Femoral Artery Rings Research Articles

Effects of the Ca2+ antagonist RO 40-5967 on endothelium-dependent responses of isolated arteries.

Experiments were designed to determine whether the Ca2+ channel inhibitor RO 40-5967 [(1S,2S)-2-[2-[[3-(2-benzimidazolyl)propyl]methylamine]ethyl]-6- fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphthyl methoxyacetate dihydrochloride] causes endothelium-dependent relaxations or inhibits endothelium-dependent contractions of isolated blood vessels. Rings of dog femoral, carotid, and basilar arteries and of rat aorta, with and without endothelium, were suspended in conventional organ chambers for measurement of isometric force. During contractions evoked by phenylephrine (full alpha 1-adrenergic agonist), St 587 (partial alpha 1-adrenergic agonist) and endothelin-1 (ET), RO 40-5967 caused concentration-dependent relaxations of rings of dog femoral arteries; the relaxations to RO 40-5967 were greater in rings with endothelium than in those without endothelium. Nitro-L-arginine (NLA) and methylene blue (MB) inhibited the endothelium-dependent component of the response to RO 40-5967 during contractions to phenylephrine (PE) St 587 and ET. The endothelium-dependent relaxations evoked by RO 40-5967 during contractions to PE were not affected by diltiazem in the femoral artery, suggesting that this effect of the compound may not be related to its calcium channel inhibitor properties. Under bioassay conditions, RO 40-5967 stimulated release of relaxing factors from the endothelium of canine carotid arteries; the response of the detector tissues was inhibited by MB. In strips of canine femoral artery with endothelium, in which membrane potential of vascular smooth muscle cells (VSMC) was recorded with glass microelectrodes, RQ 40-5967 did not cause endothelium-dependent hyperpolarizations.(ABSTRACT TRUNCATED AT 250 WORDS)

The Endothelium and Vascular Effects of the ACE Inhibitor Trandolaprilat

Experiments were designed to study the effects of trandolaprilat on endothelium-dependent responses in isolated blood vessels. Rings of either femoral or left circumflex coronary arteries of the dog or thoracic aortas of normotensive rats were suspended in organ chambers for isometric tension recording. During contractions induced by prostaglandin F2 alpha, trandolaprilat did not cause direct endothelium-dependent or -independent relaxation. However, when given to preparations incubated with angiotensin I or bradykinin, the compound evoked significant endothelium-dependent relaxation. By contrast, trandolaprilat failed to cause any change in tension when given in the presence of acetylcholine (ACh). In rings of femoral arteries, trandolaprilat potentiated the endothelium-dependent relaxation evoked by bradykinin and adenosine diphosphate; it did not modify the endothelium-dependent relaxations induced by ACh, substance P, or thrombin. In rings of femoral arteries without endothelium, trandolaprilat augmented relaxation induced by adenosine diphosphate (ADP) but not by adenosine. In perfused coronary arteries with but not those without endothelium, trandolaprilat caused relaxation in the absence of exogenous bradykinin (or ADP). These experiments suggest that trandolaprilat does not directly release endothelium-derived relaxing factor from the endothelial cells, does not interfere with the ability of the endothelium to release endothelium-derived relaxing factor, augments the endothelium-dependent responses to bradykinin (given exogenously or produced locally) and angiotensin I by direct interaction with converting enzyme, and potentiates the relaxation induced by ADP by augmenting its direct effect on vascular smooth muscle.

Increased production of nitric oxide in coronary arteries during congestive heart failure.

Experiments were designed to determine whether a heterogeneity of endothelium-dependent relaxations in arteries from different vascular beds exists in experimental congestive heart failure (CHF) and to determine the mediators of those responses. CHF was produced in dogs by rapid ventricular pacing for 15 d. Rings of coronary, femoral, and renal arteries with and without endothelium from control and CHF dogs were suspended in organ chambers for measurement of isometric force. In arteries contracted with prostaglandin F2 alpha, endothelium-dependent relaxations to BHT 920 (an alpha 2-adrenergic agonist) were increased in coronary arteries from dogs with CHF (maximal relaxation: control -15 +/- 9% vs CHF -92 +/- 5%; n = 5-6; P < 0.05), with a modest enhancement in renal arteries. Relaxations to adenosine diphosphate and the calcium ionophore were unchanged. Relaxations to BHT 920 in CHF were reduced by NG monomethyl-L-arginine (L-NMMA) and pertussis toxin but not by indomethacin. These data suggest that endothelium-dependent relaxations are affected heterogeneously in CHF. The enhanced response to alpha 2-adrenergic agonists in the coronary artery is mediated by nitric oxide through a mechanism sensitive to inhibition by pertussis toxin. This selective increase in endothelium-dependent relaxations in the coronary artery may contribute to preserving coronary blood flow during CHF.

Characterization of vascular postsynaptic NPY receptor function and regulation and differential sensitivity of Y 1 and Y 2 receptor function to changes in extracellular calcium availability and prior in vitro peptide exposure

Effects of calcium-free buffer, nifedipine, or prior cumulative neuropeptide Y (NPY) receptor agonist concentration exposure on vasoconstrictive responsiveness to the agonists were assessed in norepinephrine (NE)-conditioned isolated rat femoral artery rings. Calcium-free buffer and nifedipine partially inhibited responsiveness to initial NPY exposure; residual responsiveness to NPY re-exposure was unaffected. In contrast, these treatments markedly inhibited responsiveness to the Y 2 agonist NPY 13–36, the calcium channel agonist BAY K 8644 (BAY) and the partial alpha 1 adrenoceptor agonist indanidine but did not alter that to the Y 1 agonist [Leu 31, Pro 34]NPY. Responsiveness to NPY and NPY 13–36 but not to BAY or indanidine was markedly reduced 120 min following conditioning regardless of prior ring exposure to the same peptide; only prior exposure reduced responsiveness to [Leu 31, Pro 34]NPY. Responsiveness changes to NPY at various times or after various numbers of NE and/or NPY exposures indicated that pre-exposure and time-related responsiveness reductions were discriminable and temporally unrelated to conditioning. Postsynaptic vascular Y 2 receptor activation therefore accounts for the known sensitivity of NPY-induced pressor and vasoconstrictive actions to nifedipine. The ‘time-dependent’ loss of Y 2 receptor function may also explain prior failures to observe postsynaptic arterial Y 2 receptors in vitro.

Effects of monophosphoryl lipid A on myocardial ischemia/reperfusion injury in dogs.

We wished to determine if the previously observed cardioprotective effects of monophosphoryl lipid A (MLA, 65 micrograms/kg intravenously, i.v.), an endotoxin derivative, were time related and mediated by an enhancement of antioxidant defense mechanisms, i.e., myocardial catalase and superoxide dismutase (SOD) activities and neutrophil infiltration as assessed by myeloperoxidase (MPO) activity. We also wished to study the effect of pretreatment with MLA on vascular endothelial and smooth muscle function in vivo and in vitro. Barbital-anesthetized dogs were subjected to 60-min left circumflex coronary artery (LCX) occlusion followed by 5-h reperfusion. Myocardial catalase, SOD, and MPO activities were measured at the end of 5-h reperfusion. Pretreatment with MLA 24 h before ischemia produced a significant reduction in myocardial infarct size as measured by triphenyltetrazolium staining (15.3 +/- 4.4 vs. 30.9 +/- 5.2% in controls, p < 0.05), but 1-h pretreatment with MLA had no protective effect. MLA pretreatment for 24 h resulted in marked reduction (p < 0.05) in MPO activity in the border zone surrounding the infarct. Although a trend indicated an increase in catalase activity in the 24-h pretreatment group, no significant changes were observed in either catalase or SOD activities among the three groups. The cardioprotection produced by MLA was independent of differences in collateral blood flow to the ischemic region assessed by radioactive microsphere technique, systemic hemodynamics, myocardial oxygen demand, and ischemic bed size. Responses of the LCX bed to intracoronary acetylcholine (ACh) or nitroglycerin (NTG) in vivo and responses of isolated femoral artery rings to the endothelium-dependent vasodilators, ACh, A23187, bradykinin, or the nonendothelium-dependent vasodilator, sodium nitroprusside (SNP) in vitro were significantly decreased in the MLA 1-h pretreatment group but not in the 24-h pretreatment group. Incubation of the femoral artery rings from the MLA 1-h pretreatment group with 3 mM L-arginine for 1 h reversed the decreased endothelium-dependent responses to ACh and A23187, but not those to bradykinin. These results indicate that (a) the MLA-induced myocardial infarct size reduction was pronounced when MLA was administered for 24 h but was not evident at 1-h pretreatment; (b) a decrease in neutrophil infiltration into the site of ongoing tissue damage might be partially responsible for the protection; (c) vascular endothelial and/or smooth muscle function were transiently decreased by MLA administration and returned to nearly normal levels 24 h after treatment; and (d) the effect of MLA on endothelium-dependent responses might be mediated by the L-arginine/nitric oxide (NO) pathway.

Direct vascular effect of ropivacaine in femoral artery and vein of the dog

A study was conducted to examine the direct vascular effect of ropivacaine, in comparison with the effect of bupivacaine and lidocaine. Changes in tension induced by ropivacaine (10(-5)-3 x 10(-3) mol l-1) and lidocaine (10(-5)-10(-2) mol l-1) were examined cumulatively in vascular rings of dog femoral artery and vein under basal tension, or in those which had been precontracted with phenylephrine submaximally in Krebs' bicarbonate solution at 37 degrees C aerated with 95% O2 and 5% CO2 (pH 7.4). The change in tension induced by 10(-2) mol l-1 ropivacaine was tested under basal tension in vascular rings bathed in HEPES buffer (pH 6.8). Ropivacaine induced greater constriction than bupivacaine at concentrations over 10(-3) mol l-1 in vascular rings under basal tension (P < 0.01). The maximal contraction was induced by ropivacaine at 10(-3) mol l-1, averaging 51.5 +/- 2.8% (n = 11) and 27.0 +/- 3.7% (n = 12) of the maximal contraction induced by epinephrine in the artery and vein, respectively, and the contractions induced by ropivacaine at 10(-2) mol l-1 were 16.3 +/- 2.0% (n = 11) and 5.5 +/- 1.1% (n = 9), respectively. Phenylephrine (10(-6) mol l-1)-precontracted artery was contracted significantly by ropivacaine at 3 x 10(-4) mol l-1 and 10(-3) mol l-1, and by bupivacaine at 3 x 10(-4) mol l-1, whereas the phenylephrine (10(-6) mol l-1)-precontracted vein was relaxed by these anesthetics. Lidocaine did not exert constricting effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin-1 does not mediate hypoxic vasoconstriction in canine isolated blood vessels: effect of BQ-123.

1. The role of endothelin-1 in mediating the phenomenon of hypoxic vasoconstriction was examined in canine, isolated pulmonary, circumflex coronary and femoral arterial rings. 2. In tissues with an intact endothelium, the exogenous application of endothelin-1 (0.1-300 nM) caused concentration-dependent increases in canine, isolated pulmonary artery tone. Endothelin-3 (1-300 nM) was approximately 30 fold less potent than endothelin-1 as a vasoconstrictor in this tissue. In contrast, the selective ETB-receptor agonist, sarafotoxin S6c (0.01-1 microM), failed to elicit vasoconstriction in this tissue. Thus, endothelin isopeptide-induced vasoconstriction of the canine isolated pulmonary artery is mediated exclusively by the ETA-receptor subtype. 3. The concentration-dependent increases in isometric tension induced by endothelin-1 (0.1-300 nM) were antagonized by the ETA-selective antagonist, BQ-123 (10 microM); this concentration of antagonist caused a shift to the right in the concentration-response curve for endothelin-1 of approximately two orders of magnitude. This concentration of BQ-123 did not unmask any ETB-receptor-mediated vasoconstriction since sarafotoxin S6c (0.01-1 microM) still failed to elicit contraction in the presence of this concentration of BQ-123. 4. The hypoxia-induced vasoconstriction of canine, isolated pulmonary, circumflex coronary and femoral arterial rings was unaffected by pretreatment with the endothelin receptor antagonist, BQ-123 (10 microM), a concentration shown previously to antagonize the contractile actions of exogenously applied endothelin-1 in the isolated pulmonary artery. 5. These results are the first to provide direct evidence showing that the endothelium-dependent vasoconstriction observed during acute periods of hypoxia in vitro is not mediated by an endothelin-related isopeptide.

The Sydnonimine C87–3754 Evokes Endothelium-Independent Relaxations and Prevents Endothelium-Dependent Contractions in Blood Vessels of the Dog

Experiments were designed to compare the relaxing activities of the new sydnonimine C87-3754 with SIN-1 in arteries and veins of the dog, and to determine whether C87-3754 can prevent endothelium-dependent contractions. Rings of coronary and femoral arteries, and saphenous veins were suspended in organ chambers for the measurement of changes in isometric tension. SIN-1 and C87-3754 evoked concentration-dependent relaxations in all rings of blood vessels contracted with a submaximal concentration of either prostaglandin F2 alpha, endothelin-1, phenylephrine, or norepinephrine. In both arteries and veins, the concentration-relaxation curves to C87-3754 were shifted significantly to the right (by two to three logarithmic units) of that to SIN-1. The presence of endothelium significantly inhibited the relaxations to SIN-1 but did not affect those to C87-3754. The treatment of coronary arteries with methylene blue or oxyhemoglobin significantly impaired the relaxation to SIN-1 and C87-3754. Neither C87-3754 nor its prodrug pirsidomine (CAS 936) affected the membrane potential in coronary arteries. The endothelium-dependent contractions evoked by nitro L-arginine, arachidonic acid, and the calcium ionophore A23187 in basilar arteries of the dog were inhibited by C87-3754. These results indicate that the sydnonimine C87-3754 is a dilator of both arterial and venous smooth muscle, and can prevent endothelium-mediated contractions in cerebral arteries of the dog. The inhibition of vascular tone is likely to involve the activation of soluble guanylate cyclase, causing enhanced production of cyclic guanosine monophosphate in the smooth muscle without a change in membrane potential.

Hypotension in experimental cirrhosis: Is loss of vascular responsiveness to norepinephrine the cause of hypotension in chronic bile-duct-ligated dogs?

It has been postulated that one of the mechanisms of hypotension associated with cirrhosis is an attenuated responsiveness to catecholamines despite the increased activity of the sympathetic nervous system and the elevated plasma concentrations of the sympathetic neurotransmitter, norepinephrine. This abnormality was studied in a dog model of portal hypertension and cirrhosis. Twelve weeks after bile duct ligation (n = 16), intrasplenic pressure rose significantly from 6.3 +/- 0.4 to 14.6 +/- 1.6 mmHg (p < 0.05), mean arterial pressure had fallen from 106 +/- 4 to 83 +/- 8 mmHg (p < 0.01), cardiac output had risen from 3.1 +/- 0.2 to 3.8 +/- 0.8 l/min (p < 0.05) and plasma norepinephrine concentrations rose from 0.22 +/- 0.12 to 1.17 +/- 0.52 nmol/l (p < 0.05). In 7 sham-operated dogs, the changes in these 4 variables over the same period were non-significant. In vivo pressor responsiveness was tested by studying the effects of intravenous and intra-arterial infusions of norepinephrine and the non-selective beta-adrenoceptor agonist, isoproterenol. In vitro responsiveness was tested by measuring the effects of isoproterenol on the isometric twitch of isolated ventricular strips and the effects of norepinephrine on femoral, mesenteric and renal arterial rings. There was no significant change in the in vivo responses of chronic bile-duct-ligated dogs at 12 weeks compared to the preoperative assessment, or to sham-operated dogs at 12 weeks. Furthermore, there was no significant difference between the in vitro responses of ventricular strips to isoproterenol or arterial rings to norepinephrine prepared from chronic bile-duct-ligated and sham-operated dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y (NPY) functional group mimetics: design, synthesis, and characterization as NPY receptor antagonists

N,N′-bis-[2-N-(O-2,6-dichlorobenzyl-L-tyrosyl)aminoethylguanyl]cystamine 3 and N,N′-bis-[2-N-(O-2,6-dichlorobenzyl-L-tyrosyl)aminoethyl]-1,6-hexanediguanidine 4 have been designed as neuropeptide Y (NPY) functional group mimetics. Both 3 and 4 displace N-[propionyl- 3H]-NPY from rat brain binding sites, and are NPY receptor antagonists in rat femoral artery ring segments.

Variable effects of human and canine polymorphonuclear leucocytes on vascular smooth muscle tone.

Previous studies have shown variable effects of human and canine polymorphonuclear leucocytes (neutrophils) on vascular tone. The aim of this study was to identify whether these variations in neutrophil function are due to species differences. Canine and human arterial rings (with and without endothelium) were contracted with the thromboxane A2 analogue U46619, and then exposed to isolated neutrophils. Human neutrophils caused a significant relaxation of the human mammary arterial rings, and the relaxation was unaffected by the cyclo-oxygenase inhibitor indomethacin, enhanced by superoxide dismutase (SOD), and inhibited by oxyhaemoglobin. The relaxant effect of human neutrophils was also diminished upon pretreatment with NG-monomethyl-l-arginine (L-NMMA), indicating that the vasorelaxant material released by the neutrophils was nitric oxide (NO). Human neutrophils also relaxed canine femoral arterial rings, and the relaxant effect was potentiated by SOD and inhibited by pretreatment with oxyhaemoglobin or L-NMMA, confirming that the vasorelaxation was via release of NO. Canine neutrophils, on the other hand, caused an endothelium dependent contraction of autologous femoral arterial rings. This vasoconstriction was not affected by indomethacin, SOD, oxyhaemoglobin, or L-NMMA. However, treatment of canine neutrophils with the 5-lipoxygenase inhibitor piriprost attenuated (p < 0.02) their contractile effect on vascular rings, suggesting that neutrophil generated 5-lipoxygenase products were probably responsible for smooth muscle contraction. Presence of the leukotriene C4 and D4 receptor antagonist FPL 55,712 totally blocked the contractile effects of canine neutrophils, indicating that femoral arterial ring contraction was mediated by peptido-leukotrienes. The endothelium dependent nature of the canine neutrophil induced contraction suggests that the 5-lipoxygenase product leukotriene A4 is taken up by endothelial cells for conversion to peptido-leukotrienes. Since SOD had no effect and FPL 55,712 totally blocked the vasoconstrictor effects of canine neutrophils, it appears that the vasoconstrictor effects of the latter are mediated primarily through peptido-leukotrienes. In contrast, the vasorelaxation by human neutrophils is mediated through release of NO.

Vasopressin and fetal cerebrovascular regulation.

Vasopressin (AVP) may increase cerebral blood flow (CBF) during hypoxemia by selective dilatation of cerebral vessels via endothelium-derived relaxing factor (EDRF) release. To test whether this action is relevant in the fetus, we produced isocapnic hypoxemia in halothane-anesthetized pregnant ewes. Fetal infusion of a V1 AVP antagonist reduced by 55% the increase in CBF during fetal hypoxemia. To test the role of this response during development, we examined the response to AVP in intact and endothelium-denuded femoral and basilar arterial rings in vitro from fetal, newborn, and adult sheep. AVP constricted femoral rings in an endothelium-independent manner, with increased potency in newborn and fetal compared with adult rings. AVP relaxed basilar rings in an endothelium-dependent manner, which was unaffected by indomethacin treatment, with increased potency in newborn and adult compared with fetal rings. We conclude that fetal cerebral vascular endothelium is functional and responsive to AVP and that circulating AVP during fetal hypoxemia contributes to increased CBF via this effect.

Protamine releases endothelium-derived relaxing factor from systemic arteries. A possible mechanism of hypotension during heparin neutralization.

When used to reverse the anticoagulant effect of heparin, protamine sulfate often causes vasodilation that can lead to systemic hypotension. Protamine is rich in the basic amino acid arginine, which is the precursor of endothelial cell synthesis of nitric oxide, and nitric oxide is the active component of endothelium-derived relaxing factor (EDRF). To determine whether the hypotensive effect of protamine could be due to stimulated release of EDRF, we studied rings (4-5 mm) of canine coronary, femoral, and renal artery suspended in organ chambers containing physiological salt solution (37 degrees C and 95% O2-5% CO2). Arterial rings with and without endothelium were contracted with prostaglandin F2 alpha (2 x 10(-6) M) and exposed to increasing concentrations of protamine (final organ bath concentration, 40-400 micrograms/ml). In arterial segments without endothelium, protamine caused only a modest decrease in tension. However, protamine induced concentration-dependent relaxation in all arterial segments with endothelium, which was significantly greater than in segments without endothelium (p less than 0.05). The endothelium-dependent relaxation induced by protamine was inhibited by NG-monomethyl-L-arginine (L-NMMA) (10(-5) M), but L-NMMA had no effect on rings without endothelium. The action of L-NMMA could be reversed by L-arginine (10(-4) M) but not D-arginine (10(-4) M). This study demonstrates that protamine stimulates the release of EDRF from arterial endothelium, and that endothelium-dependent vasodilation may be an important cause of systemic hypotension during protamine infusion.

Converting-enzyme inhibitors potentiate bradykinin-induced relaxation in vitro.

Experiments were designed to study the effects of converting-enzyme inhibitors (captopril and S 10211) on the endothelium-dependent relaxation to bradykinin in isolated porcine arteries. Rings of femoral arteries with and without endothelium were suspended in organ chambers to record isometric tension. Rings of coronary arteries without endothelium were used as bioassay tissue to record release of endothelium-derived relaxing factor (EDRF) from perfused femoral arteries. In organ chambers, bradykinin induced endothelium-dependent relaxation and, inconsistently, endothelium-independent contraction of the femoral artery rings. The relaxation is mediated by endothelial B2 bradykinin receptors, the contraction through B1 bradykinin receptors. Converting-enzyme inhibitors induced a weak potentiation of the contractile response and weak or no potentiation of the endothelium-dependent relaxation. In the presence of indomethacin, the response to bradykinin was not modified and no potentiation from the inhibitor could be observed. Blockade of the contractile response with a B1 bradykinin antagonist did not unmask a potentiation of the bradykinin endothelium-dependent relaxation by the converting-enzyme inhibitors. However, in the presence of B2 bradykinin antagonist, when high concentrations of bradykinin are required to induce relaxation, converting-enzyme inhibitors potentiated the effects of bradykinin. In contrast, in bioassay conditions with a perfused vascular segment, converting-enzyme inhibitors selectively enhanced the release of EDRF by bradykinin. This effect is observed in the bioassay tissue and in the donor segment. These results suggest that converting enzyme is indeed a powerful modulator of bradykinin action and that other enzymatic pathways of bradykinin metabolism present in the vascular wall could mask its action.

Fibrin(ogen) degradation product peptide 6A increases femoral artery blood flow in dogs.

To determine the effects of peptide 6A (a fibrinogen-degradation product) on femoral blood flow, anaesthetized dogs were given saline or peptide 6A intravenously in random order. Bolus injection of peptide 6A (10, 20 or 50 mumoles) caused a short-lasting dose-dependent decrease in femoral bed resistance and an increase in femoral blood flow. Continuous infusion of peptide 6A (50 mumoles min-1) resulted in a sustained decrease in resistance and an increase in femoral artery blood flow (54 +/- 33%), with a small, insignificant decrease in femoral artery mean pressure. Indomethacin pretreatment caused only slight attenuation of the peptide 6A-induced increase in femoral blood flow. In in vitro experiments, peptide 6A relaxed rings of femoral artery, and this effect was associated with an increase in 6-keto-PGF1 alpha in the vascular ring supernatants and in the tissue cyclic GMP concentrations. Peptide 6A-induced relaxation was abolished by de-endothelialization, but not by treatment with indomethacin. These observations suggest that peptide 6A induces vasorelaxation largely by stimulating release of endothelium-derived relaxing factor. PGI2 release appears to play only a minor role in the vasodilator effects of peptide 6A in the femoral bed.

The calcium channel antagonist S 11568 causes endothelium-dependent relaxation in canine arteries

The new dihydropyridine calcium channel antagonist S 11568 and its optical isomers, S 12967 and S 12968 (3 × 10 −6 to 10 −4 M), caused, unlike nifedipine (10 −4 M), equipotent and rapid endothelium-dependent relaxations and increased the content of cyclic GMP in rings of canine femoral arteries. These effects were observed in the presence of indomethacin and were prevented by methylene blue, hemoglobin and N G-monomethyl-L-arginine. Thus these effects must involve endothelium-derived relaxing factor (EDRF) and be distinct from the calcium channel antagonistic effect which is stereoselective and of slow onset. The compounds did not potentiate relaxations of rings without endothelium to nitric oxide. In bioassay experiments, the compounds produced endothelium-dependent relaxation only when applied to endothelial donors. These results are compatible with an increased release of EDRF induced by the dihydropyridine compounds.

Dissociation between endothelium-dependent relaxations and increases in cGMP in systemic veins

In canine systemic veins, in contrast to what is observed in mammalian systemic arteries, endothelium-dependent relaxations to the calcium ionophore A23187 are not diminished by the inhibitor of soluble guanylate cyclase, methylene blue. Therefore, experiments were designed to determine whether these relaxations in the veins are associated with the accumulation of guanosine 3',5'-cyclic monophosphate (cGMP). Rings of canine femoral arteries and veins with and without endothelium were suspended for the measurement of isometric force in organ chambers; cGMP was measured by radioimmunoassay. In arteries and veins contracted with norepinephrine, the tissue content of cGMP was greater in rings with than without endothelium. This difference was decreased by methylene blue (10(-5) M). A23187 (3 X 10(-7) M, for 1 min) increased the accumulation of cGMP, which was temporally related with the onset of relaxation in tissues with endothelium. Methylene blue inhibited the accumulation of cGMP in both blood vessels but inhibited the relaxations only in the arteries. In rings without endothelium, sodium nitroprusside (3 X 10(-7) and 10(-5) M) initiated increases in cGMP, which followed the onset of relaxation. Neither response to sodium nitroprusside was reduced by methylene blue. These results suggest that in canine femoral arteries and veins, relaxation of the smooth muscle to sodium nitroprusside are mediated by a mechanism distinct from changes in cGMP. Likewise, in canine systemic veins, endothelium-derived factor(s) released in response to A23187 also can initiate relaxation of the smooth muscle by a mechanism distinct from changes in cGMP.

Increased vasoconstrictor response to noradrenaline in femoral vascular bed of diabetic dogs. Is thromboxane A2 involved?

The aim was to determine the role of cyclo-oxygenase products in the vasoconstrictor response of femoral arterial bed to noradrenaline and to analyse the role of vascular adrenoceptors in the synthesis of cyclo-oxygenase products. The influence of intra-arterially injected cyclo-oxygenase inhibitors indomethacin and acetylsalicylic acid on alterations in conductance of femoral arterial bed induced by noradrenaline was compared in metabolically healthy and alloxan diabetic dogs. PGI2 and TXA2 synthesising ability of isolated femoral arterial rings was measured with and without inhibition of alpha adrenoceptors by phentolamine. 18 metabolically healthy and 18 alloxan (560 mumol.kg-1) diabetic dogs of either sex, weight 16-28 kg, were studied. Noradrenaline produced greater (p less than 0.01) pressor effects in the femoral arterial bed of alloxan diabetic dogs than in the hind limb of control animals. Blockade of cyclo-oxygenase either by indomethacin 10 mumol.kg-1 or by acetylsalicylic acid 140 mumol.kg-1 markedly reduced the response to noradrenaline in alloxan treated animals, but not in controls, thereby eliminating the different responsiveness of the two groups. Femoral arterial rings from diabetic animals synthesised similar amounts of PGI2 as control rings but formed more TXA2 (p less than 0.05). Phentolamine pretreatment (5 mumol.litre-1) markedly reduced the production of TXA2, but not of PGI2, in diabetic vessels. The results show an increased release of TXA2 by isolated diabetic femoral arteries. It is therefore suggested that an alpha adrenoceptor mediated increase in TXA2 biosynthesis may play a part in the vascular hyperreactivity of the diabetic femoral arterial bed.

Differential Effects of the Antianginal Drug Nicorandil on Canine Arteries and Veins

Nicorandil, a potent coronary vasorelaxant used in the treatment of angina, has differential effects on arteries and veins in vivo. To explain this phenomenon, experiments were designed to characterize the relaxant and inhibitory actions of this compound on canine isolated arteries and veins. Paired rings of canine coronary, femoral, and saphenous arteries and saphenous veins were suspended at optimal length for isometric tension recording in organ chambers containing physiologic salt solution at 37 degrees C and gassed with 95% O2-5% CO2. In certain experiments, one ring of each pair was denuded of the endothelium. Removal of the endothelium did not affect nicorandil-induced relaxations of contracted blood vessels. Nicorandil exerted a differential relaxant effect on arteries and veins contracted with KCl (order of potency: saphenous vein greater than coronary artery greater than femoral artery). No difference in sensitivity to nicorandil was observed in arteries and veins contracted with prostaglandin F2 alpha. Contractions of saphenous arteries and veins to norepinephrine (NE) were equally sensitive to the inhibitory action of nicorandil. However, contractions of saphenous veins induced by sympathetic nerve stimulation were more sensitive to nicorandil than were contractions of saphenous arteries. Furthermore, nicorandil did not affect contractions to phenylephrine in saphenous veins, although contractions to B-HT 920 were virtually abolished by the compound. Saphenous veins contracted with St 587 were more sensitive to the relaxant action of nicorandil than when contracted with phenylephrine. These results suggest that nicorandil inhibits preferentially contractions of canine arteries and veins mediated by alpha 2- rather than alpha 1-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein Kinase C as a Modulator of Response Amplification in Vascular Smooth Muscle

The amplification of alpha-adrenoceptor-mediated vasoconstriction by angiotensin II was studied in femoral artery rings from rabbits. Threshold concentrations of angiotensin II (0.1 nM) increased the maximal response to clonidine to 139 +/- 8% of control and produced a 3.2-fold increase in sensitivity. These effects of angiotensin II were reversed when tissues were pretreated with staurosporine (50 nM), an inhibitor of protein kinase C. The amplification of the alpha-adrenoceptor-mediated vasoconstrictor effects of thrombin and norepinephrine by angiotensin II were also reversed by pretreatment with staurosporine. Angiotensin II induced a response amplification in vascular smooth muscle known to be a nonspecific phenomenon, implying postreceptor interaction at intracellular transducer systems. Our findings suggest that upon activation of protein kinase C by angiotensin II, arterial responses to alpha-adrenoceptor agonists are amplified. This provides for nonspecific changes in vascular sensitivity by tonic alterations in postsynaptic modulation by enzyme systems known to regulate Ca2(+)-dependent phenomena, e.g. those related to vascular excitation-contraction mechanisms.