General Pharmacology-the Vascular System最新文献

The aim of the study was to determine the in vitro rate-dependent cellular electrophysiological effects of ambasilide (10 and 20 μM/l), a new investigational antiarrhythmic agent, in canine isolated ventricular muscle and Purkinje fibers by applying the standard microelectrode technique. At the cycle length (CL) of 1000 ms, ambasilide significantly prolonged the action potential duration measured at 90% repolarization (APD₉₀) in both ventricular muscle and Purkinje fibers. Ambasilide (10 μM/l) produced a more marked prolongation of APD₉₀ at lower stimulation frequencies in Purkinje fibers (at CL of 2000 ms = 56.0 ± 16.1%, n = 6, versus CL of 400 ms = 15.1 ± 3.7%, n = 6; p < 0.05), but, in 20 μM/l, this effect was considerably diminished (15.2 ± 3.6%, n = 6, versus 7.3 ± 5.1%, n = 6, p < 0.05). In ventricular muscle, however, both concentrations of the drug induced an almost frequency-independent lengthening of APD₉₀ in response to a slowing of the stimulation rate (in 20 μM/l at CL of 5000 ms = 19.0 ± 1.5%, n = 9, versus CL of 400 ms = 16.9 ± 1.4%, n = 9). Ambasilide induced a marked rate-dependent depression of the maximal rate of rise of the action potential upstroke (V_max) (in 20 μM/l at CL of 300 ms = −45.1 ± 3.9%, n = 6, versus CL of 5000 ms = −8.5 ± 3.9%, n = 6, p < 0.05, in ventricular muscle) and the corresponding recovery of V_max time constant was τ = 1082.5 ± 205.1 ms (n = 6). These data suggest that ambasilide, in addition to its Class III antiarrhythmic action, which is presumably due to its inhibitory effect on the delayed rectifier potassium current, possesses I/B type antiarrhythmic properties as a result of the inhibition of the fast sodium channels at high frequency rate with relatively fast kinetics. This latter effect may play an important role in its known less-pronounced proarrhythmic (“torsadogenic”) potential.

The neuronal isoform of nitric oxide synthase (nNOS) has been localized to specific regions of the kidney, including the thick ascending limb of the loop of Henle and the macula densa. Because of this discrete localization in the renal cortex, nitric oxide (NO) produced by nNOS has been suggested to play an important role in the regulation of macula densa-mediated arteriole tone and therefore could play an important role in the regulation of whole-kidney glomerular filtration rate (GFR). We hypothesized that selective blockade of nNOS would decrease GFR. Renal hemodynamics were measured before and after acute selective blockade of nNOS by 50 mg/kg 7-nitroindazole (7-NI) in anesthetized rats. Administration of 7-NI had no significant effect on basal blood pressure (from 105 ± 3 to 101 ± 2 mm Hg), renal blood flow [from 6.08 ± 0.39 to 6.31 ± 0.33 ml/min/gram of kidney weight (gkw)], or total renal vascular resistance (from 18.1 ± 1.6 to 16.4 ± 1.0 mm Hg/ml/min/gkw) but decreased GFR by 26% (from 1.36 ± 0.15 to 1.00 ± 0.13 ml/min/gkw; p < 0.02), urinary flow rate by 28% (from 24.7 ± 1.8 to 17.8 ± 2.2 μl/min; p < 0.05), and sodium excretion by 22% (from 5.55 ± 0.53 to 4.30 ± 0.52 μEq/min; p < 0.05). However, fractional sodium excretion was not changed by nNOS inhibition. There were no such changes in vehicle-treated time controls. We conclude that, in the renal cortex, NO produced by nNOS plays an important role in the regulation of whole-kidney GFR and excretion in normal, sodium-replete rats.

In the present study, we investigated whether the correction of endothelial dysfunction can be independent of the normalization of high blood pressure levels by enalapril in deoxycorticosterone (DOCA-salt) hypertensive rats. Aorta morphology and the response of aortas with (E+) and without (E−) endothelium to noradrenaline, acetylcholine, and sodium nitroprusside were studied. DOCA-salt hypertensive and normotensive (control) rats were or were not treated with enalapril (5 mg/day/rat in the drinking fluid) for 1, 7, or 15 days. Blood pressure was measured before and after 1, 3, 7, and 15 days of enalapril treatment. Enalapril normalized the high blood pressure levels in 50% (responders) of the hypertensive rats after 3 to as many as 15 days but not after 1 day of treatment. Initial blood pressure levels were not different between responders and nonresponders. Blood pressure levels of normotensive control rats were not altered by enalapril treatment. The tunica media of aortas of DOCA-salt hypertensive rats treated or not treated with enalapril for 15 days was thicker than aortas from normotensive rats. Enalapril corrected the reduced response to acetylcholine observed in aorta from hypertensive rats from the first day of treatment. This treatment rendered aortas from normotensive control rats more sensitive (lower EC₅₀) to acetylcholine without a change in the maximal responses. The responses to sodium nitroprusside, a nitric oxide donor, were unaltered in aorta E+ or E− from control and hypertensive rats before and after enalapril treatment. Enalapril did not correct the increased responses to noradrenaline observed in aorta E+ of hypertensive rats. These results suggest that the high blood pressure in DOCA-salt hypertension is not correlated with the altered response to endothelium-dependent agents (either dilator or constrictors). The endothelium-dependent vasodilation by antihypertensive agents can be corrected independently of normalization of blood pressure levels or the vascular morphology.

Vasoconstrictor responses to exogenous adenine and pyrimidine nucleotides were measured in endothelium-denuded segments of guinea pig mesenteric vein and compared with responses in mesenteric artery. The rank order of potency for nucleotides in veins was: 2-MeSADP = 2-MeSATP > UTP > ATPγS = α,βMeATP > UDP = ATP > ADP >> β,γ-D-MeATP = β,γ-L-MeATP. In contrast 2-MeSADP, UTP, and UDP were inactive in arteries, and the rank order of potency of other nucleotides differed; that is, α,βMeATP > β,γ-D-MeATP > β,γ-L-MeATP = ATPγS = 2-MeSATP > ATP > ADP. In veins, UTP, ATP, and 2-MeSATP were more efficacious contractile agents than α,β MeATP. In addition, the ability to desensitize responses to these nucleotides and inhibit them with various blockers differed. The response to α,βMeATP in veins exhibited rapid desensitization and was inhibited by pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid tetrasodium (PPADS) and suramin. The response to 2-MeSATP in veins did not desensitize; nor was it inhibited by prior α,βMeATP desensitization, but it was inhibited by PPADS, suramin, and the selective P2Y₁ receptor antagonist adenosine 3′,5′-bisphosphate (ABP, 10–100 μM). Responses to ATP and UTP in veins did not desensitize and were not inhibited by PPADS, suramin, ABP, or α,βMeATP desensitization. In conclusion, our results suggest that venous contraction to a variety of nucleotides is mediated in large part by P2Y receptors including P2Y₁ receptors and an UTP-preferring P2Y receptor. A small component of contraction also appears to be mediated by P2X₁ receptors. This receptor profile differs markedly from that of mesenteric arteries in which P2X₁ receptors predominate.

Osmotic cell swelling activates an outwardly rectifying Cl⁻ current in endothelial cells that is mediated by volume-regulated anion channels (VRACs). In the past, we have shown that serum-induced proliferation of endothelial cells is arrested in the presence of compounds that potently block the endothelial VRACs. Here we report on the effects of four chemically distinct VRAC blockers [5-nitro-2-(3-phenylpropylamino)benzoic acid] (NPPB), mibefradil, tamoxifen, and clomiphene—on several models of experimental angiogenesis. Mibefradil (20 μM), NPPB (100 μM), tamoxifen (20 μM), and clomiphene (20 μM) inhibited tube formation by rat microvascular endothelial cells plated on matrigel by 42.9 ± 8.8%, 25.3 ± 10.4%, 32.2 ± 4.5%, and 20 ± 5.8%, respectively (p < 0.05). Additionally, NPPB (50–100 μM) and mibefradil (10–30 μM) significantly inhibited bFGF (10 ng/ml) + TNFα (2.5 ng/ml)-stimulated microvessel formation by human microvascular endothelial cells plated on fibrin by 30–70%. Furthermore, NPPB, mibefradil, and clomiphene concentration dependently inhibited spontaneous microvessel formation in the rat aorta-ring assay and vessel development in the chick chorioallantoic membrane assay. These results suggest that VRAC blockers are potent inhibitors of angiogenesis and thus might serve as therapeutic tools in tumor growth and other angiogenesis-dependent diseases.

Occlusive accelerated atherosclerosis of coronary grafts is the predominant factor that limits longevity of heart transplant recipients. This form of vascular disease affects both the large epicardial and the smaller intramyocardial vessels, leading to characteristic clinical presentation that necessitates the use of sophisticated techniques for their accurate detection. Accelerated atherosclerosis after transplantation is a multifactorial disease with many events contributing to its progression. The initial vascular injury associated with ischemia-reperfusion appears to aggravate preexisting conditions in the donor vasculature in addition to activation of new immunological and nonimmunological mechanisms. Throughout these events, the endothelium remains a primary target of cell- and humoral-mediated injury. Changes in the vascular intima leads to alterations in vascular smooth muscle cell (VSMC) physiology, resulting in VSMC phenotypic modulation with the orchestration of a broad spectrum of growth and inflammatory reactions, which might be a healing response to vascular injury. Endogenous nitric oxide (NO) pathways regulate a multiplicity of cellular mechanisms that play a major role in determining the structure and function of the vessel wall during normal conditions and during remodeling associated with accelerated atherosclerosis. Recently identified signaling pathways, including mitogen-activated protein kinase, cGMP-dependent protein kinase, phosphatidylinositol 3-kinase, and transcriptional events in which nuclear factor kappa B and activator protein 1 take part, can be associated with NO modulation of cell cycle perturbations and phenotypic alteration of VSMC during accelerated atherosclerosis. This article reviews recent progress covering the aforementioned matters. We start by summarizing the clincal aspects and pathogenesis of accelerated atherosclerosis associated with transplantation, including clinical presentation and detection. This summary is followed by a discussion of the multiple factors of the disease process, including immunological and nonimmunolgical contributions. The next section focuses on cellular responses of the VSMCs relevant to lesion formation, with special emphasis on classical and recent paradigms of phenotypic modulation of these cells. To examine the influence of NO on VSMC phenotypic modulation and consequent lesion development, we briefly overview characteristics of NO production in the normal coronary vascular bed and the changes in endogenous NO release and activity during atherosclerosis. This overview is followed by a section covering molecular mechanisms whereby NO regulates a range of signaling pathways, transcriptional events underlying cell cycle perturbation, and phenotypic alteration of VSMC in accelerated atherosclerosis.

Catecholamines induce direct vasoconstriction mediated by postsynaptic α-adrenergic receptors (α-ARs) of both the α₁ and α₂ type. To evaluate the contribution of each α₂-AR subtype (α_2A, α_2B, and α_2C) to this function, we used groups of genetically engineered mice deficient for the gene to each one of these subtypes and compared their blood pressure (BP) responses to their wild-type counterparts. Blood pressure responses to a bolus of norepinephrine (NE) were assessed before and after sequential blockade of α₁-ARs with prazosin and α₂-ARs with yohimbine. The first NE bolus elicited a brief 32 to 44 mm Hg BP rise (p < 0.001 from baseline) in all six groups. Prazosin decreased BP by 23 to 33 mm Hg in all groups, establishing a new lower baseline. Repeat NE at that point elicited lesser but still significant (p < 0.001) brief pressor responses between 32% and 45% of the previous BP rise in five of the six groups. Only the α_2A-AR gene knockouts differed, responding instead with a 20-mm Hg fall in BP, a significant change from baseline (p < 0.001) and different from the pressor response of their wild-type counterparts (p < 0.001). The addition of yohimbine produced no further BP change in the five groups, but it did produce a small 7.5-mm Hg fall (p < 0.05) in the α_2A-AR knockouts. Norepinephrine bolus during concurrent α₁ and α₂-AR blockade produced significant (p < 0.001) hypotensive responses in all subgroups, presumably attributable to unopposed stimulation of β₂-vascular wall ARs. We conclude that the α₂-AR-mediated vasoconstriction induced by catecholamines is attributable to the α_2A-AR subtype because mice deficient in any one of the other subtypes retained the capacity for normal vasoconstrictive responses. However, the α₁-ARs account for the major part (as much as 68%) of catecholamine-induced vasoconstriction.

The effect of citalopram, a selective serotonin reuptake inhibitor (SSRI) antidepressant, was studied on cardiac action potential configuration and compared with that of the tricyclic antidepressant (TCA) clomipramine. Conventional microelectrode techniques were used in right ventricular papillary muscle preparations of the guinea pig. Citalopram caused a concentration-dependent (10–100 μM) shortening of action potential duration (APD), depression of plateau and overshoot potential, and reduction of maximum velocity of depolarization (V_max). No significant changes in resting membrane potential were observed. Similar results were obtained with clomipramine; however, reduction of V_max and overshoot was more pronounced with clomipramine, whereas citalopram caused relatively greater shortening of APD. Effects of both drugs were partly reversible. The results indicate that the SSRI antidepressant citalopram, similarly to TCA compounds, alters cardiac action potential configuration in guinea pig ventricular muscle, probably owing to inhibition of cardiac Na⁺ and Ca²⁺ channels. Differences in cardiac side effects of the two drugs may be related to their different actions on cardiac action potential configuration.

The pharmacological characterization of EK112, a new combined angiotensin II and thromboxane A₂ receptor blocking agent, was examined in this study. EK112 was found to be a angiotensin II receptor antagonist, as revealed by its competitive antagonism of angiotensin II–induced smooth muscle contraction (pA₂ value of 7.63 ± 0.14) in rabbit aorta. It also had an angiotensin II blocking action in guinea pig ileum (pA₂ value of 7.87 ± 0.67). Additionally, EK112 also possessed thromboxane A₂ receptor blocking activity, since it competitively antagonized aortic contractile responses elicited by U46619 and PGF_2α(pK_B values of 6.67 ± 0.09 and 6.24 ± 0.09, respectively) in rat. In contrast, EK112 did not affect the contractile responses to many other receptor agonists. EK112 did not mimic that of the angiotensin-converting enzyme (ACE) inhibitor, captopril, to enhance the muscle contraction elicited by bradykinin in guinea pig ileum, suggesting that EK112 did not inhibit ACE. Neither cyclic AMP nor cyclic GMP content in rat aortic rings was changed by EK112. These data demonstrate that EK112 is a selective antagonist of angiotensin II and thromboxane A₂ receptor. The order of this blocking potency is angiotensin II receptor > thromboxane A₂ receptor.