Different efficacy of in vivo herpes simplex virus thymidine kinase gene transduction and ganciclovir treatment on the inhibition of tumor growth of murine and human melanoma cells and rat glioblastoma cells

Initial studies have demonstrated the therapeutic efficacy for cancer treatment of in vivo transfer of the herpes simplex virus thymidine kinase gene followed by ganciclovir (GCV) treatment. However, recent studies have questioned the validity of this approach. Using retroviral vector-producing cells (VPC) as a source for in vivo gene transfer, we evaluated the efficacy of in vivo transduction of malignant cells using three different tumor cell models: B16 murine and IIB-MEL-LES human melanomas and a C6 rat glioblastoma. In vitro studies showed a bystander effect only in C6 cells. In vivo studies showed an inhibition of tumor growth in the two melanoma models when tumor cells were coinjected with VPC-producing retroviral vectors carrying the herpes simplex virus thymidine kinase gene, followed by GCV treatment; however, 100% of mice developed tumors in both models. Under similar experimental conditions, 70% (7 of 10) of syngeneic rats completely rejected stereotactically transferred C6 tumor cells; most of them (5 of 10) showed a prolonged survival. Treating established C6 tumors with VPC-producing retroviral vectors carrying the herpes simplex virus thymidine kinase gene and GCV led to the cure of 33% (4 of 12) of the animals. Rats that rejected tumor growth developed an antitumor immune memory, leading to a rejection of a stereotactic contralateral challenge with parental cells. The immune infiltrate, which showed the presence of T lymphocytes, macrophages, and polymorphonuclear cells at the site of the first injection and mainly T lymphocytes and macrophages at the site of tumor challenge, strengthened the importance of the immune system in achieving complete tumor rejection.

Studies on the mechanisms involved in the ATP-induced relaxation in human and rabbit corpus cavernosum

The effect of ATP in human and rabbit corpus cavernosum (CC) smooth muscle was investigated. Strips of human CC were vertically mounted in an organ bath and the tonic tension was recorded. ATP (0.1-3 mM) induced a concentration-dependent relaxant effect, with a pD2 value of 3.01+/-0.3. The purine-induced relaxation was not affected by L-NAME (100 microM). In rabbit CC, ATP also induced a concentration-dependent relaxation, which was not influenced by L-NAME or by indomethacin (3 microM), with a pD2 value of 3.1 +/-0.4. The ATP-induced relaxant effect in rabbit CC was increased by both the inhibitor of adenosine reuptake, dipyridamole (3 microM) and by the inhibitor of adenosine deaminase, EHNA (0.3 microM). Moreover CGS 15943 (3 microM), an A2a adenosine antagonist, reduced the ATP-induced relaxation. UTP was not able to produce relaxation. The two ATP analogues 2-methylthioATP and alpha,beta-methylene ATP were able to induce relaxation in rabbit CC, with the following order of potency: 2-methylthioATP > ATP > alpha,beta-methylene ATP thus suggesting a role for P2y receptors. However, reactive blue (500 microM), an unspecific P2y antagonist, did not modify the ATP relaxant response. The inhibition of phospholipase C by U73122 (3 microM) and of the endoplasmic reticulum Ca2+ATPase by thapsigargin (1 microM) did not modify the ATP-induced relaxation. The P2x specific antagonist PPADS (30 microM) and suramine (500 microM) were not able to modify the ATP relaxation either in the absence or presence of CGS 15943 (3 microM). These results confirm that ATP acts as a potent and NO-independent relaxant agent of human and rabbit CC. Our findings also show that the ATP effect is partially attributable to the metabolic breakdown of ATP to adenosine, which acts through A2a receptor stimulation, but is also due to a direct stimulation of P2 receptors that are different from the classical P2y and P2X receptor subtypes for ATP.

[Antitumor gene therapy using suicide genes]

Tumor cells transduced with retrovirus carrying the herpes simplex-1 virus thymidine kinase (HSV-tk) are capable of transforming the antiviral drug ganciclovir (GVC) into a metabolic form only toxic to dividing cells. The efficiency of this suicide gene therapy is increased by a "bystander" effect resulting not only in the death of the recipient cell, but also in the death of non modified surrounding cells. Even though the mechanism of this "bystander" effect remains to be elucidated, strong evidence suggest that the immune system plays a main role to achieve complete tumor eradication. In the present study we evaluate the efficiency of this suicide system on three different tumor models: one human melanoma, one murine melanoma, and a rat glioblastoma. Tumors were established by injection of tumor cells s.c. in nude and C57Bl/6 mice, respectively, and stereotactically into the brain of Sprague Dawley rats. Animals in the treated group were co-injected with packaging cells producing recombinant retrovirus carrying the HSV-tk gene, and followed by i.p. administration of GVC. In short term studies, we observed inhibition of tumor growth for all the tumor models evaluated (p < 0.01). In long term studies, using the C6 rat glioma line, 50% of the animals survived longer than 75 days (p < 0.0001), and were able to reject a contralateral challenges with C6 parental cells. Histological and immunohistochemical analysis showed the presence at an inflammatory infiltrate composed by T lymphocytes, macrophages and polymorphonuclear cells. These data demonstrate that suicide genes might represent an attractive form of cancer gene therapy in the treatment of brain tumors and their intracerebral dissemination.

B1 receptor involvement in the effect of bradykinin on venular endothelial cell proliferation and potentiation of FGF-2 effects

1. Bradykinin (BK) contributes to the inflammatory response inducing vasodilation of postcapillary venules and has been demonstrated to induce neovascular growth in subcutaneous rat sponges. 2. In this study the ability of BK to stimulate cell growth and migration in cultured endothelium from coronary postcapillary venules (CVEC) has been investigated. 3. [3H]-thymidine incorporation in subconfluent and synchronised CVEC was used to monitor DNA synthesis over 24 h. BK promoted a concentration-dependent increase of DNA synthesis with maximal activity at 100 nM. At this concentration BK also induced 18 fold accumulation of c-Fos protein immunoreactivity in the nucleus within 1 h from peptide exposure. 4. The total number of cells recovered after 48 h exposure to BK was increased in a concentration-dependent manner. Maximal effect was produced by 100 nM concentration of the peptide which produced 50% increase in cell number. The selective B1 receptor agonist Des-Arg9-BK mimicked the proliferative effect of BK, while the B2 receptor agonist kallidin was devoid of any activity. The proliferation induced by BK was abolished in a concentration-dependent manner by the addition of the B1 selective antagonist Des-Arg9-Leu8-BK, while the selective B2 receptor antagonist HOE140 did not modify BK-induced growth. 5. DNA synthesis and growth promoted by a threshold concentration of fibroblast growth factor-2 (FGF-2) (0.25 nM) were potentiated by increasing concentrations of BK and Des-Arg9-BK. 6. Endothelial cell migration assessed by the Boyden Chamber procedure was not promoted by BK or the selective B1 and B2 receptor agonists. 7. These data are the first demonstration that BK promotes growth of endothelial cells from postcapillary venules. The mitogenic activity of BK involves c-Fos expression and potentiates the growth promoting effect of FGF-2. Only the B1 receptor appears to be responsible for the proliferation induced by BK and suggests that this type of receptor might be implicated in favouring angiogenesis of coronary venules.

Linomide blocks angiogenesis by breast carcinoma vascular endothelial growth factor transfectants

The blocking of angiogenesis provides a novel therapeutic target to inhibit tumour spreading. In this study, we investigated the effect of linomide on angiogenesis induced in vivo by highly angiogenic breast carcinoma cells. The rabbit cornea was used to assess neovascular growth in the absence of a tumour mass. MCF-7 cells stably transfected with the cDNA encoding for vascular endothelial growth factor 121 (VEGF121) (V12 clone) were used to elicit a potent VEGF-dependent corneal angiogenesis. After tumour cell implant, albino rabbits received 100 mg kg(-1) day(-1) linomide for 5 consecutive days. Daily observation of neovascular progression indicated that linomide blocked angiogenesis. The antiangiogenic effect of linomide was apparent within 48 h from the beginning of the treatment and was both angiosuppressive and angiostatic. The block of neovascular growth lasted over 10 days from treatment suspension, and preformed vessels, which had regressed, remained dormant, suggesting the persistence of unfavourable conditions for capillary progression. Linomide (50-200 microg ml[-1]) was not cytotoxic in vitro on resting capillary endothelial cells but blocked endothelial cell replication induced by VEGF. Our data indicate that linomide can efficiently and persistently block VEGF-dependent angiogenesis in vivo in the absence of a growing tumour mass. These data suggest that linomide could be a chemopreventive drug in breast cancer patients and a valuable tool in clinical settings in which metastatic spreading occurs in the absence of a detectable tumour mass.

Nitric oxide is an upstream signal of vascular endothelial growth factor-induced extracellular signal-regulated kinase1/2 activation in postcapillary endothelium

We recently demonstrated that nitric oxide (NO) significantly contributes to the mitogenic effect of vascular endothelial growth factor (VEGF), suggesting a role for the NO pathway in the signaling cascade following kinase-derivative receptor activation in vascular endothelium. The aim of this study was to investigate the intracellular pathways linked to VEGF/NO-induced endothelial cell proliferation. We assessed the activity of the mitogen-activated protein kinase (MAPK) that is specifically activated by growth factors, extracellular-regulated kinase (ERK1/2), on cultured microvascular endothelium isolated from coronary postcapillary venules. ERK1/2 was immunoprecipitated, and its activity was assessed with an immunocomplex kinase assay. In endothelial cells exposed for 5 min to the NO donor drug sodium nitroprusside at a concentration of 100 microM, ERK1/2 activity significantly increased. VEGF produced a time- and concentration-dependent activation of ERK1/2. Maximal activity was obtained after 5 min of stimulation at a concentration of 10 ng/ml. The specific MAPK kinase inhibitor PD 98059 abolished ERK1/2 activation and endothelial cell proliferation in a concentration-dependent manner in response to VEGF and sodium nitroprusside. The NO synthase inhibitor Nomega-monomethyl-L-arginine, as well as the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, blocked the activation of ERK1/2 induced by VEGF, suggesting that NO and cGMP contributed to the VEGF-dependent ERK1/2 activation. These results demonstrate for the first time that kinase-derivative receptor activation triggers the NO synthase/guanylate cyclase pathway to activate the MAPK cascade and substantiates the hypothesis that the activation of ERK1/2 is necessary for VEGF-induced endothelial cell proliferation.

Vasorelaxant effects induced by the antiangiogenic drug linomide in aortic and saphenous vein preparations of the rabbit

1. Linomide (N-phenylmethyl-1,2-dihydro-4-hydroxyl-1-methyl-2-oxoquinoline-3-carb oxa mide) inhibits vascular proliferation and has been proposed as an antiangiogenic drug. We have investigated the vascular effect of linomide in rabbit aortic and saphenous vein ring preparations and in rat cultured vascular smooth muscle cells (VSMCs). 2. Linomide (25-300 micrograms ml-1) did not alter the basal tone of the preparations. The drug induced a concentration-dependent relaxant effect in aortic rings with endothelium, preconstricted by noradrenaline (NA), 5-hydroxytryptamine (5-HT) and by the thromboxane mimetic U46619. 3. The degree of relaxation induced by linomide was significantly reduced by exposure to the cyclooxygenase inhibitors indomethacin (3 microM) and acetylsalicylic acid (500 microM), and was not influenced by pretreatment with the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (100 microM) in aortic rings with endothelium, preconstricted with NA. 4. Endothelium removal significantly reduced the relaxant response to linomide in aortic ring preparations. 5. A concentration-dependent relaxant response was observed also in rabbit saphenous vein preparations deprived of endothelium and preconstricted either by NA or U46619. The degree of relaxation obtained in a high potassium solution was consistently smaller than that observed in NA-pretreated venous preparations. 6. The vasorelaxant effect of linomide was consistently blunted by the adenylate cyclase inhibitor SQ 22536 (50 microM), both in intact aortic rings and in those deprived of endothelium. 7. In rat cultured vascular smooth muscle cells, linomide (100-200 micrograms ml-1) induced a significant increase in cyclic AMP levels, which was blocked by exposure to 50 microM SQ 22536. 8. In endothelium-deprived aortic ring preparations, the linomide-induced relaxant effect was greatly reduced in high potassium medium (KCl = 25 mM). Pretreatment with the ATP potassium channel inhibitor glibenclamide (3 microM) significantly reduced the linomide-induced relaxation. 9. The results show that linomide possesses a vasorelaxant effect which is attributable to both endothelium-dependent and -independent properties. While the former component of the drug's activity is apparently due to the release of a prostanoid from endothelial cells, the endothelium-independent mechanism involved in linomide relaxation is linked to cyclic AMP accumulation and to ATP-sensitive potassium channel activation in VSMCs.

Nitric oxide promotes proliferation and plasminogen activator production by coronary venular endothelium through endogenous bFGF

We reported previously that NO is responsible for the angiogenesis produced by endothelium-dependent vasodilating peptides. To investigate the mechanisms by which NO controls angiogenesis, NO was assessed for the ability to affect cell proliferation and upregulation of urokinase-type plasminogen activator (uPA) induced by basic fibroblast growth factor (bFGF) when added exogenously to or when produced endogenously by coronary venular endothelial cells (CVECs). The treatment of the cells with the NO donor sodium nitroprusside (NaNp) induced uPA upregulation and cell proliferation, which were prevented by anti-bFGF antibodies. Similarly, the NO-dependent mitogenic activity of the vasodilating peptide substance P (SP) was blocked by anti-bFGF antibodies, thus implicating endogenous bFGF in the NO-induced response. NaNp and SP induced bFGF expression as measured by Western blot analysis of CVEC extracts and by differential reverse transcriptase-polymerase chain reaction of bFGF mRNA. SP-induced upregulation of bFGF was prevented by the NO synthase inhibitor N omega-monomethyl-L-arginine. We conclude that NO promotes cell proliferation and uPA upregulation in CVECs by inducing endogenous bFGF and that this pathway mediates the angiogenetic response to the vasoactive neuropeptide SP. This signaling paradigm may provide an important link between shear rate, NO, bFGF, and coronary angiogenesis.

The expression of the secreted protein acidic and rich in cysteine (SPARC) is associated with the neoplastic progression of human melanoma

SPARC (secreted protein acidic and rich in cysteine) is an extracellular protein associated with tissues exhibiting high rates of cell proliferation and matrix remodeling. The current work shows that the human melanoma cell lines IIB-MEL-LES, IIB-MEL-IAN, and IIB-MEL-J and different human metastatic melanomas expressed high levels of SPARC mRNA and protein. By western blot analysis we detected a single secreted 42-kDa band in human diploid fibroblasts-conditioned medium and a 45- to 40-kDa doublet in the three melanoma cell lines and all the metastatic melanomas tested. Part of the melanoma samples and cell lines showed an additional doublet of 36-34 kDa. SPARC mRNA was expressed by the three established cell lines, 14 metastatic melanoma samples, and tumors raised in nude mice, and no spliced variants were found. The heterogeneous pattern of SPARC secreted by human melanoma cells is the result of post-translational glycosylation and a specific extracellular leupeptin-inhibitable cleavage. Unlike human fibroblasts, melanoma cells did not overexpress SPARC on addition of TGF-beta. Immunohistochemical analysis showed that SPARC was strongly expressed in 100% of primary melanomas (7 of 7) and metastatic melanomas (29 of 29), moderately expressed in most of the positive dysplastic nevi (13 of 14), and only weakly expressed in nevocellular nevi (4 of 25). Normal melanocytes did not express SPARC. The data suggest that the expression of SPARC is associated with the neoplastic progression of human melanoma.

Effect of the non-peptide blocker (+/-) CP 96,345 on the cellular mechanism involved in the response to NK1 receptor stimulation in human skin fibroblasts

The effect of the selective non-peptide antagonist for NK1 receptors (+/-)CP 96,345 on cellular transduction mechanisms elicited by the NK1 selective agonist [Sar9]-substance P-sulfone ([Sar9]-SP) was investigated in a stabilized culture of human skin fibroblasts (HF) and compared to the effects of two peptide antagonists, FK 888 and GR 82, 334. The exposure of the cells to [Sar9]-SP (100 nM) produced an early increase in inositol 1,4,5-trisphosphate (IP3) level, which peaked after 6 s, and a later rise in cellular inositol 1-phosphate (IP1) content which reached the maximum level in 15 min. The cAMP level was not significantly modified. The increase in IP1 was greatly reduced, at approximately the same extent by the 10 min pretreatment with a concentration of (+/-)CP 96,345 (100 nM) 10 times smaller than that of FK 888 and GR 82,334 (1 microM). The cytosolic Ca2+ mobilization in response to the NK1 agonist was monitored both by spectrofluorimetric and single-cell image analysis determinations on adherent cells loaded with the Ca(2+)-sensitive fluorescent indicators Fura-2/AM and Indo-1, respectively. [Sar9]-SP (100 nM) produced a rapid increase in the intracellular Ca2+ level in Fura-2/AM loaded cells. Cytosolic Ca2+ mobilization, measured by single-cell image analysis, indicated a concentration-dependent increase in both the ratio and in the number of cells responding to [Sar9]-SP. Either the non-peptide or the peptide selective NK1 receptor antagonists inhibited the increase in Ca2+ level in both the assays. In the spectrofluorimetric experiments the antagonizing effects of (+/-)CP 96,345 (1-100 nM), FK 888 (10 nM-1 microM) and GR 82,334 (10 nM-1 microM) were concentration-dependent. Moreover, the non-peptide antagonist was more potent than the two peptide antagonists, producing an 82.5% inhibition of Ca2+ mobilization at a concentration (10 nM) at which FK 888 and GR 82,334 decreased the response by only 62.3 and 60%, respectively. Stimulation of phosphatidylinositol turnover and calcium mobilization were also induced by 10 nM bradykinin; these effects were influenced neither by the previous administration of the NK1 receptor agonist nor by the three antagonists tested. These results demonstrate that the cellular transduction mechanisms induced in human skin fibroblasts by NK1 receptor stimulation are specifically and effectively antagonized by (+/-)CP 96,345, and that this non-peptide antagonist is more potent than the two peptide antagonists tested.

Thapsigargin inhibits the response to acetylcholine and substance P but does not interfere with the responses to endothelium-independent agents

We investigated the influence of the Ca(2+)-ATPase inhibitor thapsigargin (TG) on the vasorelaxant response to different endothelium-dependent and endothelium-independent relaxing agents in an isolated thoracic aorta preparation of the rabbit, precontracted by norepinephrine (NE). Pretreatment with 100 microM L-arginine methyl ester (L-NAME) an inhibitor of nitric oxide (NO) synthesis, completely prevented acetylcholine (ACh)-induced relaxation; the inactive stereoisomer D-NAME did not modify the effect of ACh. The exposure of the preparations to 1 microM TG induced a slowly developing slight increase in the basal tension during 30-min contact. The same concentration of TG also slightly reduced the response to the subsequent administration of NE. The antagonist effect of TG on the ACh response was concentration dependent in the range between 0.1 and 10 microM. A 30-min pretreatment with 1 microM TG appeared to be sufficient to induce a consistent antagonism of the ACh (0.01-10 microM) concentration-relaxant effect curve, since an increase to 60 min did not produce a further significant increment in the degree of the antagonist effect. The concentration-dependent relaxation induced by substance P (SP 0.1-3 nM) was also significantly antagonized by 1 microM TG. The effect of the calcium ionophore A23187 (0.01-1 microM) was reduced by the Ca(2+)-ATPase inhibitor only at the higher concentrations tested (0.3-1 microM). However, a 30-min contact time with 1 microM TG was completely ineffective in antagonizing the concentration-relaxant response curves to the two nitrovasodilators sodium nitroprusside (SNP 0.1-100 microM) and nitroglycerin (NTG 1-300 nM) and to the cyclic GMP analogue 8-Bromo-cyclic GMP (3-100 microM). The effects of the beta-adrenoceptor agonist isoprenaline (ISO 0.1-10 microM) and of the direct adenylate cyclase activator forskolin (FK 0.01-10 microM) were also completely unaffected by 1 microM TG. These results demonstrate that TG affects the response to agents that induce an endothelium-dependent relaxation through receptor-dependent calcium mobilization. However, they do not support the hypothesis that sarcoplasmic pump activity is essential for the development of a vasorelaxant response to endothelium-independent agents.

The tachykinin NK1 receptor mediates the migration-promoting effect of substance P on human skin fibroblasts in culture

Fibroblast migration is an important component of the tissue response during the repair process, and substance P (SP) has been shown to exert trophic effects. In the present study, cell migration was evaluated as the distance travelled by adherent human skin fibroblasts (HF) at 96 h and by the number of individual cells moving across a filter within 5 h. In control conditions (1% calf serum) adherent fibroblasts moved from the starting line by approximately 700 microns. The addition of SP (10(-11)-10(-7) M) increased HF mobilisation in a concentration-dependent manner, with maximal activity at 10(-8) M (50% increase in migration over control). Migration of individual HF in suspension was also promoted by SP in a concentration-dependent manner, with an EC50 of 2.2 x 10(-9) M. The response produced by the maximally effective concentration of SP was equal to 65 and 90% of the effect elicited by 100 ng/ml Platelet-Derived Growth Factor A/B (PDGF A/B) on adherent and individual cells respectively. The synthetic NK1 receptor agonist [Sar9]SP-sulphone (10(-11)-10(-6) M) reproduced the SP effect. The NK2 and NK3 receptor agonists [beta Ala8]NKA(4-10) and [MePhe7]NKB were devoid of any effect. The effect of SP was antagonised by two selective antagonists of NK1 receptors, namely (+/-) CP 96,345 (10(-10)-10(-8) M) and FK 888 (10(-9)-10(-7) M), while the NK2 receptor antagonist MEN 10627 (10(-8)-10(-7) M) was not effective. Our data indicate that SP is a potent effector of fibroblast migration and the NK1 receptor is responsible for this effect. These observations further support the specific role of the NK1 receptor in mediating the trophic function of SP at the cutaneous level.

Nitric oxide mediates mitogenic effect of VEGF on coronary venular endothelium

Vascular endothelial growth factor (VEGF) is a secreted protein that is a specific growth factor for endothelial cells. We have recently demonstrated that nitric oxide (NO) donors and vasoactive peptides promoting NO-mediated vasorelaxation induce angiogenesis in vivo as well as endothelial cell growth and motility in vitro; in contrast, inhibitors of NO synthase suppress angiogenesis. In this study we investigated the role of NO in mediating the mitogenic effect of VEGF on cultured microvascular endothelium isolated from coronary postcapillary venules. VEGF induced a dose-dependent increase in cell proliferation and DNA synthesis. The role of NO was determined by monitoring proliferation or guanosine 3',5'-cyclic monophosphate (cGMP) levels in the presence and absence of NO synthase blockers. The proliferative effect evoked by VEGF was reduced by pretreatment of the cells with NO synthase inhibitors. Exposure of the cells to VEGF induced a significant increment in cGMP levels. This effect was potentiated by superoxide dismutase addition and was abolished by NO synthase inhibitors. VEGF stimulates proliferation of postcapillary endothelial cells through the production of NO and cGMP accumulation.

Proliferation and migration of endothelial cells is promoted by endothelins via activation of ETB receptors

The growth and migration of endothelial cells are the prerequisites for vascular remodeling. The effects of endothelin (ET)-1 and -3 (ET-1, ET-3) on the proliferation and migration of endothelial cells isolated from bovine adrenal capillaries (BACE) and human umbilical veins (HUVEC) have been investigated. Cell proliferation (measured as DNA synthesis and as total cell number) and migration were significantly increased by ET-1 and ET-3. Dose-dependent proliferation was produced by ET-1 and ET-3 in both cell lines, with maximal effects at 0.1 nM concentration. ET-1 and ET-3 also stimulated BACE and HUVEC mobilization in a dose-dependent manner. The maximal responses were obtained at 10 nM concentration in both BACE and HUVEC. The full agonist for the ETB receptor, ET-(16--21), was able to reproduce the effects of ET on proliferation and migration of both cell lines. Modification of ET-(16--21) at Leu17 and Ile19 and amidation of the COOH-terminal were accompanied by loss of activity. The ETB-receptor antagonist IRL-1038 blocked the migration induced by ET-3 and ET-(16--21), whereas the ETA-receptor antagonist BQ-123 was not effective. We conclude that ETs, by favoring endothelial cell growth and mobilization, can contribute to neovascularization through an autocrine mechanism that requires ETB-receptor activation.

The potent relaxant effect of adenosine in rabbit corpora cavernosa is nitric oxide independent and mediated by A2 receptors

In the present study the effect of adenosine and adenosine analogues on rabbit isolated cavernosal smooth muscle has been evaluated in comparison with the effect of acetylcholine and electrical field stimulation. In the presence of guanethidine and indomethacin, acetylcholine and electrical field stimulation relaxed the rabbit corpus cavernosum, which was precontracted with phenylephrine. The nitric oxide synthesis inhibitor, N omega-nitro-L-arginine-methylester (L-NAME), greatly reduced the relaxation induced by electrical stimulation and completely abolished the relaxant effect of acetylcholine. A concentration-dependent relaxation of the rabbit corpus cavernosum was produced by adenosine; this effect was not modified by L-NAME, but was reduced by adenosine deaminase. On the other hand, the adenosine-induced relaxation was potentiated by the inhibitor of adenosine deaminase, erythro-9-(2-hydroxy-3-nonyl)adenine and by the adenosine uptake inhibitor dipyridamole. Moreover, the effect of adenosine was antagonized by the unspecific adenosine receptor antagonist 8-phenyltheophylline. The receptor subtypes involved in cavernosal relaxation were characterized by using selective receptor antagonists: 1,3-dipropyl-8-cyclopentylxanthine, a blocker of A, receptors, did not modify adenosine-induced relaxation. This effect was, however, antagonized by the A2-receptor antagonist CGS15943. A relaxant effect was also obtained with nanomolar concentrations of two synthetic adenosine analogues, the preferential A2 receptor agonist 5'-N-ethylcarboxamidoadenosine and the A2a selective agonist CGS21680. These results demonstrated that adenosine has potent relaxant activity on the corpus cavernosum, acting through a mechanism different from the nitric oxide pathway, and that receptors involved in the effect of adenosine belong to the A2a subtype.

Roles of nitric oxide and endothelium-derived hyperpolarizing factor in vasorelaxant effect of acetylcholine as influenced by aging and hypertension

We investigated vasodilator responses to acetylcholine (ACh) in isolated mesenteric vascular bed preparations (preconstricted with methoxamine) of young (2 months) and old (18 months) normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). ACh produced a similar dose-dependent vasorelaxant effect in preparations from both 2-month old normotensive and hypertensive rats. This vasodilator response to ACh decreased with age, especially in hypertensive animals. In preparations from young WKY, the vasorelaxant effect of ACh was not affected by 100 microM NG-nitro-L-arginine methyl ester (L-NAME), and was only slightly reduced by 500 microM L-NAME. The K+ channel blocker tetraethylammonium (TEA 2.5-10 mM) concentration-dependently antagonized the ACh-induced vasodilation in the same preparations. In preparations obtained from aged WKY animals, as well as in those from young and aged SHR animals, ACh-induced vasodilation was significantly and concentration-dependently reduced by 100 and 500 microM L-NAME. On the other hand, TEA induced a lesser antagonistic effect than that observed in young normotensive animals. In preparations preconstricted with 80 mM KCl, ACh caused vasodilation that was weaker in preparations from young WKY than in those from aged WKY; on the contrary, ACh was more effective in young than in aged SHR. These results confirm that the vasodilating response to ACh decreases with age and hypertension and suggest that the main mechanism responsible for the effect of ACh in vessels of young normotensive animals consists of activation of K+ channels. In preparations from old normotensive, as well as in those from young and old hypertensive animals, ACh induces vasorelaxation mainly through nitric oxide (NO) release.

Enhancement of the vasoconstrictor response to KCL by nitric oxide synthesis inhibition: a comparison with noradrenaline

The role of the vascular endothelium in the response to a vasoconstrictor agent acting through a non-receptorial mechanism, such as KCl, was tested in the isolated mesenteric vascular bed of the rat. It was confirmed that the vasoconstrictor response evoked by stimulation of sympathetic terminals was unaffected by 100 microM NG-nitro-D-arginine methyl ester (D-NAME), but was significantly potentiated by 100 microM NG-nitro-L-arginine methyl ester (L-NAME) and by removal of endothelium. Responses to exogenous noradrenaline (1-100 microM) were also enhanced by treatment with 100 microM NG-monomethyl-L-arginine (L-NMMA) and with L-NAME, but not with D-NAME. The potentiating effect of NO synthesis inhibitors was reversed by 1 mM L-arginine. Moreover, the noradrenaline-induced vasoconstriction was significantly increased by endothelium-deprivation. Potassium chloride (80 mM) induced a vasoconstrictor response which was not modified by pretreatment with prazosin (0.1 microM) and yohimbine (0.1 microM). The response to KCl was unaffected by D-NAME (100 microM) but the L-stereoisomer induced a significant increase in the perfusion pressure. In endothelium-denuded preparations the vasoconstrictor response to KCl was greater than in control conditions and was quantitatively similar to that observed in L-NAME-treated preparations. The responses to electrical field stimulation, noradrenaline and KCl in endothelium-denuded preparations were not modified by L-NAME. The results suggest that an increase in vascular tone, per se, may represent a trigger for the release of endothelium-derived relaxing factor from endothelial cells.

Bradykinin-induced vasodilation is changed to a vasoconstrictor response in vessels of aged normotensive and hypertensive rats

The vascular response to bradykinin was investigated in mesenteric vascular bed preparations preconstricted with methoxamine, obtained from 2- and 18-month old normotensive (WKY) and spontaneously hypertensive (SHR) rats. In preparations from young normotensive rats bradykinin (1 nm-10 microM) produced an endothelium-dependent vasorelaxant effect which was greatly reduced by the B2 receptor antagonist Ac-D-Arg[Hyp3,D-Phe7,Leu8]-bradykinin (1 microM), and was unaffected by the B1 receptor antagonist des-Arg9,[Leu8]-bradykinin (1 microM). The degree of vasodilation was similar in preparations from age-matched SHR rats. In vessels obtained from old animals bradykinin induced an endothelium-independent vasoconstrictor response; this effect was more pronounced in preparations from SHR than in those from WKY rats. The vasoconstriction was unaffected by both B1 and B2 receptor antagonists, and was abolished by 3 microM indomethacin. We conclude that the vasorelaxant effect of bradykinin in vessels of young animals is due to stimulation of B2 receptors. This vasodilating response can be converted by aging to a vasoconstriction and is probably due to the release of a prostanoid product; moreover it is more pronounced in spontaneously hypertensive animals.

Prejunctional prostanoid receptors on cardiac adrenergic terminals belong to the EP3 subtype

1. The effects of prostaglandin E2 (PGE2) and of several synthetic prostanoids on the cardiac response to sympathetic nerve stimulation in guinea-pig atria have been evaluated. 2. PGE2 (0.01-100 nM), sulprostone (0.01-100 nM) and misoprostol (0.1-100 nM), but not butaprost (0.1-100 nM), dose-dependently reduced the increase in cardiac contractility induced by electrical field stimulation of sympathetic terminals. 3. The EP1 antagonist AH6809 (1 microM) did not modify the inhibition of cardiac response induced by PGE2, sulprostone and misoprostol. 4. In preparations preloaded with [3H]-noradrenaline, tritium overflow induced by electrical field stimulation was greatly and significantly reduced by 100 nM PGE2 and by 100 nM sulprostone. 5. These results indicate that PGE2 and other synthetic prostanoids reduce noradrenaline release from cardiac adrenergic nerve terminals acting on prejunctional inhibitory receptors belonging to the EP3 subtype.