Reversible suppression of nitric oxide system in essential hypertension

Effects of sodium nitrite on renal function and blood pressure in hypertensive vs. healthy study participants: a randomized, placebo-controlled, crossover study

OBJECTIVE

Nitric oxide is a key player in regulating vascular tone. Impaired endothelial nitric oxide synthesis plays an important role in hypertension. Replenishing of nitric oxide by sodium nitrite (NaNO2) has not been investigated in patients with essential hypertension (EHT). We aimed to determine the effects of NaNO2 on blood pressure (BP) and renal sodium and water regulation in patients with EHT compared with healthy control study participants (CON).

METHODS

In a placebo-controlled, crossover study, we infused 240 μg NaNO2/kg/h or isotonic saline for 2 h in 14 EHT and 14 CON. During infusion, we measured changes in brachial and central BP, free water clearance, fractional sodium excretion, and urinary excretion rate of γ-subunit of the epithelial sodium channel (U-ENaCγ), and aquaporin-2 (U-AQP2).

RESULTS

Placebo-adjusted brachial SBP decreased 18 mmHg (P < 0.001) during NaNO2 infusion in EHT and 12 mmHg (P < 0.001) in CON (Pbetween = 0.024). Brachial DBP and central SBP decreased equally in both groups during NaNO2. In EHT, we found a decrease in U-ENaCγ during NaNO2 infusion. In both groups, we observed a decrease in fractional sodium excretion, free water clearance, and U-AQP2 during NaNO2 infusion.

CONCLUSION

This study demonstrated an augmented BP-lowering effect of NaNO2 in patients with EHT. We observed an antinatriuretic and antidiuretic effect of NaNO2 in both groups, and a decrease in U-ENaCγ, solely in EHT. In both groups, we detected a nonvasopressin mediated decrease in U-AQP2, which is most likely compensatory to the decline in diuresis.

Hyperglycaemia enhances nitric oxide production in diabetes: a study from South Indian patients

BACKGROUND

We have previously reported that increased glucose levels were associated with higher serum nitric oxide (NO) levels in fructose-fed insulin resistant rats. However, the relationship between hyperglycemia and serum NO level was not clear. Therefore, the present study was designed to find the association between hyperglycemia and serum NO levels in Type 2 diabetic (T2DM) patients and T2DM with cardiovascular complication.

METHODS

Endothelial cells (HUVEC) were treated with of D-glucose (10-100mM), and NO levels and NOS gene expression was measured. Hyperglycaemia was induced in Sprague-Dawley rats, and serum NO levels were measured after 8 weeks. For clinical evaluation, five groups of patients were recruited: Control (CT, n=48), Type 2 diabetes (T2DM, n=26), T2DM with hypertension (DMHT, n=46), Coronary artery diseases (CAD, n=29) and T2DM with coronary artery diseases (DMCD, n=38). NO (nitrite + nitrate) levels were measured from human serum.

RESULTS

We found a significant (p<0.05) and dose-dependent increase in NO levels in HUVEC cells after 4 hours of high glucose exposure. eNOS and iNOS gene expression was increased in HUVEC cells after different concentrations and time periods of glucose treatment. We also observed significant (149.1 ± 25 μM, p<0.01) increase in serum NO levels in hyperglycaemic rats compared to control (76.6 ± 13.2 μM). Serum NO level was significantly higher in T2DM (111.8 μM (81.7-122.4), p<0.001) and DMCD patients ((129.4 μM (121.2-143.5), p <0.001) but not in CAD patients (76.4 μM (70.5-87)), as compared to control (68.2 μM (56.4-82.3)). We found significantly lower NO levels (83.5 μM (60.5-122.9)) in subjects suffering from diabetes since more than 5 years, compared to subjects (115.3 μM (75.2-127.1), p<0.001) with less than 5 years.

CONCLUSION

In conclusion, high NO levels were observed in South Indian diabetic patients. Higher glucose levels in serum might be responsible for activation of endothelial cells to enhance NO levels.

Effect of vitamin E administration on blood pressure following reperfusion of patients with myocardial infarction

BACKGROUND

Reperfusion of infarcted myocardium by thrombolysis is the major technique used to restore blood supply. Reperfusion, however, is associated with a burst of oxygen consumption, with the resultant excessive generation of free radicals causing reperfusion injury.

OBJECTIVE

In the present study, the effect of vitamin E administration on the status of free radical-mediated injury and blood pressure in post reperfusion hypertensive patients with myocardial infarction is assessed.

METHOD

POST REPERFUSION HYPERTENSIVE PATIENTS WERE DIVIDED INTO THREE GROUPS: those not receiving a beta-blocker (group I), those receiving acetylsalicylic acid (ASA) plus a beta-blocker (group II) and those receiving ASA, a beta-blocker and 400 mg vitamin E (group III). Groups II and III were comprised of patients from group I. Levels of malondialdehyde (MDA) and xanthine oxidase (XO) activity in blood were used as an index of oxidative stress. These parameters, along with blood pressure, were monitored in these groups.

RESULTS

Patients not receiving a beta-blocker had elevated levels of MDA and XO activity when compared with healthy persons (P<0.0005 both for MDA and XO). Compared with group I, patients receiving a beta-blocker plus ASA (group II) had a significant decrease in the activity of XO (P<0.005) and the levels of MDA (P<0.005). When vitamin E was incorporated in the treatment, there was highly significant decrease in these oxidative stress parameters compared with groups I and II (P<0.0005 for XO and MDA). Use of vitamin E as an adjuvant in hypertensive therapy (group III) resulted in better management of blood pressure (systolic P<0.005, diastolic P>0.05) when compared with group II.

CONCLUSION

Inclusion of vitamin E in antihypertensive therapy in post reperfusion hypertensive patients results in better management of blood pressure.