Isometric Tension Of Aortic Rings Research Articles

Ginsenoside Rb1 Reduces Hyper-Vasoconstriction Induced by High Glucose and Endothelial Dysfunction in Rat Aorta.

Acute hyperglycemia induces oxidative damage and inflammation, leading to vascular dysfunction. Ginsenoside Rb1 (Rb1) is a major component of red ginseng with anti-diabetic, anti-oxidant and anti-inflammatory properties. Here, we investigated the beneficial effects and the underlying mechanisms of Rb1 on hypercontraction induced by high glucose (HG) and endothelial dysfunction (ED). The isometric tension of aortic rings was measured by myography. The rings were treated with NG-nitro-L-arginine methyl ester (L-NAME) to induce chemical destruction of the endothelium, and Rb1 was added after HG induction. The agonist-induced vasoconstriction was significantly higher in the aortic rings treated with L-NAME + HG50 than in those treated with HG50 or L-NAME (p = 0.011) alone. Rb1 significantly reduced the hypercontraction in the aortic rings treated with L-NAME + HG50 (p = 0.004). The ATP-sensitive K+ channel (KATP) blocker glibenclamide tended to increase the Rb1-associated reduction in the agonist-induced vasoconstriction in the rings treated with L-NAME + HG50. The effect of Rb1 in the aortic rings treated with L-NAME + HG50 resulted from a decrease in extracellular Ca2+ influx through the receptor-operated Ca2+ channel (ROCC, 10-6-10-4 M CaCl2, p < 0.001; 10-3-2.5 × 10-3 M CaCl2, p = 0.001) and the voltage-gated Ca2+ channel (VGCC, 10-6 M CaCl2, p = 0.003; 10-5-10-2 M CaCl2, p < 0.001), whereas Rb1 did not interfere with Ca2+ release from the sarcoplasmic reticulum. In conclusion, we found that Rb1 reduced hyper-vasoconstriction induced by HG and ED by inhibiting the ROCC and the VGCC, and possibly by activating the KATP in rat aorta. This study provides further evidence that Rb1 could be developed as a therapeutic target for ED in diabetes.

Abstract 245: Prevention of Glyceryl Trinitrate Tolerance by Flavonoids

Background and propose: The anti-ischemic effects of glyceryl trinitrate (GTN) are rapidly blunted after continuous application. This phenomenon of GTN tolerance may be the result of an increased oxidative stress and/or a reduced bioactivation of GTN by the enzyme aldehyde dehydrogenase (ALDH). The polyphenolic compounds flavonoids are reported to potentiate vascular relaxation and inhibit oxidation. Therefore, in the present study, we assessed the hypothesis that flavonoids can prevent GTN tolerance. Whether or not this effect of flavonoids is related to their anti-oxidative property or modulation of the activity of ALDH was also examined. Experimental approach: Isolated rat aortic rings were incubated with modified Krebs-Henseleit solution containing GTN (30 μM) in organ chamber at 37°C for 1 hour to induce tolerance. Flavonoids (10 μM of apigenin, luteolin, kaempferol, quercetin, genistin, genistein, narigenin, catechin or epicatechin) or the vehicle (1 mM dimethyl sulfoxide) were added to the aortic rings 30 minutes before GTN treatment. Those rings without incubation with GTN were served as the respective control groups. After removing the treatment solution, rings were contracted with phenylephrine (1 μM) followed by cumulative addition of GTN (0.1 nM to 30 μM). GTN-induced relaxation was calculated as change in isometric tension of aortic rings from the contraction induced by phenylephrine. Vascular ALDH activity was assayed by spectrophotometry as the rate of NAD+ consumption. Key results: GTN-induced relaxation in rat aortic rings was reduced by prior incubation with GTN; this reduction was prevented by apigenin (10 μM), which did not affect the relaxations in the group without prior treatment with GTN. Apigenin (10 μM) also increased the vascular ALDH activity which was reduced by prior GTN incubation. Conclusion: Apigenin appears to have the potential to prevent the development of GTN tolerance, likely by restoring the bioactivation of GTN by ALDH.

Characterization of imidazoline receptors in blood vessels for the development of antihypertensive agents.

It has been indicated that activation of peripheral imidazoline I2-receptor (I-2R) may reduce the blood pressure in spontaneously hypertensive rats (SHRs). Also, guanidinium derivatives show the ability to activate imidazoline receptors. Thus, it is of special interest to characterize the I-2R using guanidinium derivatives in blood vessels for development of antihypertensive agent(s). Six guanidinium derivatives including agmatine, amiloride, aminoguanidine, allantoin, canavanine, and metformin were applied in this study. Western blot analysis was used for detecting the expression of imidazoline receptor in tissues of Wistar rats. The isometric tension of aortic rings isolated from male rats was also estimated. The expression of imidazoline receptor on rat aorta was identified. However, guanidinium derivatives for detection of aortic relaxation were not observed except agmatine and amiloride which induced a marked relaxation in isolated aortic rings precontracted with phenylephrine or KCl. Both relaxations induced by agmatine and amiloride were attenuated by glibenclamide at concentration enough to block ATP-sensitive potassium (KATP) channels. Meanwhile, only agmatine-induced relaxation was abolished by BU224, a selective antagonist of imidazoline I2-receptors. Taken together, we suggest that agmatine can induce vascular relaxation through activation of peripheral imidazoline I2-receptor to open KATP channels. Thus, agmatine-like compound has the potential to develop as a new therapeutic agent for hypertension in the future.

Changes of imidazoline receptors in spontaneously hypertensive rats

The role of imidazoline receptors in the regulation of vascular function remains unclear. In this study, we evaluated the effect of agmatine, an imidazoline receptor agonist, on systolic blood pressure (SBP) in spontaneously hypertensive rats (SHRs) and investigated the expressions of imidazoline receptors by Western blot. The isometric tension of aortic rings isolated from male SHRs was also estimated. Agmatine decreased SBP in a dose-dependent manner in SHRs but not in the normal group [Wistar-Kyoto (WKY) rats]. This reduction in SBP in SHRs was abolished by BU224, a selective antagonist of imidazoline I(2) -receptors. Higher expression of imidazoline receptors in SHR was observed. Moreover, agmatine-induced relaxation in isolated aortic rings precontracted with phenylephrine or KCl. This relaxation was also abolished by BU224 but was not modified by efaroxan, an imidazoline I(1) -receptor antagonist. Agmatine-induced relaxation was also attenuated by PNU 37883, a selective blocker of vascular ATP-sensitive potassium (K(ATP) ) channels. Additionally, vasodilatation by agmatine was reduced by an inhibitor of protein kinase A (PKA). We suggest that agmatine can lower blood pressure in SHRs through activation of the peripheral imidazoline I(2) -receptor, which is expressed more highly in SHRs.

Activation of Peripheral Opioid µ-Receptors in Blood Vessel May Lower Blood Pressure in Spontaneously Hypertensive Rats

Background/Aims: The role of opioid receptors in the regulation of vascular function remains unclear. In the current study, we evaluated the ability of loperamide, a peripheral opioid receptor agonist, to regulate blood pressure in spontaneously hypertensive rats (SHRs) and examined the mechanism(s) by which loperamide exerts its effects. Methods: In male SHRs, mean arterial pressure (MAP) was measured and hemodynamic analysis was recorded. Additionally, the isometric tension of aortic rings isolated from SHRs was determined. Results: Loperamide dose-dependently decreased MAP in SHRs but not in the normal group of Wistar-Kyoto rats. This reduction of MAP in conscious SHRs was abolished by the selective opioid µ-receptor antagonist cyprodime, but not by naloxonazine, the µ₁-opioid receptor antagonist. However, cardiac output was not altered by loperamide in anesthetized SHRs. Moreover, loperamide-induced relaxation in isolated aortic rings precontracted with phenylephrine or vasopressin. This relaxation was abolished by cyprodime, but not by naloxonazine. Loperamide-induced relaxation was also attenuated by glibenclamide, an ATP-sensitive potassium (K_ATP) channel blocker. Additionally, vasodilatation by loperamide was reduced by an inhibitor of protein kinase A (PKA) and enhanced by an inhibitor of phosphodiesterases. Conclusion: We suggest that loperamide can lower MAP in SHRs via µ₂-opioid receptor-dependent cAMP-PKA pathway that induces vascular relaxation by opening K_ATP channels.

Different effects of ascorbate deprivation and classical vascular nitrate tolerance on aldehyde dehydrogenase‐catalysed bioactivation of nitroglycerin

Vascular tolerance to nitroglycerin (GTN) may be caused by impaired GTN bioactivation due to inactivation of mitochondrial aldehyde dehydrogenase (ALDH2). As relaxation to GTN is reduced but still sensitive to ALDH2 inhibitors in ascorbate deficiency, we compared the contribution of ALDH2 inactivation to GTN hyposensitivity in ascorbate deficiency and classical in vivo nitrate tolerance. Guinea pigs were fed standard or ascorbate-free diet for 2 weeks. Reversibility was tested by feeding ascorbate-deficient animals standard diet for 1 week. Nitrate tolerance was induced by subcutaneous injection of 50 mg x kg(-1) GTN 4 times daily for 3 days. Ascorbate levels were determined in plasma, blood vessels, heart and liver. GTN-induced relaxation was measured as isometric tension of aortic rings; vascular GTN biotransformation was assayed as formation of 1,2- and 1,3-glyceryl dinitrate (GDN). Two weeks of ascorbate deprivation had no effect on relaxation to nitric oxide but reduced the potency of GTN approximately 10-fold in a fully reversible manner. GTN-induced relaxation was similarly reduced in nitrate tolerance but not further attenuated by ALDH inhibitors. Nitrate tolerance reduced ascorbate plasma levels without affecting ascorbate in blood vessels, liver and heart. GTN denitration was significantly diminished in nitrate-tolerant and ascorbate-deficient rings. However, while the approximately 10-fold preferential 1,2-GDN formation, indicative for active ALDH2, had been retained in ascorbate deficiency, selectivity was largely lost in nitrate tolerance. These results indicate that nitrate tolerance is associated with ALDH2 inactivation, whereas ascorbate deficiency possibly results in down-regulation of ALDH2 expression.

Long‐term Exercise Intervention Ameliorates Vasorelaxation Mediated by Insulin and Insulin‐like Growth Factor‐1 in Aortas of Diabetic Rats

In order to investigate whether exercise ameliorates insulin‐ and insulin‐like growth factor‐1 (IGF‐1)‐mediated vasorelaxation in the diabetes, male Wistar rats were randomly divided into non‐diabetic control (Con), diabetic control (DM), and diabetes with exercise (DM+Ex) groups. Diabetic groups were induced by the intravenous injection of streptozotocin. The DM+Ex group performed an 8‐week treadmill exercise program for 60 min/day, 5 day/week. At the end of experiments, the vasorelaxant responses to insulin, IGF‐1, acetylcholine (ACh), and sodium nitroprusside (SNP) were evaluated by the isometric tension of aortic rings in the organ baths. In addition, the roles of phosphatidylinositol 3‐kinase (PI3‐K) and nitric oxide synthase (NOS) in the vasorelaxation were examined by treating selective inhibitors. We found that 1) insulin‐, IGF‐1‐, and ACh‐induced vasorelaxant responses were significantly impaired in the DM group, compared with those in the Con group (P&lt;0.05); 2) the exercise intervention significantly ameliorated the impaired vascular responses to insulin, IGF‐1, and ACh in the DM+Ex group, compared with those in the DM group (P&lt;0.05); 3) these alternations of vascular responses affected by diabetes and exercise were mainly due to the release of PI3‐K and NOS; 4) no significant difference was found in SNP‐induced vasorelaxation among the three groups. Our results suggest that long‐term exercise intervention ameliorates vasorelaxation mediated by insulin and IGF‐1 in type 1 diabetic rats. The PI3K‐NOS‐dependent pathway is mainly involved in the exercise‐induced beneficial effects. This study was partly supported by the National Science Council, Taiwan (NSC95‐2314‐B‐006‐073‐MY2).

Exercise training improves insulin-induced and insulin-like growth factor-1-induced vasorelaxation in rat aortas

Improved vasorelaxant response is one of the beneficial effects of exercise training on vascular function. The mechanism for this response is, however, poorly understood. The aim of this study was to investigate the effects of exercise training on insulin-induced and insulin-like growth factor-1 (IGF-1)-induced vasorelaxation. Fourteen 6-week-old male Wistar rats were randomly divided into sedentary control and exercise groups. For 12 weeks, the exercise group ran on a treadmill 60 min/day, 5 days/week. After exercise training, insulin-induced and IGF-1-induced vasorelaxant responses were evaluated by measuring the isometric tension of aortic rings. The vasorelaxant role of phosphatidylinositol 3-kinase (PI3K) and nitric oxide synthase (NOS) was examined by applying inhibitors, such as wortmannin (an inhibitor of PI3K) and N ω-nitro- l-arginine methyl ester ( l-NAME, a NOS inhibitor). In addition, we examined the vascular response to the NO donor, sodium nitroprusside (SNP). We found that: (1) exercise training significantly enhanced both insulin-induced and IGF-1-induced vasorelaxation in rat aortas; (2) this vasorelaxant effect disappeared after the use of wortmannin or l-NAME; (3) there was no significant difference in SNP-induced vasorelaxation between control and exercise groups. Our findings indicate that exercise training enhances insulin-induced and IGF-1-induced vasorelaxant responses which are mediated through the PI3K-NOS-dependent pathway.

Altered insulin-mediated and insulin-like growth factor-1-mediated vasorelaxation in aortas of obese Zucker rats

Insulin and insulin-like growth factor-1 (IGF-1) have vasorelaxant effects in vivo, which is dependent on nitric oxide (NO) production. The aim of this study was to investigate the vasorelaxant responses mediated by insulin and/or IGF-1 in aortas of obese Zucker rats. The thoracic aortas of eight lean and eight obese Zucker rats (6 months old) were isolated for vasorelaxation analysis. Insulin-induced and IGF-1-induced vasorelaxant responses were evaluated by the isometric tension of aortic rings in the organ bathes. The roles of phosphatidylinositol 3-kinase (PI3K) and nitric oxide synthase (NOS) in vasorelaxant responses were examined by treating selective inhibitors, such as wortmannin (an inhibitor of PI3K) and N (omega)-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor). In addition, the vascular responses to sodium nitroprusside (SNP), a direct vasodilator of vascular smooth muscle, were examined. The insulin-induced vasorelaxation in aortas of obese rats was significantly decreased, whereas the IGF-1-induced vasorelaxation was significantly increased, compared with that in lean rats. After the pre-administration of wortmannin or L-NAME, the altered insulin-induced or IGF-1-induced vasorelaxation was abolished. There was no significant difference in the SNP-induced vasorelaxation between lean and obese rats. Our findings suggested that the decreased insulin-mediated vasorelaxation in obese rats appeared to be counteracted by the increased IGF-1-mediated vasorelaxation. Furthermore, the NO-dependent pathway was involved in the altered vasorelaxant responses. However, the SNP-induced vasorelaxation was not changed in obese rats.

Endothelial responses of the aorta from adrenomedullin transgenic mice and knockout mice.

Adrenomedullin (AM) is a potent vascular wall-derived vasorelaxing peptide which induces the release of nitric oxide (NO). To explore the role of endogenous AM in vascular function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists [AM (22-52), and calcitonin gene-related peptide (CGRP) (8-37)] on the isometric tension of aortic rings isolated from AM transgenic (TG) and knockout (KO) mice and wild type littermates (WT). ACh and AM caused a dose-dependent reduction of the isometric tension of aortic rings, but the degree of vasodilatation was smaller in TG than in KO or WT (% delta tension [10(-6) mol/l ACh]: KO -69 +/- 10%, WT -39 +/- 8%, TG -29 +/- 1%, p < 0.01). On the other hand, N(G)-nitro-L-arginine methyl ester, an NO synthase inhibitor, induced greater vasoconstriction in TG (% delta tension 10(-5)mol/l: KO +78 +/- 16%, WT +99 +/- 27%, TG +184 +/- 20%, p < 0.01), whereas E-4021, a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase inhibitor, caused greater vasodilation in TG mice. Both AM antagonists increased tension in TG to a greater extent than in KO or WT mice (% delta tension [10(-6) mol/l CGRP (8-37)]: KO +24 +/- 5%, WT +51 +/- 6%, TG +75 +/- 7%, p < 0.01). Endothelial denudation of the aorta diminished the vasoconstriction caused by the AM antagonists. In conclusion, the amounts of AM expressed in the aortic endothelium influenced baseline NO release. AM antagonists increased vascular tone in WT as well as in TG, suggesting that endogenous AM plays a physiological role in the regulation of aortic tone.

Reduced endothelial vasomotor function and enhanced neointimal formation after vascular injury in a rat model of blood pressure lability.

Increased short-term blood pressure variability is known to be associated with hypertensive target organ damage. Sinoaortic denervation (SAD) induces a marked increase in blood pressure lability without affecting the average blood pressure level. The aim of this study was to investigate the effects of blood pressure lability on endothelial vasomotor function and neointimal formation after balloon injury in SAD rats. Direct longterm measurement of mean arterial pressure showed no significant difference in the average of mean arterial pressure between the SAD group and sham-operated control group. In contrast, the standard deviation of mean arterial pressure, as an index of blood pressure lability, was 3-fold greater in SAD rats. To study endothelial function, isometric tension of aortic rings was measured 4 weeks after SAD or sham operation. Endothelium-dependent vasorelaxation induced by acetylcholine was significantly reduced in the SAD group (20% reduction at maximum relaxation). Endothelium-independent vasorelaxation induced by sodium nitroprusside was similar in each group. Acetylcholine-induced NO release from aortic rings was significantly reduced in the SAD group. Next, we examined neointimal formation in carotid arteries in SAD and sham-operated rats at 2 weeks after balloon injury. The neointimal-to-medial area ratio in the SAD group was 50% higher than that in the sham-operated group. The percentage of proliferating cell nuclear antigen-positive cells in the intima was significantly higher in the SAD group. These findings suggest that increased blood pressure lability, independently of average blood pressure level, impairs endothelial function by inhibiting NO production, enhances neointimal formation after balloon injury, and may thereby contribute to atherogenesis.

Increases in intracellular calcium of arterial smooth muscle cells in transgenic mice overexpressing Na+/H+ exchanger.

We produced transgenic mice overexpressing Na+/ H+ exchanger as a model of salt-sensitive hypertension and reported that dietary salt loading elevates blood pressure in these transgenic mice. We speculate that this blood pressure elevation may be attributed to the elevation of intraarterial smooth muscle Ca2+ concentration through Na+/Ca2+ exchange. To test this hypothesis, we measured the isometric tension of aortic rings and intracellular free calcium ([Ca2+]i) of cultured smooth muscle cells. In the transgenic mice, the aortic ring contraction induced by 5 mM caffeine (percentage of 60 mM K-induced contraction) was significantly greater than control mice (60.1 +/- 5.5% vs. 44.8 +/- 3.1%). The mean [Ca2+]i in vascular smooth muscle cells (VSMCs) of transgenic mice (123.1 +/- 19.7 nM) was higher than those in VSMCs of control mice (66.6 +/- 7.2 nM). These observations suggest that dietary salt loading increases the concentration of calcium in arterial smooth muscle cells in this transgenic mice. These findings are helpful in tracing the causes of salt-sensitive hypertension.

Oxygen-derived free radical-induced vasoconstriction by thromboxane A2 in aorta of the spontaneously hypertensive rat.

This study was performed to clarify the mechanism of vasoconstriction induced by oxygen-derived free radicals in spontaneously hypertensive rats. The isometric tension of aortic rings from spontaneously hypertensive rats and Wistar-Kyoto rats was measured in Krebs-Henseleit solution. Oxygen-derived free radicals were generated by mixing xanthine and xanthine oxidase. The removal of endothelium enhanced the contractions induced by oxygen-derived free radicals. The inhibition of nitric oxide production with NG-nitro-L-arginine methyl ester (10(-4) M) enhanced the contractions. Treatment with the thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (10(-4) M) or RS-5186 (10(-4) M) markedly reduced the contractions. Treatment with the cyclooxygenase inhibitor indomethacin (10(-5) M) and a TXA2/prostaglandin H2 (PGH2) receptor antagonist, ONO-3708 (10(-6) M), completely abolished the oxygen-derived free radical-induced contractions. In contrast, treatment with the PGI2 synthetase inhibitor tranylcypromine (10(-4) M) did not attenuate the oxygen-derived free radical-induced contractions. Whether endothelium was present or not, the release of TXB2, PGE2, and 6-keto-PGF1alpha, but not PGF2alpha, was increased by the production of oxygen-derived free radicals. Catalase and the hydroxyl radical scavenger deferoxamine plus mannitol markedly inhibited the oxygen-derived free radical-induced contractions. These results suggest that oxygen-derived free radical-induced vasoconstriction in spontaneously hypertensive rat aorta is caused by TXA2 and PGH2 released in smooth muscle.

Chronic Estrogen Treatment in Female Transgenic (m Ren2)27 Hypertensive Rats Augments Endothelium-Derived Nitric Oxide Release

Postmenopausal estrogen replacement therapy is associated with a reduction in cardiovascular events in women, but the mechanisms for this protection are unclear, especially in hypertensive subjects. In this study we investigated the effects of 17 β-estradiol (E 2) treatment on blood pressure and endothelial function of transgenic [(m Ren2)27] hypertensive and normotensive rats. Thirty female transgenic negative [Tg(−)] and hypertensive positive [Tg(+)] rats were ovariectomized and received either E 2 (1.5 mg/rat, subcutaneously, for 3 weeks) or placebo. Chronic 17 β-estradiol treatment lowered mean blood pressure in both Tg hypertensive (159 ± 4 v 145 ± 4 mm Hg, P < .05, placebo v E 2) and normotensive rats (119 ± 4 v 108 ± 2 mm Hg, P < .05, placebo v E 2). Pressor responses to intravenous injection of phenylephrine were augmented in the Tg(+) as compared with Tg(−) rats. With chronic E 2 treatment the pressor responses to phenylephrine were attenuated in both groups. Isometric tension of aortic rings was measured in vitro in organ chambers. The acetylcholine (Ach)-induced endothelium-dependent vascular relaxation was less potent in Tg(+) versus Tg(−) rats. E 2 treatment significantly enhanced the Ach-induced relaxation of both Tg(+) and Tg(−) groups (ED 50: 55.5 ± 11.7 v 10.3 ± 2.6; 23.8 ± 6.5 v 5.1 ± 1.2 nmol/L, placebo v E 2 in Tg(+) and Tg(−), respectively). After E 2 treatment the ED 50 response in Tg(+) rats was no different from Tg(−) rats. However, the maximum vasodilation elicited by Ach was attenuated in Tg(+) as compared with Tg(−) rats. The calcium ionophore (A23187)-induced endothelium-dependent relaxation was less potent in Tg(+) as compared to Tg(−) rats and was enhanced by E 2 treatment only in Tg(+) animals. There were no differences in the vasodilator responses elicited by sodium nitroprusside. Removal of endothelium and blockade of NO production abolished the endothelium-dependent vasodilation. The selective NO synthase inhibitor, N G-monomethyl- l-arginine (LMMNA), was used to evaluate indirectly the basal contribution of NO in vascular rings. The response to LMMNA was attenuated in untreated Tg(+) as compared to Tg(−) rats. E 2 treatment augmented the contraction response to NOS inhibition in both Tg(+) and Tg(−) rats, resulting in a response in Tg(+) rats that was no different from Tg(−) rats. These results indicate that untreated, surgically ovariectomized hypertensive rats show deficiencies in endothelial function, which can be improved by estrogen replacement.

Developmental dynamics of endothelial and neurogenic control of canine thoracic aorta

The purpose of the study was to confront the range of endothelial relaxation and neurogenic contraction of the thoracic aorta in fetuses (1 week before birth), puppies (1, 2, 4 and 6 weeks old), and in adult dogs. Isometric tension of aortic rings was monitored in organ bath. Acetylcholine-induced dose-dependent relaxation of aortic rings precontracted by phenylephrine was pronounced already in fetuses and puppies and significantly larger than in adults. Indomethacin, a cyclooxygenase inhibitor, did not affect the magnitude of aortic relaxation to acetylcholine. Transmural nerve stimulation induced but very slight contractions of the thoracic aorta in fetuses, while in puppies the extent of contractions was increasing with increasing age, reaching its maximum in adults. Contractile responses of aortic rings induced by KCl were fully detectable in fetuses and puppies and increased with increasing age of the animals. Thus in ontogenesis, the extent of endothelium-dependent relaxation and neurogenic contraction of the thoracic aorta displayed an opposite trend. The acetylcholine-induced relaxation was fully operative already in fetuses and puppies and its extent was declining toward adulthood, whereas the neurogenic contraction was hardly detectable in fetuses, increasing in puppies, and showed the highest values in adults.

Correlation with blood pressure of the acetylcholine-induced endothelium-derived contracting factor in the rat aorta.

To examine a relation between the production of acetylcholine-induced endothelium-derived contracting factor and an increase in blood pressure, endothelium-dependent contraction and relaxation were evaluated by measuring the isometric tension of aortic rings from spontaneously hypertensive rats and Wistar-Kyoto rats at 5, 10, 20, and 30 weeks of age. In norepinephrine-precontracted rings, acetylcholine (10(-8) to 10(-5) M)-induced relaxations diminished at the doses of 10(-6) to 10(-5) M in both strains except at 5 weeks of age. Treatment with a thromboxane A2/prostaglandin H2 antagonist (ONO-3708) prevented this reduction in acetylcholine-induced relaxations in both strains and induced dose-dependent relaxations, which were completely inhibited by treatment with a nitric oxide inhibitor, NG-nitro-L-arginine methyl ester. In aorta treated with NG-nitro-L-arginine methyl ester without precontraction, acetylcholine induced dose-dependent contractions, which were greater in spontaneously hypertensive rats than in Wistar-Kyoto rats. These acetylcholine-induced contractions, which were observed only in rings with endothelium, were completely inhibited by treatment with ONO-3708 but not with a thromboxane A2 synthetase inhibitor (OKY-046). There was a statistically significant correlation between the acetylcholine-induced contractions and blood pressure. Release of 6-ketoprostaglandin F1 alpha by acetylcholine from the aorta was greater in spontaneously hypertensive rats. In vivo administration of another thromboxane A2/prostaglandin H2 antagonist (ONO-8809) (10 or 30 micrograms per body per day) for 3 weeks (5-8 weeks of age) did not affect blood pressure in either rat strain.(ABSTRACT TRUNCATED AT 250 WORDS)