Prostaglandin H2 may be the endothelium-derived contracting factor released by acetylcholine in the aorta of the rat

The present experiment was performed to identify endothelium-derived contracting factor produced by acetylcholine stimulation in the aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. The rings of the thoracic aorta were obtained from age-matched SHR and WKY rats, and changes in isometric tension were recorded. The relaxant responses to acetylcholine in the aortic rings from SHR were significantly weaker than those from WKY rats. The relaxant responses to acetylcholine were significantly enhanced by pretreatment with a cyclooxygenase inhibitor (indomethacin) or thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708) in aortic rings from both SHR and WKY rats. A thromboxane A2 synthetase inhibitor (OKY-046) did not affect the acetylcholine-induced relaxation in the aortic rings from SHR or WKY rats. In the organ bath solution, after acetylcholine stimulation, prostaglandin E2 and 6-keto-prostaglandin F1 alpha concentrations increased but not prostaglandin F2 alpha and thromboxane B2 concentrations. Exogenous prostaglandin H2, a stable analogue of thromboxane A2, and prostaglandin F2 alpha induced contractions of the SHR rings at a lower concentration than prostaglandin E2, prostaglandin D2, and prostaglandin I2. These contractile responses to various prostaglandins were markedly inhibited by pretreatment with ONO-3708. A prostacyclin synthetase inhibitor did not affect the relaxant responses to acetylcholine in the SHR rings. These results show that endothelium-derived contracting factor is produced and released by acetylcholine stimulation not only in the aorta of SHR but also in those of WKY rats and suggest that prostaglandin H2, a precursor of the released prostaglandins, is a strong candidate for endothelium-derived contracting factor produced by acetylcholine stimulation.     

The role of endothelium-derived contracting factor (EDCF) and endothelium-derived relaxing factor (EDRF) in the aorta of the rat: identification of EDCF

The present experiment was performed to identify endothelium-derived contracting factor produced by acetylcholine stimulation in the aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The rings of the thoracic aorta were obtained from age-matched SHR and WKY, and changes in isometric tension were recorded. The relaxant responses to acetylcholine in the rings from SHR were significantly weaker than those obtained in WKY. The relaxant responses to acetylcholine were significantly enhanced by pretreatment with a cyclooxygenase-inhibitor (indomethacin) or thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708) both in the SHR and WKY rings. A thromboxane A2 synthetase inhibitor (OKY-046) did not affect the acetylcholine-induced relaxation in the rings from SHR or WKY. In the organ bath solution, following acetylcholine stimulation, prostaglandin E2 and 6-keto-prostaglandin F1 alpha concentrations increased, but prostaglandin F2 alpha and thromboxane B2 concentrations did not increase. Exogenous prostaglandin H2, a stable analogue of thromboxane A2 (STA2) and prostaglandin F2 alpha induced contractions of the SHR rings at a lower concentration than prostaglandin E2, prostaglandin D2 and prostaglandin I2. These contractile responses to various prostaglandins were markedly inhibited by pretreatment with ONO-3708. A prostacyclin synthetase inhibitor did not affect the relaxant responses to acetylcholine in the SHR rings. These results show that endothelium-derived contracting factor is produced and released by acetylcholine stimulation not only in the aorta of SHR but also in that of WKY. The results also suggest that prostaglandin H2, a precursor of the released prostaglandins, is a strong candidate for endothelium-derived contracting factor produced by acetylcholine stimulation.     

Endothelium-dependent contractions to acetylcholine in the aorta of the spontaneously hypertensive rat

To study the mechanism of decreased endothelium-dependent relaxations in spontaneously hypertensive rats (SHR), rings of thoracic aorta with and without endothelium were taken from age-matched male SHR and normotensive Wistar-Kyoto rats (WKY) and suspended for isometric tension recording. Acetylcholine caused endothelium-dependent contractions in quiescent rings from SHR but not in those from WKY. These contractions were inhibited by atropine but not by hexamethonium and were prevented by inhibitors of phospholipase A2 or cyclooxygenase but not by inhibitors of prostacyclin synthetase, thromboxane synthetase, or leukotriene synthetase. Prostaglandin D2, E1, E2, and F2 alpha caused concentration-dependent contractions in rings without endothelium from both SHR and WKY; the responses to the highest concentration (10(-5) M) of the individual prostaglandins were comparable in both strains. Endothelium-dependent relaxations evoked by high but not by low concentrations of acetylcholine were significantly depressed in SHR as compared with those in WKY (p less than 0.05). Indomethacin normalized endothelium-dependent relaxations in SHR. Thus, acetylcholine can activate muscarinic receptors that evoke endothelium-dependent contractions in the aorta of SHR but not in that of WKY. The contraction probably is mediated by a cyclooxygenase product(s) other than prostacyclin or thromboxane A2. The reduced endothelium-dependent relaxations to acetylcholine in the SHR probably are not due to a decreased release of endothelium-derived relaxing factor(s) but to the simultaneous release of endothelium-derived contracting substance(s).     

Prostaglandin H2 as an endothelium-derived contracting factor and its interaction with endothelium-derived nitric oxide.

The possibility that prostaglandin H2 is an endothelium-derived contracting factor (EDCF) was evaluated in rings of thoracic aorta of spontaneously hypertensive rats (SHR). When the aortic rings were contracted with norepinephrine (10(-7) mol/l) and treated with acetylcholine (10(-5) mol/l), a relaxant response with a peak after approximately 1 min and a contractile response with a peak after approximately 7 min were observed. When these rings were pretreated with a thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708), the later contractile response was clearly inhibited and only a sustained relaxant response was observed. This relaxant response was completely inhibited by pretreatment with an inhibitor of nitric oxide production (N-nitroarginine methylester; NNM). When aortic rings in the basal condition were treated with NNM and then with acetylcholine, a contractile response with a peak after 7 min was observed, but this reaction was completely inhibited by pretreatment with ONO-3708. The rate of 6-keto-prostaglandin F1 alpha production showed a peak of 1.4 x 10(-6) mol/l per min per tissue, 2-4 min after administration of acetylcholine. With exogenous prostaglandin H2 (5 x 10(-7) mol/l), a peak contraction was observed after approximately 4 min, the degree and pattern of which were similar to that induced by acetylcholine. Endogenous prostaglandin H2 is considered to be produced by the aortic rings in an amount sufficient to induce vascular contraction within 30 s, and the pattern of this contraction induced by acetylcholine resembles that induced by exogenous prostaglandin H2. These findings most strongly suggest that prostaglandin H2 is an EDCF.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endothelium-derived contracting factor in carotid artery of hypertensive Dahl rats.

The present study is designed to investigate whether acetylcholine (ACh) elicits an endothelium-derived contracting factor (EDCF) and whether it contributes to decreased relaxant response induced by ACh in Dahl rats. Dahl salt-sensitive (DS) and -resistant (DR) rats were fed a 0.4% NaCl or an 8% NaCl diet for 4 weeks. High sodium intake significantly increased blood pressure in DS rats but not in DR rats. The carotid rings were suspended for isometric tension recording. ACh caused an endothelium-dependent contraction in carotid rings from hypertensive DS rats but not from normotensive Dahl rats. Atropine, indomethacin, SQ29548, or ONO-3708 (prostaglandin H(2) [PGH(2)]/thromboxane A(2) [TXA(2)] receptor antagonist) abolished ACh-induced contraction, and OKY-046 (inhibitor of TXA(2) synthetase) partially attenuated the contraction. High sodium intake significantly enhanced contraction evoked by U46619, a PGH(2)/TXA(2) receptor agonist, in both DS and DR rats. In contrast, ACh-induced relaxation was significantly depressed in the rings from hypertensive DS rats, and ONO-3708 partially improved the depressed relaxation. Administration of ONO-8809 (an orally active PGH(2)/TXA(2) receptor antagonist; 30 micrograms per body per day) for 4 weeks neither reduced blood pressure nor improved the depressed ACh-induced relaxation in hypertensive DS rats. These results suggest that ACh causes release of EDCF in carotid rings of hypertensive DS rats, which is likely to be PGH(2) and TXA(2). The EDCF contributed in part to the depressed ACh-induced relaxation.     

Effect of 5-lipoxygenase blockade on blood pressure and acetylcholine-evoked endothelium-dependent contraction in aorta from spontaneously hypertensive rats

OBJECTIVE: Cysteinyl leukotrienes (cysLT) are pro-inflammatory and vasoactive products suspected to be involved in the regulation of vascular tone and blood pressure in hypertension. DESIGN: We investigated, in spontaneously hypertensive rats (SHR), the involvement of cysLT in the in-vivo regulation of blood pressure and the in-vitro endothelium-dependent contraction to acetylcholine in isolated aorta. METHODS: SHR and Wistar-Kyoto rats (WKY) were orally treated for 3 weeks with either the cysLT biosynthesis inhibitor MK-886 (0.1 mg/ml) or vehicle. After mean arterial blood pressure (MABP) measurement, aortic ring preparations were removed from all groups of animals, and contractions and relaxations were monitored subsequent to stimulation with acetylcholine. RESULTS: MABP was higher in SHR. Chronic treatment with MK-886 did not alter MABP in either SHR or WKY. In the presence of the N-nitro-L-arginine (L-NA, 100 micromol/l), and on prostaglandin F2alpha (PGF2alpha)-induced tone, acetylcholine evoked concentration-dependent contractions in intact aortic rings from SHR only. Pretreatment with either MK-886 (10 micromol/l), the 5-lipoxygenase (5-LO) inhibitor AA861 (10 micromol/l), or the cysLT1 receptor antagonist MK571 (1 micromol/l) reduced (P < 0.05) acetylcholine-induced contractions in intact aortic rings from SHR only. Acetylcholine-induced contractions were weaker (P < 0.01) in SHR chronically treated with MK-886 than in SHR. In the presence of L-NA, leukotriene (LT) D4 induced greater (P < 0.05) concentration-dependent contractions in aortic rings from SHR than from WKY. MK571 abolished LTD4-evoked contractions. CONCLUSION: These data suggested that 5-LO-derived products, through the activation of cysLT1 receptors, could be involved in the endothelium-dependent contraction to acetylcholine in aorta from SHR but not in the regulation of MABP in SHR.     

Age and hypertension promote endothelium-dependent contractions to acetylcholine in the aorta of the rat

This study was undertaken to compare age-related changes in endothelium-dependent vascular responses in both hypertensive and normotensive rats. Aorta from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) aged 4-6 weeks (young), 3-6 months (adult), and 12-25 months (old) were examined for relaxation to acetylcholine, adenosine 5'-triphosphate (ATP), and sodium nitroprusside. Rubbed (endothelium denuded) aorta from all groups displayed neither relaxation nor contraction to acetylcholine. Maximal relaxation responses to acetylcholine were reduced progressively with increasing age in unrubbed aorta of both SHR and WKY rats. In addition, acetylcholine caused not only dose-dependent relaxations at lower concentrations but also increases in tension at higher concentrations in unrubbed aorta of old WKY rats as well as adult and old SHR. However, indomethacin completely inhibited the tension development. As a result, aorta treated with indomethacin demonstrated similar acetylcholine-induced, endothelium-dependent relaxations in all groups. The thromboxane A2 synthetase inhibitor (E)-7-phenyl-7-(3-pyridyl)-6-heptanoic acid (CV-4151) partially but significantly depressed the increases in tension in aorta of old WKY rats. The degrees of endothelium-dependent relaxations to ATP and endothelium-independent relaxations to sodium nitroprusside were almost similar in all groups. These findings suggest that the release of or vascular responsiveness to endothelium-derived relaxing factor in the aorta is well maintained through senescence in both strains and that, in the aorta of not only SHR but also old normotensive WKY rats, the endothelium releases contracting factors that may be thromboxane A2 and other vasoconstrictor prostanoids.     

Eicosanoids and membrane properties in arteries of aged spontaneously hypertensive rats

OBJECTIVE: The arteries of aged spontaneously hypertensive rats (SHR) exhibit spontaneous electrical activity together with membrane depolarization. Vascular eicosanoid production is increased in SHR, which is further accelerated with aging. We tested the hypothesis that eicosanoids are involved in spontaneous electrical activity, membrane depolarization or both in mesenteric arteries of aged SHR. DESIGN AND METHODS: Membrane potentials were recorded with microelectrodes from the mesenteric arteries of aged (24 months and older) SHR, aged Wistar-Kyoto (WKY) rats and adult (6- to 8-month-old) SHR. RESULTS: The membrane potential was less negative in aged SHR (-38.5 +/- 0.9 mV) than in either aged WKY rats or adult SHR (-49.8 +/- 0.5 and -47.2 +/- 0.6 mV, respectively; P < 0.05 for both). Spontaneous electrical activity (5-20 mV, 1-7/min) was present only in arteries of aged SHR. Spontaneous electrical activity was not affected by phentolamine, atropine or tetrodotoxin, but was abolished by indomethacin, a cyclooxygenase inhibitor, and ONO-3708, a thromboxane A2/prostaglandin H2 receptor antagonist. Furthermore, indomethacin and ONO-3708 hyperpolarized the membrane by about 5 mV in aged SHR but not in the other two groups. Spontaneous electrical activity was enhanced by a thromboxane A2 analog and prostaglandin H2, and was abolished by a Ca2+ antagonist, nicardipine, and Ca(2+)-free solution. CONCLUSIONS: These findings suggest that cyclooxygenase-dependent eicosanoids contribute importantly to both spontaneous electrical activity and membrane depolarization, presumably through activation of the thromboxane A2/prostaglandin H2 receptor, in mesenteric arteries of aged SHR, and that spontaneous electrical activity is mediated by a Ca2+ influx through voltage-dependent Ca2+ channels.     

Endothelin in hypertensive resistance arteries. Intraluminal and extraluminal dysfunction

The effects of intraluminal and extraluminal endothelin-1 and its interactions with endothelium-derived relaxing factor were studied in perfused mesenteric resistance arteries of Wistar-Kyoto rats and spontaneously hypertensive rats. Changes in intraluminal diameter were recorded. In adult Wistar-Kyoto rats, but not spontaneously hypertensive rats, low concentrations of intraluminal endothelin-1 (10(-10) to 10(-9) M) caused relaxations of quiescent arteries blocked by indomethacin. After endothelial removal, intraluminal endothelin-1 evoked concentration-dependent contractions in both strains. Extraluminal endothelin-1 caused greater contractions of arteries with endothelium than intraluminal endothelin-1, and the sensitivity was lower in adult hypertensive rats; endothelial removal enhanced the contractions to extraluminal endothelin-1 to a greater extent in hypertensive than in normotensive rats. In arteries without endothelium, intraluminal and extraluminal endothelin-1 caused comparable contractions, but the sensitivity was reduced in adult but not young hypertensive as compared with normotensive rats. Both young spontaneously hypertensive and normotensive rats exhibited a high sensitivity to the peptide. In arteries precontracted with endothelin-1, endothelium-dependent relaxation to intraluminal acetylcholine was reduced in hypertensive as compared with normotensive rats, whereas relaxations to extraluminal acetylcholine were increased in hypertensive rats. Thus, endothelin-1 interacts with both vascular smooth muscle and the endothelium. The sensitivity of vascular smooth muscle to endothelin-1 is reduced in adult hypertensive rats. Intraluminal activation of the endothelium by endothelin-1 or acetylcholine is reduced in spontaneously hypertensive rats, whereas extraluminal activation causes more pronounced responses in hypertensive than in normotensive rats, suggesting a prominent dysfunction of the intraluminal surface of the endothelium in hypertension.     

L-Arginine improves endothelial function in renal artery of hypertensive Dahl rats

OBJECTIVES: To clarify whether endothelium-derived contracting factor (EDCF) is developed in renal artery of hypertensive Dahl rats and whether prolonged oral L-arginine treatments prevent development of EDCF and hypertension. DESIGN: The effect of prolonged salt treatment with or without L-arginine on the renal artery was examined. METHODS AND RESULTS: Dahl salt-sensitive and -resistant rats were fed a 0.4 or an 8% NaCl diet for 4 weeks. High sodium intake increased arterial pressure in Dahl salt-sensitive rats. The rings of renal arteries were suspended for isometric tension recording. Only in the hypertensive rats, more than 1 micromol/l acetylcholine induced an endothelium-dependent contraction response. The contraction was completely inhibited by indomethacin or ONO-3708 [prostaglandin H2 (PGH2)/thromboxane A2 (TXA2) receptor antagonist], and partially inhibited by OKY-046 (TXA2 synthetase inhibitor). Acetylcholine-induced relaxation was significantly depressed in hypertensive rats, which was partially improved by SQ29548 (PGH2/TXA2 receptor antagonist). Oral L-arginine, but not ONO-8809 (orally active PGH2/TXA2 receptor antagonist) treatment, inhibited the contraction and amended the relaxation. The endothelium-independent contraction to TXA2 receptor agonist U46619 and relaxation to nitroprusside were not altered by L-arginine treatment The L-Arginine treatment reduced blood pressure and sodium retention with increases in urinary NO2-/NO3- and cGMP excretion. Hydralazine treatment also inhibited development of EDCF. CONCLUSIONS: The present results suggest that impaired endothelium-dependent relaxation to acetylcholine is caused in part by induction of EDCF synthesis/release in renal arteries of hypertensive Dahl rats. L-arginine can attenuate sodium retention and development of hypertension, which lead to a decrease in EDCF synthesis in renal arteries.     

Nitric oxide inactivates endothelium-derived contracting factor in the rat aorta.

Acetylcholine evokes the simultaneous release of endothelium-derived relaxing and contracting factors in aortas from spontaneously hypertensive rats. Only relaxing factors are released in aortas from normotensive controls. Experiments were designed to determine whether inhibitors of endothelium-dependent relaxations modify endothelium-dependent contractions. Rings of thoracic aortas of normotensive and spontaneously hypertensive rats, with and without endothelium, were suspended in organ chambers for isometric tension recording. Oxyhemoglobin (a scavenger of endothelium-derived relaxing factor) and NG-monomethyl L-arginine (an inhibitor of nitric oxide formation) augmented the contractions to acetylcholine. Methylene blue (an inhibitor of soluble guanylate cyclase) and superoxide dismutase (a scavenger of superoxide anions) did not modify these contractions. The contractions in the presence of oxyhemoglobin or NG-monomethyl L-arginine, like those in untreated rings, were endothelium-dependent; they only occurred in aortas from spontaneously hypertensive rats and were abolished by indomethacin. The contractions to acetylcholine in the presence of oxyhemoglobin were not affected by superoxide dismutase or deferoxamine. These data suggest that endothelium-derived relaxing factor inhibits endothelium-dependent contractions to acetylcholine in the spontaneously hypertensive rat aorta, probably by chemical inactivation of the endothelium-derived contracting factor rather than by stimulation of guanylate cyclase or scavenging of oxygen-derived free radicals.     

Endothelium-dependent relaxation and L-arginine metabolism in genetic hypertension.

This study characterizes the effects of L-arginine and NG-monomethyl L-arginine on dilator responsiveness of vascular tissue from Wistar-Kyoto rats and stroke-prone spontaneously hypertensive rats. Rings of abdominal aorta were suspended in tissue baths for measurement of isometric force. After contraction induced by phenylephrine, cumulative addition of acetylcholine, L-arginine, or A23187 to the muscle bath caused a similar relaxation of aortic rings in both animal groups. To test the hypothesis that arginine metabolism is altered in hypertension, aortic rings were incubated with NG-monomethyl L-arginine. NG-monomethyl L-arginine (10-300 microM) did not affect contractile responses to phenylephrine (10(-10) to 10(-4) M) in either animal group (EC50, 10(-7) M). Exposure of aortic rings to NG-monomethyl L-arginine resulted in a greater inhibition of relaxation response to acetylcholine (10(-10) to 10(-6) M) in hypertensive animals. NG-monomethyl L-arginine (300 microM) caused complete inhibition of relaxation to acetylcholine in the hypertension group. Incubation with L-arginine (10-100 microM) overcame the inhibition of acetylcholine-induced relaxation produced by NG-monomethyl L-arginine in both groups. Exposure of aortic ring segments to NG-monomethyl L-arginine attenuated relaxation responses to A23187 (10(-10) to 3 x 10(-6) M) in both groups. L-Arginine-induced reversal of the inhibitory effect of NG-monomethyl L-arginine on the relaxation responses to A23187 was similar between groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impaired endothelium-dependent relaxations in rabbits subjected to aortic coarctation hypertension

Rabbits were rendered hypertensive by suprarenal coarctation of the abdominal aorta. Seven days later, endothelium-dependent and endothelium-independent vascular relaxations were examined in vascular rings taken from hypertensive (thoracic aorta, carotid artery) and normotensive (abdominal aorta) regions. Relaxation of phenylephrine-contracted rings in response to endothelium-dependent agonists (acetylcholine, A23187) was impaired, compared with that in sham-operated and intact controls, in regions exposed to the elevated blood pressure (i.e., above the coarctation). Responses to acetylcholine and A23187 in the abdominal aorta, below the coarctation, were not altered. The diminished endothelium-dependent responses in the thoracic aorta were not affected by pretreatment with the cyclooxygenase inhibitor indomethacin. In contrast to acetylcholine and A23187, responses to the endothelium-independent agonist nitroprusside were not attenuated in vessels from hypertensive regions, indicating that the defect occurred in the endothelium. The EC50 for acetylcholine-induced relaxations of thoracic aorta correlated significantly with mean arterial pressure above the coarctation, indicating that the extent to which endothelium-dependent relaxation is impaired is in proportion to the degree of blood pressure elevation. This study suggests that the diminished relaxations by endothelium-dependent agonists is a local response to the elevation of blood pressure and is not due to a circulating factor.     

Chlorogenic acid attenuates hypertension and improves endothelial function in spontaneously hypertensive rats

BACKGROUND AND OBJECTIVES: Epidemiologic studies indicate that ingestion of vegetables and fruit inhibits the development of cardiovascular disease. Chlorogenic acids are abundant phenolic compounds contained in vegetables and fruits, but the impact of dietary chlorogenic acids on vascular function in hypertension is not known. We therefore examined the effects of 5-caffeoylquinic acid (CQA), a representative chlorogenic acid, on blood pressure and vascular function in age-matched normotensive Wistar-Kyoto rats and spontaneously hypertensive rats. METHODS AND RESULTS: A single ingestion of CQA (30-600 mg/kg) reduced blood pressure in spontaneously hypertensive rats, an effect that was blocked by administration of a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester. When spontaneously hypertensive rats were fed diets containing 0.5% CQA for 8 weeks (approximately 300 mg/kg per day), the development of hypertension was inhibited compared with the control diet group. CQA ingestion increased urinary excretion of nitric oxide metabolites and decreased urinary excretion of hydrogen peroxide; decreased NADPH-dependent superoxide anion production in the aorta, suggesting that dietary CQA inhibited vascular NADPH oxidase activity; significantly improved acetylcholine-induced endothelium-dependent vasodilation in the aorta; and markedly reduced the degree of immunohistochemical staining for nitrotyrosine and media hypertrophy in aorta sections. In contrast, CQA had no effects in Wistar-Kyoto rats. CONCLUSIONS: Dietary CQA reduces oxidative stress and improves nitric oxide bioavailability by inhibiting excessive production of reactive oxygen species in the vasculature, and leads to the attenuation of endothelial dysfunction, vascular hypertrophy, and hypertension in spontaneously hypertensive rats.     

Contractions to Endothelin in Normotensive and Spontaneously Hypertensive Rats: Role of Endothelium and Prostaglandins

Contractions to endothelin-1 in aortas of the spontaneously hypertensive rats (SHR) were compared with those of normotensive controls (WKY); rings with and without endothelium were studied in organ chambers. Contractions to endothelin were smaller in aortas of SHR compared to WKY, whether the endothelium was present or not. The presence of a functional endothelium reduced contractions to the peptide in both strains. Endothelium-dependent relaxations to acetylcholine and endothelium-independent relaxations to nitric oxide were observed in rings from both strains during contraction with endothelin. Indomethacin reduced the contractions to endothelin in the aorta from SHR with endothelium, but not in those without endothelium; it did not significantly affect endothelin-induced contractions in rings of WKY with or without endothelium. These experiments demonstrate that contractions of the vascular smooth muscle to endothelin are reduced in the aorta of the SHR. The basal and stimulated release of endothelium-derived relaxing factor inhibits contractions to endothelin in the aorta from both strains. The inhibitor of cyclooxygenase indomethacin does not prevent the response of the vascular smooth muscle to endothelin; however, endothelin may stimulate the release of an indomethacin-sensitive endothelium-derived contracting factor in the SHR aorta.     

Activation of endothelial L-arginine pathway in resistance arteries. Effect of age and hypertension

In conduit arteries, nitric oxide is formed from L-arginine in the endothelium and released after stimulation with acetylcholine. The contribution of the L-arginine pathway and the effects of age and hypertension on endothelium-dependent vascular regulation were studied, using a video dimension analyzer, in pressurized and perfused mesenteric resistance arteries of 8- and 16-20-week-old Wistar-Kyoto and spontaneously hypertensive rats. Norepinephrine and phenylephrine caused contractions, which were similarly augmented after removal of the endothelium. NG-Monomethyl-L-arginine, an inhibitor of nitric oxide formation, augmented the contraction, but less than endothelial removal. Acetylcholine caused endothelium-dependent relaxations that were much more pronounced with intraluminal than with extraluminal application. NG-Monomethyl-L-arginine, methylene blue, and hemoglobin only partially inhibited the response. With aging, the endothelium-dependent inhibition of the response to norepinephrine decreased in Wistar-Kyoto rats; in spontaneously hypertensive rats this inhibition was smaller as compared with age-matched Wistar-Kyoto rats. In Wistar-Kyoto rats, the difference between intraluminal and extraluminal activation became more pronounced in adult rats. In the adult but not the young spontaneously hypertensive rats, the response to intraluminal but not extraluminal acetylcholine was reduced as compared with Wistar-Kyoto rats. Thus, in mesenteric resistance arteries of the rat, nitric oxide is released from L-arginine under basal conditions and after stimulation with acetylcholine but only in part accounts for endothelium-dependent responses. With aging and hypertension, the inhibitory effects of the endothelium against norepinephrine-induced contractions decrease. In hypertension, the intraluminal but not extraluminal activation of the release of endothelium-derived relaxing factors is impaired.     

Treatment with the arginase inhibitor N(omega)-hydroxy-nor-L-arginine improves vascular function and lowers blood pressure in adult spontaneously hypertensive rat

OBJECTIVE: High vascular arginase activity and subsequent reduction in vascular nitric oxide production were recently reported in animal models of hypertension. The present study investigated the effects of in-vivo arginase inhibition on blood pressure and vascular function in adult spontaneously hypertensive rats. METHODS: Ten-week-old spontaneously hypertensive rats and normotensive age-matched Wistar-Kyoto rats were treated with or without the selective arginase inhibitor N-hydroxy-nor-L-arginine for 3 weeks (10 or 40 mg/kg per day, intraperitoneally). Systolic blood pressure and cardiac rate were measured before and during treatment. Flow and pressure-dependent reactivity as well as remodeling of mesenteric arteries, acetylcholine-dependent vasodilation of aortic rings, cardiac hypertrophy, arginase activity and nitric oxide production were investigated in 13-week-old spontaneously hypertensive rats. RESULTS: In spontaneously hypertensive rats, N-hydroxy-nor-L-arginine treatment decreased arginase activity (30-40%), reduced blood pressure ( approximately 35 mmHg) and improved the reactivity of mesenteric vessels. However, vascular and cardiac remodeling was not different between treated and untreated spontaneously hypertensive rats. In Wistar-Kyoto rats, N-hydroxy-nor-L-arginine did not affect blood pressure. Finally, arginase inhibition was associated with increased nitric oxide production. Consistent with this, the response of aortic rings to acetylcholine was fully restored by N-hydroxy-nor-L-arginine, and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester significantly reduced the effect of N-hydroxy-nor-L-arginine on flow-dependent vasodilation. CONCLUSION: Pharmacological inhibition of arginase in adult spontaneously hypertensive rats decreases blood pressure and improves the reactivity of resistance vessels. These data represent in-vivo argument in favor of selective arginase inhibition as a new therapeutic strategy against hypertension.     

Role of endothelium-derived prostanoid in angiotensin-induced vasoconstriction

To test the hypothesis that prostanoids contribute to angiotensin II-induced vascular contraction, we compared the effect of angiotensin II on isometric tension development by rings of descending thoracic aorta bathed in Krebs' bicarbonate buffer with and without indomethacin (10 microM) to inhibit cyclooxygenase, CGS13080 (10 microM) to inhibit thromboxane A2 synthesis, or SQ29548 (1 microM) to block thromboxane A2/prostaglandin endoperoxide receptors. The comparisons were made in rings of aorta taken from normotensive rats and from rats with aortic coarctation-induced hypertension at 12 days and 90-113 days after coarctation. These rings released thromboxane B2, which was found to be endothelium dependent, increased in hypertensive rats, and stimulated by angiotensin II (10(-6) M) in normotensive rats and in hypertensive rats at 12 days after coarctation. The angiotensin II (10(-6) to 10(-5)M)-induced contraction of aortic rings was increased by about 30% at 12 days after coarctation and decreased at 90-113 days after coarctation. Removal of the endothelium increased the contractile effect of angiotensin II (10(-6) M) in aortic rings of normotensive rats and hypertensive rats at 90-113 days after coarctation but decreased the effect in aortic rings of hypertensive rats at 12 days after coarctation. In rats at 12 days after coarctation, the angiotensin II (10(-6) M)-induced contraction of aortic rings with endothelium was attenuated by indomethacin and SQ29548 but not by CGS13080. These data suggest that a prostanoid-mediated and endothelium-dependent mechanism of vasoconstriction contributes to the constrictor effect of angiotensin II in aortic rings of rats in the early phase of aortic coarctation-induced hypertension.     

口服L-精氨酸对腹主动脉缩窄后大鼠血压、心肌肥厚和血管舒张功能的影响

本文利用缩窄大鼠腹主动脉的方法制备高血压模型，观察了正常大鼠、未服和口服Ｌ－精氨酸两周的腹主动脉狭窄的大鼠的血压、心肌肥厚及血管舒张功能的改变，旨在了解Ｌ－精氨酸对腹主动脉缩窄性高血压大鼠的作用。研究发现腹主动脉狭窄后大鼠发生了严重的高血压及心肌肥厚。未服Ｌ－精氨酸的大鼠心肌肥厚，且血管环对１０－８～１０－５ｍｏｌ／Ｌ乙酰胆碱诱导的舒张反应明显减低；而Ｌ－精氨酸口服治疗两周能减轻其心肌肥厚，并部分改善乙酰胆碱诱导的血管舒张功能，但两组大鼠腹主动脉缩窄后的血压均升高，两者相比较差别无统计学意义（Ｐ＞０．０５）。结果提示：Ｌ－精氨酸（１０－５～１０－３ｍｏｌ／Ｌ）有直接舒张该大鼠血管环的作用，且呈剂量依赖关系，长期口服Ｌ－精氨酸可减轻腹主动脉缩窄性大鼠的心肌肥厚，改善其血管的舒张功能，而其血压的变化与上述作用无关。     

Sex-specific acute effect of estrogen on endothelium-derived contracting factor in the renal artery of hypertensive Dahl rats

OBJECTIVE : To determine whether estrogen rapidly affects endothelium-derived contracting factor (EDCF) in the renal artery of hypertensive Dahl rats, and whether factors other than nitric oxide (NO) contribute to the effect of estrogen. DESIGN : Acute effects of estrogen on the acetylcholine-induced vasomotor responses and on prostaglandin H2/thromboxane A2 mimetic, U46619,-induced contraction were examined in isolated arterial rings. METHODS AND RESULTS : Dahl salt-sensitive male and female rats were fed an 8% NaCl diet for 4 weeks. The blood pressure increased more rapidly and to a greater extent in males than in females. Renal arterial rings were prepared for isometric tension recording. 17beta-Estradiol, but not the biologically less active stereoisomer, 17alpha-estradiol, improved the relaxation response to acetylcholine in renal arteries from females. Estrogen also rapidly decreased the contraction evoked by acetylcholine (10(-6) to approximately 10(-4) mol/l) in renal arteries from females and it was effective at a physiological concentration (10(-9) mol/l) in the presence of Nomega-nitro-l-arginine methyl ester (an NO synthase inhibitor). The estrogen receptor antagonist, ICI 182,780, abolished the effect of estrogen, whereas the cytochrome P450 inhibitor, miconazole, had no effect. The contraction induced by U46619 was also suppressed by estrogen, without any contribution from NO. Estrogen had no effect on either relaxation or contraction responses in renal arteries from males. CONCLUSION : 17beta-Estradiol antagonizes increases in vascular tone in hypertensive females by enhancing NO-dependent relaxation, and by suppressing EDCF-mediated mechanisms in an NO-independent manner.