Contraction Of Mesenteric Arteries Research Articles

Serotonin-induced contraction in mesenteric resistance arteries: signaling and changes in deoxycorticosterone acetate-salt hypertension.

Large arteries from hypertensive subjects are hyperresponsiveness to 5-hydroxytryptamine (5-HT). We tested the hypothesis that small arteries (225 micro ID) have a profile similar to conduit arteries, including signal transduction mechanisms and the 5-HT receptor subtype(s) mediating arterial contraction in normal and high blood pressure. Aorta and mesenteric arteries from Sprague-Dawley (232+/-6 micro ID), sham (229+/-7 micro ID; systolic blood pressure, 120+/-2 mm Hg), or deoxycorticosterone acetate (DOCA)-salt rats (255+/-11 micro ID, 192+/-8 mm Hg) were mounted in a wire-based myograph. In resistance arteries from Sprague-Dawley rats, the 5-HT2A receptor mediated contraction; agonists of the 5-HT1B, 5-HT1D, 5-HT1F, and 5-HT2B receptor were inactive. The tyrosine kinase inhibitor genistein (5 micromol/L, 4.8-fold rightward shift), PD 098,059 (10 micromol/L, 3.2-fold shift), phospholipase C inhibitor NCDC (100 micromol/L), and nifedipine (50 nmol/L) reduced maximum 5-HT-induced contraction in small arteries (4.5% and 53% control, respectively). As in aorta, 5-HT had a decrease in threshold (100-fold lower), increase in potency (11.6-fold leftward shift), and increase in efficacy (140% sham response) in small arteries from DOCA-salt rats compared with sham. Unlike in aorta, 5-HT-induced contraction in DOCA-salt small arteries was shifted competitively by the 5-HT2A receptor antagonist ketanserin (-log K(B) [mol/L] for both sham and DOCA-salt, 9.25+/-0.1), and contraction to the 5-HT2B agonist BW723C86 was not observed. Thus, the 5-HT2A receptor remains the contractile receptor in hypertension in small arteries. Although similarities were observed for large and small arteries, differences under the condition of DOCA-salt hypertension exist that may determine serotonergic compounds effective in lowering blood pressure.

Noradrenaline-Induced Paxillin Phosphorylation, ERK Activation and MEK-Regulated Contraction in Intact Rat Mesenteric Arteries

In rat mesenteric arteries, noradrenaline (NA) induces a time-dependent increase in tyrosine phosphorylation of a number of proteins, one of which was identified as paxillin. NA-induced protein tyrosine phosphorylation was ablated by tyrosine kinase inhibition, virtually unaffected by protein kinase C (PKC) inhibition or PKC downregulation and was mimicked by KCl. NA also caused a time-dependent activation of the extracellular signal-regulated kinases (ERK)1 and ERK2. These responses were blocked by the ERK-activating kinase (MEK) inhibitor PD98059 and by tyrosine kinase inhibition but only modestly attenuated by PKC downregulation or inhibition. Pretreatment of cannulated mesenteric arteries (50 mm Hg internal pressure) with PD98059 significantly reduced the contractile responsiveness of the vessels to NA (1.56 ± 0.14 µM, EC₅₀ control; 3.32 ± 0.49 µM, EC₅₀ + PD98059, p < 0.01). Thus, NA induces time-dependent increases in protein-tyrosine phosphorylation and ERK activation in rat mesenteric arteries that could suggest a role for Ca²⁺-dependent non-receptor tyrosine kinases and ERKs in the response of small arteries to NA. In addition, the modulation of NA-induced mesenteric artery contraction by inhibition of the MEK/ERK pathway further implicates ERK in the regulation of, though perhaps not the mediation of NA-induced small artery contraction.

Enhanced contraction to 5-hydroxytryptamine is not due to "unmasking" of 5-hydroxytryptamine(1b) receptors in the mesenteric artery of the deoxycorticosterone acetate-salt rat.

5-Hydroxytryptamine(1B) (5-HT(1B)) receptors have been implicated in mediating arterial contraction to 5-HT. Additionally, the 5-HT(1B) receptor has been reported to be "unmasked" by depolarizing stimuli. We hypothesized that 5-HT(1B) receptors in arteries from hypertensive animals, arteries reported to have a depolarized resting membrane potential in smooth muscle cells, are unmasked and participate in the supersensitivity observed to 5-HT in hypertension. We used the isolated tissue bath apparatus and examined the response of superior mesenteric arteries from normotensive sham and hypertensive deoxycorticosterone acetate (DOCA)-salt rats. The 5-HT(1B) agonists CP93129 and sumatriptan (10(-9) to 10(-5) mol/L) caused a maximal contraction (50+/-12% of phenylephrine [10(-5) mol/L] contraction) in arteries from DOCA-salt rats; no contraction was observed in arteries from normotensive rats. The 5-HT(1B) receptor antagonist GR55562 (100 nmol/L) inhibited both the 5-HT- (4-fold rightward shift) and CP93129-induced (11-fold rightward shift) contractions in mesenteric arteries from hypertensive DOCA-salt rats. In other experiments, arteries from normotensive rats were incubated with 15 mmol/L KCl, as a depolarizing stimulus, and then exposed to 5-HT and CP93129. In the presence of KCl, a small leftward shift to 5-HT was observed. However, the presence of a depolarizing stimulus was unable to produce changes in the 5-HT maximal response to resemble that of arteries from DOCA-salt rats, nor was contraction to CP93129 observed. These data support the conclusions that 5-HT(1B) receptors mediate contraction in mesenteric arteries from hypertensive rats and that this enhanced response to 5-HT is not due to membrane depolarization alone.

Effects of methylenedioxymethamphetamine on noradrenaline-evoked contractions of rat right ventricle and small mesenteric artery

We have compared the effects of methylenedioxymethamphetamine (MDMA) and cocaine on contractions to noradrenaline in 1 Hz paced rat right ventricular strips, and in rat small mesenteric artery and aorta. Noradrenaline increased the force of contraction of 1 Hz paced ventricular strips with a pD 2 (−log EC 50) of 5.64±0.07. Both cocaine (10 μM) and MDMA (10 μM) significantly increased the potency of noradrenaline to 6.31±0.11 and 6.42±0.13, respectively. However, in the presence of cocaine (10 μM) which increased the potency of noradrenaline to 6.78±0.15, MDMA (10 μM) no longer increased the potency of noradrenaline (pD 2 of 6.78±0.32). Likewise, following chemical sympathectomy, MDMA failed to increase the potency of noradrenaline. The potency of the agonist isoprenaline, which is not a substrate for the noradrenaline transporter, was not increased by either cocaine or MDMA. In rat small mesenteric artery, but not aorta, MDMA and cocaine significantly increased the potency of noradrenaline, but in the presence of cocaine, MDMA had no further effect. Hence, MDMA shares with cocaine an ability to potentiate the actions of noradrenaline, an action in the case of MDMA which may involve competitive blockade of the noradrenaline transporter, rather than simply displacement of noradrenaline. Since cocaine is linked to an increased incidence of myocardial infarction, these results may have implications in terms of cardiac morbidity of MDMA.

Nerve evoked P2X receptor contractions of rat mesenteric arteries; dependence on vessel size and lack of role of L-type calcium channels and calcium induced calcium release.

1. Contractile responses to short trains of nerve stimulation have been characterized in small, medium and large arteries from the rat mesenteric circulation (5th - 6th, 2nd - 3rd and 1st order, respectively). In addition, sources of calcium for smooth muscle contraction have been investigated. 2. Nerve stimulation (10 pulses at 10 Hz) evoked reproducible contractions. The P2 receptor antagonist suramin (100 microM) reduced constrictions by 65.3+/-7.4, 82.7+/-3.3 and 3.1+/-6.1% in small, medium and large arteries respectively. The alpha-adrenoceptor antagonist prazosin (0.1 microM) reduced responses by 32.6+/-2.6, 27.0+/-1.5 and 97.0+/-1.9% respectively. 3. The L-type calcium channel antagonist nifedipine (1 microM) reduced nerve-evoked contractions by 2.8+/-3.3, 10.0+/-3.7 and 13.5+/-2.7% in small, medium and large arteries respectively. When the adrenergic component of contraction was blocked by prazosin (0.1 microM) nifedipine reduced responses by 4.6+/-7.9, 14.3+/-2.0 and 3.0+/-1.9% respectively. Contractile responses to exogenous alpha,beta-meATP were unaffected by the depletion of calcium stores with cyclopiazonic acid (30 microM). This indicates that mobilization of calcium from internal stores is not required for P2X receptor mediated smooth muscle contraction. We conclude that for neurogenic responses, the P2X receptor mediated component of constriction dominates in small mesenteric arteries (3rd -- 6th order) while in large arteries (1st order) noradrenaline mediates contraction. For P2X receptor mediated responses all the calcium required for smooth muscle contraction enters the cell directly through P2X receptor channels.

Mechanisms of blockade by the novel migraine prophylactic agent, dotarizine, of various brain and peripheral vessel contractility

The novel antimigraineur, dotarizine, inhibited 5-HT (5 hydroxytryptamine)-evoked contractions of rabbit vertebral, aorta, femoral and mesenteric arteries, with IC 50s of 1.35, 1.40, 0.52 and 1.09 μM, respectively. Flunarizine had little effect on these contractions, while ketanserin was more potent (IC 50s of 0.17 μM for vertebral, 0.22 μM for aorta, 0.05 μM for femoral and 0.03 μM for mesenteric arteries). At 10 μM, dotarizine caused 40% blockade of K +-evoked contractions of rabbit aorta, and 70% inhibition of 5-HT-evoked responses; these values were 30% and 20% for 10 μM flunarizine. Contractions of rabbit aorta elicited by noradrenaline, angiotensin II or prostaglandin F 2α were not affected by 10 μM dotarizine or flunarizine. Ketanserin shifted to the right, in parallel, the concentration–response curves for 5-HT in rabbit aorta; however, dotarizine caused a non-competitive type of blockade, increasing the maximum 5-HT contraction at 30 nM and decreasing it at 3 and 30 μM. K +-evoked contractions of rabbit aorta were halved by 3 μM dotarizine in a voltage-independent manner; flunarizine caused a delayed-type, non-reversible post-drug blockade, and exhibited some voltage-dependence. Blockade by nifedipine was voltage-dependent and fully reversible. Ca 2+-evoked contractions of depolarised bovine middle cerebral arteries were blocked by 1–3 μM dotarizine in a non-surmountable manner. Contraction of these vessels evoked by electrical stimulation was blocked 50% and 70% by 1 and 3 μM dotarizine, respectively. Dotarizine (1–3 μM) also inhibited to a similar extent the K +-evoked [ 3H]noradrenaline release from cultured rat sympathetic neurones. These data suggest that the mechanism of blockade by dotarizine of cerebral vessels contractility has three components: (i) presynaptic inhibition of noradrenaline release; (ii) blockade of postsynaptic vascular 5-HT receptors; (iii) blockade of Ca 2+entry into the vascular smooth muscle cell cytosol. The compound does not affect the vascular receptors for noradrenaline, angiotensin II or prostaglandin F 2α.

Endothelin-1-induced contraction of mesenteric small arteries is mediated by ryanodine receptor Ca2+ channels and cyclic ADP-ribose.

Contraction of vascular smooth muscle by endothelin-1 is dependent on extracellular and intracellular Ca2+. However, the role of ryanodine-sensitive Ca2+ stores in endothelin-1-induced contraction is unknown. Vascular contraction was measured in mesenteric small arteries (200-300 microm intraluminal diameter) isolated from Sprague-Dawley rats and maintained at a constant intraluminal pressure of 40 mm Hg. The presence of functional ryanodine receptor Ca2+ release channels (RyRC) was demonstrated by the finding that ryanodine (10 microM), which locks the RyRC in a subconductance state, produced significant contraction of small arteries in the presence of 15 mM KCl. This effect was inhibited by dantrolene (10 microM), a RyRC inhibitor. Dantrolene significantly reduced the ET(A) receptor-mediated contraction to endothelin-1 (10(-11)-10(-9) M). The ability of dantrolene to reverse contraction induced by endothelin-1 was also determined. Dantrolene (1-10 microM) produced concentration-dependent relaxation of vessels precontracted to 38+/-3% of resting diameter with endothelin-1 but had no effect in vessels precontracted to a similar degree with phenylephrine or KCl. Because activation of RyRC may be dependent on production of cyclic ADP-ribose, the effect of nicotinamide (2 mM), an inhibitor of ADP-ribosyl cyclase, on contraction to endothelin-1 was determined. Nicotinamide had an inhibitory effect similar to that produced by dantrolene. A combination of nicotinamide and dantrolene had no greater effect than either agent alone, suggesting a common pathway for cyclic ADP-ribose and RyRC. In summary, endothelin-1 induces contraction of small mesenteric arteries through ET(A) receptor-mediated production of cyclic ADP-ribose and activation of RyRC.

Properties of P2X and P2Y receptors are dependent on artery diameter in the rat mesenteric bed.

P2 receptor mediated contractile responses have been characterized in different diameter arteries from the rat mesenteric arterial vasculature (first, second to third and fifth to sixth order for large, medium and small arteries) using wire myograph and diamtrak video imaging. alpha,ss-methylene ATP (alpha,beta-meATP) evoked transient concentration-dependent contractions in mesenteric arteries with EC(50) values of 0.4, 2.5 and 107 microM for small, medium and large arteries respectively. Suramin (10 - 100 microM) produced substantial parallel rightward shifts of the concentration-response curve to alpha,beta-meATP in small and medium-sized arteries with pA(2) of 5.1. Responses in large vessels were unaffected by suramin. Immunohistochemical analysis of arterial sections revealed no substantial differences in expression patterns of P2X receptors between different sizes of artery. P2X(1) receptors were expressed at high levels, P2X(4) and P2X(5) receptors were also detected on smooth muscle. The P2X receptor response is dominated by P2X(1) receptor in small and medium arteries but the nature of the receptor mediating the suramin insensitive alpha,beta-meATP mediated response in large arteries is unclear. The P2Y receptor agonist UTP was significantly more potent in small than in medium or large arteries (EC(50) values: 15.0 microM small, 88.5 microM diamtrak medium 1.6 mM myography medium and 1.4 mM large). Responses in both small and medium-sized vessels were reduced by suramin (30 - 100 microM). The sensitivity to UTP and suramin indicates the presence of P2Y(2) receptors. This study shows that P2 receptors do not have a homogenous phenotype throughout the mesenteric vascular bed and that the properties depend on artery size.

Effect of tyrosine kinase inhibition on sepsis-induced vascular hyporesponsiveness, inos mrna expression and NF-kappaB nuclear translocation in rats.

The dependence of the critical steps in the sepsis cascade on the transcription factor NF-kappaB andation to nitric oxide (NO) production are controversial. Tyrosine kinase (TK) is involved in several of the steps, and TK inhibitors (TKI) inhibit lipopolysaccharide (LPS)-induced vascular hyporesponsiveness in septic animals. We studied the relationship of TK inhibition, hemodynamics, vascular contraction, iNOS mRNA expression and NF-kappaB translocation in anesthetized endotoxic rats. The TKI AG556 (2.5 mg/kg i.p.), given 1 h before i.v. endotoxin (LPS) resulted in attenuation of early (<60 min) and late (60-120 min) hypotension, improved contraction of mesenteric arteries to norepinephrine 4 h after LPS, and attenuated tissue iNOS mRNA expression. LPS-induced NF-kappaB translocation was unaffected. The observed dissociation between NF-kappaB translocation and the salutary effect of TKI in vivo and ex vivo and its effect on iNOS mRNA expression suggest that although NF-kappaB may be involved in the sepsis cascade, it may not be essential for some of the molecular and vascular consequences of septic shock.

INOS gene expression modulates microvascular responsiveness in endotoxin-challenged mice.

Septic shock is characterized by vasodilation and decreased responsiveness to vasoconstrictors. Recent studies suggest this results from nitric oxide (NO) overproduction after expression of the calcium-independent isoform of NO synthase (iNOS) in smooth muscle cells. However, direct evidence linking iNOS (NOS2) expression and decreased microvascular responsiveness after septic stimuli is lacking. In the present study, we determined the effect of bacterial lipopolysaccharide (LPS, 20 mg/kg, IP) on smooth muscle contraction and endothelial relaxation in mesenteric resistance arteries from wild-type and iNOS knockout mice. Four hours after challenge with LPS or saline in vivo, concentration-dependent responses to norepinephrine (NE) and acetylcholine (NE+ACh) were measured in cannulated, pressurized vessels ex vivo. In vessels from wild-type mice, NE-induced contraction was markedly impaired after LPS, and pretreatment with the iNOS inhibitor aminoguanidine (AG) partly restored the NE contraction. In contrast, NE contraction in microvessels from iNOS knockout mice was unaffected by LPS. ACh-induced relaxation was unaffected by LPS in vessels from either genotype. These data provide direct evidence that iNOS gene expression mediates the LPS-induced decrease in microvascular responsiveness to vasoconstrictors. Moreover, the observation that AG did not fully restore NE contraction after LPS, whereas iNOS gene deficiency did, suggests that iNOS expression plays a central role in the development of the NO-independent effect of LPS on microvascular responsiveness. Finally, our data indicate that LPS or iNOS expression has little effect on endothelium-dependent relaxation, and eNOS activity does not appear to play a role in the decreased smooth muscle responsiveness after LPS in this model. The full text of this article is available at http://www.circresaha.org.

Room D, 10/16/2000 9: 00 AM - 11: 00 AM (PS) Involvement of Endothelium-Dependent Mechanisms in Phenylephrine-Induced Phasic Contraction of Mesenteric Small Artery in Rat

<b>Room D, 10/16/2000 9: 00 AM - 11: 00 AM (PS) Involvement of Endothelium-Dependent Mechanisms in Phenylephrine-Induced Phasic Contraction of Mesenteric Small Artery in Rat</b>

Effect of captopril on neurally induced contraction and relaxation of mesenteric arteries of renal hypertensive rats

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 microM) and atropine (1 microM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 microM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.

Effect of losartan and benazepril on mesenteric arteries in spontaneously hypertension rats

The aim of this study is to investigate the effect of losartan, benazepril on vasomotion function of mesenteric arteries in spontaneously hypertensive rats. 16 wks male SHR were treated for 16 weeks with losartan (10 mg · kg−1 · d−1), benazepril (10 mg · kg−1 · d−1) and the combination of these two agents (10 mg · kg−1 · d−1 losartan, 10 mg · kg−1 · d−1 benazepril), respectively. Sex- and age-matched SHR and WKY served as controls. Vascular reactivity to vasoactive substances was studied with isolated rings of mesenteric arteries from rats. SHR was characterized by a decreased endothelium-dependent relaxation in response to ACh. Both concomitant and alone treatment of losartan, benazeptil increased the relaxation sensitivity to ACh. Effect of concomitant treatment on relaxation sensitivity to ACh was similar to that in losartan group, and was more significant than benazepril alone (pD2: SHR-L: 7.28 ± 0.26, SHR-BL: 7.48 ± 0.70 VS SHR-B: 6.32 ± 0.62 P < 0.05). ACh also caused remarked endothelium-dependent contraction in SHR mesenteric arteries compared with WKY, which was augmented by inhibitors of NO-syntheses L-NAME. At the present of L-NAME, ACh-induced endothelium-dependent contraction was similarly inhibited by the three therapies (Cmax: SHR-BL: 2.00 ± 0.49, SHR-B: 2.42 ± 1.64, SHR-L: 2.67 ± 1.94 VS SHR-C: 6.18 ± 1.12 P < 0.05). SNP-induced endothelium-independent relaxation was impaired, which was completely normalized by the treatment of either losartan, benazepril or their concomitant. These results indicate that the treatment of losartan and benazepril had effects on meliorated the endothelial dysfunction in mesenteric arteries rings from SHR. The effect of concomittant treatment is more effective or equivalent to the treatment of each alone.

Effect of captopril on neurally induced contraction and relaxation of mesenteric arteries of renal hypertensive rats

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 µM) and atropine (1 µM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 µM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.Key words: neurogenic vasodilation, calcitonin gene-related peptide, angiotensin, renal hypertension, angiotensin converting enzyme.

P-418 - Role of non-N-type calcium channels in the sympathetic neurogenic contraction of rat mesenteric artery in response to electrical field stimulation

P-418 - Role of non-N-type calcium channels in the sympathetic neurogenic contraction of rat mesenteric artery in response to electrical field stimulation

Effects of diadenosine polyphosphates (Ap(n)As) and adenosine polyphospho guanosines (Ap(n)Gs) on rat mesenteric artery P2X receptor ion channels.

Diadenosine polyphosphates (Ap(n)As, n=3 - 7) and adenosine polyphospho guanosines (Ap(n)Gs, n=3 - 6) are naturally occurring vasoconstrictor substances found in platelets. These vasoconstrictor actions are thought to be mediated through the activation of P2X receptors for ATP. The effects of Ap(n)As and Ap(n)Gs at P2X receptors on rat mesenteric arteries were determined in contraction studies and using the patch clamp technique on acutely dissociated artery smooth muscle cells. P2X(1) receptor immunoreactivity was detected in the smooth muscle layer of artery rings. The sensitivity to alpha,beta-methylene ATP and desensitizing nature of rat mesenteric artery P2X receptors correspond closely to those of recombinant P2X(1) receptors. Ap(4)A, Ap(5)A and Ap(6)A evoked concentration dependent P2X receptor inward currents which desensitized during the application of higher concentrations of agonist. The agonist order of potency was Ap(5)A> or = Ap(6)A> or = Ap(4)A >> Ap(3)A. Ap(2)A and Ap(7)A were ineffective. Similar results were obtained in contraction studies except for Ap(7)A which evoked a substantial contraction. Ap(n)Gs (n=2 - 6)(30 microM) evoked P2X receptor inward currents in mesenteric artery smooth muscle cells. Ap(n)Gs (n=4 - 6) were less effective than the corresponding Ap(n)A. This study shows that at physiologically relevant concentrations Ap(n)As and Ap(n)Gs can mediate contraction of rat mesenteric arteries through the activation of P2X(1)-like receptors. However the activity of the longer chain polyphosphates (n=6 - 7) may be overestimated in whole tissue studies due to metabolic breakdown to yield the P2X receptor agonists ATP and adenosine tetraphosphate. British Journal of Pharmacology (2000) 129, 124 - 130

Significant role of neuronal non-N-type calcium channels in the sympathetic neurogenic contraction of rat mesenteric artery.

1. The possible involvement of pre-junctional non-N-type Ca2+ channels in noradrenaline (NA)-mediated neurogenic contraction by electrical field stimulation (EFS) was examined pharmacomechanically in the isolated rat mesenteric artery. 2. EFS-generated contraction of endothelium-denuded mesenteric artery was frequency-dependent (2 - 32 Hz) and was abolished by tetrodotoxin (TTX, 1 microM), guanethidine (5 microM) or prazosin (100 nM), indicating that NA released from sympathetic nerve endings mediates the contractile response. 3. NA-mediated neurogenic contractions to lower frequency stimulations (2 - 8 Hz) were almost abolished by an N-type Ca2+ channel blocker, omega-conotoxin-GVIA (1 microM) whereas the responses to higher frequency stimulations (12 - 32 Hz) were less sensitive to omega-conotoxin-GVIA. The omega-conotoxin-GVIA-resistant component of the contractile response to 32 Hz stimulation was inhibited partly (10 - 20%) by omega-agatoxin-IVA (10 - 100 nM; concentrations which are relatively selective for P-type channels) and to a greater extent by omega-agatoxin-IVA (1 microM) and omega-conotoxin-MVIIC (3 microM), both of which block Q-type channels at the concentrations used. 4. omega-Agatoxin-IVA (10 - 100 nM) alone inhibited 32 Hz EFS-induced contraction by 10 approximately 20% whereas omega-conotoxin-MVIIC (3 microM) alone inhibited the response by approximately 60%. 5. These omega-toxin treatments did not affect the contractions evoked by exogenously applied NA. 6. These findings show that P- and Q-type as well as N-type Ca2+ channels are involved in the sympathetic neurogenic vascular contraction, and suggest the significant role of non-N-type Ca2+ channels in NA release from adrenergic nerve endings when higher frequency stimulations are applied to the nerve.

Relaxant effects of antidepressants on human isolated mesenteric arteries.

The therapeutic action of tricyclic agents may be accompanied by unwanted effects on the cardiovascular system. The evidence for the effects on vascular and nonvascular smooth muscle comes from animal studies. Whether these studies can be extrapolated to human vessels remains to be determined. Therefore, the present study was designed to investigate the influence of amitriptyline, nortriptyline and sertraline on the contractile responses of human isolated mesenteric arteries to electrical field stimulation, noradrenaline and potassium chloride. Arterial segments (lumen diameter 0.8-1.2 mm) were obtained from portions of the human omentum during the course of 41 abdominal operations (22 men and 19 women), and rings 3 mm long were mounted in organ baths for isometric recording of tension. In some artery rings the endothelium was removed mechanically. In precontracted artery rings amitriptyline, nortriptyline and sertraline (3x10(-7)-10(-4) m ) produced concentration-dependent relaxation that was independent of the presence or absence of vascular endothelium. Incubation with indomethacin (3x10(-6) m ) reduced the pD2 values thus indicating the participation of dilating prostanoid substances in this response. Amitriptyline and nortriptyline inhibited both the neurogenic-and noradrenaline-induced contractions. In contrast, only the highest concentration of sertraline reduced the adrenergic responses. Amitriptyline, nortriptyline and sertraline inhibited contractions elicited by KCl and produced rightward shifts of the concentration-response curve to CaCl2 following incubation in calcium-free solution. These results indicate that amitriptyline and nortriptyline could act as adrenoceptor antagonists and direct inhibitors of smooth muscle contraction of human mesenteric arteries, whereas sertraline might principally exert its action only as direct inhibitor of smooth muscle contraction. This relaxant mechanism involves an interference with the entry of calcium.

Analysis of alpha 1L-adrenoceptor pharmacology in rat small mesenteric artery.

1. To illuminate the controversy on alpha 1A- or alpha 1L-adrenoceptor involvement in noradrenaline-mediated contractions of rat small mesenteric artery (SMA), we have studied the effects of subtype-selective alpha 1-adrenoceptor agonists and antagonists under different experimental conditions. 2. The agonist potency order in rat SMA was: A61603 >> SKF89748-A > cirazoline > noradrenaline > ST-587 > methoxamine. Prazosin antagonized all agonists with a low potency (pA2: 8.29-8.80) indicating the involvement of alpha 1L-rather than alpha 1A-adrenoceptors. 3. The putative alpha 1L-adrenoceptor antagonist JTH-601, but not the alpha 1B-adrenoceptor antagonist chloroethylclonidine (10 microM) antagonized noradrenaline-induced contractions of SMA. The potency of the selective alpha 1D-adrenoceptor antagonist BMY 7378 against noradrenaline (pA2 = 6.16 +/- 0.13) and of the selective alpha 1A-adrenoceptor antagonist RS-17053 against noradrenaline (pKB = 8.35 +/- 0.10) and against the selective alpha 1A-adrenoceptor agonist A-61603 (pKB = 8.40 +/- 0.09) were too low to account for alpha 1D- and alpha 1A-adrenoceptor involvement. 4. The potency of RS-17053 (pKB/pA2's = 7.72-8.46) was not affected by lowering temperature, changing experimental protocol or inducing myogenic tone via KCl or U46619. 5. Selective protection of a putative alpha 1A-adrenoceptor population against the irreversible action of phenoxybenzamine also failed to increase the potency of RS-17053 (pA2 = 8.25 +/- 0.06 against A61603). 6. Combined concentration-ratio analysis demonstrated that tamsulosin, which does not discriminate between alpha 1A- and alpha 1L-adrenoceptors, and RS-17053 competed for binding at the same site in the SMA. 7. In summary, data obtained in our experiments in rat SMA indicate that the alpha 1-adrenoceptor mediating noradrenaline-induced contraction displays a distinct alpha 1L-adrenoceptor pharmacology. This study does not provide evidence for the hypothesis that alpha 1L-adrenoceptors represent an affinity state of the alpha 1A-adrenoceptor in functional assays. Furthermore, there is no co-existing alpha 1A-adrenoceptor in the SMA.

NEW alpha 1-ADRENOCEPTOR ANTAGONIST, JTH-601, SHOWS MORE THAN 10 TIMES HIGHER AFFINITY FOR HUMAN PROSTATES THAN ARTERIES

Purpose We compared the affinities of a new alpha 1-adrenoceptor (AR) antagonist, JTH-601 with those of several alpha 1-AR antagonists in human prostates and arteries. Results In the functional study, noradrenaline produced concentration-dependent contractions in human prostates and mesenteric arteries. The pA 2/pK B values for the antagonists in the human prostate were 9.78 for tamsulosin, 8.84 for JTH-601, 8.39 for WB4101, 8.23 for prazosin, 8.12 for JTH-601-G1 (a main metabolite of JTH-601 in human) and 6.57 for BMY7378. Compared these affinities with those in the mesenteric artery, only JTH-601 and JTH-601-G1 exhibited unique uroselectivity, showing 10- to 20-fold higher affinity for the human prostate than for mesenteric artery. The affinity profile of these antagonists suggested that the noradrenaline-induced contractions in the human prostate and the mesenteric artery were mediated by the alpha 1L-AR and alpha 1B-AR, respectively. In the competition binding study, the pharmacological profiles of the antagonists against [( 3) H]-prazosin were examined in the human prostate and aorta. The resulting pK i values for JTH-601 and JTH-601-G1 were also approximately 10- to 20-fold higher for the human prostate than for the human aorta. Conclusion These results have suggested that JTH-601 and JTH-601-G1 are unique uroselective alpha 1-AR antagonists that show higher affinity for the human prostate than for the human arteries.