Contribution of Splenic Resistance Arteries to Splanchnic Blood Overflow in Cirrhosis.

BACKGROUND: In liver cirrhosis, a marked splanchnic vasodilation causes an increase in portal blood flow, contributing to the development of portal hypertension. AIM: To evaluate if, in experimental cirrhosis, a different vascular reactivity exists between splenic and mesenteric components of the splanchnic circulation. METHODS: Liver cirrhosis was induced in Sprague Dawley rats by common bile duct ligation. In sections of splenic and superior mesenteric arteries, cumulative dose-response curves were obtained. mRNA expression of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), and prostaglandin I2 synthase (PTGIS) was evaluated. RESULTS: In cirrhotic rats, mesenteric but not splenic arteries showed a significant increase in endothelium-dependent relaxation to acetylcholine. In control and cirrhotic rats, COX inhibition alone did not significantly change the response of mesenteric arteries to acetylcholine; after inhibiting also NOS, the relaxation was completely abolished in control but only partially decreased in cirrhotic rats. After the inhibition of COX and NOS, the relaxation to acetylcholine was similarly decreased in splenic arteries from control and cirrhotic animals. The contraction induced by phenylephrine of both mesenteric and splenic arteries was decreased in cirrhotic rats. PTGIS mRNA expression did not differ in splenic and mesenteric arteries from control and cirrhotic rats; in cirrhotic rats, eNOS and iNOS mRNA expression was increased in mesenteric but not in splenic vascular bed. CONCLUSION: In cirrhotic rats, a decreased splenic arterial response to vasoconstrictors, rather than an increased response to vasodilators, contributes to splanchnic vasodilation, while in mesenteric arteries also an increased response to vasodilators secondary to, but not only, eNOS and iNOS overexpression, plays a role.

Proximal Splenic Artery Embolization in Chemotherapy-Induced Thrombocytopenia: A Retrospective Analysis of 13 Patients.

PURPOSE: To determine if proximal splenic artery embolization (PSAE) provides a safe and effective alternative to alleviate chemotherapy-induced thrombocytopenia (CIT), allowing patients with cancer to resume chemotherapy regimens. MATERIALS AND METHODS: Thirteen patients (9 men, 4 women; mean age, 63 y) with underlying malignancy (pancreatic adenocarcinoma, n = 6; cholangiocarcinoma, n = 5; other, n = 2) complicated by CIT underwent PSAE. Mean platelet counts were calculated before the initiation of chemotherapy, at the nadir that resulted in discontinuation of chemotherapy before the PSAE procedure, at peak values after the procedure, and at a mean follow-up of 9.2 months. The time to reinitiation of chemotherapy after PSAE was calculated. RESULTS: Baseline platelet count before initiation of chemotherapy was 162 × 10(9)/L (range, 90-272 × 10(9)/L). The platelet count nadir resulting in cessation of chemotherapy was 45 × 10(9)/L (range, 23-67 × 10(9)/L), and the pre-PSAE platelet count was 88 × 10(9)/L (range, 49-131 × 10(9)/L). The post-PSAE peak platelet count improved significantly (to 209 × 10(9)/L; range, 83-363 × 10(9)/L) compared with the nadir counts and the pre-PSAE counts (P < .01) at a mean short-term follow-up of 35 days (range, 7-91 d). The counts at follow-up to 9.2 months (range, 3-15 mo) were 152 × 10(9)/L (range, 91-241 × 10(9)/L). All patients became eligible to resume chemotherapy. The time to initiation of chemotherapy after PSAE averaged 22 days (range, 4-58 d) in 12 patients; one patient declined chemotherapy. CONCLUSIONS: Proximal splenic artery embolization appears to be safe and effective in alleviating CIT, allowing resumption of systemic chemotherapy. Further studies may help guide patient selection by identifying characteristics that allow a sustained improvement in thrombocytopenia.

Distinct mechanisms of relaxation to bioactive components from chamomile species in porcine isolated blood vessels.

German chamomile (Matricaria recutita L.), a widely-used herbal medicine, has been reported to have a wide range of biological effects, including smooth muscle relaxation. The aim of this study was to compare the effects of representative compounds from chamomile (apigenin, luteolin, (-)-α-bisabolol, farnesene, umbelliferone; 3-30 µM) on vascular tone using porcine coronary and splenic arteries mounted for isometric tension recording in isolated tissue baths and precontracted with the thromboxane-mimetic U46619. Apigenin, luteolin, and (-)-α-bisabolol produced slow, concentration-dependent relaxations in both the coronary and splenic arteries that were not blocked by inhibition of nitric oxide synthase or potassium channels. Removal of extracellular calcium inhibited the relaxations to all three compounds, and these compounds also inhibited calcium re-addition-evoked contractions, indicating that the relaxation response may be mediated through inhibition of calcium influx. Apigenin and luteolin, but not (-)-α-bisabolol, enhanced the relaxation to the nitric oxide donor sodium nitroprusside, indicating that apigenin and luteolin may act to regulate cyclic GMP levels. Umbelliferone produced a rapid, transient relaxation in the splenic artery, but not the coronary artery, that was inhibited by L-NAME and removal of the endothelium, suggesting an influence on nitric oxide production. Farnesene, at concentrations up to 30 µM, was without effect in either blood vessel. In conclusion, hydroxylated compounds (apigenin, luteolin and (-)-α-bisabolol) found in chamomile all caused a slow relaxation of isolated blood vessels through an effect on calcium influx. Umbelliferone, on the other hand, produced a rapid, transient relaxation dependent upon release of nitric oxide from the endothelium.

Pre-contraction with the thromboxane-mimetic U46619 enhances P2X receptor-mediated contractions in isolated porcine splenic artery.

We have previously demonstrated that the thromboxane-mimetic U46619 enhances α(2)-adrenoceptor-mediated contractions through increased activation of extracellular signal-regulated kinase (ERK). In this study, we determined whether U46619 also enhances P2X-mediated contractions through the same pathway. Segments of porcine splenic artery were mounted in isolated tissue baths. Tissues were pre-contracted with U46619 to 10-20% of the response to 60 mM KCl prior to addition of α,ß-methylene ATP (P2X receptor agonist). The effect of inhibition of ERK activation with the mitogen-activated protein (MAP)/ERK kinase inhibitor PD98059 (50 µM), Rho kinase inhibition with Y27632 (10 µM), p38 MAP kinase with SB203580 (10 µM) or L-type calcium channels with nifedipine (1 µM) on both the direct and enhanced contractions was then determined. U46619 enhanced the contractions to α,ß-methylene ATP. Although PD98059 inhibited the direct contractions to α,ß-methylene ATP, it had no effect on the U46619-enhanced contractions. Similarly, Y27632 and SB203580 inhibited the direct contractions to α,ß-methylene ATP, but had no effect on the enhanced contractions. Nifedipine inhibited the responses to α,ß-methylene ATP in the absence and presence of U46619. This study demonstrates that pre-contraction with U46619 enhances P2X-mediated contractions in the porcine splenic artery through a mechanism independent of ERK, Rho kinase and p38 MAP kinase. Further studies are required to determine the exact mechanism involved.

The impacts of different embolization techniques on splenic artery embolization for blunt splenic injury: a systematic review and meta-analysis.

BACKGROUND: Splenic artery embolization (SAE) has been an effective adjunct to the Non-operative management (NOM) for blunt splenic injury (BSI). However, the optimal embolization techniques are still inconclusive. To further understand the roles of different embolization locations and embolic materials in SAE, we conducted this system review and meta-analyses. METHODS: Clinical studies related to SAE for adult patients were researched in electronic databases, included PubMed, Embase, ScienceDirect and Google Scholar Search (between October 1991 and March 2013), and relevant information was extracted. To eliminate the heterogeneity, a sensitivity analysis was conducted on two reduced study sets. Then, the pooled outcomes were compared and the quality assessments were performed using Newcastle-Ottawa Scale (NOS). The SAE success rate, incidences of life-threatening complications of different embolization techniques were compared by χ2 test in 1st study set. Associations between different embolization techniques and clinical outcomes were evaluated by fixed-effects model in 2nd study set. RESULTS: Twenty-three studies were included in 1st study set. And then, 13 of them were excluded, because lack of the necessary details of SAE. The remaining 10 studies comprised 2nd study set, and quality assessments were performed using NOS. In 1st set, the primary success rate is 90.1% and the incidence of life-threatening complications is 20.4%, though the cases which required surgical intervention are very few (6.4%). For different embolization locations, there was no obvious association between primary success rate and embolization location in both 1st and 2nd study sets (P > 0.05). But in 2nd study set, it indicated that proximal embolization reduced severe complications and complications needed surgical management. As for the embolic materials, the success rate between coil and gelfoam is not significant. However, coil is associated with a lower risk of life-threatening complications, as well as less complications requiring surgical management. CONCLUSIONS: Different embolization techniques affect the clinical outcomes of SAE. The proximal embolization is the best option due to the less life-threatening complications. For commonly embolic material, coil is superior to gelfoam for fewer severe complications and less further surgery management.

[Application of perfusion of low molecular dextran via splenic artery in portal azygous devascularization for portal hypertension].

OBJECTIVE: To evaluate the effects of the perfusion of low molecular dextran via the splenic artery in portal azygous devascularization for portal hypertension in the prevention from portal vein thrombosis. METHODS: A total of 92 patients with portal hypertension were randomly divided into a control group (46 cases) that received the extensive devascularization around the cardia, and a trial group (46 cases) that received the above-mentioned operation and the perfusion of low molecular dextran via the splenic artery. The incidence of portal vein thrombus after the operation and the preoperative and postoperative blood transfusion were observed and the results were analyzed and compared between the two groups. RESULTS: The incidence of thrombosis and blood transfusion were 26.1% (12/46) and CRBC 4~6 U respectively in the control group, while those were 4.3% (2/46) and CRBC 2~3 U respectively in the trial group. The differences were statistically significant (P < 0.05). CONCLUSION: The perfusion of low molecular dextran via the splenic artery in portal azygous devascularization for portal hypertension is effective and safe in the prevention from portal vein thrombosis.

Antagonism of the response of human isolated arteries to noradrenaline.

1. Spirally-cut strips from human visceral arteries isolated in vitro were contracted by noradrenaline and this contraction was antagonized by the alpha-receptor blocking agent, thymoxamine.2. The cumulative log dose-response curves to noradrenaline in the presence of thymoxamine were moved to the right of and parallel to the curve for noradrenaline alone. The blockade was surmountable and reversible.3. The quantitative criteria for simple competitive antagonism were satisfied. When log (x - 1) was plotted against pA(x) the points fitted a straight line with a slope (-n) of 0.91. The pA(2) for thymoxamine was 7.54 and the mean value for log K(2) was 7.82. These values are in approximate agreement with those previously reported for animal isolated arterial strips.

The role of endothelial cells in the relaxations induced by 13-hydroxy- and 13-hydroperoxylinoleic acid in canine arteries.

1. One of the major fatty acids in the arterial wall is linoleic acid. It has been shown that its 13-hydroxy metabolite (13-HODE) is generated in significant amounts by cultured endothelial cells. The aim of the present study was to investigate the relaxations to 13-HODE and its hydroperoxyprecursor (13-HPODE) and to examine the role of the endothelial cells. 2. Ring segments of canine circumflex and splenic artery were mounted in organ chambers for isometric tension recording. During contractions induced by prostaglandin F2 alpha or noradrenaline, 13-HODE and 13-HPODE evoked dose-dependent relaxations. Removal of the endothelial cells reduced the relaxations to 13-HODE, but had no effect on those elicited by 13-HPODE. 3. Indomethacin and meclofenamate (0.3 microM to 30 microM) blocked the relaxations evoked by 13-HODE and 13-HPODE in endothelium-denuded rings. In segments with endothelium, both cyclo-oxygenase inhibitors again abolished the relaxations to 13-HODE, but only diminished those to 13-HPODE. 4. Prostacyclin biosynthesis, as measured by radioimmunoassay, increased upon incubation with 13-HODE and 13-HPODE (10 microM). Bioassay of the release of nitric oxide (NO) indicated that NO was not involved in the relaxations elicited by either metabolite. Moreover, L-NG-nitroarginine (100 microM), a specific inhibitor of NO synthesis, did not influence the relaxations to 13-HODE and 13-HPODE. The responses to 13-HPODE were also not altered by superoxide dismutase. 5. In the splenic artery 13-HPODE and 13-HODE induced contractions above 3 microM which were blocked by the thromboxane receptor antagonist, daltroban.In the circumflex artery contractile responses to high concentrations of 13-HODE could be observed only after inhibition of cyclo-oxygenase.6. We conclude that the vasodilatation induced by 13-HODE and 13-HPODE was due to stimulation of prostacyclin biosynthesis both in the endothelium and smooth muscle cells or other subendothelial structures. An additional, unidentified intermediate, which was neither NO nor a cyclo-oxygenase product nor superoxide anion, contributed to the relaxations to 13-HPODE in arteries with endothelium.

Effects of a selective neuropeptide Y Y(1) receptor antagonist BIBP 3226 on double peaked vasoconstrictor responses to periarterial nerve stimulation in canine splenic arteries.

The periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient constriction (first peak) followed by a prolonged response (second peak) in the isolated, perfused canine splenic artery. At low frequencies (1 and 4 Hz), a neuropeptide Y (NPY) Y(1) receptor antagonist BIBP 3226 (0.1-1 microM) produced a dose-dependent inhibitory effect on the second peak, but did not modify the first peak. At a high frequency (10 Hz), 1 microM BIBP 3226 induced a slight, but significant inhibition on both the first and second peaked responses. At a low frequency (1 Hz), the first peak was not influenced by blockade of alpha(1)-adrenoceptors or NPY Y(1) receptors with prazosin (0.1 microM) or BIBP 3226 (1 microM), respectively, but abolished by P2X receptor desensitization with alpha,beta-methylene ATP (alphabeta-m ATP, 1 microM). At a high frequency (10 Hz), the first peak was mostly inhibited by alphabeta-m ATP and partially by prazosin and BIBP 3226. On the other hand, the second peak at a low frequency was largely decreased by BIBP 3226 and partially by prazosin and alphabeta-m ATP, whereas at a high frequency, it was largely attenuated by prazosin and partially by alphabeta-m ATP and BIBP 3226. The results suggest that at a low frequency, the firstly transient constriction of double peaked responses is mainly induced via an activation of P2X-receptors, whereas at a high frequency, it is mostly mediated by the P2X-receptors, and partially by alpha(1)-receptors and NPY Y(1)-receptors. The secondary prolonged vasoconstriction at frequencies used is predominantly mediated via both alpha(1)-receptor and NPY Y(1) receptor activations, and in part by P2X-receptors. Furthermore, an activation of NPY Y(1) receptors may play an important role in evoking the prolonged vasoconstrictor response to longer pulse trains of stimulation at a low frequency, whereas an alpha(1)-adrenoceptor activation exerts a main vasomotor effect for the prolonged response at a high frequency.

Differential effects of omega-conotoxin GVIA and tetrodotoxin on vasoconstrictions evoked by electrical stimulation and nicotinic receptor stimulation in canine isolated, perfused splenic arteries.

1. The effects of omega-conotoxin GVIA (omega-CgTX) and tetrodotoxin (TTX) on vasoconstrictions induced by acetylcholine (ACh) and nicotine were investigated and compared with those induced by periarterial electrical stimulation in the isolated and perfused canine splenic arteries. 2. ACh and nicotine at doses of 0.01 to 1 mumol constricted the splenic artery, dose-dependently. ACh induced consistent responses, but the vasoconstrictor responses to nicotine became significantly smaller with repeated administration of nicotine. 3. Periarterial electrical stimulation produced a vasoconstriction that was abolished by either TTX (30 nmol) or omega-CgTX (3 nmol), but the vasoconstrictor response to nicotine was not significantly affected by the same doses of TTX and omega-CgTX. Inhibitions by TTX and omega-CgTX of ACh-induced vasoconstrictions were small but statistically significant, showing that the percentage inhibition was less than 15%. TTX and omega-CgTX did not affect the vasoconstrictor responses to exogenous noradrenaline (NA). 4. ACh did not produce any vasoconstriction in the preparations treated either with alpha-adrenoceptor antagonists (10 microM bunazosin and 10 microM midaglizole) or with 30 microM guanethidine. NA-induced responses were abolished by alpha-adrenoceptor antagonists, but not affected by guanethidine treatment. 5. Vascular responses to ACh were completely inhibited by 1 mumol hexamethonium. In the preparations treated with 100 nmol nicotine, ACh did not produce any vasoconstriction. However, the NA-induced vasoconstriction was affected by neither hexamethonium nor nicotine treatment. 6. Atropine (1 microM) significantly inhibited but did not abolish the vasoconstrictor responses to ACh. The vascular responses to nicotine and NA were also significantly inhibited by atropine treatment. 7. These results indicate that (1) ACh constricts the splenic artery through the activation of presynaptic nicotinic receptors present on the sympathetic nerves; (2) differential effects of TTX and omega-CgTX on the vascular responses to ACh and nicotine, and to electrical stimulation suggest that the receptor-operated ion channels are mainly responsible for NA release induced by nicotinic receptor stimulation, but N-type VOCCs are responsible for that by electrical stimulation; (3) atropine may have an inhibitory action on nicotine-related responses, in addition to its inhibitory action on NA.

Pharmacological evidence for the presence of a peripheral postjunctional D2-like dopamine receptor in rabbit splenic artery.

1. This study was designed to investigate the involvement of postjunctional D2-like receptors in a rabbit vasculature model used to evaluate the D1-like agonist activity. Dopamine, epinine and (-)-DP-5,6-ADTN, three mixed D1/D2-like agonists, fenoldopam and SKF 82958, two selective D1-like agonists and SKF 89124, a selective D2-like agonist, were administered cumulatively in precontracted and alpha/beta-blocked rabbit splenic artery rings in order to evaluate their D1-like-mediated vasorelaxant activity before and after pretreatment with the selective D2-like antagonist YM 09151-2 (1 nM). 2. Dopamine (pD2=6.35+/-0.09), epinine (pD2=6.73+/-0.13), (-)-DP-5,6-ADTN (pD2=7.56+/-0.09) and SKF 82958 (pD2=8.55+/-0.10) reversed completely the U46619-induced contracture whereas SKF 89124 was inactive up to 10 microM and fenoldopam acted like a partial agonist (pD2=8.31+/-0.09, alpha=0.62). The selective D2-like dopamine receptor antagonist YM 09151-2 (1 nM) significantly (P<0.05) potentiated the vasorelaxant activity of dopamine (pD2=7.01+/-0.07), epinine (pD2=7.14+/-0.08), (-)-DP-5,6-ADTN (pD2=8.19+/-0.09) and SKF 89124 (40% relaxation at 10 microM), whereas it did not alter the effects of fenoldopam (pD2=8.40+/-0.09, alpha=0.68) and SKF 82958 (pD2=8.58+/-0.08). 3. The D2-like antagonist YM 09151-2 induced the same degree of effect with all the substances tested in both endothelium-denuded and endothelium-intact preparations. 4. The selective D2-like dopamine receptor agonist SKF 89124 did not produce any intrinsic effect on the splenic artery, but was able to produce a rightward shift of the forskolin-induced relaxation. 5. The results of these experiments support the existence of a non-endothelial postjunctional D2-like dopamine receptor counteracting the D1-like-mediated vasodilatation in rabbit splenic artery, probably by the inhibition of adenylate cyclase.

Effects of prolonged cold storage on double peaked vasoconstrictor responses to periarterial nerve stimulation in isolated canine splenic arteries.

1. P2X-Purinoceptors and alpha1-adrenoceptors have previously been shown to involve in the double peaked vasoconstrictor responses to periarterial electrical nerve stimulation in the isolated and perfused canine splenic artery. The present study made an attempt to investigate effects of prolonged cold storage (7 days at 4 degrees C) on vasoconstrictor responses to periarterial electrical nerve stimulation, tyramine, noradrenaline and adenosine 5'-triphosphate (ATP) in the isolated canine splenic artery. 2. The periarterial nerve stimulation (1-10 Hz) readily causes a double peaked vasoconstriction in the non-stored preparations. After cold stored for 7 days, the double peaked vasoconstriction was still recognized, although the response became significantly smaller. The first phase was decreased relatively greater than the second phase by the cold storage. 3. In the cold stored preparations, the dose-response curve for tyramine was shifted to the right in a parallel manner. Prazosin almost completely inhibited tyramine-induced vasoconstriction but alpha,beta-methylene ATP failed to influence the response to tyramine. 4. The vasoconstrictor responses to noradrenaline and ATP were not significantly modified by the prolonged cold storage. 5. From these results, it is concluded that the functions of sympathetic co-transmission of purinergic components might be influenced more than that of adrenergic components in the cold storage canine splenic artery.

Existence of different alpha(1)-adrenoceptor subtypes in junctional and extrajunctional neurovascular regions in canine splenic arteries.

The present study attempted to characterize the alpha(1)-adrenoceptor subtypes mediating vasoconstrictor responses to administered and nerve stimulation-evoked noradrenaline (NA) release in the isolated and perfused canine splenic artery. A previous study demonstrated that periarterial electrical nerve stimulation (30 s trains of pulses at a frequency of 1, 4 or 10 Hz) induced a double peaked vasoconstriction consisting of an initial transient, predominantly P2X-purinoceptor-mediated constriction followed by a prolonged, mainly alpha(1)-adrenoceptor-mediated response in the canine splenic artery. The effects of alpha(1)-adrenoceptor subtype antagonists on neuronally-mediated second peaked vasoconstrictions were analysed. BMY 7378 (10 - 100 nM), a selective alpha(1D)-adrenoceptor antagonist produced a dose-dependent inhibition of the second peak responses at all frequencies used. BMY 7378 (100 nM) reduced these responses by approximately 30%. Exposure of tissues to chloroethylclonidine (CEC, 60 microM), a selective alpha(1B)-adrenoceptor antagonist attenuated the second peak response by approximately 60%, even in the presence of BMY 7378 (100 nM). On the other hand, WB 4101 (100 nM), a selective alpha(1A)-adrenoceptor antagonist potentiated nerve-stimulation-evoked double peaked vasoconstrictions, especially at low frequencies (1 and 4 Hz). Vasoconstrictor responses to administered NA were dose-dependently antagonized by WB 4101 (10 - 100 nM), but were not significantly affected by either BMY 7378 (10 - 100 nM) or by CEC (60 microM). The present results indicate that NA released from sympathetic nerves may junctionally exert its vasoconstrictor effect via activation of postjunctional alpha(1B)- and in part alpha(1D)-adrenoceptors, whereas exogenous NA extrajunctionally activates alpha(1A)-adrenoceptors to produce its vascular action in canine splenic arteries.

Prominent sympathetic purinergic vasoconstriction in the rabbit splenic artery: potentiation by 2,2'-pyridylisatogen tosylate.

1. Vasoconstrictions induced by transmural electrical field stimulation were frequency-dependent from 2 to 32 Hz in the rabbit isolated splenic artery. All contractions were abolished in the presence of tetrodotoxin 1 microM or guanethidine 100 microM. Stimulation at a frequency of more than 32 Hz induced both neurogenic and myogenic responses. 2. Prazosin (1 microM) did not significantly affect vascular contractions to electrical stimulation. Desensitization of P2X-purinoceptors with alpha, beta-methylene ATP (alpha, beta-meATP, 3 microM) abolished the contractions to stimulation at 2-8 Hz and inhibited more than 80% of the vascular response at 16 Hz, but it did not significantly change the responses at 32 Hz. Contractile responses at 32 Hz were inhibited by a combination of prazosin and alpha, beta-meATP. Effects of pyridoxal-phosphate-6-azophenyl-2', 4'-disulphonic acid tetrasodium salt (a selective P2X-purinoceptor antagonist) and suramin (a competitive P2-purinoceptor antagonist) on the neurogenic responses were investigated in this study. 3. 2,2'-Pyridylisatogen tosylate (PIT, 0.3-3 microM) significantly potentiated the vasoconstrictions to electrical stimulation at 2-32 Hz in a concentration-dependent manner. Potentiated responses were restored to the control level 30 min after washing. Concentration-dependent response curves for noradrenaline (NA) or alpha, beta-meATP were not significantly changed by 3 microM PIT, and vasoconstriction by adenosine 5'-triphosphate (ATP, 300 microM) was unaffected by PIT. Coomassie brilliant blue-G (1 microM), which shares the potentiating effect on a recombinant P2Y-purinoceptor with PIT (King et al., 1996), did not inhibit or potentiate the purinergically-mediated component of the response to sympathetic nerve stimulation. The selective alpha 2-adrenoceptor antagonist yohimbine (1 microM) also potentiated the vascular responses to electrical stimulation. 4. The present results indicate that ATP evokes postjunctional contractile responses at low and high frequency electrical stimulation of sympathetic nerves supplying the rabbit splenic artery. PIT potentiates the responses to sympathetic (purinergic) nerve stimulation; this appears to be mainly via prejunctional rather than postjunctional actions.

Effects of omega-conotoxin GVIA and diltiazem on double peaked vasoconstrictor responses to periarterial electric nerve stimulation in isolated canine splenic artery.

The actions of omega-conotoxin (omega-CTX) and diltiazem on adrenergic and purinergic components of double peaked vasoconstrictor responses to periarterial nerve stimulation have been investigated in the isolated, perfused canine splenic arterial preparation. Double peaked vasoconstrictions (biphases of vasoconstrictors) were consistently observed in the conditions of 30 s trains of pulses at 1 - 10 Hz frequencies. omega-CTX (1 - 30 nM) produced similar inhibitory effects on the first phase and second phase responses in a dose-related manner. Thirty nM omega-CTX almost completely inhibited the biphasic vasoconstrictions at any used frequencies but did not affect the vasoconstrictor responses to exogenous applied ATP (0.01 - 1 micromol) and noradrenaline (0.03 - 3 nmol). Intraluminal application of a large dose of diltiazem (3 - 10 microM) also produced a dose-dependent inhibitory effect on biphasic vasoconstrictions at any used frequencies. Three microM diltiazem exerted rather a larger inhibitory effect on the second phase than the first phase response at low frequencies (1 - 3 Hz), but a similar inhibition on first and second phasic responses at high frequencies (6 - 10 Hz). An extremely high dose of diltiazem (10 microM) almost completely inhibited the biphasic vasoconstrictor responses to nerve stimulation, and slightly inhibited the contractile responses to exogenous applied ATP (0.01 - 1 micromol) and noradrenaline (0.03 - 3 nmol). The present results indicate that omega-CTX selectively acts prejunctionally to inhibit the release of transmitters from sympathetic nerve terminals, and omega-CTX-sensitive calcium channels may produce a parallel controlling of purinergic and adrenergic components of sympathetic cotransmission. A large dose of diltiazem has inhibitory effects on both prejunctional and postjunctional sympathetic co-transmission. British Journal of Pharmacology (2000) 129, 47 - 52

The relationship between density of alpha-adrenoceptor binding sites and contractile responses in several porcine isolated blood vessels.

1. The aim of this study was to investigate constrictor alpha-adrenoceptors in three isolated blood vessels of the pig, the thoracic aorta (TA), the splenic artery (SA) and marginal ear vein (MEV) and then compare the functional response with the densities of alpha 1- and alpha 2-adrenoceptor binding sites in these and several other porcine vascular tissues, palmar common digital artery (PCDA), palmar lateral vein (PLV) and ear artery (EA). 2. Noradrenaline (NA), phenylephrine (PE) and UK14304 (all at 0.03-10 microM) elicited concentration-dependent contractions in the TA and MEV, with a rank order of potency of UK14304 > NA > PE. UK14304 produced maximal responses which were 58% (TA) and 65% (MEV) of that of NA. In the SA, UK14304 and PE produced maximal responses which were less than 10% and 50% of the NA-induced maximal response respectively, with an order of potency of NA > PE. In the SA, NA-induced contractions were competitively antagonized by prazosin (pA2 = 8.60 +/- 0.15). Further, rauwolscine (1-10 microM) antagonized NA-induced contractions with an apparent pKB of 6.09 +/- 0.11 (n = 6), indicating an action at alpha 1-adrenoceptors. The combination of the two antagonists at concentrations selective for alpha 1- (0.1 microM) and alpha 2-adrenoceptors (1 microM) had no greater effect than either antagonist alone. This suggests that the SA expresses only post-junctional alpha 1-adrenoceptors. 3. In the TA, prazosin produced non-parallel shifts in the NA-induced CRC and this was also observed with rauwolscine, where reductions in the maximal responses were also observed. In the MEV, prazosin was largely inactive in antagonizing NA-induced contractions. In both these vessels a combination of these two antagonists had a greater effect than either alone, indicating the presence of functional alpha 1- and alpha 2-adrenoceptors. The post-junctional alpha 2-adrenoceptors in all of these vessels were resistant to prazosin, suggesting the alpha 2-adrenoceptor to be of the alpha 2A/2D subtype. The expression of functional alpha 2-adrenoceptors was MEV > TA > PLV > PCDA > SA. 4. In radioligand binding studies using TA P2 pellet membranes, [3H]-prazosin and [3H]-RX821002 ([1,4-[6,7(n)-3H] benzodioxan-2-methoxy-2-yl)-2-imidazole) labelled different high affinity sites, and in competition studies using identical membranes corynanthine displaced [3H]-prazosin with 10 fold higher affinity than rauwolscine, indicating that [3H]-prazosin was selectively binding to alpha 1-adrenoceptor sites. Further, rauwolscine displaced [3H]-RX821002 with approximately 100 fold greater affinity compared to corynanthine, which is indicative of selective alpha2-adrenoceptor binding.5. Separation of the P2 pellet into plasma membrane and mitochondrial fractions was carried out using a differential sucrose density gradient. [3H]-prazosin and [3H]-RX821002 binding sites were found in both the plasma membrane and mitochondrial fractions.6. In saturation studies all tissues produced single site saturation curves with no difference in the Kd(range 0.13-0.20nM) of the alpha1-adrenoceptor sites for [3H]-prazosin. However, there was considerable variation in Bmax of alpha 1-adrenoceptor sites; the highest density was found in the TA (397.9 =/- 52.7 fmol mg-1, n = 4), followed by the PCDA (256.7 +/- 22.7 fmol mg-1, n = 4), the PLV and SA having approximately equal density (143.6 +/- 3.9 and 159.1 +/- 7.0 fmol mg-1 respectively, n = 4 for both), followed bythe EA (91.3 +/- 10.5 fmol mg-1, n = 3) and the MEV had the lowest density (48.9 +/- 11.4 fmol mg-1,n = 3).7. In saturation studies using [3H]-RX821002, all tissues produced single site saturation curves with no differences in the Kd values (range 1.31 +/- 2.16 nM) but the highest densities were found in the TA and MEV (545.3 +/- 36.2 and 531.0 +/- 40.9 fmol mg-1 respectively), followed by the PLV (418.4 +/- 39.4 fmol mg-1), then the EA (266.3 +/- 40.0 fmol mg-1), and low densities of [3H]-RX821002 binding being found in the PCDA and SA (155.9 +/- 18.1 and 117.5 +/- 19.3 fmol mg-1 respectively).8. The pattern of binding site distribution for alpha l- and alpha 2-adrenoceptors is in reasonable agreement with functional studies carried out in these porcine vascular tissues; the TA has the highest densities of alpha 1-and alpha2-adrenoceptors; in the SA and PCDA there is a predominance (although small) of alpha l-adrenoceptor binding sites, the reverse of which is observed both in the PLV and MEV (i.e. greater density of alpha2-adrenoceptor sites). Thus, it would appear that alpha 1- and alpha2-adrenoceptor densities play a role in the expression of functional responses via these receptor subtypes; although it is interesting to note that the SA did have a small density of alpha 2-adrenoceptor binding sites, no functional response was observed after alpha2-adrenoceptor activation.

The pharmacology of fenoldopam.

Fenoldopam is a selective dopamine1 (DA1) receptor agonist. Most of the DA1 receptor agonist activity of fenoldopam resides in the R-enantiomer, which also shows weaker alpha 2-adrenoceptor antagonist activity Fenoldopam produces vasodilation in vascular beds that are rich in vascular DA1 receptors, eg, renal and mesenteric receptors, and produces an increase in renal blood flow at doses that do not affect blood pressure. At higher doses, fenoldopam lowers blood pressure but still maintains renal perfusion. In addition to its renal vasodilator activity, fenoldopam is natriuretic, possibly resulting from a direct effect of DA1 receptors on the proximal convoluted tubule. In animals with spontaneous or drug-induced renal failure, fenoldopam improves renal function.

Purinergic and adrenergic transmission and their presynaptic modulation in canine isolated perfused splenic arteries.

Vasoconstrictions induced by periarterial electrical stimulation were analysed pharmacologically in the canine isolated perfused splenic artery. Phentolamine enhanced the vasoconstrictions at 1 Hz but inhibited those at 10 Hz. Suramin and P2x purinoceptor desensitization with alpha,beta-methylene ATP abolished the phentolamine-enhanced and -resistant vasoconstrictions. alpha,beta-Methylene ATP inhibited the vasoconstrictions at 1 Hz and by exogenous ATP but did not change those at 10 Hz and by exogenous noradrenaline. Suramin reduced the vasoconstrictions by the electrical stimulations and alpha,beta-methylene ATP but did not affect those by exogenous ATP. Prazosin did not affect the vasoconstrictions at 1 Hz but inhibited those at 10 Hz. Rauwolscine enhanced the prazosin-resistant vasoconstrictions. These results suggest that the electrical stimulation at 1 Hz releases purinergic transmitters (ATP or a closely related compound) as a dominant candidate for the vasoconstrictions, and a co-released noradrenaline may inhibit the release of purinergic transmitters through presynaptic alpha 2-adrenoceptors in the canine splenic artery.

Interaction between neuropeptide Y Y1 receptors and alpha1B-adrenoceptors in the neurovascular junction of canine splenic arteries.

Previous study has demonstrated that periarterial electrical nerve stimulation (30-s trains of pulses at a frequency of 1 or 4 Hz) induces a double-peaked vasoconstriction consisting of an initial transient, predominantly P2X-receptor-mediated constriction followed by a prolonged, mainly alpha(1)-adrenoceptor-mediated response in the isolated canine splenic artery. Treatment with 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY 7378, 0.1 micromol/l), a selective alpha(1D)-adrenoceptor antagonist, produced a slight but significant inhibition of the second peaked responses. A marked inhibition of second peaked responses was obtained by exposure of the tissues to chloroethylclonidine (60 micromol/l), an alpha(1B)- and alpha(1D)-adrenoeptor antagonist. Neither BMY 7378 nor chloroethylclonidine affected the first peaked vasoconstrictor responses. [Leu(31),Pro(34)]Neuropeptide Y (10-30 nmol/l), a selective neuropeptide Y Y(1) receptor agonist, enhanced the second peaked responses in the presence of BMY 7378 but failed to enhance the responses in the presence of chloroethylclonidine. The results indicate that the postjunctional alpha(1B)-adrenoceptor subtype is likely coupled to neuropeptide Y Y(1) receptors responsible for the cooperation of the sympathetic adrenergic and neuropeptide Yergic transmission in the canine splenic artery.

Characteristics of the dopamine receptors in the rabbit isolate splenic artery.

After blockade of alpha- and beta-adrenoceptors, the tension induced by PGF2alpha in splenic artery strips was relaxed by dopamine, 6, 7-ADTN, N-methyldopamine, apomorphine, N, N-di-n-propyl 5, 6-ADTN, N, N-di-n-propyl 6, 7-ADTN and Sandoz 27-403; their equipotent concentrations (relative to dopamine = 1) were 0.2: 0.3: 0.4: 1.1: 3.9 and 3.9 respectively. 5, 6 ADTN, N-methyl 5,6ADTN, N, N-diethyldopamine, N, N-di-n-propyldopamine and SKF 38393 were weakly active or inactive at relaxing the splenic artery strip. Bulbocapnine and cis-alpha-flupenthixol were specific, competitive, reversible antagonists of dopamine. Fluphenazine, clozapine, trifluoperazine, haloperidol and spiroperidol also antagonised dopamine, but were relatively weak antagonists and a small part of their action was non-specific. Sulpiride was inactive against dopamine. SKF 38393 selectively antagonised the effects of dopamine demonstrating that SKF 38393 has affinity, but little efficacy at the dopamine receptors in the splenic artery. The findings with both agonists and antagonists suggest that the vascular dopamine receptors in the rabbit splenic artery resemble those in the dog renal and mesenteric vascular beds.