In vitro guinea pig tracheal contraction to 5-hydroxytryptamine (5-HT) and to KCl increased significantly with time, an effect specific to the trachea because contraction of the rat aorta to KCl changed only modestly with time. The possibility that with time, contractile agonists could release endogenous contractile substances was considered and ruled out. Neither the neurotoxin tetrodotoxin, the muscarinic antagonist atropine, the thromboxane synthase inhibitor (E)-3-[4-(1-imidazolylmethyl)phenyl]-2-propanoic acid hydrochloride monohydrate (OKY 046), the leukotriene D4 and E4 antagonists 7-(3-hydroxy-2-prophylphenoxy[2-hydroxypropoxyl]-4- oxo-8-propyl-4H-1-benzopyran-2-carboxylate) (FPL55712) and 4-(5-cyclopentyloxycarbonylamino-1-methylindol-3-ylmythyl )-3-methoxy-N-o-toylsulfonyl benzamide (ICI 204,219), or the lipoxygenase inhibitor N-(3-phenoxycinnamyl)-acetohydroxamic acid (BWA4C) markedly affected the tracheal increase in contraction to KCl over time. The possibility that bronchodilatory substances were released and opposed contractility at early times, but not later was also considered. However, adenosine was not likely to be involved because 8-(p-sulfophenyl)theophylline, an inhibitor of adenosine, did not modify agonist-induced tracheal contractility. Propranolol (10(-6) M) also had no effect on tracheal improvement, suggesting that beta receptor activation of relaxation was not involved. Interestingly, incubation of trachea with the cyclooxygenase inhibitors indomethacin (10(-5) and 10(-6) M) or piroxicam (10(-6) M) increased the initial tracheal contraction to KCl, permitting the trachea to reach maximal force sooner, thereby minimizing the apparent improvement in contractility.(ABSTRACT TRUNCATED AT 250 WORDS)
Serotonin (5-hydroxytryptamine, 5-HT) infusion in a normal conscious rat decreases mean arterial pressure (MAP), in part by reduction in total peripheral resistance. Microsphere experiments have shown 5-HT increases blood flow within the splanchnic vascular bed, with the greatest being in the intestine and spleen. Interestingly, 5-HT does not cause a direct relaxation of resistant (small or large) mesenteric arteries. The present study addresses the possibility of the venous circulation contributing to the 5-HT induced fall in blood pressure. Our working hypothesis is venous dilation, specifically dilation of veins measurable within the splanchnic vascular bed, contributes to 5-HT-induced hypotension. Using an ultrasound imaging system (Vevo 2100 imaging system; 21 MHz probe,Visual Sonics Inc.), telemetry-implanted, anesthetized male Sprague Dawley rats underwent cross-sectional imaging which was controlled for respiration and cardiac cycles. The following vessels were imaged: abdominal aorta (AA); portal vein (PV); abdominal inferior vena cava (IVC); and superior mesenteric vein (SMV). Following the collection of baseline MAP and vessel diameter measurements, Alzet osmotic mini-pumps containing vehicle (saline; n=9) or 5-HT (25 ug/kg/min; n=9) were implanted for 1 week. After, 24 hours of infusion, 5-HT increased the vein diameter (SMV 17.48±2%; PV 17.67±2%; IVC 46.87±8%) and maintained the AA diameter ( AA 0.93±1%) from baseline while reducing MAP (vehicle 101.93±3; 5-HT 84.68±2 mm Hg; p<0.05).One-week post removal of all osmotic mini-pumps, there was no difference in the MAP or diameter of all noted vessels between the two treatment groups. To correlate with in vivo findings, the PV and IVC, when isolated in a tissue bath for measurement of isometric force and contracted with endothelin 1, relaxed in a concentration dependent fashion to 5-HT and 5-carboxamidotryptamine (5-HT 1/7 receptor agonist;1 nM-10 uM). Collectively, these findings highlight the contribution of splanchnic venous dilation in 5-HT-induced hypotension and propose a possible mechanism for 5-HT reduction in blood pressure.
Vascular capacitance is reduced by endothelin-1 (ET-1) in deoxycorticosterone (DOCA)-salt hypertensive rats. This may contribute to hypertension development. Because the splanchnic blood vessels (especially veins) are important in determining vascular capacitance, we tested the hypothesis that ET-1 levels in the splanchnic vasculature are elevated in hypertensive DOCA-salt compared with normotensive rats. Tissue ET-1 content was measured by ELISA in aorta, vena cava, superior mesenteric artery and vein, and small mesenteric arteries and veins from normotensive sham-operated (sham) and 4-wk DOCA-salt rats. We also determined ET-1 concentration in aortic and portal venous blood (draining the nonhepatic splanchnic organs) in anesthetized and conscious sham and DOCA-salt rats before and after acute blockade of ETB receptor-mediated plasma clearance of ET-1. Results showed a higher ET-1 content in veins than in arteries of similar size. However, ET-1 content was similar in vessels from sham and DOCA-salt rats, except in aorta and superior mesenteric artery, where ET-1 content was greater in DOCA-salt rats. ET-1 concentration was significantly higher in portal venous than in aortic blood, indicating net nonhepatic splanchnic release (nNHSR) of ET-1. However, nNHSR of ET-1 was similar in sham and DOCA-salt rats. Although nNHSR of ET-1 increased significantly after ETB receptor blockade in sham rats, it was completely unchanged in DOCA-salt rats. These data suggest that, despite the absence of ETB receptor-mediated plasma clearance of ET-1, neither the venous peptide content nor the net release of ET-1 is increased in the splanchnic vasculature of DOCA-salt rats. These results argue against the hypothesis that increased venomotor tone in DOCA-salt hypertension is caused by increased ET-1 concentration around splanchnic venous smooth muscle cells.
Objective— Obesity and hypertension are comorbid in epidemic proportion, yet their biological connection is largely a mystery. The peptide chemerin is a candidate for connecting fat deposits around the blood vessel (perivascular adipose tissue) to arterial contraction. We presently tested the hypothesis that chemerin is expressed in perivascular adipose tissue and is vasoactive, supporting the existence of a chemerin axis in the vasculature. Approach and Results— Real-time polymerase chain reaction, immunohistochemistry, and Western analyses supported the synthesis and expression of chemerin in perivascular adipose tissue, whereas the primary chemerin receptor ChemR23 was expressed both in the tunica media and endothelial layer. The ChemR23 agonist chemerin-9 caused receptor, concentration-dependent contraction in the isolated rat thoracic aorta, superior mesenteric artery, and mesenteric resistance artery, and contraction was significantly amplified (more than 100%) when nitric oxide synthase was inhibited and the endothelial cell mechanically removed or tone was placed on the arteries. The novel ChemR23 antagonist CCX832 inhibited phenylephrine-induced and prostaglandin F2α-induced contraction (+perivascular adipose tissue), suggesting that endogenous chemerin contributes to contraction. Arteries from animals with dysfunctional endothelium (obese or hypertensive) demonstrated a pronounced contraction to chemerin-9. Finally, mesenteric arteries from obese humans demonstrate amplified contraction to chemerin-9. Conclusions— These data support a new role for chemerin as an endogenous vasoconstrictor that operates through a receptor typically attributed to function only in immune cells.
Vascular 5-Hydroxytryptamine2A (5-HT2A) receptor signaling and contraction has been associated with the activation of L-type calcium channels, phospholipase C (PLC) and, as we previously demonstrated, tyrosine kinase activation. We hypothesize the 5-HT2A receptor activates all three pathways independently to elicit contraction and that one of the tyrosine kinases activated by 5-HT is mitogen-activated protein kinase kinase (MEK). Endothelium-denuded rat thoracic aorta was mounted into isolated tissue baths for measurement of isometric contractile force. 5-HT, alpha-methyl-5-HT and 2,5-dimethoxy-4-iodoamphetamine all contracted the rat aorta, whereas the 5-HT2A receptor antagonist ketanserin (30 nM) blocked contraction to 5-HT. The tyrosine kinase inhibitor genistein (5 microM) shifted contraction to 5-HT, alpha-methyl-5-HT and DOI approximately 10-fold to the right, whereas daidzein (5 microM), the inactive isomer of genistein, was unable to shift 5-HT-induced contraction. PD098059 (10 microM), an inhibitor of MEK, shifted contraction to 5-HT approximately 7-fold to the right. We next examined the integration of tyrosine kinase activation in 5-HT2A receptor signaling. 5-HT-induced contraction was reduced individually by the PLC inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC; 100 microM) or the Ca++ channel inhibitor nifedipine (50 nM); the remaining response to 5-HT was reduced by further addition of either genistein or PD098059. When nifedipine and NCDC were used in combination, a part of the contraction to 5-HT remained: this contraction was further reduced by genistein or PD098059. In cultured aortic smooth muscle cells, 5-HT (0.01-100 microM) stimulated tyrosyl-phosphorylation of 42- and 44-kDa proteins identified as Erk MAPKs; this phosphorylation was reduced by PD098059 (10 microM). Neither nifedipine nor NCDC reduced 5-HT (1 microM)-stimulated Erk MAPK tyrosyl-phosphorylation, but the combination of nifedipine, NCDC and PD098059 abolished 5-HT (1 microM)-stimulated Erk MAPK tyrosyl-phosphorylation. Taken together, these studies indicate that stimulation of a vascular 5-HT2A receptor activates Ca++ channels and PLC as well as MEK to cause rat aortic contraction and that MEK activation is at least partially independent of the two pathways classically associated with 5-HT2A receptors.
