Regional specificity in deltamethrin induced cytochrome P450 expression in rat brain

Oral administration of deltamethrin (5 mg/kg x7 or 15 or 21 days) was found to produce a time-dependent increase in the mRNA expression of xenobiotic metabolizing cytochrome P450 1A1 (CYP1A1), 1A2 and CYP2B1, 2B2 isoenzymes in rat brain. RT-PCR studies further showed that increase in the mRNA expression of these CYP isoenzymes observed after 21 days of exposure was region specific. Hippocampus exhibited maximum increase in the mRNA expression of CYP1A1, which was followed by pons-medulla, cerebellum and hypothalamus. The mRNA expression of CYP2B1 also exhibited maximum increase in the hypothalamus and hippocampus followed by almost similar increase in midbrain and cerebellum. In contrast, mRNA expression of CYP1A2 and CYP2B2, the constitutive isoenzymes exhibited relatively higher increase in pons-medulla, cerebellum and frontal cortex. Immunoblotting studies carried out with polyclonal antibody raised against rat liver CYP1A1/1A2 or CYP2B1/2B2 isoenzymes also showed increase in immunoreactivity comigrating with CYP1A1/1A2 or 2B1/2B2 in the microsomal fractions isolated from hippocampus, hypothalamus and cerebellum of rat treated with deltamethrin. Though the exact relationship of the xenobiotic metabolizing CYPs with the physiological function of the brain is yet to be clearly understood, the increase in the mRNA expression of the CYPs in the brain regions that regulate specific brain functions affected by deltamethrin have further indicated that modulation of these CYPs could be associated with the various endogenous functions of the brain.     

Dopamine receptor subtypes in the human pulmonary arterial tree

Dopamine induces vasorelaxation of pulmonary artery primarily through an endothelium-dependent mechanism, but dopamine receptor subtypes involved in these mechanisms have not been identified yet. The expression and localization of dopamine D1-like (D1 and D5) and D2-like (D2, D3 and D4) receptors were investigated in hilar, lobar and intrapulmonary branches of human pulmonary artery by immunoblotting and immunohistochemistry. Pulmonary artery expresses dopamine D1, D2, D4 and D5 receptor subtypes, but not the D3 receptor subtype. Dopamine D1 and to a lesser extent D5 receptors were accumulated primarily in the endothelium of extrapulmonary branches of pulmonary artery. A faint dopamine D1 and D5 receptor immunoreactivity was found in the inner media of extrapulmonary and of large sized intrapulmonary branches of pulmonary artery, but not in medium- or small-sized intrapulmonary artery branches. Dopamine D2 and to a lesser extent D4 receptor immunoreactivity co-localized with the tyrosine hydroxylase-immunoreactive sympathetic plexus supplying pulmonary artery was found in the adventitia and in the adventitia-media of both extra- and different-sized intrapulmonary branches of pulmonary artery. These findings suggest the possible role of dopamine receptors in the pulmonary endothelium-dependent vasorelaxing activity. The D1 receptor subtype seems to be the most involved in this mechanism. Dopamine D2-like receptors are prejunctional and are located at the level of sympathetic neuroeffector plexus. The heterogeneous distribution and density of dopamine receptor subtypes along the human pulmonary arterial tree may be related to the different functional roles of dopamine at various levels of the pulmonary circulation.     

Uptake and inactivation of prostaglandin E2 methyl analogues in the rat pulmonary circulation

1 The fate of (15S)-15-methyl prostaglandin E(2) methyl ester and 16,16-dimethyl prostaglandin E(2) in the pulmonary circulation of rat isolated lungs was compared with that of prostaglandin E(2) by means of bioassay.2 Calculated on the basis of height of response of the assay tissues, the inactivation of prostaglandin E(2) was 96 +/- 1%, of 15-methyl prostaglandin E(2) methyl ester, 53 +/- 6% and of 16,16-dimethyl prostaglandin E(2), 50 +/- 4%.3 Responses of the hamster stomach strip to the prostaglandin E(2) analogues passing through the pulmonary circulation were prolonged and slower in onset than those to the analogue given directly to the tissue. No such difference was observed with prostaglandin E(2).4 Bromocresol green, bromothymol blue, bromocresol purple and thymol blue (10(-5) M) all inhibited the inactivation of the three prostaglandins studied, as did diphloretin phosphate (1.5 x 10(-6) M). All five inhibitors also reversed the shape change in response seen after transpulmonary injection of 16-16-dimethyl prostaglandin E(2).5 We conclude that the inactivation of the methyl analogues is due to uptake, as they are not substrates for prostaglandin dehydrogenase.6 The lung may act as a depot for some compounds taking them up from the pulmonary vessels and later releasing them slowly into the systemic circulation.     

Inhibitory purinergic P2 receptor characterisation in rat distal colon

The aim of this study was to characterise the P2 receptors involved in purinergic relaxant responses in rat distal colon circular muscle. Concentration-response curves for purinergic agonists were constructed on methacholine-precontracted circular muscle strips of rat distal colon in the absence and presence of the nerve blocker TTX and the ecto-nucleotidase inhibitor ARL67156. The effects of the P2 receptor antagonists RB2, PPADS, suramin, MRS2179 and NF279, the NO-synthase inhibitor L-NAME and the small conductance K(+) channel blocker apamin were investigated. The localisation of the different P2 receptors was examined immunocytochemically. Immunocytochemistry demonstrated the expression of P2Y(1), P2Y(6) and P2X(1) receptors on smooth muscle cells and P2Y(2), P2Y(12), P2X(2) and P2X(3) receptors in the myenteric plexus; almost a quarter of the P2Y(2)-immunopositive neurons co-expressed nNOS. The P2X-selective agonist alphabetameATP and the P2Y-selective agonist ADPbetaS were the most potent relaxants; their effects were abolished by apamin. The effect of ADPbetaS was antagonised by the P2Y(1)-selective antagonist MRS2179 pointing to interaction with the muscular P2Y(1)-receptors. The relaxant effect of alphabetameATP was partially reduced by TTX and concentration-dependently antagonised by PPADS, suramin, RB2 and the P2X(1)-selective antagonist NF279; this correlates with an interaction with neuronal P2X(3) and muscular P2X(1) receptors. UTP was the least potent agonist; its effect was markedly increased by ARL67156, nearly abolished by TTX and reduced by L-NAME. This points to interaction with the neuronal P2Y(2)-receptors inducing relaxation, at least partially, by NO release.     

Activation of P2X(7) receptors stimulates the expression of P2Y(2) receptor mRNA in astrocytes cultured from rat brain

Under pathological conditions brain cells release ATP at concentrations reported to activate P2X(7) ionotropic receptor subtypes expressed in both neuronal and glial cells. In the present study we report that the most potent P2X(7) receptor agonist BzATP stimulates the expression of the metabotropic ATP receptor P2Y(2) in cultured rat brain astrocytes. In other cell types several kinds of stimulation, including stress or injury, induce P2Y(2) expression that, in turn, is involved in different cell reactions. Similarly, it has recently been found that in astrocytes and astrocytoma cells P2Y(2) sites can trigger neuroprotective pathways through the activation of several mechanisms, including the induction of genes for antiapoptotic factors, neurotrophins, growth factors and neuropeptides. Here we present evidence that P2Y(2) mRNA expression in cultured astrocytes peaks 6 h after BzATP exposure and returns to basal levels after 24 h. This effect was mimicked by high ATP concentrations (1 mM) and was abolished by P2X(7)-antagonists oATP and BBG. The BzATP-evoked P2Y(2) receptor up-regulation in cultured astrocytes was coupled to an increased UTP-mediated intracellular calcium response. This effect was inhibited by oATP and BBG and by P2Y(2)siRNA, thus supporting evidence of increased P2Y(2) activity. To further investigate the mechanisms by which P2X(7) receptors mediated the P2Y(2) mRNA up-regulation, the cells were pre-treated with the chelating agent EGTA, or with inhibitors of mitogen-activated kinase (MAPK) (PD98059) or protein kinase C, (GF109203X). Each inhibitor significantly reduced the extent to which BzATP induced P2Y(2) mRNA. Both BzATP and ATP (1 mM) increased ERK1/2 activation. P2X(7)-induced ERK1/2 phosphorylation was unaffected by pre-treatment of astrocytes with EGTA whereas it was inhibited by GF109203X. Phorbol-12-myristate-13-acetate (PMA), an activator of PKCs, rapidly increased ERK1/2 activation. We conclude that activation of P2X(7) receptors in astrocytes enhances P2Y(2) mRNA expression by a mechanism involving both calcium influx and PKC/MAPK signalling pathways.     

Discrimination by PPADS between endothelial P2Y- and P2U-purinoceptors in the rat isolated mesenteric arterial bed.

1. The main aim of this study was to characterize the antagonistic effects of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) at coexisting endothelial P2Y- and P2U-purinoceptors. Studies were conducted in Krebs-perfused mesenteric arterial preparations isolated from the rat, with tone raised by methoxamine (5-50 microM). 2. Purine and pyrimidine compounds elicited vasodilatation with a rank order of potency of 2-methylthio ATP (2-MeSATP) = ADP > ATP = UTP > P1, P3-diadenosine triphosphate (Ap3A) > P1, P2-diadenosine pyrophosphate (Ap2A) > NADP > adenosine. 8-para-Sulphophenyltheophylline (8-PSPT; 3 microM) had no effect on vasodilator responses to 2MeSATP, ADP, ATP, UTP, Ap3A or NADP, but blocked responses to adenosine and the maximal response to Ap2A. 3. PPADS (3-100 microM) attenuated vasodilator responses to the P2Y-selective agonists 2MeSATP and ADP, shifting the dose-response curves to the right. The pA2 values for PPADS at 2MeSATP and ADP were 5.97 +/- 0.69 and 5.98 +/- 0.86 respectively. In contrast, PPADS had no effect on vasodilator responses mediated by the P2U-selective agonist, UTP, or on vasodilator responses mediated by ATP. 4. PPADS (10 microM) was used to characterize responses mediated by the adenine dinucleotides; dose-response curves for vasodilator responses to Ap3A and NADP, but not those to Ap2A, were shifted to the right by PPADS. The estimated pA2 values for the effect of PPADS on Ap3A and NADP were 6.38 and 6.26 respectively. 5. Indomethacin (10 microM) had no effect on vasodilator responses to 2MeSATP, ADP, ATP or UTP. 6. In conclusion, these results show that PPADS is an antagonist at endothelial P2Y- but not P2U-purinoceptors in rat mesenteric arteries. These receptors cannot be discriminated by inhibition of prostaglandin synthesis; P2Y-purinoceptors are, however, sensitive to ADP. Selective antagonism by use of PPADS showed that ATP acts at P2U- and not P2Y-purinoceptors. Ap3A and NADP mediate vasodilatation via P2Y-purinoceptors, whereas vasodilatation to Ap2A is mediated partly via P1- and possibly via P2U-purinoceptors.     

内皮素受体拮抗剂在肺动脉高压治疗中的应用

内皮素是强的缩血管因子,肺动脉高压患者内皮素表达明显增加,内皮素受体拮抗剂已经作为靶向药物治疗肺动脉高压,其疗效及前景备受瞩目。波生坦、安立生坦分别为口服的双重和选择性内皮素受体拮抗剂(ERAs),均能显著降低肺动脉高压,改善患者的生存,Macitentan是一种新型的口服非肽类双重ERAs,现已完成Ⅲ期临床研究,疗效可观;西他生坦是选择性的内皮素受体拮抗剂,因其肝脏毒性已经退市。对于这些双重或选择性内皮素受体拮抗剂的选择问题至今仍存在分歧,长期疗效、联合用药及肝脏安全性等问题都需要更多循证医学证实。     

Regional variation in electrically-evoked contractions of rabbit isolated pulmonary artery

1. Electrically-evoked contractions in different regions of the rabbit isolated pulmonary artery have been investigated using stimulation parameters generally assumed to stimulate nerves selectively. 2. In extrapulmonary artery, trains of stimuli (10 Hz; pulse width 0.1 ms) evoked monophasic contractions. In contrast, a biphasic contraction was evoked in the intrapulmonary artery consisting of an initial fast component followed by a secondary very long-lasting component. 3. The contraction in the extrapulmonary artery was prazosin-sensitive (1 micro M) whereas that in the intrapulmonary artery was prazosin-resistant. 4. alpha,beta-Methylene ATP (1 micro M), atropine (1 micro M), losartan (1 micro M), BIBO3304 (1 nM) or nifedipine (1 micro M) had no effect on the biphasic contraction of the intrapulmonary artery. Bretylium (2 micro M) abolished the contraction of extrapulmonary artery but only partially inhibited the initial component in the intra region with no effect on the second component. 5. Tetrodotoxin (0.3-1 micro M), abolished the contraction of extrapulmonary artery but only partially reduced the electrically-evoked contraction of intrapulmonary artery. 6. Removal of the endothelium and application of sulphisoxazole (0.6-22 micro M) had no effect. 7. Varying the resting tone on the arteries, or applying gadolinium, had no effect on contractions. 8. Using confocal microscopy and calcium imaging, reproducible whole cell calcium transients were evoked in individual smooth muscle cells in intact preparations but only when direct muscle stimulation was used (pulse width of 5-10 ms). No detectable changes in calcium were elicited when brief pulse widths were used (0.1-2 ms). 9. Together, these data suggest that noradrenaline is the neurotransmitter inducing contraction in extrapulmonary artery. Noradrenaline and sympathetic nerves appear to play a less important role in the intrapulmonary artery. The tetrodoxin-resistant component is not mediated by ATP, NPY, acetylcholine, angiotensins, ET-1, stretch-activation or Ca(2+) influx through L-type Ca(2+) channels. Smooth muscle cells do not appear to be damaged by the stimulation protocol. The mechanism underlying the long lasting contraction of intrapulmonary artery evoked by brief electrical stimuli remains to be elucidated.     

Acute nociception mediated by hindpaw P2X receptor activation in the rat

1. The functional consequences of P2X receptor activation on peripheral sensory neurones have been investigated in vivo. Behavioural indices of acute nociception were monitored in the conscious rat following subplantar injection of adenosine 5′-triphosphate (ATP), α,β-methylene ATP, adenosine 5′-diphosphate (ADP) and adenosine.
2. Signs of overt nociception, i.e. hindpaw lifting and licking, were apparent in animals injected subplantar with the P2X receptor agonist, α,β-methylene ATP. Nociceptive behaviours continued for 15 min following administration of α,β-methylene ATP (200 nmol) and were dose-related (0–5 min hindpaw lifting times after injection of α,β-methylene ATP 100 nmol and 1000 nmol were 89±26 s and 232±11 s, respectively). Subplantar ATP evoked a modest response only at the highest dose tested (1000 nmol; 0–5 min hindpaw lifting time 66±19 s) whilst ADP or adenosine (both 600 nmol) elicited negligible spontaneous nociceptive activity.
3. Morphine (3 mg kg⁻¹, i.v.) abolished hindpaw licking behaviour induced by subplantar injection of either α,β-methylene ATP (600 nmol) or bradykinin (1 nmol) and substantially reduced (88±5%) paw licking in formalin (0.5%, 0.1 ml) injected animals. In contrast, hindpaw lifting was only modestly inhibited (34±11%) in morphine-pretreated animals that had received subplantar bradykinin and was unaffected in rats in which the noxious stimulus was either subplantar α,β-methylene ATP or formalin. Pretreatment of hindpaws with subplantar bupivacaine (1% w/v, 0.1 ml) abolished α,β-methylene ATP-evoked nociceptive behaviours.
4. Hindpaw lifting and licking mediated by α,β-methylene ATP (600 nmol, subplantar) were inhibited (72±15% and 95±5%, respectively) by 30 min local pretreatment with 600 nmol α,β-methylene ATP. Subplantar α,β-methylene ATP pretreatment did not inhibit behaviour stimulated by subsequent bradykinin (1 nmol) or formalin (0.5%, 0.1 ml) injection into the hindpaw.
5. Desensitization of small diameter sensory neurones with a single subplantar injection of capsaicin (100 μg) abolished all behaviours indicative of spontaneous nociceptive sensation in animals subsequently injected with α,β-methylene ATP (600 nmol), bradykinin (1 nmol) or formalin (0.5%, 0.1 ml).
6. We conclude that activation of P2X receptors present on small diameter (capsaicin-sensitive) primary afferent neurones in the rat hindpaw mediates behaviour indicative of acute nociception.

     

Endothelin receptor antagonists for the treatment of pulmonary arterial hypertension

INTRODUCTION: Endothelin is a key mediator in the pathophysiology of pulmonary arterial hypertension (PAH). Its effects are mediated through the activation of two associated receptor subtypes, termed A and B. Therapeutic strategies that modulate the activity of endothelin are, therefore, of interest to improve the functional status of patients with PAH. AREAS COVERED: The rationale for the use of endothelin receptor antagonists as a therapeutic class in PAH and pertinent data from important clinical studies are presented in this review. Areas for future research are also suggested. EXPERT OPINION: The availability of the endothelin receptor antagonist class of agents represents a significant addition to the therapeutic armamentarium which is available for the treatment of PAH. Comparative studies are warranted to establish whether selective endothelin-A receptor antagonism is more advantageous than dual receptor antagonism. Future studies of endothelin receptor antagonists will increasingly focus on the potential of a combination of different PAH therapeutic classes and will employ 'harder' clinical end points. This is of crucial importance to ensure that future developments are both worthwhile and acceptable to patients, physicians, health system payers and regulatory authorities.     

Endothelin receptor antagonists for the treatment of pulmonary arterial hypertension

Introduction: Endothelin is a key mediator in the pathophysiology of pulmonary arterial hypertension (PAH). Its effects are mediated through the activation of two associated receptor subtypes, termed A and B. Therapeutic strategies that modulate the activity of endothelin are, therefore, of interest to improve the functional status of patients with PAH.

Areas covered: The rationale for the use of endothelin receptor antagonists as a therapeutic class in PAH and pertinent data from important clinical studies are presented in this review. Areas for future research are also suggested.

Expert opinion: The availability of the endothelin receptor antagonist class of agents represents a significant addition to the therapeutic armamentarium which is available for the treatment of PAH. Comparative studies are warranted to establish whether selective endothelin-A receptor antagonism is more advantageous than dual receptor antagonism. Future studies of endothelin receptor antagonists will increasingly focus on the potential of a combination of different PAH therapeutic classes and will employ ‘harder’ clinical end points. This is of crucial importance to ensure that future developments are both worthwhile and acceptable to patients, physicians, health system payers and regulatory authorities.     

The removal of noradrenaline in the pulmonary circulation of rat isolated lungs

1. Removal of noradrenaline by isolated lungs of the rat, perfused via the pulmonary artery with Krebs bicarbonate solution has been studied.2. A constant removal (40.2%) was observed over a concentration range of 2-50 ng noradrenaline/ml (12-300 nM). At 100 ng/ml (600 nM), the removal is significantly reduced to 33.5%.3. The removal of noradrenaline was inhibited by cocaine (1 muM), but not by normetanephrine (5 muM), metaraminol (10 muM), phenoxybenzamine (10 muM) and 5-hydroxytryptamine (110 and 560 nM).4. We conclude that the removal of noradrenaline in the lungs does not involve an uptake process comparable with those previously described for this amine. The uptake process for noradrenaline in the lung is similar to that for 5-hydroxytryptamine and may be unique to this tissue.     

Photoperiodic variation in substance P induced plasma extravasation in the rat

Photoperiodic variation in plasma extravasation was examined following exogenous perfusion of substance P over a vacuum-induced blister base on the rat hind footpad. The results showed a generalised suppression of plasma extravasation during the dark or active phase of the light/dark cycle which appears to be independent of the circadian fluctuations in endogenous corticosterone. These findings emphasise the need to consider photoperiodic conditions as a possible source of variability in neurogenic inflammatory responses.     

Removal of 5-hydroxytryptamine in the pulmonary circulation of rat isolated lungs

1. Rat isolated lungs perfused via the pulmonary artery with Krebs solution removed 92% of the 5-hydroxytryptamine (5-HT) infused through it. This degree of removal was independent of concentration in the range from 5 to 100 g/ml.2. The removal of 5-HT by the lungs was inhibited by amitriptyline and desmethylimipramine (10(-6)-10(-5)M).3. The monoamine oxidase inhibitors, mebanazine and iproniazid (10(-6)-10(-5)M), inhibited the initial removal slightly, but their main effect was to preserve the 5-HT taken up and this 5-HT slowly reappeared in the effluent from the lungs. Tranylcypromine (5 x 10(-7)-10(-6)M) showed a combination of amitriptyline-like and mebanazine-like effects on the 5-HT removal in rat lung.4. Experiments with (3)H-5-HT showed that although under normal conditions only 10% of the radioactivity appeared in the lung effluent as 5-HT within the first 5 min, the rest of radioactivity administered could be recovered in the effluent over 50 min as a metabolite, probably 5-hydroxyindoleacetic acid.5. The following amines were without effect on the removal of 5-HT by rat lungs: noradrenaline (6 x 10(-7)M), normetanephrine (5 x 10(-6)M), metaraminol (10(-6)M), reserpine (10(-6)-10(-5)M) and phenoxybenzamine (10(-5)M).6. We conclude that the removal of 5-HT by rat lungs involves a process of uptake and metabolism rather than one of uptake and storage, but this process is not the catecholamine Uptake(2). The cells involved in this process might be either capillary endothelial cells or septal cells.     

Pharmacological characterization of endothelin-induced rat pulmonary arterial dilatation

1. The aim of study was to characterize endothelin (ET)-induced vasodilatation in isolated extrapulmonary rat arteries (EPA) and in intrapulmonary arteries (IPA) preconstricted with 1 μM phenylephrine.
2. The ET-3 (1 nM–100 nM)- and ET-1 (10 nM–100 nM)-induced transient vasodilatations in EPA were more potent than those in IPA. The vasodilatation induced by ET-3 (100 nM) was larger than that induced by ET-1 (100 nM).
3. Both the ET_B antagonist, BQ788 (3 μM) and or endothelium denudation, but not the ET_A antagonist, BQ123 (3 μM), abolished the vasodilatation induced by ET-1 or ET-3 (100 nM each) in EPA and in IPA. The ATP-sensitive K+channel blocker, glibenclamide (20 μM) and the nitric oxide synthase inhibitor, N^G-monomethyl-L-arginine (L-NMMA, 1 mM) suppressed the ET-induced vasodilatation in EPA and in IPA.
4. We conclude that the vasodilatation induced by endothelins is markedly reduced in rat isolated IPA, and suggest that the endothelial ET_B-mediated vasodilatation varies depending on rat pulmonary arterial regions. Furthermore, ET_B-mediated vasodilatation involves activation of ATP-sensitive K⁺ channels and of nitric oxide synthase in rat isolated EPA and IPA.

     

Selectivity of diadenosine polyphosphates for rat P2X receptor subunits

The pharmacological activity of diadenosine polyphosphates was investigated at three recombinant P2X receptors (rat P2X1, rat P2X3, rat P2X4) expressed in Xenopus oocytes and studied under voltage-clamp conditions. For the rat P2X1 receptor, only P1,P6-diadenosine hexaphosphate (Ap6A) was a full agonist yet 2-3 folds less potent than ATP. At rat P2X3, P1,p4-diadenosine tetraphosphate (Ap4A), P1,P5-diadenosine pentaphosphate (Ap5A) and Ap6A were full agonists and more potent than ATP. Ap4A alone was equipotent with ATP at rat P2X4, but only as a partial agonist. Compared to known data for rat P2X2 and human P2X1 receptors, our findings contrast with rat P2X2 where only Ap4A is a full agonist although four folds less potent than ATP. At rat and human orthologues of P2X1, Ap5A was a partial agonist with similar potency. These data provide a useful basis for selective agonists of P2X receptor subunits.     

Benzenesulfonamide attenuates monocrotaline-induced pulmonary arterial hypertension in a rat model

In this study, we examined the effects of LASSBio-965 (N-[2-(3,4-dimethoxyphenyl) ethyl]-benzenesulfonamide), a compound designed as a simplified structure of a non-selective phosphodiesterase 4 inhibitor, on vascular smooth muscle in vitro as well as in a rat model of monocrotaline (MCT)-induced pulmonary arterial hypertension. LASSBio-965 (50 mg/kg) treatment caused a significant decrease in right systolic ventricular pressure (32.47 ± 3.09 mmHg) compared to the MCT-vehicle group (51.88 ± 3.23 mmHg; P<0.05) and in the ratio of right ventricular weight to left ventricular weight plus septum (0.42 ± 0.03 g compared to 0.59 ± 0.06 g, respectively; MCT-vehicle group; P<0.05). LASSBio-965 induced a concentration-dependent relaxation of rat aortic rings, which was decreased by mechanical removal of the endothelium. Milrinone, rolipram, and sildenafil reduced the maximum relaxation (100%) to 22.4 ± 5.8, 69.5 ± 5.6 and 80.1 ± 10.7%, respectively (P<0.05). Maximum relaxation responses of aortic and pulmonary artery rings were decreased in the MCT-vehicle group (54.80 ± 5.69 and 35.87 ± 4.78, respectively) compared to the control (91.51 ± 4.79 and 54.32 ± 2.39, respectively) but improved with LASSBio-965 treatment (50mg/kg; 88.43 ± 4.54 and 59.36 ± 4.83, respectively). These results indicate that LASSBio-965 can attenuate the pulmonary arterial hypertension in an animal model most likely through the nonselective inhibition of phosphodiesterases 3, 4, and 5.