15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and 5-carboxamidotryptamine

Vasoactive agents were examined in arteries from control rats and rats exposed to intermittent hypoxia (10% oxygen; 8 h/day) for 3, 5 or 20 days. Hypoxic rats developed right ventricular hypertrophy after 5 days, but became pulmonary hypertensive (elevated right ventricular systolic pressure; RVSP) only after 20 days. In pulmonary arteries (main and intralobar), responses to acetylcholine and ionomycin (endothelium-dependent vasodilators) were reduced after 20 and 5 days of intermittent hypoxia, whereas contractions to 5-hydroxytryptamine (5-HT) were enhanced (potency increase >10-fold) after 20, 5 and 3 days. Contractions to endothelin-1 and a thromboxane-mimetic, but not Ca(2+), were also increased. No changes in vascular function occurred in aorta. Since changes in pulmonary vascular function preceded the increase in RVSP they do not result from, but may contribute to, the development of hypoxia-induced pulmonary hypertension. If similar changes occur in humans, they may be important in conditions characterised by intermittent, as opposed to continuous, hypoxia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Animals; Endothelin-1; Endothelium, Vascular; Hypoxia; In Vitro Techniques; Ionomycin; Male; Muscle, Smooth, Vascular; Potassium Chloride; Pulmonary Artery; Rats; Rats, Wistar; Serotonin; Vasoconstrictor Agents; Vasodilator Agents

1. The receptors responsible for 5-hydroxytryptamine (5-HT)-mediated contraction of rabbit isolated epicardial coronary artery denuded of endothelium was examined by bioassay. 2. A variety of 5-HT mimetics caused concentration-dependent contractions. The rank order of agonist potency was 5-carboxamidotryptamine (5-CT) > 5-HT > (+/-)-alpha-methyl-5-hydroxytryptamine ((+/-)-alpha-me-5-HT) = sumatriptan. This was not consistent with relative potencies at any single recognized 5-HT receptor, suggesting the presence of a mixed receptor population. In one subset of preparations precontracted with U46619 (10-30 nM) with the endothelium intact, none of the agonists caused a relaxation. 3. Contractions to 5-HT were antagonized by ketanserin, a 5-HT2A-selective antagonist, but the displacement of concentration-response curves was inconsistent with an interaction between 5-HT and a single receptor population; the slope of regression between antagonist log M concentration and agonist log (concentration-ratio -1) was shallow (0.57). Responses to 5-HT were also antagonized by the 5-HT(1B/1D)-receptor antagonist GR127935 and, again, the slope of regression was shallow (0.68). These data suggest a possible involvement of 5-HT2A and 5-HT1B or 5-HT1D receptors in the response to 5-HT. 4. Contractions to (+/-)-alpha-me-5-HT, which is selective for 5-HT2A over 5-HT1B and 5-HT1D receptors, were competitively antagonized by low concentrations of ketanserin. The regression between antagonist log M concentration and agonist log (concentration-ratio -1) fitted the Schild equation with a slope that was not significantly different from unity (0.95), giving a pA2 value of 9.0. GR127935 (3-30 nM), had no effect on the contractile response to (+/-)-alpha-me-5-HT. These data establish, unequivocally, the presence of 5-HT2A receptors in the tissue. 5. Sumatriptan, a relatively selective 5-HT(1B/1D)-receptor agonist, induced contractions that were antagonized competitively by GR127935 (3-30 nM), although there was a reduction in the maximum response when concentrations of GR127935 exceeded 3 nM. The apparent pA2 (estimated by imposing a unit slope on the log agonist (concentration-ratio -1) value in the presence of 3 nM GR127935) was 8.92. Contractions to sumatriptan were not affected by low (5-HT2A receptor-selective) concentrations of ketanserin, but were antagonized in a competitive manner at higher concentrations (pA2 6.5). These data appear to confirm the presence of 5-HT1B and/or 5

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Coronary Vessels; Endothelium, Vascular; In Vitro Techniques; Muscle Contraction; Muscle, Smooth, Vascular; Oxadiazoles; Pericardium; Piperazines; Rabbits; Receptor, Serotonin, 5-HT1B; Receptor, Serotonin, 5-HT1D; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Sumatriptan; Vasoconstrictor Agents

1. 5-Hydroxytryptamine (5-HT) receptors mediating contraction and relaxation are present in Cynomolgus monkey isolated jugular vein denuded of endothelium. 2. In the absence of spasmogen, alpha-methyl-5-HT and sumatriptan contracted the tissues with potency values (pEC50) of 6.8 (n = 2) and 6.4 +/- 0.1 (mean +/- s.e. mean, n = 3), respectively. In contrast, 5-HT caused an initial contraction (10 nM - 1 microM), followed by relaxation (1 microM - 32 microM). The contractile effect of alpha-methyl-5-HT was antagonized by ketanserin with a pKB value of 8.1 (n = 2). 5-Carboxamidotryptamine (5-CT), 5-methoxytryptamine (5-MeOT) and 8-OH-DPAT did not contract or relax the tissues in the absence of spasmogen. 3. In tissues precontracted with U46619 (10 nM) and in the presence of 5-HT1A, 5-HT1B, 5-HT2A, 5-HT3, and 5-HT4 receptor blockade, 5-CT and 5-MeOT caused endothelium-independent relaxation with potency values of 7.5 +/- 0.1 (n = 21) and 5.7 +/- 0.1 (n = 4), respectively. The potency of 5-HT was 7.2 (n = 2) while alpha-methyl-5-HT did not start to relax the tissues below a concentration of 10 microM. 4. Relaxations elicited by 5-CT were antagonized by the following compounds (with pKB values in parentheses): methiothepin (9.7), mesulergine (8.1), metergoline (8.0), clozapine (7.8), mianserin (7.7), spiperone (7.3), ritanserin (7.1), methysergide (7.0) and ketanserin (5.7). 5. It is concluded that the 5-HT receptor mediating endothelium-independent relaxation may be a functional correlate of the putative 5-ht7 receptor.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Female; In Vitro Techniques; Jugular Veins; Macaca fascicularis; Male; Prostaglandin Endoperoxides, Synthetic; Receptors, Serotonin; Serotonin; Serotonin Receptor Agonists; Thromboxane A2; Vasoconstrictor Agents; Vasodilation

1. A series of 5-hydroxytryptamine (5-HT) receptor agonists including 5-HT, 5-carboxamidotryptamine (5-CT) and sumatriptan produced little or no contraction of rabbit isolated mesenteric arteries under resting tone conditions, even at concentrations up to 10(-4) M. 2. When the same agonists were retested in mesenteric artery preparations pre-contracted with the thromboxane-mimetic, U46619, each demonstrated concentration-related vasoconstrictor activity. 5-CT and 5-HT were especially potent and effective in this model giving EC50 values of 4.3 x 10(-9) M and 1.6 x 10(-8) M respectively and maximum effects equivalent to those of KCl 80 mM. In preparations precontracted by U46619 (conditions retained throughout the rest of the study) the order of agonist potency was 5-CT > 5-HT > RU 24969 = sumatriptan > 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT) > cisapride. 3. The vasoconstrictor effects of 5-CT were competitively antagonized by methiothepin (pA2 8.20) but resistant to antagonism by a range of other 5-HT receptor antagonists, i.e. pindolol (5-HT1A/5-HT1B), propranolol (5-HT1B), spiperone (5-HT2A), ondansetron (5-HT3), ICS 205930 (5-HT3/5-HT4) and SDZ 205557 (5-HT4). 5-CT responses were slightly antagonized by a high concentration of ritanserin (5-HT2A/5-HT2C). Responses to 5-HT and sumatriptan were also antagonized by methiothepin with similar affinity (pA2/pKB values congruent to 8.0). 4. Metergoline and rauwolscine (10(-7)-10(-6) M) antagonized the effects of 5-CT in a non-competitive fashion giving pKBapp values of 7.13 (metergoline) and 6.86 (rauwolscine). 5. Vasoconstrictor responses to 5-HT were not modified in the presence of ritanserin (3 x 10-7 M) orspiperone (3 x 10-7 M) and only modestly antagonized by ketanserin (10-6 M) suggesting that 5-HT2Areceptors do not make a significant contribution in this model.6. Hence, precontraction of rabbit mesenteric arteries reveals potent vasoconstrictor effects of 5-HT and related agonists. Based on the agonist potency order and the antagonist studies performed, the receptor subtype responsible has the characteristics of a 5-HT1-like (probably 5-HTlD) receptor. This study therefore demonstrates a particularly striking example of vasoconstrictor synergy involving 5-HT1-like receptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; In Vitro Techniques; Male; Mesenteric Arteries; Muscle Contraction; Muscle, Smooth, Vascular; Potassium Chloride; Prostaglandin Endoperoxides, Synthetic; Rabbits; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Sumatriptan; Thromboxane A2; Vasoconstriction; Vasoconstrictor Agents

Rabbit renal arteries were virtually unresponsive to 5-hydroxytryptamine (5-HT) and 5-carboxamidotryptamine (5-CT) under control conditions (including the presence of ketanserin 10(-6) M). However, both agents produced prominent contractions over the range 10(-9)-10(-5) M in tissues pre-contracted with threshold concentrations of either histamine or U46619. These responses were considered to be mediated by activation of 5-HT1-like receptors based on the potency order 5-CT > or = 5-HT and the sensitivity of agonist responses to antagonism by methiothepin (10(-7) M). Pre-contraction with different types of vasoconstrictor can therefore unmask functional 5-HT1-like receptors in rabbit renal artery.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Dose-Response Relationship, Drug; Drug Interactions; Histamine; Male; Muscle Contraction; Muscle, Smooth, Vascular; Prostaglandin Endoperoxides, Synthetic; Rabbits; Receptors, Serotonin; Renal Artery; Serotonin; Serotonin Receptor Agonists; Vasoconstrictor Agents

1. Using a number of agonist and antagonist compounds, we have attempted to characterize the responses and receptors involved in the effects of 5-hydroxytryptamine (5-HT) in the rabbit isolated renal artery. 2. In vessel segments precontracted with the thromboxane-mimetic agent, U46619 (100 nM), neither 5-HT (10(-8) to 10(-4) M) nor 5-carboxamidotryptamine (5-CT; 10(-8) to 3 x 10(-4) M) caused relaxations like those observed with methacholine. Both 5-HT and 5-CT further increased the tone of the vessels, with pD2 values of 7.1 and 7.9, respectively. 3. In the absence of U46619, both 5-HT (10(-7) to 3 x 10(-3) M) and 5-CT (10(-7) to 10(-3) M) contracted the rabbit renal artery, but with reduced potencies. The contractions to 5-HT were reproducible and the rank order of potency (pD2) of the agonists was: alpha-methyl-5-HT (5.7), sumatriptan (5.3), 5-HT (5.1), 8-hydroxy-2(di-n-propylamino)tetralin (5.0), 5-CT (4.7) and 5-methoxytryptamine (4.3). 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane, flesinoxan and RU 24969 elicited either only small contractions or none at all. 4. The contractile effect of 5-HT was unaffected by MDL 72222 (10(-6) M) and metergoline (10(-8) and 10(-7) M), was weakly antagonized by ketanserin and phentolamine (pKB: 6.6 and 6.8, respectively), but was effectively antagonized by methiothepin (pKB: 8.6). Responses to 5-CT and sumatriptan were affected by ketanserin, phentolamine and methiothepin similarly to 5-HT-induced responses. 5. Ketanserin was ineffective against noradrenaline-induced contractions, which were antagonized by phentolamine with a pKB of 7.3. The pKB values of phentolamine against 5-HT, 5-CT or sumatriptan were about half a log unit lower than against noradrenaline.6. In vascular preparations treated with cocaine (3 x 10- I M), the potency (pKB) of phentolamine as an antagonist of the responses to noradrenaline (7.6) and 5-HT (6.7) did not differ significantly from the values in untreated preparations. However, the difference between the pKB values of phentolamine against the two agonists was now about one log unit.7. Pretreatment of the vascular strips with 6-hydroxydopamine (1.5 x 10- 3M) did not significantly affect responses to 5-HT or 5-CT, but almost eliminated those to tyramine. Cocaine (3 x 10- 5M) slightly potentiated noradrenaline-induced contractions, but did not significantly affect those induced by 5-HT.8. These data suggest that: (i) 5-HT receptors mediating vasodilatation are not present in the rabbit re

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Cocaine; In Vitro Techniques; Indoles; Ketanserin; Muscle Contraction; Muscle, Smooth, Vascular; Norepinephrine; Oxidopamine; Phentolamine; Prostaglandin Endoperoxides, Synthetic; Rabbits; Receptors, Serotonin; Renal Artery; Serotonin; Serotonin Antagonists; Sulfonamides; Sumatriptan; Sympathectomy; Tetrahydronaphthalenes; Tyramine; Vasoconstrictor Agents; Vasodilation

1. 5-Hydroxytryptamine (5-HT) relaxes rings of neonatal porcine isolated vena cava by both an endothelium-dependent and an endothelium-independent mechanism. The receptor mediating the latter response has been shown to be a 5-HT1-like receptor (positively coupled to adenylyl cyclase) located on the vascular smooth muscle. The features of the endothelium-dependent response to 5-HT in this preparation are now described. 2. In ring preparations contracted with the stable thromboxane-A2-mimetic, U-46619 (10 nM), and in the presence of the 5-HT2 receptor antagonist ketanserin (1 microM), low concentrations of 5-HT (1-100 nM) evoked an endothelium-dependent, rapid, 'spike-like' relaxation. Higher concentrations of 5-HT (0.1-10 microM) elicited a more sustained, but endothelium-independent relaxation. 3. Relaxation induced by low concentrations (1-100 nM) of 5-HT was abolished by endothelium removal, and was markedly (but not totally) inhibited by the guanylate cyclase inhibitor, methylene blue (10 microM) or by the inhibitor of endothelium-derived nitric oxide (NO) synthesis, L-NG-monomethylarginine (L-NMMA; 100-500 microM). 4. The endothelium-dependent response to 5-HT was mimicked by alpha-methyl-5-HT, 5-methoxytryptamine, tryptamine and 2-methyl-5-HT, but not by sumatriptan or 8-hydroxy-di-n-propylaminotetralin (8-OH-DPAT) at concentrations up to 10 microM. In contrast, relaxation evoked by 5-carboxamidotryptamine (5-CT) was endothelium-independent. 5. The endothelium-dependent relaxation induced by 5-HT or alpha-methyl-5-HT was antagonized by methysergide, methiothepin, cyproheptadine and metergoline, but not by ketanserin, spiperone, ondansetron, verapamil, cyanopindolol, mesulergine, ICS 205-930, or indomethacin. 6. These results suggest that the endothelium-dependent relaxation of porcine vena cava induced by 5-HT is largely mediated by the release of NO (although other endothelium-derived relaxing factors may also be involved) and that 5-HT is acting at a receptor which is not '5-HT1-like', 5-HT2, 5-HT3 or 5-HT4 and is not comparable to recognised 5-HT receptor ligand binding sites. The characteristics of this receptor are discussed in relation to the endothelial 5-HT receptor types in other blood vessels.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; alpha-Methyltyrosine; Animals; Animals, Newborn; Arginine; Endothelium, Vascular; Ketanserin; Methyltyrosines; Muscle Relaxation; Muscle, Smooth, Vascular; omega-N-Methylarginine; Prostaglandin Endoperoxides, Synthetic; Receptors, Serotonin; Serotonin; Swine; Venae Cavae

1. The effects of selective thromboxane antagonists and a thromboxane synthase inhibitor on the contraction to 9,11-dideoxy-11 alpha,9 alpha-epoxymethano-prostaglandin F2 alpha (U46619) and oxygen in the human umbilical artery (HUA) were examined. The effect of the antagonists on contractions to both 5-hydroxytryptamine (5-HT) and 5-carboxamidotryptamine (5-CT) were also examined. 2. U46619 (0.3 nM-10 microM) contracted the HUA. This contraction was antagonized by two selective thromboxane receptor antagonists EP092 (10 nM-1 microM) and GR32191B (10 nM-1 microM). The contraction was not affected by the selective thromboxane synthase inhibitor, dazoxiben (10 nM-1 microM). 3. When the oxygen tension was increased from 16 mmHg to 120 mmHg, the HUA transiently contracted. Both thromboxane antagonists inhibited this contraction in a concentration-dependent manner with 1 microM almost completely abolishing the response (the oxygen-induced contraction of the control preparation normally increases with a second exposure to 120 mmHg oxygen). 4. In low (16 mmHg) oxygen, responses to both 5-HT and 5-CT were unaffected by both thromboxane receptor antagonists at concentrations up to 1 microM. In high oxygen (120 mmHg) responses to both 5-HT and 5-CT were biphasic in nature, with an additional initial high sensitivity phase, which was abolished by a cyclo-oxygenase inhibitor. In high oxygen, EP092 and GR32191B blocked this initial phase in a concentration-dependent manner, returning sensitivity to 5-HT and 5-CT to that seen in low oxygen. 5. The thromboxane synthase inhibitor, dazoxiben, at concentrations greater than 10 nm inhibited the contraction to 120 mmHg oxygen and at 1 microM, dazoxiben almost abolished the response. In low oxygen, the response to 5-HT was unaffected by dazoxiben at concentrations up to 10 microM. In high oxygen, the initial phase of the contraction to 5-HT was inhibited by concentrations greater than 10 nm, with no effect on the maximum response. 6. The results show that thromboxane receptor antagonism or blockade of thromboxane synthesis selectively attenuates oxygen-induced contractions and those responses to 5-HT and 5-CT which are dependent on high oxygen for their expression. This suggests that the contractions caused by high oxygen tension, and the enhancement of the contractile effects of low concentrations of 5-HT and 5-CT in the presence of high oxygen tension are mediated by endogenously released thromboxane A2.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Biphenyl Compounds; Female; Heptanoic Acids; Humans; Imidazoles; In Vitro Techniques; Muscle Contraction; Muscle, Smooth, Vascular; Oxygen; Pregnancy; Prostaglandin Endoperoxides, Synthetic; Prostaglandins, Synthetic; Serotonin; Thromboxane-A Synthase; Thromboxanes; Umbilical Arteries