Mohamed Yassine Mallem

Impairment of the low-affinity state β1-adrenoceptor-induced relaxation in spontaneously hypertensive rats

In hypertension, a decrease of the vascular β‐adrenergic relaxation has been described. However, the specific involvement of each β‐adrenoceptor (β‐AR) subtype, in particular the low‐affinity state of β1‐AR, has not yet been evaluated. We investigated whether the low‐affinity state of β1‐AR‐induced relaxation was impaired in Spontaneously Hypertensive Rats (SHR). The relaxant responses to CGP 12177 and cyanopindolol, low‐affinity state β1‐AR agonists (with β1‐/β2‐AR antagonistic and partial β3‐AR agonistic properties) were evaluated on thoracic aortic rings isolated from 12‐weeks‐old Wistar Kyoto rats (WKY) and SHR. In WKY, CGP 12177 and cyanopindolol produced an endothelium and nitric oxide (NO)‐independent relaxation. CGP 12177‐induced endothelium‐independent relaxation was not modified either by β1‐, β2‐AR (nadolol) or β3‐AR (L‐748337 or SR 59230A) antagonists but was significantly reduced by high concentrations of CGP 20712A (P<0.05). This relaxation was also reduced by adenylyl cyclase inhibitors, SQ 22536 or MDL 12330A. In SHR, CGP 12177 produced mainly an endothelium and NO‐dependent relaxation. This effect was not modified by nadolol, but was strongly reduced by β3‐AR blockade. Endothelium‐independent relaxation to CGP 12177 was not altered by adenylyl cyclase inhibition, but was amplified in preparations from pertussis toxin‐pretreated SHR. The immunohistochemical analysis revealed an upregulation of β3‐AR in the endothelial layer of SHR aorta, whereas the β3‐AR‐induced relaxation was not modified. In conclusion, we demonstrated an impaired low‐affinity state of the β1‐AR‐induced relaxation and an upregulation of the β3‐AR in hypertension. Some clinical implications of those findings are discussed.

Vasodilatory effect of pentoxifylline in isolated equine digital veins.

The direct vasodilatory action of pentoxifylline (1-(5-oxohexyl)-3,7-dimethylxanthine) and its signalling pathway was evaluated in equine digital veins. Cumulative concentration-response curves to pentoxifylline (1 nM to 300 μM) were recorded in phenylephrine-precontracted equine digital vein rings under different experimental conditions. Relaxation to pentoxifylline was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (a non-xanthine adenosine receptor antagonist; 3 μM). Nitric oxide synthase (NOS), soluble guanylate cyclase and cyclooxygenase (COX) inhibitors (Nω-nitro-L-arginine methyl ester (100 μM), ODQ (30 μM) and indomethacin (10 μM), respectively) significantly reduced the maximum relaxation induced by pentoxifylline. Moreover, pentoxifylline-induced relaxation was strongly reduced by Rp-8-Br-PET-cyclic guanosine monophosphate-S (a protein kinase G inhibitor; 3 μM), but remained unaffected by H-89 (a protein kinase A inhibitor; 2 μM). Pentoxifylline-induced relaxation was associated with a 3.4-fold increase in tissue cGMP content. To investigate whether pentoxifylline can affect cAMP- and cGMP-mediated relaxations, curves to forskolin, to sodium nitroprusside (SNP) and 8-bromo-cGMP were also recorded in endothelium-denuded equine digital vein rings pretreated with pentoxifylline (10 and 100 μM). Pentoxifylline only potentiated the SNP-mediated relaxation at the highest concentration (100 μM). Thus, pentoxifylline relaxed equine digital veins via endothelium-dependent and endothelium-independent components. The effect was mediated through both the NOS and COX pathways and could also result from inhibition of cGMP specific-phosphodiesterase activity at the highest concentrations used.

Nonlinear mixed effects models applied to cumulative concentration–response curves

Objectives In experimental pharmacology, drug effect studies currently establish and analyse cumulative concentration–response curves (CCRC) under repeated measurements designs. Usually the CCRC parameters are estimated using the Hills function in a nonlinear regression for independent data. The two‐way analysis of variance is generally used to identify a statistical difference between the responses for two treatments but that analysis does not take into account the nonlinearity of the model and the heteroscedasticity (uneven distribution) of the data. We presently tested the possibility of finding a statistical solution for the nonlinear response in repeated measurements data using the nonlinear mixed effects (nlme) models.

Positive influence of AT1 receptor antagonism upon the impaired celiprolol-induced vasodilatation in aorta from spontaneously hypertensive rats

We evaluated celiprolol-induced vasodilatation in aorta taken from 12-week-old spontaneously hypertensive rats (SHR) and the effect of AT(1) angiotensin II receptor antagonism on the vasodilatory action of celiprolol in Wistar Kyoto (WKY) rats and SHR. In WKY rats, the celiprolol-induced relaxation was greatly decreased in denuded aorta, and completely abolished in intact aorta by N(omega)-nitro-l-arginine methyl ester (l-NAME, 100 microM). In SHR, celiprolol-induced relaxation was reduced compared to WKY rats (E(max) (value obtained for the highest concentration, 300 microM)=39.1+ or - 3.78%, n=21 vs. 80.4 + or - 3% in WKY rats, n=10; P<0.0001). Endothelium removal or pre-treatment with l-NAME did not alter celiprolol-induced relaxation in SHR. In both strains, relaxation to celiprolol was decreased in the presence of nadolol (a beta(1)/beta(2)-adrenoceptor antagonist, 10 microM). N-[[3-[(2S)-2-hydroxy-3-[[2-[4-[(phenylsulfonyl)amino] phenyl]ethyl]amino] propoxy]phenyl]methyl]-acetamide (L748337, a beta(3)-adrenoceptor antagonist, 7 microM) had no effect. A 12-day treatment with candesartan cilexetil (an AT(1) receptor antagonist, 0.37 or 1mg/kg/day) reduced systolic blood pressure in both strains, but only improved relaxation to celiprolol in SHR, and only at the highest dose (E(max)=64.2+/-3.9%, n=10, P<0.0001 vs. SHR control). In both strains, local aortic AT(1) receptor antagonism with candesartan CV11974 (100 microM) had no effect. The endothelial beta(1)/beta(2) relaxation induced by celiprolol was therefore impaired in SHR aorta and AT(1) receptor antagonism improved the response to celiprolol, in conjunction with a reduction in blood pressure. This work highlights the need to analyse the potential benefit of a combination of celiprolol/AT(1) receptor antagonist in the treatment of hypertension.

Evaluation of the role of superoxide anions in endotoxin-induced impairment of β-adrenoceptor-mediated vasodilation in equine digital veins.

OBJECTIVE To investigate the role of superoxide anions in the lipopolysaccharide (LPS)-induced impairment of beta-adrenoceptor-mediated equine digital vein (EDV) vasodilation. SAMPLE POPULATION EDVs isolated from forelimbs of 24 healthy adult horses. PROCEDURES Endothelium-intact or endothelium-denuded EDV rings were incubated with or without LPS (10 microg/mL) of Escherichia coli (O55:B5) for 4 hours. Cumulative concentration-relaxation curves resulting from administration of isoprenaline, a nonselective beta-adrenoceptor agonist, or from administration of SR 58611A, a selective beta(3)-adrenoceptor agonist, were recorded in phenylephrine-preconstricted EDVs in the absence or the presence of superoxide dismutase (200 U/mL). Isoprenaline-induced relaxation was also evaluated with or without the cyclooxygenase inhibitors indomethacin (10 microM) and NS-398 (10 microM). RESULTS Isoprenaline and SR 58611A induced concentration-dependent relaxation of EDV rings, which was inhibited by LPS exposure. Superoxide dismutase abolished the inhibitory effect of LPS on the isoprenaline- and SR 58611A-mediated relaxation. Pretreatment of the LPS-treated EDVs with indomethacin or NS-398 restored the isoprenaline-mediated relaxation and abolished the LPS-induced impairment to a similar extent as superoxide dismutase. CONCLUSIONS AND CLINICAL RELEVANCE Results supported a role of superoxide anions in the LPS-induced impairment of beta-adrenoceptor-mediated EDV vasodilation. The LPS-induced oxidative stress in EDVs may contribute to vascular dysfunctions associated with laminitis in horses.

Low-affinity state beta1-adrenoceptor-induced vasodilation in SHR

Low-affinity state beta1-adrenoceptor (beta1-AR) was functionally expressed in some blood vessels and was different from beta1, beta2 and beta3-AR. In rat aorta, low-affinity state beta1-AR activation produced an endothelium-independent relaxation which was impaired in spontaneously hypertensive rats (SHRs). In the present work, we investigated whether renin-angiotensin system was involved in this alteration by evaluating the effects of enalapril, an angiotensin converting enzyme (ACE) inhibitor or losartan, an AT1 angiotensin receptor antagonist. Cumulative concentration-response curves to low-affinity state beta1-AR agonists (CGP 12177, cyanopindolol or alprenolol) and to NS 1619, a large conductance Ca2+-activated K+ channels (BK) agonist were performed in denuded aortic rings isolated from control or treated Wistar Kyoto (WKY) rats or SHRs in different experimental conditions. The low-affinity state beta1-AR-mediated aortic vasodilation was impaired in 5 and 12 weeks old SHRs when compared to age-matched WKY. Twelve days enalapril (5 mg/kg/day) or losartan (15 mg/kg/day) treatments reduced systolic blood pressure (SBP) only in 12 weeks old SHRs whereas no significant change was observed in other groups. These treatments improved low-affinity state beta1-AR effect only in SHRs groups. In 12 weeks old WKY rats, CGP 12177-induced relaxation was insensitive to glibenclamide, a K(ATP)+ channel blocker, but was reduced by TEA or iberiotoxin, two large conductance Ca2+-activated K+ channel (BK) blockers. The impairment of NS 1619-induced vasodilation in both 5 and 12 weeks old SHRs was restored by enalapril or losartan. These results suggested that improvement of the low-affinity state beta1-AR-mediated vasodilation in 5 and 12 weeks old SHRs could be attributed to enhanced BK channels-induced hyperpolarization in SHRs independently of lowering of SBP.

Effect of nebivolol treatment during pregnancy on the genital circulation, fetal growth and postnatal development in the Wistar rat.

The aim of study was to evaluate the effects of nebivolol, a cardioselective beta-1 adrenergic receptor blocker of the third generation with vasodilatory properties, vs. bisoprolol on the genital circulation, uterine vasculature, fetal growth and postnatal development in pregnant Wistar rats. Non invasive measurements of systolic and diastolic blood pressure (SBP and DBP) and heart rate (HR), and invasive measurement of genital blood flow (GBF) were taken in pregnant rats, by tail cuff and transonic probe methods respectively, after an oral treatment by gastric gavage with nebivolol (8mg/kg/day) or bisoprolol (10mg/kg/day) from day 11 to day 18 of pregnancy. Other morphometrical and histological measurements were performed on the ovarian and uterine arteries to evaluate the effect of nebivolol on the uterine vasculature. Furthermore, postnatal mortality and pup growth were recorded. The data demonstrated that nebivolol (compared with bisoprolol) induced a significant decrease in SBP, HR and GBF while DBP remained unchanged. Moreover, nebivolol increased the diameter and the length of ovarian and uterine arteries and the number of uterine artery segmental branches. The results also showed that the body weight gain of newborns in the nebivolol group was significantly lower vs. bisoprolol and vs. control with a higher mortality rate. The nebivolol action is not only limited to its favorable hemodynamic effects represented by a decrease in blood pressure, but it also produces adverse effects on fetal growth and postnatal development that may limit its therapeutic use in females during pregnancy.

Cardiac effects of long-term active immunization with the second extracellular loop of human β1- and/or β3-adrenoceptors in Lewis rats

β1- and β3-adrenoceptor (AR) auto-antibodies were detected in patients with dilated cardiomyopathy. Many studies have shown that β1-AR auto-antibodies with partial agonist-like effect play an important role in the pathogenesis of this disease. Moreover, a recent study carried out in our laboratory has shown that β3-AR antibodies (β3-ABs), produced in rats, were able to reduce cardiomyocyte contractility via β3-AR activation. The aims of this study were (1) to investigate, in isolated cardiomyocytes from rabbit, the role of Gi proteins in the β3-ABs-induced cardiac negative inotropy, (2) to determine whether β3-ABs may exhibit β3-AR antagonistic property which is characteristic of partial agonists, and (3) to determine whether long-term active immunization producing both β1-ABs and/or β3-ABs leads to the development of cardiac dysfunction in Lewis rats. Lewis rats were immunized for 6 months with peptidic sequences corresponding to the second extracellular loop of human β3-AR and/or β1-AR. Agonistic effect of β3-ABs was evaluated on electrically field-stimulated isolated cardiomyocytes from adult rabbit by measuring the cell shortening. Echocardiography and ex vivo isolated perfused heart studies were conducted on immunized rats. Finally, β-AR expression was quantified by immunofluorescence and RT-qPCR. SR58611A (10 nM), a preferential β3-AR agonist, and purified β3-ABs (25 μg/ml) induced a decrease in cell shortening (-39.71±4.9% (n=10) and -17.06±3.9% (n=10) respectively). This effect was significantly inhibited when the cardiomyocytes were preincubated with pertussis toxin (0.3 μg/ml), a Gi protein inhibitor (p<0.05). In addition, SR58611A-mediated negative inotropic effect was decreased when cardiomyocytes were preincubated with β3-ABs (p<0.0001). Echocardiography revealed a decrease in the fractional shortening and ejection fraction in rats immunized against β1-AR and both β1- and β3-AR. However, the study on isolated heart showed a decrease of the isoproterenol-induced lusitropic and inotropic effects in the 3 groups of immunized rats. These systolic and diastolic dysfunctions are correlated with a decrease in the expression of β1-ARs and an increase of β3-ARs in rats immunized against the β1-AR and an increase of both β3-AR and β1-AR in rats immunized against the β3-AR. For the first time, these results showed that β3-ABs had a β3-AR partial agonist-like activity which might play a role in the pathogenesis of cardiac dysfunction.

CGP12177-induced haemodynamic and vascular effects in normotensive and hypertensive rats.

CGP12177 is a non-conventional partial agonist, known to have cardiostimulating and vasorelaxant properties related to its agonist action on the low affinity state of the beta(1)-adrenoceptor (beta(1LA)-adrenoceptor). In normotensive Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHR), CGP12177-induced vasorelaxant effects were analysed in hindquarter vessels to assess modifications in hind limb vascular resistance, and in femoral artery rings. The global haemodynamic effects induced by CGP12177 were also investigated using telemetry in conscious animals. In hindquarters vasculature precontracted with 5-hydroxytryptamine, CGP12177 (0.16 to 475 microg) produced a similar dose-dependent decrease in hindquarters perfusion pressure in both strains. Vasorelaxation was not modified by nadolol, a beta(1) and beta(2)-adrenoreceptor antagonist, nor by L748337, a beta(3)-adrenoceptor antagonist, but was concentration dependently inhibited by bupranolol, a beta(1LA)-adrenoceptor antagonist at high concentrations. In femoral artery rings from WKY rats and SHR, CGP12177 produced a concentration-dependent relaxation, which was unaffected by nitric oxide synthases inhibition but was significantly reduced in the presence of bupranolol. With double cardiac autonomic blockade (atropine plus atenolol) in conscious WKY rats and SHR, CGP12177 greatly increased heart rate with minor changes in mean arterial pressure in both strains. Conversely, in the absence of double cardiac autonomic blockade, the amplitude of CGP12177-induced heart rate increase was less pronounced and had an hypotensive effect. The reduction in tachycardia and the hypotension were significantly greater in SHR compared to WKY rats. In conclusion, in both strains, CGP12177 produced vasodilating effects in hindquarter vessels and femoral arteries that can be attributed to a beta(1LA)-adrenoceptor stimulation. In conscious WKY rats and SHR, CGP12177-induced cardiostimulation and hypotension were not significantly different after baroreflex blockade, but were decreased and increased respectively, in the presence of baroreflex activity.

Change in vascular smooth muscle response to 5-HT due to short- or long-term endothelial denudation of the bovine digital vein.

Several chronic progressive vascular diseases, such as laminitis, show vasocontractile dysfunction that might evolve into reperfusion injury and/or vessel structural remodelling, which may be traced back to aberrant endothelial function. In the present study, the vasomotor responses of bovine digital veins (BDVs) to 5-hydroxytryptamine (5-HT) were investigated in blood vessels, with and without endothelium present, and in samples deprived of endothelium before or after overnight incubation in tissue culture medium, to evaluate the effects of short- and long-term endothelial damage on vascular smooth muscle (VSM) reactivity. No significant effects were observed in the blood vessels tested immediately after the removal of endothelium. In contrast, a significant increase in VSM reactivity to 5-HT was seen in vessels incubated without endothelium. This long-term change in smooth muscle reactivity was prevented by exposure to the nitric oxide (NO) donor nitroprusside (P < 0.01), suggesting that the long-term lack of inhibitory control exerted by endothelium-derived NO is involved in increased VSM reactivity. The RhoA/ROCK pathway inhibitor fasudil reduced VSM hyper-contractility to ~65% (P < 0.001), the superoxide dismutase-mimetic tempol normalised the vascular response and the non-selective COX-inhibitor indomethacin exerted a moderate inhibitory effect (P < 0.05). Thus, over-activation of the RhoA/ROCK pathway and production of reactive oxygen species could account for VSM hyper-reactivity, triggered by long-term endothelium-deprivation in BDVs, suggesting that these biochemical mechanisms are potential targets for controlling the progressive vasocontractile dysfunction of digital veins in animals affected with laminitis.