Effect of quinapril on the albumin excretion rate in patients with mild to moderate essential hypertension. Multicenter Study Group

In patients with essential hypertension, correlations have been reported between the albumin excretion rate (AER) and ambulatory and casual blood pressure. Microalbuminuria has been indicated as a possible predictor of cardiovascular morbidity and mortality. The objective of this trial was to evaluate the effect of quinapril, an angiotensin converting enzyme inhibitor with high tissue affinity for the enzyme, on the AER in patients with mild to moderate essential hypertension and no evidence of diabetes mellitus. In this 12 week, 24 center study, quinapril was administered to 213 patients and titrated to 10, 20, or 40 mg/day alone or 20 mg/day plus 12.5 mg/day hydrochlorothiazide. Overall, blood pressure was reduced from 155.2 +/- 18.1/101.8 +/- 6.7 mm HG (mean +/- SD) to 144.4 +/- 17.8/92.3 +/- 8.9 mm HG (P = .0001) and AER decreased from 20.6 +/- 24.3 mg/24 h to 14.5 +/- 15.4 mg/24 h (P = .0001). The BP reductions were significant in all age groups. AER at endpoint was reduced 37.5% in elderly, 29.8% in middle-aged, and 11.8% in young patients from 32.5 +/- 45.0 mg/24 h, 19.1 +/- 20.9 mg/24 h, and 16.1 +/- 16.9 mg/24 h, respectively. The AER decreased in 60% of patients who had normal AER (0 to 30 mg/24 h), in 79% of those who had microalbuminuria (30 to 300 mg/24 h), and in 90% of those who had proteinuria (> 300 mg/24 h) at baseline. Baseline log-AER correlated with SBP (P = .0126, R = 0.19) and creatinine clearance (P = .026, R = 0.17), while endpoint log-AER correlated with SBP (P = .0015, R = 0.25) and DBP (P = .03, R = 0.17). In summary, we showed, in a large group of patients with mild to moderate essential hypertension and no evidence of diabetes mellitus, that quinapril not only lowers BP significantly but also reduces microalbuminuria.

Prostaglandins and renal function in hypertensive patients with unilateral renal artery stenosis and patients with essential hypertension

OBJECTIVE

This study was designed to compare the effects of prostaglandin synthesis inhibition on calculated preglomerular and postglomerular resistance in hypertensive patients with unilateral renal artery stenosis (RAS) and in patients with essential hypertension.

DESIGN AND METHODS

Sixteen patients with suspected renovascular hypertension underwent renal angiography: eight had unilateral renal artery stenosis > or = 70% and eight had normal angiograms or stenosis < or = 40%. Radionuclide renography and 6 h urinary collection were performed twice for each subject, at baseline and after indomethacin administration. Levels of urinary vasodilatory prostaglandins were measured by specific radioimmunoassays. Visual image analysis was performed to determine the parenchymal transit time (PTT). The glomerular filtration rate (GFR) was calculated from the plasma clearance of [99mTc]-diethylenetriamine pentaacetic acid (DTPA). The preglomerular and postglomerular resistances were estimated according to Gomez's equations.

RESULTS

The prostaglandin excretion decreased significantly after indomethacin administration both in RAS and in essential hypertension patients. The PTT increased from 230 +/- 10 to 340 +/- 40s in the stenotic kidney compared with the contralateral kidney and the kidneys of essential hypertension patients. The GFR was decreased both in stenotic and in contralateral kidneys (48 +/- 4 to 37 +/- 5 and 60 +/- 4 to 52 +/- 5 ml/min, respectively) but did not decline in the kidneys of essential hypertension patients. The preglomerular resistance increased both in stenotic and in contralateral kidneys, whereas it did not rise significantly in the kidneys of essential hypertension patients. The postglomerular resistance in stenotic and contralateral kidneys of RAS patients was not altered.

CONCLUSIONS

Prostaglandins limit GFR decreases in RAS by preventing preglomerular constriction without interfering with postglomerular constriction. Thus, the action of vasoactive prostaglandins on preglomerular resistance might maintain renal function in the short term by limiting the fall in GFR in the stenotic kidney and by increasing the GFR in the contralateral kidney.

Progressive improvement in the structure of resistance arteries of hypertensive patients after 2 years of treatment with an angiotensin I-converting enzyme inhibitor. Comparison with effects of a beta-blocker

To investigate the effects of antihypertensive drugs on resistance artery structure, 17 essential hypertensive patients were randomly assigned to be treated with an angiotensin I-converting enzyme inhibitor, cilazapril, or a beta-blocker, atenolol, for 2 years. Blood pressure was well controlled throughout the 2 years. Before starting treatment, at the end of the first year and at the end of the second year, patients were subjected to gluteal subcutaneous fat biopsies, from which resistance-size arteries were dissected to be studied. The media width to lumen diameter ratio of arteries from patients in the cilazapril group was 7.5 +/- 0.3% before starting treatment, and decreased significantly (P < .05) to 6.3 +/- 0.2% at the end of the first year, and to 5.8 +/- 0.2% at the end of the second year, at which time it was not different from that of arteries from normotensive subjects (5.2 +/- 0.2%). In patients treated with atenolol, resistance arteries exhibited a media-to-lumen ratio of 8.0 +/- 0.6% before treatment, 8.1 +/- 0.5% after 1 year of treatment, and 7.9 +/- 0.3% at the end of the second year of treatment, all significantly higher (P < .01) than that of arteries from normotensive subjects. Thus, treatment for 2 years with the angiotensin I-converting enzyme inhibitor cilazapril resulted in progressive normalization of the structure (media-to-lumen ratio) of gluteal subcutaneous fat resistance arteries of essential hypertensive patients, whereas there was no change in patients treated with the beta-blocker atenolol.(ABSTRACT TRUNCATED AT 250 WORDS)

A postmarketing surveillance evaluation of quinapril in 3742 Canadian hypertensive patients: the ACCEPT Study. Accupril Canadian Clinical Evaluation and Patient Teaching

The Accupril Canadian Clinical Evaluation and Patient Teaching (ACCEPT) study was a multicenter, 6-month, open-label, postmarketing surveillance study where the efficacy and safety of quinapril, an angiotensin-converting enzyme (ACE) inhibitor, was evaluated in a general population of patients with essential hypertension. Participating physicians followed their normal office procedures for the initiation of quinapril therapy (a dose of 10 mg QD in the majority of cases). The dose was titrated to blood pressure response, generally at 2-week intervals, for a maintenance dose of 10 mg QD to 20 mg QD in most cases (86% at 6 months) and not to exceed 40 mg QD. The use of concomitant antihypertensive medications was left to the discretion of the physician. By random assignment, physicians obtained patient informed consent on either a detailed form that listed possible quinapril side effects or a less specific form, which did not list particular side effects. The purpose of using two different forms was to assess any potential association between the frequency of adverse-event reporting and patient's awareness of quinapril side effects. The patients also received an educational package that provided general information on hypertension and lifestyle modifications known to reduce cardiovascular risk factors. An intent-to-treat analysis included data from 3742 patients in whom the median age was 56 years and the median duration of hypertension was 5 years. The demographic characteristics of these patients were similar to those identified in Canadian hypertensive patients in a recent population-based survey. Nearly 80% of the ACCEPT study patients had more than one cardiovascular risk factor, in addition to hypertension. Among 2979 patients receiving quinapril at 3 months, 77% were stabilized. Among 2517 patients continuing to receive quinapril at 6 months, 84% were stabilized. Greater declines in both diastolic and systolic blood pressures were evident among patients who continued to receive quinapril as part of an antihypertensive regimen than among those who discontinued quinapril treatment. Blood pressure responses to quinapril were similar in newly diagnosed patients and those with a history of hypertension. A total of 980 patients (26.2%) reported one or more adverse events. Cough was most frequently reported and was deemed as definitely related to quinapril therapy by the treating physician in 3.6% of cases. Serious adverse events occurred in 55 patients (1.5%) and were assessed as possibly related to quinapril in only three patients.(ABSTRACT TRUNCATED AT 400 WORDS)

[Prospective study of the effects of an angiotensin converting enzyme inhibitor and a beta blockader on the structure and function of resistant arteries in mild essential hypertension]

Seventeen male untreated mild essential hypertensive patients with a mean age of 41 years agreed to participate in a double-blind randomized trial to test the effects of treatment with cilazapril, an inhibitor of angiotensin I converting enzyme, in comparison to treatment with atenolol, a beta-blocker, on the structure and function of subcutaneous resistance arteries. Patients were randomized to receive either cilazapril 2.5-5 mg or atenolol 25-100 mg per day per day. Blood pressure before treatment was 147/99 and 148/99 mmHg in both groups respectively. At 1 year of treatment blood pressure was 132/86 and 131/85 mmHg in both groups of patients respectively. Treatment for one year with cilazapril resulted in a reduction in the media/lumen ratio of resistance arteries (150-400 microns lumen diameter) dissected from subcutaneous gluteal biopsies from 7.5 +/- 0.3% before treatment to 6.3 +/- 0.2% 1 year later (p < 0.05), still slightly but significantly larger (p < 0.05) than the media/lumen ratio of resistance arteries of normotensive controls (5.1 +/- 0.3%). In arteries from patients treated with atenolol there was no significant change with treatment (8.0 +/- 0.6% before and 8.1 +/- 0.5% after 1 year of treatment). Active wall tension responses to endothelin-1 were blunted in hypertensive patients and normalized in the cilazapril-treated patients, but were unchanged in those taking atenolol. Relaxation in response to acetylcholine of norepinephrine pre-contracted arteries was still significantly reduced after one year (< 0.05) in comparison to those of normotensive patients in the patients treated with atenolol, whereas they were not in those who had received cilazapril.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal effects of immersion in essential hypertension. Carvedilol Study Group

Plasma concentrations of atrial natriuretic factor (ANF) have been reported to be unchanged or increased in patients with essential hypertension. Head out of water immersion (HOI) in a thermoneutral bath induces diuresis and natriuresis, an increase in plasma ANF, and reductions in plasma renin activity and aldosterone concentrations. HOI was used in this study to stimulate the secretion of ANF, and compare its release in patients with essential hypertension (EH) (n = 14) and normotensive subjects (n = 13). Renal function changes induced by HOI were also monitored. HOI that lasted 2 h was compared with a control-seated period in each subject. Blood pressure was significantly reduced (P < .05) in normotensive controls from 112 +/- 3/74 +/- 2 to 100 +/- 3/61 +/- 2 mm Hg, and in patients with EH from 137 +/- 4/93 +/- 3 to 123 +/- 3/78 +/- 2 mm Hg. Plasma levels of ANF increased significantly (P < .05) in both groups from 5.9 +/- 1.3 to 16.3 +/- 3 pmol/L in normotensive controls and from 6.0 +/- 0.9 to 13.2 +/- 2.5 pmol/L in patients with EH. Plasma cyclic guanosine monophosphate concentrations increased more (P < .05) in the patients with EH (3.9 +/- 0.4 to 6.1 +/- 0.5 nmol/L) than in controls (3.4 +/- 0.3 to 4.8 +/- 0.4 nmol/L), whereas plasma renin activity levels decreased in controls (2.29 +/- 0.58 to 1.63 +/- 0.55 ng/mL/h) and to a greater degree in patients with EH (1.62 +/- 0.52 to 0.77 +/- 0.19 ng/mL/h, P < .05) by HOI.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a beta-blocker or a converting enzyme inhibitor on resistance arteries in essential hypertension

Seventeen male untreated mild essential hypertensive patients aged 41 +/- 2 years agreed to participate in a double-blind randomized trial to test the effects of antihypertensive treatment on the structure and function of subcutaneous resistance arteries. Patients were treated with either 50 to 100 mg/d atenolol or 2.5 to 5 mg/d cilazapril. Blood pressure before treatment was 148 +/- 6/99 +/- 1 and 147 +/- 2/99 +/- 1 mm Hg, respectively. At 1 year of treatment blood pressure was 131 +/- 4/85 +/- 2 and 132 +/- 2/87 +/- 1 mm Hg, respectively. Resistance arteries (200 to 400 microns lumen diameter) dissected from subcutaneous gluteal biopsies obtained before treatment and at 1 year showed that the media-lumen ratio of arteries from patients treated with cilazapril was reduced to 6.31 +/- 0.21% from 7.54 +/- 0.31% before treatment (P < .05), still slightly but significantly larger (P < .05) than the media-lumen ratio of resistance arteries of normotensive control subjects (5.15 +/- 0.30%). In contrast, in arteries from patients treated with atenolol there was no significant change with treatment (7.97 +/- 0.60% before and 8.07 +/- 0.45% after 1 year of treatment). Active wall tension responses to endothelin-1 were blunted in hypertensive patients and normalized in the cilazapril-treated patients. Depressed active media stress responses to norepinephrine, arginine vasopressin, and endothelin-1 were accordingly normalized in the patients receiving cilazapril as the media width became thinner but were unchanged in those taking atenolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intravenous atrial natriuretic peptide on gas exchange in humans

The aim of this work was to establish whether a physiological increase in atrial natriuretic peptide (ANP) plasma levels affects pulmonary gas exchange in humans. Ten volunteers received an infusion of either ANP (4 pmol.kg-1.min-1) or physiological saline, for 60 min. Baseline measures of the alveolar-arterial PO2 difference and of the physiological dead space were within normal limits and remained stable during and after the infusion of ANP or saline, although plasma ANP and cGMP rose significantly (p < 0.01) (mean +/- SEM: ANP: 13.4 +/- 3.9 to 56.0 +/- 10.4 pmol/l; cyclic GMP: 3.8 +/- 0.3 to 17.0 +/- 3.8 nmol/l). We conclude that a physiological increase in plasma ANP does not affect pulmonary gas exchange significantly in humans.

Renal effects of a nonhypotensive i.v. dose of felodipine

To evaluate the natriuretic effect of a nonhypotensive dose of felodipine, 11 healthy volunteers (age: 21-28 years) on a high-sodium diet received the drug or its vehicle in a double-blind, randomized, crossover study. Administered intravenously at a dose level of 7.5 micrograms/min for 30 minutes followed by 5 micrograms/min for 120 minutes, felodipine increased natriuresis (546 +/- 69 vs. 454 +/- 39 mumol/min, P < 0.001) and diuresis (8.9 +/- 0.6 vs. 7.5 +/- 0.5 mL/min), compared to its vehicle. Renal plasma flow tended to be augmented, but there was a significant reduction of renal vascular resistance (0.085 +/- 0.004 vs. 0.101 +/- 0.012 mm Hg/mL/min, P < 0.03). The glomerular filtration rate was slightly decreased and proximal sodium reabsorption was diminished with no measurable effect on distal function. Felodipine stimulated plasma renin activity, but produced no changes in plasma atrial natriuretic factor, cGMP, aldosterone, and atrial vasopressin levels. In conclusion, felodipine induced natriuresis and diuresis while reducing proximal tubular sodium reabsorption.

Morphology of resistance arteries and comparison of effects of vasoconstrictors in mild essential hypertensive patients

We have compared the response of small subcutaneous resistance arteries from 15 mild essential hypertensive patients and 13 normotensive controls to various potentially pathophysiologically important vasoconstrictors. Blood vessels obtained from gluteal subcutaneous biopsies from hypertensive patients exhibited a significantly smaller external diameter and lumen and greater media/lumen ratio than those of normotensive subjects, but no significant difference in media thickness or cross-sectional area. Vasoconstrictor peptides produced varying effects on resistance arteries of hypertensive patients relative to controls: angiotensin II and arginine vasopressin elicited normal active media stress responses, while the contractile effect of endothelin-1 was depressed. Norepinephrine media stress responses were also blunted in hypertensive patients. Cocaine produced a shift to the left of the norepinephrine dose-response in vessels from both controls and hypertensive patients. Since the lumen diameter of blood vessels was reduced in hypertensive patients, vasoconstrictor responses were amplified, resulting in calculated pressor responses to endothelin-1 similar to those of normotensive controls. These results demonstrate the structural and functional alterations present in resistance arteries of mild essential hypertensive patients, which may be involved in maintaining elevated blood pressure.

Renal tubular effects of calcium antagonists

Calcium channel blockers have diuretic and natriuretic properties in normal animals and humans. The renal mechanism by which this natriuresis is produced has not yet been completely defined although dihydropyridine derivatives evoke it in experimental animals independently of any effects on renal blood flow or on the glomerular filtration rate. Injections or infusions into the renal artery indicate that the renal excretory effect is secondary to a direct action on renal tubular water and solute reabsorption but not to renal hemodynamic changes. Studies undertaken to localize the site of action of dihydropyridine calcium antagonists on renal tubules by renal clearance and micropuncture techniques suggest that both proximal and distal tubular sites are involved. Primary sites of action in distal convoluted tubules and in the collecting duct have been identified for felodipine and nisoldipine during sodium infusion, whereas sites for nitrendipine in proximal tubules have been demonstrated in strict hydropenia. Both changes in the tubuloglomerular feedback setting and suppression of aldosterone secretion have been proposed to explain some of these effects. The changes do not, however, seem to be dependent on renal innervation. In normal humans, the degree and duration of natriuresis and diuresis correlate with the dose of dihydropyridine derivatives and the extent of systemic pressure reduction. Clearance studies of normal subjects indicate an effect of different dihydropyridine derivatives on tubular fluid and electrolyte reabsorption. Nicardipine and nifedipine are reported to exert proximal tubular actions based either on urate and phosphate excretion or water and lithium clearance. The measurement of tubular indices following felodipine administration suggests a proximal tubular site of action.(ABSTRACT TRUNCATED AT 250 WORDS)

Blunted effects of endothelin upon small subcutaneous resistance arteries of mild essential hypertensive patients

OBJECTIVE

In experimental models of hypertension in the rat, resistance arteries present a blunted response to endothelin, a potent vasoconstrictor peptide. The primary objective of this study was to investigate whether, as in hypertensive rat blood vessels, the response of human resistance arteries to endothelin was altered in essential hypertensive patients, in order to further understand the possible physiopathological involvement of this peptide in human hypertension.

DESIGN

Normotensive male subjects and sex- and age-matched mild essential hypertensive patients who had not received antihypertensive drugs for more than 6 months were investigated.

METHODS

Small arteries were dissected from gluteal subcutaneous biopsies and mounted on a wire-myograph. Blood vessels were measured and dose-response curves to different agents tested.

RESULTS

The external diameter of blood vessels of the hypertensive patients tended to be smaller and the width of their media tended to be thicker, but the cross-sectional area of the wall was similar in both groups. Lumen diameters were significantly smaller in hypertensives and the media:lumen ratio was significantly increased in hypertensive patients. Active tension responses and sensitivity to norepinephrine, arginine vasopressin and angiotensin II were similar in both groups, but calculated active pressure responses were enhanced in hypertensives due to the smaller blood vessel lumen. Tension responses to endothelin-1 at increasing concentrations of 0.1 to 100 nmol/l were lower in hypertensive patients, but the calculated transmural active pressure developed was not significantly different at or above 10 nmol/l.

CONCLUSION

These results suggest that gluteal subcutaneous small resistance arteries of male essential hypertensive patients exhibit a decrement in responsiveness to endothelin-1. The altered design of the hypertensive blood vessels enhanced calculated pressure responses, which may contribute to the maintenance of elevated blood pressure.

Glomerular capillary pressure and hypertension

In patients with essential hypertension, glomerular filtration rate remains normal or elevated, whereas renal blood flow tends to be lower, which results in an increased filtration fraction. The afferent (preglomerular) arteriolar resistance determines the fraction of the pressure that is transmitted to the glomerular capillary network, whereas the efferent (postglomerular) arteriolar resistance determines the outgoing pressure. The relationship between these two resistances, renal plasma flow and the ultrafiltration coefficient will determine the glomerular capillary pressure. In hypertension the glomerular capillary pressure tends to increase because the reduction in afferent arteriolar resistance is greater than the reduction in efferent resistance. Because these resistances and the systemic pressure do not change similarly, reduction in systemic pressure may not translate necessarily or completely into a reduction of glomerular capillary pressure. The choice of antihypertensive drugs may influence the progression of any reduction in renal function based as much on their effect on the glomerular capillary pressure as on their effect on the systemic pressure.

Single-dose pharmacokinetics of 14C-lovastatin in chronic renal failure

An open study on the pharmacokinetics of lovastatin was conducted in six patients with chronic renal failure (mean creatinine clearance, 0.40 ml/sec; range, 0.20 to 0.65 ml/sec) and seven healthy subjects. Plasma levels of 3-hydroxy-3-methylglutaryl-coenzyme reductase inhibitory activity (total and active) and total radioactivity were determined over 168 hours after a single dose of 80 mg 14C-lovastatin. The mean area under the plasma concentration-time curve for active inhibitors were 606 +/- 346 and 282 +/- 138 ngEq.hr/ml (p = 0.04) in patients and control subjects, respectively. Total inhibitors in plasma and total radioactivity were similarly elevated in patients with chronic renal failure. Results indicate that patients with severe renal dysfunction have altered elimination kinetics of lovastatin. Current ongoing clinical studies in patients with renal dysfunction will allow better assessment of the pharmacodynamic meaning of our observations.

Effect of a novel monoamine-oxidase inhibitor, moclobemide on the sensitivity to intravenous tyramine and norepinephrine in humans

This study compared the effects of moclobemide (Ro11-1163), a selective and reversible inhibitor of monoamine-oxidase (MAOI) type A and phenelzine, an irreversible non-selective MAOI, on the pressor responses to IV tyramine and norepinephrine. Because of the reversibility of this inhibition, the pressor effect of tyramine was expected to be minimal. Twelve healthy men participated in this randomized double-blind, placebo-controlled, crossover study. Volunteers began with oral treatment of moclobemide (100 mg TID) or phenelzine (15 mg TID) for 1 week followed by placebo treatment for 2 weeks and then moclobemide or phenelzine treatment for another week. The tyramine and norepinephrine challenge tests were conducted at baseline and then at weekly intervals, for a total of five challenges. The average tyramine dose that was required to increase systolic blood pressure by 25 mm Hg (PD25) was 1.6 +/- 0.2 mg after moclobemide treatment, which was lower (P less than .01) than the baseline value of 3.6 +/- 0.7 mg and that after phenelzine (3.0 +/- 0.5 mg) treatment. Moclobemide did not influence norepinephrine sensitivity. In conclusion, moclobemide mildly decreased the sensitivity to IV tyramine as compared with placebo and phenelzine.

Hypertension in the elderly

Cardiovascular disease in all its clinical manifestations progresses significantly as age advances and takes its heaviest toll in the elderly. Hypertension becomes the dominant risk factor for cardiovascular disease in this age group because of its high incidence. Traditionally, diastolic rather than systolic blood pressure has been regarded as the main risk factor for cardiovascular complications in hypertension, although it is becoming clearer that the risk of cardiovascular complications is likely to be associated mainly with systolic pressure in the elderly. Various intervention drug trials in elderly patients seem to indicate that hypotensive drug treatment can decrease cardiovascular mortality, mainly by decreasing cerebrovascular mortality. The EWPHE used a diuretic combination with methyldopa, and the HEP study used atenolol with a thiazide diuretic. The multicenter Systolic Hypertension in the Elderly Program (SHEPS) currently underway in the United States is likely to also provide some answers. The place of newer agents such as ACE inhibitors or calcium antagonists is still undetermined. Calcium antagonist drugs have been reported to be effective, and possibly more so in the elderly than in a younger population, although this assumption is not proven and may not be valid. Pharmacokinetic studies in the elderly are very few, although the studies reported indicate a reduced clearance. Studies also indicate that Nifedipine Retard tablets are effective, with a low incidence of adverse effects. There are no trials, however, looking at the long-term benefit of treating elderly hypertensive patients with either nifedipine tablets or other calcium-channel blockers.

Prolonged low dose infusion of atrial natriuretic factor in essential hypertension

The C-terminal fragment of atrial natriuretic factor (ANF) was infused intravenously at 0.5 pmol/kg/min during 12 hours in 6 patients with mild to moderate essential hypertension, and in 6 normotensive volunteers, all recumbent and well hydrated, under a daily intake of 200 and 120 mmoles of sodium and potassium, respectively. Plasma C-terminal ANF tended to increase during ANF and to decrease during vehicle infusions. Plasma concentrations of the N-terminal fragment of ANF decreased by 20 to 40% (p less than 0.05) during ANF and remained unchanged following vehicle infusion, suggesting that exogenous ANF reduces endogenous ANF secretion. ANF increased significantly plasma cyclic guanosine monophosphate (p less than 0.01) from 3.1 +/- 0.4 to 4.3 +/- 0.8 and from 2.8 +/- 0.4 to 5.1 +/- 0.5 nmol/L in controls and patients respectively. ANF reduced systolic diastolic blood pressure during the last 8 hours of the infusion, by about 5% (p = 0.055) in patients, but did not alter blood pressure in controls. Sodium excretion during ANF increased 42% vs vehicle (p less than 0.05), in the patients group and remained unchanged in controls. Hematocrit levels increased significantly in both groups with ANF infusion. We conclude that a prolonged infusion of ANF at a physiological rate causes a modest increase in plasma cyclic guanosine monophosphate, hemoconcentration, and reduces endogenous ANF secretion. It also stimulates diuresis and natriuresis and slightly reduces systolic blood pressure in patients with essential hypertension.

Plasma measurements and effects of atrial natriuretic factor

The plasma levels of atrial natriuretic factor (ANF) a potent diuretic and vasoactive hormone, are reported to increase or remain unchanged in essential hypertension. There are, however, correlations between plasma ANF and both age and systolic blood pressure. Plasma ANF levels seem to be influenced by these two factors, as well as by chronic hypertension, and possibly by previous use of antihypertensive drugs. Injections or infusions of ANF produced a transient reduction of blood pressure with significant diuresis and natriuresis. In some cases, the hormone elicits bradycardia followed by hypotension. ANF infusions are also associated with an increase of plasma cyclic GMP, which is especially evident in essential hypertension and accompanied by enhanced diuresis and natriuresis, indicating a heightened response of these patients to ANF. Its therapeutic potential, however, remains to be determined by studies of longer duration with variable doses.

Effect of prolonged infusion of ANF in normotensive and hypertensive monkeys

It is now recognized that bolus and short-term infusions of atrial natriuretic factor (ANF) into different species lead to a slight and transient decrease of blood pressure, while prolonged infusions cause a significant blood pressure reduction in hypertensive but not in normotensive rats. The present study was designed to evaluate the effects of prolonged ANF infusions on blood pressure and humoral parameters in normotensive and hypertensive African green monkeys (Cercopithecus aethiops). Human-ANF infusions (100 ng/kg.hr) in conscious, normotensive vervets for a period of 48 hours evoked highly significant decreases of blood pressure (from 124/65 to 104/53 mm Hg), plasma renin activity, aldosterone, and hematocrit. This fall in blood pressure was not accompanied by an increase of plasma cGMP levels at the end of the infusion. Forty-eight hours after the infusion was terminated, the decrease in blood pressure was still significant (97/46 mm Hg), as was the drop in aldosterone. In hypertensive monkeys, systolic blood pressure declined from 175 +/- 8 to 130 +/- 8 mm Hg, while diastolic pressure fell from 117 +/- 10 to 88 +/- 4 mm Hg. These data demonstrate that the chronic infusion of ANF in both normotensive and hypertensive vervets has more profound effects than does acute bolus administration, effects that persist for a prolonged period of time after discontinuation of the infusion.

Release of atrial natriuretic factor (ANF) induced by acute airway obstruction

The aim of this study was to measure the effects of an increase in negative intrathoracic pressure on the release of ANF. With the subjects seated comfortably, 3 control blood samples were obtained over 30 minutes. Eight subjects then breathed for 30 min. through an inspiratory resistance in such a way that maximal inspiratory pleural pressures were between -30 to -40 cmH2O. Three blood samples were withdrawn after 20, 25, and 30 min., with the subject still breathing against the artificial resistance. Plasma concentrations of ANF were analysed by RIA. They measured: control value 24.6 +/- 3.7 pg ANF/mL (X +/- SE); with resistance 37.1 +/- 8.1 pg/mL (p less than or equal to .05). These results suggest that ANF could be released during an asthma attack.

Cardiovascular, renal and endocrine responses to low doses of atrial natriuretic factor in mild essential hypertension

The purpose of this study was to evaluate the cardiovascular, renal and endocrine effects of human atrial natriuretic factor (ANF), infused at a rate of 0.8 microgram/min (about 4 pmol/kg/min) for three hours in normal subjects and patients with essential hypertension. This infusion rate was chosen to obtain a range of plasma ANF levels which can be generated by physiological manoeuvres and to reduce the likelihood of hypotension. Five patients and six healthy volunteers participated in the study. The infusion had to be prematurely discontinued in one patient and in one control because of hypotension with relative bradycardia. Blood pressure otherwise remained unchanged during infusion whereas heart rate rose transiently. Plasma ANF levels increased similarly during infusion from 8.9 +/- 2.6 to 23.9 +/- 6.4 pmol/l in patients and from 3.7 +/- 0.7 to 25.4 +/- 6.9 pmol/l in the controls, remained stable during the infusion, and decreased similarly in both groups after the infusion, with a half-life of 7 min. Plasma guanosine cyclic phosphate (cGMP) was augmented by about four-fold in both groups. In both groups, plasma aldosterone levels fell whereas plasma noradrenaline increased. The diuretic effect of ANF was similar in both controls and patients (1354 +/- 161 vs 1542 +/- 116 ml/3 hrs respectively), whereas its natriuretic effect was exaggerated in hypertensive patients (90 +/- 11 vs 62 +/- 9 mmol/3 hrs, P less than 0.05). In conclusion, this low infusion rate of ANF produced similar changes in plasma ANF, cGMP, aldosterone and noradrenaline levels but patients with mild essential hypertension demonstrated an exaggerated diuretic and natriuretic response to ANF infusion.