in human umbilical vein endothelial cell (HUVEC) in a concentration-dependent manner. When we measured activations of multiple signaling pathways by using a high-throughput phosphospecific antibodies platform, 5-HT stimulated the extracellular signal-regulated kinase 1/2 (ERK1/2) in HUVEC. Moreover, we found that the physiological level of 5-HT induced phosphorylation of both ERK1/2 and eNOS in HUVEC. Human umbilical vein endothelial cell expressed both 5-HT(2B) and 5-HT(2C) receptors. SB204741, a specific 5-HT(2B) receptor inhibitor, blocked 5-HT-induced ERK1/2 and eNOS phosphorylations, whereas RS102221, a specific 5-HT(2C) receptor inhibitor, did not in HUVEC. SB204741 reduced microvessel density in tumors and inhibited the proliferation of HUVEC in vitro. These results suggest that regulation of 5-HT and 5-HT receptors, especially the 5-HT(2B) receptor, may serve as a therapeutic strategy in cancer therapy.

The nitric oxide synthesis/pathway mediates the inhibitory serotoninergic responses of the pressor effect elicited by sympathetic stimulation in diabetic pithed rats

We investigated the involvement of the nitric oxide pathway in the inhibitory mechanisms of 5-hydroxytryptamine (5-HT) in the pressor responses induced by stimulation of sympathetic vasopressor outflow in diabetic pithed rats. Diabetes was induced in male Wistar rats by a single s.c. injection of alloxan. Four weeks later, the animals were anaesthetized, pretreated with atropine, and pithed. Electrical stimulation of the sympathetic outflow from the spinal cord (0.1, 0.5, 1 and 5 Hz) resulted in frequency-dependent increases in blood pressure. The inhibition of electrically induced pressor responses by 5-HT (10 microg/kg/min) in diabetic pithed rats could not be elicited after i.v. treatment with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 microg/kg), a guanylyl cyclase inhibitor, or N-omega-L-Arginine methyl ester hydrochloride (L-NAME) (10 mg/kg), a nitric oxide synthase (NOS) inhibitor. The inhibitory effect produced by infusion of the selective 5-HT(1A) receptor agonist 8-hydroxydipropylaminotretalin hydrobromide (8-OH-DPAT) (20 microg/kg/min) was abolished in the presence of ODQ (10 microg/kg), or L-NAME (10 mg/kg) in diabetic pithed rats. The administration of L-Arginine (100 mg/kg) 30 min after L-NAME reproduced the inhibitory effect caused by 5-HT (10 microg/kg/min) and 8-OH-DPAT (20 microg/kg/min) on the electrically induced pressor responses, whereas in the presence of D-Arginine (100 mg/kg)+L-NAME the 5-HT or 8-OH-DPAT inhibitory effect on the pressor responses was abolished. In conclusion, in diabetic pithed rats, the inhibition produced by prejunctional 5-HT(1A) activation on electrically induced sympathetic pressor responses is mediated by the NO synthesis/pathway.

The ratio of plasma to whole-blood serotonin may be a novel marker of atherosclerotic cardiovascular disease

Because atherosclerotic vascular lesions stimulate platelets, the platelets release serotonin (5-hydroxytryptamine, aka 5-HT). We therefore measured 5-HT concentrations not only in platelet-poor plasma but also in whole blood as a means of assessing vascular lesions. The plasma concentration of 5-HT tended to increase with age, whereas that in whole blood decreases. Therefore the ratio of the plasma to the whole-blood concentration of 5-HT (P/WB) increases with age. This may be a result of the activation of platelets in older subjects with atherosclerotic vascular damage. Patients who underwent coronary angiography (CAG) were classified into 4 groups according to diagnosis: effort-induced angina pectoris (eAP), old myocardial infarction (OMI), vasospastic angina pectoris (VSAP), and unstable angina (uAP). The mean plasma 5-HT concentration was significantly (P <.01) greater in patients with eAP, uAP, OMI, and VSAP than in healthy controls, whereas the concentration in whole blood was lower in patients with eAP than in healthy controls. When the P/WB ratios were calculated, the mean levels in all disease groups were significantly higher than that in the healthy controls. These findings suggested that 5-HT is released into the plasma from the platelets and that the concentration in the platelets decreases in patients with atherosclerosis.

Src kinase mediates angiotensin II-dependent increase in pulmonary endothelial nitric oxide synthase

We have previously demonstrated that angiotensin II (Ang II) stimulates nitric oxide (NO) production in bovine pulmonary artery endothelial cells (BPAECs) by increasing NO synthase (NOS) expression via the type 2 receptor. The purpose of this study was to identify the Ang II-dependent signaling pathway that mediates this increase in endothelial NOS (eNOS). The Ang II-dependent increase in eNOS expression is prevented when BPAECs are pretreated with the tyrosine kinase inhibitors, herbimycin A and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-D]pyrimidine, which also blocked Ang II-dependent mitogen-activated protein kinase (MAPK) kinase/extracellular-regulated protein kinase (MEK)-1 and MAPK phosphorylation, suggesting that Src is upstream of MAPK in this pathway. Transfection of BPAECs with an Src dominant negative mutant cDNA prevented the Ang II-dependent Src activation and increase in eNOS protein expression. PD98059, a MEK-1 inhibitor, prevented the Ang II-dependent phosphorylation of extracellular-regulated protein kinases 1 and 2 and increase in eNOS expression. Neither AG1478, an epidermal growth factor receptor kinase inhibitor, nor AG1295, a platelet derived growth factor receptor kinase inhibitor, had any effect on Ang II-stimulated Src activity, MAPK activation, or eNOS expression. Pertussis toxin prevented the Ang II-dependent increase in Src activity, MAPK activation, and eNOS expression. These data suggest that Ang II stimulates Src tyrosine kinase via a pertussis toxin-sensitive pathway, which in turn activates the MAPK pathway, resulting in increased eNOS protein expression in BPAECs.

Cholesterol in mood and anxiety disorders: review of the literature and new hypotheses

Cholesterol plays an integral role in the structure and function of the cell membrane and may also affect neurotransmission in the central nervous system. Previous work has identified abnormalities in serum cholesterol levels in patients with mood and anxiety disorders as well as in suicidal patients. However, the biological significance of these abnormalities remains to be clarified. An understanding of how serum cholesterol relates to the pathophysiology of mood disorders may generate biological markers that predict treatment response as well as targets for novel therapeutic strategies. In this article, we review the literature studying the significance of cholesterol in mood and anxiety disorders, with an emphasis on new studies focusing on the adverse impact of hypercholesterolemia on the treatment of major depressive disorder (MDD). We then propose possible mechanisms that would account for the relationship between elevated cholesterol and treatment non-response in MDD.

Serum cholesterol and serotonergic function in major depressive disorder

Studies have revealed a relationship between serum cholesterol levels and serotonergic (5HT) function in healthy young adults. Patients with major depressive disorder (MDD) may have significant differences in cholesterol levels compared with healthy adults, while MDD patients with elevated cholesterol have a poorer prognosis for treatment response. The goal of the present study is to examine (1) the relationship between serum cholesterol levels and central 5HT function by way of the cortisol and prolactin response to the 5HT-selective agonist DL-fenfluramine in MDD patients and (2) differences in 5HT-function between MDD patients who present with and without elevated cholesterol. Fasting serum cholesterol levels were measured in 21 outpatients with MDD. After oral administration of 60 mg of DL-fenfluramine in these patients, cortisol and prolactin responses were measured to test whether cholesterol levels predicted the degree of cortisol or prolactin response. Cortisol and prolactin responses were compared between patients with and without elevated cholesterol levels, defined as >/=200 mg/dl. MDD patients with elevated cholesterol levels were more likely to demonstrate an attenuated cortisol response. There was no relationship between cholesterol levels and cortisol or prolactin response. Excess cholesterol may adversely affect the function of membrane-bound serotonergic structures, and this may explain why MDD patients with elevated cholesterol are more likely to exhibit attenuated neuroendocrine responses, less likely to respond to treatment and more likely to relapse.

Hydrogen peroxide stimulates tetrahydrobiopterin synthesis through the induction of GTP-cyclohydrolase I and increases nitric oxide synthase activity in vascular endothelial cells

Tetrahydrobiopterin (BH4), which is an essential cofactor for nitric oxide synthase (NOS), is generally accepted as an important molecular target for oxidative stress. This study examined whether hydrogen peroxide (H(2)O(2)), one of the reactive oxygen species (ROS), affects the BH4 level in vascular endothelial cells (ECs). Interestingly, the addition of H(2)O(2) to ECs markedly increased the BH4 level, but not its oxidized forms. The H(2)O(2)-induced increase in the BH4 level was blocked by the inhibitor of GTP-cyclohydrolase I (GTPCH), which is the rate-limiting enzyme of BH4 synthesis. Moreover, H(2)O(2) induced the expression of GTPCH mRNA, and the inhibitors of protein synthesis blocked the H(2)O(2)-induced increase in the BH4 level. The expression of the inducible isoform of NOS (iNOS) was slightly induced by the treatment with H(2)O(2). Additionally, the L-citrulline formation from L-arginine, which is the marker for NO synthesis, was stimulated by the treatment with H(2)O(2), and the H(2)O(2)-induced L-citrulline formation was strongly attenuated by NOS or GTPCH inhibitor. These results suggest that H(2)O(2) induces BH4 synthesis via the induction of GTPCH, and the increased BH4 is coupled with NO production by coinduced iNOS. H(2)O(2) appears to be one of the important signaling molecules to regulate the BH4-NOS system.

Antagonism of nitrous oxide-induced anxiolytic-like behavior in the mouse light/dark exploration procedure by pharmacologic disruption of endogenous nitric oxide function

RATIONALE

Previous studies have shown the anxiolytic-like effects of nitrous oxide (N(2)O) to be sensitive to antagonism by non-specific inhibitors of nitric oxide synthase (NOS).

OBJECTIVES

The present study was conducted to demonstrate further the involvement of nitric oxide (NO) and ascertain whether a specific isoform of NOS is involved in N(2)O-induced behavior in mice.

METHODS

Male NIH Swiss mice were tested in the light/dark exploration test to determine how N(2)O-induced behavior was affected by the following pretreatments: the NO scavenger hemoglobin (Hb); the selective nNOS-inhibitor S-methyl- l-thiocitrulline (SMTC); the selective eNOS-inhibitor N(5)-(1-iminoethyl)- l-ornithine ( l-NIO); and the selective iNOS-inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT). Furthermore, NOS activity was assessed in the whole brain as well as five brain areas of N(2)O- versus room air-exposed mice to determine the effects of N(2)O on NOS activity.

RESULTS

The behavioral effects of N(2)O in the light/dark exploration test were significantly attenuated following pretreatment with Hb (2.0 nmol, i.c.v.), SMTC (0.3 micro g and 1.0 micro g per mouse, i.c.v.) and the higher dose of l-NIO (30 mg/kg, s.c.). However, the N(2)O-induced behavioral effect was unaltered by pretreatment with either the lower dose of l-NIO (10 mg/kg, s.c.) or AMT (1.0 mg/kg and 3.0 mg/kg, s.c.). Finally exposure to 50% N(2)O for 15 min significantly increased NOS activity in the cerebellum and corpus striatum but not in other brain regions or whole brain.

CONCLUSION

These findings provide further support for the hypothesis that NO is involved in N(2)O-induced anxiolytic-like behavior and that this NO is the product of nNOS enzyme activity.

5-HT moduline: an endogenous inhibitor of 5-HT(1B/1D)-mediated contraction in pulmonary arteries

(1) 5-HT moduline (5-HTm) is tetrapeptide (Leu-Ser-Ala-Leu) previously shown to act as a specific endogenous antagonist to central 5-HT(1B/1D) receptors. Its effects were investigated in rat and rabbit pulmonary arteries (PAs). (2) In rabbit PAs, contractile responses to the 5-HT(1B/1D) receptor agonist 5-carboxamidotryptamine (5-CT) were inhibited by 1 and 10 micro M 5-HTm in a non-competitive fashion with the maximum contractile response (E(max), per cent of response to 50 mM KCl) being reduced from 65.6+/-7% (n=6) to 39.7+/-6.5% (n=6) and 25.2+/-7.9 (n=4), respectively. The ability of 5-HTm to inhibit responses to 5-CT was increased by the aminopeptidase inhibitor bestatin (10 micro M). (3) In the rabbit PAs, the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methylester (L-NAME) potentiated responses to 5-CT (E(max): 106+/-22.5 (n=4)) and this response was also inhibited by 10 micro M 5-HTm (E(max): 38+/-13% (n=8)). (4) 5-HTm (10 micro M) inhibited responses to 5-CT in rat PAs, the E(max) being reduced from 24.8+/-4.1% (n=7) to 15.5+/-3.7% (n=9). 5-HTm induced relaxation of 5-CT-pre-constricted rat PAs with a pIC(50) of 9.0+/-0.6 (n=9). (5) In PAs from chronic hypoxic, pulmonary hypertensive rats, the maximum response to 5-CT was increased to 80+/-8.5% (n=11). 5-HTm reduced this response to 34.4+/-6.3% (n=12). L-NAME markedly inhibited the ability of 5-HTm to inhibit responses to 5-CT (E(max) before 5-HTm: 100.5+/-16% (n=5), E(max) after 5-HTm: 107+/-11.3% (n=4)). (6) In conclusion we show here for the first time that 5-HTm is a non-competitive inhibitor of 5-HT(1B/1D) receptor-mediated constriction in PAs. In rat PAs, L-NAME can inhibit this effect of 5-HTm.

Stimulation of tetrahydrobiopterin synthesis by cyclosporin A in mouse brain microvascular endothelial cells

We examined the effect of the immunosuppressant, cyclosporin A (CsA) on the synthesis of tetrahydrobiopterin (BH4), a cofactor for nitric oxide (NO) synthase and a scavenger of reactive oxygen species (ROS), in mouse brain microvascular endothelial cells. Treatment with CsA increased the BH4 content and the expression of mRNA level of GTP cyclohydrolase I, the rate-limiting enzyme of BH4 synthesis. 2,4-Diamino-6-hydroxypyrimidine, an inhibitor of GTP cyclohydrolase I, strongly reduced the CsA-induced increase in BH4 content. Cycloheximide (CHX), a protein synthesis inhibitor, also reduced CsA-induced BH4 synthesis. These findings suggest that CsA stimulates BH4 synthesis via a de novo pathway with the induction of GTP cyclohydrolase I. Moreover, CsA-induced the mRNA level of the inducible type of NO synthase, and stimulated the L-citrulline formation from L-arginine, which is a marker for NO synthesis. The CsA-stimulated L-citrulline formation was attenuated by the co-treatment with GTP cyclohydrolase I inhibitor. The expression of the endothelial type of NO synthase was low under basal condition, and was not affected by the treatment with CsA. These findings suggest that increase in BH4 content induced by CsA is coupled with NO production by inducible type of NO synthase.

Differential contributions of nitric oxide synthase isoforms at hippocampal formation to negative feedback regulation of penile erection in the rat

We established previously that a novel negative feedback mechanism for the regulation of penile erection, which is triggered by ascending sensory inputs initiated by tumescence of the penis, exists in the hippocampal formation (HF). This study further evaluated the participation of nitric oxide (NO) and the contribution of nitric oxide synthase (NOS) isoforms at the HF in this process. Adult, male Sprague-Dawley rats that were anaesthetized and maintained with chloral hydrate were used, and intracavernous pressure (ICP) recorded from the corpus cavernosum of the penis was employed as our experimental index for penile erection. Microinjection bilaterally of a NO donor, S-nitroso-N-acetylpenicillamine (0.25 or 1 nmoles), or the NO precursor, L-arginine (1 or 5 nmoles), into the hippocampal CA1 or CA3 subfield or dentate gyrus elicited a significant reduction in baseline ICP. Bilateral hippocampal application of a NO trapping agent, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (10 nmoles), significantly potentiated the elevation in ICP induced by intracavernous administration of papaverine (400 microg). Microinjection bilaterally into the HF of equimolar doses (0.5 or 2.5 pmoles) of two selective neuronal NOS inhibitors, 7-nitroindazole or N(omega)-propyl-L-arginine; or equimolar doses (50 or 250 pmoles) of two selective inducible NOS inhibitors, aminoguanidine or S-methylisothiourea, significantly enhanced the magnitude and/or duration of the papaverine-induced elevation in ICP. In contrast, hippocampal application of a potent endothelial NOS inhibitor, N5-(1-iminoethyl)-L-ornithine (18 or 92 nmoles), was ineffective. Neither of these inhibitors, furthermore, affected baseline ICP. These results suggest that NO generated via both neuronal and inducible NOS at the HF may participate in negative feedback regulation of penile erection.

Multiplicity of mechanisms of serotonin receptor signal transduction

The serotonin (5-hydroxytryptamine, 5-HT) receptors have been divided into 7 subfamilies by convention, 6 of which include 13 different genes for G-protein-coupled receptors. Those subfamilies have been characterized by overlapping pharmacological properties, amino acid sequences, gene organization, and second messenger coupling pathways. Post-genomic modifications, such as alternative mRNA splicing or mRNA editing, creates at least 20 more G-protein-coupled 5-HT receptors, such that there are at least 30 distinct 5-HT receptors that signal through G-proteins. This review will focus on what is known about the signaling linkages of the G-protein-linked 5-HT receptors, and will highlight some fascinating new insights into 5-HT receptor signaling.

Is obesity an inflammatory condition?

Obesity may be a low-grade systemic inflammatory disease. Overweight and obese children and adults have elevated serum levels of C-reactive protein, interleukin-6, tumor necrosis factor-alpha, and leptin, which are known markers of inflammation and closely associated with cardiovascular risk factors and cardiovascular and non-cardiovascular causes of death. This may explain the increased risk of diabetes, heart disease, and many other chronic diseases in the obese. The complex interaction between several neurotransmitters such as dopamine, serotonin, neuropeptide Y, leptin, acetylcholine, melanin-concentrating hormone, ghrelin, nitric oxide, and cytokines and insulin and insulin receptors in the brain ultimately determines and regulates food intake. Breast-feeding of more than 12 mo is associated with decreased incidence of obesity. Breast milk is a rich source of long-chain polyunsaturated fatty acids (LCPUFAs) and brain is especially rich in these fatty acids. LCPUFAs inhibit the production of proinflammatory cytokines and enhance the number of insulin receptors in various tissues and the actions of insulin and several neurotransmitters. LCPUFAs may enhance the production of bone morphogenetic proteins, which participate in neurogenesis, so these fatty acids might play an important role in brain development and function. It is proposed that obesity is a result of inadequate breast feeding, which results in marginal deficiency of LCPUFAs during the critical stages of brain development. This results in an imbalance in the structure, function, and feedback loops among various neurotransmitters and their receptors, which ultimately leads to a decrease in the number of dopamine and insulin receptors in the brain. Hence, promoting prolonged breast feeding may decrease the prevalence of obesity. Exercise enhances parasympathetic tone, promotes antiinflammation, and augments brain acetylcholine and dopamine levels, events that suppress appetite. Acetylcholine and insulin inhibit the production of proinflammatory cytokines and provide a negative feedback loop for postprandial inhibition of food intake, in part, by regulating leptin action. Statins, peroxisome proliferator-activated receptor-gamma binding agents, non-steroidal antiinflammatory drugs, and infant formulas supplemented with LCPUFAs, and LCPUFAs themselves, which suppress inflammation, may be beneficial in obesity.

The relationship between depression and cardiovascular disorders

Expanding scientific evidence supports a long-recognized link between cardiovascular disease and depression. As an independent risk factor, depression increases patient vulnerability to both cardiac events and mortality. Several important pathophysiologic mechanisms have been proposed, including hypothalamic-pituitary axis hyperactivity, autonomic nervous system dysfunction, and increased platelet reactivity, among others. The recently completed Sertraline Antidepressant Heart Attack Randomized Trial (SADHART) inaugurates a series of studies intended to address the impact of antidepressant therapy on cardiovascular risk.

5-hydroxytryptamine stimulates phosphorylation of p44/p42 mitogen-activated protein kinase activation in bovine aortic endothelial cell cultures

5-Hydroxytryptamine (5-HT) is sequestered and released by endothelial cells, acts as an endothelial cell mitogen, promotes the release of nitric oxide (NO), and has been associated with the p44/p42 mitogen-activated protein kinase (MAPK) cascade. NO also acts as a cell mitogen and promotes signals that culminate in the phosphorylation of MAPK. The aim of this study was to test whether endothelial 5-HT receptors stimulate dual (tyrosyl- and threonyl-) phosphorylation of MAPK through a mitogen-activated protein kinase kinase-1 (MEK-1) and eNOS-dependent pathway in bovine aortic endothelial cells (BAECs). As shown by Western blot analysis, 5-HT and the 5-HT1B-selective agonist 5-nonyloxytryptamine (5-NOT) stimulate time- and concentration-dependent (0.001-10 microM) phosphorylation of MAPK in these cells. The agonist-stimulated phosphorylation of MAPK was blocked by the 5-HT1b-receptor antagonist isamoltane (0.01-10 p3M) and the MEK-1 inhibitor PD 098059 ([2-(2'-amino-3'-methoxy-phenyl)-oxanaphthalen-4-one]; 0.01-10 microM¿. The eNOS inhibitor L-N(omega)-iminoethyl-L-ornithine (L-NIO; 0.01-10 microM) failed to block the 1 microM 5-NOT-stimulated responses. Our findings suggest that the 5-HT receptors (specifically 5-HT1B) mediate signals to MEK-1 and subsequently to MAPK through an eNOS-independent pathway in BAECs.