Crucial role of nitric oxide synthases system in endothelium-dependent hyperpolarization in mice

The endothelium plays an important role in maintaining vascular homeostasis by synthesizing and releasing several relaxing factors, such as prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). We have previously demonstrated in animals and humans that endothelium-derived hydrogen peroxide (H(2)O(2)) is an EDHF that is produced in part by endothelial NO synthase (eNOS). In this study, we show that genetic disruption of all three NOS isoforms (neuronal [nNOS], inducible [iNOS], and endothelial [eNOS]) abolishes EDHF responses in mice. The contribution of the NOS system to EDHF-mediated responses was examined in eNOS(-/-), n/eNOS(-/-), and n/i/eNOS(-/-) mice. EDHF-mediated relaxation and hyperpolarization in response to acetylcholine of mesenteric arteries were progressively reduced as the number of disrupted NOS genes increased, whereas vascular smooth muscle function was preserved. Loss of eNOS expression alone was compensated for by other NOS genes, and endothelial cell production of H(2)O(2) and EDHF-mediated responses were completely absent in n/i/eNOS(-/-) mice, even after antihypertensive treatment with hydralazine. NOS uncoupling was not involved, as modulation of tetrahydrobiopterin (BH(4)) synthesis had no effect on EDHF-mediated relaxation, and the BH(4)/dihydrobiopterin (BH(2)) ratio was comparable in mesenteric arteries and the aorta. These results provide the first evidence that EDHF-mediated responses are dependent on the NOSs system in mouse mesenteric arteries.

Short-term and long-term FK506 treatment alters the vascular reactivity of renal and mesenteric vascular beds

The aims of this study were to investigate the role of endothelin-1 in FK506-induced hypertension and vascular dysfunction of rats treated with the drug for 8 (short-term) or 30 (long-term) days and to measure malondialdehyde levels in the kidneys. Kidney and mesentery of rats were perfused. In the short-term treated groups, there was no significant change in systolic blood pressure. The response to noradrenaline only in renal vascular beds was significantly increased by FK506 and this increase was prevented by Bosentan. FK506 had no significant effect on sodium nitroprusside-induced vasodilation in comparison with solvent in both vascular beds. Bosentan failed to prevent these responses. In the long-term treated groups, at the end of the treatment with FK506, there was a significant increase in blood pressure, but no change in the response to noradrenaline in either kidneys or mesentery. The increase in blood pressure was prevented by bosentan treatment. FK506 increased malondialdehyde levels in the kidneys of the rats from only the long-term treated groups. Bosentan did not change this increase. Our results indicated that endothelin-1 plays a key role in the FK506-induced change in vascular reactivity to noradrenaline in renal vascular beds and drug-induced hypertension in the rats. There was no relationship between oxidative stress and FK506-induced hypertension.

Investigation of serotonin receptors in the isolated penile bulb of rats

The aim of this study was to investigate serotonin (5-HT) receptors in the penile bulb, which have been suggested to play a role in penile erection. Serotonin (10(-7)-3 x 10(-4) M) contracted penile bulbs in a concentration-dependent manner. Ketanserin (5-HT(2A) antagonist, 10(-9)-10(-7) M) and prazosin (alpha(1)-adrenergic receptor blocker, 10(-9)-10(-7) M) suppressed the lower and upper parts of concentration-response curves to 5-HT, respectively. Guanethidine (adrenergic neuron blocker, 5 x 10(-5) M) reduced the responses to 5-HT at only 10(-4) and 3 x 10(-4) M concentrations. NAN-190 (5-HT(1A) antagonist, 10(-8), 10(-7) M) shifted the concentration-response curve to the right with a reduction in the maximum response to 5-HT. While ondansetron (5-HT(3) antagonist, 10(-6)-10(-5) M) and GR55562 (5-HT(1B/1D) antagonist, 10(-6)-10(-5) M) had no effect on the concentration-response curve to 5-HT. The 5-HT(1A) agonist 8-OH-DPAT (10(-7)-3 x 10(-4) M) contracted penile bulbs in a concentration-dependent manner with a lower pD(2) value than that of 5-HT. Sumatriptan (5-HT(1B/1D) agonist, 10(-8)-10(-4) M) did not produce any contractile response in the penile bulbs. Prucalopride, a selective 5-HT(4) agonist (R093877, 10(-7)-3 x 10(-4) M) produced concentration-dependent relaxation in penile bulbs contracted by phenylephrine (10(-5) M). 5-HT(4) agonists cisapride (10(-7)-10(-4) M) and metoclopramide (10(-7)-3 x 10(-4) M) also relaxed the tissue, concentration-dependently. Selective 5-HT(4) antagonists GR125487 (10(-6)-10(-5) M) and GR113808 (10(-6)-10(-5) M) slightly, but not significantly, decreased prucalopride- and cisapride-induced relaxation. Propranolol (beta-adrenergic receptor blocker, 10(-6)-10(-5) M) and L-NOARG (nitric oxide synthase inhibitor, 10(-4) M) had no effect on prucalopride-induced relaxation. These results suggest the existence of alpha(1)-adrenergic, 5-HT(1A) and 5-HT(2A) serotonergic receptors in the penile bulb of rats, which are responsible for 5-HT-induced contraction. Additionally, a serotonergic receptor resembling a 5-HT(4)-type plays a role in the relaxation. The latter receptor is activated by 5-HT(4) agonists, but is not antagonized by 5-HT(4) antagonists.

The role of endothelin in FK506-induced vascular reactivity changes in rat perfused kidney

Tacrolimus (FK506) is an immunosuppressant agent that is widely used in transplanted patients. The aim of this study was to investigate the role of endothelin in the acute effects of FK506 on the vascular reactivity in perfused isolated rat renal and mesenteric vasculature. Left kidney/mesentery of male Wistar rats (230-300 g) were perfused by a constant flow and perfusion pressure was recorded. The responses to noradrenaline and sodium nitroprusside were obtained both in the absence and presence of FK506 (10(-7) M) or polyoxyethylene hydrogenated castor oil 60 (HCO-60 and solvent of the drug at equivalent concentrations). FK506 significantly increased the noradrenaline-induced vasoconstrictor responses in renal, but not in mesenteric vascular beds. Bosentan (10(-5) M), a nonselective endothelin ET-1 receptor antagonist given by perfusion, reversed the increase in noradrenaline responses in the kidney. Sodium nitroprusside-induced vasodilator responses in both renal and mesenteric vascular beds were significantly decreased by FK506. However, in renal vasculature, there was no significant difference between the inhibitory effects of FK506 and HCO-60, although the effect of the solvent was not significantly different from that of the control. While in the mesenteric bed, the solvent significantly inhibited nitroprusside-induced vasodilation, similar to that of FK506. The effect of FK506 on vasodilation in both vascular beds was not reversed by bosentan. Our results indicated that FK506 increased the reactivity of the renal vascular bed to noradrenaline through endothelin ET-1 receptor activation. The mechanism of impaired vasodilation due to FK506 appears to be due to its solvent action and is independent of endothelin release.

Mechanism of action of the cisapride-induced vasodilatation in renal vasculature of rat

BACKGROUND & OBJECTIVES

Cisapride is a prokinetic agent with cholinomimetic and 5-HT4 receptor agonistic properties. It has been proposed that cisapride-induced hypotension is partly mediated by cholinergic system. The aim of this study was to investigate the mechanism of cisapride-induced dilatation in the rat isolated perfused kidney.

METHODS

Left kidneys of Wistar rats were isolated and perfused via renal artery and the perfusion pressure was recorded. Cisapride given as bolus injections (10(-10)-3x10(-5) mol/l) produced dose-dependent dilatations. Perfusion of antagonists or inhibitors was started 30min before the onset of phenylephrine perfusion.

RESULTS

4-Diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP; blocker of M1, and M3 muscarinic receptors; 10(-7) mol/l) inhibited the responses to the lower doses of cisapride while, dextran (10(-7) mol/l), glibenclamide (inhibitor of ATP-sensitive potassium channels; 10(-5) mol/l) and capsaicin (for neuromediator depletion; 10(-6) mol/l) inhibited those to the higher doses. Dilatations induced by most of the doses of cisapride were inhibited by atropine (non-selective muscarinic receptor antagonist; 10(-7) mol/l), methylene blue (inhibitor of soluble guanylate cyclase; 10(-5) mol/l), 1H-[1,2,4] oxadiazolo-[4,3-a] Quinoxalin-1-One (ODQ; inhibitor of soluble guanylate cyclase; 10(-5) mol/l), and NG-nitro-L-arginine (L-NOARG; NO synthase inhibitor; 10(-4) mol/l). Inhibition induced by L-NOARG was reversed by L-arginine (10(-3) mol/l). The dilatation induced by cisapride was not affected by GR113808 (5-HT4 receptor antagonist; 10(-7) mol/l) and indomethacin (cyclooxygenase inhibitor; 10(-5) mol/l).

INTERPRETATION & CONCLUSION

The findings indicated that cisapride caused vasodilatation through the release of nitric oxide (NO) as a result of the release of a substance acting on muscarinic receptors, in the renal vascular bed of the rat. The role of 5-HT4 receptors and prostanoids seemed unlikely.