Study of correlation between elevation of blood pressure and tissue ACE activity during development of hypertension in 1K1C rats

Mechanisms of Arsenic Exposure-Induced Hypertension and Atherosclerosis: an Updated Overview

Arsenic is an abundant element in the earth's crust. In the environment and within the human body, this toxic element can be found in both organic and inorganic forms. Chronic exposure to arsenic can predispose humans to cardiovascular diseases including hypertension, stroke, atherosclerosis, and blackfoot disease. Oxidative damage induced by reactive oxygen species is a major player in arsenic-induced toxicity, and it can affect genes expression, inflammatory responses, and/or nitric oxide homeostasis. Exposure to arsenic in drinking water can lead to vascular endothelial dysfunction which is reflected by an imbalance between vascular relaxation and contraction. Arsenic has been shown to inactivate endothelial nitric oxide synthase leading to a reduction of the generation and bioavailability of nitric oxide. Ultimately, these effects increase the risk of vascular diseases such as hypertension and atherosclerosis. The present article reviews how arsenic exposure contributes to hypertension and atherosclerosis development.

The Effect of Soybean Peptides on Improving Quality and the ACE Inhibitory Bioactivity of Extruded Rice

It is crucial to address the dietary problems of hypertensive patients. The effect and mechanism of different contents of soybean protein on cooking quality and angiotensin-converting enzyme (ACE) inhibitory action in the extruded rice were firstly investigated. The results showed that the extruded rice with soybean protein possessed the higher taste value (90.32 ± 2.31), hardness (2.65 ± 0.01 g), and good pasting quality (p ≤ 0.05). Meanwhile, the soybean protein notably retarded the starch digestibility; the sample with 6% soybean protein showed the fewest rapidly digestible starch (RDS) content (78.82 ± 0.01 mg g−1) and the most slowly digestible starch (SDS) content (8.97 ± 0.45 mg g−1). Importantly, the ACE inhibition rate improved from 17.09 ± 0.01% to 74.02 ± 0.65% in the 6% soybean protein sample because of the production of peptides. The peptide composition of samples were compared, which showed that the effective ACE-inhibitory peptides usually contain 2~20 amino acids, and Pro, Leu, Ile, Val, Phe, and Ala were the main components. Overall, moderate soybean protein would give a good quality and lower ACE activity in extruded food.

Cardiac Natriuretic Peptide Profiles in Chronic Hypertension by Single or Sequentially Combined Renovascular and DOCA-Salt Treatments

The involvement of natriuretic peptides was studied during the hypertrophic remodeling transition mediated by sequential exposure to chronic hemodynamic overload. We induced hypertension in rats by pressure (renovascular) or volume overload (DOCA-salt) during 6 and 12 weeks of treatment. We also studied the consecutive combination of both models in inverse sequences: RV 6 weeks/DS 6 weeks and DS 6 weeks/RV 6 weeks. All treated groups developed hypertension. Cardiac hypertrophy and left ventricular ANP gene expression were more pronounced in single DS than in single RV groups. BNP gene expression was positively correlated with left ventricular hypertrophy only in RV groups, while ANP gene expression was positively correlated with left ventricular hypertrophy only in DS groups. Combined models exhibited intermediate values between those of single groups at 6 and 12 weeks. The latter stimulus associated to the second applied overload is less effective than the former to trigger cardiac hypertrophy and to increase ANP and BNP gene expression. In addition, we suggest a correlation of ANP synthesis with volume overload and of BNP synthesis with pressure overload-induced hypertrophy after a prolonged treatment. Volume and pressure overload may be two mechanisms, among others, involved in the differential regulation of ANP and BNP gene expression in hypertrophied left ventricles. Plasma ANP levels reflect a response to plasma volume increase and volume overload, while circulating BNP levels seem to be regulated by cardiac BNP synthesis and ventricular hypertrophy.

Arsenic, cadmium, and mercury-induced hypertension: mechanisms and epidemiological findings

Arsenic (As), cadmium (Cd), and mercury (Hg) are toxic elements widely distributed in the environment. Exposure to these elements was attributed to produce several acute and chronic illnesses including hypertension. The aim of this review is to provide a summary of the most frequently proposed mechanisms underlying hypertension associated with As, Cd, and Hg exposure including: oxidative stress, impaired nitric oxide (NO) signaling, modified vascular response to neurotransmitters and disturbed vascular muscle Ca²⁺ signaling, renal damage, and interference with the renin-angiotensin system. Due to the complexity of the vascular system, a combination rather than a singular mechanism needs to be considered. In addition, epidemiological findings showing the relationship between various biomarkers of metal exposure and hypertension are described. Given the complex etiology of hypertension, further epidemiological studies evaluating the roles of confounding factors such as age, gender, and life style are still necessary.

Studying the correlation of renin-angiotensin-system (RAS) components and insulin resistance in polycystic ovary syndrome (PCOs)

OBJECTIVE

It is estimated that 5-7% of women of reproductive age have polycystic ovary syndrome (PCOS). Chronic anovulation, hyperandrogenism, and insulin resistance (IR) are the main characters of this complex syndrome. IR, diabetes and obesity are all strongly correlated with PCOS; moreover, the possibility of direct androgen mediated renin-angiotensin system (RAS) stimulation in women with PCOS is also reported. The aim of the present study was to investigate the correlation between RAS, IR and PCOS.

STUDY DESIGN

Thirty one women with PCOS, diagnosed by the Rotterdam criteria, were compared with thirty six control subjects. Both case and control groups were evaluated regarding to their basal hormonal profile, fasting blood sugar, IR, angiotensin converting enzyme (ACE) activity, plasma renin activity (PRA) and angiotensin II (AngІІ) levels.

RESULTS

Compared to controls both ACE activity (p = 0.04) and AngΙΙ levels (p = 0.01) were significantly higher in case group. No significant differences between patients and controls were found in PRA. The results demonstrated that IR (p = 0.02) and fasting insulin (p = 0.004) were higher in case group, there was also a positive correlation between ACE activity and IR in case group (p = 0.02, r = 0.2).

CONCLUSION

These results may suggest that there is an important correlation between ACE activity and IR in patients with PCOS.

Sex differences in angiotensin-converting enzyme modulation of Ang (1-7) levels in normotensive WKY rats

BACKGROUND

Levels of the vasodilatory peptide angiotensin (Ang) (1-7) have been reported to be greater in females than in males, although the molecular mechanism responsible for this is unknown. Angiotensin-converting enzyme (ACE), ACE2, and neprilysin are key enzymes regulating Ang (1-7) formation. We conducted a study to determine the effect of sex on the activities of ACE, ACE2, and neprilysin in the kidneys of normotensive rats. We hypothesized that greater ACE2 or neprilysin activity in females would result in enhanced Ang (1-7) formation as compared with that in males.

METHODS

We measured the enzymatic activities of ACE, ACE2, and neprilysin in the renal cortex and medulla of 12-week-old male and female WKY rats. We treated additional rats with vehicle or enalapril (10 mg/kg/day in drinking water) for 14 days, and measured their Ang II and Ang (1-7) levels.

RESULTS

Renal cortical activity of ACE was greater in female than in male WKY rats (P < 0.05), but the activity of ACE in the renal medulla was not significantly different in the two sexes. Renal cortical and medullary ACE2 and neprilysin activities were comparable in male and female WKY rats. Treatment with enalapril significantly decreased Ang II levels in the renal cortex and medulla of male and female WKY rats as compared with those in vehicle-treated controls (P < 0.05); enalapril did not change the plasma levels of Ang II. Cortical levels of Ang (1-7) were higher in vehicle-treated females than in vehicle-treated males (P < 0.05), and treatment with enalapril decreased Ang (1-7) levels only in females (P < 0.05).

CONCLUSIONS

Our data supports a role for ACE in the formation of renal cortical Ang (1-7) in female WKY rats that is absent in males.

Hydrogen sulfide inhibits plasma renin activity

The development of renovascular hypertension depends on the release of renin from the juxtaglomerular (JG) cells, a process regulated by intracellular cAMP. Hydrogen sulfide (H2S) downregulates cAMP production in some cell types by inhibiting adenylyl cyclase, suggesting the possibility that it may modulate renin release. Here, we investigated the effect of H2S on plasma renin activity and BP in rat models of renovascular hypertension. In the two-kidney-one-clip (2K1C) model of renovascular hypertension, the H2S donor NaHS prevented and treated hypertension. Compared with vehicle, NaHS significantly attenuated the elevation in plasma renin activity and angiotensin II levels but did not affect plasma angiotensin-converting enzyme activity. Furthermore, NaHS inhibited the upregulation of renin mRNA and protein levels in the clipped kidneys of 2K1C rats. In primary cultures of renin-rich kidney cells, NaHS markedly suppressed forskolin-stimulated renin activity in the medium and the intracellular increase in cAMP. In contrast, NaHS did not affect BP or plasma renin activity in normal or one-kidney-one-clip (1K1C) rats, both of which had normal plasma renin activity. In conclusion, these results demonstrate that H2S may inhibit renin activity by decreasing the synthesis and release of renin, suggesting its potential therapeutic value for renovascular hypertension.

Lifelong inorganic arsenic compounds consumption affected blood pressure in rats

Chronic arsenic exposure is a known risk factor for cardiovascular disease and has a strong correlation with hypertension. Oxidative stress may be one of the major contributors to arsenic-induced hypertension. To investigate the antioxidative and CYP systems through which inorganic arsenic compounds may contribute to blood pressure elevation in rats, we administered 50ppm arsenic (as arsenite and arsenate) in drinking water to Wistar rats for 200 successive days. Systolic blood pressure was determined every 20 days, and blood samples and tissues were collected at each time point for biological analysis. Compared to the control group, weight gain in the arsenic-exposed animals was slightly but significantly lower, whereas the relative weights of the various tissues was higher. Blood pressure was elevated until day 80 in both arsenic groups followed by a time-dependent change in the antioxidative enzyme system. The hypertensive effect remained until day 200 for arsenite when the change by arsenate was minimized. Patterns of antioxidative enzyme change differed between arsenite and arsenate. However, the most common marker of hypertension, the angiotensin-converting enzyme, showed no significant change in either arsenic group. CYP4A was highly expressed in both arsenic groups, particularly in the arsenite group. These results indicate that low but chronic arsenic exposure might cause elevated blood pressure and antioxidative interference. Furthermore, CYP4A might be more important than ACE in contributing to arsenic-induced hypertension.

CHRONIC SALT LOADING AND CARDIOVASCULAR-ASSOCIATED CHANGES IN EXPERIMENTAL DIABETES IN RATS

1. High-sodium intake may increase blood pressure and diabetes is a salt-sensitive condition. In the present study, we evaluated cardiovascular changes and their neurohumoral mechanisms in streptozotocin (STZ)-diabetic rats that underwent chronic salt loading. 2. We studied male Wistar rats (150-280 g) 14 days after the injection of either STZ (50 mg/kg, i.v.; D; n = 18) or citrate buffer (C; n = 16). After the induction of diabetes, animals were maintained for 14 days with free access to standard rat chow and tap water (C and D groups) or 1% NaCl solution (C-S and D-S groups). We conducted two experiments. Experiment 1 consisted of basal arterial pressure (AP) measurement (30 min) followed by the evaluation of AP responsiveness to phenylephrine and sodium nitroprusside. One day later, with the rats anaesthetized, a blood sample was collected to test for glycaemia, plasma angiotensin-converting enzyme (ACE) activity and renin. Kidneys were removed for the determination of tissue ACE activity. Experiment 2 comprised 24 h urine collection followed by 3 days of cardiovascular records, which consisted of a 30 min basal AP measurement, followed by injection of blockers of the vasopressin system, the renin-angiotensin system (RAS) and the sympathetic system. Basal haemodynamic data, baroreflex evaluation and AP responses to blockade of the vasopressin system with vasopressin V(1) receptor antagonist (aAVP; 10 mg/kg, i.v.), the RAS by losartan (10 mg/kg, i.v.) and the sympathetic system by hexamethonium (20 mg/kg, i.v.) were determined. 3. Glycaemia was similar between C and C-S (P = 0.612) and between D and D-S (P = 0.552), but higher in diabetic compared with non-diabetic rats (P < 0.0001). The D-S rats had an increment of 24% in mean AP compared with D (120 +/- 4 vs 97 +/- 2 mmHg, respectively; P = 0.0001), which was not seen in C-S compared with C rats. A positive association was noted between urinary sodium and mean AP (r = 0.37; P = 0.04). Plasma renin was undetectable in D-S rats. The response to acute drug blockade of vasopressin and the RAS was similar among groups, but hexamethonium elicited a more pronounced decrease in AP in D-S compared with D rats (P = 0.001). 4. The main neurohumoral mechanisms of salt-induced cardiovascular changes in STZ-diabetes are increased sodium and vascular sensitivity to adrenergic stimuli, which act in combination to produce a final result of higher AP levels, a finding not observed in control rats. Baroreflex derangements induced by diabetes were not affected by salt overload.

Effects of intravenous urocortin on angiotensin-converting enzyme in rats

We investigated the relationship between urocortin and the activity of angiotensin-converting enzyme (ACE), which plays a key role in producing the potent vasoconstrictor angiotensin II (Ang II). Urocortin was acutely and subchronically administered to Sprague-Dawley (SD) rats and then the serum and tissue (lung and aorta) ACE levels were evaluated. The tissue ACE mRNA was determined by using reverse transcription and polymerase chain reaction (RT-PCR) analysis. Immunofluorescence studies were also preformed to evaluate the effect of urocortin on ACE in cultured rat aortic endothelial cells (RAECs). Urocortin decreased the serum ACE level 1h after administration, whereas tissue ACE immunoreactivity and mRNA did not change. The prolonged administration of urocortin enhanced tissue ACE activity but the serum ACE level remained low. RT-PCR analysis showed that tissue ACE mRNA was elevated. Immunofluorescence studies also demonstrated an increase of ACE intensity in RAECs exposed to urocortin for 72 h. Corticotropin-releasing factor (CRF) receptor blocker, astressin, abolished the effects of urocortin. Extracellular signal-regulated kinase 1/2 (ERK1/2) pathway blocker, PD98059, also markedly inhibited these effects, suggesting urocortin affects the activity of ACE through the ERK1/2 pathway in rats. These findings support the changes in mean arterial pressure (MAP) following acute and subchronic injections of urocortin in previous studies. Thus, the changes of the ACE activity and its production of Ang II may play a role in the vasodilatory property of urocortin.