Effect of antihypertensive drugs on the renin-angiotensin system

Combined vaccines against angiotensin II receptor type 1 and alpha 1D-adrenergic receptor for hypertension

PURPOSE

Compared with monotherapy, combination therapy with multiple antihypertensive drugs has demonstrated superior efficacy in the management of hypertension. The aim of this study was to explore the efficacy of multitarget combined vaccines in achieving simultaneous antihypertensive and target organ protection effects.

METHODS

Our team has developed ATRQβ-001 and ADRQβ-004 vaccines targeting Ang II type 1 receptor (AT1R) and α1D-adrenergic receptor (α1D-AR), respectively. In NG-nitroarginine methyl ester ( l -NAME) + abilities spontaneously hypertensive rats (SHRs) model, SHRs were simultaneously inoculated with ATRQβ-001 and ADRQβ-004 vaccines. Histological and biochemical analyses were performed to evaluate the antihypertensive effects and target organ protection of the ATRQβ-001 and ADRQβ-004 combined vaccines in comparison with those of the single vaccine.

RESULTS

Both ATRQβ-001 and ADRQβ-004 vaccines induced robust antibody production, resulting in persistent high antibody titers in rats. Notably, the combined administration of both vaccines significantly decreased SBP in SHRs compared with treatment with a single vaccine, both before and after l -NAME administration. Furthermore, the combined vaccine regimen demonstrated superior efficacy in protecting against vascular remodeling, myocardial hypertrophy and fibrosis, and kidney injury in SHRs. Mechanistically, the combined vaccines exhibited significantly downregulated the expression of angiotensin II type 1 receptor (AT1R) and α1D-adrenergic receptor (α1D-AR). Importantly, no apparent immune-related adverse effects were observed in animals immunized with the combined vaccines.

CONCLUSION

Preliminary findings from this investigation suggest that co-administration of the novel ATRQβ-001 and ADRQβ-004 vaccines holds potential as a groundbreaking therapeutic strategy for managing hypertension.

Body fluid volumes and the response of renin and aldosterone to short- and long-term thiazide therapy of essential hypertension

Plasma volume (PV), extracellular fluid volume (ECV) serum electrolytes, renin and aldosterone were measured before and after 1 week and 4 months of hydrochlorothiazide (HCT) treatment, 50 mg twice daily, in nine male patients with uncomplicated essential hypertension. All studies were carried out under strictly standardized conditions in a metabolic ward. After 1 week of HCT treatment, significant reductions were found in PV and ECV, but after 4 months only ECV was significantly reduced. During HCT therapy, renin and aldosterone were permanently elevated whereas serum sodium and potassium were lowered. After 1 week, renin was inversely correlated with PV and ECV and directly correlated with heart rate. After 4 months, renin was inversely correlated with serum sodium. These results indicate a permanent decrease in ECV during long-term HCT therapy. It is further suggested that the mechanisms responsible for the renin response during short- and long-term HCT treatment are different, changes in body fluid volumes and increased neural activity being responsible for the initial rise in renin, and serum sodium being the predominant factor during chronic treatment.

Influence of minoxidil on ischemic cutaneous flaps in rats

PURPOSE: To evaluate the influence of minoxidil, a well known vasodilator, on ischemic flap necrosis prevention in rats. METHODS: Ventral cutaneous flaps, measuring 8x4cm, were designed in 20 Wistar rats based on the right cranial epigastric artery. In the experiment group, 50 mg/kg/day of minoxidil sulfate was administered by orogastric tube and the same amount of saline solution was administered to the control group. Such procedure was initiated 24h before surgery and kept once a day through the 7th postoperative day. Microcirculation was evaluated with laser fluxometry 24h before surgical procedure, at immediate postoperative and at the 7th postoperative day. Flap necrosis area was evaluated by 2 methods: planimetry and weight/paper ratio. RESULTS: A significant flow increase in distal and medial extremity at M1 (medial point 1) (p=0,0484) was observed in the experiment group. There was significant difference in flap necrosis prevention in the experiment group (p=0,0433), although after necrosis took place there was no significant difference in necrosis size. (p=0,1051 and p=0,2799). CONCLUSION: Minoxidil sulfate is effective in avoiding necrosis in ischemic flaps, but after necrosis is present there is no difference in survival area between experimental and control groups.

Labetalol therapy in pregnancy induced hypertension: the effects on fetoplacental circulation and fetal outcome

We prospectively studied the effects of oral labetalol therapy in patients with moderate to severe pregnancy induced hypertension (PIH). The outcome variables were blood pressure control, effect on umbilical artery flow velocity waveforms (UAFVW) and fetal outcome. Forty-two patients were recruited, all had moderate to severe PIH. The mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) on entry were 154 +/- 7 mmHg and 104 +/- 5 mmHg, respectively. All had significant proteinuria. After 1 week on labetalol therapy, 85% of patients had their blood pressure controlled. The reduction in both SBP and DBP was statistically significant. There were no significant changes in UAFVW, Resistance Index (RI), uric acid or platelets. The mean fetal age on entry was 246 +/- 10 days while gestation at delivery was 258 +/- 17 days. The mean birth weight was 2712 +/- 609 g. No perinatal mortality occurred in this study. Labetalol is an effective drug in controlling blood pressure and does not adversely affect the UAFVW. No neonatal problems were attributed directly to the drug. Fetal outcome was satisfactory despite the 12 fetuses that were growth-retarded. Labetalol allows safe prolongation of pregnancies complicated by PIH.

A comparison of the haemodynamic and hormonal effects of low and conventional dose cyclopenthiazide in normal volunteers

In this study we compared low (125 micrograms) and conventional (500 micrograms) doses of cyclopenthiazide on the renin angiotensin system, plasma and extracellular fluid volumes and the pressor responsiveness to angiotensin II since we have previously shown that the two doses have the same antihypertensive effect but different effects on plasma renin activity. Following a two week placebo run-in period, 8 healthy male volunteers received 125 micrograms or 500 micrograms of cyclopenthiazide for 2 treatment periods of 4 weeks as part of a double blind, 2-part crossover study with treatment periods separated by a 4-week placebo washout phase. Measurements were made on two study days at the beginning and end of the active treatment periods. On the first day serum potassium, plasma renin activity and plasma angiotensin II levels were measured after a 1 h period of supine rest. Plasma and extracellular fluid volumes were also measured after appropriate equilibration times. The blood pressure responses to angiotensin II were assessed on day 2. The 500 micrograms dose of cyclopenthiazide had a greater effect than the 125 micrograms dose on plasma renin activity, serum potassium, angiotensin II levels and extracellular fluid volumes. Neither drug had any effect on plasma volume or the responsiveness to infused angiotensin II. Low dose cyclopenthiazide failed to increase angiotensin II levels, contract body fluid volumes or attenuate vascular reactivity in normotensive volunteers.

The role of renin substrate in hypertension

A positive correlation between blood pressure and renin substrate concentration is found in a wide variety of conditions in human beings and in animal experiments. The evidence concerning this relationship is reviewed and the exceptions are discussed. The frequent positive correlation between renin substrate and elevated blood pressure suggests that increased renin substrate concentration may be a causal factor in hypertension.

Effects of prostaglandins inhibition on changes in active and inactive renin induced by antihypertensive drugs

The behaviour of active (AR) and inactive (IR) renin was studied in 48 hypertensive patients (37 with uncomplicated essential hypertension and 11 with reno-vascular hypertension) treated with indomethacin alone or with AR stimulating (bumetanide, tienilic acid, captopril) and inhibiting (atenolol) drugs before and after indomethacin addition. In 10 pts indomethacin (50mg q.i.d./3 days) reduced (p less than 0.05) AR and to a lesser extent IR. In 6 pts bumetanide (1 mg) increased (p less than 0.05) only AR and this effect was abolished by indomethacin. In 6 pts tienilic acid (250 mg) increased (p less than 0.05) only AR and this action was unchanged by indomethacin. In 11 renovascular pts captopril (100mg) increased AR (p less than 0.01) and lesser IR and both these effects were uninfluenced by indomethacin. In 11 essential hypertensive pts captopril (25mg b.i.d./3 days) increased only AR (p less than 0.02), but after 1 year both AR and IR were increased (p less than 0.05) and these effects were abolished by indomethacin. In all the above reported protocols we did never find any inverse correlation between either AR and IR values or their induced changes. These data suggest that prostaglandins stimulate, even if not to a similar extent, both AR and IR and that drugs, which stimulate renin either through or independently of PGs, did not cause any apparent interconversion of plasma IR into AR. In 6 pts atenolol (100 mg daily/6 days) reduced AR (p less than 0.05) and tended to increase IR. Indomethacin addition further decreased AR and reduced IR (both p less than 0.05 vs atenolol alone): however the proportion (% of total) of IR was still reduced. These findings suggest that beta 1-adrenoreceptors blockade exerts a divergent effect on active and inactive renin and that this action is not influenced by PGs synthesis inhibition.

Malignant hypertension in a child with hemolytic-uremic syndrome treated with captopril

A 5-year-old boy is presented suffering from malignant hypertension due to hemolytic-uremic syndrome. Captopril, an oral angiotensin-1-converting enzyme inhibitor, was able to curb the natural course of the malignant hypertension. Haemodialysis could be discontinued after 2 months. The glomerular filtration rate recovered to 63 ml/min/1.73 m2 11 months after the acute phase.

A comparison between spironolactone and hydrochlorothiazide with and without alpha-methyldopa in the treatment of hypertension

In a single blind crossover trial, spironolactone (50 mg twice a day), and hydrochlorothiazide (50 mg twice a day) were equally effective hypotensive agents in 16 patients with untreated essential hypertension. The addition of alpha-methyldopa (250 mg three times a day) to each agent produced a further significant and equal fall in blood pressure. Spironolactone therapy was assoicated with fewer clinical and biochemical side effects. The hypotensive effect of the diuretics was independent of the renin status of the patients.