Intact Aortic Rings Research Articles

Dietary n-3 fatty acids alter angiotensin-induced contraction and 1,2-diacylglycerol fatty acid composition in thoracic aortas from diabetic rats

The effect of diabetes on the incorporation of long-chain n-3 fatty acids into thoracic aorta smooth muscle phospholipids and 1,2-diacylglycerol, and on the contractile response of aortic rings to angiotensin II, was examined in streptozotocin-induced diabetic rats. In diabetic animals fed a diet containing 1% of fatty acids as n-3 fatty acids, smooth muscle membrane levels of 18:2n-6 were elevated in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, whereas 20:4n-6 was depleted. The resultant decreased ratios of 20:3 18:2 and 20:4 20:3 indicate inhibition of Δ 6- and Δ 5-desaturase activity in the diabetic state. A diet containing 5% of fatty acids as n-3 fatty acids increased phospholipid levels of eicospentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) several-fold, but with a further reduction in 20:4n-6. Similarly, 1,2-diacylglycerol from rats fed the high n-3 diet was enriched in EPA, DPA and DHA. When incubated with 10 −8 M angiotensin II, the contractile response of intact aortic rings from diabetic animals fed the high n-3 diet was only 60.8 ± 9.3% that of controls fed the same diet. However, contractile response was not significantly different from control animals fed the low n-3 diet (55.6 ± 7.9%). The results indicate that vascular smooth muscle phospholipid n-6 and n-3 fatty acid metabolism is altered in diabetes, resulting in changes to the fatty acid profile of 1,2-diacylglycerol. Moreover, elevating membrane phospholipid and 1,2-diacylglycerol content of EPA, DPA and DHA partially ameliorates the depressed response to angiotensin II seen in the diabetic state.

A prostaglandin, not NO, mediates endothelium-dependent dilation in ventral aorta of shark (Squalus acanthias).

In mammals, the vascular endothelium releases a variety of paracrine factors, including the vasodilatory prostaglandin (PG)I2 and nitric oxide (NO), which is generally accepted as the major endothelium-derived relaxing factor (EDRF) in mammals. Current evidence for the vascular NO-EDRF system in fishes is contradictory. In addition, the role of PGs in the control of fish vascular tension is also unclear. We have utilized isolated rings of the ventral aorta of the spiny dogfish shark to examine the ability of various components of the NO system to dilate this vessel. Neither the NO precursor L-arginine, the NO donor sodium nitroprusside, nor NO itself dilated the rings. The Ca2+ ionophore A-23187 did produce an endothelium-dependent dilation that was not inhibited by the NO synthase inhibitor NG-nitro-L-arginine methyl ester but was inhibited by the cyclooxygenase inhibitor indomethacin, suggesting that PGs are involved. PGE1 and carbaprostacyclin, but not PGI2, produced concentration-dependent dilation, and intact aortic rings secreted five times as much PGI2 as PGE in both the unstimulated state and after stimulation with A-23187. Our data suggest strongly that a PG, most probably PGI2, is the EDRF in the ventral aorta of this shark species.

Role of insulin preincubation in the contractile reactivity of rat aortic rings.

Preincubation with physiological concentrations of insulin affects contractile reactivity of isolated smooth muscle cells. We studied the effects of insulin on intact aortic rings of Wistar rats preincubated 1-2 h with 240 pM (I1) and 960 pM (I2) insulin with and without NO synthesis inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME). Resting force was tripled by 0.1 mM L-NAME in control (C) and I1 groups, but not in I2 groups. I1 treatment decreased the tachyphylaxis to two successive 1 microM arginine vasopressin (AVP) stimulations. Single contractions elicited by 1 microM AVP, 1 microM angiotensin II (AngII), or 0.01 microM endothelin (ET1) were not affected by insulin preincubation in either maximal force (Fmax) or relaxation times. L-NAME enhanced Fmax of AngII contractions by about 75% in C, 120% in I1, and 74% in I2 groups; accordingly, it augmented the final steady-state force in C and I1 but not in I2. Similarly, L-NAME increased Fmax (30-40%) of AVP and ET1 contractions in C and I1 groups but failed to do so in contractions of I2 group. Results obtained with 10 microM indomethacin suggest that this is due to insulin stimulation of prostacyclin effects.

Vasorelaxant effects induced by the antiangiogenic drug linomide in aortic and saphenous vein preparations of the rabbit

1. Linomide (N-phenylmethyl-1,2-dihydro-4-hydroxyl-1-methyl-2-oxoquinoline-3-carb oxa mide) inhibits vascular proliferation and has been proposed as an antiangiogenic drug. We have investigated the vascular effect of linomide in rabbit aortic and saphenous vein ring preparations and in rat cultured vascular smooth muscle cells (VSMCs). 2. Linomide (25-300 micrograms ml-1) did not alter the basal tone of the preparations. The drug induced a concentration-dependent relaxant effect in aortic rings with endothelium, preconstricted by noradrenaline (NA), 5-hydroxytryptamine (5-HT) and by the thromboxane mimetic U46619. 3. The degree of relaxation induced by linomide was significantly reduced by exposure to the cyclooxygenase inhibitors indomethacin (3 microM) and acetylsalicylic acid (500 microM), and was not influenced by pretreatment with the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (100 microM) in aortic rings with endothelium, preconstricted with NA. 4. Endothelium removal significantly reduced the relaxant response to linomide in aortic ring preparations. 5. A concentration-dependent relaxant response was observed also in rabbit saphenous vein preparations deprived of endothelium and preconstricted either by NA or U46619. The degree of relaxation obtained in a high potassium solution was consistently smaller than that observed in NA-pretreated venous preparations. 6. The vasorelaxant effect of linomide was consistently blunted by the adenylate cyclase inhibitor SQ 22536 (50 microM), both in intact aortic rings and in those deprived of endothelium. 7. In rat cultured vascular smooth muscle cells, linomide (100-200 micrograms ml-1) induced a significant increase in cyclic AMP levels, which was blocked by exposure to 50 microM SQ 22536. 8. In endothelium-deprived aortic ring preparations, the linomide-induced relaxant effect was greatly reduced in high potassium medium (KCl = 25 mM). Pretreatment with the ATP potassium channel inhibitor glibenclamide (3 microM) significantly reduced the linomide-induced relaxation. 9. The results show that linomide possesses a vasorelaxant effect which is attributable to both endothelium-dependent and -independent properties. While the former component of the drug's activity is apparently due to the release of a prostanoid from endothelial cells, the endothelium-independent mechanism involved in linomide relaxation is linked to cyclic AMP accumulation and to ATP-sensitive potassium channel activation in VSMCs.

Loss of nitric oxide release in passively sensitized guinea-pig aorta with purified immunoglobulin Gl

Vascular hyperresponsiveness can be reproduced by in vitro passive sensitization of isolated aorta with immunoglobulin G1 (IgG1) taken from ovalbumen-sensitized BFA guinea-pig. The aim of the present work was to investigate the role of nitric oxide in the sensitization-induced alteration of the contractile and relaxant responses of guinea-pig aorta to noradrenaline (NA) and acetylcholine (ACh), respectively. Cumulative concentration-response curves to NA or ACh were established before and after IgG1 sensitization and then after successive treatments. IgG1 in vitro passive sensitization of aorta caused a significant hyperreactivity to NA and completely inhibited the relaxation to ACh. After sensitization, the addition of an intact aortic ring (with endothelium) in the organ chamber restored the maximal response to NA and ACh close to control but was ineffective in the presence of hemoglobin. The restoration of the control reactivity to NA was also inhibited in the presence of L-NAME or when the added aortic ring was endothelium-denuded. Moreover, L-arginine, a nitric oxide (NO) precursor, was able to restore the control reactivity to NA. The present results show that IgG1 in vitro sensitization induced a loss of NO release from the vascular endothelium. This loss of NO probably plays a great role in vascular hyperreactivity by increasing the contractile response and decreasing the relaxant response to mediators and would be a component of allergic diseases pathogenesis.

Aminoguanidine reverses aortic hyporeactivity to noradrenaline in portal vein-ligated rats

To evaluate the role of the inducible and endothelial constitutive nitric oxide synthase in vascular hyporeactivity to vasopressors in portal hypertension, in vitro experiments were performed on intact and endothelium-denuded isolated thoracic aortic rings from portal vein-ligated and sham-operated rats in control conditions, in the presence of aminoguanidine alone, considered to be a selective inhibitor of the inducible nitric oxide synthase, and of aminoguanidine and the nonselective nitric oxide synthase inhibitor N G-nitro- l-arginine. In control conditions, hyporeactivity to noradrenaline was observed in both rings with and without endothelium from portal hypertensive versus sham-operated rats. In the rings with endothelium, aminoguanidine reverted this hyporeactivity in portal hypertensive rats. N G-Nitro- l-arginine caused an additional shift to the left of the concentration-response curves to noradrenaline in portal hypertensive and a similar shift in sham-operated rats. In the endothelium-denuded rings, aminoguanidine caused no significant changes in portal hypertensive rats, whereas a significant shift to the right in the sham-operated rats was noted, however similar as the shift in the time controls not preincubated with aminoguanidine. No significant further changes were observed after preincubation with the two inhibitors. The endothelium-dependent relaxations to acetylcholine were attenuated in portal hypertensive versus sham-operated rats; addition of aminoguanidine shifted the relaxation curves to the left in portal hypertensive but not in sham-operated rats. These results provide indirect evidence for an increased activity of the inducible nitric oxide synthase in the intact aortic rings but not in the endothelium-denuded rings from portal vein-ligated rats, where other factors seem to be responsible for the observed hyporeactivity to noradrenaline. The endothelial constitutive nitric oxide synthase in rings from portal vein-ligated rats shows a reduced activity which is alleviated after inhibition of the inducible enzyme by aminoguanidine.

Endothelium-dependent and NO-mediated desensitization to vasopressin in rat aorta.

1. The present study was performed to characterize the tachyphylaxis of rat aortae to vasopressin. Isometric tension generated by rat thoracic aorta sliced in 4 mm rings, was recorded. 2. Tension generated by intact rings increased with cumulative additions of vasopressin up to 10 nM (1.51 +/- 0.15 g). After this concentration, most rings lost their tension and relaxed to 1.09 +/- 0.17 g (P < 0.001) despite further addition of vasopressin. This tachyphylaxis was not observed in endothelium-denuded rings (from 2.87 +/- 0.12 g to 2.68 +/- 0.17 g). 3. Repeated administrations of supramaximal concentration (100 nM) of vasopressin confirmed an enhanced desensitization in intact rings, compared to endothelium-denuded rings. No desensitization to phenylephrine was observed in intact or in endothelium-denuded rings. 4. Dose-response curves to a V1 receptor agonist, [Phe2, Ile3, Orn8]-vasopressin, and to a V2 receptor agonist, [deamino-Cys1,D-Arg8]-vasopressin, were performed in intact preparations. An increase in tension, followed by a desensitization was observed with the V1 receptor agonist. In contrast, the V2 receptor agonist did not induce any response. 5. Pretreatment of intact aortic rings with the cyclo-oxygenase inhibitor, diclofenac (1 microM), did not prevent the desensitization to vasopressin. In contrast, NO synthase inhibition with NG-nitro-L-arginine (30 microM) resulted in an attenuated desensitization to vasopressin in intact rings (from 2.46 +/- 0.17 to 2.25 +/- 0.22 g, NS). 6. To confirm the involvement of NO, endothelium-denuded rings were pretreated with sodium nitroprusside (SNP). At a concentration of 10 nM, SNP induced a desensitization to vasopressin comparable with that observed in intact rings. 7. Pretreatment of endothelium-denuded rings with 8-bromo-cyclic GMP (100 microM) reduced maximum contraction to vasopressin without producing any desensitization. In contrast, guanylate cyclase inhibition with either LY 83,583 (10 microM) or methylene blue (10 microM) blocked completely the desensitization of intact rings to vasopressin. 8. The results suggest that the endothelium-dependent tachyphylaxis to vasopressin is due to rapid desensitization and is mediated by NO. However, it is unclear whether this effect of NO involves cyclic GMP.

Chronic exercise enhances endothelium-mediated dilation in spontaneously hypertensive rats

This study investigated the effect of physical training on endothelial function in spontaneously hypertensive rats (SHR). After 3 months, in conscious trained- and untrained-SHR body weight, systolic blood pressure and heart rate were 220 ± 6 g vs. 271 ± 9 g, 172 ± 7 mmHg vs. 210 ± 8 mmHg and 314 ± 10 vs. 348 ± 12 beats/min, respectively. In vitro, the dose-response curves of norepinephrine in isolated intact aortic and mesenteric rings from the exercise trained-SHR were significantly lower than those from the untrained-SHR. With denuded preparations, norepinephrine concentration-response curves were shifted to the left both in the trained- and untrained-SHR. This shift in the trained-SHR exceeded that in the untrained-SHR. The vasodilator response to acetylcholine in the trained-SHR was significantly greater than that in the untrained-SHR. Either N ω-nitro-L-arginine (100 μmol/l) or methylene blue (10 μmol/l) inhibited acetylcholine-induced vasodilator effect in aorta of trained- and untrained-SHR, but not in mesenteric artery of trained-SHR. Tetraethylammonium (10 mmol/l) inhibited significantly the N ω-nitro-L-arginine and methylene blue-resistant relaxation in mesenteric artery of trained-SHR,but not by indomethacin (10 μmol/l). Collectively, these data demonstrate that chronic exercise increases EDRF/EDHF production (presumably by increasing endothelial shear stress), and may contribute to the enhanced effects of post-exercise hypotension.1

Vascular actions of thrombin receptor-derived polypeptides: structure-activity profiles for contractile and relaxant effects in rat aorta.

1. Using endothelium-denuded and intact rat aortic rings, we have determined the contractile and relaxant structure-activity profile for a series of thrombin receptor-derived polypeptides (TRPs) based on the human and rat receptor sequences: SFLLR (P5), SFLLR-NH2 (P5-NH2) SFFLR (Rat P5), SFFLR-NH2 (Rat P5-NH2), SFLLRNP (P7), SFLLRNP-NH2 (P7-NH2), SFFLRNP (Rat P7), SFFLRNP-NH2 (Rat P7-NH2), and SFLLRNPNDKYEPF (P14). 2. A contractile response to thrombin and the TRPs in the endothelium-denuded aortic tissue was minimal or absent in preparations obtained from animal weighing less than 180 g (< 6 weeks of age), but increased with animal size, plateauing in tissues derived from animals weighing between 320 and 420 g (about 9 to 14 weeks of age). In contrast, the contractile responses to KCl and noradrenaline did not differ in the tissues and relaxant responses to the TRPs in endothelium-intact aortic preparations were comparable for tissues obtained from either young (< or = 180 g) or older (> or = 320 g) animals. 3. The contractile response of the endothelium-denuded preparation to thrombin and the TRPs showed marked cross-desensitization: the relaxation response of the intact rings did not desensitize to the TRPs. 4. The relative potencies for the TRPs in the aortic contraction assay were comparable to those for the relaxation assay, but were distinct from the relative potencies we measured previously in a rat gastric longitudinal muscle contraction assay. Further, P5 behaved as a partial agonist in the aortic contraction assay, whereas it had been observed to be a full agonist in the gastric contraction assay. 5. The contractile activity of P5-NH2 in endothelium intact aortic rings was low or absent, but in the presence of the nitric oxide synthase inhibitor, N omega-nitro-L-arginine-methyl ester (L-NAME), the contractions in the intact preparation were equivalent to the response of the endothelium-denuded preparation in the absence of L-NAME.6. The contractile response of the endothelium-denuded aortic preparation to P5-NH2 was inhibited by nifedipine and the kinase C antagonist, chelerythrine, but was resistant to the action of indomethacin,tetrodotoxin and the tyrosine kinase inhibitor, genistein.7 We conclude that the receptor system for the TRPs in the aortic smooth muscle elements, responsible for the contractile response, is similar to the aortic endothelial cell receptor responsible for the relaxation response, but is distinct from the receptor that we have previously characterized in gastric longitudinal smooth muscle, results pointing to the presence of receptor subtypes in the vascular and gastric smooth muscle elements.

Impairment of Endothelium-Dependent Relaxation by Diesel Exhaust Particles in Rat Thoracic Aorta

Nitric oxide released from vascular endothelium plays important regulatory roles in cardiovascular and pulmonary systems. Epidemiological studies suggest that diesel exhaust particles (DEP) seem to be one of the causative factors responsible for the recent increase in pulmonary diseases. To clarify the pathogenic mechanism, the effects of DEP on vascular endothelial functions were investigated in terms of endothelium-dependent relaxation. Ring preparations of rat thoracic aorta were preincubated for 10 min with a DEP suspension (1, 10, 100 μg/ml) at 37 °C in organ baths and relaxed with cumulative additions of acetylcholine following precontraction with phenylephrine (10−6 M). The relaxation was attenuated by DEP-exposure in a concentration-dependent manner. An addition of super oxide dismutase (SOD) completely abolished the inhibitory effect of DEP at lower concentrations, but only partially at the higher concentration. DEP (10 μg/ml) neither affected the contractile response to phenylephrine in intact aortic rings nor the endothelium-independent relaxation by sodium nitroprusside in denuded rings, while DEP (100 μg/ml) significantly attenuated both responses. These results suggest that 1) inhaled DEP causes pulmonary inflammation by inhibiting the endothelial formation and/or the effect of nitric oxide and 2) SOD reduces the adverse effects.

Impairment of endothelium-dependent relaxation by diesel exhaust particles in rat thoracic aorta.

Nitric oxide released from vascular endothelium plays important regulatory roles in cardiovascular and pulmonary systems. Epidemiological studies suggest that diesel exhaust particles (DEP) seem to be one of the causative factors responsible for the recent increase in pulmonary diseases. To clarify the pathogenic mechanism, the effects of DEP on vascular endothelial functions were investigated in terms of endothelium-dependent relaxation. Ring preparations of rat thoracic aorta were preincubated for 10 min with a DEP suspension (1, 10, 100 micrograms/ml) at 37 degrees C in organ baths and relaxed with cumulative additions of acetylcholine following precontraction with phenylephrine (10(-6) M). The relaxation was attenuated by DEP-exposure in a concentration-dependent manner. An addition of superoxide dismutase (SOD) completely abolished the inhibitory effect of DEP at lower concentrations, but only partially at the higher concentration. DEP (10 micrograms/ml) neither affected the contractile response to phenylephrine in intact aortic rings nor the endothelium-independent relaxation by sodium nitroprusside in denuded rings, while DEP (100 micrograms/ml) significantly attenuated both responses. These results suggest that 1) inhaled DEP causes pulmonary inflammation by inhibiting the endothelial formation and/or the effect of nitric oxide and 2) SOD reduces the adverse effects.

Angiotensin (1???7) is an antagonist at the type 1 angiotensin II receptor

The present study investigated the antagonism of the amino-terminal heptapeptide fragment of angiotensin II ([des-Phe8]-angiotensin II; Ang(1-7)) to angiotensin II (Ang II) both in vitro in rabbit aortae and in vivo in rats. In rabbit isolated endothelium intact aortic rings Ang(1-7) caused a concentration-related rightward displacement of the Ang II curve and depressed the maximum response to Ang II. By applying the data to a Schild plot an apparent pA2 of 5.5 was calculated. This depression of maximum response could be reversed by co-incubation of Ang(1-7) with the competitive angiotensin antagonist losartan. Ang(1-7) had no effect on the contractile responses of several other agonists. Intravenous infusion of 10 or 100 micrograms/kg per min Ang(1-7) had no effect on the resting blood pressure in the anaesthetized rat but inhibited Ang II-induced pressor responses. The present results show that Ang(1-7) is a specific non-competitive antagonist of Ang II at type 1 angiotensin II receptors.

36 Role of constitutive and inducible endothelial nitric oxide synthases in the angiotensin II-induced contractile response in Wistar-Kyoto rat and spontaneously hypertensive rat isolated aortae

Background and objective: Dysfunctions of the endothelium-derived relaxing factor L-arginine-nitric oxide (NO) pathway have been demonstrated in genetic and experimental hypertension. NO is produced through the conversion of L-arginine to L-citruline by NO synthases (NOS), which exist in at least two isoforms. Constitutive NOS (NOSc) is located in the endothelium of the vascular wall, and results in basal and stimulated NO production. Inducible NOS (NOSi) produces large amounts of NO, and can be expressed in both smooth muscle and endothelial cells. The aim of the study was to examine and compare the activity of the two isoforms of endothelial NO synthases and their influence on the constrictor response induced by angiotensin II (Ang II) in isolated aortic rings of Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Methods and results: On phenylephrine-preconstricted endothelium intact aortic rings (10-6 mol/1; WKY rats, 1.2±0.04g; SHR. 1.2±0.07g; n=7), carbachol (10-5 mol/1) induced a greater relaxation in WKY rats (84 ±2.5%) than in SHR (63 ±8.5%). This suggests the presence of a low NOSc-stimulated activity in the hypertensive strain. When the incubation period was limited to 30min after equilibration period, L-arginine (3.10-4 mol/1) did not induce relaxation. When the incubation period was prolonged (180 min), L-arginine induced relaxation (WKY rats, 75±8%; SHR, 58±10%; n=7). This relaxation was not observed in a medium containing actinomycin D (10-6 mol/1) or after endothelium removal, indicating the induction of an endothelial NOSi in the two strains. The contractile responses to Ang II (10-7 mol/1; WKY rats, 0.49±0.04 g; SHR, 0.59±0.08 g), after a 30-min incubation period, were similarly enhanced in the presence of nitro-L-arginine (10-4 mol/l) or in denuded rings (WKY rats, +119 and +63%; SHR, +130 and +42%). These results provide evidence that basal NOSc modulation was similar in WKY rats and SHR. After a 180-min incubation period, the Ang II-in-duced constrictor response was significantly reduced (WKY rats, 0.27±0.07g; SHR, 0.37±0.11g). Addition of cycloheximide (7.1 per 10-5 mol/l) to the medium or endothelium removal prevented the desensitization phenomenon. This assessed the participation of the endothelial NOSi in the time-dependent reduced contraction of Ang 11 in rat aorta. Moreover, the prolonged inhibition (180 min) of NO synthesis by nitro-L-arginine potentiated the contractile response to Ang II in SHR, but not in WKY rat, rings compared with the 30-min incubation period. This result is consistent with a specific liberation of vasoconstrictor factors by SHR. Conclusions: These results indicate that SHR aortae have a lower stimulated NOSc but a similar basal NOSc to WKY rat aortae. Prolonged incubation of rings allowed the expression of endothelial NOSi in the two strains, but resulted in the release of vasoconstrictor factors in only SHR when the NO synthesis was inhibited.

Vascular Effects of Commercially Available Preparations of Xanthine Oxidase

Xanthine oxidase (XO) has been generally used with xanthine or hypoxanthine as a pharmacological probe to generate oxygen free radicals, which are known to affect the tension of the isolated vessels in vitro. However, it was reported that commercially available XO itself caused vasorelaxation. This study was undertaken to evaluate the vascular effects of four commercially available XO from Sigma [grade 1 (XO1) and 4 (XO2)], Biozyme Laboratories (XO3) and Boehringer Manheim (XO4). All XO preparations (0.01 U/ml) produced rapid and transient relaxation of endothelium intact rat aortic rings precontracted with phenylephrine in the presence of indomethacin (10 −5M). This relaxation was accompanied by an increase in tissue cyclic GMP level. Removal of the endothelium abolished the relaxation. XO-induced relaxation was inhibited markedly b pretreatment with NG-monomethyl-L-arginine (3 × 10 −4M), oxyhemoglobin (10−5M) and methylene blue (10−5M). Trypsin inhibitor (5 μg/ml) also abolished the relaxation induced b...

The role of extracellular calcium in pregnancy-induced attenuation of phenylephrine contraction in rat aorta with functional endothelium.

The effect of pregnancy on the supply of calcium ions for the contractile responses of rat aortic rings to phenylephrine was investigated. The contractility of intact aortic rings from pregnant rats, compared with that of similar rings from non-pregnant rats, to phenylephrine and potassium chloride was significantly decreased. Contractions of rings from non-pregnant rats, pretreated with phenylephrine or potassium chloride, in response to calcium chloride were greater than those of similarly treated rings from pregnant rats. When the concentration of calcium chloride in the medium bathing the rings was reduced to 0.8 mmol.l-1, the contractile response to phenylephrine was significantly (P < 0.005) inhibited in rings from both pregnant and non-pregnant rats but to a greater extent in rings from non-pregnant rats. Contractions of aortic rings from pregnant rats in response to phenylephrine in calcium-free medium were similar to those of rings from non-pregnant rats, suggesting equal dependence on calcium from intracellular stores. The results suggest that pregnancy decreased the response to calcium influx into the aortic smooth muscle cells through both receptor- and voltage-operated calcium entry pathways. Since de-endothelialization reversed the pregnancy-induced diminished contraction to phenylephrine, it is likely that pregnancy interfered with contractions induced by activation of receptors with phenylephrine through enhanced production of endothelium-derived relaxing factor(s).

ENDOTHELIUM‐DERIVED RELAXING FACTOR, HYPERTENSION AND CHRONIC PARATHYROIDECTOMY IN SPONTANEOUSLY HYPERTENSIVE AND WISTAR‐KYOTO RATS

1. Parathyroidectomy (PTX) lessens the development of hypertension in young spontaneously hypertensive rats (SHR) and the involved mechanisms remain to be elucidated. We have studied here the aortic vascular reactivity to both norepinephrine (NE) and acetylcholine in 10 week old male PTX SHR and Wistar-Kyoto (WKY) rats. 2. Depolarized (KCl 100 mmol/L) and NE (1 mumol/L or cumulative 10(-9)-10(-5) mol/L) precontracted intact aortic rings from PTX rats show a significant and unexpected increase of maximal contractile responses in normotensive and hypertensive animals. These results are also obtained with low extracellular ionized calcium levels (0.625 and 0.9 mmol/L) similar to PTX ionized plasma calcium. N omega-Nitro-L-arginine methyl ester (L-NAME, 20 mumol/L) potentiates the NE response in SHR and WKY rats, more significantly in control than in PTX animals. 3. In the presence of indomethacin (10 mumol/L) in SHR the potentiating effect of PTX on NE contraction is still observed, ruling out a specific production of vasoconstrictors from the arachidonic cascade by the PTX rat aortic endothelium. 4. After PTX a moderate impairment of acetylcholine relaxant responses is observed in SHR and WKY rat aortas and basal aortic cyclic guanosine 3'-5' monophosphate (cGMP) content is also decreased; nevertheless sodium nitroprusside causes a similar relaxation. Furthermore in L-NAME-treated aortas and in the presence of L-arginine (100 mumol/L), acetylcholine (1 mumol/L) produces a significantly less pronounced relaxation in PTX rats. 5. In conclusion, the enhancement of NE contractile response in PTX rat aortas is not linked to the strain but probably related to a decrease in endothelial nitric oxide (NO) release or activity. Enhancement of force generation that we describe does not directly participate in the attenuated hypertension observed in SHR after parathyroidectomy.

The role of endothelium in phenylephrine- and potassium-induced contractions of the rat aorta during pregnancy.

The involvement of endothelium in the contractile responses of rat aortic rings to phenylephrine and potassium chloride in pregnancy was examined. Contractions in response to both agents were significantly greater in rings from non-pregnant rats than in rings from pregnant rats, and they were unaltered by treatment of the rings with indomethacin. De-endothelialization potentiated the contractions of rings from pregnant rats in response to phenylephrine, but had no significant effect on similar rings contracted with potassium chloride. Whereas de-endothelialization had no significant effect on the contractions to phenylephrine in rings from non-pregnant rats, it decreased those of rings from the same type of rats, contracted with potassium chloride. Pregnancy significantly inhibited contractions in response to calcium chloride of rings treated with phenylephrine or potassium chloride. The effect of endothelium removal on contractions to calcium chloride in rings from pregnant and non-pregnant rats treated with phenylephrine or potassium chloride was similar to that observed for phenylephrine-induced and potassium chloride-induced contractions, respectively. Contractions of intact aortic rings from pregnant and non-pregnant rats to phenylephrine in calcium-free medium were similar. Results of the study suggest that the effect of pregnancy on the contractions of the rat aorta in response to phenylephrine and potassium chloride is at least partly mediated by the endothelium and is independent of prostaglandin synthesis. The endothelial factor involved in this effect appears to modulate contractions by interfering with calcium influx through the receptor-operated calcium channels and the voltage-operated calcium channels.

Angiotensin II stimulates increased protein synthesis, not increased DNA synthesis, in intact rat aortic segments, in vitro.

There is considerable controversy regarding whether angiotensin II (AngII) stimulates hypertrophy or hyperplasia of vascular smooth muscle cells (SMC). The purpose of the present study was to determine whether stretch of the vessel wall or AngII treatment increased protein or DNA synthesis in intact aortic rings in vitro and whether stretch of the vessel wall altered the growth responses to AngII. Rat aortic rings were mounted on steel supports in serum-free medium for 16 h and subjected to 0 or 1.5 g of preload (i.e. passive stretch). Fetal bovine serum (13%, FBS) or AngII [1 microM, in the presence or absence of angiotensin receptor antagonist, losartan (DuP753) 10 microM] was administered and isometric tension development was measured. 35S-methionine (3 microCi/ml) was added to the baths at 14-16 h for measurement of protein synthesis. Passive stretch did not increase protein synthesis as compared to vessels mounted under no-preload conditions. AngII and FBS elicited similar increases in isometric tension development, but tension development in FBS-treated rings was sustained 4 times longer than in rings treated with AngII. AngII and FBS increased protein synthesis by 35 and 121%, respectively, but there was no difference in the extent of contractile agonist-induced protein synthesis between rings subjected to 0 or 1.5 g of passive stretch. Losartan totally abolished AngII-induced tension development and protein synthesis. AngII and FBS did not stimulate increased DNA synthesis in aortic rings, as measured by 3H-thymidine incorporation. These results suggest that AngII stimulates hypertrophy rather than hyperplasia of fully contractile SMC in an intact vessel.

Presence of an Endothelial Esterase in the Rat Aorta: Effects on the actions of Ester and Non-Ester Muscarinic Antagonists

The actions of ester and non-ester muscarinic antagonists on the acetylcholine-induced relaxation of phenylephrine-contracted endothelium intact rat aortic rings were investigated. Atropine, scopolamine and 4-diphenyI-acetoxy-N-methylpiperidine (4-DAMP) inhibited the relaxation in the nanomolar range, homatropine at 10−6M, pirenzepine at 10−6M, AFDX 116 at 10−5M while gallamine at 10 −5M was without effect. Methyl-butyrate (10 −4 M) potentiated the inhibition by atropine and homatropine by one order of concentration and normalized the gradient to within 0.9–1.1 of the Schild regression for the two compounds. This was not observed with scopolamine. Our findings indicate that the endothelium of the rat aortic ring may contain an esterase that hydrolyses the tropine but not the scopine esters of the belladonna alkaloids. In addition, our data also show that the endothelial muscarinic receptor of the rat aorta is of the M3 subtype. These findings may provide an explanation for our earlier binding study showin...

Effects of chronic ethanol consumption on α-adrenergic-induced contractions in rat thoracic aorta

1. 1. The effects of chronic oral administration of ethanol (EtOH, 80 mM daily during 15–18 days) on the modulation exerted by the endothelium on the contractions induced by phenylephrine (Ph) and clonidine (C) were studied in rat aortic rings with and without endothelium. 2. 2. The maximal contraction induced by a 70 mM KCl depolarizing solution was similar in control and EtOH treated-rings. 3. 3. EtOH pretreatment significantly enhanced the contractile response to Ph in vessels with intact endothelium, but did not significantly affect the response of endothelium-denuded rings. 4. 4. This effect reflects a reduction of the modulation exerted by the endothelial cells on α 1-adrenergic vasoconstriction. 5. 5. C did not contract control aortic rings with endothelium, but after EtOH treatment, the response reached about 20% of the maximal KCl-induced contraction. 6. 6. EtOH pretreatment significantly enhanced the contractile response to C both in endothelium-denuded and intact aortic rings. 7. 7. The results indicate that chronic EtOH consumption significantly potentiates α-andrenergic-induced contractions in rat aortic rings, probably through interference with the production and/or the release of EDRF.