F. Ledda

Nitric oxide mediates angiogenesis in vivo and endothelial cell growth and migration in vitro promoted by substance P.

We evaluated the effects of nitric oxide (NO) generators and endogenous production of NO elicited by substance P (SP) in the angiogenesis process. Angiogenesis was monitored in the rabbit cornea in vivo and in vitro by measuring the growth and migration of endothelial cells isolated from coronary postcapillary venules. The angiogenesis promoted in the rabbit cornea by [Sar9]-SP-sulfone, a stable and selective agonist for the tachykinin NK1 receptor, and by prostaglandin E1 (PGE1), was potentiated by sodium nitroprusside (SNP). Conversely, the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME), given systemically, inhibited angiogenesis elicited by [Sar9]-SP-sulfone and by PGE1. Endothelial cells exposed to SNP exhibited an increase in thymidine incorporation and in total cell number. Exposure of the cells to NO generating drugs, such as SNP, isosorbide dinitrate, and glyceryl trinitrate, produced a dose-dependent increase in endothelial cell migration. Capillary endothelial cell proliferation and migration produced by SP were abolished by pretreatment with the NO synthase inhibitors N omega-mono-methyl-L-arginine (L-NMMA), N omega-nitro-L-arginine (L-NNA), and L-NAME. Exposure of the cells to SP activated the calcium-dependent NO synthase. Angiogenesis and endothelial cell growth and migration induced by basic fibroblast growth factor were not affected by NO synthase inhibitors. These data indicate that NO production induced by vasoactive agents, such as SP, functions as an autocrine regulator of the microvascular events necessary for neovascularization and mediates angiogenesis.

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 bradykinin/B1 receptor promotes angiogenesis by up- regulation of endogenous FGF-2 in endothelium via the nitric oxide synthase pathway

Bradykinin (BK) mediates inflammation and contributes to angiogenesis. We assessed the mechanisms for BK contribution to angiogenesis. Nanomolar concentrations of BK induced angiogenesis in rabbit corneas in absence of inflammation. The effect was dose‐dependent and mediated by the B1 receptor. B2 receptor stimulation failed to directly promote vascular growth unless inflammation was induced. Anti‐fibroblast growth factor‐2 (FGF‐2) antibody blocked the effect of BK or B1 receptor agonist. In postcapillary venular endothelial cells (CVEC), B2 receptor activation induced inositol phosphate turnover and calcium transients, whereas the B1 receptor was coupled to nitric oxide synthase (NOS) up‐regulation and activation and cGMP increase. Differential RT‐PCR and Western blot analysis revealed FGF‐ 2 up‐regulation in cells exposed to BK or to the selective B1 agonist, whereas the B2 agonist was without effect. Consistently, BK and the B1 but not the B2 agonist exerted a proliferative effect on CVEC, which was prevented by anti‐FGF‐2 antibody and by NOS inhibition. These results demonstrate that BK is angiogenic despite its proinflammatory activity and that the B1 receptor is involved. The B1 receptor is coupled to NOS activation and FGF‐2 up‐regulation, events not shared by the B2 receptor activation.

Electrophysiological and antiarrhythmic properties of propafenon in isolated cardiac preparations.

Propafenon, a new antiarrhythmic drug, caused a 30% decrease in maximal driving frequency and a 65 ms net increase in functional refractory period of isolated guinea pig atria at a concentration as low as 0.5 μg/ml. The spontaneous rate of isolated atria and the contractility of electrically driven ventricular strips were reduced after treatment with propafenon 1μg/ml. Propafenon 0.5 μg/ml also altered action potentials of sheep Purkinje fiber. It reduced the action potential and overshoot amplitudes, decreased the maximum rate of depolarization of the action potential upstroke in a frequency-dependent fashion, shortened the action potential and effective refractory period, and depressed the membrane responsiveness. Moreover, propafenon antagonized the chronotropic and inotropic effects of isoprenaline in isolated guinea pig heart preparations; the pA2 value was about 6.4. Finally, propafenon possessed very weak calcium antagonist properties, being about 100 times less potent than verapamil in this respect. We conclude that propafenon is an antiarrhythmic drug with β-adrenoceptor blocking and “membrane stabilizing” activities in the same range of concentrations and that it has a calcium antagonistic activity only at much higher concentrations.

Tachykinins activate guinea-pig alveolar macrophages: involvement of NK2 and NK1 receptors.

1 The effects of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were evaluated on superoxide anion () production by guinea‐pig alveolar macrophages (AM). 2 SP dose‐dependently (ED50 = 0.7 nm) evoked production from guinea‐pig AM; the N‐terminal heptapeptide, SP(1–7), was ineffective. In the presence of thiorphan (10−5 m), an enkephalinase inhibitor, the stimulating effects of SP were not significantly modified. NKA and NKB were both able to induce production from guinea‐pig AM, ED50 values being 0.1 and 1.3 nm, respectively. Therefore, the rank order of activity of natural tachykinins was NKA > SP > NKB. Tachykinin‐evoked effects were quantitatively similar to those elicited by the autacoid mediator PAF‐acether and less than those induced by the synthetic peptide N‐formylmethionyl‐leucyl‐phenylalanine (FMLP). 3 The NK2 receptor agonist [β‐Ala8]‐NKA (4–10) dose‐dependently evoked production from guinea‐pig AM; the NK1 receptor agonist [Pro9]‐SP sulphone acted only at high concentrations, while the NK3 receptor agonist [Me, Phe7]‐NKB was ineffective. 4 These findings indicate that guinea‐pig AM possess NK2 and possibly some NK1 tachykinin receptors and further suggest tachykinin involvement in lung pathophysiology.

Effects of noradrenaline and isoprenaline, in combination with α‐ and β‐receptor blocking substances, on the action potential of cardiac Purkinje fibres

1. The effects of noradrenaline and isoprenaline on the repolarization phase of the action potential have been studied in the Purkinje fibres of sheep heart, electrically driven at constant rates.

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.

STUDIES ON THE POSITIVE INOTROPIC EFFECT OF PHENYLEPHRINE: A COMPARISON WITH ISOPRENALINE

1 The effects of phenylephrine and isoprenaline on the isometric contraction of guinea‐pig ventricle were compared over the whole range of their respective dose‐response curves. 2 In preparations driven at 2.5 Hz the increase in contractile force induced by either isoprenaline or phenylephrine was linearly correlated to an increase in maximum velocity of force development. The relaxation time was shortened by isoprenaline but not by phenylephrine. 3 The negative inotropic effect induced by δ[N‐(3,4‐dimethoxyphenethyl)‐N‐methyl‐amino]‐α‐(3,4,5‐trimethoxyphenyl)α‐isopropylvaleronitrile hydrochloride (D600) was reversed by isoprenaline, but little influenced by phenylephrine. 4 The study of the interval‐force relationship shows that the increase in contractile force induced by phenylephrine (3 × 10−5 M) was relatively greater at low frequencies of stimulation, and that the maximum effect was reached at the frequency of 1 Hz. 5 The positive inotropic effect of phenylephrine (10−4 M) was significantly higher at a frequency of 1 Hz than at 2.5 Hz; the effect of isoprenaline (3 × 10−8 M) was not significantly different at the two driving frequencies. 6 In preparations driven at 1 Hz the inotropic effect of the lower concentrations of phenylephrine was due to an increase in the time to peak tension without any change of the maximum velocity of force development; however an increase of this parameter became evident only after higher concentrations of the amine (10−5 M or more), associated with a progressive shortening of the time to peak. 7 A correlation between mechanical and electro physiological effects of phenylephrine is attempted; the suggestion is advanced that the prolongation of the action potential and of the active state duration may be an important factor in the inotropic effect of phenylephrine.

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.

Identification, localization and functional activity of oxytocin receptors in epididymis

Oxytocin (OT) is a neurohypophysial hormone with unclear physiological functions in the male. Several previous studies indicated that OT might have a role in the ejaculatory process, stimulating sperm release from the epididymal storage. In this study we investigated on the presence and function of OT receptor (OTR) in rabbit and human epididymis. By using RT-PCR, Western and binding studies, we found that OTR gene and protein is expressed in the human epididymis and stimulates in vitro contractility. The immunolocalization of OTR suggests that the receptor is not only present in the smooth muscle cells of the human epididymis but also in the epithelial compartment. Experiments performed in rabbit epididymal epithelial (rEE) cells in culture indicate that OT induces the release of an other potent stimulator of epididymal contractility, endothelin-1 (ET-1), Blocking the ET(A) subtype of the ET-1 receptors, by using a specific antagonist (BQ-123), partially counteracts the contractile effect of OT, suggesting positive interactions between the two peptides in regulating epididymal contractility. Finally, to investigate whether an acute OT administration increases sperm release also in humans, we treated oligozoospermic patients with an intravenous bolus of OT (2.5 IU), just before sperm collection. In a small, single blind study, we found that OT almost doubled sperm retrieval when compared with vehicle administration. Our results indicate that OT might have physiological functions also in the male, controlling epididymal motility and sperm progression through the male genital tract.