Koch's postulates and the digitalis-like factor

Substantial, but still circumstantial evidence, supports strongly a role for a circulating digitalis-like factor in the pathogenesis of salt-sensitive hypertension. Although supported by many lines of evidence, this intriguing concept remains controversial, in large part because the responsible factor has proven to be very elusive. A very large number of candidates from a wide range of chemical classes have been proposed. Indeed, the large number of candidates, none supported by absolutely definitive evidence, has contributed to the controversy. In this essay, we have attempted to define the information that will be required before a candidate becomes widely accepted. Because the current situation resembles so strikingly the situation late in the nineteenth century--when efforts focused on the attempt to identify a specific micro-organism as the agent responsible for specific disease--we employed Koch's postulates as the organizing principle. The challenge faced by Robert Koch over a century ago is identical to the challenge that we face today.

Relation of pressor responsiveness to angiotensin II and insulin resistance in hypertension

To test the hypothesis that the hypertension associated with insulin resistance is secondary to an altered responsiveness of the vasculature to pressor agents, we evaluated the relationship between insulin resistance and pressor responses to angiotensin II (AII) in 21 hypertensive (HT) and 8 normotensive (NT) subjects on both a high (200 meq) and a low (10 meq) sodium diet. When sodium balance was achieved, each supine fasting subject underwent an AII infusion at a rate of 3 ng/kg per min for 60 min, with blood pressure monitored every 2 min. On the next day under similar conditions, a euglycemic hyperinsulinemic clamp was performed, with plasma glucose clamped at 90 mg/dl for 120 min. There was no significant relationship between the glucose disposal rate (M) or the insulin sensitivity index (M divided by the mean insulin level [M/I]) and blood pressure response to AII in the NTs, but a highly significant (P < 0.019) negative correlation (r = -0.55) in the HTs. Furthermore, in eight lean HTs whose body mass index was identical to that observed in the NTs, the relationship was even more striking (P < 0.008; r = -0.85). The results on high and low salt diets were similar; however, the M and M/I were significantly increased (P < 0.05) in the NTs but not HTs with sodium restriction. In conclusion, HTs but not NTs display a striking correlation between pressor response to AII and insulin resistance. This relationship is independent of the level of sodium intake. Furthermore, sodium intake modifies insulin sensitivity in NTs but not HTs. These results strongly suggest that a primary change in pressor response to vasoactive agents in insulin-resistant subjects can contribute to their elevated blood pressure.

Sustained volume expansion and [Na,K]ATPase inhibition in chronic renal failure

Hypotheses regarding the pathogenesis of volume-dependent hypertension have invoked an endogenous sodium pump inhibitor or digitalis-like factor (DLF) to link altered sodium homeostasis to the rise in blood pressure. Our goal was to develop a clinical protocol that achieved predictable, sustained volume expansion, with the premise that renal failure patients on peritoneal dialysis would increase intravascular volume, gain weight, and raise blood pressure (BP) in relation to measured increases in DLF. In a 5-day protocol, dialysis was kept constant but dietary NaCl and fluids were modified in 7 patients. DLF was measured as inhibition of [Na,K]ATPase. Likewise, the first 2 L of daily peritoneal dialysate (PD) was processed on HPLC and the eluate analyzed for DLF. The group achieved significant weight gain (WT) by day 3 (delta WT = 4.1 +/- 1.2 kg, P < .05). Likewise, mean arterial pressure (MAP) and plasma DLF activity increased significantly. All variables were highly correlated (DLF v WT: R = 0.88, P = .004; MAP v DLF: R = 0.82, P = .01; MAP v WT: R = 0.90, P = .003). Although a number of HPLC fractions contained agents that interacted with the assay, only one PD HPLC fraction (at 19.5 min) contained DLF activity that correlated with changes in MAP (R = 0.60, P = .002), and body weight (R = 0.67, P = .0003). We conclude that candidate DLF responds to sustained volume expansion and the relationship suggests that it could influence blood pressure. Moreover, the application of stringent criteria to the confusing array of factors in plasma that may affect assays for DLF appears to reduce the field dramatically, to a single candidate in this setting.

Converting enzyme inhibition and renal tissue angiotensin II in the rat

Multiple observations suggest local control of renal function via an intrarenal renin-angiotensin system, including evidence for local angiotensin (Ang) II production. Our first goal was to examine renal tissue Ang I:Ang II relations to ascertain whether Ang II formation differs in the circulation and in renal tissue. We have recently shown an authentic Ang II/Ang I ratio of 1.5:1 in renal lymph, the opposite of the Ang II:Ang I relation in plasma. Our second goal was to examine the influence of maximal angiotensin converting enzyme inhibition on these relations in plasma and in renal tissue. We used two converting enzyme inhibitors with differing lipid solubility, on the premise that tissue penetration and action might differ on that basis. We measured Ang I and Ang II in plasma and renal tissue of rats given an intravenous dose of either vehicle, enalapril, or ramipril, over a wide dose range, from 0.1 to 10.0 mg/kg i.v. Renal and plasma angiotensin concentrations were measured by high-performance liquid chromatography and radioimmunoassay. Whereas the Ang I concentration in normal rat plasma (273 +/- 84 fmol/mL) was over threefold the plasma Ang II concentration (83 +/- 12 fmol/mL), the ratio was reversed in the kidney (Ang II, 178 +/- 12 versus Ang I, 91 +/- 3 fmol/g; P < .001). Although ramipril and enalapril induced an indistinguishable dose-related acute fall in blood pressure and plasma Ang II concentration, lower enalapril doses were less effective in reducing renal tissue Ang I:Ang II conversion and Ang II concentration (P < .025).(ABSTRACT TRUNCATED AT 250 WORDS)

Nonmodulating trait may precede the development of hypertension

The nonmodulating trait thought to explain development of hypertension in 25 to 35% of patients, is characterized by abnormal angiotensin II (AII)-mediated control of aldosterone release and renal blood flow (RBF). Some data support the possibility that nonmodulation is an inherited trait, but others argue that it is an acquired epiphenomenon of the hypertensive state. We report the first case of a normotensive patient with nonmodulation who subsequently developed frank hypertension. Patient RR was studied on six occasions over a 5-year period, two while normotensive, four while hypertensive. This patient consistently demonstrated an abnormally low plasma aldosterone response to AII (3 ng/kg/min) on a low salt (10 mEq sodium) diet while both normotensive and hypertensive. A consistently abnormally depressed RBF response to AII on a high salt (150 to 200 mEq sodium) diet as well as a depressed RBF increment when the diet was changed from low salt to high salt were also noted. Thus, RR demonstrated nonmodulation by multiple criteria while both normotensive and hypertensive. We conclude that the nonmodulating trait may be a heritable defect that leads to the development of hypertension and is not an epiphenomenon.

Age and the renal blood supply: renal vascular responses to angiotensin converting enzyme inhibition in healthy humans

OBJECTIVE

To assess the relation between age, sodium intake, renal blood flow (RBF) and the renal vascular response to an angiotensin converting enzyme (ACE) inhibitor, captopril.

DESIGN

Blood flow studies were performed before and during the acute response to an oral 25-mg dose of captopril, selected to induce a maximal response, after 5 to 7 days on a metabolic ward, sufficient time to have achieved external balance on a fixed low-salt (10 mE/day) or high salt (200 mEq/day) diet. Blood flow was measured as radioxenon transit through the kidney.

SETTING

The study was performed on a metabolic ward, the Clinical Research Center, and in the Cardiovascular Radiology Laboratories of the Brigham and Women's Hospital in Boston.

PARTICIPANTS

The participants, all community dwellers, were potential kidney donors, in a renal transplant program. They were thought to be sufficiently healthy to consider donation of a kidney. The age range was 18 to 69 years.

RESULTS

Renal blood flow showed the anticipated decline with increasing age, whether the subjects were on a restricted or a liberal salt intake. Captopril induced an acute increase in RBF, averaging 88 +/- 7 mL/100 g/min in subjects on a high-salt diet, but no influence of age was identified on the renal vasodilator response on either diet. Increasing age did not limit the renal vasodilator response, although subjects beyond the sixth decade were not studied.

CONCLUSIONS

The limited renal vascular response to vasodilators we had documented in earlier studies does not extend to ACE inhibitors. Although ACE inhibitors lack the pharmacological specificity required to prove a role for angiotensin II (Ang II), the data are compatible with a contribution of Ang II to the maintenance of renal vascular tone that does not change with increasing age, at least to 70 years of age.

Regulation of aldosterone secretion in hypertensive blacks

Hypertension in blacks is common, often severe, and largely unexplained. Recent studies have suggested that aldosterone secretion in blacks may be reduced, whereas older data demonstrate no racial differences in aldosterone excretion. We performed this study to examine adrenal responsiveness in black hypertensive patients under controlled metabolic conditions. Thirty-one black hypertensive patients and 7 black normotensive subjects were studied on intakes of 10 mmol/d sodium and 100 mmol/d potassium, with the renin-angiotensin-aldosterone system further stimulated by upright posture or infusion of angiotensin II (Ang II). Forty-six hypertensive and 14 normotensive whites underwent the same protocol as a comparison group. Hypertensive blacks and whites had similar mean basal plasma aldosterone levels on a low salt diet, lower in both groups than in normotensive subjects. In the black patients, however, plasma aldosterone responses were significantly lower than responses in white hypertensive patients when further stimulated by either posture (1451 +/- 216 versus 2571 +/- 225 pmol/L [52.3 +/- 7.8 versus 92.7 +/- 8.1 ng/dL], P < .002) or Ang II infusion (843 +/- 122 versus 1617 +/- 189 pmol/L [30.4 +/- 4.4 versus 58.3 +/- 6.8 ng/dL], P < .001). Renin status did not account for the difference. Basal and stimulated plasma aldosterone concentrations, on the other hand, were similar in normotensive white and black subjects. Blunted adrenal responses to upright posture and Ang II infusion are common among black hypertensive patients. These abnormalities may be part of a larger constellation of abnormalities in blacks, reflecting perhaps a greater, more frequent underlying disturbance in salt handling than in whites.

Responses to converting enzyme and renin inhibition. Role of angiotensin II in humans

We compared the renal vascular responses to angiotensin converting enzyme inhibition and renin inhibition to assess the influence of angiotensin II (Ang II). We examined the renal and endocrine responses to the renin inhibitor enalkiren, to captopril, and to placebo in nine healthy and nine hypertensive men on a 10-mmol sodium diet. Ang II was infused to assess effects of the agents on renal and adrenal responsiveness to Ang II. Plasma Ang II concentration was suppressed similarly with enalkiren and captopril--an identical level of blockade was achieved. Although renal plasma flow was stable during placebo, a substantial rise was seen with both enalkiren (+133 +/- 26 mL/min per 1.73 m2) and captopril (+99.4 +/- 22.6). There was remarkable intrasubject concordance between the renal plasma flow responses to renin inhibition and converting enzyme inhibition (r = .90, P < .004). The vasodilator response to both agents correlated inversely with the fall in renal plasma flow induced by Ang II alone (r = -.66, P < .05). Both agents significantly enhanced the renal vascular response to Ang II (P = .01), and, furthermore, the renal vasodilator response to captopril predicted the potentiation of the renal plasma flow response to Ang II after either agent (enalkiren: r = .91, P < .001; captopril: r = .56, P < .05). Concordance of the maximal renal plasma flow response to the two agents appeared in the hypertensive men as well. Our results indicate that the acute renal response to captopril largely reflects a reduction in Ang II formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid modulation of renal and adrenal responsiveness to angiotensin II

Reciprocal changes in adrenal and vascular responsiveness to angiotensin II (Ang II) are part of the normal adaptation to shifts in salt intake. When dietary salt intake is abruptly reduced from high to low, enhancement in aldosterone secretion requires several days to develop. Once established it is not known how quickly the enhancement is reversed with salt repletion. We investigated the time course and relative contributions of salt, volume expansion, or both to this process by studying 15 normotensive subjects; 5 were studied during both high-salt and low-salt balance, and 10 were studied only in low-salt balance. For rapid volume expansion to reverse low-salt balance, 5 subjects received in random order an infusion of normal saline or dextran. The adrenal glomerulosa and renal vascular responses to Ang II were assessed after each volume expansion maneuver. Saline and dextran infusions suppressed plasma renin activity and aldosterone equally, although dextran acted more slowly. Both also increased renal perfusion and renal vascular and pressor responses to Ang II, which in 3 to 7 hours became identical to responses seen during high-salt intake ("modulation"). Saline infusion also blunted adrenal responsiveness to Ang II during that same interval. Despite suppression of the renin-angiotensin system by dextran infusion, aldosterone responsiveness to Ang II remained enhanced. These observations suggest that the renal and vascular responses to Ang II are modulated rapidly by the effects of volume expansion per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibition and renal protection. An assessment of implications for therapy

The role of hypertension in the pathogenesis of renal damage is a subject of both historical interest and current investigation. Because of the difficulty associated with studying the pathophysiologic role of glomerular injury in systemic hypertension, experimental models have provided much of the data in this field. The mechanisms leading to glomerular injury are complex and not fully elucidated. Mesangial and endothelial cell injury are thought to be important pathophysiologic mechanisms in the renal injury associated with hypertension. One hypothesis suggests that glomerular hypertension (ie, a hemodynamic event) is the primary pathogenetic mechanism, but another supports the notion that glomerular hypertrophy (ie, abnormal growth-related events) contributes to injury. The intrarenal renin-angiotensin system may play an important pathogenetic role in end-stage renal disease. Angiotensin-converting enzyme (ACE) inhibition has been shown to arrest the progression of renal injury in animal models. Although the clinical database is incomplete, the findings of anecdotal reports and short-term studies suggest that ACE inhibition may preserve renal function in patients with scleroderma renal crisis, reduce proteinuria in patients with diabetic nephropathy, and normalize renal hemodynamics in patients with a variety of renal diseases. The beneficial effects of ACE inhibition may be due to both hemodynamic (eg, reduction in glomerular capillary and intraglomerular pressures) and nonhemodynamic (eg, potassium-sparing and reduction in mesangial proliferation) mechanisms. The precise role of ACE inhibitors in the prevention of renal damage awaits the results of ongoing long-term, double-blind clinical studies. Nevertheless, ACE inhibition may be an appropriate therapeutic alternative in the hypertensive patient whose renal injury is progressing despite aggressive antihypertensive therapy.

Quality of life and antihypertensive therapy in men. A comparison of captopril with enalapril. The Quality-of-Life Hypertension Study Group

BACKGROUND

We conducted a multicenter trial comparing two angiotensin-converting-enzyme inhibitors to determine whether effects on quality of life during antihypertensive therapy are uniform within this pharmacologic class of agents, and to relate the effects of the drugs on quality of life to objective adverse events, such as the loss of a job or the death of a spouse.

METHODS

After a four-week washout period when they received placebo, 379 men with mild-to-moderately-severe hypertension were randomly assigned to receive captopril (25 to 50 mg twice daily, with or without hydrochlorothiazide) or enalapril (5 to 20 mg per day, with or without hydrochlorothiazide) for 24 weeks. Blood pressure, quality of life, and life events were monitored. Differences between treatments were evaluated by calibrating measures of quality of life with objective life events.

RESULTS

Throughout the treatment period, no differences were found in blood pressure, frequency of withdrawal of patients from the study, or major side effects. Patients treated with captopril had more favorable changes in overall quality of life, general perceived health, vitality, health status, sleep, and emotional control (P < 0.05 for each). The changes varied according to the quality of life at base line (P < 0.001); patients with a low quality of life at base line remained stable or improved with either drug, whereas those with a higher quality of life remained stable with captopril but worsened with enalapril. The quality-of-life scales correlated with life events and symptom distress (P < 0.001), and calibration analysis indicated that differences between treatments were clinically important.

CONCLUSIONS

Two angiotensin-converting-enzyme inhibitors, captopril and enalapril, indistinguishable according to clinical assessments of efficacy and safety, had different effects on quality of life. Calibration with life events showed that drug-induced changes are substantial and that the different effects of these two agents on quality of life can be clinically meaningful.

Hypertension and the kidney: determinants of the response to antihypertensive therapy and their implications

Medicine has long recognized an association between hypertension and the kidney. The kidney may be a culprit or a victim in the process. As a culprit, the kidney may be responsible for the pathogenesis of hypertension in many patients, and in virtually all patients the renal response to antihypertensive therapy is a major determinant of its success or failure. In some patients, hypertension can lead to renal injury and even end-stage renal disease. Indeed, 25% of patients entering dialysis or transplant programs in the United States today have hypertension as the primary or sole mechanism, and another 25% have the complex combination of diabetes and hypertension as the cause. Antihypertensive therapy appears to be successful in preventing or arresting the renal response in accelerated hypertension, regardless of the treatment used to reduce blood pressure. However, treatment appears to be less successful in preventing the progression of moderate hypertension to end-stage renal disease. Substantial evidence suggests that angiotensin-converting enzyme inhibition and calcium channel blockade may prevent this progression when other antihypertensive therapy does not. The renal response to an angiotensin-converting enzyme inhibitor or a calcium channel-blocking agent appears to be determined by the pathogenetic features of the hypertension, and this may be an important determinant of the efficacy of the agents selected. Although still indistinct, the guidelines favoring selection of a specific antihypertensive agent are gradually emerging.

Non-modulation as an intermediate phenotype in essential hypertension

Non-modulation is a trait characterized by abnormal angiotensin-mediated control of aldosterone release and the renal blood supply. To determine whether non-modulation defines a specific subgroup of the hypertensive population and its utility as an intermediate phenotype, we have studied the distribution of this quantitative trait, whether its features are reproducible on repeated testing, and whether there is concordance of its multiple features. Essential hypertensive patients (224) and normotensive subjects (119) received an infusion of angiotensin II (Ang II) at 3 ng.kg-1.min-1 for 30-45 minutes. p-Aminohippurate (PAH) clearance was assessed as an index of renal plasma flow while the subjects were on a 200 meq sodium diet; plasma aldosterone levels were measured while the subjects were on a 10 meq sodium diet. In 54 subjects, diuretic-induced volume depletion superimposed on a low salt diet was substituted for the Ang II infusion. The results of each study were submitted to maximum likelihood analysis to assess bimodality. In response to both diuretic-induced volume depletion (p < 0.000023) and Ang II infusion (p < 0.0009), aldosterone responses were bimodally distributed in the essential hypertensive but not in the normotensive subjects, suggesting that this trait identifies a discrete subgroup. In the 59 subjects who had both an adrenal and renal study, 50 (85%) were concordant. Finally, in 27 subjects studied two to six times over a span of 1-60 months, the intraclass correlations of the adrenal, PAH, or both responses were highly significant (p values between 0.001 and 0.00007), indicating high reproducibility of results on repeated testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous modeling of the pharmacokinetic and pharmacodynamic properties of enalkiren (Abbott-64662, a new renin inhibitor). I: Single dose study

This study describes the relationship between the measured effects (angiotensin I and renal plasma flow) and plasma drug levels using a combined pharmacokinetic-pharmacodynamic model after 90 min iv infusion of enalkiren in 15 healthy, salt-depleted subjects. Doses from 0.002 to 0.512 mg/kg were evaluated. One hour prior to enalkiren dosing, para-aminohippuric acid infusion was started for each subject and continued until 3 hr after the start of enalkiren infusion. Timed blood samples were obtained to measure enalkiren, para-aminohippuric acid, and angiotensin I levels in plasma. Enalkiren-induced effect changes lagged in time behind the plasma enalkiren level changes, showing a counterclockwise hysteresis loop. To relate the temporal relationship of effect changes accurately to plasma drug levels, a pharmacokinetic model was combined with a pharmacokinetic model that incorporated a hypothetical effect compartment. The magnitude of the time lag was quantified by the half-time of equilibration between concentrations in the hypothetical effect compartment and the plasma enalkiren levels (t1/2keo). The t1/2keo for angiotensin I (0.002 hr) is significantly shorter than that of renal plasma flow (0.267 hr), indicating that enalkiren equilibrates more rapidly with the angiotensin I-related effect compartment than the renal plasma flow-related effect compartment. Moreover, the model allows for estimation of the effect site concentration that causes one-half of the maximal predicted effect (EC50), which is a measure of an individual's sensitivity to enalkiren. The EC50 of angiotensin I (81.1 ng/ml) is substantially lower than that of renal plasma flow (4414 ng/ml), indicating that angiotensin I may be a more sensitive measure of enalkiren effects than renal plasma flow.

Abnormal norepinephrine and aldosterone responses to upright posture in nonmodulating hypertension

The subgroup of patients with nonmodulating hypertension demonstrates a number of abnormalities of the renin-angiotensin-aldosterone axis. We previously identified abnormalities in plasma and urinary dopamine in nonmodulators and posited that this may be in part due to a generalized defect in sympathetic nervous system activity. In the present study we assessed the state of activation of the renin-angiotensin system and the sympathetic nervous system in normal subjects and patients with modulating, nonmodulating, and low renin essential hypertension during sodium depletion and change from supine to upright posture. Levels of plasma norepinephrine were higher in non-modulators during the posture study (P < 0.05). PRA rose with upright posture in all groups, but low renin subjects had a blunted response. Nonmodulators and low renin subjects had lower aldosterone levels both supine (P< 0.05) and upright (P< 0.01). However, the aldosterone/PRA increment ratio was increased in low renin subjects (P< 0.01), whereas it was decreased in nonmodulators. Twenty-four-hour urine collections for catecholamine determinations were obtained in a subgroup of the subjects, with nonmodulators showing higher levels of norepinephrine excretion which approached significance (P = 0.08). In vitro experiments using rat and human adrenal glomerulosa cells showed that norepinephrine does not affect aldosterone secretion per se. These observations extend the series of abnormalities observed in nonmodulating hypertension. However, it is likely that the alterations in norepinephrine levels during sodium depetion and upright posture are a secondary event and not linked to the altered aldosterone production in these patients.

Evolution of the treatment of hypertension: what really matters in the 1990s?

Over the past decade we have seen a shift in the strategy for the treatment of hypertension, from stepped therapy--involving a highly structured, unvarying series of steps--to recommendations for more individualized treatment. How shall we accomplish that goal? Severe hypertension provides a clear indication to bypass earlier recommendations. Demographic data such as age, gender, and race, often cited, have proved less helpful. Concomitant medical problems, which are found in greater than 50% of hypertensive patients, are most often the crucial determinants in the selection of antihypertensive therapy. Concurrent coronary artery disease, diabetes mellitus, heart failure, azotemia, asthma, chronic obstructive pulmonary disease, borderline cognitive dysfunction, anxiety, and depression are all common. Each has implications for antihypertensive therapy. Moreover, blood pressure reduction is a surrogate for our real goal, which is reduction of cardiovascular risk. Thus, consideration of concomitant medical problems has extended to left ventricular hypertrophy, obesity, hyperlipidemia, and insulin resistance as additional risk factors in hypertension. Consideration of all of these factors makes it possible to individualize antihypertensive therapy in most patients.

Arterial response to ketanserin and aspirin in patients with advanced peripheral atherosclerosis

BACKGROUND

In advanced atherosclerosis, endothelial lesions and turbulent flow in stenotic vessels result in platelet aggregation with the liberation of vasoactive factors, including thromboxane A2 and serotonin. This study was designed to assess the combined effect of these factors on arterial dimensions at the time of limb angiography in patients with advanced peripheral vascular disease.

METHODS

Diameter changes of 53 segmental stenosis of large arteries were measured in digitized angiograms by a computerized objective method in response to either placebo (13 segments in 7 patients), ketanserin (23 segments in 23 patients), or ketanserin superimposed on aspirin (17 segments in 7 patients). Responses of arterial collaterals were evaluated by a coded assessment. Statistically significant vasodilatation was observed in both the stenotic and post-stenotic segments of the large arteries only when serotonin-2 receptor blockade with ketanserin and cyclo-oxygenase inhibition with aspirin were combined.

RESULTS

In the area of the stenosis and in the post-stenotic segment diameter increased 8.2% +/- 2.3% (P = .032) and 7.3% +/- 1.3% (P less than .001), respectively, when aspirin was combined with ketanserin. Significant changes did not occur in either the placebo group or in the group receiving only ketanserin. In the area of stenosis, there was a good correlation between the relative baseline narrowing of the vessel and its vasodilatation after combined ketanserin and aspirin (r = .689; P = .002). Vasodilatation at the level of arterial collaterals also was significantly more pronounced when the combination was used (P less than .001).

CONCLUSIONS

These findings suggest a component of vasoconstriction related to the deposition of activated platelets in stenotic segments of the large arteries in atherosclerosis.

"Tissue need" and limb collateral arterial growth. Skeletal contractile power and perfusion during collateral development in the rat

Among the factors that might influence collateral arterial growth after arterial occlusion, the capacity to deliver blood flow in relation to metabolic need and work performance are obvious candidates. In this study in rats after superficial femoral artery ligation, we assessed collateral arterial growth (by arteriography), basal and peak limb blood flow during acetylcholine-induced vasodilation (by electronic drop counting), pressure-flow relations, and contractile power of the gastrocnemius muscle (force transduction during sciatic nerve stimulation) at intervals over 3 months after superficial femoral artery ligation. Basal and peak blood flow and muscle contractile power were clearly reduced 1 week after ligation but had returned to normal by 3 weeks. Major collateral arterial growth, however, progressed between 3 weeks and 3 months. The limb perfusion pressure-blood flow relation was still altered at 3 weeks, with blunting of the normal autoregulation, and became more normal by 3 months after superficial femoral artery ligation. Collateral arterial growth continues after blood flow adequate to maintain work performance has been restored and may reflect a response to more subtle abnormalities involving distal pressure delivery, evident in altered pressure-flow relations.

Renal and adrenal responsiveness to angiotensin II: influence of beta adrenergic blockade

The increase in aldosterone secretion that occurs in response to Angiotensin II (AII) is enhanced when normal humans are in external balance on a low salt diet. The responsible mechanism has not been identified. Angiotensin converting enzyme inhibition reduces blood levels of AII and aldosterone, but does not decrease PRA or AI and does not modify adrenal responsiveness to AII in the sodium-depleted state. This study was designed to assess the possibility that the enhanced adrenal response reflects plasma renin activity (PRA), plasma AI concentration, or catecholamines acting via a beta adrenergic receptor. Nine healthy males were studied when in balance on a high sodium intake (200 mmol Na/day), a low sodium diet (10 mmol Na) and after 4 days of beta adrenergic blockade with either nadolol or propranolol. The adequacy of beta adrenergic blockade was assessed with a postural stimulus and significant blockade was achieved, somewhat more with nadolol (40 mg/day) than with propranolol (Inderal LA, 80 mg every 12 hrs). Beta blockade enhanced the renal vascular and pressor response to AII but did not modify the adrenal response to posture or to AII. This study confirms the role for AII levels in the modulation of renal vascular and pressor responses to AII and rules out a role for PRA, AI, or catecholamines acting via a beta adrenergic receptor in the modulation of adrenal responsiveness to AII.

Treatment of hypertension: the place of angiotensin-converting enzyme inhibitors in the nineties

The past decade has seen a shift in the strategy for hypertension treatment from stepped therapy--a highly structured monolithic series of steps--to recommendations for a more individualized selection of treatment. Severe hypertension is a clear indicator to bypass traditional steps. Demographic factors, such as age, gender, and race, are often cited, but have proved to be less helpful. Concomitant medical conditions and problems are very common and are more often the crucial determinants in the selection of antihypertensive therapy. Coronary artery disease, diabetes mellitus, heart failure, azotemia, asthma, and chronic obstructive pulmonary artery disease, anxiety, and depression are all common, and each has implications for the selection of antihypertensive therapy. Blood pressure reduction is a surrogate for reduction of cardiovascular risk, and therefore, consideration of concomitant medical problems has extended to left ventricular hypertrophy, obesity, mild hyperlipidemia, and insulin resistance, as additional risk factors in hypertension. Consideration of all these factors makes it possible to individualize antihypertensive therapy in most patients today.

Effect of CLS 2210 (calcium dobesilate) on survival and myocardial infarction size in the rat: influence of dose and duration of treatment

CLS 2210 (calcium dobesilate) has been shown to reduce the volume of myocardium infarcted after coronary artery occlusion in the dog. This study, in rats, was designed to determine whether CLS 2210 would reduce mortality and infarct size after coronary occlusion. Another goal was to ascertain whether a duration of administration exceeding 6 h improves survival. Experiments were performed in rats with myocardial infarction induced by coronary artery ligation. In one series, rats were blindly randomized into four groups receiving, over a period of 6 h, either 200, 400 or 800 mg/kg of CLS 2210 or a placebo. In a second series, the animals were randomized to receive as initial dose a bolus of either 50 mg/kg of CLS 2210 by intravenous infusion or placebo followed by 25 mg/kg/h of the same drug or placebo over 24 h: mortality and infarct size were assessed after 24 h. A third series of rats received the same dosage schedule of CLS 2210 or placebo, but mortality was evaluated after 1 week, to ascertain whether CLS 2210 merely postponed death. Our first goal in this study was to ascertain whether CLS 2210 would improve survival after coronary artery occlusion in the rat. In the placebo group, death occurred in 61 of 112 rats (54.5%). In the CLS-2210-treated group, mortality was sharply reduced, to 68 of 182 (37.3%; p less than 0.01). Mortality in rats receiving CLS 2210 for 6 h was significantly lower, 35.6%, when compared to the placebo which was 51.9% (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional derangements in the regulation of aldosterone secretion in hypertension

Excess production of aldosterone secondary to an adrenal tumor or bilateral hyperplasia is a known, but infrequent, cause of hypertension. A more frequent adrenal abnormality, observed in 30-40% of hypertensive patients, is a functional derangement in aldosterone secretion. Two such conditions have been described: low renin essential hypertension and non-modulating essential hypertension. Both have in common 1) an abnormality in the interaction of angiotensin II (Ang II) with the adrenal and 2) sodium sensitivity of the blood pressure. However, the pathophysiological mechanisms for the sodium sensitivity and hypertension are different. In normal subjects, the response of the adrenal glomerulosa cell to Ang II varies with the level of sodium intake, with sodium restriction enhancing the response. In one group of hypertensive patients with low plasma renin levels, the normally reduced aldosterone responses to Ang II on the high salt diet do not occur. Thus, these individuals have an enhanced adrenal response to Ang II under circumstances in which it should be reduced, thereby leading to lower renin levels and a tendency toward sodium retention. The second group has the opposite defect; that is, on a low sodium diet, they have a reduced adrenal response to Ang II. This results in a normal or high plasma renin level. The sodium sensitivity of their blood pressure arises not from the adrenal abnormality but from the associated defect in sodium-dependent, Ang II-mediated changes in renal blood flow. Thus, on a high salt diet, these patients, who are termed "non-modulators," fail to increase renal blood flow, thereby leading to a sodium-retaining state.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in apparent serum digitalis-like factor levels with different digoxin antibodies. The "immunochemical fingerprint"

Increased levels of a circulating digoxin-like factor (DLF) occur in a number of physiologic states in which sodium homeostasis is altered, and may contribute to the pathogenesis of hypertension. We exploited the different affinities for DLF of seven antisera directed at digoxin to develop an immunochemical profile, and then employed this index to address two questions: does the same DLF species exist in several conditions associated with increased DLF levels, including pregnancy, renal failure, hepatic failure, and neonatal cord blood? Will this approach prove useful in assessing candidates proposed to be DLF? An identical profile was identified in serum from pregnant women and patients with renal or hepatic failure, and a highly significant correlation existed between DLF levels measured with antisera of high and intermediate affinity in 42 subjects with increased levels (r = 0.93; P less than .001). In patients with renal failure, when endogenous DLF levels were too low to assess the profile, concentration of the serum resulted in measurable DLF levels that had an identical profile. The profile was somewhat altered in umbilical cord blood, perhaps reflecting an influence of increased steroid hormone levels. Among agents suggested as candidates for DLF, neither lysophosphatidylcholine nor ouabain showed a profile resembling DLF. Progesterone, 17-OH-progesterone, and bufalin, on the other hand, did show substantial similarity, perhaps providing a clue to the structure of DLF. The normal plasma levels of progesterone and 17-OH-progesterone are 100- to 1000-fold too low to be candidates for DLF and bufalin was sufficiently dissimilar not to be a candidate. DLF in at least three different patient populations probably represents identical chemical species.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercholesterolemia enhances macrophage recruitment and dysfunction of regenerated endothelium after balloon injury of the rabbit iliac artery

BACKGROUND

We studied the effects on and possible interaction of balloon denudation and hypercholesterolemia on large arteries in the rabbit with special regard to structure and vascular reactivity.

METHODS AND RESULTS

New Zealand White rabbits fed a 1% cholesterol diet or a standard diet for 14 weeks underwent balloon denudation of the left iliac artery 4 weeks before death. Both the balloon-injured and the control iliac arteries were harvested for in vitro studies of vascular reactivity, for immunohistochemical staining with monoclonal antibodies directed at smooth muscle cells and macrophages, and for scanning electron microscopy. Balloon injury caused intimal smooth muscle proliferation with little macrophage infiltration and was followed by recovery of endothelium-dependent vasodilator function within 4 weeks. Hypercholesterolemia caused macrophage-rich lesions confined to the intima with moderate impairment of endothelial vasodilator function. Balloon injury in the setting of hypercholesterolemia caused intimal smooth muscle cell proliferation and intense macrophage infiltration throughout the arterial wall and severe impairment of endothelial vasodilator function. Scanning electron microscopy confirmed regrowth of the endothelium in all balloon-injured vessels. In the balloon-injured arteries of hypercholesterolemic animals, the regenerated endothelium exhibited areas of atypical morphology not seen after balloon injury or hypercholesterolemia alone.

CONCLUSIONS

The present study shows that balloon injury, hypercholesterolemia, and their combination cause distinct lesions and functional disturbances. An arterial balloon injury in the setting of hypercholesterolemia produces a diffuse inflammatory response that is accompanied by a sustained impairment of endothelial function and a marked proliferative response.

Embolization of platelets after endothelial injury to the aorta in rabbits. Assessment with 111indium-labeled platelets and angiography

This study exploits the ability of a collateral arterial network to trap platelet aggregates in order to document the frequency of macroembolization in rabbits after endothelial damage. Two weeks after ligation of the right superficial femoral artery, endothelial injury was induced in the distal aorta; within 3 hours the rabbits were studied using either angiography or 111indium-labeled (111In) platelet scintigraphy. Angiography indicated visible aggregates in the thigh region in eight of 19 and arterial occlusion in three of 19 rabbits. The collateral-dependent thigh also showed more 111In-labeled platelet activity than the contralateral side (P less than .001), whether platelets were injected before or 2 hours after injury. Radioactivity in the limbs of rabbits with no injury was distributed symmetrically. Blood pool volume, assessed with technetium-99m-labeled red blood cells, was the same in both thighs, and could not account for these observations. The findings indicate that platelet activation and aggregation after endothelial injury lead to microembolization much more frequently than it leads to macroaggregate formation and visible artery occlusion.

Dysregulation of aldosterone secretion and its relationship to the pathogenesis of essential hypertension

The level of sodium intake has a reciprocal influence on the vascular and adrenal responses to angiotensin II, with sodium restriction enhancing the adrenal responses and reducing vascular, and particularly renal vascular, responses. In two subgroups of the essential hypertensive population, this relationship is abnormal. Both subgroups have sodium-sensitive hypertension. One is a subset of the low renin essential hypertensive subgroup and its abnormality is an enhanced aldosterone response to angiotensin II with sodium loading, ie, a failure to down-regulate the aldosterone response. The other subgroup, termed nonmodulators, is a subset of the normal-high renin essential hypertensive subgroup. In these patients, sodium intake modifies either adrenal or vascular responses, including renal vascular responses, to angiotensin II--resulting in a reduced aldosterone response to angiotensin II with sodium restriction. Of clinical importance, the nonmodulator's abnormality is corrected by the administration of converting enzyme inhibitors--this class of drugs therefore being a specific form of therapy in these patients.

Renal and endocrine responses to a renin inhibitor, enalkiren, in normal humans

Interpretation of renin-angiotensin blockade with angiotensin converting enzyme inhibitors is potentially confounded by their multiple effects. We used a selective renin inhibitor (enalkiren, A-64662) to explore the renal and endocrine effects of angiotensin II in healthy men. Each received 90-minute enalkiren infusions at 2-day intervals, on a low (10 mmol, 16 subjects) and high (200 mmol, 12 subjects) salt diet. Plasma renin activity, immunoreactive plasma angiotensin II and aldosterone concentrations, inulin, and p-aminohippurate clearance were measured by standard methods. Plasma renin activity fell at 0.1 micrograms/kg, but the threshold for biologic effect was 256 micrograms/kg, where plasma immunoreactive angiotensin II and aldosterone concentration fell, and renal plasma flow rose (p less than 0.01). The maximal renal vascular response (+152 +/- 23 ml/min/1.73 m2) occurred at 512 micrograms/kg (p less than 0.01). Diastolic and mean blood pressure fell modestly but significantly (p less than 0.05). Responses were limited on a high salt diet. We confirm that conventional plasma renin activity measurement is misleading in humans receiving a renin inhibitor. The renal vascular response to renin inhibition in this study appeared to substantially exceed reported responses to angiotensin converting enzyme inhibition, perhaps reflecting a crucial and relatively inaccessible intrarenal locus.

Assessment of quality of life by patient and spouse during antihypertensive therapy with atenolol and nifedipine gastrointestinal therapeutic system

To evaluate differences in efficacy, safety, and quality of life, 394 male patients with mild-to-moderate hypertension were randomized to receive 20 weeks of either atenolol or nifedipine gastrointestinal therapeutic system (GITS) in a multicenter double-blind trial. A four-week placebo washout was followed by 8 weeks of titration and 12 weeks of maintenance therapy. Quality-of-life evaluation included clinical assessments by the patient and parallel take-home assessments by patient and spouse. Blood pressure was controlled equally in both groups. The total incidence of adverse reactions was similar in both groups, but a greater percentage of nifedipine GITS patients withdrew due to peripheral edema. Patients completing 20 weeks of therapy demonstrated a more favorable quality-of-life profile (P less than .05) for nifedipine GITS over atenolol in psychosocial (P less than .01), well-being (P less than .05), general affect (P less than .05), emotional ties (P less than .01), emotional control (P less than .05), vitality (P less than .05), and leisure (P less than .05) scores. Treatment differences were particularly pronounced for patients over 50 years of age and were not fully detectable until after 14 weeks of therapy. Deterioration in quality of life was associated with withdrawal. Spouses of younger patients receiving atenolol reported deterioration in sexual satisfaction as compared to spouses of patients taking nifedipine GITS (P less than .02). Thus age, length of trial, and third-party observation are important factors in quality-of-life assessment. Comparison of adverse reactions provides an incomplete measure of how well a drug is tolerated. In contrast, findings indicate that even subtle CNS-mediated effects on mood and well-being can be detected by quality-of-life evaluation.

Quality of life as a therapeutic end-point. An analysis of therapeutic trials in hypertension

The term 'quality of life' is finding increasing use in the popular press and the medical community. In both areas, its use often lacks precision: a comprehensive and universal definition probably does not exist. Indeed, the precise elements contributing probably vary from person to person and from time to time. There is broad agreement that 5 major areas always need assessment, including physical and emotional state, performance of social roles, intellectual function and general feelings of well-being or life satisfaction. A wide range of instruments has been employed in a large number of studies on the effects of antihypertensive agents on quality of life in the patient with hypertension. Hypertension represents a special problem in which the patient is thought to be free of related symptoms, and treatment designed to improve natural history brings with it the burden of adverse reactions. Although some insights have been gained on the relative influence of various therapeutic regimens on the quality of life of treated patients, in many of the studies too little consideration has been given to the use of instruments that have been validated in the patient population to be studied, to the power of the study and its design, to the contribution of confounding variables such as age and gender, and to evidence that short term trials (measured in weeks) can miss important changes that occur over months in a process where treatment is life-long. For these reasons, we believe, the literature on the subject is burdened by many reports that describe no difference among treatment regimens where important differences might exist. On the positive side, important advances have been made in our understanding of the elements that contribute to quality of life and in approaches to its assessment.

Management of hypertension and cardiovascular risk

Blood pressure reduction in hypertensive patients is a surrogate for the real therapeutic goal of reducing the risks consequent to hypertension. This surrogate is convenient but its use may have important therapeutic implications. Results of treatment with new antihypertensive agents, data from clinical trials, and insights into underlying mechanisms are reviewed. The overall success of antihypertensive therapy has been undeniable, but has reduced minimally the frequency of atherosclerosis and coronary events; metabolic disarray resulting from the agents used, especially thiazides and beta blockers, may have contributed to this. Electrolyte abnormalities predispose to malignant arrhythmias and sudden death during myocardial infarction. Left ventricular hypertrophy, a chief risk factor for coronary events, arrhythmias, and heart failure, responds selectively to antihypertensive agents. Similarly, progression of renal injury may be sensitive to the agents used. Obesity and hypertension frequently coexist. Evidence is growing that atherogenic abnormalities common in obese patients, such as insulin resistance, also occur in the nonobese patient and are sensitive to the antihypertensive agent selected.

Constrictive effect of serotonin on visible renal arteries: a pharmacoangiographic study in anesthetized dogs

Serotonin (5HT) has been implicated in the pathogenesis of several arterial disorders. Experimental intrarenal infusion of 5HT has produced initial decreases, and later sustained increases in total renal blood flow in the dog, and flow limiting renal artery spasm in other species. We assessed renal angiographic responses to 5HT infused into one renal artery of nine dogs before and after treatment with indomethacin (I). On blinded assessment of arteriograms, 5HT-induced narrowing was detected (p less than 0.001), and the effect was accentuated by I (p less than 0.001). Ketanserin (K), a 5HT-2 receptor antagonist, reversed the arteriographic vasoconstrictor effect of 5HT in five I-treated dogs (p less than 0.05). Linear cortical defects and decreased contrast intensity were seen in the nephrogram phase during 5HT infusion after I. This appearance resembled the arteriographic findings in hemorrhagic shock, suggesting profound impairment of renal cortical perfusion. This study suggests that 5HT constricts visible renal arteries via interaction with the 5HT-2 receptor, and that this in vivo effect is modified by arterial synthesis of vasodilator prostaglandins in the anesthetized dog.

Platelet activation and aggregation after endothelial injury. Assessment with indium-111-labeled platelets and angiography

Although platelet activation and aggregation after endothelial injury are well documented, the time course of platelet deposition and the relationship between platelet aggregation and the release of vasoactive products have not been fully clarified in vivo. To study the effect of platelet vasoactive products, a collateral blood supply was induced by ligating the superficial femoral artery in male New Zealand white rabbits. Two weeks later, endothelial injury to the distal abdominal aorta was produced by cytologic brush or mimicked with a metal coil embolus. Platelet aggregation was assessed with indium-111 (111In)-labeled platelets, and scintigraphy demonstrated significant, progressive platelet deposition up to 3 hours after injury and evidence of residual activity 24 hours later. Angiography showed that the time course of peripheral vasoconstriction matched closely that of platelet deposition, indicating release of vasoactive substances from the aggregating platelets. These pathophysiologic changes secondary to endothelial injury may have significant implications for intravascular interventional procedures.

Myocardial infarction treated with two lymphagogues, calcium dobesilate (CLS 2210) and hyaluronidase: a coded, placebo-controlled animal study

The effects on the evolution of canine myocardial infarction (MI) of the lymphagogues hyaluronidase (hyaluronate glucanohydrolase) (known to reduce the size of MIs) and calcium dobesilate (calcium, 2,5-dihydroxybenzenesulfonate, CLS 2210) were compared in a coded, placebo-controlled study in 48 dogs, during the first 24 h after coronary occlusion. MI was induced by embolization of the anterior descending branch of the left coronary artery. The animals were given either a placebo, CLS 2210, or hyaluronidase by intravenous infusion begun immediately after embolization and continued for 24h. The volume of myocardial tissue at risk was evaluated at 2 and 24 h by ungated computed tomography (CT), and after necropsy by staining myocardial sections with triphenyl tetrazolium chloride (TTC). Electrocardiography and estimation of serum creatine kinase (CK) activity were also performed. In the 25 animals that survived 24 h, the results of all tests showed that there was less myocardial damage in the animals treated with the two lymphagogues than in those treated with placebo, and less damage with CLS 2210 than with hyaluronidase. The good correlation between the volume of ischemic tissue as assessed by CT in vivo and as assessed by TTC staining after necropsy (r = 0.959) confirms that the CT perfusion phase defect accurately reflects the volume of tissue at risk during the evolution of MI. This study has shown that CLS 2210 is at least as effective as hyaluronidase in reducing myocardial damage due to coronary artery occlusion in dogs.

Dopamine and nonmodulating hypertension

Sodium loading reduces aldosterone responses to angiotensin II (AII) when compared to the sodium restricted state. Recent investigations suggest that dopamine inhibits the aldosterone secretion and may contribute to the alteration in aldosterone response to AII with sodium intake, since administration of the dopamine antagonist, metoclopramide, enhances the aldosterone responses to AII on a high but not a low salt diet. Nonmodulating hypertension is characterized, in part, by a decreased aldosterone response to AII, raising the possibility that an increased dopaminergic inhibition of aldosterone secretion underlies the adrenal defect in nonmodulating hypertension. To assess this possibility, 69 patients with hypertension were characterized in relationship to their modulation status on a low sodium intake. Dopamine levels were significantly higher (P less than .05) in nonmodulators. To assess the physiologic relevance of these findings, the aldosterone response to AII infusion was assessed before and during administration of the dopamine antagonist, metoclopramide, in 13 patients. The adrenal response to AII did not change after metoclopramide in either hypertensive subgroup. Thus, it is unlikely that the adrenal defect is due to the increase in dopamine levels observed in nonmodulators. In the next study, the impact of dietary sodium intake on urinary dopamine levels was compared in normotensive and hypertensive subjects characterized as modulators and nonmodulators. Both modulators and normotensive subjects demonstrated an increase in urinary dopamine excretion in response to a high sodium intake--a feature that was not observed in the nonmodulators. Thus, the sodium retaining tendency of nonmodulators may reflect, at least in part, a reduction in intrarenal dopamine production in response to a sodium load.

Persistent dysfunction of regenerated endothelium after balloon angioplasty of rabbit iliac artery

This study investigated the vasodilator function of endothelium that regenerated after balloon angioplasty and the relation of this function to the extent of vascular injury and to subsequent intimal proliferation. Balloon angioplasty was performed in the left iliac artery of 47 New Zealand White rabbits. Vascular responses were examined in vitro 2 and 4 weeks after a "severe" injury (3.0-mm balloon) or a "moderate" injury (2.5-mm balloon). Both degrees of balloon injury caused complete endothelial denudation. Endothelial regrowth 2 weeks after either injury was confirmed histologically. Although the regenerated cells had irregular sizes and polygonal shapes and lacked the typical alignment in the direction of blood flow, immunocytochemical staining for factor VIII-related antigen identified these cells as endothelium. To study the vasodilator function of regenerated endothelium, rings of balloon-injured and control (contralateral) iliac arteries were suspended in organ chambers for recording of isometric force. Endothelium-dependent relaxation of balloon-injured vessels to acetylcholine and to the calcium ionophore A23187 were reduced at 2 and at 4 weeks after severe injury. After moderate injury, endothelium-dependent relaxations to these agents were reduced at 2 weeks but had normalized by 4 weeks. Endothelium-independent relaxation to sodium nitroprusside, however, was preserved in all study groups. Morphometric analysis revealed an inverse correlation between the degree of intimal thickening and maximal relaxation to acetylcholine (r = 0.45, p less than 0.01). Thus, there is a persistent attenuation of receptor- and nonreceptor-mediated endothelium-dependent relaxations after arterial injury. The regenerated cells have an altered morphological appearance, but staining for factor VIII-related antigen confirms their endothelial origin. The degree and duration of endothelial dysfunction depends on the severity of the initial injury and is related to the extent of intimal thickness.

Atherosclerosis, peripheral arterial disease and the vascular response to ketanserin

Platelet activation releases thromboxane A2 and serotonin, which acts on blood vessels through a specific, 5-hydroxytryptamine (5-HT2) receptor. The development of ketanserin, the selective 5HT2 receptor blocker, has made it possible to explore the role of serotonin in patients with advanced atherosclerotic disease. Ketanserin in low doses (3 to 30 micrograms/kg) was administered intra-arterially to 23 patients with symptomatic peripheral occlusive vascular disease during peripheral angiography: an additional seven patients received a placebo. The angiographic response was evaluated by coded reading and by computer-assisted measurement of arterial segments in four anatomical regions (pelvis, thigh, knee, and lower leg). Hemodynamic changes were assessed by mercury strain gauge plethysmography and Doppler pressure measurement. Unequivocal vasodilatation was observed in zero of seven placebo-treated patients and in 13 of 23 (57%) treated patients primarily at the level of collateral vessels. Dilation of the geniculate arteries, a major source of collaterals to the calf, was associated with a significant increase in the blood flow delivery to the calf. There was a moderate drop of systemic blood pressure in patients who failed to respond with peripheral vasodilatation. Ketanserin induces hemodynamically significant vasodilatation in some patients with peripheral vascular disease, suggesting that serotonin may contribute to ischemia in some patients with advanced atherosclerosis.

Time course of enhanced adrenal responsiveness to angiotensin on a low salt diet

To assess the rate of activation of the renin-angiotensin-aldosterone axis and enhancement of adrenal responsiveness to angiotensin II (Ang II) with restriction of sodium intake, 16 healthy male subjects were placed initially on a 200 meq daily sodium intake; adrenal responsiveness to Ang II was assessed, and then daily sodium intake was reduced abruptly to 10 meq. Adrenal responses to Ang II were assessed again during the non-steady state interval 24 and 48 hours later, and after balance was achieved in 5-7 days. Renin-angiotensin system activation was evident within 24 hours after sodium intake was restricted. The increase in basal plasma aldosterone concentration and enhancement of the adrenal response to Ang II, on the other hand, tended to lag. Within 24 hours of restricting sodium intake, despite a significant increase in both plasma renin activity (1.0 +/- 0.2 vs. 2.4 +/- 0.7 ng/ml/hr, p less than 0.01) and Ang II concentration (22.0 +/- 1.9 vs. 29.5 +/- 1.3 pg/ml, p less than 0.05), there was no increase in basal plasma aldosterone concentration (10.4 +/- 1.3 vs. 11.7 +/- 1.2 ng/dl). At 48 hours, despite little further change in plasma renin activity or plasma Ang II concentration, there was a sharp increase in basal plasma aldosterone concentration (22.5 +/- 3.6 ng/dl, p less than 0.01). The adrenal response to Ang II was increased significantly at 24 hours, evident at only a 10 ng/kg/min dose, but showed progressive further enhancement with time.(ABSTRACT TRUNCATED AT 250 WORDS)