Peripheral Arterial Vasodilation Research Articles

Hepatorenal Syndrome

Hepatorenal syndrome is a life-threatening complication of severe liver disease. It is generally accepted that the syndrome is the final stage of complex hemodynamic derangements associated with portal hypertension, ie, peripheral arterial vasodilation, effective hypovolemia, and hyperkinetic status. In spite of reduced systemic resistances, intrarenal vascular resistances are increased. This is probably the consequence of the activation of systemic vasoactive factors, such as the renin-angiotensin system, the sympathetic nervous system, and vasopressin aimed at restoring arterial filling pressure. Recently, it has been shown that intrarenal vasoconstrictors, such as leukotrienes and endothelins, are activated with the progression of liver disease. The renal vasoconstriction is counterbalanced by the intrarenal hyperproduction of vasodilating prostaglandins and kallikreins. When this balance is lost, for whatever mechanism, the renal vascular resistances dramatically increase and the hepatorenal syndrome develops. In spite of increased knowledge about pathogenesis, the treatment of hepatorenal syndrome remains unresolved. Low-dose dopamine or ornipressin are currently employed in many liver units to avoid further deterioration of renal function in patients with severe liver disease who are waiting for liver transplantation that remains, at present, the only effective treatment for hepatorenal syndrome. (Arch Intern Med. 1993;153:1957-1967)

Edematous disorders

The pathogenesis of renal sodium and water retention in cardiac failure, cirrhosis, and the nephrotic syndrome may be explained by the unifying hypothesis of body fluid volume regulation. According to this hypothesis, underfilling of the arterial vascular compartment initiates a sequence of events, including activation of various neurohormonal vasoconstrictor systems, which results in enhanced renal sodium and water reabsorption, the failure to escape from the sodium-retaining effect of aldosterone, and renal resistance to atrial natriuretic peptide. In patients with low-output cardiac failure, a decrease in cardiac output results in arterial underfilling. Peripheral arterial vasodilation diminishes the fullness of the arterial vascular compartment in patients with high-output cardiac failure and cirrhosis. In the nephrotic syndrome, the decrease in plasma oncotic pressure due to hypoalbuminemia initiates arterial underfilling. The factors that are responsible for the peripheral arterial vasodilation in patients with cirrhosis remain obscure. Diuretics are initially effective in reducing the excess of total-body sodium and water in edematous patients. Loop diuretics, with or without metolazone or a thiazide diuretic, are quite useful in patients with heart failure. In cirrhosis and the nephrotic syndrome, the specific aldosterone antagonist spironolactone, alone or in combination with other diuretics, has proven to be highly efficacious. However, in all instances, the emergence of diuretic resistance represents a major limitation of diuretic therapy for the edematous patient. This diuretic resistance may be mediated by further activation of vasoconstrictor, antinatriuretic neurohormones.

Arterial underfilling does not cause sodium retention in cirrhosis

purpose: To test the peripheral arterial vasodilation hypothesis of sodium retention in cirrhosis. This states that sodium retention is triggered by arterial underfilling and predicts that development of sodium retention will be associated with significant and related declines in indices of arterial filling that reverse when sodium retention resolves. design: Longitudinal evaluation of a cohort of patients with alcoholic liver disease. patients and methods: Eighteen men, 8 of whom were studied twice, 3 three times, 2 four times, and 5 five times (40 between-study comparisons). Between 23 studies, the patients were ascites-free (Group NN). Ascites spontaneously disappeared between seven studies (Group YN), appeared between six studies (Group NY), and remained present between four studies (Group YY). Between-study changes in blood volume, arterial blood pressure, cardiac output, systemic vascular resistance, left atrial volume, left ventricular diastolic diameter, aortic root diameter, aortic blood velocity, plasma norepinephrine and atrial natriuretic factor concentrations, plasma renin activity, and urinary sodium excretion were evaluated by paired t-tests. These changes were also compared among groups by analysis of variance. In addition, correlations among the changes were sought. results: Systolic, diastolic, and mean arterial pressures, left ventricular diastolic diameter, aortic root diameter, stroke volume, cardiac output, plasma norepinephrine concentration, and systemic vascular resistance were unchanged between studies. Left atrial volume increased between studies in Group NY. Pulse pressure fell more in Group NY than in Groups NN and YN, principally as a result of a decline in systol ic blood pressure. Plasma norepinephrine concentration, plasma renin activity, and blood volume rose more in Group NY than in Groups NN, YN, and YY. Changes in both systolic and pulse pressures were directly correlated with the change in sodium excretion but unrelated to the change in plasma norepinephrine concentration. Changes in plasma norepinephrine concentration and plasma renin activity were unrelated to changes in blood pressure, systemic vascular resistance, and urinary sodium excretion. conclusions: None of the indices of arterial filling tested except pulse pressure were related to sodium retention. Reduced pulse pressure is inconsistent with arterial underfilling, as peripheral vasodilation instead increases pulse pressure by increasing diastolic run-off. These data do not support the hypothesis that arterial underfilling is the stimulus for sodium retention in alcoholic cirrhosis.

Effects of dopexamine on hemodynamics and oxygen consumption after beta blockade in lambs

Dopexamine is a synthetic catecholamine with predominantly beta 2 and dopaminergic adrenergic receptor activities. We investigated its effects on systemic and myocardial hemodynamics and oxygen consumption (VO2) in a newborn species and studied its predominant mechanism of action. Prospective dose-response study with each animal serving as it own control. Eight chronically instrumented, unanesthetized lambs, 9 to 11 days of age. After surgical instrumentation and recovery for 72 hrs, animals were infused with dopexamine at increasing doses (1, 10, and 100 micrograms/kg/min) for 5 mins each before and after beta 1 (metoprolol) and beta 1, beta 2 (propranolol) adrenergic receptor blockade. All studies were performed during normoxia. Heart rate (HR) increased with increasing infusion rates of dopexamine and systemic arterial pressure and vascular resistance decreased. Cardiac index, left ventricular pressure development, and systemic VO2 were unchanged, as was the rate x pressure product. Left circumflex coronary artery blood flow and myocardial VO2 were unaltered. After beta 1-blockade, dopexamine produced an increase in HR and decreased systemic arterial pressure and vascular resistance. After beta 1-adrenergic receptor blockade, no change was noted in systemic or myocardial VO2, coronary blood flow, or rate x pressure product. After beta 1, beta 2-blockade with propranolol, increasing infusion rates of dopexamine resulted in decreases in systemic pressure and vascular resistance. Dopexamine produced significant cardiovascular effects mediated primarily by beta 2-adrenergic receptors, and also produced residual peripheral arterial vasodilation after combined beta 1- and beta 2-blockade. The latter finding suggests that dopaminergic receptor stimulation may partly mediate dopexamine's effects in newborn lambs.

Low-dose oral isosorbide in the treatment of coronary artery disease

Background: Isosorbide dinitrate (ISDN) is commonly administered in a dosage of 10 to 20 mg, two to three times daily, as an antianginal agent. The purpose of this study was to investigate the dose-response curve of very low ISDN doses concerning their acute therapeutic effect. Methods: The acute antianginal and peripheral vasodilating effects of a single oral dose of 0.3 mg, 1.25 mg, 5 mg, and 20 mg of isosorbide dinitrate (ISDN) were studied in 30 patients with stable, exercise-induced ST-segment depression and angina pectoris. Mean age was 56 ± 12 years (29 men, 1 woman), and all patients had angiographically documented coronary artery disease. In the randomized, double-blind, placebo-controlled trial, the hemodynamic response to each dose was studied by exercise stress testing and finger-pulse plethysmography. Results: The average 1-hour post-dose increase in serum concentration of the major biologically active metabolite isosorbide-5-mononitrate (IS-5-MN) was below the detection limit (< 5 ng/mL) after 0.3 mg ISDN, and 7 ±16, 45 ± 55, and 127 ±59 ng/mL after 1.25 mg, 5 mg, and 20 mg ISDN, respectively. Compared with placebo, the lowest ISDN dose had no anti-ischemic effect, whereas 1.25 mg of ISDN resulted in a 10% reduction of ST-segment depression (P < 0.05), 5 mg achieved a reduction of 36%, and 20 mg of ISDN, 45%, respectively (P < 0.001). The heart rate at rest decreased 4% after 0.3 mg (P < 0.01) and 3% after 1.25 mg ISDN (P < 0.01), was unchanged after 5 mg, and increased 6% after 20 mg ISDN (P < 0.01). Supine systolic blood pressure decreased 2% after 1.25 mg (NS), 7% after 5 mg (P < 0.01), and 12% after 20 mg ISDN (P < 0.001); corresponding changes for the diastolic blood pressure were 0%, −1 %, −2% (NS). Changes in Wood pressure and heart rate in the upright position were comparable, but augmented with significant decreases in diastolic blood pressure after 5 and 20 mg ISDN, as well (P < 0.001). Peripheral vasodilation, measured by digital pulse plethysmography, occurred with higher ISDN doses: 5 mg ISDN achieved 31 % (P < 0.001); 20 mg, 66% peripheral arterial vasodilation (P < 0.001). Conclusions: These data demonstrate an antianginal efficacy of a very low oral dose of ISDN. The dose-response relationship of the antianginal and hemodynamic effects of ISDN were closely related, both starting at single oral doses of 1.25 mg ISDN.

Pathophysiology and treatment of ascites and the hepatorenal syndrome

Ascites indicates the accumulation of fluid in the peritoneal cavity, due to a wide range of causes. These causes can be classified according to the presence of portal hypertension, severe blood dyscrasia and peritoneal disease. Cirrhosis is the most frequent cause of ascites. The occurrence of ascites in cirrhosis is due to portal hypertension, which is responsible for the increase in hydrostatic pressure at the sinusoidal level and the alterations of splanchnic and systemic haemodynamics. These latter include increased splanchnic inflow, reduced systemic resistance and increased plasma volume and cardiac output. Portal hypertension also plays a major role in determining sodium retention, which occurs in the setting of increased RAA system and SNS activity. The mechanisms by which portal hypertension leads to the activation of antinatriuretic factors and sodium retention are not completely understood; three main hypotheses have been proposed to explain this relationship, namely the underfilling, the overflow and the peripheral arterial vasodilatation theories. In patients with cirrhosis and ascites, there is an overall activation of the renal prostaglandin system, which probably acts to maintain renal haemodynamics and GFR by counteracting the vasoconstricting effects of AII and noradrenaline on renal circulation. In advanced stages, ascites may become refractory to medical treatment and renal function shows a progressive impairment and eventually acute renal failure, the so-called HRS, due to a marked vasoconstriction of the renal arteries and the opening of the intrarenal-arteriovenous (A-V) shunts. In this condition, the reduced renal synthesis of vasodilating prostaglandins is probably of pathogenic importance. Treatment of ascites is usually based on bed rest, low-sodium diet and administration of aldosterone antagonists and loop diuretics. A sequential treatment of ascites based on the progressive addition of more potent drugs is the best way to relieve ascites while avoiding potentially dangerous side-effects. Patients who fail to respond to the above manoeuvres are said to have refractory ascites. Current treatment of this latter condition is mainly based on therapeutic paracentesis and the application of the LeVeen shunt, but long-term results are unsatisfactory.

Unifying hypothesis of sodium and water regulation in health and disease.

Sodium and water retention is characteristic of edematous disorders including cardiac failure, cirrhosis, nephrotic syndrome, and pregnancy. Nonosmotic vasopressin release has been implicated in the water retention of these edematous disorders. The nonosmotic release of vasopressin is consistently associated with activation of the sympathetic nervous and renin-angiotensin-aldosterone systems in both experimental animals and in edematous patients. Moreover, the sympathetic nervous system has been shown to be involved in the nonosmotic release of vasopressin and activation of the renin-angiotensin system. These findings have led to our proposal that body fluid volume regulation involves the dynamic interaction between cardiac output and peripheral arterial resistance. Neither total extracellular fluid volume nor blood volume is a determinant of renal sodium and water excretion. Rather, renal sodium and water retention is initiated by a decrease in effective arterial blood volume (EABV) due to either a fall in cardiac output or peripheral arterial vasodilation. The acute response to a decrease in EABV involves vasoconstriction mediated by angiotensin, sympathetic mediators, and vasopressin. The slower response to restoring EABV involves vasopressin-mediated water retention and aldosterone-mediated sodium retention. The resultant renal vasoconstriction limits the distal tubular delivery of sodium and water, thus maximizing the water-retaining effect of vasopressin and impairing the normal escape from the sodium-retaining effects of aldosterone. The elevated glomerular filtration rate and filtered sodium load in pregnancy allows increased distal sodium and water delivery in spite of a decrease in EABV, thus limiting edema formation during gestation.

Pharmacology ofCasimiroa edulis; II. Cardiovascular Effects in the Anesthesized Dog

The cardiovascular effects of an aqueous extract of seeds of Casimiroa edulis were assessed in pentobarbital-anesthetized dogs. The extract produced marked hypotension which lasted more than two hours; it was accompanied by moderate and less persistent bradycardia. The histaminergic nature of these effects was investigated in animals pretreated with the specific antagonists diphenhydramine, cimetidine, or a combination of both agents. These experiments showed that both H1- and H2-receptors were involved in the hypotensive response, while the bradycardia was mediated solely through an H1-mechanism. In open-chest dogs instrumented for recording cardiac output (ascending aortic flow), left ventricular contractility (dp/dt), central venous pressure (superior vena cava), systemic blood pressure, heart rate, total peripheral resistance and stroke volume, the extract decreased blood pressure and peripheral resistance and increased cardiac output and stroke volume, without modifying the other parameters. It was concluded that the cardiovascular pattern of Casimiroa edulis in the dog is that of a peripheral arterial vasodilator and that it increases cardiac output by reducing left ventricular afterload.

Temporal relationship between the decrease in arterial pressure and sodium retention in conscious spontaneously hypertensive rats with carbon tetrachloride–induced cirrhosis

It has been proposed that the initial event of sodium retention in cirrhosis is a peripheral arteriolar vasodilation causing underfilling of the arterial vascular compartment and stimulation of the renin-aldosterone and sympathetic nervous systems. To test this hypothesis, systolic blood pressure, sodium balance and urinary excretion of sodium and aldosterone were sequentially measured in 13 conscious spontaneously hypertensive rats submitted to a cirrhosis induction program with carbon tetrachloride and phenobarbital and in 14 control hypertensive animals. No significant differences were found between control and cirrhotic rats in any of the measured parameters during the first 7 wk of the study. The eighth week sodium retention developed in cirrhotic rats as indicated by a positive sodium balance and a marked decrease of sodium excretion. At the same time a significant reduction in systolic blood pressure and a great increase in urinary excretion of aldosterone were detected. These changes were more marked the ninth week of the study. In cirrhotic rats there was a highly significant direct correlation between systolic blood pressure and urinary sodium excretion. Postmortem examination showed a histological picture of cirrhosis in all animals given carbon tetrachloride and ascites in six of them. These results indicate that the onset of hyperaldosteronism and sodium retention in conscious spontaneously hypertensive rats with carbon tetrachloride-induced cirrhosis is chronologically related to a significant decrease in arterial pressure, thus supporting the "peripheral arterial vasodilation hypothesis" of ascites.

The effects of calcium channel blockers on random skin flap survival in the pig model

This study was designed to evaluate the influence of two calcium channel blockers, verapamil and nifedipine, on skin flap survival. These agents were selected because they inhibit the passage of calcium through calcium selective channels in the plasma membrane, thereby blocking calcium mediated electromechanical coupling in contractile tissue and resulting in peripheral arterial vasodilation. Three groups of pigs were used in this study. All skin flaps in this study were 3 cm wide and 12 cm long. The first group (10 flaps) served as controls with no pharmacologic manipulations. Pigs in group II (15 flaps) received verapamil (80 mg orally, three times a day) for 7 days postoperatively. Pigs in group III (15 flaps) received nifedipine (10 mg orally, three times a day) for 7 days postoperatively. Statistical analysis of the results demonstrated that both verapamil and nifedipine resulted in significant enhancement of skin flap survival. The increased survival of the skin flaps produced by nifedipine as compared to verapamil was statistically significant.

Clinical evidence for the peripheral arterial vasodilatation hypothesis of renal sodium retention in cirrhosis

Clinical evidence for the peripheral arterial vasodilatation hypothesis of renal sodium retention in cirrhosis

Pathophysiology of ascites formation in cirrhosis of the liver.

Current concepts of the pathophysiology of ascites formation in cirrhosis of the liver have become more complex. Traditionally, the initiating event of renal sodium and water retention in cirrhosis was considered to be ascites formation ("underfilling" hypothesis) or primary renal dysfunction ("overflow" hypothesis). Changes in systemic, splanchnic and renal hemodynamics, as well as of volume regulating hormones observed in cirrhosis are compatible with a decrease in effective blood volume as suggested by the "underfilling" hypothesis. These changes, however, have been shown to precede ascites formation. This observation, together with the demonstration of an increase in total blood volume in cirrhosis prompted the "overflow" hypothesis. However, many studies are incompatible with this concept and, in addition, the agent causing primary renal sodium retention in cirrhosis still remains to be defined. The recently proposed "vasodilation" hypothesis reconciles the most salient features of both theories, proposing peripheral arterial vasodilation as the initiating event of decreased effective blood volume and renal sodium retention. Further studies are needed to elucidate the temporal relationship and more precisely define the character of hemodynamic, humoral and renal changes in cirrhosis of the liver.

Body Fluid Volume Regulation in Health and Disease: A Unifying Hypothesis

In studies in experimental animals and in edematous patients, the nonosmotic release of vasopressin has been found to be consistently associated with activation of the sympathetic nervous and renin-angiotensin-aldosterone systems. Moreover, the sympathetic nervous system is known to modulate the nonosmotic release of vasopressin and activation of the renin-angiotensin-aldosterone system. These findings led to our proposal that body fluid volume regulation involves dynamic interaction between cardiac output and peripheral arterial resistance. In this context, neither total extracellular fluid volume nor total blood volume are determinants of renal sodium and water excretion. With a decrease in effective arterial blood volume (EABV) initiated by either decreased cardiac output or peripheral arterial vasodilation, the acute response involves vasoconstriction mediated by angiotensin, sympathetic mediators, and vasopressin. The renal vasoconstriction, which accompanies either decreased cardiac output or peripheral arterial vasodilation, causes a decreased distal tubular delivery of sodium and water, thus maximizing the water-retaining effect of vasopressin and impairing normal escape from the sodium-retaining effect of aldosterone. The elevated glomerular filtration rate and filtered sodium load seen in pregnant women allow increased distal sodium and water delivery despite a decrease in EABV, thus limiting edema formation during gestation.

A Unifying Hypothesis of Sodium and Water Regulation in Health and Disease

Sodium and water retention is characteristic of edematous disorders including cardiac failure, cirrhosis, nephrotic syndrome, and pregnancy. In recent years, the use of a sensitive radioimmunoassay for plasma vasopressin has implicated the role of nonosmotic vasopressin release in the water retention of these edematous disorders. In experimental studies and studies in man, it has been found that the nonosmotic release of vasopressin is consistently associated with the activation of the sympathetic nervous and renin-angiotensin-aldosterone systems. Moreover, the sympathetic nervous system has been shown to be involved in the nonosmotic release of vasopressin (carotid and aortic baroreceptors) and in the activation of the renin-angiotensin system (renal beta-adrenergic receptors). These findings have led to our proposal that body fluid volume regulation involves the dynamic interaction between cardiac output and peripheral arterial resistance. In this context, neither total extracellular-fluid (ECF) volume nor blood volume are determinants of renal sodium and water excretion. Rather, renal sodium and water retention is initiated by either a fall in cardiac output (e.g. ECF volume depletion, low-output cardiac failure, pericardial tamponade, or hypovolemic nephrotic syndrome) or peripheral arterial vasodilation (e.g. high-output cardiac failure, cirrhosis, pregnancy, sepsis, arteriovenous fistulae, and pharmacologic vasodilators). With a decrease in effective arterial blood volume (EABV). initiated by either a fall in cardiac output or peripheral arterial vasodilation, the acute response involves vasoconstriction mediated by angiotensin, sympathetic mediators, and vasopressin. The slower response to restoring EABV involves vasopressin-mediated water retention and aldosterone-mediated sodium retention. The renal vasoconstriction which accompanies those states that decrease EABV, by either decreasing cardiac output or causing peripheral arterial vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of vasopressin in edematous disorders.

Sodium and water retention is characteristic of edematous disorders including cardiac failure, cirrhosis, nephrotic syndrome and pregnancy. In recent years the use of a sensitive radioimmunoassay for plasma vasopressin has implicated the role of nonosmotic vasopressin release in the water retention of these edematous disorders. In experimental studies and studies in humans it has been found that the nonosmotic release of vasopressin is consistently associated with activation of the sympathetic nervous and renin-angiotensin-aldosterone systems. Moreover, the sympathetic nervous system has been shown to be involved in the nonosmotic release of vasopressin (carotid and aortic baroreceptors) and activation of the renin-angiotensin system (renal beta-adrenergic receptors). These findings have led to our proposal that body fluid volume regulation involves the dynamic interaction between cardiac output and peripheral arterial resistance. In this context neither total extracellular fluid (ECF) volume nor blood volume are determinants of renal sodium and water excretion. Rather, renal sodium and water retention is initiated by either a fall in cardiac output (e.g. ECF volume depletion, low-output cardiac failure, pericardial tamponade or hypovolemic nephrotic syndrome) or peripheral arterial vasodilation (e.g. high-output cardiac failure, cirrhosis, pregnancy, sepsis, arteriovenous fistulae and pharmacologic vasodilators). With a decrease in effective arterial blood volume (EABV), initiated by either a fall in cardiac output or peripheral arterial vasodilation, the acute response involves vasoconstriction mediated by angiotensin, sympathetic mediators and vasopressin. The slower response to restoring EABV involves vasopressin-mediated water retention and aldosterone-mediated sodium retention. The renal vasoconstriction which accompanies those states that decrease EABV, by either decreasing cardiac output or causing peripheral arterial vasodilation, limits the distal tubular delivery of sodium and water thus maximizing the water-retaining effect of vasopressin and impairing the normal escape from the sodium-retaining effects of aldosterone. The elevated glomerular filtration rate and filtered sodium load in pregnancy allows increased distal sodium and water delivery in spite of a decrease in EABV, thus limiting edema formation during gestation.

Pathogenesis of sodium and water retention in high-output and low-output cardiac failure, nephrotic syndrome, cirrhosis, and pregnancy (2)

This article has analyzed the pathogenesis of sodium and water retention in several circumstances. The initiator of retention has been proposed to be either a fall in cardiac output (e.g., low-output cardiac failure and vasoconstrictor hypovolemic nephrotic syndrome) or peripheral arterial vasodilatation (e.g., high-output cardiac failure, cirrhosis, arteriovenous fistula, and pregnancy). In the only state discussed, in which the kidney is diseased and not merely responding to extrarenal reflexes--i.e., nephrotic syndrome--intrarenal mechanisms may predominate and lead to expansion of the arterial vascular tree and suppression of the renin-angiotensin-aldosterone system (i.e., hypervolemic nephrotic syndrome). Otherwise, when kidneys are healthy, either a fall in cardiac output or peripheral arterial vasodilatation may diminish arterial vascular filling and thereby initiate a series of hemodynamic and hormonal events that result in renal sodium and water retention (Fig. 7). Finally, the approach presented in this article should be considered to be a vantage point from which to evaluate states of sodium and water retention, but not to be an exclusive position.

Peripheral arterial vasodilation hypothesis: a proposal for the initiation of renal sodium and water retention in cirrhosis.

Renal sodium and water retention and plasma volume expansion have been shown to precede ascites formation in experimental cirrhosis. The classical "underfilling" theory, in which ascites formation causes hypovolemia and initiates secondary renal sodium and water retention, thus seems unlikely. While the occurrence of primary renal sodium and water retention and plasma volume expansion prior to ascites formation favors the "overflow" hypothesis, the stimulation of the renin-angiotensin-aldosterone system, vasopressin release and sympathetic nervous system associated with cirrhosis is not consonant with primary volume expansion. In this present article, the "Peripheral Arterial Vasodilation Hypothesis" is proposed as the initiator of sodium and water retention in cirrhosis. Peripheral arterial vasodilation is one of the earliest observations in the cirrhotic patient and experimental animals with cirrhosis. Arterial vasodilators and arteriovenous fistula are other examples in which renal sodium and water retention occur secondary to a decreased filling of the arterial vascular tree. An increase in cardiac output and hormonal stimulation are common features of cirrhosis, arteriovenous fistula and drug-induced peripheral arterial vasodilation. However, a predilection for the retained sodium and water to transudate into the abdominal cavity occurs with cirrhosis because of the presence of portal hypertension. The Peripheral Arterial Vasodilation Hypothesis also explains the continuum from compensated to decompensated cirrhosis to the hepatorenal syndrome.

Hemodynamic Effects of α-Human Atrial Natriuretic Peptide in Healthy Volunteers

The hemodynamic effects of synthetic alpha-human atrial natriuretic peptide (alpha-hANP) were evaluated in a double-blind, placebo-controlled study with echocardiography and systolic time intervals in 11 healthy volunteers. During an infusion of alpha-hANP for 30 min, when plasma ANP concentration increased to a peak level of approximately 300 pg/ml, an increase occurred in diuresis (+174%, p less than 0.01 vs. placebo) and natriuresis (+148%, p less than 0.05). Heart rate increased (+10%, p less than 0.05), but the mean arterial pressure remained unchanged. The left ventricular end-diastolic diameter was reduced (-3%, p less than 0.01), as was the left ventricular end-systolic diameter (-11%, p less than 0.001). Total peripheral resistance (-12%, p less than 0.05) and midsystolic circumferential wall stress (-16%, p less than 0.05) decreased, while cardiac output increased (+15%, p less than 0.05), as did fractional shortening (+15%, p less than 0.001). Within 30 min postinfusion, all differences between the ANP and placebo treatments had disappeared. No significant difference between the treatments was observed in preejection period or preejection period/left ventricular ejection time ratio. In conclusion, when administered as a short infusion, alpha-hANP causes peripheral arterial vasodilation and thus, by reducing left ventricular afterload, improves the pump function of the heart. Venous vasodilating effect of alpha-hANP may contribute to the decrease in left ventricular preload, but a diuresis-induced reduction in circulating intravascular volume may also be influenced.

A Reappraisal of Nitrate Therapy

Nitroglycerin and the long-acting nitrates are beneficial in stable and unstable angina pectoris and acute myocardial infarction and as adjunctive therapy in congestive heart failure. Nitroglycerin compounds relax vascular smooth muscle, producing venous, arterial, and arteriolar dilatation. These actions are modulated by stimulation of intracellular cyclic guanosine monophosphate. Nitrate efficacy in ischemic heart disease is due to peripheral venous and arterial vasodilatation that results in decreased myocardial oxygen consumption. Nitrates also dilate coronary arteries and collaterals, reverse coronary vasoconstriction, and enlarge some coronary atherosclerotic lesions. Nitrates improve exercise performance in stable angina pectoris. Intravenous nitroglycerin should be used in the initial treatment of unstable angina. Nitrates may be beneficial in myocardial infarction for control of ischemic pain, acute hypertension, and left ventricular failure. In subjects with congestive heart failure, nitrates reduce symptoms and improve exercise tolerance. Nitrate tolerance is a problem with continuous nitrate therapy. Tolerance is most likely to occur with frequent dosing or the use of long-acting nitrates, particularly transdermal nitroglycerin disks, and can be prevented or reversed with intermittent-dosing regimens.

Clinical Pharmacology of Pinacidil, A Prototype for Drugs That Affect Potassium Channels

The clinical pharmacology of potassium channel openers has been reviewed using pinacidil as a prototype drug. When administered acutely or chronically, the hemodynamic and neuroendocrine profile is that of a peripheral arterial vasodilator. The drug produces decreases in peripheral vascular resistance, and subsequent blood pressure decreases are associated with reflex increments in heart rate. When studied, plasma catecholamines increased about twofold during chronic therapy. Plasma renin activity, however, was not increased during chronic therapy with pinacidil monotherapy. When patients were treated with pinacidil doses ranging from 12.5 to 75 mg b.i.d., 66.9% of patients had a decrease in supine diastolic blood pressure to below 91 mm Hg and 10 mm Hg less than baseline, whereas only 23.9% of patients had similar falls during placebo treatment. During maintenance therapy with pinacidil, the average blood pressure during the daytime dosing interval was 137.8 +/- 1.2/83.4 +/- 0.7 mm Hg (mean +/- SEM). Titration of pinacidil as monotherapy resulted in a characteristic adverse event profile dominated by the presence of dose-related edema. Other characteristic events included tachycardia, palpitations and headache. When pinacidil was given to patients unresponsive to hydrochlorothiazide (25 mg b.i.d.), similar efficacy relative to placebo was noted with a change of post-dose supine diastolic blood pressure in the pinacidil group of 13.5 +/- 0.8 mm Hg and 7.3 +/- 0.9 mm Hg in the placebo group.(ABSTRACT TRUNCATED AT 250 WORDS)