The α1-adrenergic receptor not the DA1-dopaminergic receptor mediates cyclosporine–SKF38393 renovascular interaction

Dopamine D2 receptor upregulates leptin and IL-6 in adipocytes

Leptin is a pro-inflammatory cytokine secreted by the adipose tissue. Dopamine D2 receptors (D2Rs) have anti-inflammatory effects in the brain and kidney tissues. Mouse and human adipocytes express D2R; D2R protein was 10-fold greater in adipocytes from human visceral tissue than subcutaneous tissue. However, the function of D2R in adipocytes is not well understood. 3T3-L1 cells were treated with D2-like receptor agonist quinpirole, and immunoblot and quantitative PCR were performed. Quinpirole increased the protein and mRNA expression of leptin and IL-6, but not adiponectin and visfatin (24 h). It also increased the mRNA expression of TNF-α , MCP1, and NFkB-p50. An acute increase in the protein expression of leptin and TNF-α was also found in the cells treated with quinpirole. The leptin concentration in the culture media was increased by quinpirole-bathing the 3T3-L1 adipocytes. These quinpirole effects on leptin and IL-6 expression were prevented by the D2R antagonist L741,626. Similarly, siRNA-mediated silencing of Drd2 decreased the leptin, IL-6, mRNA, and protein expressions. The D2R-mediated increase in leptin expression was prevented by the phosphoinositide 3-kinase inhibitor LY294002. Acute quinpirole treatment in C57Bl/6J mice increased serum leptin concentration and leptin mRNA in visceral adipocyte tissue but not in subcutaneous adipocytes, confirming the stimulatory effect of D2R on leptin in vivo. Our results suggest that the stimulation of D2R increases leptin production and may have a tissue-specific pro-inflammatory effect in adipocytes.

Nitric oxide synthase/K+ channel cascade triggers the adenosine A(2B) receptor-sensitive renal vasodilation in female rats

Adenosine A2B-receptors mediate the adenosine-evoked renal vasodilations in male rats. Here, we tested whether this finding could be replicated in female renal vasculature and whether K(+) hyperpolarization induced by nitric oxide synthase (NOS) and/or heme oxygenase (HO) accounts for adenosine A2B receptor-sensitive renal vasodilations. In phenylephrine-preconstricted perfused kidneys, vasodilations caused by the adenosine analog 5'-N-ethylcarboxamidoadenosine (NECA, 1.6-50 nmol) were attenuated after blockade of adenosine A2B (alloxazine) but not A2A [8-(3-Chlorostyryl) caffeine, CSC] or A3 receptors (N-(2-methoxyphenyl)-N'-[2-(3-pyridinyl)-4-quinazolinyl]-urea, VUF 5574), confirming the preferential involvement of A2B receptors in NECA responses. NOS activation mediated the A2B receptor-mediated NECA response because: (i) NOS inhibition (N(ω)-nitro-L-arginine-methyl ester, L-NAME) attenuated NECA vasodilations, (ii) concurrent L-NAME/alloxazine exposure caused more inhibition of NECA responses, and (iii) inhibition of NECA responses by alloxazine disappeared in L-arginine-supplemented preparations. Although HO inhibition (zinc protoporphyrin) failed to modify NECA responses, the attenuation of these responses by alloxazine disappeared in hemin (HO inducer)-treated preparations. NECA vasodilations were also attenuated after exposure to BaCl2, glibenclamide but not tetraethylammonium (blockers of inward rectifier, ATP-sensitive, and Ca(2+)-dependent K(+)-channels, respectively). The combined alloxazine/BaCl2/glibenclamide infusion caused no additional attenuation of NECA vasodilations. Vasodilations caused by minoxidil (K(+)-channel opener) were reduced by L-NAME or BaCl2/glibenclamide, supporting the importance of NOS signaling in K(+) hyperpolarization. NECA or minoxidil vasodilations were attenuated by ouabain, Na(+)/K(+)-ATPase inhibitor, and in KCl-preconstricted preparations. Overall, facilitation of adenosine A2B receptor/NOS/K(+) channel/Na(+)/K(+)-ATPase cascade underlies NECA vasodilations in female rats. Enhancing HO activity, albeit not causally related to NECA vasodilations, improves the pharmacologically compromised (alloxazine) NECA response.

Comparable renovascular protective effects of moxonidine and simvastatin in rats exposed to cigarette smoke

Renovascular impairment plays a major role in smoking-induced nephrotoxicity. This study investigated the effect of the imidazoline I(1)-receptor/alpha(2)-adrenoceptor agonist moxonidine, as compared to the lipid lowering drug simvastatin, on abnormalities induced by cigarette smoke (CS) in renovascular reactivity. Six rat groups were used: control, CS (twice a day for 6weeks), simvastatin, moxonidine, CS+simvastatin, and CS+moxonidine. CS exposure increased plasma urea and creatinine and reduced plasma and renal nitrate/nitrite (NOx). In isolated perfused phenylephrine-preconstricted kidneys of CS rats, vasodilator responses to carbachol or isoprenaline, but not papaverine, were attenuated. Nitric oxide synthase (NOS) inhibition by N(G)-nitro-L-arginine (L-NNA) reduced carbachol vasodilations in control but not CS kidneys, suggesting the impairment of NOS activity by CS. Simultaneous administration of moxonidine or simvastatin abolished CS-induced abnormalities in indices of renal function, NOx, and vasodilations caused by carbachol or isoprenaline. The possibility whether alterations in antioxidant or lipid profiles contributed to the interaction was investigated. CS increased renal malondialdyde and decreased glutathione, and glutathione peroxidase, superoxide dismutase and catalase activities. Further, CS reduced plasma HDL and increased cholesterol, triglycerides, and LDL. Simvastatin or moxonidine abolished the deleterious CS effects on antioxidant activity; the lipid profile was normalized by simvastatin only. These findings highlight that renovascular dysfunction caused by CS and the underlying oxidative damage is evenly attenuated by moxonidine and simvastatin.

Exacerbation by nicotine of the cyclosporine A-induced impairment of beta-adrenoceptor-mediated renal vasodilation in rats

Nicotine is implicated in smoking-related renovascular impairment and worsening of existing nephropathies. In the present study, we investigated whether nicotine aggravates the deleterious effect of the immunosuppressant drug cyclosporine A (CsA) on renal vasodilation induced by the beta-adrenoceptor agonist isoprenaline. Bolus isoprenaline (0.03-8.0 micromol) elicited dose-dependent vasodilation of phenylephrine-preconstricted perfused kidneys that was attenuated by infusion at 5 mL/min of nicotine (5 x 10(-4) mol/L) or CsA (2 micromol/L). Further, chronic administration of nicotine (0.4 mg/kg per day) or CsA (20 mg/kg per day) for 3 weeks reduced isoprenaline-induced vasodilation and elevated plasma urea and creatinine concentrations, effects that were magnified when both nicotine and CsA were administered concurrently. The role of endothelial and smooth muscle signalling in the acute nicotine/CsA renovascular interaction was investigated. Vasodilation caused by 0.25 micromol isoprenaline was attenuated by 6 micromol/L propranolol and 10 mmol/L tetraethylammonium (TEA), potentiated by 100 micromol/L hexamethonium and 7 micromol/L diclophenac, and virtually abolished in 80 mmol/L KCl-preconstricted tissues. N(G)-Nitro-L-arginine (L-NNA; 200 micromol/L), methylene blue (10 micromol/L), 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propane-sulphonate (CHAPS; 0.2% for 30 s), nifedipine (750 nmol/L), atropine (1 micromol/L) and SQ22536 (an adenylyl cyclase inhibitor; 3 x 10(-5) mol/L) had no effect on isoprenaline responses. Nicotine (5 x 10(-4) mol/L) reduced isoprenaline-induced vasodilation and this effect was potentiated by concurrent CsA (2 micromol/L) infusion. Nicotine-induced impairment of the vasodilator response to isoprenaline was reduced by hexamethonium and potentiated by L-NNA, methylene blue, CHAPS and nifedipine. Alternatively, CsA exacerbation of the nicotine-isoprenaline interaction was abolished by propranolol, L-NNA, methylene blue, CHAPS, L-arginine, TEA and nifedipine. 5. In summary, nicotine and CsA produce additive impairment of kidney function and beta-adrenoceptor-mediated renovascular control, nitric oxide (NO)-cGMP signalling tonically restrains nicotine-induced impairment of isoprenaline vasodilation and the endothelial NO-K+ pathway modulates the aggravating effect of CsA on nicotine-isoprenaline interactions.

Inhibition of nitric oxide-guanylate cyclase-dependent and -independent signaling contributes to impairment of beta-adrenergic vasorelaxations by cyclosporine

This study investigated the role of endothelium- and smooth muscle-dependent mechanisms in the interaction of cyclosporine (CyA), an immunosuppressant drug, with beta-adrenoceptor (isoprenaline)-mediated relaxations in isolated rat aortas precontracted with phenylephrine. CyA effects were assessed in the absence and presence of NG-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), methylene blue (guanylate cyclase inhibitor), or propranolol (beta-adrenoceptor antagonist). In aortas with intact endothelium (E+), pretreatment with L-NAME or methylene blue significantly reduced isoprenaline (1 x 10(-9) to 1 x 10(-7)M) relaxations in contrast to no effect for tetraethylammonium (K+ channel blocker), or diclophenac (cyclooxygenase inhibitor), suggesting a major role for the nitric oxide-guanylate cyclase (NO-GC) pathway, but not endothelial hyperpolarizing factor or vasodilator prostanoids, in isoprenaline responses. Isoprenaline relaxations were still evident, though significantly attenuated, in endothelium-denuded aortas (E-) and were resistant to L-NAME or methylene blue. Acute exposure to CyA (2 microM) caused propranolol-sensitive reductions in isoprenaline responses in E+ and E- aortas. The CyA-induced attenuation of isoprenaline responses in E+ aortas largely disappeared in L-NAME-treated aortas and after supplementation with L-arginine, the substrate of nitric oxide. CyA also reduced the endothelium-independent, GC-dependent aortic relaxations evoked by sodium nitroprusside, an effect that was virtually abolished by methylene blue. We conclude that: (i) endothelial and smooth muscle mechanisms contribute to aortic beta-adrenoceptor relaxations and both components are negatively influenced by CyA, and (ii) NO-GC signaling plays an integral role in the vascular CyA-beta-adrenoceptor interaction. The clinical relevance of the present study is warranted given the established role of impaired vascular function in CyA toxicity.