Isotope renography in the investigation of renal artery stenosis in hypertensive patients

Isotope renography is a commonly used investigation for the detection of renal artery stenosis (RAS) in hypertensive patients, although its predictive accuracy is poor in an unselected population with a low prevalence of RAS. The aim of the present study was to identify characteristics of hypertensive patients that raise the clinical suspicion of underlying RAS, and which are predictive of an abnormal isotope renogram. The characteristics of 75 patients who had undergone either conventional or ACE-inhibitor-enhanced renography were retrospectively assessed and correlated with the renogram results. The presence of a raised serum creatinine, severe systolic hypertension at presentation and the requirement for triple drug therapy best predicted abnormalities on renography. However, it would appear that the false-positive rate of this investigation is high and its predictive accuracy is poor even in a highly selected group of patients. We conclude that isotope renography is of no practical value in the screening of hypertensive patients for RAS. Renal angiography remains the investigation of choice.

The economic evaluation of antibiotic therapy: relevance to urinary tract infection

Economic analyses of health care interventions can be performed with various levels of sophistication but all aid in decision-making processes which determine funding priorities. Pharmacoeconomics is the application of health economic techniques to the evaluation of drug therapy. In this article the pharmacoeconomic principles underlying the rational choice of an antibiotic for the treatment of urinary tract infections are discussed. Examples of pharmacoeconomic, adverse reaction and non-compliance studies are quoted to illustrate these principles. Efficacy and freedom from adverse effects are the principal determinants of favourable cost-effectiveness ratios, rather than antibiotic costs alone. Doctors should bear this in mind when choosing drugs to treat urinary tract infection.

Left ventricular hypertrophy in hypertension--general and local trends in diagnosis and therapy

LVH is a frequent echocardiographic finding in the general population but it should be regarded as an ominous predictor of future cardiovascular events rather than an innocent compensatory phenomenon. Echocardiography is the most sensitive and specific method for its detection but the ECG should not be regarded as superfluous since additional prognostic information and information about coexisting myocardial damage is present. The decreasing prevalence of LVH suggests that LVH can be prevented by control of hypertension and prevention of weight gain. Once LVH is present then antihypertensive drugs, weight reduction or salt restriction may promote its reversal, with early studies demonstrating associated improvement in mortality and morbidity.

Primary non-compliance with prescribed medication in primary care

OBJECTIVE

To determine the rate of patients not redeeming their prescriptions (primary noncompliance) and assess the factors influencing this.

DESIGN

Observational study comparing copies of prescriptions written by general practitioners with those dispensed by pharmacists and subsequent case record review.

SETTING

A large rural general practice in Tayside.

SUBJECTS

All 4854 patients who received prescriptions (20,921) written between January 1989 and March 1989.

MAIN OUTCOME MEASURES

The rate of non-redemption of prescriptions.

RESULTS

Seven hundred and two patients (14.5%) did not redeem 1072 (5.2%) prescriptions during the study period, amounting to 11.5% of men and 16.3% of women. Non-redemption was highest in women aged 16-29 (27.6% of women) and men aged 40-49 (18.3% of men). Of prescriptions issued to women for oral contraceptives 24.8% were not redeemed during the study period. In those who redeemed prescriptions 17% were not exempt from prescription charges compared with 33% of patients who failed to redeem them. The non-redemption rate was highest for prescriptions issued at the weekends, although this was a small proportion of all prescribing. Prescriptions issued by trainee general practitioners were also less likely to be redeemed.

CONCLUSIONS

Non-redemption varies with age, sex, general practitioner, exemption status, and with day of the week the prescription was written. Observational studies of drug exposure can be more accurately estimated from dispensing rather than prescribing data.

The risks of symptomatic vaginal candidiasis after oral antibiotic therapy

It is generally accepted that antibiotic use can result in vaginal fungal overgrowth, although evidence estimating the extent to which this causes symptomatic vaginitis is scant. In a study using the prescription of vaginal antifungal preparations as a surrogate measure of vaginal candidiasis, a cohort of women taking antibiotics had a higher incidence of vaginal candidiasis after antibiotic exposure than beforehand (relative risk 2.3; 95% confidence interval 1.9-3.0); this risk was highest in those aged 36-40 years (RR 6.0, 95% CI 2.9-12.5). The attributable risk was highest among those who were taking cephalosporins (AR 12.8%, 95% CI 9.1-16.5). In a case-control study, comparing previous antibiotic exposure among women using vaginal antifungal agents and matched controls, antibiotic exposure was higher among those using vaginal antifungal agents during the previous 28 days, with an odds ratio of 5.5 (95% CI 3.8-7.9).

Echocardiography in chronic heart failure in the community

A total of 128 patients from a single practice population who were receiving loop diuretics for treatment of presumptive cardiac failure were identified from prescribing data captured by the Medicines Monitoring Unit. A subgroup of 78 patients underwent echocardiography to determine the prevalence of true left ventricular systolic dysfunction in this population and the validity of the diagnosis of cardiac failure in primary care. A further 50 patients were studied to assess the workload generated by these patients for both primary health care and hospital services. The estimated prevalence of left ventricular systolic dysfunction was 0.84%, whereas 1.6% of the population received loop diuretics for this indication. A false-positive diagnosis occurred in 47% and was more likely in females (73%) than males (37%). Of all consultations 79% were seen by GPs, 14% as hospital out-patients and 7% as in-patients. Within the hospital general physicians have most contact with these patients. In summary chronic heart failure is common within the community, although the false-positive rate for diagnosis of this condition is high. GPs and general physicians treat the majority of these patients and should therefore receive continuing education regarding recent advances in this area. Echocardiography should be performed early in the management of all patients suspected of having cardiac failure.

Decreased cardiac parasympathetic activity in chronic heart failure and its relation to left ventricular function

BACKGROUND

Activation of the sympathetic nervous system has been extensively studied in patients with chronic heart failure, but the parasympathetic nervous system has received relatively little attention. The objective in this study was to investigate cardiac parasympathetic activity in chronic heart failure and to explore its relation to left ventricular function.

METHODS

Heart rate variability was measured from 24 hour ambulatory electrocardiograms by counting the number of times each RR interval exceeded the preceding RR interval by more than 50 ms (counts). This method provided a sensitive index of cardiac parasympathetic activity.

RESULTS

Mean (range) of counts were: waking 48 (1-275)/h, sleeping 62 (0-360)/h, and total 1310 (31-7278)/24 h. These were lower than expected, and in 26 (60%) of the 43 patients counts fell below the lower 95% confidence intervals (95% CI) for RR counts in normal subjects. A significant correlation between total 24 hour RR counts and left ventricular ejection fraction was present (r = 0.49, p less than 0.05).

CONCLUSIONS

These results indicate that most patients with chronic heart failure have reduced heart rate variability and therefore reduced cardiac parasympathetic activity. The degree of parasympathetic dysfunction is related to the severity of left ventricular dysfunction. This may be relevant to the high incidence of ventricular arrhythmias and poor prognosis of patients with chronic heart failure.

Caffeine restriction: effect on mild hypertension

OBJECTIVE

To determine the effects on blood pressure of modifying dietary caffeine intake in patients with mild and borderline hypertension by monitoring ambulatory and clinic blood pressure.

DESIGN

Four way, randomised, crossover trial of four consecutive two week dietary regimens: normal diet, caffeine free diet alone, caffeine free diet with decaffeinated instant coffee, caffeine free diet with caffeinated instant coffee (instant coffee phases conducted double blind).

SETTING

Hospital hypertension clinic, Scotland.

PATIENTS

52 patients (23 men; aged 26-67 years) with untreated borderline or mild hypertension (diastolic blood pressure 90-105 mm Hg) who normally drank a minimum of three cups of coffee daily.

MAIN OUTCOME MEASURES

Mean ambulatory blood pressure over 24 hours; mean morning, daytime, and night time ambulatory blood pressure; sitting clinic blood pressure at 1700; plasma caffeine concentration at 1700 on the last day of each regimen.

RESULTS

Mean 24 hour ambulatory blood pressure was not different between regimens. There was no difference in blood pressure variability between regimens. During the caffeine free diet alone morning ambulatory diastolic blood pressure was higher (2.8 mm Hg) than during the caffeine free diet with caffeinated coffee. Mean sitting clinic systolic blood pressure was higher at 1700 (4.7 mm Hg) with a caffeine free diet than with the caffeine free diet with caffeinated coffee (p less than 0.05). Dietary compliance as assessed by plasma caffeine concentration was excellent. There was no significant correlation between plasma caffeine concentration and blood pressure.

CONCLUSIONS

Drinking caffeinated instant coffee over a two week period does not adversely influence blood pressure in patients with borderline or mild hypertension; abstinence is of no benefit.

Disposition of gamma-glutamyl levodopa (gludopa) after intravenous bolus injection in healthy volunteers

1. The pharmacokinetics of gludopa in healthy volunteers were studied at two doses, 250 micrograms kg-1 and 100 micrograms kg-1, after rapid intravenous bolus injection. 2. Gludopa had a clearance of 4.43 +/- 1.50 ml min-1 kg-1 and 4.92 ml min-1 kg-1 at the higher and lower doses, respectively. Corresponding half-lives were 29.2 +/- 3.7 min and 32.5 +/- 5.6 min, and volumes of distribution were 0.183 +/- 0.052 l kg-1 and 0.235 +/- 0.07/ l kg-1. 3. Urinary excretion of dopamine rose sharply after injection of gludopa at both doses, peaking at 30 min. At this time, amounts were over 215 and 60 times baseline values at the higher and lower dose of gludopa, respectively. Urinary dopamine rose in parallel with urinary levodopa excretion, supporting the view that levodopa is the precursor of urinary dopamine. 4. Less than 1% of the injected dose of gludopa was excreted unchanged in the urine. 5. These findings suggest that, in man, gludopa is an efficient pro-drug for dopamine. Gludopa may find therapeutic use in conditions where the beneficial renal effects of dopamine may be indicated.

Metoclopramide, domperidone and dopamine in man: actions and interactions

The effects of oral doses of the dopamine antagonist antiemetics metoclopramide and domperidone on baseline and dopamine stimulated renal function and systemic haemodynamics were assessed in a placebo controlled crossover study in 9 healthy volunteers. Metoclopramide did not change baseline ERPF, GFR or FF over 2 h post dosing but it significantly reduced baseline UNaV, UKV, urine flow, urinary dopamine excretion, supine and erect diastolic blood pressure and supine systolic blood pressure. Domperidone and placebo did not cause these effects. Metoclopramide caused a marked rise and domperidone a small fall in plasma aldosterone concentration (PAC) but placebo was without effect. Neither antiemetic altered plasma renin activity (PRA) but a small fall occurred with placebo. Two hours after pretreatment with placebo dopamine (2 micrograms/kg/min) increased effective renal plasma flow (ERPF), glomerular filtration rate (GFR), sodium excretion rate (UNaV), urine flow rate, urinary dopamine excretion rate, supine systolic blood pressure and supine and erect pulse rate and decreased the potassium excretion rate (UKV), filtration fraction (FF) and supine diastolic blood pressure. Metoclopramide pretreatment, did not attenuate the dopamine induced rise in ERPF, GFR, urine flow, urinary dopamine excretion or supine systolic blood pressure but it did attenuate the rise in pulse rate, the fall in diastolic pressure, and the antikaliuretic effect of dopamine leading to a net kaliuresis when compared to placebo. Domperidone was similar to placebo. Neither metoclopramide nor domperidone given orally caused clinically important antagonism of the renal haemodynamic effects of dopamine. However the effects of metoclopramide on blood pressure and electrolyte excretion may have clinical importance.(ABSTRACT TRUNCATED AT 250 WORDS)

A single dose study of the effects of fenoldopam and enalapril in mild hypertension

To clarify the contribution made by the renin-angiotensin system activation to the short lived hypotensive response to fenoldopam, the haemodynamic effects of a combination of fenoldopam (100 mg) and enalapril (5 mg) were compared with fenoldopam alone, enalapril alone and placebo in a balanced, randomised, double blind, single dose study in eight hypertensive patients. Fenoldopam caused an acute fall in blood pressure which lasted approximately 3 h after dosing and was associated with a reflex tachycardia. Enalapril caused a more gradual fall in blood pressure (onset 2 h) without a reflex tachycardia. The combination of drugs produced greater reductions in blood pressure sustained for a longer period than fenoldopam alone and with a more rapid onset than enalapril alone. In combination the hypotensive effects of fenoldopam and enalapril were clearly additive and not synergistic. Activation of the renin-angiotensin system does not antagonise significantly the hypotensive effect of fenoldopam.

The pharmacokinetics of gamma-glutamyl-L-dopa in normal and anephric rats and rats with glycerol-induced acute renal failure

1. The pharmacokinetics of gamma-glutamyl-L-dopa (gludopa) and its metabolite, L-dopa, have been studied in normal rats at three dose levels of gludopa: 2 mg kg-1, 5 mg kg-1 and 7.5 mg kg-1. The extent of metabolism in normal rats, and the pharmacokinetics in anephric rats and rats with glycerol-induced acute renal failure (ARF) were also studied at a gludopa dose of 2 mg kg-1. 2. Gludopa was extensively metabolised to L-dopa with only about 10% of an injected dose being excreted unchanged. Normal rats had a rapid gludopa clearance of 50.9 +/- 9.6 ml min-1 kg-1 and elimination rate constant of 2.99 +/- 0.27 h-1. The mean residence time and half-life were 20.9 +/- 1.4 and 14.4 +/- 1.0 min, respectively. The apparent volume of distribution at steady state was 1.05 +/- 0.18 l kg-1. 3. No statistically significant differences were found in the main pharmacokinetic parameters between ARF and controls for either gludopa or its metabolite L-dopa. 4. In anephric rats and controls the kidneys were found to contribute about 68.5% and 67.2% to the elimination of gludopa and the metabolite L-dopa, respectively. 5. These results confirm that gludopa is an efficient pro-drug for L-dopa, and that the kidneys are the major site of gludopa metabolism. It seems likely that the renal specificity of gludopa persists in ARF.

Bench and ambulatory field evaluation of the A & D TM-2420 automated sphygmomanometer

Adequate evaluation of automated sphygmomanometers, in terms of safety, accuracy, mechanical reliability, patient acceptability and ability to record ambulatory blood pressure is essential before these devices are used in clinical practice and in clinical trials. We have evaluated the accuracy and performance of the A & D TM-2420 automated sphygmomanometer, an auscultatory device designed for ambulatory blood pressure recording. Four devices were tested for accuracy by simultaneous comparison against two experienced observers using standard mercury column sphygmomanometers. Two of these devices developed faults that precluded complete evaluation. One of the remaining devices met and one failed to meet the somewhat liberal criteria for accuracy recommended by the American Association for the Advancement of Medical Instrumentation, the current standard for evaluation (mean difference of less than or equal to 5 mmHg and standard deviation of differences less than or equal to 8 mmHg). The mean differences (standard deviation of differences) between observers for simultaneous triplicate observations of systolic/diastolic pressure in 50 subjects, including 35 hypertensives, were 0.8 (3.0)/-0.6 (2.4) mmHg. In comparison, the differences between each device and each observer were: device 11, observer 1, -6.4 (5.4)/-6.3 (9.9); device 11, observer 2, -5.6 (4.7)/-7.0 (10.4); device 12, observer 1, -4.9 (5.2)/-4.0 (7.5); device 12, observer 2, -4.1 (4.9)/- -4.5 (7.7) mmHg. Ambulatory trials were carried out with a further 10 devices. Of these, seven developed faults requiring their return to the supplier. Numerous additional problems were encountered with microphones, cuffs, leads and connections, the processing unit, error algorithms and data-handling software. The device was not capable of making truly ambulatory recordings. We do not confirm the previously favourable, but limited, evaluation of this device. We stress the vital importance of subjecting a number of devices to benchtesting for accuracy, and the need to undertake extensive 'field' testing before any devices can be considered suitable for ambulatory recording. Exercise testing under laboratory conditions is not an adequate substitue for true ambulatory evaluation.

Effect of prolonged intravenous infusion of gludopa in humans and a preliminary study of its oral bioavailability

Intravenous infusion of gamma-glutamyl-L-dopa (25 micrograms/kg/min) for 10 h in normal humans caused a natriuresis of 46.5 mmol of sodium without an increase in plasma renin activity and was associated with small but significant falls in blood pressure. In a second study the oral bioavailability of gludopa was estimated in normal subjects and found to be low (less than 2%). The increase in urine dopamine excretion and the natriuretic effect of gludopa were much larger after intravenous infusion than oral dosing.

An evaluation of the A&D UA-751 semi-automated cuff-oscillometric sphygmomanometer

We compared blood pressure recordings made with the A&D UA-751 semi-automated cuff-oscillometric sphygmomanometer (A&D Co. Ltd, Tokyo, Japan) and with a conventional Hawksley random-zero mercury sphygmomanometer (Hawksley and Sons Ltd, Lancing, UK). Simultaneous single-arm recordings were obtained in duplicate with both devices in 200 subjects having blood pressure in the ranges 92-221/51-121 mmHg. The measurements obtained by three observers using the Hawksley sphygmomanometer were compared with recordings from two A&D UA-751 devices. In most cases, there was an acceptable level of agreement between the results, according to the criteria suggested by the Association for the Advancement of Medical Instrumentation (range of differences systolic: mean - 0.9 to 1.4 mmHg, s.d. 4.6-9.8 mmHg; diastolic: mean - 0.6 to 1.3 mmHg, s.d. 2.9-5.1 mmHg), although there were sizeable discrepancies in individual subjects. Thus the A&D UA-751 device appears to be an acceptable alternative to a conventional sphygmomanometer; it should be suitable for routine clinical and limited research use, including intermittent home blood pressure recording.

A preliminary study of the dopamine DA1 agonist fenoldopam in the treatment of chronic left ventricular failure due to ischaemic heart disease

The effects of chronic oral fenoldopam in the treatment of NYHA grade II-III heart failure secondary to ischaemic heart disease, were studied in a placebo controlled, double blind, randomised, parallel group fashion in 20 patients. Nine patients taking placebo and six taking fenoldopam completed the study. Adverse events were similar in each group. There were no significant changes in exercise capacity, ejection fraction, body weight or symptom questionnaires with either treatment. This preliminary study has not revealed any benefit of fenoldopam in heart failure due to ischaemic heart disease.

Frusemide, ACE inhibition, renal dopamine and prostaglandins: acute interactions in normal man

1. The acute effects of intravenous frusemide (30 mg) on prostaglandin dependent renal haemodynamics, urinary prostaglandin excretion, urinary dopamine excretion and electrolyte excretion were studied in six salt replete healthy volunteers with and without pretreatment with the angiotensin converting enzyme (ACE) inhibitor, ramipril (5 mg) and compared with the effects of ramipril alone in order to clarify the role of the renin-angiotensin system in these responses. 2. Frusemide increased natriuresis (UNaV), kaliuresis (UKV), inulin clearance and plasma renin activity (PRA) and ramipril pretreatment significantly enhanced these effects suggesting that the acute generation of angiotensin II (AII) may attenuate these actions of intravenous frusemide. 3. Frusemide increased para-aminohippurate (PAH) clearance, osmolar clearance and urine flow but did not change filtration fraction or urinary kallikrein excretion. Pretreatment with ramipril did not affect these responses. 4. Frusemide increased the excretion of urinary PGE2 and 6-keto-PGF1 alpha. Ramipril pretreatment did not suppress this rise in prostaglandin excretion. Since the frusemide induced prostaglandin dependent renal haemodynamic changes were also not suppressed with ACE inhibition, this suggests that in salt-replete volunteers AII does not significantly modulate renal prostaglandin production after frusemide. 5. Urinary free dopamine excretion increased with frusemide alone. With ramipril pretreatment this rise showed a tendency to increase. AII may therefore inhibit the rise in urinary dopamine excretion after frusemide. However this requires further study.

The renal and haemodynamic effects of a 10 h infusion of glutamyl-L-dopa in normal man

1. gamma-L-glutamyl-L-dopa (gludopa) and placebo were given by intravenous infusion to 12 healthy salt replete men for 10 h in a single-blind randomised fashion. 2. Gludopa caused a cumulative natriuresis of 46.5 mmol compared with placebo with a biphasic pattern and this was associated with a small reduction in body weight. 3. A small fall in arterial blood pressure and rise in pulse rate was seen with gludopa. 4. Plasma renin activity, atrial natriuretic peptide and urine kallikrein excretion were unchanged by gludopa but a small fall in urine aldosterone excretion, urine flow rate and free water clearance occurred. 5. The renal effects of gludopa are modest and last for only a few hours after the start of infusion.

The renal effects of atrial natriuretic peptide in man are not attenuated by (+)-sulpiride

1. Human alpha atrial natriuretic peptide (ANP) was infused intravenously for 1 h in eight healthy salt-replete men on two occasions, with and without pretreatment with (+)-sulpiride. 2. ANP increased sodium excretion and urine flow rate but did not alter blood pressure or plasma renin activity. 3. (+)-sulpiride had no significant effect on baseline creatinine clearance, sodium excretion or urine flow rate and did not alter the increases in these parameters with ANP. 4. It is unlikely that the renal effects of ANP are mediated by dopamine DA1-receptors in man.

The effect of carbidopa and lithium on the systemic and renal response to acute intravenous saline loading in normal man

To assess a possible role for endogenous renal dopamine in sodium excretion, the dopa decarboxylase inhibitor carbidopa was given during intravenous salt loading. In addition, the effect of lithium on tubular sodium handling was separately determined. Nine males were studied randomly on three occasions, receiving placebo, lithium carbonate (1000 mg, 11 h prior to study) or carbidopa (100 mg x 2). On each day a baseline period was followed by infusion of isotonic saline (20 ml/kg per hour) over 3 h, and 6 h recovery. With placebo, sodium excretion increased markedly to a peak in the hour after infusion (0.15 +/- 0.03 to 0.73 +/- 0.12 mmol/min, P less than 0.01). Urine dopamine excretion increased modestly (1.33 +/- 0.12 to 1.67 +/- 0.13 mmol/min, P less than 0.01). Carbidopa effectively blocked dopamine output during the study. However, the natriuretic response was comparable to values on placebo at all time points. Fractional lithium clearance, a proposed measure of proximal tubular fluid rejection, increased significantly during saline infusion. However, baseline sodium excretion was greater in the presence of lithium, and plasma renin activity (PRA) was significantly elevated. In addition, the peak natriuretic response was smaller and cumulative sodium excretion reduced by 40% (P less than 0.01) compared to placebo. This study provides no evidence for a facilitatory role for dopamine in the natriuretic response to intravenous salt loading. Lithium, at subtherapeutic levels, cannot be presumed to be an inert marker, and clearance data must be interpreted with caution.

The effect of carbidopa and indomethacin on the renal response to gamma-L-glutamyl-L-dopa in normal man

1. The renal response to gamma-L-glutamyl-L-dopa (gludopa, 25 micrograms kg-1 min-1) was investigated in seven normal male volunteers. The effects of oral carbidopa (100 mg) and indomethacin (100 mg) on the response to gludopa were studied in the same group. 2. Gludopa at this dose level produced a 900-fold increase in urine dopamine excretion and caused a natriuresis and suppression of plasma renin activity with only minor effects on pulse rate and blood pressure. 3. Carbidopa inhibited the increase in dopamine excretion by 97% and abolished the renal actions of gludopa. 4. The increase in urine dopamine produced by gludopa was not altered by indomethacin and the urine sodium output was similar to that caused by gludopa alone. 5. Gludopa is an effective renal dopamine prodrug whose activity can be blocked by the dopa decarboxylase inhibitor carbidopa. The results with indomethacin suggest that dopamine and the prostaglandins form separate natriuretic systems in the kidney.

(+)-sulpiride antagonises the renal effects of gamma-L-glutamyl-L-dopa in man

1. gamma-L-glutamyl-L-dopa (gludopa) was given by intravenous infusion to six healthy salt-replete men on two occasions, with and without pretreatment with (+)-sulpiride. 2. Gludopa increased sodium excretion, glomerular filtration rate and effective renal plasma flow whilst decreasing plasma renin activity. 3. (+)-sulpiride had no significant effect on baseline natriuresis, renal haemodynamics or plasma renin activity, but significantly attenuated the rise in sodium excretion, glomerular filtration rate and effective renal plasma flow produced by gludopa. 4. (+)-sulpiride abolished the acute fall in plasma renin activity seen with gludopa. 5. (+)-sulpiride raised serum prolactin concentration but did not affect the ris in urine dopamine excretion rate caused by gludopa. 6. Gludopa exerts its renal effects by stimulating specific dopamine receptors which are principally of the DA1 subtype.

A comparison of the renal actions of gamma-L-glutamyl-L-dopa and gamma-L-glutamyl-L-tyrosine in normal man

1. The renal responses to the dipeptides gamma-L-glutamyl-L-dopa (gludopa) and gamma-L-glutamyl-L-tyrosine (glutyrosine) were compared when given intravenously in six normal male volunteers. 2. Gludopa is natriuretic and diuretic at a dose of 25 micrograms min-1 kg-1. At the same dose, glutyrosine had no effect on the volume or sodium content of the urine. 3. There was a 400-600-fold increase in urine dopamine output after gludopa; there was no conversion of glutyrosine to dopamine. 4. Gludopa significantly inhibited plasma renin activity, whereas with glutyrosine there was a non-significant increase. 5. Gludopa is a potent pro-drug for renal dopamine production and exerts natriuretic and hormonal effects. Glutyrosine appears to be inactive. The results support the contention that circulating L-dopa is the important physiological precursor for renal dopamine.