Effect of cilostazol, a phosphodiesterase type III inhibitor, on histamine-induced increase in [Ca2+]i and force in middle cerebral artery of the rabbit

Long-acting cilostazol versus isosorbide mononitrate for patients with vasospastic angina: a randomized controlled trial

BACKGROUND

Cilostazol has a vasodilatory function that may be beneficial for patients with vasospastic angina (VSA). We conducted a randomized, open-label, controlled trial to compare the efficacy and safety of long-acting cilostazol and isosorbide mononitrate (ISMN) for VSA.

METHODS

The study included patients with confirmed VSA between September 2019 and May 2021. Participants were randomly assigned to receive long-acting cilostazol (test group, 200 mg once daily) or conventional ISMN therapy (control group, 20 mg twice daily) for 4 weeks. The clinical efficacy and safety were evaluated using weekly questionnaires.

RESULTS

Forty patients were enrolled in the study (long-acting cilostazol, n = 20; ISMN, n = 20). Baseline characteristics were balanced between the two groups. Long acting cilostazol showed better angina symptom control within the first week compared to ISMN [reduction of pain intensity score, 6.0 (4.0-8.0) vs. 4.0 (1.0-5.0), P = 0.005; frequency of angina symptom, 0 (0-2.0) vs. 2.0 (0-3.0), P = 0.027, respectively]. The rate of neurological adverse reactions was lower in the cilostazol group than in the ISMN group (headache or dizziness, 40 vs. 85%, P = 0.009; headache, 30 vs. 70%, P = 0.027).

CONCLUSION

Long-acting cilostazol provided comparable control of angina and fewer adverse neurologic reactions within 4 weeks compared to ISMN. Long-acting cilostazol provides more intensive control of angina within 1 week, suggesting that it may be an initial choice for the treatment of VSA.

Progress in the Mechanism and Clinical Application of Cilostazol

Cilostazol is a unique platelet inhibitor that has been used clinically for more than 20 years. As a phosphodiesterase type III inhibitor, cilostazol is capable of reversible inhibition of platelet aggregation and vasodilation, has antiproliferative effects, and is widely used in the treatment of peripheral arterial disease, cerebrovascular disease, percutaneous coronary intervention, etc. This article briefly reviews the pharmacological mechanisms and clinical application of cilostazol.

A randomised, multicentre, double blind, placebo controlled trial to evaluate the efficacy and safety of cilostazol in patients with vasospastic angina

OBJECTIVES

We conducted a randomised, double blind, placebo controlled trial to assess the efficacy and safety of cilostazol, a selective inhibitor of phosphodiesterase 3, in patients with vasospastic angina (VSA).

BACKGROUND

Cilostazol has been shown to induce vascular dilatation, but its efficacy in patients with VSA is unknown.

METHODS

Between October 2011 and July 2012, 50 patients with confirmed VSA who had ≥1 angina episodes/week despite amlodipine therapy (5 mg/day) were randomly assigned to receive either cilostazol (up to 200 mg/day) or placebo for 4 weeks. All patients were given diaries to record the frequency and severity of chest pain (0-10 grading). The primary endpoint was the relative reduction of the weekly incidence of chest pain.

RESULTS

Baseline characteristics were similar between the two groups. Among 49 evaluable patients (25 in the cilostazol group, 24 in the placebo group), the primary endpoint was significantly greater in the cilostazol group compared with the placebo group (-66.5±88.6% vs -17.6±140.1%, respectively, p=0.009). The secondary endpoints, including a change in the frequency of chest pain (-3.7±0.5 vs -1.9±0.6, respectively, p=0.029), a change in the chest pain severity scale (-2.8±0.4 vs -1.1±0.4, respectively, p=0.003), and the proportion of chest pain-free patients (76.0% vs 33.3%, respectively, p=0.003) also significantly favoured cilostazol. Headache was the most common adverse event in both groups (40.0% vs 20.8%, respectively, p=0.217).

CONCLUSIONS

Cilostazol is an effective therapy for patients with VSA uncontrolled by conventional amlodipine therapy, and has no serious side effects.

TRIAL REGISTRATION NUMBER

NCT01444885.

Cilostazol prevents endothelin-induced smooth muscle constriction and proliferation

Cilostazol is a phosphodiesterase inhibitor that has been shown to inhibit platelet activation. Endothelin is known to be the most potent endogenous growth promoting and vasoactive peptide. In patients and animal models with stroke, the level of circulating endothelin increases and complicates the recovery progress contributed by vascular constriction (an immediate pathology) and vascular proliferation (a long-term pathology). However, the effects of cilostazol on endothelin have not been explored. To demonstrate the dual-antagonizing effects of cilostazol on vasoconstriction and cell proliferation induced by endothelin, we used primary culture of mouse vascular smooth muscle cells in vitro, mouse femoral artery ex vivo, and intracranial basilar artery ex vivo. We show that the dual-inhibition effects of cilostazol are mediated by blocking endothelin-induced extracellular calcium influx. Although cilostazol does not inhibit endothelin-induced intraorganellar calcium release, blockade of extracellular calcium influx is sufficient to blunt endothelin-induced vasoconstriction. We also show that cilostazol inhibits endothelin-induced cellular proliferation by blocking extracellular calcium influx. Inhibition of cAMP-dependent protein kinase (PKA) can block anti-proliferation activity of cilostazol, confirming the downstream role of PKA in cellular proliferation. To further demonstrate the selectivity of the dual-antagonizing effects of cilostazol, we used a different phosphodiesterase inhibitor. Interestingly, sildenafil inhibits endothelin-induced vasoconstriction but not cellular proliferation in smooth muscle cells. For the first time, we show selective dual-antagonizing effects of cilostazol on endothelin. We propose that cilostazol is an excellent candidate to treat endothelin-associated diseases, such as stroke.

Phosphodiesterase inhibitor modulation of brain microvascular endothelial cell barrier properties

BACKGROUND AND PURPOSE

Brain microvascular disorders, including cerebral microscopic hemorrhage, have high prevalence but few treatment options. To develop new strategies for these disorders, we analyzed the effects of several phosphodiesterase (PDE) inhibitors on human brain microvascular endothelial cells (HBECs).

METHODS

We modified barrier properties and response to histamine of HBECs using cilostazol (PDE3 inhibitor), rolipram (PDE4 inhibitor), and dipyridamole (non-specific PDE inhibitor).

RESULTS

Cilostazol and dipyridamole altered the distribution of endothelial F-actin. Cilostazol increased expression of tight junction protein claudin-5 by 118% compared to control (p<.001). Permeability to albumin was decreased by cilostazol (21% vs control, p<.05), and permeability to dextran (70Kd) was decreased by both cilostazol (37% vs control, p<.001) and dipyridamole (44% vs control, p<.0001). Cilostazol increased trans-endothelial electrical resistance (TEER) after 12h by 111% compared to control (p<.0001). Protein kinase A (PKA) inhibitors H89 and KT5720 attenuated the TEER increase by cilostazol. Transient increased permeability in response to histamine was significantly mitigated by cilostazol, but not by other PDE inhibitors.

CONCLUSIONS

These findings demonstrate distinctive effects of cilostazol and other PDE inhibitors on HBECs, including enhanced barrier characteristics and mitigation of response to histamine. PKA-mediated effects of cilostazol were prominent in this model. These in vitro findings are consistent with therapeutic potential of PDE inhibitors in human brain microvascular disorders.

Cilostazol suppresses angiotensin II-induced vasoconstriction via protein kinase A-mediated phosphorylation of the transient receptor potential canonical 6 channel

OBJECTIVE

The goal of this study was to determine whether inhibition of transient receptor potential canonical (TRPC) channels underlies attenuation of angiotensin II (Ang II)-induced vasoconstriction by phosphodiesterase (PDE) 3 inhibition.

METHODS AND RESULTS

Pretreatment of rat thoracic aorta with cilostazol, a selective PDE3 inhibitor, suppressed vasoconstriction induced by Ang II but not that induced by KCl. The Ang II-induced contraction was largely dependent on Ca(2+) influx via receptor-operated cation channels. Cilostazol specifically suppressed diacylglycerol-activated TRPC channels (TRPC3/TRPC6/TRPC7) through protein kinase A (PKA)-dependent phosphorylation of TRPC channels in HEK293 cells. In contrast, we found that phosphorylation of TRPC6 at Thr69 was essential for the suppression of Ang II-induced Ca(2+) influx by PDE3 inhibition in rat aortic smooth muscle cells (RAoSMCs). Cilostazol specifically induced phosphorylation of endogenous TRPC6 at Thr69. The endogenous TRPC6, but not TRPC3, formed a ternary complex with PDE3 and PKA in RAoSMCs, suggesting the specificity of TRPC6 phosphorylation by PDE3 inhibition. Furthermore, inhibition of PDE3 suppressed the Ang II-induced contraction of reconstituted ring with RAoSMCs, which were abolished by the expression of a phosphorylation-deficient mutant of TRPC6.

CONCLUSIONS

PKA-mediated phosphorylation of TRPC6 at Thr69 is essential for the vasorelaxant effects of PDE3 inhibition against the vasoconstrictive actions of Ang II.

The biological investigation of prostacyclin in preeclamptic women seen reduced endothelial function

OBJECTIVE

Our aim was to determine the biological investigation of prostacyclin in preeclamptic women seen reduced endothelial vasodilatation by non-invasive technique in vivo.

METHODS

Using a high resolution ultrasound transducer, diameters of brachial arteries were determined after reactive hyperemia in 15 non-pregnant, 20 normotensive pregnant and 20 preeclamptic women. The concentrations of 6-keto-prostaglandin F 1alpha (6keto-PGF 1alpha) in plasma and the concentrations of adenosine-3', 5'-cyclic monophosphate (cyclic AMP) in platelets and serum were measured among the groups.

RESULTS

Flow-mediated vasodilatation at 1 min after reactive hyperemia was higher in normotensive pregnant than in the non-pregnant or preeclamptic women. The plasma concentration of 6 keto-PGF 1alpha as well as the serum concentration of cyclic AMP were lower in preeclamptic than those in normotensive pregnant women. The increase in cyclic AMP in the presence of a prostacyclin analogue in platelets was seen at similar levels in all three groups.

CONCLUSION

From these results, the concentrations of prostacyclin in plasma and cyclic AMP in serum might be low possibly due to reduced production of prostacyclin in preeclamptic women seen reduced endothelial function.

Differential vasodilation response to olprinone in rabbit renal and common carotid arteries

PURPOSE

Olprinone, one of the most frequently used phosphodiesterase-3 inhibitors, exerts its positive inotropic and vasodilation effects by inhibiting the degradation of intracellular cyclic adenosine monophosphate (cAMP). The vasodilation response to olprinone is not uniform among the different vascular beds. This study was designed to compare the vasorelaxation response to olprinone between renal and common carotid arteries, and investigate its underlying mechanisms.

METHODS

Isometric force measurement, enzyme immunoassay, and western blotting techniques were used to investigate the vasorelaxation action of olprinone in isolated rabbit renal and common carotid arteries.

RESULTS

Olprinone inhibited the contractile response to phenylephrine (PE) both in the renal and carotid arteries in a concentration-dependent manner with IC50 values of 40 +/- 10 and 103 +/- 43 nM, respectively. The IC50 value was lower (P = 0.004) and the maximal inhibition was greater (P = 0.002) in the renal artery compared with the carotid artery. A cell-permeable cAMP analogue, 8-bromo-cAMP, also inhibited the contractile response to PE in the renal and carotid arteries with IC50 values of 581 +/- 150 and 740 +/- 179 microM, respectively; however no differences were observed both in the IC50 value and the maximal inhibition between two arteries. Olprinone (0.1 microM) increased the intracellular cAMP level in the renal arterial smooth muscle cells (ASMCs) but not in the carotid ASMCs. The expression of PDE3A was greater (P = 0.008) in the carotid ASMCs than the renal ASMCs.

CONCLUSION

The enhanced vasodilator action of olprinone in the renal artery is presumably because of its ability to stimulate the cAMP production, which might be attributable to the heterogeneous expression of PDE3A.

Cerebrovascular Effects of Cilostazol in Patients With Atherosclerotic Disease

BACKGROUND

Cilostazol is a potent selective inhibitor of phosphodiesterase-3 of proven efficacy in intermittent claudication. It has antiplatelet effect and produces vasodilatation in several vascular territories. This drug has been approved in some countries for the prevention of recurrence of cerebral infarction. Limited data in patients with cerebral infarcts suggest improvement in cerebral blood flow. Dilatation of cerebral vessels with carbon-dioxide challenge can be assessed by transcranial Doppler technique. The percentage increase in blood flow velocity is called cerebral vasomotor reactivity (CVR).

OBJECTIVE

In this investigation we sought to measure CVR before and after oral administration of cilostazol.

METHODS

We studied patients with risk factors for atherosclerosis before they received cilostazol (100 mg twice daily) for intermittent claudication. CVR was assessed by measuring bilateral middle cerebral artery blood flow velocity during normoventilation and after 3 minutes of breathing 8% carbon dioxide. One average value was obtained from each patient. CVR was measured the day before cilostazol first dose, at 1 month, and 3 to 6 months later.

RESULTS

We examined 9 patients (8 men and 1 woman) aged 67.6 +/- 8.4 years. All patients had hypertension, 5 had diabetes, 4 were smokers, 5 had high cholesterol levels, and 4 had coronary artery disease. CVR was 54.4 +/- 14.4% at baseline, and increased to 64.2 +/- 18.6% after 1 month (P < .05) and to 67.1 +/- 13.3% at 3 to 6 months later (P < .01).

CONCLUSION

Our findings suggest that cilostazol increases CVR in patients with atherosclerotic disease.

Relaxant effect of sildenafil in the rabbit basilar artery

We hypothesized that sildenafil, inhibitor of phosphodiesterase-5 (PDE-5), interacts with the nitric oxide (NO)-cGMP pathway in the cerebral arteries and shows vasoactive effects. To prove it in the isolated rabbit basilar artery, we compared the effects of sildenafil with other PDE-5 inhibitors, assessed the endothelial dependence of the vasoactive responses, and used modulators of the cGMP and cAMP signaling processes. Sildenafil (10 nM-0.1 mM) induced concentration-dependent relaxations of endothelin-1 (10 nM)-precontracted basilar artery, which were partially inhibited both in endothelium-denuded arteries and in arteries precontracted by depolarization with KCl (50 mM). Endothelin-1 (1 pM-30 nM) induced concentration-dependent contractions that were inhibited by sildenafil (0.1-100 microM). Zaprinast (10 nM-0.1 mM) and MBCQ (1 nM-0.1 mM), PDE-5 inhibitors, induced concentration-dependent relaxations with lower and higher potency than sildenafil, respectively. Sildenafil-induced relaxation was inhibited in arteries preincubated with the NO synthase inhibitor L-NAME (0.1 mM) or the soluble guanylyl cyclase inhibitor ODQ (10 microM). Preincubation with sildenafil (0.1 microM) enhanced the relaxations induced by acetylcholine (0.1 nM-0.1 mM) and the NO donor sodium nitroprusside (0.1 nM-0.1 mM), but not those induced by the cell-permeable cGMP analogue 8-Br-cGMP (1 nM-0.1 mM) and the adenylyl cyclase activator forskolin (0.1 nM-10 microM). These results show that sildenafil has vasoactive effects in isolated cerebral arteries. By enhancing the NO-cGMP signaling pathway in the cerebrovascular wall, sildenafil induces vasodilation, prevents vasoconstriction, and potentiates the effect of other NO-dependent vasodilators.

The phosphodiesterase 3 inhibitor cilostazol dilates large cerebral arteries in humans without affecting regional cerebral blood flow

Cilostazol, an inhibitor of phosphodiesterase (PDE) type 3, is used clinically in peripheral artery disease. PDE3 inhibitors may be clinically useful in the treatment of delayed cerebral vasospasm after subarachnoid hemorrhage. The authors present the first results on the effect of cilostazol on cerebral hemodynamics in normal participants. In this double-blind, randomized, crossover study, 200 mg cilostazol or placebo was administered orally to 12 healthy participants. Cerebral blood flow was measured using 133Xe inhalation and single photon emission computerized tomography. Mean flow velocity in the middle cerebral arteries (VMCA) was measured with transcranial Doppler, and the superficial temporal and radial arteries diameters were measured with ultrasonography. During the 4-hour observation period, there was no effect on systolic blood pressure (P = 0.28), but diastolic blood pressure decreased slightly compared with placebo (P = 0.04). VMCA decreased 21.5 +/- 5.7% after cilostazol and 5.5 +/- 12.2% after placebo (P = 0.02, vs. placebo), without any change in global or regional cerebral blood flow. The superficial temporal artery diameter increased 17.6 +/- 12.3% (P < 0.001 vs. baseline) and radial artery diameter increased 12.6 +/- 8.6% (P < 0.001 vs. baseline). Adverse events, especially headache, were common. The findings suggest that cilostazol is an interesting candidate for future clinical trials of delayed cerebral vasospasm.

The cerebrovascular dilatation effects of olprinone, a phosphodiesterase III inhibitor, in comparison with acetazolamide—a pliot study

To examine the effects of olprinone, a phosphodiesterase III inhibitor, on cerebral blood flow (CBF), we compared the effects of olprinone on CBF to that of acetazolamide. Using technetium-99m-ethyl cysteinate dimer (99mTc-ECD) brain SPECT, we measured regional CBF (rCBF) at 33 sites, including 16 right and left pairs of non-infarct cerebral cortexes, in seven stroke patients (66.0+/-3.2 years) in a resting state and 15 min after the administration of acetazolamide. Within 1 week, rCBF at each site was measured 15 min after the initiation of olprinone infusion. Resting rCBF showed a significant negative correlation with the change in rCBF (DeltaCBF) during olprinone infusion (r = -0.43, P=0.013), but no significant correlation was seen following acetazolamide administration. The difference in rCBF between the right and left cortex increased more following acetazolamide administration (14.1+/-10.9 ml/(min 100 g)) than during olprinone infusion (5.4+/-4.8 ml/(min 100 g), P=0.013). The rCBF at four regions of interest (ROI) with low-resting CBF (< 49 ml/(min 100 g)) further decreased following the administration of acetazolamide. The vasodilatory effects of olprinone are dependent on resting CBF instead of on the intracerebral steal phenomenon that occurs with acetazolamide.

Olprinone: a phosphodiesterase III inhibitor with positive inotropic and vasodilator effects

Olprinone is a newly developed phosphodiesterase III inhibitor characterized by several properties. First, olprinone has positive inotropic and vasodilator actions and improves myocardial mechanical efficiency. Second, olprinone augments cerebral blood flow by a direct vasodilatory effect on cerebral arteries. The cerebrovascular reactivity to olprinone is marked in patients with impaired cerebral circulation. Third, olprinone selectively improves carotid artery distensibility, which may be attributable to differences in the arterial structural components or the reactivity of smooth muscle cells to olprinone. Fourth, olprinone improves inadequate redistribution of brain perfusion and may prevent cerebral metabolic abnormalities in heart failure.

Effects of cilostazol, a selective cyclic AMP phosphodiesterase inhibitor on isolated rabbit spinal arterioles

Cilostazol, a potent inhibitor of guanosine 3':5'-cyclic monophosphate (cGMP)-inhibited adenosine 3':5'-cyclic monophosphate (cAMP) phosphodiesterase (PDE3), has been used clinically for the treatment of chronic peripheral arterial occlusive disease. The beneficial effect of cilostazol is attributed to both anti-platelet aggregating activity and vasodilation. However, the effect of cilostazol on resistance-sized vasculature is not well documented. Furthermore, mechanisms of vasodilation and influence on endothelium function are not fully understood. Thus, we investigated the vasodilator action of cilostazol using isolated, pressurized rabbit spinal arterioles with special reference to the functional endothelium. Cilostazol, acetylcholine (ACh), isocarbacyclin (prostacyclin analogue), and sodium nitroprusside (SNP) all produced concentration-dependent vasodilations of isolated spinal arterioles with endogenous myogenic tone. The order of potency of these agonists was isocarbacyclin>ACh>SNP>cilostazol. Indomethacin (10 micro M, a cyclo-oxygenase inhibitor), N(omega)-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor, 30 micro M), or chemical denudation of the endothelial cells did not significantly alter the cilostazol-induced arteriolar dilation. Furthermore, stimulating the release of endothelium-derived relaxing factors by administering ACh (100 nM), or treating with isocarbacyclin (1 nM) or SNP (3 nM) did not significantly modify the cilostazol-induced vasodilation. These results suggest that cilostazol produces the vasodilation of isolated, pressurized rabbit spinal arterioles independent of the functional endothelium. We infer that the vasodilator action of cilostazol in the spinal arterioles may be attributed to a yet unknown mechanism that is independent of the PDE3 inhibition.

Mechanism underlying histamine-induced intracellular Ca2+ movement in PC3 human prostate cancer cells

The effect of histamine on intracellular free Ca2+ levels ([Ca2+]i) in PC3 human prostate cancer cells and the underlying mechanism were evaluated using fura-2 as a Ca2+ dye. Histamine at concentrations between 0.1 and 50 microM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 1 microM. The [Ca2+]i response comprised an initial rise and a slow decay, which returned to baseline within 3 min. Extracellular Ca2+ removal inhibited 50% of the [Ca2+]i signal. In the absence of extracellular Ca2+, after cells were treated with 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), 10 microM histamine did not increase [Ca2+]i. After pretreatment with 10 microM histamine in a Ca2+-free medium for several minutes, addition of 3 mM Ca2+ induced [Ca2+]i increases. Histamine (10 microM)-induced intracellular Ca2+ release was abolished by inhibiting phospholipase C with 2 microM 1-(6-((17 beta-3- methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122), and by 10 microM pyrilamine but was not altered by 50 microM cimetidine. Collectively, the present study shows that histamine induced [Ca2+]i transients in PC3 human prostate cancer cells by stimulating H1 histamine receptors leading to Ca2+ release from the endoplasmic reticulum in an inositol 1,4,5-trisphosphate-dependent manner, and by inducing Ca2+ entry.

A comparison of effects measured with isotonic and isometric recording: I. Concentration-effect curves for agonists

Concentration-effect curves were obtained with carbachol tested on isolated preparations of guinea-pig ileum taken from adjacent sites in the same animal, one recorded isotonically, the other isometrically: similar experiments were made with histamine as agonist and with carbachol on rat uterus (in oestrus). The position and steepness of the curves was expressed as the values of [EC(50)] and the exponent, P: with carbachol or histamine on guinea-pig ileum the curves were significantly steeper with isotonic recording (P<0.02, sign test) and displaced towards lower concentrations (P<0.005) but there were significant correlations (P<0.05) between values obtained with tissues from the same animal. The curves for carbachol on the rat uterus were very steep: with isotonic recording the exponent (often eight or more) was consistently higher than with isometric (P<0.001): there was no significant displacement but there was a significant correlation (P<0.05) between values of [EC(50)] obtained with tissues from the same animal. Although the results obtained by the two methods are different, they are correlated. These effects are to be expected because with isotonic recording there can be no change in length until the tension exceeds the load and the tissue bulk sets an upper limit to shortening: the range within which an effect can be measured (the "operational window") is smaller. The observed effects on [EC(50)] and P have been reproduced with theoretical data.

Mechanisms of histamine-induced intracellular Ca 2+ release and extracellular Ca 2+ entry in MG63 human osteosarcoma cells 1 1Abbreviations: [Ca2+]i; Cytosolic free Ca2+ concentration; and IP3, inositol 1,4,5-trisphosphate

The effect of histamine on intracellular free Ca2+ levels ([Ca2+](i)) in MG63 human osteosarcoma cells was explored using fura-2 as a Ca2+ dye. Histamine increased ([Ca2+](i)) in a concentration-dependent fashion with an EC(50) value of 0.5 microM. Extracellular Ca2+ removal inhibited the ([Ca2+](i)) signals. Histamine failed to increase ([Ca2+](i)) in Ca2+-free medium after cells were pretreated with thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor). Addition of Ca2+ induced concentration-dependent ([Ca2+](i)) increases after preincubation with histamine in Ca2+-free medium. Histamine-induced intracellular Ca2+ release was abolished by inhibiting phospholipase C with 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). The ([Ca2+](i)) increase induced by histamine in Ca2+ medium was abolished by cimetidine, but was not altered by pyrilamine, nifedipine, verapamil, and La(3+). Together, this study shows that histamine increased in ([Ca2+](i)) in osteosarcoma cells by stimulating H2 histamine receptors. The Ca2+ signal was caused by Ca2+ release from the endoplasmic reticulum in a phospholipase C-dependent manner. The Ca2+ release was accompanied by Ca(2+) influx.

Effects of olprinone, a phosphodiesterase 3 inhibitor, on regional cerebral blood flow of cerebral cortex in stroke patients

The effects of olprinone (0.2 microg/kg per minute, i.v.) on cerebral blood flow were examined using technetium-99m-ethyl cysteinate dimer (99mTc-ECD) brain single-photon emission computed tomography in 14 stroke patients (69.0 +/- 5.6 years) and 12 normal subjects (68.1 +/- 6.2 years). The regional cerebral blood flow of the cerebral cortex was measured at six sites for each stroke patient (stroke group: n = 68, excluding 16 infarct areas confirmed on computed tomography image) and for each normal subject (normal group: n = 72). 99mTc-ECD brain single-photon emission computed tomography was repeated as the baseline 7 days after olprinone treatment study. The percent increment of the rCBF was 14.4 +/- 9.8% in the normal group and 10.7 +/- 11.7% in the stroke group (p = 0.002). The baseline value of the regional cerebral blood flow had a significant negative correlation with the increase of the regional cerebral blood flow in the normal group (r = -0.73, p < 0.0001) and in the stroke group (r = -0.43, p < 0.001). Although olprinone could dilate the cerebral vessels of stroke patients as well as those of normal subjects, smooth muscle dysfunction of the cerebral vessels due to advanced arteriosclerosis may reduce this effect.

Characterization of changes in mechanical responses to histamine in omental resistance arteries in pre-eclampsia

Changes in the effect of histamine on the smooth muscle of resistance arteries in pre-eclampsia were investigated by measuring isometric contractions in endothelium-denuded strips of omental resistance arteries from pre-eclamptic and normotensive pregnant women (pregnancy-term matched). Histamine (0.03 -1 microM) caused concentration-dependent relaxation of the contraction induced by 9, 11-epithio-11,12-methano-thromboxane A(2) (STA(2)) in strips from both groups. Sensitivity (for pre-eclampsia: pD(2)=6.66+/-0.04, n=5 and for normotensive pregnant women: pD(2)=7.07+/-0.03, n=10, P<0.001) was lower and the maximum response (90.6+/-0.6% vs 95.5+/-1.1%, P<0.05) was smaller in strips from pre-eclamptic women. Although 8-bromoadenosine-3', 5'-cyclic monophosphorothioate (Sp-isomer: Sp-8-Br-cAMPS, 0.1 - 0.3 mM), a phosphodiesterase (PDE)-resistant activator of adenosine-3',5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase, concentration-dependently attenuated the contraction induced by STA(2) in strips from both groups, the sensitivity (for pre-eclampsia: pD(2)=3.68+/-0.04, n=5 and for normotensive pregnant women: 3.94+/-0.09, n=7, P:=0.02) was lower and the maximum response (64.2+/-2.4% vs 74.9+/-4.4%, P:<0.05) was smaller in pre-eclampsia. In beta-escin-skinned strips, the pD(2) value for the contraction-inducing effect of Ca(2+) did not differ significantly between the two groups (for pre-eclampsia, n=6; for normotensive pregnant women, n=6). Thus, omental resistance arteries from human subjects with pre-eclampsia showed (i) a weaker H(2)-receptor-mediated relaxation to histamine and (ii) a weaker cyclic AMP-analogue-induced relaxation, suggesting that the reduced action of histamine may be partly due to a decreased effect of cyclic AMP.

Role of intracellular Ca(2+) release in histamine-induced depolarization in rabbit middle cerebral artery

The role of Ca(2+) mobilization from intracellular stores and Ca(2+)-activated Cl(-) channels in caffeine- and histamine-induced depolarization and contraction of the rabbit middle cerebral artery has been studied by recording membrane potential and isometric force. Caffeine induced a transient contraction and a transient followed by sustained depolarization. The transient depolarization was abolished by ryanodine, DIDS, and niflumic acid, suggesting involvement of Ca(2+)-activated Cl(-) channels. Histamine-evoked transient contraction in Ca(2+)-free solution was abolished by ryanodine or by caffeine-induced depletion of Ca(2+) stores. Ryanodine slowed the development of depolarization induced by histamine in Ca(2+)-containing solution but did not affect its magnitude. In arteries treated with 1 mM Co(2+), histamine elicited a transient depolarization and contraction, which was abolished by ryanodine. DIDS and niflumic acid reduced histamine-evoked depolarization and contraction. Histamine caused a sustained depolarization and contraction in low-Cl(-) solution. These results suggest that Ca(2+) mobilization from ryanodine-sensitive stores is involved in histamine-induced initial, but not sustained, depolarization and contraction. Ca(2+)-activated Cl(-) channels contribute mainly to histamine-induced initial depolarization and less importantly to sustained depolarization, which is most likely dependent on activation of nonselective cation channels.

Histamine-induced depolarization: ionic mechanisms and role in sustained contraction of rabbit cerebral arteries

The role of membrane depolarization in the histamine-induced contraction of the rabbit middle cerebral artery was examined by simultaneous measurements of membrane potential and isometric force. Histamine (1-100 microM) induced a concentration-dependent sustained contraction associated with sustained depolarization. Action potentials were observed during depolarization caused by histamine but not by high-K(+) solution. K(+)-induced contraction was much smaller than sustained contraction associated with the same depolarization caused by histamine. Nifedipine attenuates histamine-induced sustained contraction by 80%, with no effect on depolarization. Inhibition of nonselective cation channels with Co(2+) (100-200 microM) reversed the histamine-induced depolarization and relaxed the arteries but induced only a minor change in K(+)-induced contraction. In the presence of Co(2+) and in low-Na(+) solution, histamine-evoked depolarization and contraction were transient. We conclude that nonselective cation channels contribute to histamine-induced sustained depolarization, which stimulates Ca(2+) influx through voltage-dependent Ca(2+) channels participating in contraction. The histamine-induced depolarization, although an important and necessary mechanism, cannot fully account for sustained contraction, which may be due in part to augmentation of currents through voltage-dependent Ca(2+) channels and Ca(2+) sensitization of the contractile process.

Vasorelaxant effect of olprinone, an inhibitor of phosphodiesterase 3, on mesenteric small artery and vein of rabbits

The effects of olprinone, a cardiotonic agent that inhibits cyclic GMP (cGMP)-inhibited phosphodiesterase, was studied on isolated rabbit mesenteric small artery and vein. In the presence of indomethacin and propranolol, olprinone at concentrations of 10 nM to 10 microM and 1 microM to 100 microM relaxed norepinephrine-stimulated mesenteric artery and vein in a concentration-dependent manner, respectively. The relaxation was not endothelium-dependent in the artery. Removal of the endothelium, however, increased marginally the response of the vein to olprinone. Olprinone-induced relaxation was less pronounced in arteries contracted with high KCl solution + norepinephrine than in those contracted with norepinephrine alone. Nicardipine inhibited this attenuating effect of high KCl solution on the olprinone-induced relaxation. Olprinone (1 microM) enhanced the relaxation of artery and vein in response to a cAMP-increasing agent, 6-(3-dimethylaminopropionyl) forskolin (NKH477), but not to a cGMP- increasing agent, glyceryl trinitrate. Norepinephrine (10 microM) and caffeine (5 mM) elicited a transient, phasic contraction of the artery in Ca2+-free solution. Both olprinone and NKH477 attenuated more potently the norepinephrine-induced contraction than the caffeine-induced contraction. When norepinephrine (10 microM) and caffeine (5 mM) were successively applied in Ca2+-free solution, the contractile effect of caffeine was diminished compared to that in artery which had not been pretreated with norepinephrine. When the contraction in response to norepinephrine was partially attenuated by 1 microM olprinone, the following contraction evoked by caffeine was enlarged. It is concluded that olprinone relaxes the small artery more strongly than the vein via its direct action on smooth muscles. It is suggested that olprinone attenuates norepinephrine-induced contraction through inhibition of receptor-operated transmembrane Ca2+ influx and Ca2+ release from intracellular storage sites.