Enalapril attenuates endothelin-1-induced hypertension via increased kinin survival

Deletion of AT1a (Angiotensin II Type 1a) Receptor or Inhibition of Angiotensinogen Synthesis Attenuates Thoracic Aortopathies in Fibrillin1C1041G/+ Mice

Objective: A cardinal feature of Marfan syndrome is thoracic aortic aneurysm. The contribution of the renin-angiotensin system via AT1aR (Ang II [angiotensin II] receptor type 1a) to thoracic aortic aneurysm progression remains controversial because the beneficial effects of angiotensin receptor blockers have been ascribed to off-target effects. This study used genetic and pharmacological modes of attenuating angiotensin receptor and ligand, respectively, to determine their roles on thoracic aortic aneurysm in mice with fibrillin-1 haploinsufficiency (Fbn1C1041G/+). Approach and Results: Thoracic aortic aneurysm in Fbn1C1041G/+ mice was found to be strikingly sexual dimorphic. Males displayed aortic dilation over 12 months while aortic dilation in Fbn1C1041G/+ females did not differ significantly from wild-type mice. To determine the role of AT1aR, Fbn1C1041G/+ mice that were either +/+ or -/- for AT1aR were generated. AT1aR deletion reduced expansion of ascending aorta and aortic root diameter from 1 to 12 months of age in males. Medial thickening and elastin fragmentation were attenuated. An antisense oligonucleotide against angiotensinogen was administered to male Fbn1C1041G/+ mice to determine the effects of Ang II depletion. Antisense oligonucleotide against angiotensinogen administration attenuated dilation of the ascending aorta and aortic root and reduced extracellular remodeling. Aortic transcriptome analyses identified potential targets by which inhibition of the renin-angiotensin system reduced aortic dilation in Fbn1C1041G/+ mice. Conclusions: Deletion of AT1aR or inhibition of Ang II production exerted similar effects in attenuating pathologies in the proximal thoracic aorta of male Fbn1C1041G/+ mice. Inhibition of the renin-angiotensin system attenuated dysregulation of genes within the aorta related to pathology of Fbn1C1041G/+ mice.

Pre-treatment considerations in childhood hypertension due to chronic kidney disease

Hypertension (HTN) develops very early in childhood chronic kidney disease (CKD). It is linked with rapid progression of kidney disease, increased morbidity and mortality hence the imperative to start anti-hypertensive medication when blood pressure (BP) is persistently > 90^th percentile for age, gender, and height in non-dialyzing hypertensive children with CKD. HTN pathomechanism in CKD is multifactorial and complexly interwoven. The patient with CKD-associated HTN needs to be carefully evaluated for co-morbidities that frequently alter the course of the disease as successful treatment of HTN in CKD goes beyond life style modification and anti-hypertensive therapy alone. Chronic anaemia, volume overload, endothelial dysfunction, arterial media calcification, and metabolic derangements like secondary hyperparathyroidism, hyperphosphataemia, and calcitriol deficiency are a few co-morbidities that may cause or worsen HTN in CKD. It is important to know if the HTN is caused or made worse by the toxic effects of medications like erythropoietin, cyclosporine, tacrolimus, corticosteroids and non-steroidal anti-inflammatory drugs. Poor treatment response may be due to any of these co-morbidities and medications. A satisfactory hypertensive CKD outcome, therefore, depends very much on identifying and managing these co-morbid conditions and HTN promoting medications promptly and appropriately. This review attempts to point attention to factors that may affect successful treatment of the hypertensive CKD child and how to attain the desired therapeutic BP target.

Non-endothelial endothelin counteracts hypoxic vasodilation in porcine large coronary arteries

Background

The systemic vascular response to hypoxia is vasodilation. However, reports suggest that the potent vasoconstrictor endothelin-1 (ET-1) is released from the vasculature during hypoxia. ET-1 is reported to augment superoxide anion generation and may counteract nitric oxide (NO) vasodilation. Moreover, ET-1 was proposed to contribute to increased vascular resistance in heart failure by increasing the production of asymmetric dimethylarginine (ADMA). We investigated the role of ET-1, the NO pathway, the potassium channels and radical oxygen species in hypoxia-induced vasodilation of large coronary arteries.

Results

In prostaglandin F_2α (PGF_2α, 10 μM)-contracted segments with endothelium, gradual lowering of oxygen tension from 95 to 1% O₂ resulted in vasodilation. The vasodilation to O₂ lowering was rightward shifted in segments without endothelium at all O₂ concentrations except at 1% O₂. The endothelin receptor antagonist SB217242 (10 μM) markedly increased hypoxic dilation despite the free tissue ET-1 concentration in the arterial wall was unchanged in 1% O₂ versus 95% O_2. Exogenous ET-1 reversed hypoxic dilation in segments with and without endothelium, and the hypoxic arteries showed an increased sensitivity towards ET-1 compared to the normoxic controls. Without affecting basal NO, hypoxia increased NO concentration in PGF_2α-contracted arteries, and an NO synthase inhibitor, L-NOARG,(300 μM, N^G-nitro-L-Arginine) reduced hypoxic vasodilation. NO-induced vasodilation was reduced in endothelin-contracted preparations. Arterial wall ADMA concentrations were unchanged by hypoxia. Blocking of potassium channels with TEA (tetraethylammounium chloride)(10 μM) inhibited vasodilation to O₂ lowering as well as to NO. The superoxide scavenger tiron (10 μM) and the putative NADPH oxidase inhibitor apocynin (10 μM) leftward shifted concentration-response curves for O₂ lowering without changing vasodilation to 1% O₂. PEG (polyethylene glycol) catalase (300 u/ml) inhibited H₂O₂ vasodilation, but failed to affect vasodilation to O₂ lowering. Neither did PEG-SOD (polyethylene glycol superoxide dismutase)(70 u/ml) affect vasodilation to O₂ lowering. The mitochondrial inhibitors rotenone (1 μM) and antimycin A (1 μM) both inhibited hypoxic vasodilatation.

Conclusion

The present results in porcine coronary arteries suggest NO contributes to hypoxic vasodilation, probably through K channel opening, which is reversed by addition of ET-1 and enhanced by endothelin receptor antagonism. These latter findings suggest that endothelin receptor activation counteracts hypoxic vasodilation.

Ace inhibitors - activators of kinin receptors

Angiotensin converting enzyme (ACE) inhibitors are widely used for treatment of cardiovascular diseases. The effects of ACE inhibitors on the human bradykinin receptors were investigated. The mode of action of ACE inhibitors is considered. There is evidence that ACE inhibitors exert effects on the vascular system that cannot be attributed simply to the inhibition of ACE activity and accumulation of locally produced bradykinin. ACE inhibitors augment bradykinin effects on receptors indirectly by inducing cross-talk between ACE and the B2 receptor when enzyme and receptor molecules are sterically close, possibly forming a heterodimer. ACE inhibitors activate B1 receptors directly and independently of ACE via the zink-binding consensus sequence HEXXH, which is present in B1, but not in B2 receptor. Particular structure of B2 and B1 are represented, as well as receptor amino acids coupled with the G-proteins. Activation of kinin receptors by ACE inhibitors leads to clinically beneficial effects of ACE inhibitors.

Synergistic actions of enalapril and tempol during chronic angiotensin II-induced hypertension

Experiments were designed to test the hypothesis that antioxidant treatment would increase the anti-hypertensive actions of endogenous kinins during angiotensin converting enzyme (ACE) inhibition. Four groups of rats, all given angiotensin II (Ang II) for 2 weeks, were studied: 1) control, 2) enalapril, 3) tempol or 4) both tempol and enalapril. Ang II significantly increased systolic blood pressure (BP) when compared with the baseline (170+/-8 vs. 128+/-4 mm Hg, P<0.05). Neither enalapril nor tempol alone was able to attenuate the elevation in BP (165+/-7 and 164+/-6 mm Hg, respectively). In contrast, combined administration of tempol and enalapril prevented the increase in BP (137+/-5 mm Hg). Plasma 8-isoprostane increased in Ang II-infused rats when compared with control untreated rats (69+/-14 vs. 23+/-0.5 pg/ml, P<0.05). Tempol alone or tempol plus enalapril significantly attenuated the increase in plasma 8-isoprostane (29+/-6 and 34+/-7 pg/ml, respectively). In additional experiments, we used the bradykinin B(2) antagonist, icatibant to determine if increased B(2) receptor contributes to the anti-hypertensive effect of combined tempol and enalapril in Ang II-infused rats. Icatibant decreased the ability of this combination to lower arterial pressure. Additionally, a significant increase in B(1) receptor protein expression in renal cortex of Ang II-infused rats was observed compared to control suggesting that bradykinin receptor activation could account for the effect of enalapril to enhance the actions of tempol. These data support the hypothesis that combined reduction of superoxide along with enhanced endogenous kinins may facilitate blood pressure lowering in Ang II hypertension.

Olmesartan Improves Endothelin-Induced Hypertension and Oxidative Stress in Rats

Recent studies have indicated that both endothelin (ET) and angiotensin (Ang) II stimulate oxidative stress, which contributes to the development of hypertension. Here, we examined the effects of Ang II type 1 (AT1) receptor blockade on reactive oxygen species (ROS) formation in ET-dependent hypertension. Chronic ET-1 infusion (2.5 pmol/kg/min, i.v., n=7) into rats for 14 days increased systolic blood pressure from 113+/-1 to 141+/-2 mmHg. ET-1-infused rats showed greater plasma renin activity (8.1+/-0.8 Ang I/ml/h), and greater Ang I (122+/-28 fmol/ml) and Ang II levels (94+/-13 fmol/ml) than vehicle (0.9% NaCl)-infused rats (3.1+/-0.6 Ang I/ml/h, 45+/-8 and 47+/-7 fmol/ml, respectively, n=6). Angiotensin converting enzyme and AT1 receptor expression in aortic tissues were similar between the vehicle- and ET-1-infused rats. Vascular superoxide anion (O2-) production and plasma thiobarbituric acid-reactive substance (TBARS) levels were greater in ET-1-infused rats (27+/-1 counts per minutes [CPM]/mg dry tissue weight and 8.9+/-0.8 micromol/l, respectively) than vehicle-infused rats (16+/-1 CPM/mg and 5.1+/-0.1 micromol/l, respectively). The ET-1-induced hypertension was prevented by simultaneous treatment with a new AT1 receptor antagonist, olmesartan (0.01% in chow, 117+/-5 mmHg, n =7), or hydralazine (15 mg/kg/day in drinking water, 118+/-4 mmHg, n=6). Olmesartan prevented ET-1-induced increases in vascular O2- production (15+/-1 CPM/mg) and plasma TBARS (5.0+/-0.1 micromol/l). Vascular O2- production and plasma TBARS were also decreased by hydralazine (21+/-1 CPM/mg and 7.0+/-0.3 micromol/l, respectively), but these levels were significantly higher than in vehicle-infused rats. These data suggest that ET-dependent hypertension is associated with augmentation of Ang II levels and ROS formation. The combined effects of the elevations in circulating ET-1 and Ang II, as well as the associated ROS production, may contribute to the development of hypertension induced by chronic ET-1 infusion.