Hypertension management in patients with renal cell cancer treated with anti-angiogenic agents

Inhibitors of the vascular endothelial growth factor (vegf-is) signalling pathway have fundamentally changed the treatment of metastatic renal cell carcinoma (mrcc). Hypertension is one of the most common side effects of vegf-is and has been reported with almost every vegf-i used for treatment to date. The exact mechanism of vegf-i-induced hypertension appears complex and multifactorial, and it remains to be fully explained. No randomized clinical trials are available to guide the management of hypertension during vegf-i treatment in mrcc patients. The guiding principles suggested here summarize the consensus of opinions on the diagnosis and management of vegf-i-induced hypertension during treatment of mrcc obtained from an expert working group composed of 4 Canadian medical oncologists and 5 Canadian hypertension specialists. The Canadian Hypertension Education Program guidelines, available literature, and expert opinion were used to develop the guiding principles.

Effect of Ketoprofen on Blood Pressure, Endocrine and Renal Responses to Chronic Dosing with Captopril in Patients with Essential Hypertension

The effects of non-steroidal anti-inflammatory drugs (NSAIDs) on the blood pressure and renal function of essential hypertensive patients depend on the specific type of NSAID and antihypertensive drug administered. Twelve patients with essential hypertension, aged 35 to 59 years, stabilized (blood pressure less than 140/90 mmHg) with captopril, received ketoprofen (100 mg bid for 7 days) or matching placebo in a randomized double-blind cross-over fashion. A 3-week wash-out period was included between treatment periods. Blood pressure on the first and last days of the placebo treatment period (137 +/- 7 (SD)/80 +/- 8 and 139 +/- 11/81 +/- 9 mmHg) was similar to respective values during ketoprofen therapy (136 +/- 10/79 +/- 7 and 143 +/- 10/81 +/- 9 mmHg). The mean differences in systolic and diastolic blood pressures, at the end of the treatment periods, between ketoprofen and placebo were 4 (95% confidence intervals -5, +13) and 0 (-8, +8) mmHg, respectively. Ketoprofen had no effect on 24-h urinary sodium excretion (160 +/- 33 and 147 +/- 39 mmol/24 h for ketoprofen and placebo, respectively). Ketoprofen was without effect on glomerular filtration rate, renal plasma flow and filtration fraction. In conclusion, our data suggest that ketoprofen is a safe choice when short-term treatment with a NSAID is indicated in an essential hypertensive patient treated with a converting enzyme inhibitor such as captopril.

Antihydrogen production within a Penning-Ioffe trap

Slow antihydrogen (H) is produced within a Penning trap that is located within a quadrupole Ioffe trap, the latter intended to ultimately confine extremely cold, ground-state H[over ] atoms. Observed H[over ] atoms in this configuration resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap. The number of detected H atoms actually increases when a 400 mK Ioffe trap is turned on.

Antiproton confinement in a Penning-Ioffe trap for antihydrogen

Antiprotons (p[over]) remain confined in a Penning trap, in sufficient numbers to form antihydrogen (H[over ) atoms via charge exchange, when the radial field of a quadrupole Ioffe trap is added. This first demonstration with p[over] suggests that quadrupole Ioffe traps can be superimposed upon p[over] and e(+) traps to attempt the capture of H[over] atoms as they form, contrary to conclusions of previous analyses.

Effects of individual risk factors on the incidence of cardiovascular events in the treated hypertensive patients of the Hypertension Optimal Treatment Study. HOT Study Group

BACKGROUND

The Hypertension Optimal Treatment (HOT) Study has provided information about cardiovascular events in 18790 hypertensives, subjected to pronounced blood pressure (BP) lowering for a mean of 3.8 years. The HOT study data have subsequently been analysed after stratification of the patients according to global cardiovascular risk, and it has been found that, despite intensive blood pressure lowering in all risk strata, morbid event rates increased with increasing risk stratum.

OBJECTIVES

Previously analysed global risk strata were based on combinations of risk factors. The analyses presented here were intended to provide information on the relative role that the presence of each individual factor may have in increasing cardiovascular risk, despite good BP control.

METHODS

Risk ratios (RR) for patients with and those without a risk factor were calculated with 95% confidence intervals (CI) using a Cox proportional hazard model, and adjusted for all variables except the one under examination.

RESULTS

For all risk factors considered and for all types of event, RR were always greater than 1, indicating a greater risk in the presence, compared with that in the absence of each factor. The male gender was a statistically significant risk for cardiovascular (CV) events, CV and total mortality and particularly for myocardial infarction (MI); age > or = 65 years for CV events, stroke, CV and particularly total mortality; smoking for all events analysed, but particularly for total mortality (twice higher in smokers than in non-smokers); high serum cholesterol (> 6.8 mmol/l) for CV events, MI and CV mortality; high serum creatinine (> 155 micromol/l) for CV events, stroke, CV and total mortality; diabetes for CV events, stroke, total mortality and particularly CV mortality; and ischaemic heart disease for all events analysed. Adjusted RR were often close to or greater than 2.

CONCLUSIONS

Each of the risk factors considered was found to be an important cause of residual risk, despite good BP control. These findings emphasize the importance of addressing other correctable risk factors, e.g. smoking, hypercholesterolaemia and diabetes, as well as rigorous control of blood pressure, and of initiating antihypertensive therapy before cardiovascular and renal damage becomes manifest.

Adverse events associated with prescription drug cost-sharing among poor and elderly persons

CONTEXT

Rising costs of medications and inequities in access have sparked calls for drug policy reform in the United States and Canada. Control of drug expenditures by prescription cost-sharing for elderly persons and poor persons is a contentious issue because little is known about the health impact in these subgroups.

OBJECTIVES

To determine (1) the impact of introducing prescription drug cost-sharing on use of essential and less essential drugs among elderly persons and welfare recipients and (2) rates of emergency department (ED) visits and serious adverse events associated with reductions in drug use before and after policy implementation.

DESIGN AND SETTING

Interrupted time-series analysis of data from 32 months before and 17 months after introduction of a prescription coinsurance and deductible cost-sharing policy in Quebec in 1996. Separate 10-month prepolicy control and postpolicy cohort studies were conducted to estimate the impact of the drug reform on adverse events.

PARTICIPANTS

A random sample of 93 950 elderly persons and 55 333 adult welfare medication recipients.

MAIN OUTCOME MEASURES

Mean daily number of essential and less essential drugs used per month, ED visits, and serious adverse events (hospitalization, nursing home admission, and mortality) before and after policy introduction.

RESULTS

After cost-sharing was introduced, use of essential drugs decreased by 9.12% (95% confidence interval [CI], 8.7%-9.6%) in elderly persons and by 14.42% (95% CI, 13.3%-15.6%) in welfare recipients; use of less essential drugs decreased by 15.14% (95% CI, 14.4%-15.9%) and 22.39% (95% CI, 20.9%-23.9%), respectively. The rate (per 10 000 person-months) of serious adverse events associated with reductions in use of essential drugs increased from 5.8 in the prepolicy control cohort to 12.6 in the postpolicy cohort in elderly persons (a net increase of 6.8 [95% CI, 5.6-8.0]) and from 14.7 to 27.6 in welfare recipients (a net increase of 12.9 [95% CI, 10.2-15.5]). Emergency department visit rates related to reductions in the use of essential drugs also increased by 14.2 (95% CI, 8.5-19.9) per 10 000 person-months in elderly persons (prepolicy control cohort, 32.9; postpolicy cohort, 47.1) and by 54.2 (95% CI, 33.5-74.8) among welfare recipients (prepolicy control cohort, 69.6; postpolicy cohort, 123.8). These increases were primarily due to an increase in the proportion of recipients who reduced their use of essential drugs. Reductions in the use of less essential drugs were not associated with an increase in risk of adverse events or ED visits.

CONCLUSIONS

In our study, increased cost-sharing for prescription drugs in elderly persons and welfare recipients was followed by reductions in use of essential drugs and a higher rate of serious adverse events and ED visits associated with these reductions.

[Calcium channel blocking agents and albuminuria in diabetic and hypertensive patients. A pilot study]

Diltiazem tends to decrease proteinuria in hypertensive diabetic subjects in comparison to amlodipine that does not modify it. Since estimated glomerular pressure is identical in amlodipine treated and diltiazem treated subjects, differences in albuminuria may be explained by different renal tubular reabsorption rates.

OBJECTIVES

To compare plasma clearances (PC) of technetium labeled albumin (albumin-Tc99m) obtained by serial plasma measurements with PC obtained by urinary excretion measurements. Indirectly evaluate tubular reabsorption of albumin-Tc99m. Test the hypothesis that amlodipine decreases renal tubular reabsorption of albumin in diabetic hypertensive subjects.

METHODS

Fourteen diabetic and hypertensive subjects (DH) (average plasma creatinine: 94 mmol/L) and 6 normal subjects (average plasma creatinine: 82 mmol/L) had previously been assessed for albumin-Tc99m PC. Eleven of these 14 DH subjects were then randomized to diltiazem 300 mg/daily (6 subjects) or amlodipine 10 mg/daily (5 subjects). Their glomerular filtration, glomerular pressure and albumin-Tc99m PC were then assessed on the 3rd, 6th, and 12th month of the study.

RESULTS

Albumin-Tc99m PC obtained from serial blood draws: A decrease in PC between months 0 and 3 from 14 to 10.6 cc/min was observed in subjects treated with amlodipine but subjects on diltiazem showed PC stability (from 11.9 to 12 cm3/min). PC obtained from urinary excretion: Amlodipine and diltiazem treated subjects showed PC stability. Plasma volume in amlodipine treated subjects decreased from 156 to 127% and diltiazem treated subjects from 128 to 117%.

CONCLUSION

A decrease in PC obtained with plasma measurements and stability of PC based on urinary excretion measurements tends to identify a decrease in plasma volume. A decrease in albumin-Tc99m tubular reabsorption was not observed. The estimate of albumin PC with Tc 99m labelled albumin measurements still needs to be validated.

Role of tumor necrosis factor-alpha gene locus in obesity and obesity-associated hypertension in French Canadians

Obesity represents a serious risk factor for the development of cardiovascular diseases, including hypertension. Segregation studies suggest that obesity and obesity-associated hypertension may share some genetic determinants. The results of the present candidate gene investigation suggest that in hypertensive pedigrees of French-Canadian origin, one such determinant is the tumor necrosis factor (TNF)-alpha gene locus. Gender-pooled quantitative sib-pair analysis demonstrated a significant effect of the gene locus on 3 global and 7 regional measures of obesity (P=0.05 to 0.0004). Gender-separate quantitative sib-pair analyses showed that the impact of the locus on obesity is most significant in the abdominal region in men and in the thigh region in women. Furthermore, the haplotype relative-risk test demonstrated a significant association between the TNF-alpha gene locus and both obesity (P=0.006) and obesity-associated hypertension (P=0.02). These effects were most significant in individuals with nonmorbid obesity. In conclusion, the results of linkage and association analyses suggest that in hypertensive pedigrees of French-Canadian origin, the TNF-alpha gene locus contributes to the determination of obesity and obesity-associated hypertension. In addition, the data indicate that gender modifies the effect of the locus on the regional distribution of body fat.

1999 Canadian recommendations for the management of hypertension. Task Force for the Development of the 1999 Canadian Recommendations for the Management of Hypertension

OBJECTIVE

To provide updated, evidence-based recommendations for health care professionals on the management of hypertension in adults.

OPTIONS

For patients with hypertension, there are both lifestyle options and pharmacological therapy options that may control blood pressure. For those patients who are using pharmacological therapy, a range of antihypertensive drugs is available. The choice of a specific antihypertensive drug is dependent upon the severity of the hypertension and the presence of other cardiovascular risk factors and concurrent diseases.

OUTCOMES

The health outcomes considered were changes in blood pressure and in morbidity and mortality rates. Because of insufficient evidence, no economic outcomes were considered.

EVIDENCE

MEDLINE searches were conducted from the period of the last revision of the Canadian Recommendations for the Management of Hypertension (January 1993 to May 1998). Reference lists were scanned, experts were polled and the personal files of the authors were used to identify other studies. All relevant articles were reviewed, classified according to study design and graded according to levels of evidence.

VALUES

A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension.

BENEFITS

Harms and costs: The diagnosis and treatment of hypertension with pharmacological therapy will reduce the blood pressure of patients with sustained hypertension. In certain settings, and for specific drugs, blood pressure lowering has been associated with reduced cardiovascular morbidity and mortality.

RECOMMENDATIONS

This document contains detailed recommendations pertaining to all aspects of the diagnosis and pharmacological therapy of hypertensive patients. With respect to diagnosis, the recommendations endorse the greater use of non-office-based measures of blood pressure control (i.e., using home blood pressure and automatic ambulatory blood pressure monitoring equipment) and greater emphasis on the identification of other cardiovascular risk factors, both in the assessment of prognosis in hypertension and in the choice of therapy. On the treatment side, lower targets for blood pressure control are advocated for some subgroups of hypertensive patients, in particular, those with diabetes and renal disease. Implicit in the recommendations for therapy is the principle that for the vast majority of hypertensive patients treated pharmacologically, practitioners should not follow a stepped-care approach. Instead, therapy should be individualized, based on consideration of concurrent diseases, both cardiovascular and noncardiovascular.

VALIDATION

All recommendations were graded according to the strength of the evidence and the consensus of all relevant stakeholders.

SPONSORS

The Canadian Hypertension Society and the Canadian Coalition for High Blood Pressure Prevention and Control.

Clinical problem solving based on the 1999 Canadian recommendations for the management of hypertension

The 1999 Canadian Recommendations for the Management of Hypertension are notable for the trends that they represent with regard to the evolution of the management of hypertension. Diagnostically, the Recommendations endorse the greater use of non-office-based measures of blood pressure control and greater emphasis on the assessment of other atherosclerotic risk factors, both when considering prognosis in hypertension and in the choice of therapy. On the treatment side of the equation, lower targets for blood pressure control have been advocated in subgroups of hypertensive patients, particularly in those with diabetes and renal disease. In conjunction with the recently published recommendations on lifestyle management, there is a greater emphasis on lifestyle modification, both as initial and adjunctive therapy in hypertension. Implicit in the recommendations for therapy is the principle that for the vast majority of hypertensive patients treated pharmacologically, practitioners should not follow a stepped-care approach. Instead, therapy should be individualized, primarily based on consideration of concurrent diseases, both cardiovascular and noncardiovascular (Tables 1 and 2). Through the consensus process, there was a general appreciation of how far we have come in the development of evidence-based recommendations for hypertension management. However, there was also an increasing appreciation of how far we have to go in effectively translating these recommendations into better blood pressure control.

Sibling resemblance of erythrocyte ion transporters in French-Canadian sibling-pairs affected with essential hypertension

OBJECTIVES

Erythrocyte Na+/Li+ countertransport and Na+,K+ cotransport are increased in some Caucasians with essential hypertension. This study examines the relative contributions of genetic and shared environmental factors to the activity of these ion carriers in French-Canadian sibling-pairs affected with essential hypertension.

DESIGN

The activity of Na+/Li+ countertransport and Na+,K+ cotransport (rate of Na+ o-dependent Li+ efflux and bumetanide-sensitive 86Rb influx, respectively) was measured in 122 French-Canadian siblings with essential hypertension, including 36 brother/brother and 48 sister/sister pairs. Sibling/sibling correlations were estimated using the FCOR program of the S.A.G.E. package.

RESULTS

Na+/Li+ countertransport and Na+,K+ cotransport were respectively higher by 27% (P = 0.002) and 42% (P = 0.0009) in erythrocytes from men compared with women. Intra-individual correlation analysis did not reveal a significant effect of age on the activity of these ion transporters in both males and females, and an influence of plasma lipids (triglycerides, cholesterol, low-density lipoprotein, high-density lipoprotein) in females. In males, Na+,K+ cotransport was correlated with the level of serum triglycerides only (P = 0.01). Familial correlation analysis showed that sibling resemblance of Na+/Li+ countertransport and Na+,K+ cotransport was higher in men (r = 0.26 and 0.39) than in women (r = 0.01 and 0.03, respectively).

CONCLUSION

The present data indicate that different factors contribute to the regulation of monovalent ion carriers in erythrocytes from Caucasian men and women with essential hypertension. The activity of erythrocyte Na+/Li+ countertransport and Na+,K+ cotransport appears to be more strongly determined by inheritable factors in men than in women.

Lifestyle modifications to prevent and control hypertension. 5. Recommendations on dietary salt. Canadian Hypertension Society, Canadian Coalition for High Blood Pressure Prevention and Control, Laboratory Centre for Disease Control at Health Canada, Heart and Stroke Foundation of Canada

OBJECTIVE

To provide updated, evidence-based recommendations concerning the effects of dietary salt intake on the prevention and control of hypertension in adults (except pregnant women). The guidelines are intended for use in clinical practice and public education campaigns.

OPTIONS

Restriction of dietary salt intake may be an alternative to antihypertensive medications or may supplement such medications. Other options include other nonpharmacologic treatments for hypertension and no treatment.

OUTCOMES

The health outcomes considered were changes in blood pressure and in morbidity and mortality rates. Because of insufficient evidence, no economic outcomes were considered.

EVIDENCE

A MEDLINE search was conducted for the period 1966-1996 using the terms hypertension, blood pressure, vascular resistance, sodium chloride, sodium, diet, sodium or sodium chloride dietary, sodium restricted/reducing diet, clinical trials, controlled clinical trial, randomized controlled trial and random allocation. Both trials and review articles were obtained, and other relevant evidence was obtained from the reference lists of the articles identified, from the personal files of the authors and through contacts with experts. The articles were reviewed, classified according to study design and graded according to level of evidence. In addition, a systematic review of all published randomized controlled trials relating to dietary salt intake and hypertension was conducted.

VALUES

A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension.

BENEFITS, HARMS AND COSTS

For normotensive people, a marked change in sodium intake is required to achieve a modest reduction in blood pressure (there is a decrease of 1 mm Hg in systolic blood pressure for every 100 mmol decrease in daily sodium intake). For hypertensive patients, the effects of dietary salt restriction are most pronounced if age is greater than 44 years. A decrease of 6.3 mm Hg in systolic blood pressure and 2.2 mm Hg in diastolic blood pressure per 100 mmol decrease in daily sodium intake was observed in people of this age group. For hypertensive patients 44 years of age and younger, the decreases were 2.4 mm Hg for systolic blood pressure and negligible for diastolic blood pressure. A diet in which salt is moderately restricted appears not to be associated with health risks.

RECOMMENDATIONS

(1) Restriction of salt intake for the normotensive population is not recommended at present, because of insufficient evidence demonstrating that this would lead to a reduced incidence of hypertension. (2) To avoid excessive intake of salt, people should be counselled to choose foods low in salt (e.g., fresh fruits and vegetables), to avoid foods high in salt (e.g., pre-prepared foods), to refrain from adding salt at the table and minimize the amount of salt used in cooking, and to increase awareness of the salt content of food choices in restaurants. (3) For hypertensive patients, particularly those over the age of 44 years, it is recommended that the intake of dietary sodium be moderately restricted, to a target range of 90-130 mmol per day (which corresponds to 3-7 g of salt per day). (4) The salt consumption of hypertensive patients should be determined by interview.

VALIDATION

These recommendations were reviewed by all of the sponsoring organizations and by participants in a satellite symposium of the fourth International Conference on Preventive Cardiology. They have not been clinically tested.

SPONSORS

The Canadian Hypertension Society, the Canadian Coalition for High Blood Pressure Prevention and Control, the Laboratory Centre for Disease Control at Health Canada, and the Heart and Stroke Foundation of Canada.

Effects of antihypertensive therapies on the sympathetic nervous system

The sympathetic nervous system is a major modulator of cardiovascular function. Over the past three decades, numerous studies, using various methodologies, have reported the existence of a variety of pre- and postsynaptic sympathetic dysfunctions in essential hypertension. Most of these abnormalities facilitate sympathetic neurotransmission, resulting in a chronic increase in the sympathetic tone and reactivity in a significant proportion of hypertensive patients. Chronic sympathetic activation is also associated with major alterations in the balance among postsynaptic adrenergic receptors in cardiovascular tissues. Indeed, an attenuation of beta-adrenergic function and a potentiation of alpha1-adrenergic function has been demonstrated in cardiovascular tissues in hypertensive patients, suggesting the development of a sympathetic postsynaptic alpha1 dominance during the development and evolution of hypertension. Chronic activation of the sympathetic system is deleterious and could contribute to the development of most cardiovascular complications associated with hypertension. One of the major aims of antihypertensive therapy should thus be to attenuate pre- or postsynaptic sympathetic tone. Most antihypertensive drugs have been found to improve either pre- or postsynaptic sympathetic function in hypertensive patients. At the presynaptic level, diuretics were found to increase the liberation of noradrenalin, presumably through baroreflex sympathetic activation. In contrast, beta-blockers were shown to attenuate noradrenalin release from sympathetic nerves by blocking presynaptic facilitatory beta-receptors, thus reducing the sympathetic tone on postsynaptic receptors. Similarly, angiotensin-converting enzyme inhibitors or angiotensin II type 1 (AT1) receptor antagonists have been found to reduce sympathetic reactivity by acting on the central nervous system, but also by blocking AT1-mediated facilitatory mechanisms located on sympathetic fibres and in the adrenal medulla. Short acting dihydropyridine calcium channel blockers (CCBs) were found to enhance noradrenalin release from sympathetic nerves, but longer acting CCBs seems to have variable effects. Indeed, while the chronic slow release formulation of nifedipine gastrointestinal therapeutic system (GITS) did not raise circulating noradrenalin levels, treatment with amlodipine increased circulating noradrenalin levels, suggesting that nifedipine GITS is neutral on the sympathetic tone but that amlodipine chronically activates the sympathetic system. At the postsynaptic level, however, dihydropyridine CCBs were shown to attenuate the sympathetic tone on alpha1-adrenoceptors. In conclusion, it appears that most antihypertensive drugs interfere with pre- or postsynaptic sympathetic mechanisms and that these mechanisms could contribute to their hypotensive effects.

Different effects of nifedipine and amlodipine on circulating catecholamine levels in essential hypertensive patients

OBJECTIVE

To compare the acute and chronic effects of nifedipine retard (NPA), nifedipine gastrointestinal therapeutic system (NGITS) and amlodipine at trough and peak plasma concentrations of drug on blood pressure and heart rate, and on plasma norepinephrine and epinephrine levels in patients with mild-to-moderate hypertension (diastolic blood pressure 95-115 mmHg).

DESIGN AND METHODS

After 3-4 weeks' placebo treatment, patients of both sexes were randomly allocated to be administered 10 or 20 mg NPA twice a day, 30 or 60 mg NGITS once a day, and 5 or 10 mg amlodipine once a day for 6 weeks. Initially, for the first 2 weeks, the lowest dose of each drug was used, but higher doses were administered after 2 weeks if sitting diastolic blood pressure was > 90 mmHg. Patients were evaluated after administration of the first dose and after 6 weeks' therapy in a hospital setting. Blood samples were taken for high-performance liquid chromatography measurement of catecholamine and drug levels at various intervals for a period covering trough to peak drug level ranges.

RESULTS

Administration of all three drugs reduced clinic blood pressure to the same level after 6 weeks' therapy, but heart rate was increased slightly only with amlodipine (P < 0.05). Administration of NPA reduced blood pressure more abruptly whereas administrations of NGITS and amlodipine induced smoother falls after acute and chronic treatments: a significant increase in heart rate was observed with amlodipine after chronic treatment. Both acute and chronic treatments with NPA (n = 19) increased norepinephrine levels (P < 0.01) transiently (2-4 h). In contrast, administration of NGITS (n = 22) did not increase norepinephrine levels and even induced a slight but significant decrease in norepinephrine levels 5-6 h after chronic treatments. Although administration of amlodipine (n = 22) did not increase norepinephrine levels transiently either after acute or after chronic administration, it did induce a sustained rise in basal norepinephrine levels by more than 50% after chronic therapy (P < 0.01). Plasma epinephrine levels were not increased by any of the treatments and even a slight decrease was observed 4 h after administration of a dose following chronic treatments with NGITS and amlodipine (P < 0.05).

CONCLUSIONS

The transient increase in norepinephrine levels observed with NPA and the sustained increases in norepinephrine levels observed after chronic treatment with amlodipine suggest that sympathetic activation occurs with those two drugs. The lack of increase in norepinephrine levels after administration of NGITS suggests that this formulation does not activate the sympathetic system. The lowering of epinephrine levels after administrations of NGITS and amlodipine suggests that inhibition of release of epinephrine by the adrenal medulla occurs with longer-acting dihydropyridine formulations.

Different effects of nifedipine and amlodipine on circulating catecholamine levels in essential hypertensive patients

OBJECTIVE

To compare the acute and chronic effects of nifedipine retard (NPA), nifedipine gastrointestinal therapeutic system (NGITS) and amlodipine at trough and peak plasma concentrations of drug on blood pressure and heart rate, and on plasma norepinephrine and epinephrine levels in patients with mild-to-moderate hypertension (diastolic blood pressure 95-115 mmHg).

DESIGN AND METHODS

After 3-4 weeks' placebo treatment, patients of both sexes were randomly allocated to be administered 10 or 20 mg NPA twice a day, 30 or 60 mg NGITS once a day, and 5 or 10 mg amlodipine once a day for 6 weeks. Initially, for the first 2 weeks, the lowest dose of each drug was used, but higher doses were administered after 2 weeks if sitting diastolic blood pressure was > 90 mmHg. Patients were evaluated after administration of the first dose and after 6 weeks' therapy in a hospital setting. Blood samples were taken for high-performance liquid chromatography measurement of catecholamine and drug levels at various intervals for a period covering trough to peak drug level ranges.

RESULTS

Administration of all three drugs reduced clinic blood pressure to the same level after 6 weeks' therapy, but heart rate was increased slightly only with amlodipine (P < 0.05). Administration of NPA reduced blood pressure more abruptly whereas administrations of NGITS and amlodipine induced smoother falls after acute and chronic treatments: a significant increase in heart rate was observed with amlodipine after chronic treatment. Both acute and chronic treatments with NPA (n = 19) increased norepinephrine levels (P < 0.01) transiently (2-4 h). In contrast, administration of NGITS (n = 22) did not increase norepinephrine levels and even induced a slight but significant decrease in norepinephrine levels 5-6 h after chronic treatments. Although administration of amlodipine (n = 22) did not increase norepinephrine levels transiently either after acute or after chronic administration, it did induce a sustained rise in basal norepinephrine levels by more than 50% after chronic therapy (P < 0.01). Plasma epinephrine levels were not increased by any of the treatments and even a slight decrease was observed 4 h after administration of a dose following chronic treatments with NGITS and amlodipine (P < 0.05).

CONCLUSIONS

The transient increase in norepinephrine levels observed with NPA and the sustained increases in norepinephrine levels observed after chronic treatment with amlodipine suggest that sympathetic activation occurs with those two drugs. The lack of increase in norepinephrine levels after administration of NGITS suggests that this formulation does not activate the sympathetic system. The lowering of epinephrine levels after administrations of NGITS and amlodipine suggests that inhibition of release of epinephrine by the adrenal medulla occurs with longer-acting dihydropyridine formulations.

A randomized, double-blind, placebo-controlled, parallel-group, multicenter trial of four doses of tasosartan in patients with essential hypertension. Tasosartan Investigator's Group

Tasosartan, a new, long-acting, nonpeptide angiotensin II receptor antagonist was evaluated in a randomized, double-blind, placebo-controlled, multicenter trial at 21 sites in the United States and Canada. After a 2-week, placebo washout qualification period, 278 patients (187 men/91 women) with a mean age of 53.4+/-9.5 years (range, 30 to 70 years) and a baseline sitting diastolic blood pressure (DBP) of 95 to 114 mm Hg were randomly assigned to receive placebo (n = 56), or 10 mg (n = 57), 30 mg (n = 55), 100 mg (n = 55), or 300 mg (n = 55) tasosartan for 4 weeks. The treatment period was followed by a 2-week washout period. Ambulatory blood pressure (BP) monitoring was performed at the end of the placebo washout period and after at least 4 weeks of double-blind treatment. Clinically significant placebo-adjusted differences in baseline sitting systolic blood pressure (SBP)/DBP were observed in the 10 mg (5/3 mm Hg), 30 mg (5/4 mm Hg), 100 mg (10/7 mm Hg) and 300 mg (10/7 mm Hg) dose groups (P < .05). A dose-response relationship (P < .001) was observed within 1 to 2 weeks of treatment initiation and was maintained throughout the double-blind period. Discontinuation of tasosartan therapy was not associated with rebound hypertension. Moreover, significant (P < .05) placebo-adjusted differences in ambulatory SBP/DBP and a significant dose-response relationship (P < .001) were observed with all tasosartan dosages during the 24-h, daytime, and nighttime periods. Placebo-adjusted trough-to-peak ratios ranged from 87% to 100% for ambulatory SBP and 64% to 81% for DBP. In general, no significant differences were observed between the tasosartan treatment groups and the placebo group in the incidence of adverse events. Headache incidence was significantly lower in the 300 mg dose group than the placebo group. In conclusion, tasosartan at dosages of 10, 30, 100, or 300 mg given once daily produced a significant and dose-related reduction in both clinic and ambulatory BP that was maintained over the 24-h period. Tasosartan was generally well tolerated.

Effects and tolerability of irbesartan versus enalapril in patients with severe hypertension. Irbesartan Multicenter Investigators

In this double-blind, randomized study, an antihypertensive regimen based on irbesartan, an angiotensin II receptor antagonist, reduced systolic and diastolic blood pressure by 40/30 mm Hg at week 12 in patients with severe hypertension; this reduction was at least equivalent to that of a regimen using enalapril up to 40 mg. The irbesartan-based regimen had a better tolerability profile with fewer adverse events (55% vs 64%) and significantly less cough (2.5% vs 13.1%, p = 0.007).

Patterns of compliance with once versus twice daily antihypertensive drug therapy in primary care: a randomized clinical trial using electronic monitoring

OBJECTIVE

To evaluate patterns of compliance with once versus twice daily administration of antihypertensive therapy (primary-outcome measure) and relevance of partial compliance for blood pressure control (secondary outcome measure).

DESIGN

Multicentre, nonblinded, parallel group randomized design.

SETTING

Nonacademic primary care practices across Canada.

STUDY POPULATION

Patients with mild essential hypertension (diastolic blood pressure 95 to 110 mmHg) of either sex (40% women), age 18 to 80 years (average 55 years). One hundred and ninety-eight patients were randomized to active treatment; 14 patients discontinued the study because of side effects.

INTERVENTIONS

After a four-week placebo run-in period, patients were randomized to amlodipine 5 mg once-a-day or diltiazem slow release formulation (SR) 90 mg twice daily. Doses were increased to 10 mg and 180 mg to achieve sitting diastolic blood pressure of 90 mmHg or less.

OUTCOME MEASURE

During 20 weeks on active treatment, compliance was assessed by pill counts and medication event monitoring system (MEMS), assessing percentage of prescribed doses taken, percentage days correct doses taken, percentage prescribed doses taken on time and blood pressure control as determined by office blood pressure measurement.

RESULTS

The percentage prescribed doses taken (by either pill count of MEMS) showed a high degree of compliance, similar for the two treatments. However, other parameters of compliance were significantly better with once versus twice daily therapy. Partial compliance (less than 80% by pill count) led to less blood pressure control with the short acting diltiazem, but did not affect blood pressure control for the long acting amlodipine. Side effects profiles did not differ between the two treatments.

CONCLUSIONS

Within the constraints of a clinical trial, hypertensive patients in primary care show a high degree of overall compliance with once or twice daily pill-taking, but patterns of pill-taking are more erratic with twice versus once daily medication, particularly in men. The results suggest that the negative consequences of partial compliance for blood pressure control can be offset by choosing agents with a duration of action well beyond the dosing interval.

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.