Analysis of Rabbit Vascular Responses to DBI,an Ingol Derivative Isolated from Euphorbia canariensis

We have analysed the effects of 7,12-O-diacetyl-8-O-benzoil-2,3-diepiingol (DBI), an ingol derivative isolated from E. canariensis, on isometric tension developed by isolated rabbit basilar and carotid arteries. Concentration-response curves to DBI (10^?8 - 3 × 10^?5 m) were obtained cumulatively in both arteries at resting tension and active tone (KC1, 50 mm). At resting tension, DBI induced a concentration-dependent contraction, which was not inhibited in Ca²⁺-free medium. H7 (1-(5-isoquinoline sulphonyl)-2-methylpiperazine dichloride) (10^?4 m) inhibited the DBI-induced contraction both in basilar and in carotid arteries. Calmidazolium (10^?4 m) inhibited the maximum contraction of the carotid artery to DBI, and completely abolished the response in the basilar artery. In pre-contracted basilar arteries DBI induced a concentration-dependent relaxation that was not modified by incubation with N^G-nitro-l-arginine (l-NOARG; 10^?5 m) or indomethacin (10^?5 m). In the carotid artery with active tone DBI induced further contractions, which were not significantly modified by l-NOARG (10^?5 m) and were potentiated by indomethacin (10^?5 m). These results suggest that DBI contracts rabbit basilar and carotid arteries by a mechanism that is independent of extracellular Ca²⁺ and involves the participation both of protein kinase C and of calmodulin. DBI relaxes basilar but not carotid arteries by a mechanism independent of the liberation of nitric oxide and prostacyclin. In the carotid artery prostacyclin but not nitric oxide partially counteracts the contractile action of DBI.     

Balloon catheter injury abolishes phenylephrine-induced relaxation in the rat contralateral carotid

BACKGROUND AND PURPOSE

The consequences of compensatory responses to balloon catheter injury in rat carotid artery, on phenylephrine-induced relaxation and contraction in the contralateral carotid artery were studied.

EXPERIMENTAL APPROACH

Relaxation and contraction concentration–response curves for phenylephrine were obtained for contralateral carotid arteries in the presence of indomethacin (COX inhibitor), SC560 (COX-1 inhibitor), SC236 (COX-2 inhibitor) or 4-hydroxytetramethyl-L-piperidine-1-oxyl (tempol; superoxide dismutase mimetic). Reactive oxygen species were measured in carotid artery endothelial cells fluorimetrically with dihydroethidium.

KEY RESULTS

Phenylephrine-induced relaxation was abolished in contralateral carotid arteries from operated rats (E_max= 0.01 ± 0.004 g) in relation to control (E_max= 0.18 ± 0.005 g). Phenylephrine-induced contractions were increased in contralateral arteries (E_max= 0.54 ± 0.009 g) in relation to control (E_max= 0.38 ± 0.014 g). SC236 restored phenylephrine-induced relaxation (E_max= 0.17 ± 0.004 g) and contraction (E_max= 0.34 ± 0.018 g) in contralateral arteries. Tempol restored phenylephrine-induced relaxation (E_max= 0.19 ± 0.012 g) and contraction (E_max= 0.42 ± 0.014 g) in contralateral arteries, while apocynin did not alter either relaxation (E_max= 0.01 ± 0.004 g) or contraction (E_max= 0.54 ± 0.009 g). Dihydroethidium fluorescence was increased in contralateral samples (18 882 ± 435 U) in relation to control (10 455 ± 303 U). SC236 reduced the fluorescence in contralateral samples (8250 ± 365 U).

CONCLUSIONS AND IMPLICATIONS

Balloon catheter injury abolished phenylephrine-induced relaxation and increased phenylephrine-induced contraction in contralateral carotid arteries, through O₂⁻ derived from COX-2.     

Analysis of bradykinin receptor mediating relaxation of cat cerebral arteries in vivo and in vitro

Summary Bradykinin (BK), methionyl-lysyl-BK (M-L-BK) and des-Arg ⁹-BK produced, in decreasing potency, dose-related dilatations of the superficial pial arteries of the cat in vivo. The competitive, specific B₁-receptor antagonist, des-Arg ⁹-Leu⁸-BK was ineffective against BK-induced dilatations in this in vivo model.On the cat middle cerebral artery in vitro (but not the basilar artery), under resting tension and when contracted with 5-hydroxytryptamine (5-HT) or KCl, concentration related relaxations were produced by BK, M-L-BK, and des-Arg ⁹-BK, this being the order of relative potency of the three kinins.There was no increase in the sensitivity of either the middle cerebral or the basilar artery in vitro under resting tension or when contracted with 5-HT or KCl to BK or des-Arg ⁹-BK, concentration effect curves to which were produced at 2 h intervals over an 8 h period. The B₁-receptor antagonist des-Arg ⁹-Leu⁸-BK was ineffective against relaxations to BK or des-Arg ⁹-BK of the middle cerebral artery under resting tension or when contracted with 5-HT.The receptor mediating dilatation of the superficial pial arteries of the cat in vivo and relaxation of the middle cerebral artery in vitro to kinins is of the B₂-type. The cat basilar artery in vitro is relatively insensitive to the action of kinins and this is possibly due to an absence of receptors for kinins on this tissue.     

Evaluation of the vasodilating effect of naftidrofuryl oxalate using isolated canine and rat artery preparations

Using isolated ring preparations of major arteries mainly of canine origin, we attempted to explore the mechanism of the vasodilating effect of naftidrofuryl oxalate (I) at the concentration of approximately 10 microM. 1) The resting tension of canine carotid, femoral, coronary, renal and basilar arteries were not affected by I. 2) A weak or no papaverine-like activity was noted on coronary, renal and basilar arteries contracted by KCl (25 mM) or U46619 (20 nM). Porcine endothelin (30 nM)-induced contraction in the basilar artery also showed no response to I. 3) I produced a relatively strong anti-serotonergic effect in the basilar and femoral arteries, and the minimum effective concentrations of I for pretreating these arteries were 0.3 and 0.1 microM, respectively. I failed, however, to affect 8-OH-DPAT-induced contraction of the basilar artery. 4) In a low concentration such as 1 nM, I was able to release the vasodilating factor from the carotid artery. 5) The oscillatory contractions which developed in the rat thoracic aorta with phenylephrine (10 microM) were not affected by I (approximately 0.1 microM). 6) Na oxalate (approximately 1 mM) produced none of the effects of I described in 2) approximately 4). Based on the results obtained, it is concluded that I would exert its vasodilating effect not only directly via an anti-serotonergic action but also indirectly via its secretagogue-like action.     

Effect of Parasympathetic and Sensory Transmitters on Human Epicardial Coronary Arteries and Veins

Abstract: Vasomotor effects of various agonists were tested on isolated human epicardial coronary arteries and veins at resting tension and after precontraction with U46619. Acetylcholine relaxed all arteries with intact endothelium but only some endothelium-denuded arteries. Most veins did not relax to acetylcholine. Higher concentrations of acetylcholine induced powerful contractions of all arteries and veins. Preincubation with atropine significantly lowered the pD₂ values but not E_max values for contractile responses to acetylcholine in arteries and veins (pA₂ value for atropine 9.1 arteries and 9.6 veins). Vasoactive intestinal peptide, human α-calcitonin gene-related peptide and substance P potently relaxed all arteries with intact endothelium and all veins. Removal of the arterial endothelium abolished relaxation to substance P in most arteries whereas responses to vasoactive intestinal peptide were unaffected, and for a-calcitonin gene-related peptide the pD₂ value but not the E_max value was significantly lowered. In both arteries and veins, the antagonists α-calcitonin gene-related peptide (8-37) and spantide lowered significantly the potency for a-calcitonin gene-related peptide and substance P, respectively, without significant changes in E_max values (pA₂ value for α-calcitonin gene-related peptide (8-37) 7.9 arteries and 7.9 veins, for spantide 7.6 arteries and 8.1 veins).     

Mitochondrial monoamine oxidase-A-mediated hydrogen peroxide generation enhances 5-hydroxytryptamine-induced contraction of rat basilar artery

BACKGROUND AND PURPOSE

We evaluated the role(s) of monoamine oxidase (MAO)-mediated H₂O₂ generation on 5-hydroxytryptamine (5-HT)-induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

EXPERIMENTAL APPROACH

Basilar artery (endothelium-denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch-clamp electrophysiological and confocal microscopic studies.

KEY RESULTS

Under resting tension, 5-HT elicited a concentration-dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC₅₀: 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5-HT-induced tension development in SHR was eradicated by polyethylene glycol-catalase, clorgyline and citalopram whereas exogenously applied H₂O₂ enhanced the 5-HT-elicited tension development in WKY. A greater protein expression of MAO-A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5-HT generated (clorgyline-sensitive) a greater amount of H₂O₂ in SHR compared with WKY. Whole-cell iberiotoxin-sensitive Ca²⁺-activated K⁺ (BK_Ca) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF⁻¹ vs. 2.61 ± 0.66 pA·pF⁻¹). In SHR myocytes, 5-HT caused a greater inhibition (clorgyline-, polyethylene glycol-catalase- and reduced glutathione-sensitive) of BK_Ca amplitude than in those from WKY.

CONCLUSIONS AND IMPLICATIONS

5-HT caused an increased generation of mitochondrial H₂O₂ via MAO-A-mediated 5-HT metabolism, which caused a greater inhibition of BK_Ca gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.     

Effects of α-Adrenoceptor Active Drugs,Prostaglandin F2α and Vasopressin on Cystic and Hepatic Arteries of Pig and Man

Human and pig cystic and pig hepatic arteries were suspended in tissue baths and the effect of α-adrenoceptor selective drugs, prostaglandin F_2α (PGF_2α) and vasopressin were investigated. Prazosin fulfilled the criteria for competitive antagonism in concentrations 10^-9-10^-7 M. The pA₂-values were 9.53 in human cystic, 9.74 in pig cystic, and 9.57 in pig hepatic artery. Rauwolscine had no significant effect in the different arteries. In human cystic artery noradrenaline had significantly (P<0.05) higher E_max and pEC50-values (135% of the preceding K⁺-induced contraction and 6.4, respectively) compared with pig cystic (106% and 5.7, respectively) and pig hepatic artery (116% and 5.9, respectively). Vasopressin had no effect in the cystic arteries, whereas it had a high potency (pEC50 was 8.5) but low intrinsic activity (E_max was 14%) in pig hepatic artery. Prostaglandin F_2α had a significantly higher E_max in human than in pig arteries. No differences were found in pEC50-values. This study indicates a similarity in pharmacological characteristics of some vasoactive drugs especially between pig cystic and hepatic arteries. If this is also true in man, the easily obtainable cystic artery can be used for screening the effect of drugs on the hepatic artery.     

The resistance of some rat cerebral arteries to the vasorelaxant effect of cromakalim and other K+ channel openers.

1. Cromakalim (0.01-30 microM) and sodium nitroprusside (SNP, 0.01-100 microM) were tested for their ability to relax a number of pre-contracted small arteries (approximate diameter 200-700 microM at 100 mmHg) from the rat, rabbit and guinea-pig. 2. In the rat, SNP (0.01-100 microM) caused near maximal relaxation in all vessels studied including the middle cerebral, anterior cerebellar, basilar, mesenteric and renal arteries. Cromakalim (0.01-30 microM) relaxed pre-contracted mesenteric and renal arteries but was only a weak relaxant of all the rat cerebral arteries with the exception of the basilar artery. Similar experiments using mesenteric and cerebral vessels from the rabbit and guinea-pig showed cromakalim could relax pre-contracted vessels in a concentration-dependent manner. 3. Two other K+ channel openers, nicorandil and pinacidil, were also tested for their ability to relax rat cerebral arteries. Nicorandil (0.01-100 microM) was ineffective in the rat anterior cerebellar artery at concentrations up to 100 microM. Pinacidil (0.01-100 microM) caused significant vasorelaxation, although high concentrations were required (greater than 10 microM) and the response was insensitive to the effects of glibenclamide (3 microM). 4. Electrophysiological experiments with the rat anterior cerebellar artery showed that cromakalim (up to 30 microM) failed to influence the resting membrane potential of impaled single smooth muscle cells. 5. The results showed that some rat small cerebral arteries were resistant to the effects of K+ channel openers including cromakalim, pinacidil and nicorandil. This is peculiar to this vascular tree since the same vessels from other species do not exhibit the same behaviour.(ABSTRACT TRUNCATED AT 250 WORDS)     

The inhibition of nicotine-evoked relaxation of the guinea-pig isolated basilar artery by some analgesic drugs and progesterone

1. The purpose of this study was to investigate the mechanism of nicotine-evoked relaxation of the guinea-pig isolated basilar artery and to study the effects of drugs associated with the aetiology or treatment of migraine on the nicotine response. 2. The guinea-pig isolated basilar artery, pre-contracted with prostaglandin F2alpha (PGF2alpha), in the presence of atropine (3 microM) and guanethidine (3 microM), relaxed on addition of nicotine (0.1 mM) in approximately 50% of preparations. The responses to nicotine were of short duration and blocked in preparations pre-treated for 10 min with capsaicin (1 microM) and are therefore probably a consequence of the stimulation of trigeminal C fibre terminals. 3. Responses to nicotine were reduced in the presence of 5-carboxamidotryptamine, 5-hydroxytryptamine and sumatriptan in that order of potency. This is consistent with a 5-HT1 receptor mechanism. These agonists evoked small additional contractions in vessels pre-contracted with PGF2alpha. 4. Indomethacin (0.3-10 microM), aspirin (10-30 microM), and nitro-L-arginine methyl ester (L-NAME, 0.1 mM) reduced nicotine-evoked relaxation of the basilar artery, suggesting the involvement of both nitric oxide and cyclo-oxygenase products in this response. 5. Progesterone (1 microM) markedly reduced the response to nicotine, a possible reflection of the ion channel blocking activity of high concentrations of this compound. 6. The guinea-pig basilar artery is a preparation in which the effects of drugs on responses to stimulation of trigeminal nerve terminals can be studied in vitro and may thus be of interest in assessing the actions of drugs used in treatment of headache.     

Calcium antagonistic and spasmolytic activities of a new 1,5-benzothiazepine derivative in isolated canine and monkey arteries

Effects of TA-3090 ((+) (2S,3S)-3-acetoxy-8-chloro-5-(2-(dimethylamino)ethyl)-2, 3-dihydro-2-(4-methoxyphenyl)-1,5-benzothiazepin-4-(5H)-one maleate)and diltiazem on contractions induced by different spasmogens were investigated in isolated canine and monkey arteries. Ca2+-antagonistic action in canine arteries, assessed by suppression of Ca2+-induced contraction in Ca2+-free, K+-depolarizing solution, was as follows; basilar (pA2 = 8.34) greater than coronary (pA2 = 7.95) greater than renal (pA2 = 7.46) = mesenteric artery (pA2 = 7.36). The potency of TA-3090 was 10 times greater in basilar artery and 2 to 3 times greater in the other arteries than that of diltiazem. The effect of TA-3090 on the arterial segment was more persistent than that of diltiazem. Relative vasorelaxing potency of TA-3090 to diltiazem in K+-induced contractions was greatest in the basilar artery among the tested arteries of both monkeys and dogs. Spasmolytic activities of TA-3090 on 5-HT-, PGF2 alpha-, U-46619 (thromboxane A2/prostaglandin H2 agonist) and oxyhemoglobin-induced contractions in canine basilar arteries were more potent than those of diltiazem, especially on 5-HT-induced contraction. In addition, TA-3090 suppressed 3,4-diaminopyridine-induced rhythmic contraction in the canine coronary artery. These results indicate that TA-3090 has potent Ca2+-antagonistic and spasmolytic activities, and these actions are most selective for basilar artery.     

Differential Vasorelaxant Effects of K+-Channel Openers and Ca2+-Channel Blockers on Canine Isolated Arteries

Abstract— The vasorelaxant effects of the K⁺-channel openers, pinacidil and cromakalim, were compared with those of the Ca²⁺-channel blockers, verapamil and KB-2796 (1-[bis(4-fluorophenyl)methyl]-4-(2,3,4-trimethoxybenzyl)piperazine dihydrochloride), in canine isolated coronary, renal, basilar and mesenteric arteries precontracted with U46619, a thromboxane A₂ mimetic. The relaxation induced by pinacidil and cromakalim was greater in coronary than in other arteries, the magnitude of relaxation being in the order of coronary > renal > basilar > mesenteric arteries. The relaxant responses to both drugs were inhibited by glibenclamide, a blocker of ATP-sensitive K⁺ channels. The relaxation induced by verapamil and KB-2796, in contrast, was greater in basilar than in other arteries, the magnitude of relaxation being in the order of basilar > coronary > renal and mesenteric arteries. In fura-2-loaded, U46619-stimulated arteries, pinacidil and cromakalim produced a greater reduction in intracellular Ca²⁺ concentration and muscle tension in coronary than in mesenteric arteries, while verapamil and KB-2796 reduced these values more potently in basilar than in mesenteric arteries. These results suggest that K⁺-channel openers exhibit a vasorelaxant selectivity for coronary arteries, whereas Ca²⁺-channel blockers exhibit such selectivity for cerebral arteries. The selective vasorelaxant action induced by these drugs appears to correspond, in part, to their effects on the concentration of intracellular Ca²⁺.     

The stereospecificity of flobufen metabolism in isolated guinea pig hepatocytes

Background

Extracellular nucleotides play an important role in the regulation of vascular tone and may be involved in cerebral vasospasm after subarachnoidal haemorrhage. This study was designed to characterise the contractile P2 receptors in endothelium-denuded human cerebral and omental arteries. The isometric tension of isolated vessel segments was recorded in vitro. P2 receptor mRNA expression was examined by RT-PCR.

Results

In human cerebral arteries, the selective P2Y₆ receptor agonist, UDPβS was the most potent of all the agonists tested (pEC₅₀ = 6.8 ± 0.7). The agonist potency; UDPβS > αβ-MeATP > UTPγS > ATPγS > ADPβS = 0, indicated the presence of contractile P2X₁ P2Y₂, P2Y₄ and P2Y₆, but not P2Y₁ receptors, in human cerebral arteries. In human omental arteries, UDPβS was inactive. The agonist potency; αβ-MeATP > ATPγS = UTPγS > ADPβS = UDPβS = 0, indicated the presence of contractile P2X₁, and P2Y₂ receptors, but not P2Y₁ or P2Y₆ receptors, in human omental arteries. RT-PCR analysis of endothelium-denuded human cerebral and omental arteries demonstrated P2X₁, P2Y₁, P2Y₂ and P2Y₆ receptor mRNA expression. There were no bands for the P2Y₄ receptor mRNA in the omental arteries, while barely detectable in the cerebral arteries.

Conclusions

P2Y₆ receptors play a prominent role in mediating contraction of human cerebral arteries. Conversely, no such effect can be observed in human omental arteries and previous results confirm the absence of P2Y₆ receptors in human coronary arteries. The P2Y₆ receptor might be a suitable target for the treatment of cerebral vasospasm.     

Application of an activity‐based receptor bioassay to investigate the in vitro activity of selected indole‐ and indazole‐3‐carboxamide‐based synthetic cannabinoids at CB1 and CB2 receptors

Synthetic cannabinoids (SCs) are the most chemically diverse group of new psychoactive substances. This group has been associated with several intoxications, many with fatal outcomes. Although advancements have been achieved in pharmacology, metabolism, and detection of these compounds in recent years, these aspects are still unresolved for many SCs. The aim of this study was to investigate the in vitro potency of 14 indole‐ and indazole‐based SCs by applying a stable CB1 or CB2 receptor activation assay and correlating the activity with their structure. The half‐maximal effective concentration (EC₅₀) of 5‐chloropentyl, 5‐bromopentyl, and 5‐iodopentyl JWH‐122 analogs varied from 74.1 to 283.7 nM for CB1 and 7.05 to 23.4 nM for CB2, where the addition of a chlorine atom enhanced the potency at CB1 compared with the bromo and iodo analogs. AM‐2201 was the most active at CB1 within this naphthoylindole family, with an EC₅₀ of 23.5 nM but with the lowest efficacy (E_max 98.8%). Within the indole‐3‐carboxamide derivatives, 5F‐MDMB‐PICA was the most active compound, with a CB1/CB2 EC₅₀ of 3.26/0.87 nM and an E_max around three times higher than JWH‐018. ADB‐FUBINACA was the most potent tested SC overall, with a CB1/CB2 EC₅₀ of 0.69/0.59 nM, and an E_max around 3‐fold higher than that for JWH‐018 at CB1. The data obtained in this study confirm how small differences in the structure of SCs might lead to large differences in their activity, especially at CB1, which may be correlated with differences in their toxic effects in humans.     

Pinacidil-induced Relaxation in Pulmonary Arteries Isolated From Pulmonary Hypertensive and Normotensive Rats and Pre-contracted With Different Spasmogens

Summary: Vasorelaxant responses to the potassium channel opening drug, pinacidil, were obtained on preparations of pulmonary artery and aorta taken from rats with pulmonary hypertension (induced by chronic hypoxia or monocrotaline) and pre-contracted either submaximally with endothelin-1 (ET-1), PGF_2α, U46619 (thromboxane-mimetic) or noradrenaline (NA), or with 80 mM K⁺. In pulmonary artery, but not aorta, from pulmonary hypertensive rats the maximum relaxant response to pinacidil was increased, when compared with data in control rats, irrespective of the spasmogen used to precontract the tissues. The increase in maximum was associated with relaxation to below the tissue resting baseline and probably reflected the presence of inherent contractile tone in arteries from pulmonary hypertensive rats. In addition the potency (-log EC₅₀) of pinacidil was increased in pulmonary arteries from pulmonary hypertensive rats but this was seen only in preparations contracted with ET-1 (30-fold increase) or NA (seven-fold increase) and not in those contracted with PGF_2α, U46619 or K⁺. As a result, in ET-1-contracted preparations from pulmonary hypertensive rats pinacidil was 29-fold more potent on pulmonary artery than on aorta. To explain the increase in potency it is speculated that during the development of pulmonary hypertension the mechanism whereby ET-1 and NA contract pulmonary arteries may change from one in which Ca²⁺ influx plays only a minor role to one in which Ca²⁺ influx predominates, although no direct evidence to support this speculation has yet been obtained.     

Irritant contact dermatitis in humans from phorbol and related esters

Nine compounds, based on four biogenetically-related polycyclic diterpene skeletons, were subjected to open and closed patch testing on human volunteer subjects. The tigliane esters phorbol-12, 13, 20-triacetate, 12-O-2Z-4E-octadienoyl-4-deoxyphorbol-13-acetate and 12-O-tigloyl-4-deoxyphorbol-13-isobutyrate, in increasing order of potency, produced symptoms of toxicity in closed patch tests, with the dose of the most potent compound in this series being 0.5 μg in 5 μl acetone. Phorbol, a tigliane alcohol, was inactive in closed tests at a dose level of 50 μg/5 μl. The daphnane derivative, daphnetoxin, produced bullae and vesiculation in closed patch tests, but daphnetoxin-5,20-diacetate was devoid of these effects when applied at 10 times the dose of daphnetoxin. The ingenane compounds, ingenol-3,5,20-triacetate and 20-deoxy-16-hydroxyingenol-3,5,16-triacetate, and the lathyrane compound, ingol-3,7,8,12-tetraacetate, were obtained from the hydrolyzed, acetylated irritant latex of Euphorbia hermentiana. At the doses tested, ingenol-3,5,20-triacetate was the only compound derived from this plant to exhibit irritant activity in closed patch tests. In contrast, this compound is inactive as an irritant to the mouse ear at doses up to 250 μg/ear. Only three compounds, 12-O-2Z-4E-octadienoyl-4-deoxyphorbol-13-acetate, 12-O-tigloyl-4-deoxyphorbol-13-isobutyrate and daphnetoxin, produced dermatological toxicity in open patch tests at the doses used. Inflammatory signs and symptoms for several of the compounds under test persisted for over four days in open patch tests and for a week or more after application in closed patch testing.     

Comparative Relaxant Effects of the NO Donors Sodium Nitroprusside,DEA/NO and SPER/NO in Rabbit Carotid Arteries

• 1.Sodium nitroprusside (SNP, 10⁻⁹–3×10⁻⁴ M), diethylamine/NO complex (DEA/NO, 10⁻⁹–10⁻⁴ M) and spermine/NO complex (SPER/NO, 10⁻⁸–3×10⁻⁴ M) induced concentration-dependent relaxation of isolated rabbit carotid arteries precontracted with KCl (50 mM) or with histamine (3×10⁻⁶ M).
• 2.In KCl-precontracted arteries the order of potency was SNP=DEA/NO>SPER/NO, and in histamine-precontracted arteries the order of potency was SNP>DEA/NO>SPER/NO. Relaxations to the three NO donors were significantly higher in histamine-precontracted arteries than in KCl-precontracted arteries.
• 3.The guanylyl cyclase inhibitor methylene blue (10⁻⁵ M) significantly inhibited relaxations to the three NO donors in histamine-precontracted arteries and, to a lesser extent, in KCl-precontracted arteries.
• 4.In conclusion, the NO donors SNP, DEA/NO and SPER/NO induce quantitatively different relaxation of rabbit carotid artery. Both, lower relaxant effects in depolarized arteries and inhibition of relaxation by methylene blue indicate the mediation of cGMP formation in the relaxant effects of the three NO donors.

     

Responses of human and baboon arteries to prostaglandin endoperoxides and biologically generated and synthetic prostacyclin: their relevance to cerebral arterial spasm in man.

1 Isolated strips of human or baboon basilar, middle cerebral, vertebral or common carotid arteries were set up in an isolated organ bath or in a superfusion cascade system. 2 These arteries relaxed to prostacyclin but contracted to prostaglandin endoperoxide (PGH2). 3 Human and baboon isolated arteries also generated prostacyclin from exogenous endoperoxide (PGH2). 4 Human arteries generated prostacyclin 36 h post-mortem but not 40 h post-mortem. The biologically generated prostacyclin relaxed the basilar artery and overcame the contractile effects of PGH2. 5 Thromboxane A2-like activity generated during human platelet aggregation by arachidonic acid caused contractions of the human basilar artery. 6 Prostacyclin reversed contractions of human basilar arteries caused by an unidentified vasoconstrictor factor in cerebrospinal fluid obtained from patients with cerebral arterial vasospasm after subarachnoid haemorrhage following rupture of cerebral arterial aneurysms. 7. The above vasospasm may be due at least in part to disordered physiological control of the calibre of cerebral arteries caused by diminished synthesis of prostacyclin.     

Effects of angiotensin I and angiotensin II in blood vessels: greater influence of converting enzyme activity in the rabbit basilar artery

We investigated the constrictor effects of Angiotensin I (Ang I) and Angiotensin II (Ang II) on rabbit peripheral (aorta, carotid artery, mesenteric artery, saphenous artery) and cerebral (basilar artery) vessels and in rat aorta in functional organ bath studies. The effect of angiotensin converting enzyme (ACE) inhibition by captopril was also assessed in these preparations. Ang II elicited concentration-dependent contractions with comparable potency in rabbit and rat endothelium-free vascular rings (pD₂ about 8.5) which indicates a lack of species and regional variation in the contractile responses to Ang II. The responses to Ang II were reduced by the presence of a functional endothelium in rabbit mesenteric artery and in rat aorta. Since ACE determines the plasma and tissue conversion of Ang I to active Ang II, we calculated the ratio R (EC₅₀ Ang I-induced contraction: EC₅₀ Ang II-induced contraction) as an indicator of the tissue ACE effectiveness. In the aorta without endothelium, Ang I was found to be much less potent than Ang II in the rabbit (R = 44) compared with the rat (R = 3.5). This species difference in the aortic conversion of Ang I to Ang II was confirmed by the use of captopril. Captopril (10^–6M) shifted the Ang I concentration/response curve by 2- and 14-fold to the right in rabbit and rat respectively. In other rabbit blood vessels, the rank order of potency to Ang I in endothelium denuded rings was basilar artery carotid artery aorta saphenous artery. In addition, the R value was the lowest for the basilar artery (R = 2.5). This is in agreement with the highest rightward shift (78-fold) of the Ang I concentration/response curve by captopril for basilar artery in comparison with only 3-, 8- and 3-fold shifts observed in carotid artery, saphenous artery and aorta respectively. In conclusion, our data provide evidence for a greater influence of ACE in rabbit basilar artery than in peripheral vessels.     

Pharmacological evidence for the 5-HT7 receptor mediating smooth muscle relaxation in canine cerebral arteries.

1. We investigated in the present study whether 5-HT is able to exert direct relaxant responses in canine basilar and middle cerebral arteries via the 5-HT7 receptor. 2. In arterial rings deprived of endothelium and pre-contracted with prostaglandin F2 alpha (2 microM), 5-HT, 5-carboxamidotryptamine (5-CT), 5-methoxytryptamine, sumatriptan or alpha-methyl-5-HT produced further increase in tone and/or slight relaxation. Blockade of 5-HT1B 1D and 5-HT2A receptors with GR127935 (1 microM) and ketanserin (0.1 microM), respectively, antagonized the vasoconstrictor component of the response and unmasked a concentration-dependent relaxation to 5-HT, 5-CT and 5-methoxytryptamine; sumatriptan and alpha-methyl-5-HT remained inactive as relaxant agonists. The rank order of agonist potency in both arteries was 5-CT > 5-HT > 5-methoxytryptamine > sumatriptan > or = alpha-methyl-5-HT. 3. In dog basilar artery, pre-incubated with GR127935 (1 microM) and ketanserin (0.1 microM) and precontracted with prostaglandin F2 alpha (2 microM), the 5-HT7 ligands, clozapine (1 microM), mesulergine (0.3 microM), methiothepin (3 nM), risperidone (3 nM), spiperone (1 microM) and LY215840 (10-100 nM), produced significant rightward shifts of the concentration-response curves for 5-HT and 5-CT. Only methiothepin and risperidone reduced significantly the maximum relaxant response (Emax), whilst the other drugs behaved as competitive antagonists with affinity values (pKB) that significantly correlated with their binding affinity (pKi) at recombinant 5-HT7 receptors. 4. These data disclosing the involvement of the 5-HT7 receptor in cerebrovascular relaxation may be strongly relevant in the light of: (1) the involvement of 5-HT in migraine; (2) the putative linkage between cephalovascular vasodilatation and migraine headache; and (3) the relatively high 5-HT7 receptor affinity of migraine prophylactic 5-HT antagonists.