Renin release, saralasin and the vasodilator-beta-blocker drug interaction in man

α 2-Adrenoceptors: Challenges and Opportunities-Enlightenment from the Kidney

It was indeed a Don Quixote-like pursuit of the mechanism of essential hypertension when we serendipitously discovered α₂-adrenoceptors (α₂-ARs) in skin-lightening experiments in the frog. Now α₂-ARs lurk on the horizon involving hypertension causality, renal denervation for hypertension, injury from falling in the elderly and prazosin's mechanism of action in anxiety states such as posttraumatic stress disorder (PTSD). Our goal here is to focus on this horizon and bring into clear view the role of α₂-AR-mediated mechanisms in these seemingly unrelated conditions. Our narrative begins with an explanation of how experiments in isolated perfused kidneys led to the discovery of a sodium-retaining process, a fundamental mechanism of hypertension, mediated by α₂-ARs. In this model system and in the setting of furosemide-induced sodium excretion, α₂-AR activation inhibited adenylate cyclase, suppressed cAMP formation, and caused sodium retention. Further investigations led to the realization that renal α₂-AR expression in hypertensive animals is elevated, thus supporting a key role for kidney α₂-ARs in the pathophysiology of essential hypertension. Subsequent studies clarified the molecular pathways by which α₂-ARs activate prohypertensive biochemical systems. While investigating the role of α₁-adrenoceptors (α₁-ARs) versus α₂-ARs in renal sympathetic neurotransmission, we noted an astonishing result: in the kidney α₁-ARs suppress the postjunctional expression of α₂-ARs. Here, we describe how this finding relates to a broader understanding of the role of α₂-ARs in diverse disease states. Because of the capacity for qualitative and quantitative monitoring of α₂-AR-induced regulatory mechanisms in the kidney, we looked to the kidney and found enlightenment.

Hypertension's 3 Dilemmas and 3 Solutions: Pharmacology of the Kidney in Hypertension

The Hypertension Community has 3 conflicting dilemmas: a goal systolic pressure of 120 mm Hg or less (the SPRINT Trials), 40% of our 60,000,000 hypertensives still sustain blood pressures above 140/90 mm Hg, and our most potent antihypertensive drug minoxidil sits on the sidelines, imprisoned in the Food and Drug Administration's Black Box designation. My solutions to these dilemmas are: (1) review of the facts of our most potent antihypertensive drug minoxidil which is essentially free of toxicity, (2) treatment focus on the fundamental cause of high blood pressure, that is excess dietary sodium and, (3) prevention of, and/or reversal of, the fundamental mechanism of worsening hypertension, arteriolar hypertrophy.

SUMMARY

The Hypertension Community has 3 conflicting dilemmas: a goal systolic pressure of 120 mm Hg or less (the SPRINT Trials), 40% of our 60,000,000 hypertensives still sustain blood pressures above 140/90 mm Hg, and our most potent antihypertensive drug minoxidil sits on the sidelines, imprisoned in the Food and Drug Administration's Black Box designation. My solutions to these dilemmas are: (1) review of the facts of our most potent antihypertensive drug minoxidil which is essentially free of toxicity, (2) treatment focus on the fundamental cause of high blood pressure (HBP) and excess dietary sodium and, (3) prevention of, and/or reversal of, the fundamental mechanism of worsening hypertension, arteriolar hypertrophy. My focus at UT Southwestern in Dallas was on extremely severely hypertensive patients with a quantifiable, measurable complication of HBP, progression of nephrosclerotic damage to kidneys. This model had the greatest likelihood of exposing fundamental disregulatory mechanisms in hypertensive patients (which it did) and the potential for study of the most relevant antihypertensive drug interactions to achieve optimal blood pressure control (which it did). By maintaining diastolic pressures at 80 mm Hg or less in the first National Institutes of Health-supported, long-term randomized clinical trial to save the kidneys, the bases for a fundamental blood pressure support mechanism (arteriolar hypertrophy) was illuminated but not fully described until now. This fundamental hypertensinogenic mechanism results from HBP but with time and severity, becomes its own raison d'être. I am now aged 84 years. As a result of a stroke 20 years ago, which caused permanent double vision, and because of poor blood pressure control with triple therapy, I started using minoxidil 5 mg/d along with atenolol and occasional furosemide. Now, along with some dietary salt restriction, my resting blood pressure is 110/65-125/75 and, despite >30 years history of HBP, I have no retinal arteriolar hypertrophy nor arcus senilis (Dr. Schwartz-U. of Miami) which is almost universally present at this age. Yes, prevention of, or reversal of, arteriolar hypertrophy should be a central focus of HBP treatment. I simply wish to share a bit of accumulated wisdom that might be of use to others.

Resistant hypertension in nondialysis chronic kidney disease

Resistant hypertension (RH) is defined as blood pressure (BP) that remains above the target of less than 140/90 mmHg in the general population and 130/80 mmHg in people with diabetes mellitus or chronic kidney disease (CKD) in spite of the use of at least three full-dose antihypertensive drugs including a diuretic or as BP that reaches the target by means of four or more drugs. In CKD, RH is a common condition due to a combination of factors including sodium retention, increased activity of the renin-angiotensin system, and enhanced activity of the sympathetic nervous system. Before defining the hypertensive patient as resistant it is mandatory to exclude the so-called “pseudoresistance.” This condition, which refers to the apparent failure to reach BP target in spite of an appropriate antihypertensive treatment, is mainly caused by white coat hypertension that is prevalent (30%) in CKD patients. Recently we have demonstrated that “true” RH represents an independent risk factor for renal and cardiovascular outcomes in CKD patients.

Changes in plasma volume and extracellular fluid volume and after addition of hydralazine to propranolol treatment in patients with hypertension

In 16 patients with hypertension, BP could not be controlled satisfactorily by treatment with propranolol alone (mean dosage 325 mg/day). Plasma volume (PV) (T-1824) and extracellular fluid volume (ECV) (82Br-distribution space) were determined in these patients before and after the addition of hydralazine for three months (mean dosage 135 mg/day). After the addition of hydralazine, PV and ECV increased significantly, by 9% and 3%, respectively. Systolic and diastolic BPs decreased, by 15% and 13%. The mechanisms inducing fluid retention during treatment with hydralazine and the clinical significance of the problem are discussed. It is concluded that the addition of a diuretic to propranolol-hydralazine treatment is often well indicated.

Rationale for combined alpha-beta-adrenoceptor blockade: haemodynamic considerations

Increased peripheral vascular resistance is the cause of elevated blood pressure in most forms of systemic hypertension. Both structural changes in response to increased wall stress and functional alterations in vascular smooth muscle itself appear to contribute to the elevated resistance. As mediators of the vasoconstrictor responses, alpha-adrenoceptors apparently play an important if not predominant role in the initiation and/or maintenance of high resistance and pressure. In contrast to beta-receptor blockade alone, combined alpha-beta-receptor blockade lowers blood pressure predominantly by alpha-receptor-mediated reduction of the systemic vascular resistance, both when induced acutely and, in particular, during long-term administration. Cardiac output is maintained at pretreatment level, as is left ventricular filling pressure. Since a well-balanced blockade of both alpha- and beta-receptors counteracts the pathophysiological changes causing and/or maintaining hypertension and tends to restore cardiovascular dynamics towards normal, combined alpha-beta-receptor blockade appears at present to be one of the most logical and rational therapeutic approaches to hypertension.

Endocrine role of the renin-angiotensin system in human adipose tissue and muscle: effect of beta-adrenergic stimulation

The renin-angiotensin system has been implicated in obesity-related hypertension and insulin resistance. We examined whether locally produced components of the renin-angiotensin system in adipose tissue and skeletal muscle play an endocrine role in vivo in humans. Furthermore, the effects of beta-adrenergic stimulation on plasma concentrations and tissue release of renin-angiotensin system components were investigated. Systemic renin-angiotensin system components and arteriovenous differences of angiotensin II (Ang II) and angiotensinogen (AGT) across abdominal subcutaneous adipose tissue and skeletal muscle were assessed in combination with measurements of tissue blood flow before and during systemic beta-adrenergic stimulation in 13 lean and 10 obese subjects. Basal plasma Ang II and AGT concentrations were not significantly different between lean and obese subjects. Ang II concentrations were increased in obese compared with lean subjects during beta-adrenergic stimulation (12.6+/-1.5 versus 8.1+/-1.0 pmol/L; P=0.04), whereas AGT concentrations remained unchanged. Plasma renin activity increased to a similar extent in lean and obese subjects during beta-adrenergic stimulation (both P<0.01). No net Ang II release across adipose tissue and skeletal muscle could be detected in both groups of subjects. However, AGT was released from adipose tissue and muscle during beta-adrenergic stimulation in obese subjects (both P<0.05). In conclusion, locally produced Ang II in adipose tissue and skeletal muscle exerts no endocrine role in lean and obese subjects. In contrast, AGT is released from adipose tissue and muscle in obese subjects during beta-adrenergic stimulation, which may contribute to the increased plasma Ang II concentrations during beta-adrenergic stimulation in obese subjects.

Withdrawal syndrome following cessation of antihypertensive drug therapy

In this study, a review of the available information concerning abrupt withdrawal of antihypertensive drug therapy is presented. Abrupt withdrawal of these drugs can produce a syndrome of sympathetic overactivity that includes nervousness, tachycardia, headache, agitation and nausea 36-72 h after cessation of the drug. A withdrawal syndrome may occur after discontinuation of almost all types of antihypertensive drugs, but mostly occurs with clonidine, beta-blockers, methyldopa and guanabenz. Less commonly can produce a rapid increase of the blood pressure to pre-treatment levels or above, or both and/or myocardial ischaemia. Although the exact incidence of the syndrome is not known, it appears to be rare, at least in patients receiving standard doses of the above antihypertensive drugs. The best treatment is prevention. In this study regarding the withdrawal syndrome that follows cessation of antihypertensive drugs therapy, a reference to the abrupt discontinuation of the main categories of antihypertensive drugs is also attempted.

Frequency of compound genotypes associated with β-blocker efficacy in congestive heart failure

An important practical problem in pharmacogenetics is the integration of compound genotypes into individualized therapy. Polymorphisms in the genes encoding the angiotensin-converting enzyme, and β1- and β2-adrenoceptors have been identified as predictors of ‘good response’ to β-adrenergic antagonists among heart failure patients. These variants were used as the basis for exploring the concept of compound genotype assessment. The frequency of compound variants in these genes was determined using PCR and pyrosequencing to genotype population samples of 95 African–Americans and 95 European–Americans. Both groups could be divided into four subgroups according to the number of favorable genotypes present. Each subgroup accounted for a significant proportion of subjects (the smallest was 7% of total). This study provides the first look into the population frequency of these compound genotypes, and it provides the necessary first step for future evaluation of polygenic strategies to individualize therapy for heart failure.

Achievement of target blood pressure levels in chronic kidney disease: a salty question?

A large body of evidence supports the validity of lowering blood pressure (BP) to prevent cardiovascular (CV) disease in the general population. This issue becomes even more critical in renal patients because they carry a greater CV risk across the entire spectrum of chronic kidney disease (CKD). In these patients, achievement of lower BP levels also is fundamental to limit the progression of renal damage, especially in the presence of significant proteinuria. Although expert panels have strongly recommended to intensively decrease BP in patients with CKD, management of hypertension in these patients remains inadequate. Armed with the knowledge of the extreme salt-sensitivity of BP in patients with CKD, it is reasonable to hypothesize that more aggressive treatment of volume expansion can be helpful. Nevertheless, although abundant literature has evidenced that dietary sodium restriction decreases BP levels in patients with essential hypertension, no large and prospective study has been conducted to date on this issue in patients with CKD. A potential reason is the low compliance of patients with CKD to dietary prescriptions; however, this problem can be overcome by specific counseling. Alternatively, loop diuretics administered at a high dose should represent the cornerstone of therapy, but, again, well-designed studies verifying the effectiveness of these agents in a large CKD population are still awaited. Nephrologists seem to be reluctant to adequately administer diuretics because of the fear of adverse events. Conversely, the major detrimental effect, that is, excessive hypovolemia, can be prevented if daily body weight loss is limited to 0.3 to 0.5 kg during the initial period of treatment.

Possible involvement of the adipose tissue renin-angiotensin system in the pathophysiology of obesity and obesity-related disorders

Angiotensin II (Ang II), acting on the AT1 and AT2 receptors in mammalian cells, is the vasoactive component of the renin-angiotensin system (RAS). Several components of the RAS have been demonstrated in different tissues, including adipose tissue. Although the effects of Ang II on metabolism have not been studied widely, it is intriguing to assume that components of the RAS produced by adipocytes may play an autocrine, a paracrine and/or an endocrine role in the pathophysiology of obesity and provide a potential pathway through which obesity leads to hypertension and type 2 diabetes mellitus. In the first part of this review, we will describe the production of Ang II, the different receptors through which Ang II exerts its effects and summarize the concomitant intracellular signalling cascades. Thereafter, potential Ang II-induced mechanisms, which may be associated with obesity and obesity-related disorders, will be considered. Finally, we will focus on the different pharmaceutical agents that interfere with the RAS and highlight the possible implications of these drugs in the treatment of obesity-related disorders.

Endothelial apoptosis: could it have a role in the pathogenesis and treatment of disease?

Endothelial apoptosis can be found in a number of diseases. This review summarizes the current knowledge about the causes and consequences of endothelial apoptosis, and analyzes its possible role in the pathogenesis and treatment of several diseases. Novel forms of therapy based on the proposed pathophysiologic mechanisms are discussed.

Role of sympathetic nerves for the stimulation of the renin system by angiotensin II receptor blockade

OBJECTIVE

To assess the relevance of sympathetic nerves for the stimulation of renin secretion and renin gene expression during effective angiotensin II type 1 receptor blockade in vivo.

METHODS

Male Sprague-Dawley rats were treated with the angiotensin II type 1-receptor blocker losartan (40 mg/kg) for 3 days. To examine the role of renal sympathetic nerves in the stimulation of the renin system by losartan, left kidneys were denervated 4 days prior to the treatment with losartan. Also, to examine the role of circulating catecholamines in the stimulation of the renin system by losartan, the animals were administered a combination treatment of losartan with the beta1-adrenoreceptor blocker metoprolol (50 mg/kg per day) for 3 days.

RESULTS

Losartan treatment increased plasma renin activity about sevenfold and renal renin messenger RNA (mRNA) levels about fivefold and decreased systolic blood pressure from 118 to 95 mmHg. Administration of losartan elevated renin mRNA both in the innervated and in the denervated kidneys to the same level as it did in kidneys of normal animals. Losartan treatment increased plasma renin activity and renal renin mRNA levels in the beta1-blocker-treated rats to the same extent as it did in animals administered losartan only.

CONCLUSION

These findings suggest that, under sub-chronic treatment with hypotensive doses of angiotensin II receptor blockers, sympathetic outflow plays no important mediator role in the characteristic stimulation of renin secretion and renin gene expression, suggesting that it is mainly a direct disinhibition of angiotensin II's action on the level of juxtaglomerular cells that accounts for the effect.

Hyperfiltration and conservation of renal function in hypertensive nephrosclerosis patients

Renal glomerular hyperfiltration has been proposed as an important contributing factor to the progression of hypertensive nephrosclerosis in rats with reduced renal mass. However, no clinical studies have assessed the role of glomerular hyperfiltration in the pathogenesis of hypertensive nephrosclerosis in humans. In a prospective, randomized, long-term blood pressure control study with up to 3 years follow-up, we showed that good blood pressure control with a mean diastolic blood pressure < or = 95 mm Hg preceded by a 2- to 4-month period of diastolic blood pressure < or = 80 mm Hg improved renal function in hypertensive nephrosclerosis patients. Patients treated with minoxidil, an angiotensin-converting enzyme inhibitor (enalapril), or a calcium entry blocker (nifedipine) had improvement in renal function, as indicated by a positive slope of the reciprocal serum-creatine concentration versus time and an increment in glomerular filtration rate. These results suggested that improvement in renal function occurred with these major types of antihypertensive drug treatment. To assess the renal hemodynamics of minoxidil, enalapril, and nifedipine, eight patients with hypertensive nephrosclerosis were admitted to the General Clinical Research Center for renal clearance studies on each drug while ingesting a fixed-calorie, 12% protein, 40% fat, and 100 mEq Na/d diet. Mean blood pressure, effective renal plasma flow, and renal vascular resistance did not change during the three phases of treatment. However, minoxidil treatment increased the glomerular filtration rate by 48% versus enalapril and by 79% versus nifedipine. Since minoxidil treatment improves renal function while causing a relative hyperfiltration, glomerular hyperfiltration per se is an unlikely mechanism for the progression of hypertensive nephrosclerosis in humans.

Renin-angiotensin II response to the hemodynamic pathology of ovines with ventricular septal defect

We studied the response of the renin-angiotensin system (RAS) to a surgically created ventricular septal defect (VSD) in immature ovines and also the role of angiotensin II in the pathophysiology of VSD in the chronically instrumented ovine. Plasma renin activity (PRA) was increased from 2.39 +/- 1.1 to 3.78 +/- 1.4 ng/ml/hr (p less than 0.05, n = 17) after VSD but not after sham procedure. The change in PRA was positively correlated with the amount of left-to-right shunt through the VSD (r = 0.74, p less than 0.05). Inhibition of angiotensin II effect with saralasin (10 micrograms/kg/min) or angiotensin II production with captopril (2 mg/kg) lowered systemic resistance (Rs) by 14% and 34%, respectively (p less than 0.05), and raised pulmonary resistance (Rp) by 35% and 77%, respectively (p less than 0.05). Thirty minutes following captopril, the ratio of pulmonary to systemic flow (Qp/Qs) decreased from 3.31 +/- 0.18 to 2.15 +/- 0.18 (p less than 0.05) while total pulmonary flow fell from 7.15 +/- 0.38 to 5.92 +/- 0.34 l/min/M2 (p less than 0.05, n = 11). Systemic flow increased from 2.17 +/- 0.14 to 2.86 +/- 0.33 l/min/M2 (p less than 0.05) despite a reduction in left atrial pressure (17.3 +/- 1.0 vs. 13.0 +/- 1.7, p less than 0.01). Reinfusion of angiotensin II (0.02 micrograms/kg/min) into the central aorta after captopril returned the hemodynamics to baseline including a rise in Rs and fall in Rp. Exogenous angiotensin II alone (0.08 micrograms/kg/min) or a threefold stimulation in PRA with furosemide (2 mg/kg) caused little hemodynamic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic advantage of converting enzyme inhibitors in arresting progressive renal disease associated with systemic hypertension in the rat

Micropuncture and morphologic studies were performed in six groups of male Munich-Wistar rats after removal of the right kidney and segmental infarction of two-thirds of the left kidney. Groups 1 and 4 received no specific therapy. Groups 2 and 5 were treated with the angiotensin I-converting enzyme inhibitor, enalapril, 50 mg/liter, in the drinking water. Groups 3 and 6 were treated with reserpine (5 mg/liter), hydralazine (80 mg/liter), and hydrochlorothiazide (25 mg/liter). All rats were fed standard chow. Groups 1-3 underwent micropuncture study 4 wk after renal ablation. Untreated group 1 rats exhibited systemic hypertension and elevation of the single nephron glomerular filtration rate (SNGFR) due to high average values for the mean glomerular transcapillary hydraulic pressure gradient (delta P) and glomerular plasma flow rate (QA). In group 2 rats, treatment with enalapril prevented systemic hypertension and maintained delta P at near-normal levels without significant reduction in SNGFR and QA. In contrast, triple drug therapy normalized systemic hypertension, but failed to lower delta P in group 3 rats. Groups 4-6 were followed for 12 wk after renal ablation. Untreated group 4 rats demonstrated continuous systemic hypertension, progressive proteinuria, and glomerular structural lesions, including mesangial expansion and frequent areas of segmental sclerosis. In group 5 rats, treatment with enalapril maintained systemic blood pressure at normal levels over the 12-wk period and dramatically limited the development of proteinuria and glomerular lesions. Despite equivalent systemic blood pressure control in group 6 rats, failure of triple drug therapy to control glomerular hypertension was associated with progressive proteinuria and glomerular lesions comparable to those seen in untreated group 4 rats. Thus, unless glomerular capillary hypertension is corrected, control of systemic blood pressure is insufficient to prevent progressive renal injury in rats with reduced renal mass.

Hormonal and cardiovascular effects of losulazine hydrochloride in relation to sodium balance in nonhuman primates

Losulazine hydrochloride, a peripheral norepinephrine-depleting agent, was studied in conscious sodium-replete and sodium depleted cynomolgus monkeys. Blood pressure, heart rate, plasma renin activity, and plasma catecholamines were monitored before and after the oral administration of losulazine at a dose which caused a submaximal hypotension in sodium-replete monkeys. The hypotension observed in sodium depleted monkeys was not significantly different from that observed in sodium-replete monkeys. The hypotension from that observed in sodium-replete monkeys. The hypotension observed in both sodium states was accompanied by quantitatively similar decreases in plasma norepinephrine concentrations in the absence of significant alterations of heart rate and plasma renin activity. These results were consistent with the conclusion that losulazine reduced arterial blood pressure in nonhuman primates via peripheral norepinephrine depletion. These data also indicated that the hypotensive effect of losulazine in conscious monkeys was not dependent on alterations in renin-angiotensin system activity or on the state of sodium balance.

Minoxidil in severe and moderately severe hypertension, in association with methyldopa and chlortalidone

Minoxidil is a potent antihypertensive drug widely used in severe arterial hypertension and in that refractory to treatment. Its effectiveness in less severe forms of hypertension was evaluated in 15 patients who had either a severe to moderate arterial hypertension not previously treated, or who did not tolerate the side effects of other antihypertensive drugs. The usefulness of methyldopa and chlortalidone to prevent a potential minoxidil-induced tachycardia and fluid retention, respectively, was also tested. The patients were initially treated with chlortalidone 100 mg/day, and methyldopa 500 mg/day. Minoxidil was then given in increasing doses until the diastolic blood pressure was equal to or inferior to 90 mmHg. This occurred consistently at doses which ranged from 5 to 50 mg/day (average, 29 mg). Treatment with minoxidil was continued for four months; tolerance to the drugs was not observed. Low doses of methyldopa and chlortalidone were effective in controlling the tachycardia and the retention of sodium and water induced by minoxidil. The three associated drugs were well tolerated and the life quality improved in most patients. Hypertrichosis was the most consistent side effect. Two patients were withdrawn from the study after the blood pressure was controlled by minoxidil, because of the appearance of angor in one, and edema and heart failure in the other.

Comparative evaluation of the new vasodilator carprazidil and minoxidil in the treatment of moderate to severe hypertension

The efficacy and side effects of the new vasodilator carprazidil and the established vasodilator minoxidil were compared in 18 hypertensive patients inadequately controlled by 2 to 4 conventional drugs; the latter included diuretics, beta-blockers and/or sympatholytics and, in half the cases, vasodilators, such as hydralazine, diazoxide or the postsynaptic alpha-blocker prazosin. The vasodilators were withdrawn and, using a crossover design all patients received carprazidil (mean final dose 88 mg) and minoxidil (20 mg) for an average period of 5 to 6 months. The effects of the 2 agents appeared to be qualitatively and quantitatively similar. Both tended to cause sodium retention and an increase in heart rate, which required an increased dose of diuretic in one third of the cases or of a beta-blocker in a quarter. With this approach mean body weight and blood volume were not altered in the established phase of carprazidil or minoxidil treatment; heart rate and plasma norepinephrine tended to be only minimally increased, plasma renin was slightly increased, and plasma aldosterone and epinephrine were largely unchanged. Supine and upright blood pressure were reduced from initial values of 189/113 and 167/ 113 mm Hg, to 149/95 and 138/95 mm Hg (-18 and - 17%), respectively, during carprazidil, and to 154/95 and 141/96 mm Hg (-17 and - 15%) during minoxidil therapy. Hypertrichosis occurred with both agents in almost all patients, and limits their more prolonged use in females. No adverse side effects on haematological parameters, liver or renal function were observed, nor was antinuclear antibody detected. It is concluded that carprazidil and minoxidil are equivalent vasodilator agents in the treatment of severe hypertension, particularly in males.

Catecholamines, renin, aldosterone, and blood volume during chronic minoxidil therapy

Several pressor factors were studied before and during chronic minoxidil therapy (median dose 27.5 mg/day) in 16 patients with hypertension that was refractory to conventional drugs. Following treatment with minoxidil and intensified diuretic therapy, blood pressure was decreased markedly; pulse rate, body weight, plasma volume, plasma aldosterone and epinephrine levels were not significantly altered, while plasma renin activity tended to be increased. Supine and upright plasma norepinephrine concentrations were increased by 140 (P less than 0.005) and 50% (P less than 0.05), respectively, but no significant change in urinary norepinephrine excretion was apparent. The latter parameter may not be a close index of sympathetic activity in patients with severe hypertension treated with minoxidil. While a search for underlying pheochromocytoma is always indicated in refractory hypertension, it appears mandatory to evaluate plasma catecholamines prior to or following discontinuation of treatment with minoxidil, to avoid a wrong diagnosis of pheochromocytoma.

Immediate central and peripheral haemodynamic effects of a new vasodilating agent Pinacidil (P1134) in hypertensive man

The purpose of this study was to evaluate the immediate central and peripheral haemodynamic effects of a new vasodilating agent P 1134, in hypertensive man. After oral administration of 25 mg P 1134, the maximal haemodynamic changes were (mean +/- 1 SEM): mean blood pressure fell from 121.8 +/- 6.5 to 80.5 +/- 7.8 mmHg, heart rate increased 24.2 +/- 4.5 beats/min, cardiac output rose 2.9 +/- 0.3 1/min and forearm blood flow increased 1.0 +/- 0.1 ml/100 ml tissue/min. Stroke volume increased 17.0 +/- 2.1 ml and the inotropic state of the heart as judged from systolic time intervals increased. Total peripheral resistance and forearm vascular resistance were both reduced by approx. 50%. Linear correlations were found between the serum concentration of P 1134 and the change in mean blood pressure and total peripheral resistance. Changes in the other parameters mentioned above occurred progressively with changes in mean blood pressure and total peripheral resistance. It can be concluded that P 1134 is a very potent hypotensive agent with a haemodynamic profile identical to that seen with vasodilators with preferably act on precapillary resistance vessels. Potency and maximal efficacy exceeds that of hydralazine and seems like that of minoxidil. P 1134 is remarkably free from side-effects apart from causing water retention as all other vasodilators. It can be administered orally as well as intravenously. This makes P 1134 a very interesting compound in the treatment of moderate to severe hypertension, and further studies are well-founded.

Angiotensin inhibition in severe heart failure: acute central and limb hemodynamic effects of captopril with observations on sustained oral therapy

The systemic, pulmonary, and limb circulatory responses to the angiotensin-converting enzyme inhibitor, captopril, were determined in 10 patients with severe, chronic heart failure. Immediate effects include sustained reductions in arterial pressure and pulmonary capillary wedge pressure and improvement in cardiac output, as reported with other vasodilator drugs. Calf vascular resistance did not change despite substantial lowering of total systemic vascular resistance, indicating that arteriolar dilatation occurred on a selective basis. Transient reduction in mean right atrial pressure paralleled slight calf venodilatation, but effects upon the resistance vasculature predominated. Plasma renin activity and norepinephrine concentrations increased after therapy in the acute phase as plasma aldosterone levels consistently fell. During maintenance oral treatment over 7 to 15 months (median, 11.5 months), patients displayed symptomatic benefit, improved functional capacity, and greater exercise tolerance. No major adverse reactions developed. These findings suggest that angiotensin converting enzyme inhibition with captopril in congestive heart failure patients improved cardiocirculatory function through selective arteriolar dilatation. The reordering of regional blood flow which appears to result from release of angiotensin-mediated vasoconstriction, as well as the suppression of aldosterone, may underlie the prolonged benefit observed in these patients. This oral vasodilator appears to represent an effective adjunct for the treatment of advanced, chronic heart failure refractory to conventional measures.

Antihypertensive and renal effects of orally administered verapamil

In 12 in-patients with moderate uncomplicated hypertension, maintained on constant sodium intake for 15 days, single-blind oral administration of verapamil 80-160 mg t.i.d. for 10 days had a significant antihypertensive effect: in the supine position systolic blood pressure decreased from 177 +/- 5 to 150 +/- 3 mmHg, and diastolic pressure from 111 +/- 3 to 96 +/- 2 mmHg; standing values were similarly lowered from 171 +/- 7 to 143 +/- 4 mmHg, systolic, and from 118 +/- 4 to 97 +/- 2 mmHg, diastolic. The heart rate did not show any significant change (from 79 +/- 3 to 77 +/- 2 beats/min, supine, and from 92 +/- 3 to 87 +/- 3 beats/min, upright). The antihypertensive effect was uniform throughout the day, being similar 2, 3, 6 and 8 h after administration of a dose. Dynamic exercise (75-100 watts on a cycle-ergometer) caused identical increases in arterial pressure and heart rate on the last day of placebo and again on the last day with verapamil, but the peak levels of systolic pressure reached during exercise were lower after verapamil than with placebo, because of the lower blood pressure before exercise. Reduction of arterial pressure by verapamil was not accompanied by increased plasma renin activity, or by renal retention of sodium and water: there was a small increase in sodium excretion, at least during the first days of verapamil administration (from 107 +/- 15 to 113 +/- 15 mEq Na+/day), and a slight significant reduction in body weight (from 74.2 +/- 3.7 to 73.5 +/- 3.7 kg). It is concluded that oral administration of verapamil significantly lowers blood pressure without simultaneously inducing cardiac stimulation, renin secretion or salt and water retention.

Angiotensin II blockade during combined thiazide-beta-blocker treatment

Sixteen patients (11 M, 5 F), median age 41 years, with essential hypertension insufficiently controlled on hydrochlorothiazide 75 mg/day (DBP greater than or equal to 100 mmHg) were investigated. Plasma renin concentration (PRC), angiotensin II concentration (PA II), aldosterone concentration (PAC), plasma noradrenaline concentration (PNAC), plasma volume (PV) and exchangeable sodium (NaE) were determined and a saralasin-infusion (5.4 nmol/kg/min) was carried out while the patients were on thiazide alone, and in fourteen cases, repeated 3 months later after addition of a beta-blocker (propranolol 6, metoprolol 6 and atenolol 2 patients). On thiazide alone PRC, PA II and PAC was higher than normal in the group as a whole and the angiotensin II-inhibitor, saralasin, caused a significant decrease in MAP in twelve out of sixteen patients. After addition of a beta-blocker SBP and DBP decreased from 164/109 mmHg to 136/94 mmHg. PRC and PA II decreased by 40% and 58%, respectively. At this point saralasin caused no significant change in MAP. No close correlation was found between changes in BP on beta-blocker treatment and either PRC, PA II or saralasin response on thiazide treatment. PV, NaE, PAC and PNAC did not change sigificantly. It is concluded that in pts with thiazide-induced stimulation of the renin-angiotensin system (RAS) addition of a beta-blocker leads to suppression of RAS and the angiotensin II dependence of the blood pressure is nearly abolished. This mechanism might well contribute to the antihypertensive effect of beta-blockade in this particular situation. However, the pharmacological changes induced by beta-blockade are very complex, and most likely other factors are involved in the antihypertensive effect of beta-blocking drugs.

Angiotensin II, plasma renin and sodium depletion as determinants of blood pressure response to saralasin in essential hypertension

To evaluate the role of the renin-angiotensin system and sodium depletion in the hypotensive response to 1-sarcosine-8-alanine-angiotensin II (saralasin), 15 male patients with essential hypertension were studied on a diet containing 120 mEq of sodium and 100 mEq of potassium per day. After a 5-day control period, all subjects had a mild pressor response to the saralasin infusion (p less than 0.01). After 5 days of the diuretic metolazone (5 mg/day), eight of the 15 patients had a vasodepressor response; these responders had a significantly greater increase in plasma renin activity and angiotensin II concentrations than did the non-responders. Sodium deficit differed markedly (p less than 0.001) between the two groups (361 +/- 121 mEq (SD) vs 52 +/- 26 mEq sodium, respectively). The addition of spironolactone (400 mg/day) for 5 days resulted in saralasin responsiveness in all but two patients, both of whom had small sodium deficits. Thus, variability in the natriuretic response to diuretics may affect saralasin testing and limit its clinical utility.

Saralasin test as a diagnostic and prognostic aid in renovascular hypertensive patients subjected to renal operation

A positive saralasin test in patients with angiographic evidence of renovascular disease and other positive functional tests gives further assurance that these patients will achieve normal or substantially reduced blood pressure postoperatively. In our experience with proved renovascular hypertension there was a 19 per cent incidence of falsely negative saralasin tests. Therefore, saralasin should not be used as the sole screening test in hypertensive patients suspected of having surgically correctable lesions. There is a direct correlation between elevated renin activity and a positive saralasin test. In some patients saralasin may be more sensitive than any other currently used test to detect overactivity of the renin-angiotensin system. This would determine those patients with technical errors in renin sampling and assays. Of the 16 patients (all normotensive) who had 6-month followup tests 5 had elevated peripheral renin activity, probably owing to furosemide stimulation. Of these 5 patients 2 had a positive postoperative saralasin test, raising the question of potential falsely positive responses in cases of essential hypertension and coincidental non-functional renal artery stenosis. Patients with high renin essential hypertension may respond to saralasin, even in the absence of renal artery lesions. A saralasin test should be done in a hospital where all specific conditions can be met and potential complications handled promptly.

Saralasin-induced renin release: its blockade by prostaglandin synthesis inhibitors in the conscious rat

The angiotensin antagonist, saralasin, (10 and 30 mg/kg), increased serum renin activity (SRA) in normal, conscious rats from 2.7 +/- 0.4 to 16.2 +/- 3.7 and 22.5 +/- 2.4 ng/ml/hr (p less than 0.001), respectively, without markedly altering blood pressure or heart rate. Indomethacin, in a dose which inhibited the urinary excretion of prostaglandin E2 (PGE2) by 75%, and arachidonate-induced hypotension by 83%, failed to alter basal SRA but inhibited saralasin-induced renin release by 99% and 87% at the 10 and 30 mg/kg doses, respectively. Indomethacin failed to alter basal hemodynamics or the hemodynamic response to saralasin. Propranolol (1.5 mg/kg) inhibited saralasin-induced renin release by 93% and enhanced the suppressant effect of indomethacin from 79% to 100%. Meclofenamate, another prostaglandin synthesis inhibitor, also blocked saralasin-induced renin release by 99% and 72% at the 10 and 30 mg/kg doses, respectively (p less than 0.001). In sodium-depleted rats, saralasin (0.3 mg/kg) increased SRA from 12 +/- 2 to 119 +/- 6 ng/ml/hr (p less than 0.001) and decreased blood pressure by 6% (p less than 0.01). In these animals, indomethacin failed to alter basal SRA, but inhibited saralasin-induced renin release by 82%, urinary excretion of PGE2 by 79%, and arachidonate-induced hypotension by 81%. These findings suggest 1) that saralasin-induced renin release is mediated by renal prostaglandins, and 2) an interrelationship exists between the receptor controlling AII-mediated inhibition of renin release, which is blocked by saralasin, and the juxtaglomerular beta-adrenergic receptor.

Contrasting effects of acute beta blockade with propranolol on plasma catecholamines and renin in essential hypertension: a possible basis for the delayed antihypertensive response

Blood pressure, heart rate, plasma renin activity, plasma norepinephrine and plasma epinephrine were determined in 11 patients with essential hypertension at rest before and 15, 30, 45, and 60 minutes after an intravenous infusion of 0.12 mg./Kg. propranolol given over five minutes. After propranolol mean blood pressure was unchanged; heart rate decreased by 14 per cent within 15 minutes and showed no further changes. Plasma renin activity decreased progressively by 48 per cent 60 minutes after propranolol, whereas plasma norepinephrine and epinephrine were always higher after propranolol than control values. Increases in norepinephrine were statistically significant at 30, 45, and 60 minutes (respectively 49, 39, and 45 per cent, P less than 0.005 at least) and those of epinephrine even at 15 minutes (respectively 60, 82, 62, and 94 per cent P less than 0.01 for all). These results indicate that acute beta blockade with propranolol incudes increases in circulating plasma norepinephrine and epinephrine which might be consequent to rapidly induced hemodynamic changes. This augmented sympathetic activity might explain why propranolol, when acutely infused, does not decrease blood pressure despite effective cardiac and renin blockade.

Clinical evaluation of a new antihypertensive vasodilating agent PR--G 138 Cl

1 The cardiovascular effects of a new substance (PR--G 138) with vasodilating action were analysed in 12 patients with moderately severe essential hypertension on a 60 mEq sodium diet in a metabolic ward. To prevent tachycardia, propranolol 40 mg four times daily was given during the control period until blood pressure (BP) was stabilized, and continued throughout the study. 2 The compound was effective in every patient except one, who also was resistant to hydrallazine and diazoxide. Mean arterial pressure was lowered from a mean control value of 121 +/- 11 supine and 118 +/- 13 standing to 98 +/- 18 and 95+/- 15 mm Hg (P less than 0.001) respectively after a single oral dosage of 5 to 15 mg PR--G 138. The effect was maximal after 1--2 h and lasted up to 6 h. 3 With adequate dosage, there was no orthostatic reaction. Pulse rate and plasma renin activity did not rise during PR--G 138 treatment, and cardiac output increased only slightly, doubtlessly as a result of the propranolol therapy. In most patients 5 mg of the drug was sufficient to cause a drop of BP to normal levels. Exercise tolerance (bicycle ergometry) was constant or improved during drug action. One patient complained of headache, but no other side effects were seen provided that propranolol was taken when the drug was given. During 3 months treatments on an out-patient basis the effect was sustained in four of eight patients. No toxic effects have been noticed.

beta blockade with pindolol: differential cardiac and renal effects despite similar plasma kinetics in normal and uremic man

Cardiac and renal effects (measured as the reduction in exercise-induced tachycardia and PRA, respectively) and circulating drug concentrations after acute beta blockade with intravenous pindolol were compared between seven normal volunteers and six patients with terminal renal failure. Kinetic parameters were similar in both groups (total body clearance, 450 mg/min), indicating enhanced extrarenal elimination in patients. For any given drug concentration, however, the uremic patients responded to beta blockade with a greater decrease in pulse rate than did normal volunteers (P less than 0.001). Moreover, in the same group, the decrease of PRA was more marked (from 13.3 to 5.7 vs. 3.3 to 1.9 ng/ml/hr) and lasted longer (8 hours and more vs. 2 hours). Plasma aldosterone remained unchanged. These data reveal an increased dependency of both heart rate and renin release on beta adrenergic-mediated mechanisms in uremic man. They also show that kinetic findings in normal subjects cannot always be extrapolated to predict kinetic behavior in disease, and that similar kinetics do not imply similar effectiveness.

Effect of nifedipine on plasma renin, aldosterone and catecholamines in arterial hypertension

Acute sublingual administration of nifedipine 10--20 mg to 13 hypertensive patients caused a rapid decrease in blood pressure (BP) and a concomitant increase in heart rate (HR), plasma noradrenaline (NA) and plasma renin activity (PRA); there was no significant change in plasma adrenaline (A) or aldosterone (ALDO). Basal PRA was the major determinant of the rise in PRA, as a close correlation was present between the basal value and the increase caused by nifedipine (r = 0.92), p less than 0.001). The rise in PRA was also correlated with the plasma concentration of nifedipine after 60 min (r = 0.80, p less than 0.01), but it was not correlated with the decrease in BP, the rise in HR or the increase in NA. Nifedipine 30--60 mg daily for 6 weeks caused a reduction in mean BP from 133 to 113 mmHg (p less than 0.001). Body weight and serum potassium decreased but no consistent change was noted in NA, PRA, ALDO or 24 h-excretion of catecholamines. A significant correlation was present between the change in NA and that in PRA (r = 0.74, p less than 0.01). The alterations in the various parameters in the acute and chronic studies were not correlated. The findings indicate that different regulatory mechanisms are activated during acute and chronic administration of nifedipine. It is suggested that an initial rise in sympathetic activity gradually decreases during prolonged therapy, but it still remains a determinant of PRA.

Relative significance of plasma renin activity and concentration in physiologic and pathophysiologic conditions

Plasma renin activity (PRA) and concentration, measured after acid treatment of the plasma (PRC3.3), were determined on the same plasma samples in different conditions. Log PRA and log PRC3.3 were significantly (P less than 0.001) and similarly related to sodium intake, age, and plasma aldosterone concentration in normal subjects. The correlation coefficient between log PRA and log PRC3.3 was 0.49 in 80 sodium-replete and sodium-deplete normal subjects, and it was 0.84 in 84 hypertensive patients untreated or under treatment with thiazides. On the contrary, during beta adrenergic blockade, PRA decreased significantly (P less than 0.001) by 62% while the changes in PRC3.3 were not significant. At maximal exercise, PRA increased significantly by 168% while the PRC3.3 increase of 24% was not significant. In hypertensive patients with unilateral renal artery stenosis the ipsilateral renal vein/artery ratio was higher for PRA (2.46) than for PRC3.3 (1.56), whereas both ratios on the controlateral side were similar and close to one (1.14 and 1.06). The conditions in which PRA and PRC3.3 determinations are concordant or discordant are discussed.

Hypertension due to Ask-Upmark kidney

A young girl in whom severe hypertension was cured by the surgical removal of a unilateral hypoplastic kidney (Ask-Upmark kidney) is described. The clinicopathological features of the Ask-Upmark kidney are described with particular reference to the aetiology of the hypertension as well as the selection of patients for surgery. No abnormality of the renin-angiotensin system was detected.

Synergistic effects of hydralazine and alpha- or beta-adrenergic blockers: the role of plasma renin activity

Intravenous hydralazine, 0.15, 0.30 or 0.60 mg/kg, was administered to 11 supine hypertensives on two occasions: once after pretreatment with intravenous propranolol, 0.1 mg/kg, and once after pretreatment with intravenous placebo. The average fall in mean arterial pressure for each dosage of hydralazine was no different with or without propranolol, even though propranolol inhibited rises in plasma renin activity and pulse due to hydralazine. However, in each of four patients who had high supine baseline plasma renin activity, propranolol enhanced the fall in blood pressure caused by hydralazine. A second group of patients was given an infusion of 0.01 or 0.02 mg/kg per minute phentolamine, which did not change baseline blood pressure. Subsequent administration of intravenous hydralazine, 0.15 mg/kg, resulted in a fall in blood pressure which was larger than previously observed with intravenous hydralazine alone, regardless of supine baseline plasma renin activity. These data are consistent with the hypothesis that reflex catecholamine release interferes with the hypotensive effect of intravenous hydralazine. Pretreating with propranolol weakens homeostatic defenses against hydralazine such as rises in pulse rate and plasma renin activity. However, propranolol appears to enhance the alpha-adrenergic effect of released catecholamines, and the antihypertensive response to hydralazine is unaltered. In patients with high supine plasma renin activity, propranolol potentiates the fall in blood pressure induced by hydralazine, perhaps because the hypertension in such patients is renin dependent.

[Critical analysis of the saralasintest in the diagnosis of hypertension (author's transl)]

The reliability of the angiotensin II (AT II)-antagonist Saralasin in the diagnosis of AT II-dependent forms of hypertension was investigated in 61 cases of hypertension of different etiology. In 14 patients, lowering of blood pressure by Saralasin suggested an AT II-dependent hypertension which could be ascertained in 8 patients (5 had undergone successful surgery) by increased levels of plasma-renin-activity (PRA), AT II, PRA-ratio in renal vein blood and by angiography. Besides, depressor reactions by Saralasin yielded additional information in three patients with renovascular hypertension but normal levels of PRA and AT II, in two patients with high renin essential hypertension and one patient with pheochromocytoma. This test seems to be valuable in the diagnosis of renin-dependent hypertension.

Angiotensin blockade in renovascular hypertension: a controlled, prospective study

Saralasin, a specific competitive inhibitor of angiotensin II, was administered in a controlled, prospective study designed to test the hypothesis that this agent is a useful tool for the detection of renovascular hypertension. 13 patients, 11 with renovascular hypertension and 2 with high-renin essential hypertension, showed a gross, readily apparent decrease in blood pressure after receiving saralasin. 8 patients with essential hypertension and normal or low renin levels exhibited no depressor response to the drug. In the patients with renovascular hypertension, blood pressure response during angiotensin blockade compared favourably with renal vein renin determinations as a predictor of operative results. Because saralasin testing has resulted in few if any falsely positive or negative results when considered as a diagnostic procedure for renin-mediated hypertension, and because it is safe, it may become an ideal initial screening procedure. The saralasin test (either bolus injection or sustained infusion) is completely valid only if the patient is mildly salt-depleted, is not taking other antihypertensive medication, and is genuinely hypertensive at the time of the test.