Role of phosphodiesterases III and IV in the modulation of vascular cyclic AMP content by the NO/cyclic GMP pathway

Phosphodiesterases type 2, 3 and 4 promote vascular tone in mesenteric arteries from rats with heart failure

Phosphodiesterases (PDE) type 3 and 4 promote vasoconstriction by hydrolysing cAMP. In experimental heart failure (HF), PDE3 makes PDE4 redundant in aorta, but it is not known if this occurs in resistance vessels, such as mesenteric artery. As PDE2 is increased in the failing myocardium, its possible role in the vasculature also needs to be addressed. Here, the function of PDE2, PDE3 and PDE4 in rat mesenteric arteries was characterized in experimental HF. Mesenteric arteries were isolated from rats sacrificed 22 weeks after surgical stenosis of the ascending aorta (HF), or Sham surgery. PDE inhibitors were used to probe isoenzyme contributions in enzymatic and isometric tension assays. PDE2 and PDE4 activities, but not PDE3 activity, facilitate contraction produced by the thromboxane analogue U46619 in Sham arteries, while in HF all three isoenzymes contribute to this response. NO synthase inhibition by L-NAME abolished the action of the PDE2 inhibitor. L-NAME eliminated the contribution of PDE4 in HF, but unmasked a contribution for PDE3 in Sham. PDE3 and PDE4 activities attenuated relaxant response to β-adrenergic stimulation in Sham and HF. PDE2 did not participate in cAMP or cGMP-mediated relaxant responses. PDE3 and PDE4 cAMP-hydrolysing activities were smaller in HF mesenteric arteries, while PDE2 activity was scarce in both groups. Endothelial cells and arterial myocytes displayed PDE2 immunolabelling. We highlight that, by contrast with previous observations in aorta, PDE4 participates equally as PDE3 in contracting mesenteric artery in HF. PDE2 activity emerges as a promoter of contractile response that is preserved in HF.

The Complexity and Multiplicity of the Specific cAMP Phosphodiesterase Family: PDE4, Open New Adapted Therapeutic Approaches

Cyclic nucleotides (cAMP, cGMP) play a major role in normal and pathologic signaling. Beyond receptors, cyclic nucleotide phosphodiesterases; (PDEs) rapidly convert the cyclic nucleotide in its respective 5'-nucleotide to control intracellular cAMP and/or cGMP levels to maintain a normal physiological state. However, in many pathologies, dysregulations of various PDEs (PDE1-PDE11) contribute mainly to organs and tissue failures related to uncontrolled phosphorylation cascade. Among these, PDE4 represents the greatest family, since it is constituted by 4 genes with multiple variants differently distributed at tissue, cellular and subcellular levels, allowing different fine-tuned regulations. Since the 1980s, pharmaceutical companies have developed PDE4 inhibitors (PDE4-I) to overcome cardiovascular diseases. Since, they have encountered many undesired problems, (emesis), they focused their research on other PDEs. Today, increases in the knowledge of complex PDE4 regulations in various tissues and pathologies, and the evolution in drug design, resulted in a renewal of PDE4-I development. The present review describes the recent PDE4-I development targeting cardiovascular diseases, obesity, diabetes, ulcerative colitis, and Crohn's disease, malignancies, fatty liver disease, osteoporosis, depression, as well as COVID-19. Today, the direct therapeutic approach of PDE4 is extended by developing allosteric inhibitors and protein/protein interactions allowing to act on the PDE interactome.

Genetic alterations in the NO-cGMP pathway and cardiovascular risk

In the past ten years, several chromosomal loci have been identified by genome-wide association studies to influence the risk of coronary artery disease (CAD) and its risk factors. The GUCY1A3 gene encoding the α₁ subunit of the soluble guanylyl cyclase (sGC) resides at one of these loci and has been strongly associated with blood pressure and CAD risk. More recently, further genes in the pathway encoding the endothelial nitric oxide synthase, the phosphodiesterases 3A and 5A, and the inositol 1,4,5-trisphosphate receptor I-associated protein (IRAG), i.e., NOS3, PDE3A, PDE5A, and MRVI1, respectively, were likewise identified as CAD risk genes. In this review, we highlight the genetic findings linking variants in NO-cGMP signaling and cardiovascular disease, discuss the potential underlying mechanisms which might propagate the development of atherosclerosis, and speculate about therapeutic implications.

Vascular Responses to Extractable Fractions of Ilex paraguariensis in Rats Fed Standard and High-Cholesterol Diets

The authors investigated the vasorelaxant properties of the aqueous (Aq-EF) and acid n-butanolic (acn-BuOH) extractable fractions from Ilex paraguariensis leaves. Perfusion pressure was evaluated using isolated and perfused mesenteric arterial beds (MABs) from rats fed hypercholesterolemic and standard diets. Extract-induced vasorelaxation in the presence and absence of various inhibitors was examined following precontraction of the MABs with methoxamine (30 μM) solution. In hypercholesterolemic-diet rats, relaxation in intact MABs was significantly decreased with ac-n-BuOH-EF bolus (300, 600, 900 μg) in comparison to those in standard-diet rats. After the endothelium was stripped from the MABs, the vascular responses to ac-n-BuOH-EF and 900 μg bolus of Aq-EF were significantly changed. Treatment of the MABs with an inhibitor of nitric oxide synthase, NG -nitro-L-arginine methylester hydrochloride (L-NAME, 10 mM), did not change either ac-n-BuOH-EF- or Aq-EF-induced vasodilation except for the 900 g bolus of Aq-EF. The guanilate cyclase inhibitor methylene blue (100 μM) did not affect vasodilation for either fraction in the MABs from the hypercholesterolemic-diet rats. The chronic oral administration of I. paraguariensis extract in hypercholesterolemic-diet rats resulted in a significant reduction in serum levels of cholesterol and triglycerides. These results suggest that I. paraguariensis ac-n-BuOH-EF and Aq-EF induce vasodilation in standard-diet rats in a dose-dependent manner and that the hypercholesterolemic diet substantially reduced the effect of ac-n-BuOH-EF on precontracted MABs.

Endothelium-independent vasorelaxant effect of a Berberis orthobotrys root extract via inhibition of phosphodiesterases in the porcine coronary artery

BACKGROUND

Berberis orthobotrys Bien ex Aitch. (Berberidaceae) is a plant indigenous of Pakistan that is locally used for the treatment of hypertension.

HYPOTHESIS

This study evaluated the vasoactive properties of a Berberis orthobotrys root extract and its fractions, and investigated the role of the endothelium and the underlying mechanism.

STUDY DESIGN

An aqueous methanolic extract of Berberis orthobotrys roots was prepared and submitted to a multi-step liquid-liquid fractionation with solvents of increasing polarity. Vascular reactivity of the different fractions was assessed using porcine coronary artery rings either with or without endothelium, and in the presence or absence of specific pharmacological tools. The ability of Berberis orthobotrys extracts to affect phosphodiesterase (PDE) activity was evaluated using a radioenzymatic method and purified phosphodiesterases.

RESULTS

The aqueous methanol extract induced similar relaxations in coronary artery rings with and without endothelium, and, amongst the three derived preparations, the butanol fraction (BFBO) was slightly but significantly more effective than the ethyl acetate fraction and the aqueous residue in rings without endothelium. Analysis of the butanol fraction (BFBO) by LC-ELSD-MS indicated the presence of four major isoquinoline alkaloids including berberine. BFBO significantly potentiated the relaxations induced by cyclic GMP- and cyclic AMP-dependent relaxing agonists, and inhibited contractions to KCl, CaCl2, and U46619 in endothelium denuded rings. In contrast, BFBO did not affect relaxations to endothelium-dependent vasodilators. BFBO concentration-dependently inhibited the cyclic GMP-hydrolyzing activity of basal PDE1, calmodulin-activated PDE1 and PDE5, and of cyclic AMP-hydrolyzing activity of PDE3 and PDE4 with IC50 values ranging from 40 to 130µg/ml.

CONCLUSION

The butanol fraction of the aqueous methanol extract of Berberis orthobotrys roots induced pronounced endothelium-independent relaxations and inhibited contractile responses by acting directly at the vascular smooth muscle in the coronary artery. Moreover, BFBO potentiated relaxations induced by both cyclic GMP- and cyclic AMP-dependent vasodilators most likely due to its ability to inhibit several vascular PDEs, and in particular PDE4 and PDE5.

Alteration of vascular reactivity in heart failure: role of phosphodiesterases 3 and 4

BACKGROUND AND PURPOSE

This study examined the role of the main vascular cAMP-hydrolysing phosphodiesterases (cAMP-PDE) in the regulation of basal vascular tone and relaxation of rat aorta mediated by β-adrenoceptors, following heart failure (HF).

EXPERIMENTAL APPROACH

Twenty-two weeks after proximal aortic stenosis, to induce HF, or SHAM surgery in rats, we evaluated the expression, activity and function of cAMP-PDE in the descending thoracic aorta.

KEY RESULTS

HF rat aortas exhibited signs of endothelial dysfunction, with alterations of the NO pathway, and alteration of PDE3 and PDE4 subtype expression, without changing total aortic cAMP-hydrolytic activity and PDE1, PDE3 and PDE4 activities. Vascular reactivity experiments using PDE inhibitors showed that PDE3 and PDE4 controlled the level of PGF2α -stimulated contraction in SHAM aorta. PDE3 function was partially inhibited by endothelial NO, whereas PDE4 function required a functional endothelium and was under the negative control of PDE3. In HF, PDE3 function was preserved, but its regulation by endothelial NO was altered. PDE4 function was abolished and restored by PDE3 inhibition. In PGF2α -precontracted arteries, β-adrenoceptor stimulation-induced relaxation in SHAM aorta, which was abolished in the absence of functional endothelium, as well as in HF aortas, but restored after PDE3 inhibition in all unresponsive arteries.

CONCLUSIONS AND IMPLICATIONS

Our study underlines the key role of the endothelium in controlling the contribution of smooth muscle PDE to contractile function. In HF, endothelial dysfunction had a major effect on PDE3 function and PDE3 inhibition restored a functional relaxation to β-adrenoceptor stimulation.

A PKG inhibitor increases Ca(2+)-regulated exocytosis in guinea pig antral mucous cells: cAMP accumulation via PDE2A inhibition

In antral mucous cells, acetylcholine (ACh, 1 μM) activates Ca(2+)-regulated exocytosis, consisting of an initial peak that declines rapidly (initial transient phase) followed by a second slower decline (late phase) lasting during ACh stimulation. The addition of 8-bromo-cGMP (8-BrcGMP) enhanced the initial phase, which was inhibited by the protein kinase G (PKG) inhibitor guanosine 3',5'-cyclic monophosphorothoiate, β-phenyl-1,N(2)-etheno-8-bromo, Rp-isomer, sodium salt (Rp-8-BrPETcGMPS, 100 nM). However, Rp-8-BrPETcGMPS produced a delayed, but transient, increase in the exocytotic frequency during the late phase that was abolished by a protein kinase A (PKA) inhibitor (PKI-amide), suggesting that Rp-8-BrPETcGMPS accumulates cAMP. The cGMP-dependent phosphodiesterase 2 (PDE2), which degrades cAMP, may exist in antral mucous cells. The PDE2 inhibitor BAY-60-7550 (250 nM) mimicked the effect of Rp-8-BrPETcGMPS on ACh-stimulated exocytosis. Measurement of the cGMP and cAMP contents in antral mucosae revealed that ACh stimulates the accumulation of cGMP and that BAY-60-7550 accumulates cAMP similarly to Rp-8-BrPETcGMPS during ACh stimulation. Analyses of Western blot and immunohistochemistry demonstrated that PDE2A exists in antral mucous cells. In conclusion, Rp-8-BrPETcGMPS accumulates cAMP by inhibiting PDE2 in ACh-stimulated antral mucous cells, leading to the delayed, but transient, increase in the frequency of Ca(2+)-regulated exocytosis. PDE2 may prevent antral mucous cells from excessive mucin secretion caused by the cAMP accumulation.

Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments

Cyclic nucleotide phosphodiesterases (PDEs) that specifically inactivate the intracellular messengers cAMP and cGMP in a compartmentalized manner represent an important enzyme class constituted by 11 gene-related families of isozymes (PDE1 to PDE11). Downstream receptors, PDEs play a major role in controlling the signalosome at various levels of phosphorylations and protein/protein interactions. Due to the multiplicity of isozymes, their various intracellular regulations and their different cellular and subcellular distributions, PDEs represent interesting targets in intracellular pathways. Therefore, the investigation of PDE isozyme alterations related to various pathologies and the design of specific PDE inhibitors might lead to the development of new specific therapeutic strategies in numerous pathologies. This manuscript (i) overviews the different PDEs including their endogenous regulations and their specific inhibitors; (ii) analyses the intracellular implications of PDEs in regulating signalling cascades in pathogenesis, exemplified by two diseases affecting cell cycle and proliferation; and (iii) discusses perspectives for future therapeutic developments.

Effects of rolipram on U46619-induced contraction and cyclic nucleotide content in the porcine coronary artery

The effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide content in the porcine coronary artery were investigated. Various selective PDE inhibitors, vinpocetine (type 1), erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, type 2), milrinone (type 3), rolipram (type 4), Ro20-1724 (type 4), and zaprinast (type 5), inhibited U46619-induced contractions in a concentration-dependent manner. The rank order of potency for the porcine coronary artery was rolipram > Ro20-1724 >milrinone > vinpocetine > zaprinast > EHNA, which was different from that of both the porcine carotid artery and aorta. Rolipram inhibited the U46619-induced muscle tension with a decreased [Ca(2+)](i) level, but inhibited the high K(+)-induced contraction without a change in [Ca(2+)](i) level. Rolipram increased cAMP but not cGMP content. Iberiotoxin restored the inhibition of muscle tension and the [Ca(2+)](i) levels induced by rolipram. U46619 and caffeine induced a transient increase in the [Ca(2+)](i) levels in a Ca(2+)-free solution, but rolipram only inhibited the U46619-induced Ca(2+) transient. In conclusion, rolipram is the most potent inhibitor in the porcine coronary artery, but not in the carotid artery and aorta. Moreover it is suggested that the mechanism by which rolipram causes relaxation is due to a decrease in the [Ca(2+)](i) levels and of the Ca(2+) sensitivity of the contractile elements to cAMP.

PDEs1-5 activity and expression in tissues of cirrhotic rats reveal a role for aortic PDE3 in NO desensitization

Liver cirrhosis is associated with increased nitric oxide (NO) production in the vasculature. We have previously demonstrated that aorta from rats with liver cirrhosis have a reduced relaxant response to NO donors that is corrected by DMPPO, a PDE5-specific inhibitor. Vasodilator responses to DMPPO itself were also reduced in rings from cirrhotic rats. These results supported previous suggestions that upregulation of PDE5 in liver cirrhosis might contribute to renal sodium retention, and consequently modulate vascular reactivity in the context of increased NO production (Tahseldar-Roumieh et al. in Am. J. Physiol. Heart Circ. Physiol. 290, H481-H488, 2006). Here, we investigated the possible alteration in activity and expression of cyclic nucleotide phosphodiesterase PDE1-PDE5 in kidney and vascular tissues in rats 4 weeks after bile duct ligation. The kidney of rats with cirrhosis had increased activity of PDE1 and PDE4 but not PDE5, and increased expression of PDE1A. Unexpectedly and interestingly, there was no change in cirrhotic aorta PDE5, but an increase in PDE3 and PDE4 activity associated with increased expression of PDE3A and PDE3B. Cilostamide, a specific PDE3 inhibitor, corrected the decreased response to an NO donor in isolated aorta from cirrhotic rats, suggesting that the difference in response to NO donors was due to differences in PDE3-induced hydrolysis of cGMP or to cGMP-induced inhibition of PDE3, rather than to differences in PDE5 contribution. In conclusion, these changes in PDE isozymes could greatly contribute to NO desensitization and to the regulation of vascular and renal function in liver cirrhosis.

The flavonoid dioclein is a selective inhibitor of cyclic nucleotide phosphodiesterase type 1 (PDE1) and a cGMP-dependent protein kinase (PKG) vasorelaxant in human vascular tissue

The inhibitory effect of the flavonoid dioclein was assessed on purified vascular cyclic nucleotide phosphodiesterase isoforms (EC 3.1.4.17, PDE1-5) in comparison with 8-methoxymethyl-isobutylmethylxanthine (8-MM-IBMX) and vinpocetine which are currently used as PDE1 inhibitors. The mechanism underlying the vasorelaxant effect of dioclein was investigated in human saphenous vein. Dioclein inhibited PDE1 more selectively than vinpocetine and 8-MM-IBMX, with IC(50) values of 2.47+/-0.26 and 1.44+/-0.35 microM, respectively in basal- and calmodulin-activated states. Dioclein behaved as a competitive inhibitor for cGMP hydrolysis by PDE1 in basal- and calmodulin-activated states (K(i)=0.62+/-0.14 and 0.55+/-0.07 microM, respectively), indicating this inhibitory effect to be independent of calmodulin interactions. In addition, dioclein induced a concentration-dependent relaxation of human saphenous vein which was independent on the presence of functional endothelium (EC(50) values of 7.3+/-3.1 and 11+/-2.7 microM, respectively with and without endothelium). 8-MM-IBMX relaxed human saphenous vein with an EC(50)=31+/-16 microM, whereas vinpocetine did not cause any vasorelaxation at concentrations up to 100 microM. Rp-8-pCPT-cGMPS, which inhibits cGMP-dependent protein kinase (PKG), blocked the vasodilator effect of dioclein, whereas H-89, which is a cAMP-dependent protein kinase (PKA) inhibitor, had a minor inhibitory effect. Our data show that dioclein is a potent calmodulin-independent selective inhibitor of PDE1 and that inhibition of PDE1 is involved in the PKG-mediated vasorelaxant effect of dioclein in human saphenous vein. Furthermore, dioclein may represent a new archetype to develop more specific PDE1 inhibitors.

Treatment of refractory pulmonary arterial hypertension with inhaled epoprostenol in an infant with congenital heart disease

Epoprostenol is a potent arterial vasodilator, and its administration by inhalation localizes its effects to the pulmonary circulation. In this case report, we describe a 3-month-old male patient with significant refractory pulmonary hypertension after pulmonary artery banding and placement of a Blalock-Taussig shunt. This patient continued to have significant hypoxic episodes despite maximal therapy with sedation, alkalinization, sildenafil, and inhaled nitric oxide. After the addition of inhaled epoprostenol, improvements in both clinical response and echocardiography-based hemodynamics were observed. The case supports a synergistic role among the agents in the treatment of pulmonary arterial hypertension from congenital heart disease.

Endogenous nitric oxide attenuates beta-adrenoceptor-mediated relaxation in rat aorta

1. Divergent evidence suggests that the intracellular signalling pathways for beta-adrenoceptor-mediated vascular relaxation involves either cAMP/protein kinase (PK) A or endothelial nitric oxide (NO) release and subsequent activation of cGMP/PKG. The present study identifies the relative roles of NO and cAMP, as well as dependence on the endothelium for beta-adrenoceptor-mediated relaxation of rat isolated aortas. 2. Cumulative concentration-response curves to isoprenaline (0.01-3 micromol/L) in phenylephrine (0.1 micromol/L)-preconstricted endothelium-intact and -denuded aortas were constructed. Isoprenaline-mediated relaxation was partially reduced by endothelium removal and the presence of the NO synthase inhibitor N(G)-monomethyl-L-arginine (0.1 mmol/L), but not by the cAMP antagonist (Rp)-cyclic adenosine-3',5'-monophosphorothioate (Rp-cAMPS; 0.5 mmol/L). 3. In contrast, in endothelium-denuded aortas, the isoprenaline-mediated relaxation was inhibited by Rp-cAMPS and this inhibition was lost in the presence of the NO donor sodium nitroprusside (1 nmol/L). This effect was not due to phosphodiesterase (PDE) activity because the non-selective PDE inhibitor 3-isobutyl-1-methylxanthine (1 micromol/L) failed to affect the isoprenaline vasorelaxant response. 4. The K(+) channel blocker tetraethylammonium (TEA; 1 mmol/L) attenuated isoprenaline-induced relaxation in endothelium-denuded aorta, but its effect was non-additive with Rp-cAMPS, suggesting that the K(+) channel component may involve cAMP. In endothelium-intact aortas, TEA but not Rp-cAMPS reduced isoprenaline relaxation, suggesting an additional non-cAMP component. 5. These findings suggest that beta-adrenoceptors induce vascular smooth muscle relaxation by acting through the NO-cGMP pathway and, when that is disrupted by endothelium removal or the presence of an NO synthase inhibitor, the cAMP pathway in smooth muscles is used. The lack of cAMP participation in endothelium-intact vessels may be because NO suppresses or overrides the cAMP effect.

cGMP modulation of ACh-stimulated exocytosis in guinea pig antral mucous cells

In guinea pig antral mucous cells, ACh stimulates the Ca(2+)-regulated exocytosis, which has a characteristics feature: an initial transient phase followed by a sustained phase. The effects of cGMP on ACh-stimulated exocytosis were studied in guinea pig antral mucous cells using video microscopy. cGMP enhanced the frequency of ACh-stimulated exocytotic events, whereas cGMP alone did not induce any exocytotic events under the ACh-unstimulated condition. cGMP did not stimulate either Ca(2+) mobilization or cAMP accumulation. The Ca(2+) dose-response studies demonstrated that cGMP shifted the dose-response curve upward with no shift to the lower concentration. This indicates that cGMP increased maximal responsiveness of the Ca(2+)-regulated exocytosis, but not the Ca(2+) sensitivity. Moreover, under a condition of ATP depletion by dinitrophenol (DNP) or anoxia (N(2) bubbling), ACh evoked only a sustained phase in exocytotic events with no initial transient phase. However, ACh evoked an initial transient phase followed by a sustained phase with addition of cGMP before ATP depletion, whereas only a sustained phase was evoked in a case of cGMP addition after ATP depletion. Thus cGMP-induced enhancement in ACh-stimulated exocytotic events requires ATP, suggesting that cGMP modulates ATP-dependent priming of Ca(2+)-regulated exocytosis in antral mucous cells. In conclusion, cGMP increases the number of primed granules via acceleration of the ATP-dependent priming, which enhances the Ca(2+)-regulated exocytosis stimulated by ACh.

Sildenafil as Adjunct Therapy to High-Dose Epoprostenol in a Patient with Pulmonary Veno-Occlusive Disease

Pulmonary veno-occlusive disease is refractory to medical treatment and is generally associated with a poor prognosis. Treatment with vasodilators, such as prostacyclin, of patients with PVOD is controversial because of concerns regarding hemodynamic deterioration. Although a preferential pulmonary vasodilatory effect of a specific phosphodiesterase-5 inhibitor, sildenafil, has recently been reported in patients with primary pulmonary hypertension, little information is available regarding the effect of sildenafil on patients with pulmonary veno-occlusive disease. In the present case, remarkable improvement of hemodynamics and of clinical course was produced by adjunctive use of oral sildenafil in association with intravenous high-dose epoprostenol. These findings suggest that sildenafil may be a therapeutic option in the medical treatment of pulmonary veno-occlusive disease.

Cyclic nucleotide phosphodiesterase (PDE) superfamily: a new target for the development of specific therapeutic agents

Cyclic nucleotide phosphodiesterases (PDEs), which are ubiquitously distributed in mammalian tissues, play a major role in cell signaling by hydrolyzing cAMP and cGMP. Due to their diversity, which allows specific distribution at cellular and subcellular levels, PDEs can selectively regulate various cellular functions. Their critical role in intracellular signaling has recently designated them as new therapeutic targets for inflammation. The PDE superfamily represents 11 gene families (PDE1 to PDE11). Each family encompasses 1 to 4 distinct genes, to give more than 20 genes in mammals encoding the more than 50 different PDE proteins probably produced in mammalian cells. Although PDE1 to PDE6 were the first well-characterized isoforms because of their predominance in various tissues and cells, their specific contribution to tissue function and their regulation in pathophysiology remain open research fields. This concerns particularly the newly discovered families, PDE7 to PDE11, for which roles are not yet established. In many pathologies, such as inflammation, neurodegeneration, and cancer, alterations in intracellular signaling related to PDE deregulation may explain the difficulties observed in the prevention and treatment of these pathologies. By inhibiting specifically the up-regulated PDE isozyme(s) with newly synthesized potent and isozyme-selective PDE inhibitors, it may be potentially possible to restore normal intracellular signaling selectively, providing therapy with reduced adverse effects.

Lung vasodilatory response to inhaled iloprost in experimental pulmonary hypertension: amplification by different type phosphodiesterase inhibitors

Inhaled prostanoids and phosphodiesterase (PDE) inhibitors have been suggested for treatment of severe pulmonary hypertension. In catheterized rabbits with acute pulmonary hypertension induced by continuous infusion of the stable thromboxane analogue U46619, we asked whether sildenafil (PDE1/5/6 inhibitor), motapizone (PDE3 inhibitor) or 8-Methoxymethyl-IBMX (PDE1 inhibitor) synergize with inhaled iloprost. Inhalation of iloprost caused a transient pulmonary artery pressure decline, levelling off within <20 min, without significant changes in blood gases or systemic hemodynamics. Infusion of 8-Methoxymethyl-IBMX, motapizone and sildenafil caused each a dose-dependent decrease in pulmonary artery pressure, with sildenafil possessing the highest efficacy and at the same time selectivity for the pulmonary circulation. When combining a per se ineffective dose of each PDE inhibitor (200 μg/kg × min 8-Methoxymethyl-IBMX, 1 μg/kg × min sildenafil, 5 μg/kg × min motapizone) with subsequent iloprost nebulization, marked amplification of the prostanoid induced pulmonary vasodilatory response was noted and the area under the curve of P_PA reduction was nearly threefold increased with all approaches, as compared to sole iloprost administration. Further amplification was achieved with the combination of inhaled iloprost with sildenafil plus motapizone, but not with sildenafil plus 8MM-IBMX. Systemic hemodynamics and gas exchange were not altered for all combinations. We conclude that co-administration of minute systemic doses of selective PDE inhibitors with inhaled iloprost markedly enhances and prolongs the pulmonary vasodilatory response to inhaled iloprost, with maintenance of pulmonary selectivity and ventilation perfusion matching. The prominent effect of sildenafil may be operative via both PDE1 and PDE5, and is further enhanced by co-application of a PDE3 inhibitor.

Analysis of the effects of phosphodiesterase type 3 and 4 inhibitors in cerebral arteries

Inhibitors of phosphodiesterases 3 and 4, the main cyclic AMP (cAMP) degrading enzymes in arteries, may have therapeutic potential in cerebrovascular disorders. We analysed the effects of such phosphodiesterases in guinea pig cerebral arteries with organ bath technique and cyclic nucleotide assays. Guinea pig and human cerebral arteries were used for phosphodiesterase assays. Cilostazol (6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone), a phosphodiesterase 3 inhibitor, was compared to conventional phosphodiesterase 3 and 4 inhibitors. Phosphodiesterases 3 and 4 were the major contributors to total cAMP hydrolysis in the arteries examined. The phosphodiesterase 3 inhibitors additionally attenuated cyclic GMP (cGMP) hydrolysis, but relaxant responses were not dependent on an intact endothelium or on the nitric oxide-cGMP pathway. Conversely, the phosphodiesterase 4 inhibitor used was endothelium-dependent and affected by cGMP levels. This suggests that phosphodiesterase 3 inhibitors are still effective under conditions with possible dysfunctional nitric oxide-cGMP pathway, such as in ischemic stroke or cerebral vasospasm.

Cyclic nucleotide phosphodiesterase activity, expression, and targeting in cells of the cardiovascular system

Cyclic AMP (cAMP) and cGMP regulate a myriad of cellular functions, such as metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system. Considerable effort over the last 20 years has allowed identification of the cellular components involved in the synthesis of cyclic nucleotides, as well as effectors of cyclic nucleotide-mediated signaling. More recently, a central role for cyclic nucleotide phosphodiesterase (PDE) has also been elaborated in many cell types, including those involved in regulating the activities of the cardiovascular system. In this review, we introduce the PDE families whose members are expressed in cells of the cardiovascular system including cardiomyocytes, vascular smooth muscle cells, and vascular endothelial cells. Because cell behavior is a dynamic process influenced by numerous factors, we will attempt to emphasize how changes in the activity, expression, and targeting of PDE influence cyclic nucleotide-mediated regulation of the behavior of these cells.

Relaxant effects of selective phosphodiesterase inhibitors on U46619 precontracted human intralobar pulmonary arteries and role of potassium channels

We examined the influence of K+ channel antagonists on the vasorelaxation induced by theophylline (non selective PDEI), siguazodan (PDE3I), rolipram (PDE4I) and zaprinast (PDE5I) in human intralobar pulmonary arteries. All PDEI tested induced a concentration-dependent relaxation with theophylline being significantly (p < 0.05) more efficient and rolipram more potent than PDE5I and PDE3I (Emax values, expressed as a percentage of maximal relaxation by papaverine 10(-4)M, were 92% +/- 2%, 84% +/- 8%, 90% +/- 4% and 99% +/- 1%, and pD2 values were 7.30 +/- 0.35, 6.14 +/- 0.25, 5.86 +/- 0.17, and 4.85 +/- 0.47 for rolipram, siguazodan, zaprinast and theophylline, respectively). 4-Aminopyridine (4-AP, Kv, voltage dependent channel blocker, 1 mM) induced a significant increase (+17% p < 0.05) of U46619-induced vasoconstriction whereas the other K+-channels blockers, glibenclamide (KATP channels, 1 microM) charybdotoxin (predominant BKCa, large conductance Ca2+-sensitive K+ channels, 0.1 microM) and apamine (SKCa, small conductance, 0.3 microM) were without effect. The concentration response curves (CRC) for rolipram were significantly shifted to the right by glibenclamide (1 microM), charybdotoxin (0.1 microM) and 4-AP (1 mM). The CRC for siguazodan was significantly displaced to the right by 4-AP. None of the potassium channel blockers displaced the CRC for zaprinast and theophylline. Apamine was without effect on the CRC for all the PDEI used in this study. (1) PDE3, 4 and 5 are functionally present in human intralobar pulmonary arteries; (2) the vasoconstriction induced by U46619 is downregulated by 4-aminopyridine sensitive-K+ channels; (3) the relaxant effects of rolipram (PDE4I) are partly mediated through KATP, BKCa, and Kv potassium channels and those of siguazodan (PDE3I) by Kv potassium channels.

Combination of nonspecific PDE inhibitors with inhaled prostacyclin in experimental pulmonary hypertension

Inhalation of aerosolized prostacyclin (PGI(2)) exerts selective pulmonary vasodilation, but its effect is rapidly lost after termination of nebulization. Amplification of the vasodilatory response to inhaled PGI(2) might be achieved by phosphodiesterase (PDE) inhibitors to stabilize its second messenger, cAMP. We established stable pulmonary hypertension in perfused rabbit lungs by continuous infusion of U-46619. Short-term (10-min) aerosolization maneuvers of PGI(2) effected a rapid, moderate decrease in pulmonary arterial pressure, with post-PGI(2) vasorelaxation being lost within 10-15 min, accompanied by a marginal reduction in shunt flow. Preceding administration of subthreshold doses of the PDE inhibitors theophylline, dipyridamole, and pentoxifylline via the intravascular or inhalational route, which per se did not influence pulmonary hemodynamics, caused more than doubling of the immediate pulmonary arterial pressure drop in response to PGI(2) and marked prolongation of the post-PGI(2) vasorelaxation to >60 min (all PDE inhibitors via both routes of application). This was accompanied by a reduction in shunt flow in the case of aerosolized theophylline (27.5%), pentoxifylline (30.5%), and dipyridamole (33.4%). Coaerosolization of PGI(2) and PDE inhibitors may be considered as a therapeutic strategy in pulmonary hypertension.

Coaerosolization of phosphodiesterase inhibitors markedly enhances the pulmonary vasodilatory response to inhaled iloprost in experimental pulmonary hypertension. Maintenance of lung selectivity

Inhalation of aerosolized iloprost, a stable prostacyclin analog, has been suggested for treatment of primary and secondary pulmonary hypertension, but demands multiple daily inhalation maneuvers because of the short-term effect of this approach. In intact rabbits, pulmonary hypertension was induced by continuous infusion of the stable thromboxane mimetic U46619. Thereafter, the influence of aerosolized iloprost on pulmonary and systemic hemodynamics and gas exchange was investigated in the presence and absence of phosphodiesterase (PDE) inhibitors for stabilization of the second-messenger cAMP. First, dose-effect curves for pulmonary artery pressure (Ppa) decline were established for the nonspecific PDE inhibitors pentoxifylline and dipyridamole and for the dual-selective PDE3/4 inhibitor tolafentrine when being applied as sole agent, either via the intravenous or the inhalative route. Subthreshold doses for each agent and each route of administration were then combined with a standardized iloprost aerosolization maneuver, which resulted in a substantial prolongation, but not augmentation, of the lung vasodilatory response for the prostanoid. Next, higher doses of each PDE inhibitor were employed for nebulization, causing per se some pulmonary vasodilative effect, in the absence of arterial pressure decrease or impairment of gas exchange. Coaerosolization of these PDE inhibitor doses with standardized iloprost caused approximate doubling of the immediate pulmonary vasodilator response, marked prolongation of the pressure relief overtime, and a 2- to 4-fold increase in the area under the curve of pulmonary vasodilation (efficacy tolafentrine > dipyridamole > pentoxifylline). Still, systemic arterial pressure was not suppressed and gas exchange was fully maintained. We conclude that coadministration of PDE inhibitors with inhaled iloprost markedly enhances the prostanoid-induced pulmonary artery pressure decrease while maintaining the lung selectivity of the vasodilatory response, and that coaerosolization is a particularly suitable route of administration. Even nonselective clinically approved PDE inhibitors may be employed for this purpose.

Effect of LPS on the permeability of the blood-brain barrier to insulin

Insulin has emerged as an important neuropeptide. Central actions of insulin appear to oppose those in the periphery. Insulin is transported across the blood-brain barrier (BBB) by a saturable transport system. The permeability of the BBB to insulin is altered by various events, but no studies exist that have examined the permeability of the BBB to insulin during infection or inflammation, states which can induce peripheral insulin resistance. We looked at the effects of lipopolysaccharide (LPS), a bacterial endotoxin and a powerful cytokine releaser, on the permeability of the BBB to human insulin in CD-1 mice. Intraperitoneal injections of LPS significantly increased the uptake by the brain of 131I-insulin and disrupted the BBB to 125I-albumin. After subtraction of the brain/serum ratio for 125I-albumin, brain/serum ratios for insulin were increased: 10.38 +/- 0.70 microl/g (LPS) vs. 3.62 +/- 0.27 microl/g (no LPS), P<0.0001, showing that LPS increased the uptake of insulin independent of BBB disruption. This increase in insulin uptake was due to enhanced saturable transport. Pretreatment with indomethacin 10 min before LPS injections enhanced BBB disruption, but not insulin transport. Pretreatment with the nitric oxide (NO) synthase inhibitor aminoguanidine had no effect on insulin or albumin uptake, but pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) enhanced insulin transport, but not BBB disruption. We conclude that LPS increases the saturable transport of insulin across the BBB independent of disruption and prostaglandins with potentiation by NO inhibition. Such increased transport could potentiate the central effects of insulin and so contribute to the peripheral insulin resistance seen with infection and inflammation.

Nitric oxide attenuates H(2)O(2)-induced endothelial barrier dysfunction: mechanisms of protection

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated injury in porcine pulmonary artery endothelial cells (PAECs) and modulates intracellular levels of cGMP and cAMP. We hypothesized that.NO attenuates H(2)O(2)-induced PAEC monolayer barrier dysfunction through cyclic nucleotide-dependent signaling mechanisms. To examine this hypothesis, cultured PAEC monolayers were treated with H(2)O(2), and barrier function was measured as transmonolayer albumin clearance. H(2)O(2) caused significant PAEC barrier dysfunction that was attenuated by intracellular as well as extracellular.NO generation.NO increased PAEC cGMP and cAMP levels, but treatment with inhibitors of soluble guanylate cyclase or protein kinase G did not abrogate.NO-mediated barrier protection. In contrast, H(2)O(2) decreased protein kinase A activity, and inhibiting protein kinase A abrogated the protective effect of.NO. H(2)O(2)-induced barrier dysfunction was not associated with decreased levels of cGMP or cAMP. 3-Isobutyl-1-methylxanthine and the cGMP analog 8-bromo-cGMP had little effect on H(2)O(2)-mediated endothelial barrier dysfunction, whereas 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine was protective. These results indicate that.NO modulates vascular endothelial barrier function through cAMP-dependent signaling mechanisms.

Cyclic nucleotide phosphodiesterases: relating structure and function

Cyclic nucleotide phosphodiesterases (PDEs) comprise a superfamily of metallophosphohydrolases that specifically cleave the 3',5'-cyclic phosphate moiety of cAMP and/or cGMP to produce the corresponding 5'-nucleotide. PDEs are critical determinants for modulation of cellular levels of cAMP and/or cGMP by many stimuli. Eleven families of PDEs with varying selectivities for cAMP or cGMP have been identified in mammalian tissues. Within these families, multiple isoforms are expressed either as products of different genes or as products of the same gene through alternative splicing. Regulation of PDEs is important for controlling myriad physiological functions, including the visual response, smooth muscle relaxation, platelet aggregation, fluid homeostasis, immune responses, and cardiac contractility. PDEs are critically involved in feedback control of cellular cAMP and cGMP levels. Activities of the various PDEs are highly regulated by a panoply of processes, including phosphorylation events, interaction with small molecules such as cGMP or phosphatidic acid, subcellular localization, and association with specific protein partners. The PDE superfamily continues to be a major target for pharmacological intervention in a number of medically important maladies.

Investigation of the interaction between nitric oxide and vasoactive intestinal polypeptide in the guinea-pig gastric fundus

The interaction between nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) was investigated in isolated circular smooth muscle cells and strips of the guinea-pig gastric fundus. VIP induced a concentration-dependent inhibition of carbachol-induced contraction in smooth muscle cells with a maximum at 10(-6) M. The relaxation by 10(-6) M VIP was inhibited for 79.1+/-5.8% (mean+/-s.e. mean) by the NO-synthase (NOS) inhibitor L-N(G)-nitroarginine (L-NOARG; 10(-4) M) in a L-arginine reversible way. Also the inducible NOS (iNOS) selective inhibitor N-(3-(acetaminomethyl)-benzyl)acetamide (1400 W; 10(-6) M) inhibited the VIP-induced relaxation, but its inhibitory effect was not reversed by L-arginine. When cells were incubated with the guanylyl cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ, 10(-6) M), the protein kinase A-inhibitor (R)-p-cyclic adenosine-3', 5'-monophosphothioate ((R)-p-cAMPS, 10(-6) M) and the glucocorticoid dexamethasone (10(-5) M), the relaxant effect of VIP was decreased by respectively 80.9+/-7.6, 77.0+/-11.6 and 87.1+/-4.5%. In circular smooth muscle strips of the guinea-pig gastric fundus, the VIP (10(-9) - 10(-7) M)-induced relaxations were not significantly influenced by 10(-4) M L-NOARG, 10(-6) M 1400 W, 10(-6) M ODQ and 10(-5) M dexamethasone. These results suggest that iNOS, possibly induced by the procedure to prepare the smooth muscle cells, is involved in the relaxant effect of VIP in isolated smooth muscle cells but not in smooth muscle strips of the guinea-pig gastric fundus. This study illustrates the importance of the experimental method when studying the influence of NOS inhibitors on the relaxation induced by VIP in gastrointestinal smooth muscle preparations.

Low-dose systemic phosphodiesterase inhibitors amplify the pulmonary vasodilatory response to inhaled prostacyclin in experimental pulmonary hypertension

Inhalation of aerosolized prostaglandin I(2) (PGI(2)) causes selective pulmonary vasodilation, but the effect rapidly levels off after termination of nebulization. In experimental pulmonary hypertension in intact rabbits, provoked by continuous infusion of the stable thromboxane mimetic U46619, the impact of intravenous phosphodiesterase (PDE) inhibitors on pulmonary and systemic hemodynamics was investigated in the absence and the presence of aerosolized PGI(2). We employed the monoselective inhibitors motapizone (PDE 3), rolipram (PDE 4), and zaprinast (PDE 5), as well as the dual-selective blockers zardaverine and tolafentrine (both PDE 3/4). All PDE inhibitors dose-dependently reduced the pulmonary artery pressure (Ppa), with doses for an approximately 20% decrease in pulmonary vascular resistance being 5 microgram/kg for motapizone, 25 microgram/kg for rolipram, 500 microgram/kg for zardaverine, 1 mg/kg for zaprinast, and 1 mg/kg for tolafentrine. Additive efficacy was noted when combining the monoselective 3 plus 4, 3 plus 5, and 4 plus 5 inhibitors. In parallel with the pulmonary vasorelaxant effect, all PDE inhibitors caused a decrease in systemic arterial pressure and an increase in cardiac output. Nebulized PGI(2) (56 ng/kg. min) reduced the U46619-evoked increase in Ppa by approximately 30%. This vasorelaxant effect was fully lost within 10 min after termination of PGI(2) nebulization. Coapplication of subthreshold doses of intravenous PDE inhibitors, which per se did not affect pulmonary and systemic hemodynamics, resulted in a marked prolongation of the post-PGI(2) decrease in Ppa for all blockers (motapizone at 2.2 microgram/kg, rolipram at 5.5 microgram/kg, zaprinast at 100 microgram/kg). The most effective agents, zardaverine (50 microgram/kg) and tolafentrine (100 microgram/kg), augmented the maximum Ppa drop during nebulization by approximately 30-50% and prolonged the post-PGI(2) pulmonary vasodilation to > 30 min, without affecting systemic arterial pressure and arterial oxygenation. We conclude that subthreshold systemic doses of monoselective PDE 3, 4, and 5 inhibitors and in particular dual-selective PDE 3/4 inhibitors cause significant amplification of the pulmonary vasodilatory response to inhaled PGI(2), while limiting the hypotensive effect to the pulmonary circulation. Combining nebulized PGI(2) with low-dose systemic PDE inhibitors may thus offer a therapeutic strategy to achieve selective pulmonary vasodilation in acute and chronic pulmonary hypertension.

Effect of pre-exposure to vasoconstrictors on isoprenaline-induced relaxation in rat aorta: involvement of inducible nitric oxide synthase

1. The aim of this study was to determine whether a brief (30 min) episode of contractile receptor stimulation could affect the degree of a subsequent vasorelaxation. Therefore, concentration - relaxation curves of the rat aorta to isoprenaline were compared before and after exposure of the tissue to noradrenaline (100 microM) or prostaglandin F2alpha (PGF2alpha, 100 microM). 2. Exposure to noradrenaline enhanced the second maximal relaxant effect of isoprenaline (from 20 - 95% relaxation). This effect was not due to significant differences in precontraction levels and was not modified by the presence of the endothelium. Treatment with PGF2alpha mimicked the actions of noradrenaline on subsequent vasorelaxation to isoprenaline. 3. Before exposure to noradrenaline (100 microM), forskolin (10 microM) did not produce any significant relaxation of the rat aorta. After exposure to noradrenaline, forskolin caused a concentration-dependent relaxation with a maximal effect of more than 90% in rings with and without endothelium suggesting that the change in vasorelaxation to isoprenaline occurred downstream from the beta-adrenoceptor. 4. The increase in relaxation due to exposure to noradrenaline was markedly attenuated by treatment with a protein synthase inhibitor (cycloheximide), a nitric oxide (NO) synthase inhibitor (L-NG-nitroarginine methyl ester, L-NAME) and an inhibitor of the activation of soluble guanylyl cyclase (methylene blue). 5. Western blot analysis showed an increase of inducible NO synthase (iNOS) in aortic rings exposed to noradrenaline or PGF2alpha. 6. Together, these findings suggest that pretreatment of rat aorta with noradrenaline or PGF2alpha could induce vascular NOS which would in turn result in an increase in isoprenaline-induced vasorelaxation, this increase occurring downstream from receptor activation. Such a mechanism might participate in cardioprotection during preconditioning induced by noradrenaline.

Nitric oxide donors enhance calcitonin gene-related peptide-induced elevations of cyclic AMP in vascular smooth muscle cells

Vasorelaxant effects of calcitonin gene-related peptide (CGRP) are dependent on endothelium-derived nitric oxide (NO) in some arteries. The mechanism involved is still not clear. In the present study, we used NO donors (sodium nitroprusside (SNP) and 6-(2-hydroxy-1-methyl-2-nitrisohydrazino)-N-methyl-1-hyxanamine (NOC-9)), cyclic GMP elevator (brain natriuretic peptide (BNP)) and a selective type III (cyclic GMP-inhibited) phosphodiesterase (PDE) inhibitor 5-(4-acetamidophenyl)pyrazin-2(1H)-one (SK&F94120) to investigate involvement of NO, cyclic GMP and type III PDE in CGRP-induced accumulation of cyclic AMP in cultured rat aortic smooth muscle cells. SNP (10 microM), NOC-9 (10 microM) and BNP (1 microM) all increased intracellular cyclic GMP to similar levels (2- to 2.5-fold above basal) and caused significant enhancement of CGRP (10 nM)-induced cyclic AMP accumulation similar to that caused by 10 microM SK&F 94120. The data are therefore consistent with our hypothesis that the mechanism of endothelium-dependent vasorelaxation effect of CGRP involves cyclic GMP-mediated inhibition of type III PDE and subsequent accumulation of cyclic AMP in smooth muscle cells.

Endothelial defect mediates attenuated vasorelaxant response to isoproterenol after lung transplantation

We have previously demonstrated that pulmonary vasodilation in response to isoproterenol is attenuated in conscious dogs after left lung autotransplantation (LLA). Our present goal was to identify the cellular mechanism responsible for this dysfunction. Size- and position-matched pulmonary arterial rings were isolated from the right (control) and left (LLA) lungs of 23 dogs 1-14 mo post-LLA. The rings were suspended for isometric tension recording and precontracted, and the vasorelaxant responses to activators of the beta-adrenoreceptor signaling pathway were examined. With the endothelium intact the maximal pulmonary vasorelaxant response to isoproterenol was reduced (P < 0.02) to 57 +/- 9% in LLA rings, compared with 87 +/- 3% in control rings. Responses to the Gs protein activator cholera toxin were also attenuated post-LLA, with the concentration-effect curve shifted to the right (P < 0.01) and no change in the maximal response. In contrast, the vasorelaxant responses to forskolin (adenylyl cyclase activator) or dibutyryl cAMP were similar in endothelium-intact control and LLA rings. In endothelium-denuded rings the maximal vasorelaxant responses to isoproterenol were reduced (P < 0.01) to approximately 25% in both control and LLA rings. In denuded rings cholera toxin, forskolin, and dibutyryl cAMP caused 100% vasorelaxation, and the IC50 values for these agonists were similar in control and LLA rings. Isoproterenol increased (P < 0.05) tissue cAMP to the same extent in control and LLA rings with or without endothelium. In contrast, isoproterenol increased (P < 0.05) tissue cGMP only in endothelium-intact rings, and this effect was reduced (P < 0.05) approximately 50% in LLA rings compared with control. Oxypurinol (endothelial xanthine oxidase inhibitor) restored the pulmonary vasorelaxant response to isoproterenol in endothelium-intact LLA rings. Our results provide the first evidence that activation of the beta-adrenoreceptor signaling pathway in endothelium-intact pulmonary arterial rings results in an increase in cGMP. Moreover, the attenuation in beta-adrenoreceptor-mediated pulmonary vasorelaxation post-LLA is due to inactivation of nitric oxide by endothelium-derived superoxide anion.

Effects of visnagin on cyclic nucleotide phosphodiesterases and their role in its inhibitory effects on vascular smooth muscle contraction

1. Visnagin relaxed aortae previously contracted by noradrenaline. This effect was unalterated by endothelium removal and potentiated, at high concentrations, by the previous incubation with sodium nitroprusside. 2. Visnagin weakly inhibited the hydrolytic activity of the cyclic nucleotide phosphodiesterase (PDE) isozymes (PDE5, PDE4, PDE3, cyclic GMP activated PDE2 and PDE1). 3. The present results indicate an involvement of PDE inhibition in the relaxant effect of visnagin at high concentration (>5x10(-5) M).

Modulation of cAMP-mediated vasorelaxation by endothelial nitric oxide and basal cGMP in vascular smooth muscle

Recent in vitro evidence shows a role of endothelial nitric oxide (NO) in the modulation of isoproterenol-induced vasorelaxation. To elucidate roles of endothelial cells and NO in cyclic adenosine monophosphate (cAMP)-mediated vasodilators we examined the effects of removal of endothelium and a NO synthase (NOS) inhibitor on relaxant responses in vitro of rat aortic strips to beta-adrenoceptor stimulants and colforsin dapropate, a water-soluble forskolin, and changes in cAMP and cyclic guanosine monophosphate (cGMP) contents. Relaxant responses of rat aorta to isoproterenol, denopamine, salbutamol, colforsin, and dibutyryl cAMP (dbcAMP) were blunted by removal of endothelial cells or treatment with NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Relaxant response of endothelium-intact segments to isoproterenol was associated with increases in tissue cAMP and cGMP contents. Removal of endothelium or treatment with L-NAME markedly reduced basal cGMP and abolished the isoproterenol-induced increase in cGMP but not cAMP content. In endothelium-removed segments, pretreatment with sodium nitroprusside (SNP) restored the diminished relaxant response to isoproterenol and increased basal cGMP (from 0.08 +/- 0.01 to 0.16 +/- 0.02 pmol/mg protein), whereas it did not affect the isoproterenol-induced increase in cAMP. The diminished relaxant response of endothelium-removed segments to dbcAMP was not restored by SNP pretreatment. The results suggest that relaxant response of rat aorta to cAMP-mediated vasodilators is mediated, in part, by NO production in endothelium and subsequent increase in cGMP in vascular smooth-muscle cells.

Modulation of spasmogen-stimulated Ins(1,4,5)P3 generation and functional responses by selective inhibitors of types 3 and 4 phosphodiesterase in airways smooth muscle

1. The effects of isoenzyme-selective inhibitors of phosphodiesterases PDE3 and PDE4 on cyclic AMP concentration, two indices of phosphoinositide hydrolysis, and contractile responses to spasmogens have been investigated in bovine tracheal smooth muscle (BTSM). 2. Neither the PDE3-selective inhibitor ORG 9935, nor the PDE4-selective inhibitor rolipram increased cyclic AMP levels in BTSM. However, rolipram addition in the presence of PDE3 inhibition (ORG 9935; 1 microM) concentration-dependently (-log EC50 (M), 6.55+/-0.15; n = 3) increased cyclic AMP levels to about 70% of the maximal response to the beta-adrenoceptor agonist isoprenaline. 3. Rolipram per se inhibited histamine-stimulated [3H]-inositol (poly)phosphate ([3H]-InsP(X)) accumulation by > 80% (-log EC50 (M), 6.92+/-0.11; n = 3). Although ORG 9935 (1 microM) had little effect on histamine-stimulated [3H]-InsP(X) accumulation alone it greatly facilitated the inhibitory action of rolipram (-log EC50 (M), 8.82+/-0.39; n = 3). The effects of PDE3 and/or PDE4 inhibition on [3H]-InsP(X) accumulation stimulated by muscarinic acetylcholine (mACh) receptor activation were less marked. However, combined PDE3/4 inhibition significantly decreased this response at a submaximal concentration of mACh receptor agonist (carbachol; 1 microM). 4. The greater-than-additive effect of combined PDE3/4 inhibition was also observed at the level of contractile responses to histamine and carbachol. In experiments designed to investigate the effects of PDE3 and/or 4 inhibitors on the carbachol-mediated phasic contraction, additions of rolipram (10 microM) or ORG 9935 (1 microM) were without effect, whereas added together the inhibitors caused a significant (P < 0.01) 40% reduction in the peak phasic contractile response. 5. The effect on contraction correlated with a substantial inhibitory effect of PDE3/4 inhibition on the initial increase in inositol 1,4,5-trisphosphate (InsP3) accumulation stimulated by spasmogen. Thus, in the presence of ORG 9935 (1 microM) rolipram concentration-dependently inhibited carbachol-stimulated InsP3 accumulation by > or = 50% (-log EC50 (M), 6.77+/-0.21; n = 4). 6. Carbachol (100 microM) addition caused a rapid decrease (by 67% at 10 s) in BTSM cyclic AMP level in the presence of PDE3/4 inhibition. However, omission of Ca2+ from the incubation medium prevented the carbachol-evoked decrease in cyclic AMP and this coincided with a greater inhibition (> or = 80%) of the carbachol-stimulated InsP3 response. 7. These data indicate that combined PDE3 and PDE4 inhibition has greater-than-additive effects on second messenger and functional responses to spasmogens in BTSM. Furthermore, the ability of PDE3/4 inhibition significantly to attenuate mACh receptor-mediated contractile responses, may be, at least in part, attributed to an effect exerted at the level of InsP3 generation.

Effect of selective phosphodiesterase inhibitors on response of ovine pulmonary arteries to prostaglandin E2

Several adenosine 3',5'-cyclic monophosphate (cAMP)-hydrolyzing phosphodiesterase isozymes are present in the pulmonary vasculature. The present study was designed to determine the effect of selective inhibitors of phosphodiesterase subtypes on prostaglandin E2 (PGE2)-induced relaxation of isolated fourth-generation pulmonary arteries of newborn lambs. PGE2 and forskolin caused pulmonary arteries to relax and induced an increase in the intracellular cAMP content in the vessels. The relaxation and change in cAMP content were augmented by milrinone and rolipram, inhibitors of phosphodiesterase type 3 (PDE3) and type 4 (PDE4), respectively. The augmentation in relaxation and the increase in cAMP content caused by milrinone plus rolipram was greater than the sum of the responses caused by either of the inhibitors alone. 8-Methoxymethyl-1-methyl-3-(2-methylpropyl)xanthine, an inhibitor of phosphodiesterase type 1, had no effect on relaxation and change in cAMP induced by PGE2 and forskolin. Acetylcholine alone had no effect on cAMP content in the vessels but augmented the relaxation and the increase in cAMP induced by PGE2 and forskolin in arteries with endothelium. This effect was not observed in arteries without endothelium or in arteries with endothelium treated with NG-nitro-L-arginine. These results suggest that PDE3 and PDE4 are the primary enzymes hydrolyzing cAMP of pulmonary arteries of newborn lambs and that an inhibition of both PDE3 and PDE4 would result in a greater effect than that caused by inhibition of either one of the subtype isozymes alone. Furthermore, endothelium-derived nitric oxide may enhance cAMP-mediated relaxation by inhibition of PDE3.

Effect of nitroglycerin and long-term electrical stimulation on nitrergic relaxation in the pig gastric fundus

1. The effect of incubation with the nitric oxide (NO) donor nitroglycerin and of long-term electrical stimulation on relaxations induced by non-adrenergic, non-cholinergic nerve stimulation, exogenous NO, vasoactive intestinal polypeptide (VIP) and lemakalim was investigated in the pig gastric fundus. 2. In physiological salt solution containing 10(-6) M atropine and 4 x 10(-6) M guanethidine, electrical field stimulation (40 V, 0.1 ms, 0.5-8 Hz) for periods of 10 s at 5 min intervals (train stimulation) and administration of NO (2 x 10(-6)-10(-4) M) at 5 min intervals (NO boli) induced frequency- and concentration-dependent transient relaxations, respectively. Continuous electrical field stimulation with stepwise increase of the frequency (0.5-8 Hz, cumulative stimulation) induced frequency-dependent sustained relaxations. VIP (10(-7) M), lemakalim (10(-5) M) and an infusion of NO induced a sustained relaxation. 3. Pretreatment for 30 min with 5 x 10(-4) M nitroglycerin reduced the relaxations induced by train and cumulative stimulation, but also the relaxant responses to NO, both when given in boli or as an infusion. The relaxations to VIP and lemakalim were not influenced by pretreatment with nitroglycerin. 4. Long-term electrical stimulation at 4 Hz for 40 min induced a sustained relaxation of the tissues. Administration of 3 x 10(-4) M N(G)-nitro-L-arginine methyl ester after 10, 20 or 30 min reversed the relaxation to a similar extent (approximately 70%). Previous long-term electrical stimulation at 4 Hz for 30 min did not affect the responses to stimulation, NO and VIP. 5. These results illustrate that nitroglycerin can induce a postjunctional tolerance to nitrergic stimuli in the pig gastric fundus but evidence for a prejunctional inhibition of neuronal NO synthase by NO was not obtained.

Investigations into the role of nitric oxide and the large intracranial arteries in migraine headache

Previous studies suggest that nitric oxide (NO) is involved in headaches induced by i.v. infusion of the vasodilator and NO donor glyceryl trinitrate (GTN) in healthy subjects. Extending these studies to sufferers of migraine without aura, it was found that migraineurs experienced a stronger headache than non-migraineurs. In addition, most migraineurs experienced a delayed migraine attack at variable times (mean 5.5 h) after GTN provocation. This biphasic headache response in migraineurs may be linked to hypersensitivity in the NO-cGMP pathway. Thus, compared to controls, migraineurs were found to be more sensitive to GTN-induced intracranial arterial dilatation, which is known to be mediated via liberation of NO and subsequent synthesis of cGMP Furthermore, histamine infusions in migraineurs induced headache responses and intracranial arterial responses resembling those induced by GTN in migraineurs. Histamine is known to liberate NO from the endothelium via stimulation of the H1 receptor, which is present in the large intracranial arteries in man. Because both immediate histamine-induced headache and intracranial arterial dilatation and delayed histamine-induced migraine are blocked by H1-receptor blockade, a likely common pathway for GTN and histamine-induced headaches/migraines and intracranial arterial responses may be via activation of the NO-cGMP pathway. The delay in the development of these experimental migraines may reflect activation of multiple physiological processes. The intracranial arteries of migraineurs were found supersensitive to the vasodilating effect of GTN (exogenous NO). This relates to clinical findings suggesting dilatation of the large intracranial arteries on the headache side during spontaneous migraine attacks. The function of arterial regulatory mechanisms involving NO in migraine was therefore studied. In peripheral arteries, no endothelial dysfunction of NO was found and cardiovascular and intracranial arterial sympathetic function was normal. A mild parasympathetic dysfunction may be involved and may, via denervation supersensitivity, be responsible for the observed supersensitivity to NO. Another possibility is that NO initiates a perivascular neurogenic inflammation with liberation of vasoactive peptides. NO also mediates a variety of other physiological phenomena. One of these, the pain-modulating effect observed in animals, was evaluated in a human study using GTN infusion and measurements of pain thresholds. No definite effects of GTN were demonstrated. The precise mechanisms involved in NO-triggered migraines and which part of the NO-activated cascade that is involved remain to be determined. The possibilities for pharmacological stimulation and/or inhibition of several steps of the NO-activated cascade increase rapidly and soon may be available for human studies.

Calmodulin-stimulated cyclic nucleotide phosphodiesterase (PDE1C) is induced in human arterial smooth muscle cells of the synthetic, proliferative phenotype

The diversity among cyclic nucleotide phosphodiesterases provides multiple mechanisms for regulation of cAMP and cGMP in the cardiovascular system. Here we report that a calmodulin-stimulated phosphodiesterase (PDE1C) is highly expressed in proliferating human arterial smooth muscle cells (SMCs) in primary culture, but not in the quiescent SMCs of intact human aorta. High levels of PDE1C were found in primary cultures of SMCs derived from explants of human newborn and adult aortas, and in SMCs cultured from severe atherosclerotic lesions. PDE1C was the major cAMP hydrolytic activity in these SMCs. PDE expression patterns in primary SMC cultures from monkey and rat aortas were different from those from human cells. In monkey, high expression of PDE1B was found, whereas PDE1C was not detected. In rat SMCs, PDE1A was the only detectable calmodulin-stimulated PDE. These findings suggest that many of the commonly used animal species may not provide good models for studying the roles of PDEs in proliferation of human SMCs. More importantly, the observation that PDE1C is induced only in proliferating SMCs suggests that it may be both an indicator of proliferation and a possible target for treatment of atherosclerosis or restenosis after angioplasty, conditions in which proliferation of arterial SMCs is negatively modulated by cyclic nucleotides.

Decreased vasodilator response to isoproterenol during nitric oxide inhibition in humans

The vasodilator effect of beta-adrenergic agonists has traditionally been ascribed solely to a direct effect on vascular smooth muscle. Experimental studies, however, have suggested a role of endothelium-derived nitric oxide (NO) in beta-adrenergic-mediated vasodilation. The purpose of this investigation was to determine whether NO contributes to the vasodilator effect of beta-adrenergic stimulation in humans. We analyzed the forearm blood flow response to increasing doses of isoproterenol (50, 100, and 200 ng/min), a beta-adrenoceptor agonist, during the concomitant infusion of saline or N(G)-monomethylL-arginine (L-NMMA; 4 micromol/min), a blocker of NO synthesis, in 23 normal subjects (9 men and 14 women, aged 48 +/- 7 years). The effect of L-NMMA was also assessed during infusion of sodium nitroprusside (0.8, 1.6, and 3.2 microg/min), an exogenous NO donor. Drugs were infused into the brachial artery, and forearm blood flow was measured by plethysmography. The vasodilator effect of isoproterenol was significantly blunted during the administration of L-NMMA compared with saline (maximum flow, 7.7 +/- 4 versus 11.2 +/- 5 mL x min(-1) x dL(-1), respectively; P<.001). In contrast, the vasodilator response to sodium nitroprusside was not significantly affected by the infusion of L-NMMA (maximum flow, 8.8 +/- 3.7 mL x min(-1) x dL(-1) during L-NMMA versus 8.9 +/- 3.2 mL x min(-1) x dL(-1) during saline; P=.25). These findings indicate that NO inhibition blunts the vasodilator effect of beta-adrenergic agonists in the human forearm and suggest that an abnormal response to adrenergic stimulation may occur in conditions associated with impaired NO activity.

Involvement of cyclic nucleotide-dependent protein kinases in cyclic AMP-mediated vasorelaxation

1. The involvement of cyclic AMP-dependent protein kinase (PKA) and cyclic GMP-dependent protein kinase (PKC) in the effects of cyclic AMP-elevating agents on vascular smooth muscle relaxation, cyclic nucleotide dependent-protein kinase activities and ATP-induced calcium signalling ([Ca2+]i was studied in rat aorta. Cyclic AMP-elevating agents used were a beta-adrenoceptor agonist (isoprenaline), a phosphodiesterase 3 (PDE3) inhibitor (SK&F 94120) and a PDE4 inhibitor (rolipram). 2. In rat intact aorta, the relaxant effect induced by isoprenaline (0.01-0.03 microM) was decreased by a specific inhibitor of PKA, H-89, whereas a specific inhibitor of PKG, Rp-8-Br-cyclic GMPs, was without effect. NO significant difference in PKA and PKG activity ratios was detected in aortic rings when isoprenaline 10 microM was used. At the same concentration, isoprenaline did not modify ATP-induced changes in [Ca2+]i in smooth muscle cells. Neither H-89 nor Rp-8-Br-cyclic GMPs modified this response. These findings suggest that PKA is only involved in the relaxant effect induced by low concentrations of isoprenaline (0.01-0.3 microM), whereas for higher concentrations, other mechanisms independent of PKA and PKG were involved. 3. The relaxant effects induced by SK&F 94120 and rolipram were inhibited by Rp-8-Br-cyclic GMPS with no significant effect of H-89. Neither SK&F 94120, nor rolipram at 30 microM significantly modified the activity ratios of PKA and PKG. Rolipram inhibited the ATP-induced transient increase in [Ca2+]i. This decrease was abolished by Rp-8-Br-cyclic GMPS whereas H-89 had no significant effect. These results suggests that PKG is involved in the vascular effects induced by the inhibitors of PDE3 and PDE4. Moreover, since it was previously shown that PDE3 and PDE4 inhibitors only increased cyclic AMP levels with no change in cyclic GMP level, these data also suggest a cross-activation of PKG by cyclic AMP in rat aorta. 4. The combinations of 5 microM SK&F 94120 with rolipram markedly potentiated the relaxant effect of rolipram. This relaxation was decreased by H-89 and not significantly modified by Rp-8-Br-cyclic GMPS. Moreover, the association of the two PDE inhibitors significantly increased the activity ratio of PKA without changing the PKG ratio. The present findings show that PKA rather than PKG is involved in this type of vasorelaxation. The differences in the participation of PKA vs PKG observed when inhibitors of PDE3 and PDE4 were used alone or together could be due to differences in the degree of accumulation of cyclic AMP, resulting in the activation of PKA or PKG which are differently localized in the cell. 5. These findings support for both PKA and PKG in cyclic AMP-mediated relaxation in raT aorta. Their involvement depends on the cellular pathway used to increase the cyclic AMP level.

Synergistic interaction between endothelium-derived NO and prostacyclin in pulmonary artery: potential role for K+ATP channels

1. The aim of the present study was to assess interactions between nitric oxide (NO) and prostacyclin (PGI2) during endothelium-dependent relaxations evoked by bradykinin, calcium ionophore (A23187) and acetylcholine in canine isolated pulmonary artery. 2. Relaxations to low concentrations of bradykinin and A23187 were abolished by combined inhibition of NO-synthase (by N omega-nitro-L-arginine methyl ester L-NAME, 30 microM) and cyclo-oxygenase (indomethacin, 10 microM), suggesting mediation by NO and PGI2. The individual contributions of NO and PGI2 to the dilator responses were quantified by use of areas above the separate indomethacin-insensitive and L-NAME-insensitive components of the concentration-effect curves, respectively. Individually, NO and PGI2 accounted for only 53 +/- 5% and 16 +/- 9% of total bradykinin-induced relaxation, and 46 +/- 10% and 20 +/- 9% of total A23187-induced relaxation, suggesting that NO and PGI2 acted synergistically to cause endothelium-dependent relaxation. 3. Relaxation to low concentrations of acetylcholine was abolished by L-NAME but not affected by indomethacin, suggesting the response was mediated solely by NO with no interaction from PGI2. 4. Glibenclamide (1 microM), an inhibitor of ATP-sensitive potassium (K+ATP) channels, inhibited responses to bradykinin or A23187 but did not affect relaxations evoked by acetylcholine. Glibenclamide did not affect endothelium-independent relaxations to PGI2 or the NO-donor, 3-morpholinosydnonimine (SIN-1). 5. With bradykinin, glibenclamide attenuated total relaxation by 49 +/- 8%, but did not alter the individual NO and PGI2-mediated components of the response. Glibenclamide abolished the synergistic interaction between endothelium-derived NO and PGI2. 6. At high concentrations, bradykinin, A23187 or acetylcholine caused endothelium-dependent relaxation that was insensitive to L-NAME + indomethacin. With bradykinin or A23187, this component of relaxation was inhibited by glibenclamide, whereas with acetylcholine, glibenclamide had no effect. 7. The synergistic interaction between endothelium-derived NO and PGI2 in canine pulmonary artery is mediated by activation of K+ATP channels, presumably by an endothelium-derived hyperopolarizing factor (EDHF). The pattern of endothelial dilator mediators and the presence of this synergistic interaction is dependent on the nature of the endothelial stimulus.

Chelerythrine, a protein kinase C inhibitor, interacts with cyclic nucleotide phosphodiesterases

Chelerythrine, a potent inhibitor of protein kinase C, was evaluated for its effect on cyclic nucleotide phosphodiesterases (PDE) isolated from bovine aorta. Chelerythrine activated basal PDE2 and inhibited activated PDE2, PDE4 and PDE5. The effect of chelerythrine (10 microM) was also investigated on vasorelaxation induced by a beta-adrenoceptor agonist or a PDE3 inhibitor. Chelerythrine attenuated the isoprenaline-mediated relaxation whereas it potentiated the relaxation induced by SK & F 94120 (5-(4)acetamidophenyl)pyrazin-2(1 H)-one, a PDE3 inhibitor). The present study demonstrates that chelerythrine, at a concentration generally reported in the literature to inhibit protein kinase C, interacts with cyclic nucleotide phosphodiesterases and consequently modulates vasorelaxation. These results cast some doubt on the use of chelerythrine as a specific inhibitor of protein kinase C.

Role of cyclic nucleotides in vasopressin-induced piglet pial artery dilation and opioid release

It has previously been observed that the opioids methionine enkephalin and leucine enkephalin contribute to hypoxia-induced pial artery dilation in the piglet. It has also been demonstrated that vasopressin elicits pial artery dilation and contributes to hypoxia-induced pial dilation both directly and indirectly through the release of the above opioids. The present study was designed to investigate the role of cyclic nucleotides in this vasopressin-induced pial artery dilation and opioid release in newborn piglets equipped with a closed cranial window. Pial artery diameter and cortical periarachnoid cerebrospinal fluid (CSF) opioid and cyclic nucleotides were measured after topical application of vasopressin (40, 400, and 4000 pg/mL). Opioid levels and pial diameter were examined in the absence and presence of (Rp)-8-bromo-(Br)-cAMPs and (Rp)-8-Br-cGMPs, purported cAMP and cGMP antagonists, respectively. Periarachnoid cortical CSF cAMP concentration increased in response to topical vasopressin (1048 +/- 22, 1199 +/- 51, 1334 +/- 61 and 1453 +/- 59 fmol/mL for control, 40, 400, and 4000 pg/mL vasopressin, respectively, n = 9). Vasopressin elicited pial artery dilation, which was attenuated by (Rp)-8-Br-cAMPs (14 +/- 1, 22 +/- 1, and 29 +/- 2 versus 8 +/- 1, 12 +/- 2, and 18 +/- 2% dilation for 40, 400, 4000 pg/mL vasopressin, before and after (Rp)-8-Br-cAMPs, respectively, n = 7). Similarly, vasopressin-induced pial artery dilation was accompanied by elevated CSF cGMP and this dilation was attenuated in the presence of (Rp)-8-Br-cGMPs (13 +/- 1, 21 +/- 1, and 29 +/- 2 versus 5 +/- 1, 9 +/- 1, and 12 +/- 1% dilation for 40, 400, and 4000 pg/mL vasopressin before and after (Rp)-8-Br-cGMPs, respectively, n = 7). CSF opioid concentrations increased with topical vasopressin and these increases were attenuated by (Rp)-8-Br-cAMPs. CSF methionine enkephalin concentrations were 1193 +/- 60, 1530 +/- 63, 1937 +/- 89, and 2422 +/- 104 versus 1032 +/- 25, 1185 +/- 261, 1337 +/- 31, and 1519 +/- 44 pg/mL for control, 40, 400 and 4000 pg/mL vasopressin before and after (Rp)-8-Br-cAMPs. Similarly, vasopressin-induced CSF methionine enkephalin and leucine enkephalin release was attenuated in the presence of (Rp)-8-Br-cGMPs. These data show that both cAMP and cGMP contribute to vasopressin-induced pial artery dilation and the release of the opioids methionine enkephalin and leucine enkephalin.

Nitric oxide production and endothelium-dependent vasorelaxation induced by wine polyphenols in rat aorta

1. The aim of this work was to investigate the mechanism of vasorelaxation induced by red wine polyphenolic compounds (RWPC) and two defined polyphenols contained in wine, leucocyanidol and catechin. The role of the endothelium, especially endothelium-derived nitric oxide (NO), was also investigated. 2. Relaxation produced by polyphenols was studied in rat aortic rings with and without functional endothelium, pre-contracted to the same extent with noradrenaline (0.3 and 0.1 microM, respectively). RWPC and leucocyanidol, but not catechin, produced complete relaxation of vessels with and without endothelium. However, 1000 fold higher concentrations were needed to relax endothelium-denuded rings compared to those with functional endothelium. 3. High concentrations of catechin (in the range of 10(-1) gl-1) only produced partial relaxation (maximum 30%) and had the same potency in rings with and without endothelium. 4. The NO synthase inhibitor, N omega-nitro-L-arginine-methyl-ester (L-NAME, 300 microM) completely abolished the endothelium-dependent but not the endothelium-independent relaxations produced by all of the polyphenolic compounds. 5. In contrast to superoxide dismutase (SOD, 100 u ml-1), neither RWPC nor leucocyanidol affected the concentration-response curve for the NO donor, SIN-1 (3-morpholino-sydnonimine) which also produces superoxide anion (O2-). 6. In aortic rings with endothelium, RWPC (10(-2) gl-1) produced, a 7 fold increase in the basal production of guanosine 3':5'-cyclic monophosphate (cyclic GMP) which was prevented by L-NAME (300 microM). 7. Electron paramagnetic resonance (e.p.r.) spectroscopy studies with Fe(2+)-diethyldithiocarbamate as an NO spin trap demonstrated that RWPC and leucocyanidol increased NO levels in rat thoracic aorta about 2 fold. This NO production was entirely dependent on the presence of the endothelium and was abolished by L-NAME (300 microM). 8. These results show that RWPC and leucocyanidol, but not the structurally closely related polyphenol catechin, induced endothelium-dependent relaxation in the rat aorta. They indicate that this effect results from enhanced synthesis of NO rather than enhanced biological activity of NO or protection against breakdown by O2. It is concluded that some polyphenols, with specific structure, contained in wine possess potent endothelium-dependent vasorelaxing activity.

Effects of selective phosphodiesterase 3 inhibition in the perfused liver of the rat after endotoxin treatment

1. This study was designed to investigate the role of rat phosphodiesterase 3 (RPDE3) in regulation of liver metabolism in sepsis. We studied the effects of the phosphodiesterase 3 inhibitor (PDI), enoximone, alone and in combination with regulating factors of hepatic carbohydrate metabolism and bile secretion in the perfused liver of rats treated 4 h earlier with endotoxin. In addition, cyclic AMP and cyclic GMP levels were determined in the effluate and bile by radio immunoassay methods. 2. After endotoxin treatment, infusion of enoximone at three concentrations (1 microM, 10 microM) resulted in an increased glucose output from -1.4 +/- 0.9 to 7.8 +/- 2.5 mumol l-1 20 min-1. Bile acid-independent bile flow increased also, in a dose-dependent manner. 3. In untreated livers, cyclic AMP release increased in the effluate from 1000 +/- 73 fmol g-1 min-1 to 1710 +/- 143 fmol g-1 min-1 when enoximone (10 microM) was administered. In bile from untreated livers, the level of cyclic AMP was also significantly increased by enoximone. After endotoxin treatment, the enoximone (10 microM) effect on cyclic AMP levels in effluate and bile was greatly reduced. Levels of cyclic GMP in the effluate and bile appeared unchanged in the presence of enoximone. 4. During co-infusion of glucagon (1 nM) and enoximone (10 microM), cyclic nucleotide levels in the effluate and bile of livers after endotoxin treatment were determined. In the effluate, cyclic AMP release increased from 827 +/- 144 fmol g-1 min-1 to 17802 +/- 2821 fmol g-1 min-1 when glucagon was administered. The presence of enoximone enhanced cyclic AMP further to 41696 +/- 920 fmol g-1 min-1. The same changes in cyclic AMP release were found in bile. Levels of cyclic GMP in the effluate and bile were not significantly affected by the administration of glucagon and the PDI. 5. Glucose release was determined during glucagon, sympathetic nerves stimulation and phenylephrine administration in the presence and absence of enoximone. The addition of enoximone to glucagon increased glucose release by 8.2 +/- 2.8 mumol g-1 20 min-1, without alteration of lactate balance. The PDI enhanced the glycogenolytic effects of nerve stimulation and of phenylephrine, accompanied by a reduction in lactate production. 6. Enoximone significantly enhanced the bile acid independent bile flow after glucagon, nerves stimulation and after administration of phenylephrine. Bile acid secretion was unaffected by the PDI. The vasoconstrictor effect of nerve stimulation was reduced by the PDI. 7. We conclude that endotoxin treatment reduces the ability of the PDI, enoximone, to increase cyclic AMP release in the perfused liver. The significant increase in cyclic AMP release after stimulation with glucagon and enoximone favours the view that RPDE3 is involved in the degradation of cyclic AMP in the liver after exposure to endotoxin. Additionally, the inhibition of the RPDE3 results in glucose release, vasodilatation and choleresis in endotoxin pretreated livers.