Effect of metoclopramide on plasma catecholamine release in essential hypertension

The catecholamine (CA)-releasing action of metoclopramide (MCP) observed in patients with pheochromocytoma was tested in 20 subjects with essential hypertension and compared with the same effect of glucagon in 10 of them. We found that even in the absence of pheochromocytoma, MCP is a CA-releasing substance, moderately increasing systolic blood pressure and pulse rate. The release of CA is reflected by an increase in concentrations of free norepinephrine and total (free plus sulfated) epinephrine 3 minutes and of total dopamine and norepinephrine 10 minutes after the MCP bolus dose, whereas glucagon had an effect on the release of free epinephrine. Regional catheterization before and after MCP dosing in one subject showed a considerable increase in adrenal epinephrine and norepinephrine concentrations 45 seconds after the MCP bolus dose. MCP has a free CA-releasing potency much like that of glucagon. Because the released free CA is readily sulfoconjugated, the effect on CA release can be more easily detected when conjugated CA is determined. MCP should thus be used with caution in pheochromocytoma as well as in other forms of hypertension.

Hydrochlorothiazide-amiloride versus hydrochlorothiazide alone for essential hypertension: effects on blood pressure and serum potassium level

In a double-blind randomized controlled trial the effects on the blood pressure and the serum potassium concentration of hydrochlorothiazide-amiloride hydrochloride (Moduret) and hydrochlorothiazide alone were compared in 266 adults who were normokalemic and had a diastolic blood pressure greater than 95 mm Hg at the time of entry into the study. The mean ages (52.2 and 53.8 years) and the proportions of men (66% and 56%) in the groups given the combination drug and hydrochlorothiazide alone respectively were similar. In the group given the combination drug the mean blood pressure, measured while the patients were supine, and the mean serum potassium level fell significantly, from 156/99 to 138/88 mm Hg and from 4.23 to 3.91 mmol/L, after 8 weeks of treatment. In the other group both measures also fell significantly, the blood pressure from 157/99 to 138/87 mm Hg and the potassium level from 4.16 to 3.69 mmol/L. The proportions of patients in the two groups with hypokalemia (14% and 29% respectively), defined as a serum potassium level below 3.5 mmol/L, differed significantly (p = 0.0026), whereas the proportions with a potassium level exceeding 4.5 mmol/L (4.5% and 3.9% respectively) were similar. Thus, the combination drug reduced the blood pressure to the same extent as hydrochlorothiazide alone but significantly less often caused hypokalemia. In light of growing concerns about the cardiovascular complications of hypokalemia, hydrochlorothiazide-amiloride appears preferable to hydrochlorothiazide alone for the treatment of some patients with hypertension.

Orthostatic hypotension: a posture-induced hyperdopaminergic state

To explore the role of dopaminergic mechanisms in orthostatic hypotension we compared the postural responses of 20 such patients to those of a control group by radioenzymatic determination of free and sulfated catecholamines and related indices. Patients with orthostatic hypotension, unlike control subjects, experienced an increase in total plasma dopamine (DA) (free + sulfate) in response to upright posture (p less than 0.01). Of the 20 patients with orthostatic hypotension, 16 were normo- or hyperadrenergic with normal basal and posture-responsive or hyperresponsive plasma free and total norepinephrine (NE). The other 4 were hypoadrenergic with low basal and posture-unresponsive NE. Hypoadrenergic patients had, in the upright position, no increase in pulse rate and more severe hypotension, less diuresis and natriuresis, lower urinary free and total DA, lower total NE excretion, and higher plasma and urinary total DA:total NE ratio than normo- or hyperadrenergic patients or control subjects. Normo- or hyperadrenergic patients had higher PRA and plasma aldosterone in the upright position than hypoadrenergic patients or control subjects (all p less than 0.05). We suggest that an excessive increase in free DA occurs in response to upright posture, perhaps representing a compensatory reaction of the remaining autonomic nervous system to an excessive fall in blood pressure. The free dopamine may be biologically active but it is so rapidly sulfoconjugated that it can be detected only as DA sulfate. These findings, combined with reports of orthostatic hypotension precipitated by administration of dopaminomimetic drugs and relieved by administration of dopaminergic antagonists, are consistent with the interpretation that excessive DA release may perpetuate, by its vasodilating and natriuretic action, the orthostatic hypotension.

Catecholamine sulfates and platelet phenolsulfotransferase activity in essential hypertension

Because of high plasma concentrations of conjugated catecholamines and their unknown relationship to hypertension, we determined those conjugates more specifically as catecholamine sulfates together with the sulfoconjugating enzyme-phenolsulfotransferase activity in platelets of 62 patients with essential hypertension and 32 normal controls. Our results indicated: (1) that the pool of total (free and sulfated) catecholamines (dopamine, norepinephrine, and epinephrine) is higher (because of an increase in dopamine sulfate levels) but the degree of epinephrine conjugation is lower in patients with essential hypertension compared with controls; (2) that norepinephrine sulfate levels rise with age in both groups, but the increase in free norepinephrine with age observed in controls was not observed in patients with essential hypertension; and (3) that catecholamine conjugates were found to be exclusively sulfates and platelet phenolsulfotransferase activity was not different in both groups. Platelet phenolsulfotransferase activity was, however, positively correlated with plasma norepinephrine sulfate levels, and the degree of sulfoconjugation of norepinephrine was positively correlated with that of dopamine in controls but not in patients with essential hypertension. These abnormalities occurring in essential hypertension in the absence of intergroup differences in platelet phenolsulfotransferase activity suggest that the enzyme is either not a good marker of the overall activity or that other factors account for the observed differences. Thus, additional determinants of the process of generation and degradation of sulfoconjugated catecholamines, some of which may be more stable markers of sympathetic activity than free catecholamines, need to be explored.

Regional sources of free and sulfoconjugated catecholamines in hypertension

To elucidate the sources of free catecholamines (CA) and their sulfates in hyperadrenergic essential hypertensives (EH), their arteriovenous differences were determined radioenzymatically and by sulfatase hydrolysis (with correction for cross-contamination) across several organs and regions in 16 hyperadrenergic essential hypertensive patients. Comparison with arterial concentrations showed that: the adrenal venous outflow contains 240 times more free epinephrine (E), 55 times more free norepinephrine (NE), and 7 times more free dopamine (DA) concentrations, but E, NE, and DA sulfates are not different; free E concentrations are lower in the peripheral venous blood; NE sulfate concentrations are higher in the superior vena cava (p less than 0.05 for all differences noted). The data suggest the following conclusions for hyperadrenergic EH patients: with the exception of NE sulfate added into the superior vena cava region, no other organ or region can be associated with a net DA or NE sulfate release. The proportional adrenal vein concentrations of DA:NE:E are approximately 1:10:50, which are very close to those seen in other studies performed under different degrees of stress. Free E is extracted in peripheral tissues. The DA surges in hyperadrenergic EH patients probably result from the pulsatile, predominantly adrenal, release of free DA.

Effects of phenobarbital and tobacco smoking on furosemide kinetics and dynamics in normal subjects

This study was carried out to determine whether furosemide (F) kinetics and dynamics were influenced by phenobarbital and tobacco smoking. Our subjects were 10 normal men: five nonsmokers (NS) and five smokers (S). They received a single intravenous F injection of 40 mg. Regular serum and urine collections were made. In a second study, the NS group received 100 mg phenobarbital orally for 15 days and then a second dose of F. Cumulative 8-hr urinary excretion of sodium was identical for NS, NS with phenobarbital, and S at 345 +/- 30, 357 +/- 29, and 353 +/- 25 mmol. Diuresis was smaller by 800 ml (20%) in S than in NS. F increased endogenous creatinine clearance from 117 +/- 13 to 196 +/- 17 ml/min in NS and from 110 +/- 12 to 222 +/- 30 ml/min in NS with phenobarbital. In the S group, endogenous creatinine clearance showed a tendency to increase only slightly, from 136 +/- 23 to 180 +/- 34 ml/min. The increase in free water clearance caused by F was smaller in the S group than in the NS group (P less than 0.05). Protein binding and distribution of F were not affected by phenobarbital or tobacco smoking. F clearance was slightly higher in S than in NS, which was primarily the result of a slight increase in extrarenal F clearance. In the NS group, F clearance remained constant after phenobarbital. It is concluded that tobacco smoking in normal subjects affects the diuretic response to F without modifying kinetics.

Enhancement of nadolol elimination by activated charcoal and antibiotics

This study was carried out to assess whether nadolol undergoes enterohepatic circulation. Eight healthy subjects received 80 mg nadolol orally on three occasions at least 2 wk apart. The first experiment was a control. The second consisted of nadolol followed in 3 hr by 3 gm activated charcoal given over a 9-hr period. In the third, the subjects received 0.5 gm erythromycin base and 0.5 gm neomycin four times a day orally for 2 days before nadolol. After the activated charcoal, the nadolol AUC fell from 2455 +/- 155 to 1355 +/- 123 ng . hr/ml (mean +/- SE), as did the percentage nadolol recovered in urine (15.4 +/- 1.4 to 10.2 +/- 0.7%) and the nadolol t1/2 (17.3 +/- 1.7 to 11.8 +/- 1.6 hr). These data suggest that nonrenal elimination increased. After the antibiotics, nadolol AUC was constant, percentage of nadolol recovered in urine fell to 12.7 +/- 1.7%, nadolol t1/2 fell to 11.6 +/- 1.3 hr, and mean peak nadolol concentration rose from 146 +/- 15 to 397 +/- 52 ng/ml. These results suggest that there is an enterohepatic circulation for nadolol, that activated charcoal may decrease nadolol bioavailability, and that antibiotics may increase the nadolol effect.

Tixocortol pivalate, a corticosteroid with no systemic glucocorticoid effect after oral, intrarectal, and intranasal application

Tixocortol pivalate is a corticosteroid with topical anti-inflammatory activity equal to that of hydrocortisone. It was evaluated in a group of 18 normal subjects to determine whether it exerted any systemic glucocorticoid activity after single oral or intrarectal doses and after short-term dosing by the intranasal route. Effects of tixocortol pivalate were compared to those of oral dexamethasone and intrarectal betamethasone 21-phosphate. By the three routes, tixocortol pivalate does not induce any changes in plasma cortisol, leukocyte counts (neutrophils, lymphocytes, monocytes, eosinophils), blood glucose, or 24-hr urinary excretion of sodium and potassium, whereas there were changes after dexamethasone and betamethasone. Tixocortol pivalate, however, increased urinary free cortisol-like substances. It is concluded that tixocortol pivalate given for short periods by nonparenteral routes does not induce a measurable systemic glucocorticoid effect.

Comparison of chlorthalidone and spironolactone in low--renin essential hypertension

Nineteen patients with uncomplicated essential hypertension and low activity of plasma renin in response to a change from recumbency to an upright posture along with furosemide administration were given spironolactone, 400 mg/d, or chlorthalidone, 100mg/d, in a double-blind, random-sequence, crossover trial. The sequence of treatments was placebo for 2 months, one active drug for 2 months, placebo again for 1 month and the other active drug for 2 months. With both active treatments the average systolic, diastolic and mean arterial pressures decreased significantly. The two agents were equally efficacious in lowering the blood pressure regardless of the severity of hypertension during placebo treatment. Body weight, 24--hour urinary excretion of sodium, the plasma renin activity and the plasma aldosterone level at the end of the initial placebo period did not allow us to predict the response to either drug. Both drugs reduced the body weight and increased the stimulated plasma renin level activity. Chlorthalidone significantly increased the serum uric acid level and significantly reduced the serum potassium level. Three patients experienced orthostatic dizziness during spironolactone therapy, but no adverse symptoms were observed with chlorthalidone therapy. Thus, spironolactone is an effective alternative to thiazide-type drugs in patients with low-renin essential hypertension.

Once-daily dosing of acebutolol in hypertension

Twenty-six patients with essential hypertension were admitted to a protocol comparing the efficacy of the once-a-day administration of acebutolol with twice-a-day administration. A placebo was substituted initially for their beta-blocker therapy. Other therapy was continued in 14 (11, diuretics alone; two, diuretics plus hydralazine or alpha-methyldopa; one, alpha-methyldopa alone). After 4 weeks, lying blood pressures were 160 +/- 16 (SD) mm Hg systolic, and 101 +/- 7 mm Hg diastolic. Incremental twice-a-day doses of acebutolol resulted in normotension (lying systolic, 131 +/- 12 mm Hg; diastolic, 84 +/- 5 mm Hg) in all 26 patients (eight on 400 mg, four on 600 mg, seven on 800 mg, one on 1,000 mg, and six on 1,200 mg/day). The same twice-a-day acebutolol dose was continued for two visits, 4 weeks apart, recording pressures at 8 a.m., 12 noon, 4 p.m., and 8 p.m.; followed by two visits, 4 weeks apart, while taking the total daily dose after the 8 a.m. recording. Blood pressures during once-a-day dosing were not different from those during twice-a-day dosing at any time. Highest pressures were at 8 a.m. and lowest were at 12 noon or 4 p.m. Variations during the day in both systolic and diastolic pressures were greater during once-a-day dosing. Plasma acebutolol and metabolite concentrations were proportional to the administered dose. Eighteen patients continued acebutolol for 1 year without adverse effects other than an asymptomatic positive antinuclear antibody test in six. Once-a-day dosing was as effective as twice-a-day dosing in this group of hypertensive patients.

Dopamine surges in hyperadrenergic essential hypertension

From a total of 61 referred hypertensive patients, 21 were clinically suspected of pheochromocytoma but in none was this diagnosis confirmed. Instead we found nine of the 21 patients had surges of conjugated dopamine during hyperadrenergic periods unaccounted for by rise in norepinephrine (NE) or epinephrine (E). Overall, essential hypertensive (EH) patients had in plasma (ng/ml) higher conjugated dopamine (DA) (2.3 +/- 0.2 vs 1.0 +/- 0.1, p less than 0.01), increasing with age (p less than 0.01), lower conjugated NE + E (0.6 +/- 0.1 vs 1.2 +/- 0.2, p less than 0.01), and higher free E (p less than 0.007), lower urinary free DA and total DA but higher free NE + E excretions (each p less than 0.05) than 24 control subjects. Following the DA surges, a short-lived urinary overflow of total DA occurred. The patients with DA surges were older, had a higher incidence of low conjugated NE + E (less than 0.23 ng/ml), a higher proportion of arterial free DA, and higher venous baseline conjugated plasma DA than the rest of the patients. Patients with low conjugated NE + E had in turn higher plasma DA concentrations at several regional sampling sites than patients with normal conjugated NE + E. High conjugated DA in EH probably results from pulsatile DA surges leading to a rise of baseline plasma conjugated DA. In the short run DA pulses can result in temporary alpha- and beta-adrenergic actions of huge arterial free DA concentrations prior to DA conjugation; in the long run the excessive high affinity DA conjugation may take preference to the lower affinity NE and lowest affinity E conjugation and free E increases. Both result in an acute or chronic increase of sympathetic tone.

Patient self-management of continuous subcutaneous insulin infusion

Continuous subcutaneous insulin infusion (CSII) is one of the ways to control blood glucose for prolonged periods. This study was undertaken to establish the long-term feasibility and efficacy of CSII with patient self-management. Patients were instructed to maintain their calorie and carbohydrate intake. Basal infusion of insulin, representing 50% of the total pre-CSII dose, was supplemented by boluses of insulin based on carbohydrate intake for each meal. With this type of regimen, blood glucose and M-values were easily normalized during the physician-directed periods. This study demonstrated that near-normalization of blood glucose, M-values, and glycosylated hemoglobin was maintained after a 1 1/2-yr period of patient self-management. We attributed this successful management in part to the protocol used, in which boluses were related solely to carbohydrate intake while basal insulin was adjusted according to fasting blood glucose. The chronic normalization of blood glucose resulted in improvement of platelet function as witnessed by responsiveness to antiaggregating (PGE1) and aggregating (epinephrine) agents. An improvement was noticed in doppler measurement of ankle-arm blood pressure and a near-normalization of nerve latency and conductivity was observed.

The hemodynamic relevance of free and conjugated dopamine in pheochromocytoma

Two patients with adrenomedullary hypersecretion (confirmed pheochromocytoma and adrenomedullary hyperplasia) presented 15 spontaneous crises associated with hypertension or hypotension with or without tachycardia. Correlation coefficients calculated between extreme values of pulse rates and of systolic and diastolic blood pressures on the one hand and plasma free and conjugated norepinephrine, epinephrine, and dopamine (DA) sampled at the height of the crises on the other, showed no relationships between free or conjugated norepinephrine or epinephrine and blood pressure or pulse rate. However, plasma conjugated DA was negatively correlated with systolic blood pressures (P less than 0.02) and diastolic blood pressures (P less than 0.03) and free plasma DA was negatively correlated with pulse rates (P less than 0.001). These data suggest that the extremely high circulating level of conjugated DA in pheochromocytoma may, in the presence of high circulating conjugated norepinephrine and possibly high alpha-adrenergic receptor occupancy, decrease blood pressure by its predominant action on dopaminergic receptors while elevated free DA may decrease the tendency to tachycardia, possibly by lowering the venous return.

Hypertension in hyperthyroidism: is there an epinephrine connection?

Since hypertension seen in euthyroid subjects with depressed conjugated epinephrine and moderately elevated free epinephrine in plasma is strikingly similar to the beta-hyperadrenergic, high-output hypertension seen in some hyperthyroid patients, the possibility is discussed that thyroid action on sulfoconjugation could affect the biodisposability of endogenous free E and so indirectly the manifestation of sympathetic hyperactivity. There is only circumstantial evidence for such a possibility at present. Differences in the conjugation system may be operative in dealing with endogenous as well as exogenous catecholamines. If the latter are used in evaluating the adrenergic receptor reactivity, this may result in incorrect dose-response curves if the concentrations of catecholamines remaining free following infusion are not monitored. The conjugation of catecholamines, E in particular, is a variable which has to be taken account of in the investigation of catecholamine-like manifestation of T3 and T4 excess and in the evaluation of adrenergic influences on thyroid function.

Prazosin plasma concentration and blood pressure reduction

Prazosin was administered to 16 patients with essential hypertension in an initial dose of 0.5 mg, after which the blood pressure (BP), pulse, and plasma concentrations of prazosin were measured at 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, and 24 hours. The dose of prazosin was then increased over 16 to 20 weeks, and similar sequences of measurements were obtained twice. Eleven patients completed the 20-week course. All patients did not respond in a similar way; two distinct patterns of BP and pulse response emerged, although there was no significant difference in the pharmacokinetic parameters, namely, absorption rate constant (Ka), maximum plasma concentration (Cpmax), time to reach the maximum concentration (Tmax), prazosin plasma half-life (T 1/2), elimination rate constant (kel), prazosin plasma concentration-time curve (AUC), and clearance. Patients in Group 1 had a marked reduction (52/30 mm Hg) of BP after the first dose of prazosin, no pulse increase, and needed a small dose of prazosin to maintain an adequate BP response. Patients in Group 3 had a minimal reduction in BP (14/13 mm Hg) after a first dose, a significant pulse increase, and needed a high dose of prazosin to control their BP. We conclude that this effect might be due to a different drug-receptor interaction, and the BP response and dose could be predicted from the response of the first dose of prazosin.

Unconjugated hyperepinephrinemia: a hallmark of hypertension imitating pheochromocytoma?

Hypertensive patients with elevated and hyperresponsive plasma norepinephrine and epinephrine (NE + E) associated with low conjugated NE + E were previously identified by determination of the sum of NE + E. Because of their excessive E but not NE responses to glucagon and also hypertension corresponding to E excess, we explored whether an elevated unconjugated E resulting from a selective E conjugation defect could be obscured by the sum of NE + E. We found that nine patients with elevated E (reflected by the normal 4:1 ratio of plasma NE to E reversed in favor of E), had, when compared to 31 patients with plasma NE exceeding E:1) lower plasma conjugated E (mean 0.03 vs 0.27 ng/ml, p less than 0.01), lower degree of E conjugation (8 vs 51%, p less than 0.01), and a higher maximum systolic (p less than 0.05), pulse pressure (p less than 0.02) and higher pulse rates (p less than 0.04), but no differences in the unconjugated and conjugated proportions of plasma NE; and 2) an absence of conjugated E throughout the circulation and relative preponderance of E over NE at sampling points close to the peripheral venous blood (p less than 0.05). The absolutely and relatively decreased plasma conjugated E in patients with E exceeding NE (without difference in conjugated NE) is a preliminary indication that a selective sulfoconjugating defect of E results in plasma E higher than NE in accordance with the hyper-beta-adrenergic features of their hypertension. Epinephrine, a circulating hormone, is more dependent on conjugated E reflect better this defect than those measuring the sum of NE and E.

Gentamicin: use of a programmable calculator to determine dosages from pharmacokinetic data for individual patients

Gentamicin, an antibiotic frequently used in the treatment of gram-negative infections, has a narrow therapeutic index, so the correct prediction of its serum concentrations is important. Recent studies have emphasized the dubious accuracy of commonly used formulas, and computer programs that provide pharmacokinetic data for individual patients from multiple blood samples have helped to adjust dosages but are expensive. This study tested the applicability of a method using only two blood samples and a programmable calculator to estimate pharmacokinetic parameters for individual patients and adjust dosages to aim at peak and trough serum levels of 6 and 1 micrograms/ml respectively. In the 48 patients with normal renal function this method produced peak serum concentrations of gentamicin within 1 microgram/ml of the desired level in 22 (46%) and therapeutic peak concentrations (between 4 and 10 micrograms/ml) in all the patients. In 10 patients with renal failure it produced peak serum concentrations within 1 microgram/ml of the desired value in 4 and therapeutic serum concentrations in 7. Two patients had peak concentrations below 4 micrograms/ml and one had a peak concentration above 10 micrograms/ml. Two of the three patients whose serum levels were outside the therapeutic range had unstable renal insufficiency. Thus, patients with renal insufficiency need continued monitoring of the serum level of gentamicin, particularly when their renal function is changing.

Basis of false-positive glucagon tests for pheochromocytoma

In more than half of 67 patients suspected of having pheochromocytoma, glucagon stimulation increased plasma free norepinephrine (NE) and epinephrine (E) 50% or more, with rising blood pressure or pulse rate; only three patients, however, harbored a pheochromocytoma. A low degree of catecholamine conjugation accounts for most of the false-positive results. In patients with low conjugated NE +E there was a greater rise in free NE +E and free E as well as in pulse rate after glucagon stimulation than in those with normal levels of conjugated NE+E. Glucagon-sensitive adenylate cyclase was found in pheochromocytomas but not in a functional adrenocortical adenomas. After sham administration of glucagon, there were rises in blood pressure but not in free NE or E in four patients. The glucagon-induced catecholamine test can be false-positive in hyperadrenergic essential hypertensive patients with abnormally low conjugated NE +E. Saline alone in a sham glucagon test in susceptible patients raises systolic blood pressure and pulse rate, and therefore, if plasma free NE and E are measured and found not to rise this type of false-positive result can be eliminated.

Labetalol in essential hypertension

Labetalol is an orally active adrenoreceptor-blocking drug which is a competitive antagonist of both alpha- and beta-adrenoreceptor sites. Thirty patients with essential hypertension were admitted to the study. The mean of initial systolic and diastolic blood pressures of these patients was 160/101 +/- 3/1 supine and 155/104 +/- 3/1 mm Hg standing, and the mean blood pressures at the end of the 16 week trial was 142/90 +/- 4/2 supine and 131/91 +/- 3/2 mm Hg standing. The average dose of labetalol was 546 mg: eight patients received a dose of 300 mg, seven a dose of 600 mg, six a dose f 900 mg, and two a dose of 1,200 mg. The patients who needed the highest doses of labetalol had an initial lowering of their blood pressures followed by a gradual increase despite the higher doses of labetalol. There was no significant change in the mean peripheral renin activity value. Side effects were reported by 18 of the 30 patients, but only 1 patient withdrew for this reason. Two patients were considered to be treatment failures. Overall, labetalol was found to be an effective antihypertensive agent in 15 patients.