The effect of endothelins on nitric oxide and prostacyclin production from human umbilical vein, porcine aorta and bovine carotid artery endothelial cells in culture

Reduced Nitric Oxide Bioavailability In a Baboon Model of Shiga Toxin Mediated Hemolytic Uremic Syndrome (HUS)

BACKGROUND

Although there is agreement that post-diarrheal hemolytic uremic syndrome (D+ HUS) is caused by Shiga toxin (Stx)-producing E. coli, little is known about factors that mediate the host response to these toxins and potentially contribute to pathogenesis. Nitric oxide (NO) is a candidate mediator by virtue of its antiplatelet and renal vasodilatory properties.

METHODS

We used a baboon model of HUS to measure plasma and urinary NO metabolites and expression of NO synthase (eNOS and iNOS) in renal tissue following the intravenous administration of Stx-1.

RESULTS

Plasma concentrations through 60 hours of observation did not differ significantly from controls. Urinary values (indexed against urinary creatinine) tended, however, to rise during the initial 12 hours following administration of Stx-1. This was followed by a sustained reduction that coincided with the development of hemolytic anemia (schistocytosis) and other features of HUS. However, immunohistochemical staining for eNOS and iNOS in tissue obtained immediately after death at a median of 59 hours showed similar levels in control and Stx-treated animals, despite the presence of a florid thrombotic microangiopathy and tubular injury in the Stx-treated group.

CONCLUSION

We propose that urinary NO metabolite reduction was due to NO inactivation subsequent to its avid binding to free hemoglobin released from lysed red blood cells, and that this contributed to the acute renal failure by facilitating vasoconstriction and platelet aggregation and adhesion within the renal microvasculature.

Endothelin B receptor-mediated regulation of endothelin-1 content and release in cultured porcine aorta endothelial cell

Several cardiovascular diseases are associated with an increase in circulating levels of endothelin-1 (ET-1). Little is known about the consequences of this increase on endothelial cell responses with respect to ET-1 production and regulation. Confluent, passage 1, cultured porcine aorta endothelial cells were exposed to exogenous ET-1 (0.1 microM) for 24 h. BQ788 (1 microM, ETB receptor antagonist) but not BQ123 (1 microM, ETA receptor antagonist) significantly (p < 0.05) reduced 125I-ET-1 uptake. The effects of BQ788 were mimicked by dansylcadaverine (0.5 mM) but not nystatin (50 microg/ml). Immunoreactive ET-1 endothelial cell content doubled (p < 0.05) after 24 h of exogenous ET-1 treatment. Bosentan (10 microM, dual ETA/B receptor antagonist) reduced (p < 0.05) immunoreactive ET-1 content in control cells. Bosentan prevented exogenous ET-1-induced endothelial cell ET-1 loading, suggesting that exogenous ET-1 is partly recycled. PreproET-1 mRNA levels were reduced (p < 0.05) by exogenous ET-1 after 24 h, an effect blocked by BQ788 and bosentan. When used alone, both receptor antagonists increased mRNA levels. The results of this study suggest that part of ET-1 is recycled through ETB receptors and subsequently released to contribute to constitutive ET-1 overflow. ET-1 exerts a negative feedback on ET-1 gene transcription, which is dependent on ETB receptor activation and internalization of the complex ET-1/ETB receptor. The maintenance of this negative regulatory loop of ET-1 production may be essential for the normal endothelial physiology.

Effect of ABT-627 (A-147627), a potent selective ET(A) receptor antagonist, on the cardiopulmonary profile of newborn lambs with surgically-induced diaphragmatic hernia

1. Postnatal mortality in isolated congenital diaphragmatic hernia (CDH) is mainly related to the associated pulmonary hypertension (PH) and to right-to-left shunting. 2. Endothelins (ETs) are potent vasoconstrictors and pro-mitogenic peptides. Strong evidences support their participation in CDH and in the etiology of PH via the activation of ET(A) receptors (ET(A)-Rs). 3. Evaluation of the effect of ABT-627, a selective non-peptidic ET(A)-R antagonist, given from -15 to 210 min post-delivery (1 mg kg(-1) bolus +0.01 mg kg(-1) h(-1) infusion, i.v.), was conducted in the lamb model of CDH. 4. Severity of CDH was assessed in comparison to untreated controls (n=5). Untreated CDH lambs (n=7) had a higher mean pulmonary arterial pressure (MPAP; P<0.0001), lower mean blood pressure (MBP; P=0.0004), higher MPAP / MBP ratio (P<0.0001), lower arterial pH (P<0.0001), higher paCO(2) (P<0.0001), lower paO(2) (P<0.0001) and lower post-ductal pulsatile SaO(2) (P<0.0001) than untreated controls. 5. Treated controls (n=7) showed a higher MPAP, lower MBP, higher MPAP/MBP ratio, lower arterial pH, higher paCO(2), lower paO(2), lower post-ductal pulsatile SaO(2) and lower plasmatic ir-ET ratios compared to untreated controls (P<0.0001). 6. Treated CDH lambs (n=8) showed a higher MBP (P<0.0001), lower MPAP / MBP ratio (P<0.0001), higher arterial pH (P<0.0001), lower paCO(2) (P<0.0001), higher paO(2) (P=0.0228), higher post-ductal pulsatile SaO(2) (P=0.0016) and lower plasmatic ir-ET ratios (P=0.0247) when compared to untreated CDH lambs. 7. These observations revealed that, although acute perinatal treatment with a selective non-peptidic ET(A)-R antagonist had some adverse effects in controls, it attenuated the progressive cardiopulmonary deterioration that occurred after birth in CDH lambs.

Endothelium-derived endothelin-1 reduces cerebral artery sensitivity to nitric oxide by a protein kinase C-independent pathway

BACKGROUND AND PURPOSE

Nitric oxide (NO) reduces endothelin-1 (ET-1) production and blunts ET-1 dependent vasoconstriction. The direct effects of smooth muscle ET(A) receptor stimulation on NO-mediated relaxation are unknown. We hypothesized that endothelium-derived ET-1 regulates vascular tone by reducing smooth muscle sensitivity to NO, possibly through activation of protein kinase C (PKC).

METHODS

Rings of rabbit middle cerebral artery were mounted on microvessel myographs to measure isometric tension. Dose-response curves to acetylcholine (ACh) and sodium nitroprusside (SNP; an NO donor) were obtained with or without ET-1 receptor blockade. Experiments were performed in the presence of indomethacin (10 micromol/L). Results are expressed as mean+/-SEM.

RESULTS

In depolarized conditions (40 mmol/L KCl physiological solution), ACh-induced relaxation was entirely NO-dependent, as indicated by its suppression by N(omega)-nitro-L-arginine (P<0.05). Arterial sensitivity (pD(2)) to ACh (6.32+/-0.11, n=6) was increased (P<0.05) to 6.77+/-0.10 (n=6) by BQ123 (ET(A) receptor antagonist, 5 micromol/L) but not by BQ788 (ET(B) receptor antagonist, 5 micromol/L; 6.08+/-0.22, n=5). Consistent with this finding, blockade of ET(A) receptors increased (P<0.05) vascular sensitivity to SNP (6.95+/-0.10, n=8), whereas BQ788 had no influence on arterial sensitivity to SNP (6.17+/-0.07, n=7) compared with control (6.43+/-0.13, n=11). In denuded arteries, the sensitivity to SNP (7.10+/-0.08, n=8) was reduced by exogenous ET-1 (6.51+/-0.35, n=7, P<0.05). Chelerythrine, a PKC inhibitor, did not alter smooth muscle sensitivity to NO, whereas phorbol 12-myristate 13-acetate, a PKC activator, strongly increased it.

CONCLUSIONS

Blockade of ET(A) but not ET(B) receptors sensitizes vascular smooth muscle to exogenous and endothelium-derived NO. This suggests that ET-1 regulates smooth muscle sensitivity to NO by a PKC-independent pathway. This represents an alternative pathway by which NO and ET-1 interact to regulate vascular tone.

Role of endothelin-1 in regulation of the postnatal intestinal circulation

Newborn intestine is uniquely prone to vasoconstriction in response to a wide variety of perturbations. To test the hypothesis that endothelin (ET)-1 is an important factor in this process, we determined the effects of exogenous ET-1 administration and blockade of endogenous ET-1 in vivo and in vitro in 3- and 35-day-old swine. Intramesenteric artery administration of exogenous ET-1 to vascularly isolated in vivo gut loops (10(-9) M/kg bolus) caused vasoconstriction and reduced gut O(2) uptake similarly in these age groups. Selective blockade of ET(A) or ET(B) receptors with BQ-610 or BQ-788, respectively, in vascularly isolated in vivo gut loops had no effect on gut vascular resistance or O(2) uptake in either age group; within in vitro gut loops, BQ-610 significantly increased vasoconstriction when perfusion pressure was reduced below baseline, but only in 3-day-old animals; i.e., it impaired the autoregulatory response to perfusion pressure reduction. Exogenous ET-1 significantly decreased capillary perfusion within in vitro gut loops, as evidenced by a decrease in capillary filtration coefficient, but only in 3-day-old animals; furthermore, blockade of endogenous ET-1 activity with BQ-610 significantly enhanced capillary filtration coefficient in 3-day-old animals and increased O(2) extraction ratio. ET-1 did not depress intestinal metabolic rate, as evidenced by its effect on the O(2) uptake-blood flow relationship; it did compromise tissue oxygenation because of its effects on intestinal O(2) transport. ET-1 concentration in mesenteric venous effluent exceeded arterial concentration, but only in 3-day-old intestine, suggesting production of ET-1 by newborn intestine. We conclude that ET-1 exerts an age-dependent effect on intestinal hemodynamics in postnatal intestine, having a greater impact in 3- than in 35-day-old intestine.

Endothelin-1 produces heterogeneous regional haemodynamic effects in conscious rabbits

Blood flow in the renal artery, superior mesenteric artery and infra-renal abdominal aorta of conscious rabbits was measured by Doppler ultrasound. Arterial pressure, heart rate and blood flow responses were assessed following 0.2 and 0.8 nmol/kg intravenous endothelin-1. The effects of the following antagonists on these responses were examined: phentolamine, propranolol, scopolamine, captopril, nifedipine, indomethacin, the V1-vasopressin receptor antagonist d(CH2)5Tyr(Me)AVP and the competitive nitric oxide (NO) synthase inhibitor NG-nitro L-arginine (NOLA). Hindlimb resistance and arterial pressure responded in two phases, initial vasodilatation followed by vasoconstriction. Renal and mesenteric vasoconstriction occurred without initial vasodilatation. Following 0.2 nmol/kg endothelin-1, arterial pressure decreased by 18.5 +/- 0.8 mmHg, then increased by 25.2 +/- 1.7 mmHg (n = 27). Heart rate changed reciprocally. Renal resistance increased by 533 +/- 73% (n = 12). Mesenteric resistance increased by 420 +/- 34%. Hindlimb resistance decreased 54 +/- 2% (n = 12, all P < 0.01) then increased slightly (P < 0.05). All changes were greater at 0.8 nmol/kg, particularly the hindlimb vasoconstriction. The only antagonist to alter significantly these responses was NOLA, which in the hindlimb attenuated the vasodilatation and accentuated the vasoconstriction. We conclude that most of the haemodynamic effects of endothelin-1 are direct, but that NO generated by NO synthase causes part of the hindlimb vasodilatation, and that endothelin-1-induced vasoconstriction is attenuated by release of NO.

Mechanisms of adrenomedullin-induced vasodilation in the rat kidney

To explore the mechanisms of adrenomedullin-induced vasorelaxation, we tested the effects of adrenomedullin on renal function in rats in vivo and measured the release of endothelium-derived nitric oxide from isolated perfused rat kidney (using a chemiluminescence assay) and the diameters of the glomerular arterioles in the hydronephrotic kidney. Adrenomedullin decreased blood pressure in a dose-dependent manner (3 nmol/kg: -29 +/- 2% [SEM]; P < .01) and slightly increased the glomerular filtration rate and urinary sodium excretion (+108%; P < .05). These changes were associated with significant increases in urinary excretion of cyclic AMP (+54%; P < .05). Adrenomedullin decreased renal vascular resistance (10(-7) mol/L adrenomedullin: -41 +/- 2%; P < .001) and increased release of nitric oxide (+5.1 +/- 0.7 fmol/min per gram kidney weight; P < .001) in the isolated kidney. This increase in nitric oxide release was abolished by the inhibitor NG-monomethyl-L-arginine, and it also reversed the decrease in renal vascular resistance seen with adrenomedullin. Renal responses of deoxycorticosterone acetate-salt hypertensive rats to adrenomedullin were significantly smaller than those of control rats for both release of nitric oxide (10(-7) mol/L adrenomedullin: +0.8 +/- 0.2 fmol/min per gram kidney weight; P < .01 versus control) and renal vasodilation (-28 +/- 6%; P < .05). Videomicroscopic analysis revealed that adrenomedullin increased the diameters of both afferent and efferent arterioles (3 nmol/kg: +11%; P < .05). Thus, adrenomedullin-induced renal vasodilation is partially endothelium dependent and is attenuated in deoxycorticosterone acetate-salt hypertension, probably due to endothelial damage.