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Biomedical subjects

R J MacFadyen

Publications and source records attributed to R J MacFadyen.

At least 55 records · Page 3Linked to original sources

Responses to an orally active renin inhibitor, remikiren (Ro 42-5892), after controlled salt depletion in humans.

The biological effects of dose-dependent inhibition of renin have rarely been extensively studied after oral (p.o.) dosing in humans. We studied remikiren (Ro42-4892), a selective renin inhibitor, in normal volunteers after activation of the renin-angiotensin system (RAS) based on salt depletion. Twelve normal men (28 +/- 9 years, 77 +/- 10 kg), comprising three consecutive dose panels of 4 subjects, received four treatments, double-blind and randomised 2 weeks apart: panel I, placebo (P), or 30, 100, and 300 mg, remikiren; panel II, placebo or 300, 600 mg, 1,000; panel III, placebo or 30, 600, and 1,000 mg. The RAS was activated by 40 mmol/day sodium diet plus frusemide (40 mg BDS), for 3 days before each study day. Data (mean +/- SD) were examined by repeated-measures analysis of variance (ANOVA). RAS activation was confirmed by 24-h urinary sodium excretion (screen, 142 +/- 74 mmol/24 h; prestudy, 66 +/- 33, 59 +/- 41, 78 +/- 4, 73 +/- 30 mmol/24 h) and increase in plasma renin activity (PRA) (screen, 0.8 +/- 0.3 ng AI/ml/h; before dosing, P, 6.5 +/- 3.1; 30 mg, 8.2 +/- 3; 100 mg, 9.4 +/- 5.7; 300 mg, 6.5 +/- 2.4; 600 mg, 5.2 +/- 2; 1,000 mg, 6.2 +/- 4.4 ng AI/ml/h).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Haemodynamic and renal responses to oral losartan potassium during salt depletion or salt repletion in normal human volunteers.

We examined the haemodynamic and renal response to oral losartan potassium (100 mg) during activation of the renin system in humans. Eight healthy volunteers followed a low-salt (40 mmol sodium) diet for 4 days on four occasions 2 weeks apart. Double-blind salt depletion was achieved by 3-day administration of frusemide (40 mg twice daily, b.i.d.) with placebo salt replacement, salt repletion by placebo frusemide (b.i.d.), and active salt replacement (100 mmol/day). On day 4, subjects received randomised double-blind placebo or losartan. Prestudy salt depletion was associated with nonsignificant decreases in serum sodium (138 +/- 2 mM), potassium (3.5 +/- 0.2 mM) and increased urea (6.5 +/- 1.1 mM), and creatinine (91 +/- 6 microM) as compared with screening. Prestudy (day 3) 24-h urinary volume was similar during deplete preparation (placebo 1.707 +/- 0.81 L, losartan 1.509 +/- 0.626 L) or deplete preparation (placebo 1.726 +/- 0.5 L, losartan 1.764 +/- 0.52 L), but sodium excretion was greater during replete preparation. Salt replete supine blood pressure (BP) profiles showed little effect of losartan (mean maximal supine BP -9 +/- 6 mm Hg) as compared with placebo (-1 +/- 4 mm Hg), with a similar relative result for erect BP. After salt depletion, losartan caused a greater response in both supine (-24 +/- 9) and erect (-33 +/- 15) BP than did placebo (supine -12 +/- 5, erect -14 +/- 9). In this protocol after salt depletion, losartan caused a transient increase in urea and creatinine (143 +/- 40 microML) 8 h after dosing as compared with placebo (105 +/- 13 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Comparison of the oral angiotensin II receptor antagonist UP 269-6 or enalapril 20 mg on blood pressure and neurohormonal effects in salt-deplete man.

We compared the response of the oral angiotensin II (Ang II) receptor antagonist (ARA) UP 269-6 with an angiotensin converting enzyme inhibitor (ACEI) enalapril 20 mg or placebo, during salt depletion in normal men. We also evaluated safety and tolerability. Sixteen healthy, normotensive male volunteers followed a standardised salt-depletion regimen for 3 days before each study day. Seven different doses of UP 269-6 (5, 10, 20, 40, 80, 120 and 180 mg) were administered double blind in a four-panel dose escalation, with enalapril and placebo randomised within each panel. Supine and erect blood pressure (BP) and heart rate (HR); serum and urinary electrolytes; plasma active renin (PAR), aldosterone, and Ang II were measured at intervals. Urinary electrolytes and aldosterone were measured for the 24 h before dosing and for 24 h after dosing. Dizziness and light-headedness on standing were reported after UP 269-6 at higher doses. Enalapril caused one episode of symptomatic postural hypotension. No other drug-related adverse events (AE) were noted. There was a dose-related decrease in supine and erect systolic and diastolic BP (SBP, DBP) with UP 269-6 at > or = 40 mg, with no change in HR. Based on the maximal decrease in mean arterial pressure (MAP), UP 269-6 at 180 mg had an effect largely comparable to that of enalapril 20 mg. There was a dose-related increase in PAR with UP 269-6. Although this was greater with UP 269-6 180 mg than with enalapril, serum and 24-h urinary aldosterone suppression was greater with enalapril than with any dose of UP 269-6.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

Elevated blood pressure during the first two hours of ambulatory blood pressure monitoring: a study comparing consecutive twenty-four-hour monitoring periods.

OBJECTIVE AND DESIGN: Ambulatory blood pressure monitoring is being used increasingly in clinical practice and hypertension research. We have noted elevated blood pressure during the initial hours of monitoring. The objective of the present study was to examine the consistency, magnitude and duration of this elevation, and to determine whether this effect causes significant differences in the mean ambulatory blood pressure monitoring values comparing the first (day 1) and second (day 2) consecutive 24-h periods of monitoring. METHODS: Fifty patients who were hypertensive based on repeated clinic readings were studied prospectively. Each underwent continuous 48-h ambulatory blood pressure monitoring with a SpaceLabs 90207 monitor. The device recorded blood pressure at 15-min intervals during the daytime (0600-2159 h) and at 30-min intervals at night-time (2200-0559 h). From these readings hourly means were calculated. Repeated-measures analysis of variance was performed to compare the hourly means of days 1 and 2. RESULTS: Repeated-measures analysis of variance indicated that a significant difference existed for both systolic and diastolic blood pressure between day 1 and day 2. Paired Student's t-test revealed that this difference occurred during the first 2 h of monitoring. The daytime blood pressure was higher on day 1 as a result of the initial elevation of blood pressure at the onset of monitoring. The initial elevation of blood pressure was present both in white-coat hypertensives and in essential hypertensives. CONCLUSION: The first 2 h of ambulatory blood pressure monitoring are associated with elevated blood pressure both in white-coat hypertensives and in essential hypertensives. This has a minor effect on mean daytime and 24-h ambulatory blood pressures. We propose that improved ambulatory blood pressure monitoring recordings would be obtained in clinical practice, and more particularly in research applications, if 26-h ambulatory blood pressure monitoring was carried out, excluding the first 2 h from the summary analyses.

Adult↗

Responses to low dose intravenous perindoprilat infusion in salt deplete/salt replete normotensive volunteers.

1. Intravenous ACE inhibitor therapy appears to have a role in the treatment of acute heart failure and early after myocardial infarction. Practical experience with intravenous administration with activation of renin is limited. We report responses to perindoprilat (Pt, 0.67 mg) or placebo (P) infused over 4 h in normotensive male volunteers (n = 12, 19-28 years, 53-77 kg) with double-blind, placebo controlled salt depletion (SD) or salt repletion (SR) as a model of the activated renin system. 2. Salt depletion caused no significant fall in serum sodium (P, 139.4 +/- 2.4; Pt, 138.3 +/- 1.9) compared with salt replete preparation (P, 139.9 +/- 1.2; Pt, 139.7 +/- 0.9) but elevation of plasma renin activity 2-3-fold. Pretreatment baseline systolic blood pressure following salt depletion (P, 121 +/- 9.3/71 +/- 7.9; Pt, 121.5 +/- 9.6/69 +/- 8.1) was higher than following salt replete preparation (P, 114 +/- 9.5/61 +/- 7.2; Pt, 116.9 +/- 6.9/67 +/- 7.2). 3. Baseline corrected supine SBP fell significantly and to a similar extent following active treatment regardless of activation of the renin system (SD, -14.6 +/- 9.5/-9.4 +/- 6.4; SR, -12 +/- 14/-10.1 +/- 6.6) compared with placebo (SD, -6.1 +/- 6/-3.7 +/- 5.6; SR, -4.7 +/- 10/-1.3 +/- 6.5). Heart rate was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Blood pressure response to the first dose of angiotensin-converting enzyme inhibitors in congestive heart failure.

Angiotensin-converting enzyme (ACE) inhibitors improve survival in heart failure and delay progression to clinical heart failure in patients with left ventricular dysfunction after myocardial infarction. Increasing numbers of older patients are being considered for such treatment. However, there are reports of excessive and prolonged decreases in blood pressure (BP) after the first dose of some ACE inhibitors. We have studied the hemodynamics, pharmacokinetics, and neurohumoral responses to the first dose of oral captopril 6.25 mg, enalapril 2.5 mg, perindopril 2.0 mg, intravenous enalaprilat 1.5 mg, and perindoprilat 1.0 mg, compared with oral or intravenous placebo in 6 parallel groups of 12 elderly patients each with moderate-to-severe (New York Heart Association classes II-IV) heart failure. Oral dosing with active drugs led to different temporal responses. After captopril, there was an early short-lived decrease in BP. Enalapril led to a later long-lasting decrease, but perindopril was not different from placebo. Intravenous enalaprilat and intravenous perindoprilat each lowered BP to a similar extent. The doses of drugs used appeared to be comparable because plasma ACE inhibition was similar following perindopril or enalapril and also comparing perindoprilat and enalaprilat. These studies indicate that oral ACE inhibitors have different profiles of acute BP changes after the first dose. The explanation is not clear, but could include physicochemical differences in the interaction between prodrug ester and diacid metabolites leading to differences in tissue distribution and local enzyme inhibition.

Aged↗

Angiotensin-converting enzyme inhibitors in heart failure: blood pressure changes after the first dose.

Angiotensin-converting enzyme (ACE) inhibitors prevent the formation of angiotensin II in the circulation and a range of tissues. ACE inhibitors not only are effective, well-tolerated antihypertensive drugs but also improve symptoms and signs in patients with congestive cardiac failure. In addition, they improve long-term survival in these latter patients. Although ACE inhibitors are relatively free of side effects in patients with heart failure, hypotension after the first dose has been reported that may lead to symptomatic renal, cardiac, or cerebral hypoperfusion. Most reports have been uncontrolled and anecdotal. We report a double-blind placebo-controlled study in a parallel group of patients with cardiac failure (New York Heart Association classes II through IV). In total, 72 patients (6 groups of 12) were studied after either placebo, captopril, 6.25 mg, enalapril, 2.5, or perindopril, 2 mg orally, enalaprilat 1.5 mg, or perindoprilat, 1.0 mg intravenously. The blood pressure responses differed between the groups, with a short-lived early fall after captopril and a long-lasting fall after enalapril, whereas perindopril was no different from placebo. There was no significant difference between the two active intravenous regimens. Plasma ACE measurements suggested that the relative doses used were at least comparable. Further studies are in progress to investigate the mechanisms underlying the differential hemodynamic responses and also to explore the clinical relevance to safety and efficacy in the management of heart failure.

Acetylcholinesterase↗

Haemodynamic and hormonal responses to losartan (DuP753/MK954) infusion during cardiac catheterization in conscious salt-deplete dogs.

1. Haemodynamic and hormonal responses to infused angiotensin II were studied in conscious salt-deplete dogs during infusion of D-glucose or losartan (DuP753/MK954). 2. Mean arterial pressure (118 +/- 13 mmHg) fell rapidly after losartan (60 min 106 +/- 18 mmHg) with a rise in heart rate (107 +/- 16 beats/min) from baseline (98 +/- 17 beats/min). Pressor responses to angiotensin II during D-glucose infusion (6 ng min-1 kg-1, 99 +/- 10 mmHg; 18 ng min-1 kg-1, 140 +/- 15 mmHg; 54 ng min-1 kg-1, 157 +/- 12 mmHg; 162 ng min-1 kg-1, 178 +/- 14 mmHg) showed a parallel shift during losartan infusion with very similar pressures in response to higher rates of angiotensin II infusion (54 ng min-1 kg-1, 108 +/- 17 mmHg; 162 ng min-1 kg-1, 138 +/- 14 mmHg; 486 ng min-1 kg-1, 155 +/- 14 mmHg; 1458 ng min-1 kg-1, 177 +/- 12 mmHg). Losartan caused a fall in baseline systemic vascular resistance. Despite the similar mean arterial pressure, the rise in systemic vascular resistance after angiotensin II during D-glucose infusion (162 ng min-1 kg-1, 8065 +/- 1967 dyn s cm-5) was reduced during losartan infusion (1458 ng min-1 kg-1, 6645 +/- 1720 dyn s cm-5. Losartan caused a small rise in cardiac output related to a rise in heart rate and increased stroke volume. Pressure infusions of angiotensin II caused a fall in cardiac output during D-glucose infusion, which was blocked during losartan infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗

Dose-ranging study of the angiotensin type I receptor antagonist losartan (DuP753/MK954), in salt-deplete normal man.

In a dose-ranging study, the angiotensin type I receptor antagonist losartan (DuP753/MK954) was administered orally to normal volunteers in whom the renin-angiotensin system (RAS) had been activated by a low sodium diet (40 mmol) and frusemide (40 mg twice daily) for 3 days before study. On the fourth day, subjects (n = 12) received placebo and three active doses (5, 10, 25, 50, or 100 mg) in a randomized, double-blind, three-panel, dose-ranging design. On the study day, 24-h urinary sodium excretion was approximately 10-20 mmol Na, with an increase in renin and aldosterone levels at baseline. Dose-dependent decreases in supine and erect blood pressures (BP) were statistically significant for 50 and 100 mg and were associated with a modest increase in supine heart rate (HR) at the higher dose. The peak BP decreases observed suggested that the highest dose studied (100 mg) was not necessarily the maximal response. Active treatments caused no increase in the sodium loss on the study day. Renin was significantly increased by doses > 10 mg in a dose-dependent fashion but there was little change in plasma aldosterone profile. Increase in renin was evident at doses (10 mg) below those significantly affecting overall BP (50 mg). Adverse symptoms were uncommon and limited to postural lightheadedness which was largely dose related. Our results indicate a BP and plasma renin dose-response relation for the orally active angiotensin II (AII) receptor blocker losartan in normotensive subjects with an activated RAS.

Adult↗

Haemodynamic and hormonal responses to oral enalapril in salt depleted normotensive man.

A combination of dietary sodium restriction (40 mmol day-1) and frusemide pretreatment has been used to activate the renin angiotensin system (RAS) in order to characterise the haemodynamic and hormonal responses to enalapril in young normotensives. Enalapril significantly reduced supine blood pressure with a mean maximum fall of 19 +/- 7.6, compared with 6.5 +/- 6.8 mm Hg with placebo. Similar but greater responses were seen in erect blood pressure. Mean maximal plasma ACE inhibition (78 +/- 5.7%) was associated with a significant increase in PRA from 5.2 +/- 2.1 ngAI ml-1 h-1 to a peak of 29.1 +/- 6 ngAI ml-1 h-1. This simple well tolerated regimen produced consistent RAS activation and gave readily measurable falls in blood pressure following enalapril. This model may be used to undertake detailed assessments of ACE inhibition, renin inhibition and angiotensin receptor blockade.

Analysis of Variance↗

Double blind controlled study of low dose intravenous perindoprilat or enalaprilat infusion in elderly patients with heart failure.

OBJECTIVE: Comparison of the first dose responses to low dose constant rate infusions of diacid angiotensin converting enzyme (ACE) inhibitors. DESIGN: Double blind, randomised, placebo controlled, parallel group prospective study. SETTING: General hospital inpatient admissions for supervised diuretic withdrawal (24-48 hours) and the introduction of ACE inhibitor treatment. PATIENTS: 36 unselected elderly (aged 60-87 years) patients with symptomatic but stable chronic cardiac failure (New York Heart Association grades II-IV). ACE inhibitor started under double blind conditions with blood pressure monitoring. INTERVENTION: Patients were randomly allocated to receive intravenous placebo (saline), enalaprilat (1.5 mg over six hours) or perindoprilat (1 mg over six hours) by constant rate intravenous infusion (5 ml/hour). The protocol allowed for discontinuation of infusion if mean arterial blood pressure fell by 30% from the value before treatment. MAIN OUTCOME MEASURES: Blood pressure and heart rate responses, drug concentration, plasma renin, and ACE activities. RESULTS: The three groups had similar age, severity of heart failure, diuretic dose before treatment, plasma renin activity, and serum electrolyte state. All patients remained symptom free throughout the study. Infusions were only ended early with active treatment: 5/12 perindoprilat cases, (mean (SD) dose 0.88 (0.18) mg, and 5/12 enalaprilat cases (mean (SD) dose 1.2 (0.4) mg. Both active treatments lowered mean arterial pressure until discontinuation of infusion. Heart rate was not altered. Two patients (one perindoprilat, one enalaprilat) showed transient and symptom free renal impairment. CONCLUSIONS: Slow intravenous infusion of diacid ACE inhibitors may allow safe initiation of treatment in patients with heart failure and with activated renin angiotensin systems. The similar effects of intravenous perindoprilat and enalaprilat on blood pressure contrast with previously reported differences when perindopril and enalapril were given orally.

Aged↗

Role of the circulating and tissue-based renin-angiotensin system in the development of heart failure: implications for therapy.

The renin-angiotensin system (RAS) is believed to play a central role in the pathophysiology of heart failure. However, there is a wide variability in plasma renin levels in patients with heart failure, and normal plasma renin activity has been documented in patients with mild or compensated disease. Recent evidence has demonstrated the existence of endogenous RAS in a number of tissues associated with cardiovascular homeostasis. It is possible that these tissue RAS are activated in the early stages of heart failure when plasma renin activity is normal, and therefore contribute to the progression of this condition. Angiotensin-converting enzyme (ACE) inhibitors reduce both circulating and tissue RAS activity. They are of symptomatic benefit and reduce the mortality associated with heart failure. A number of large studies initiated to investigate the effects of the ACE inhibitor enalapril in patients with all degrees of heart failure have been published recently. These studies show that addition of this drug to therapy significantly decreases patient morbidity and mortality, an effect which is most likely due to the suppression of circulating and tissue RAS activity this agent affords. The relationship of the profile of hormonal suppression seen with enalapril and drug dosage to observed beneficial effects on morbidity or mortality is unclear. Given the large range of alternative ACE inhibitors available, their variable structure, potency and duration of action, the potential for differences between agents needs further consideration. Although direct comparative studies are rare, there is a body of work suggesting that such differentiation may be present and may be of clinical significance.

Angiotensin-Converting Enzyme Inhibitors↗

Enalapril clinical pharmacokinetics and pharmacokinetic-pharmacodynamic relationships. An overview.

The conventional pharmacokinetic profile of the angiotensin converting enzyme (ACE) inhibitor, enalapril, is a lipid-soluble and relatively inactive prodrug with good oral absorption (60 to 70%), a rapid peak plasma concentration (1 hour) and rapid clearance (undetectable by 4 hours) by de-esterification in the liver to a primary active diacid metabolite, enalaprilat. Peak plasma enalaprilat concentrations occur 2 to 4 hours after oral enalapril administration. Elimination thereafter is biphasic, with an initial phase which reflects renal filtration (elimination half-life 2 to 6 hours) and a subsequent prolonged phase (elimination half-life 36 hours), the latter representing equilibration of drug from tissue distribution sites. The prolonged phase does not contribute to drug accumulation on repeated administration but is thought to be of pharmacological significance in mediating drug effects. Renal impairment [particularly creatinine clearance < 20 ml/min (< 1.2 L/h)] results in significant accumulation of enalaprilat and necessitates dosage reduction. Accumulation is probably the cause of reduced elimination in healthy elderly individuals and in patients with concomitant diabetes, hypertension and heart failure. Conventional pharmacokinetic approaches have recently been extended by more detailed descriptions of the nonlinear binding of enalaprilat to ACE in plasma and tissue sites. As a result of these new approaches, there have been significant improvements in the characterisation of concentration-time profiles for single-dose administration and the translation to steady-state. Such improvements have further importance for the accurate integration of the pharmacokinetic and pharmacodynamic responses to enalapril(at) in a concentration-effect model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Role of angiotensin in the extravascular system.

Angiotensin receptors are present in many tissue types, including adrenal cortex, renal glomeruli, heart, hypothalamus, liver, pancreas, pituitary, platelets, renal tubules, uterus and vascular smooth muscle. Two high-affinity receptor subtypes have been identified by radioligand binding with antagonists: losartan (DuP 753/MK954) identifies AT1 receptors; PD123177 and CGP42112A are markers for AT2 receptors. Angiotensin II may be produced locally in tissues outside the humoral system. For example, it is found in the brain, kidney and heart. Within the brain, the heptapeptide angiotensin(1-7) mimics some effects of angiotensin II, but may be formed directly from angiotensin I. Evidence for non-ACE-mediated angiotensin II production has been reported in the heart. Intravascular angiotensin II receptors are implicated in the central release of vasopressin and other hypophyseal hormones, in increasing sympathetic outflow, in the thirst response and, possibly, in cognitive function; in the inotropic and chronotropic effects of angiotensin II on the heart as well as in growth/hypertrophy; in the control of aldosterone release and in the balance between cortisol and aldosterone secretion; and in modulating sodium, chloride and bicarbonate transport within the kidney. Effects on the reproductive system, liver and pancreas have not been established. The pharmacological effects of angiotensin II antagonists will depend on their distribution characteristics as well as affinity for specific receptor subtypes. At present, however, the physiological role of AT2 receptors has not been defined.

Angiotensin II↗

Effects of the angiotensin II receptor antagonist Losartan (DuP 753/MK 954) on arterial blood pressure, heart rate, plasma concentrations of angiotensin II and renin and the pressor response to infused angiotensin II in the salt-deplete dog.

1. The blood pressure, heart rate, hormonal and pressor responses to constant rate infusion of various doses of the angiotensin (type 1) receptor antagonist Losartan (DuP 753/MK 954) were studied in the conscious salt-deplete dog. 2. Doses in the range 0.1-3 micrograms min-1 kg-1 caused no change in blood pressure, heart rate or pressor response to angiotensin II (54 ng min-1 kg-1), and a dose of 10 micrograms min-1 kg-1 had no effect on blood pressure, but caused a small fall in the pressor response to angiotensin II. Infusion of Losartan at 30 micrograms min-1 kg-1 for 3 h caused a fall in mean blood arterial pressure from baseline (110.9 +/- 11.2 to 95.0 +/- 12.8 mmHg) and a rise in heart rate (from 84.6 +/- 15.1 to 103 +/- 15.2 beats/min). Baseline plasma angiotensin II (42.5 +/- 11.8 pg/ml) and renin (64.5 +/- 92.7 mu-units/ml) concentrations were already elevated in response to salt depletion and rose significantly after Losartan infusion to reach a plateau by 70 min. The rise in mean arterial blood pressure after a test infusion of angiotensin II (35.3 +/- 11.6 mmHg) was reduced at 15 min (11.8 +/- 6.8 mmHg) by Losartan and fell progressively with continued infusion (3 h, 4.3 +/- 3.3 mmHg). The peak plasma angiotensin II concentration during infusion of angiotensin II was unaffected by Losartan, but the rise in plasma angiotensin II concentration during infusion was reduced because of the elevated background concentration. Noradrenaline infusion caused a dose-related rise in mean blood arterial pressure (1000 ng min-1 kg-1, +19.9 +/- 8 mmHg; 2000 ng min-1 kg-1, +52.8 +/- 13.9 mmHg) with a fall in heart rate (1000 ng min-1 kg-1, -27.9 +/- 11.5 beats/min; 2000 ng min-1 kg-1, -31.2 +/- 17.3 beats/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗