Effects of alpha-adrenergic and beta-adrenergic receptor blockade on lipid metabolism

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α₁-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α₂-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α₁-AR subtypes (α_1A, α_1B, α_1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.

Management of hypertriglyceridemia

Hypertriglyceridemia is one of the most common lipid abnormalities encountered in clinical practice. Many monogenic disorders causing severe hypertriglyceridemia have been identified, but in most patients triglyceride elevations result from a combination of multiple genetic variations with small effects and environmental factors. Common secondary causes include obesity, uncontrolled diabetes, alcohol misuse, and various commonly used drugs. Correcting these factors and optimizing lifestyle choices, including dietary modification, is important before starting drug treatment. The goal of drug treatment is to reduce the risk of pancreatitis in patients with severe hypertriglyceridemia and cardiovascular disease in those with moderate hypertriglyceridemia. This review discusses the various genetic and acquired causes of hypertriglyceridemia, as well as current management strategies. Evidence supporting the different drug and non-drug approaches to treating hypertriglyceridemia is examined, and an easy to adopt step-by-step management strategy is presented.

The role of α1-adrenergic receptors in regulating metabolism: increased glucose tolerance, leptin secretion and lipid oxidation

The role of α₁-adrenergic receptors (α₁-ARs) and their subtypes in metabolism is not well known. Most previous studies were performed before the advent of transgenic mouse models and utilized transformed cell lines and poorly selective antagonists. We have now studied the metabolic regulation of the α_1A- and α_1B-AR subtypes in vivo using knock-out (KO) and transgenic mice that express a constitutively active mutant (CAM) form of the receptor, assessing subtype-selective functions. CAM mice increased glucose tolerance while KO mice display impaired glucose tolerance. CAM mice increased while KO decreased glucose uptake into white fat tissue and skeletal muscle with the CAM α_1A-AR showing selective glucose uptake into the heart. Using indirect calorimetry, both CAM mice demonstrated increased whole body fatty acid oxidation, while KO mice preferentially oxidized carbohydrate. CAM α_1A-AR mice displayed significantly decreased fasting plasma triglycerides and glucose levels while α_1A-AR KO displayed increased levels of triglycerides and glucose. Both CAM mice displayed increased plasma levels of leptin while KO mice decreased leptin levels. Most metabolic effects were more efficacious with the α_1A-AR subtype. Our results suggest that stimulation of α₁-ARs results in a favorable metabolic profile of increased glucose tolerance, cardiac glucose uptake, leptin secretion and increased whole body lipid metabolism that may contribute to its previously recognized cardioprotective and neuroprotective benefits.

Selective alpha(1)-adrenoceptor blockade prevents fructose-induced hypertension

The purpose of this study was to investigate the effect of chronic treatment with prazosin, a selective α1-adrenoceptor antagonist, on the development of hypertension in fructose-fed rats (FFR). High-fructose feeding and treatment with prazosin (1 mg/kg/day via drinking water) were initiated simultaneously in male Wistar rats. Systolic blood pressure, fasted plasma parameters, insulin sensitivity, plasma norepinephrine (NE), uric acid, and angiotensin II (Ang II) were determined following 9 weeks of treatment. FFR exhibited insulin resistance, hyperinsulinemia, hypertriglyceridemia, and hypertension, as well as elevations in plasma NE and Ang II levels. Treatment with prazosin prevented the rise in blood pressure without affecting insulin levels, insulin sensitivity, uric acid, or Ang II levels, while normalizing plasma NE levels in FFR. These data suggest that over-activation of the sympathetic nervous system, specifically α1-adrenoceptors, contributes to the development of fructose-induced hypertension, however, this over-activation does not appear to an initial, precipitating event in FFR.

Serum lipids alterations in adenoid hypertrophy or adenotonsillar hypertrophy children with sleep disordered breathing

OBJECTIVES

We aimed to investigate metabolic parameters in children with adenoid hypertrophy (AH) only or adenotonsillar hypertrophy (ATH) and compare them with healthy controls.

METHODS

Forty-four prepubertal children aged 6-12 years who were obstructive symptoms and 16 healthy children were recruited in this study. All children underwent a complete otolaryngologic examination and sleep screening. The patients were divided into three groups according to obstruction type: normal, AH (adenoid grade III or IV, tonsil grade 1 or 2), and ATH (adenoid grade III or IV, tonsil grade 3 or 4). All participants underwent hematologic and biochemical tests including fasting blood glucose, insulin, and plasma lipids.

RESULTS

(1) The children with AH and ATH had lower high-density lipoprotein cholesterol (HDL-C), when compared to normal children. (2) The level of HDL-C was negatively correlated with the sum of adenoid and tonsillar size scores and the apnea-hypopnea index (AHI) (r=-0.477, p<0.001 vs. r=-0.548, p<0.001, respectively). There was a modest association between HDL-C and minimal SpO₂ (r=0.332, p=0.009). (3) Stepwise multiple regression analysis identified the AHI, triglycerides, and fasting insulin as independent predictors for HDL-C.

CONCLUSIONS

Patients with adenoid and tonsil hypertrophy had low HDL-C. HDL-C levels are inversely related to the sum of adenoid and tonsillar size scores and AHI in SDB children. HDL-C may be a sensitive indicator of serum lipids changes in SDB children.

The effects of phentolamine on fructose-fed rats

Metabolic syndrome (MS) is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. MS is associated with obesity, increased blood pressure, hyperlipidemia, and hyperglycemia. This study was designed to investigate the pharmacological profile of phentolamine, a nonselective α adrenergic receptor antagonist, in the prevention of increased blood pressure in fructose-fed rats. Phentolamine prevented the fructose-induced increase in systolic blood pressure without affecting insulin sensitivity and major metabolic parameters. The levels of plasma noradrenaline and angiotensin II, 2 proposed contributors to the development of fructose-induced elevated blood pressure, were examined. Neither noradrenaline nor angiotensin II levels were affected by phentolamine treatment. Since overproduction of nitric oxide has been shown to lead to an elevation in peroxynitrite, the role of oxidative stress, a proposed mechanism of fructose-induced elevated blood pressure and insulin resistance, was examined by measuring plasma levels of total nitrate/nitrite. Plasma nitrate/nitrite was significantly elevated in all fructose-fed animals, regardless of treatment with phentolamine. Another proposed contributor toward fructose-induced MS is an elevation in uric acid levels. In this experiment, plasma levels of uric acid were found to be increased by dietary fructose and were unaffected by phentolamine treatment.

Association between the severity of obstructive sleep apnea and the ratio of low-density lipoprotein cholesterol to high-density lipoprotein cholesterol

The positive association between the ratio of serum low-density lipoprotein cholesterol (LDL-C) to serum high-density lipoprotein cholesterol (HDL-C) and cardiovascular events has recently been receiving much attention. However, the association between the severity of obstructive sleep apnea (OSA) and this ratio has not yet been investigated. Accordingly, we sought to clarify this association and the effect of continuous positive airway pressure (CPAP) therapy on the ratio. We performed polysomnography and LDL-C/HDL-C measurements in 215 patients who were suspected of having OSA. Furthermore, LDL-C/HDL-C was again evaluated 6 months after polysomnography in 30 OSA patients for whom CPAP therapy was initiated and continued, and in 11 age- and sex-matched OSA patients for whom the therapy could not be initiated. The LDL-C/HDL-C correlated positively with apnea-hypopnea index (ρ = 0.28, P < .001) and negatively with the lowest arterial oxyhemoglobin saturation (ρ = -0.30, P < .001). Multivariate regression analysis revealed that ln apnea-hypopnea index (or ln lowest arterial oxyhemoglobin saturation) was independently associated with LDL-C/HDL-C. The LDL-C/HDL-C decreased after 6 months in the CPAP group (2.29 ± 0.67 to 2.11 ± 0.74, P = .02), whereas it did not change in the non-CPAP group (2.65 ± 0.82 to 2.62 ± 0.66, P = .81). The severity of OSA was independently associated with LDL-C/HDL-C, and LDL-C/HDL-C was significantly reduced at 6 months after CPAP therapy. These findings suggest that LDL-C/HDL-C increases in proportion to the severity of OSA, which may contribute partly to an increased risk for cardiovascular events in OSA patients.

Obstructive sleep apnoea/hypopnea influences high-density lipoprotein cholesterol in the elderly

BACKGROUND AND PURPOSE

An association between obstructive sleep apnoea/hypopnea (OSAH) and cardiovascular risk factors such as dyslipidemia has been described in adults and high-risk populations.

PATIENTS AND METHODS

We examined this association in a prospective cohort (SYNAPSE study) of 846 elderly (68.5+/-1.1 years) volunteers (41.6% of men). No subject presented with recognized OSAH syndrome, heart disease, or any neurological disorder. Unattended at-home polygraphy was done by all subjects. OSAH severity was defined as moderate (apnoea/hypopnea index: AHI>15/h) or severe (AHI>30/h). High-density lipoprotein cholesterol (HDL-c) was measured by immuno-separation-based homogenous assay.

RESULTS

The prevalence of severe cases reached 21.5% (AHI mean+/-SD: 43.5+/-11.9). Using univariate linear regression analysis, AHI (R=-0.172; p<0.0001), oxyhemoglobin desaturation index (ODI) (R=-0.108; p<0.002), mean SaO(2) (R=0.125; p<0.0003) and Nadir SaO(2) (R=0.094; p<0.007) were significantly associated with HDL-c. Multiple regression analysis demonstrated that male gender, BMI, waist to hip ratio, ODI, and AHI represent independent predictors of HDL-c. Logistic regression analysis showed a significant association between severe OSAH and low HDL-c serum levels (p<0.03) after adjustment for gender, BMI, hypertension, glycaemia, waist to hip ratio, alcohol intake and treated dyslipidemia. The association appears more evident in subjects free of lipid-lowering medications and beta-blockers (p<0.007). There was no independent association of OSAH syndrome with low-density lipoprotein (LDL) cholesterol.

CONCLUSION

Unrecognized moderate to severe apnoea/hypopnea syndrome was independently associated with low HDL-c serum levels in the present cross-sectional based elderly population. This could explain the deleterious effect of OSAH syndrome on cardiovascular risk.

The beta(2)-adrenergic receptor Arg16-gly polymorphism and interactions involving beta(2)- and beta(3)-adrenergic receptor polymorphisms are associated with variations in longitudinal serum lipid profiles: the Bogalusa Heart Study

We examined the effects of combined genotypes of the beta(2)-adrenergic receptor (AR) Arg(16)-Gly and beta(3)-AR Trp(64)-Arg polymorphisms on longitudinal serum total (T-C) and low-density lipoprotein cholesterol (LDL-C) profiles in 1,198 subjects examined multiple times (6,488 observations) from 1973 to 1996 in the Bogalusa Heart Study, at ages from 4.5 to 38 years. Within 5-year age groups, T-C was significantly (P <.05) higher in beta(2)-AR Arg(16)/Arg(16) homozygotes than in Gly(16) carriers among those 4 to 8 (171.4 +/- 30.0 v 161.5 +/- 27.7 mg/dL), 9 to 13 (167.7 +/- 28.6 v 162.4 +/- 27.4 mg/dL), and 14 to 18 (158.8 +/- 29.6 v 154.7 +/- 27.5 mg/dL) years of age, but not in those 19 to 23, 24 to 28, 29 to 33, or 34 to 38 years of age. The beta(3)-AR polymorphism was not associated with variation in either T-C or LDL-C. In multilevel polynomial growth curve models, the combination of the beta(2)-AR Arg(16)/Arg(16) genotype with either the beta(3)-AR Arg(64)/Arg(64) or Trp(64)/Arg(64) genotypes, denoted AA/AX, was associated with variation in longitudinal T-C (P <.01) and LDL-C (P <.01) profiles. The association between combined beta(2)/beta(3)-AR genotype and lipid profiles differed among race/sex groups, being most marked in black females, in whom the AA/AX combination was associated with higher T-C and LDL-C profiles across all ages. In White males, the AA/AX combination was most strongly associated with higher lipids in adults. In black males and white females, lipid profiles differed little between genotype groups. Our findings suggest that the beta(2)-AR Arg(16)-Gly genotype influences T-C and LDL-C levels in an age-specific manner, that it may interact with beta(3)-AR Trp(64)-Arg genotypes to influence longitudinal T-C and LDL-C profiles, and that the effect of combined beta(2)/beta(3)-AR genotypes on T-C and LDL-C profiles may differ among race/sex groups.

Effect of doxazosin on the size of LDL particle in the type 2 diabetic patients with hypertension

Hypertension is common in patients with type 2 diabetes mellitus (DM), and contributes to the progression of its complications in patients with diabetes. Doxazosin is a selective alpha1-adrenoceptor-blocking anti-hypertensive agent and has a favorable impact upon lipid metabolism. We investigated the effect of doxazosin on the lipid metabolism in hypertensive patients with type 2 diabetes, especially low-density lipoprotein (LDL) particle size that is associated with many elements of the insulin resistance syndrome. Cross-sectional study (n=19) was designed to determine whether doxazosin, administered with an angiotensin II-converting enzyme inhibitor (ACEI) and a Ca antagonist, affects LDL particle size. As a follow-up study (n=6), lipid and glucose metabolism and LDL particle size were followed for 12 weeks before and after the initiation of doxazosin administration (1-4 mg/day). The average size of LDL particle was significantly larger in the patients treated with doxazosin (LDL-migration index (LDL-MI): 0.348+/-0.027) than those in the patient treated without doxazosin (0.378+/-0.035), although LDL cholesterol levels did not differ between the two groups. The plasma glucose and HbA1c levels remained unchanged. Lipid profile showed normolipemia throughout the period of the study. However, LDL particle size was demonstrated to become larger during the following period. Small LDL fraction (LDL3-7) diminished remarkably and large LDL (LDL1-2) increased on the polyacrylamide gel electrophoresis (PAGE) LDL system (LipoPrint). From this pilot study, it was concluded that doxazosin is a useful anti-hypertensive agent for hypertensive type 2 diabetic patients in improving the size of LDL particle.

Effect of terazosin on blood pressure and serum lipids

In an open multicenter prospective study, the effects of short-term (4 weeks, n = 101) and long-term (6 months, n = 38) terazosin treatment on blood pressure, serum lipids and safety in the patients with mild to moderate essential hypertension were observed. Mean systolic and diastolic blood pressure in sitting position were significantly reduced by 16.4% and 14.0% respectively (P < 0.01) after 4 weeks of terazosin therapy, with the total efficacy rate being 87.1%. During a 6 month therapy, antihypertensive effect of terazosin could be maintained. Total cholesterol (TC) and low density lipoprotein (LDL) cholesterol in serum were significantly decreased P < 0.05-0.01) in patients with hypercholesterolemia (TC > or = 6 mmol/ml) after 4 week terazosin treatment; the levels of TC, LDL and triglyceride were significantly improved in hypertensive patients after 3-6 month terazosin treatment. The improvement of lipid metabolism was related to the dosage of terazosin but not to antihypertensive effects of terazosin. The results suggested that terazosin is effective in decreasing blood pressure and improving lipid metabolism. It may serve as a good antihypertensive agent for hypertensive patients with hypercholesterolemia.

Long-term alpha1-adrenergic blockade attenuates diet-induced dyslipidemia and hyperinsulinemia in the rat

This study evaluated the ability of alpha1-adrenergic blockade to interfere with the development of diet-induced hyperlipidemia and deterioration of insulin action. Diets having extremely divergent effects on glucose and lipid metabolism were contrasted. Rats were fed for 4 weeks either a nonpurified diet (chow) or a hyperlipidemic (HL) purified diet containing 40% energy as sucrose, 40% as fat, and 20% as casein. Half of each dietary cohort was given the alpha1-adrenergic antagonist prazosin (3 mg/kg/day in the food). Blood was collected in the fasted state (10 h after food removal) and 2 h after the intake of a meal. In the fasted state, plasma triacylglycerols (TGs) were higher in rats fed the HL diet than in those given chow and were not affected by long-term treatment with prazosin. Postprandially, plasma TG increased twofold in the chow-fed group, with or without long-term prazosin. In contrast, prazosin reduced by more than half the eightfold increase in TG that followed intake of the high-fat meal (Diet x Blocker interaction; p < 0.002) in the HL cohort. The HL-fed animals also displayed fasting hypercholesterolemia (+30%; p < 0.0001), which was prevented by long-term treatment with prazosin. Likewise, the 50% increase in plasma cholesterol that followed meal ingestion only in the HL cohort was blunted by the alpha1-blocker (Diet x Blocker interaction; p < 0.001). Long-term prazosin also abolished fasting hyperinsulinemia in the HL cohort, whereas it did not alter fasting insulin in chow-fed animals (Diet x Blocker interaction; p < 0.005). Measurement of postprandial lipoprotein lipase activity in several tissues did not suggest the involvement of changes in the absolute availability of the enzyme as a determinant of the hypotriacylglycerolemic action of the alpha1-blocker. Thus long-term alpha1-adrenergic blockade, with minimal effects in rats fed a hypolipidemic diet, strongly attenuates several of the fasting and postprandial alterations in plasma variables of lipid and glucose metabolism induced by an extremely lipogenic diet.

Drugs causing dyslipoproteinemia

Diuretics and beta-blockers have a strong tendency to affect serum lipids adversely, whereas the peripherally acting alpha-blocking agents consistently result in beneficial effects. Most of the other antihypertensive agents (calcium channel blockers, ACE inhibitors, angiotensin II receptor antagonists, and drugs that act centrally) are lipid neutral. The effect of steroid hormones varies with the drug, dose, and route of administration. In general, androgens lower HDL-C and have a variable effect on LDL-C. The effects of progestins vary greatly depending on their androgenicity, and estrogens are beneficial except when hypertriglyceridemia occurs with oral estrogens. Glucocorticoids raise HDL-C and may also increase triglycerides and LDL-C. Retinoids increase triglycerides and LDL-C and also reduce HDL-C. Interferons can cause hypertriglyceridemia. Following organ transplantation, a dyslipidemia often ensues. This is caused in part by the medications used to prevent rejection (glucocorticoids, cyclosporine, and FK-506) and requires close attention and, in some patients, drug therapy to prevent coronary artery disease.

Effects of a cardioselective beta-blocker on postprandial triglyceride-rich lipoproteins, low density lipoprotein particle size and glucose-insulin homeostasis in middle-aged men with modestly increased cardiovascular risk

Beta-adrenergic receptor-blocking agents are commonly used for treatment of hypertension, angina pectoris and arrhythmias and as secondary prevention after myocardial infarction. The modest protection against myocardial infarction conferred by these compounds in primary-preventive studies has suggested that beneficial effects of beta-blockade are counteracted by known adverse influences on lipid and glucose metabolism. As most beta-blockers increase plasma triglycerides and decrease the high density lipoprotein (HDL) cholesterol concentration, a randomized, double-blind, cross-over study was conducted to evaluate whether a 12-week treatment with metoprolol (100 mg o.d.) or placebo affected the metabolism of postprandial triglyceride-rich lipoproteins in 15 middle-aged men with a modestly increased cardiovascular risk. Metoprolol treatment significantly increased the postprandial responses of very low density lipoprotein (VLDL) and VLDL remnants to a mixed meal-type of oral fat tolerance test. The effect was particularly prominent for larger (Svedberg flotation rate (Sf) > 400 and Sf 60-400) particle species (P < 0.001 in repeated measures ANOVA), whereas the smaller (Sf 20-60) particles were less affected (P < 0.05). The changes in the postprandial responses of the different VLDL species were mainly related to an effect on the fasting plasma concentrations, with limited or no influences on VLDL catabolism during the postprandial state. In contrast, metoprolol treatment did not significantly influence the postprandial responses of chylomicrons and chylomicron remnants. Notably, the enhanced fasting and postprandial triglyceridaemia during metoprolol treatment was neither accompanied by a rise in fasting or postprandial free fatty acid concentrations, nor by alterations of the glucose and insulin responses to a standard oral glucose challenge. The ensuing shift in the LDL particle size distribution towards smaller particles was limited (fraction small LDL: metoprolol 22.8 +/- 15.7% versus placebo 19.3 +/- 15.0%, P < 0.05). In conclusion, metoprolol treatment primarily enhances fasting and postprandial triglyceridaemia in middle-aged men by increasing the basal hepatic production of VLDL.

Failure of the nonselective beta-blocker propranolol to affect lipoprotein lipase gene expression in the rat

Treatment with beta-blockers has been reported to be associated with the development of hypertriglyceridemia. The etiology, even the existence, of this phenomenon is controversial. The purpose of our study was to examine whether the nonselective beta-blocker propranolol causes hypertriglyceridemia in the rat and whether its action is mediated by the modulation of lipoprotein lipase (LPL) messenger RNA (mRNA) accumulation or activity. LPL activity was assayed in fresh tissue by incubation with tritiated triglycerides. LPL mRNA was quantified in total RNA by slot-blot analysis using a mouse LPL complementary DNA probe. We have conducted three series of experiments in unanaesthetized rats in order to study the effects of different single doses of propranolol (1.5 to 6 mg i.p.) and different durations of treatment (15 min to 4 wk). We measured triglyceride and cholesterol levels in plasma as well as the LPL activity and mRNA levels in the heart and adipose tissue before and after propranolol administration. In these experiments we did not find any significant decrease in either the activity or the amount of mRNA of lipoprotein lipase nor was there any change in plasma lipids following treatment. Our results lead us to the conclusion that the nonselective beta-blocker propranolol affects neither the activity nor the mRNA level of LPL in the rat.

Genetic variant showing a positive interaction with beta-blocking agents with a beneficial influence on lipoprotein lipase activity, HDL cholesterol, and triglyceride levels in coronary artery disease patients. The Ser447-stop substitution in the lipoprotein lipase gene. REGRESS Study Group

BACKGROUND

Lipoprotein lipase (LPL) is the rate-limiting enzyme in the lipolysis of triglyceride-rich lipoproteins, and the gene coding for LPL is therefore a candidate gene in atherogenesis. We previously demonstrated that two amino acid substitutions in LPL, the Asn291-Ser and the Asp9-Asn, are associated with elevated triglycerides and lower HDL cholesterol and are present with greater frequency in coronary artery disease (CAD) patients than in normolipidemic control subjects. Conversely, a third frequent mutation in this gene, the Ser447-Stop, is reported by some investigators to underlie higher HDL cholesterol levels and would represent a beneficial genetic variant in lipoprotein metabolism. We therefore sought conclusive evidence for these allegations by investigating the effects of the LPL Ser447-Stop mutation on LPL and hepatic lipase (HL) activity, HDL cholesterol, and triglycerides in a large group of CAD patients (n = 820) with normal to mildly elevated total and LDL cholesterol levels.

METHODS AND RESULTS

Carriers of the Ser447-Stop allele (heterozygotes and homozygotes) had significantly higher postheparin LPL activity (P = .034), normal postheparin HL activity (P = .453), higher HDL cholesterol levels (P = .013), and lower triglyceride levels (P = .044) than noncarriers. The influence of the Ser447-Stop allele on LPL activity was pronounced in patients using beta-blockers (P = .042) and not significant in those not using them (P = .881), suggesting a gene-environment interaction between the Ser447-Stop mutation and beta-blockers.

CONCLUSIONS

We conclude that the LPL Ser447-Stop mutation has a significant positive effect on LPL activity and HDL cholesterol and triglyceride levels and that certain subgroups of CAD patients carrying the Ser447-Stop mutation will have less adverse metabolic effects when placed on beta-blockers. The LPL Ser447-Stop mutation therefore should have a protective effect against the development of atherosclerosis and subsequent CAD.

Effect of doxazosin therapy on glucose tolerance and lipid metabolism in hypertensive patients with impaired glucose tolerance

The effects of long-term monotherapy with doxazosin, an alpha 1-blocker, or placebo on blood pressure (BP), glucose tolerance, and serum lipid levels were investigated prospectively in 43 hypertensive patients with impaired glucose tolerance. The levels of plasma glucose, serum lipids, fructosamine, and glycated hemoglobin A1c (Hb A1c) were determined before and during long-term (mean treatment period, 6.7 months) therapy with doxazosin (n = 23) or placebo (n = 20). A 75-g oral glucose tolerance test was performed before and during therapy. Significant decreases in both systolic and diastolic BP were maintained during doxazosin therapy; BP did not change in the placebo group. Neither fasting nor post-glucose-load venous plasma glucose levels were altered, and there was no significant change in the insulinogenic index in either group. Glucose intolerance was slightly improved with significant reductions in Hb A1c and fructosamine levels during doxazosin therapy. Serum total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol levels were significantly decreased, and high-density lipoprotein cholesterol levels were significantly increased in patients treated with doxazosin. Moreover, TC, LDL cholesterol, and apolipoprotein B levels were significantly decreased in patients with hypercholesterolemia (TC > or = 5.69 mmol/L). In contrast, there were no significant changes in Hb A1c, fructosamine, and lipid levels in the placebo group. These results suggest that long-term doxazosin therapy may improve glucose and lipid metabolism in hypertensive patients. Doxazosin appears useful as an antihypertensive agent for hypertensive patients with either impaired glucose metabolism or dyslipidemia.

Urapidil treatment decreases plasma fibrinogen concentration in essential hypertension

The effects of antihypertensive drugs on cardiovascular metabolic risk factors were monitored in 42 patients with essential hypertension (diastolic blood pressure [DBP] >95 mm Hg). In a double-blind randomized parallel-group study, they were treated with atenolol 50 mg once per day (n = 25) or urapidil 60 mg twice per day (n = 17), a peripheral alpha1-receptor blocker with an additional central serotonin 1A (5HT1A) receptor agonistic effect, for 12 weeks. Plasma fibrinogen concentration decreased by 24% (P < .0001) during urapidil treatment and by 9% (P = .05) during atenolol treatment, with the effects of the two drugs differing significantly. Plasminogen activator inhibitor (PAI) activity tended to increase by 17% (nonsignificant [NS]) in the atenolol-treated group and to decrease by 4% (NS) in the urapidil group. Differences between the effects of the two drugs on very-low-density lipoprotein (VLDL) triglycerides (TG) and on total TG were significant. During urapidil medication, these two parameters were reduced by 22% and 13%, respectively, but the changes were nonsignificant (P = .11 and P = .14, respectively). In contrast, atenolol treatment caused a significant increase in both VLDL TG and total TG of 31% and 21%, respectively. Hemoglobin A1c (HbA1c) increased by 4% (P = .06) during atenolol treatment, but was unaffected by urapidil. There were no significant changes within or between atenolol- and urapidil-treated groups regarding glucose disposal on an oral glucose tolerance test (OGTT) or the insulin sensitivity index on a hyperinsulinemic-euglycemic clamp test. In conclusion, urapidil treatment was characterized by neutral or favorable effects on several variables associated with the metabolic syndrome. Atenolol treatment had neutral properties in some metabolic aspects, but deleterious effects on lipid status.

Review: the effects of antihypertensive agents on serum lipids

Because various antihypertensive drugs adversely affect lipid metabolism, these drugs may increase associated risks for coronary artery disease and thus offset some of the beneficial effects of blood pressure reduction. In this paper the current literature regarding the effects of antihypertensive agents on serum lipids is reviewed. Differing effects of various classes of antihypertensives are assessed to further our understanding of this very important subject.

Felodipine therapy may not alter glucose and lipid metabolism in hypertensives. Felodipine Multicenter Prospective Study Group in Japan

The effects of long-term monotherapy with felodipine, a calcium antagonist, on blood pressure, glucose tolerance, and serum lipid profiles were prospectively investigated in 51 hypertensive patients: 13 with normal glucose tolerance and 38 with glucose intolerance. The levels of plasma glucose, serum lipids, and glycosylated hemoglobin A1c were determined before and during long-term (7.5 +/- 0.5 months; range, 6 to 9 months) therapy with felodipine. A 75-g oral glucose tolerance test was performed before and during long-term felodipine therapy. Significant decreases in both systolic and diastolic blood pressures in both patient groups were maintained during the therapy. Neither fasting nor post-glucose load venous plasma glucose levels were altered in either group of patients, and no patients with normal glucose tolerance developed diabetes mellitus during the study. Serum lipid levels did not change significantly in either group of patients except for significant decreases in high-density lipoprotein cholesterol and apolipoprotein A-I in the group with normal glucose tolerance tests, but those changes remained within the normal range. Furthermore, neither serum lipid nor apolipoprotein levels were altered, even in patients with hypercholesterolemia (total cholesterol levels, > 5.69 mmol/L = 220 mg/dL). These results suggest that long-term therapy with felodipine may not alter glucose and lipid metabolism in hypertensive patients, and felodipine appears to be useful as an antihypertensive agent for hypertensive patients with either dyslipidemia or impaired glucose metabolism.

Mechanisms of action of adrenergic receptor blockers on lipids during antihypertensive drug treatment

The objective of this article is to focus on the antihypertensive agents blocking adrenergic receptors, both alpha and beta blockers, and attempt to construct potential explanations for their effects on lipids in a mechanistic manner. The essential thesis is that adrenergic control of lipid metabolism is responsible for the effect on lipids and lipoproteins of antihypertensive agents that block adrenergic receptors. Agonists and antagonists show the opposite action on lipoprotein lipase, lecithin:cholesterol acyltransferase (LCAT) and LDL-cholesterol uptake by LDL receptors in a manner that might explain the findings of increases in triglycerides and LDL cholesterol with decreases in HDL cholesterol in patients receiving beta blockers without intrinsic sympathomimetic activity and the reverse in patients on treatment with alpha adrenergic receptor blockers.

Doxazosin and captopril in mildly hypercholesterolemic hypertensive patients. The Doxazosin-Captopril in Hypercholesterolemic Hypertensives Study

The evidence linking hypertension and hypercholesterolemia is strong and has fueled research into possible adverse effects of some antihypertensive agents on serum lipid profile. This multicenter, open, parallel study compares the effects of doxazosin and captopril on blood pressure, serum lipid levels, and quality of life in 224 hypercholesterolemic hypertensive patients. Blood pressure was significantly reduced in both treatment groups (p < 0.001) and was normalized (standing diastolic pressure < or = 90 mm Hg) in 73% of the doxazosin patients and 67% of the captopril group. Serum total cholesterol level was favorably reduced by both doxazosin (from 238 to 223 mg/dl, p < 0.001) and captopril (from 245 to 233 mg/dl, p < 0.001), whereas high density lipoprotein cholesterol concentration increased only in the doxazosin group (from 33 to 36 mg/dl, p < 0.001). The calculated 10-year risk for the development of coronary heart disease was reduced significantly (p < 0.001) by 28% in the doxazosin group and by 19% in the captopril group. The quality of life evaluation showed beneficial changes in both treatment groups. As a result of proven antihypertensive efficacy and a lack of unfavorable effects on lipid parameters and health status measures, these findings support the use of both doxazosin and captopril as agents of first choice in the treatment of hypertensive patients with associated lipid abnormalities.

Antihypertensive and metabolic effects of long-term treatment with amosulalol in non-insulin dependent diabetics

In this open study, 41 hypertensive patients with non-insulin dependent diabetes mellitus were treated with the combined alpha- and beta-adrenoceptor blocker amosulalol hydrochloride for 24 weeks, either alone or added to existing antihypertensive therapy. The effects on blood pressure, glucose and lipid metabolism were examined. Daily administration of 20 to 60 mg amosulalol caused a significant reduction in both systolic and diastolic blood pressure within 2 weeks. This effect was stable, lasting for the entire trial period. The mean systolic and diastolic blood pressure decreased from 174 +/- 13/92 +/- 9 mmHg at the beginning to 148 +/- 16/80 +/- 11 mmHg at the end of the trial. Heart rate was not affected. Plasma glucose and haemoglobin Alc levels showed a tendency to decrease without any statistical significance. Total and HDL-cholesterol and triglyceride levels also remained unchanged. Although 3 patients had complained of dizziness, all were easily manageable. The results indicate that amosulalol is effective in the treatment of hypertension in non-insulin dependent diabetics and does not affect glucose and lipid metabolism.

Hypertension, plasma lipids and antihypertensive drugs

Treatment of hypertension is quite effective in preventing cerebrovascular disease. Morbidity and mortality from coronary heart disease, the major complications of high blood pressure are not, however, generally affected when mild to moderate hypertension is treated with antihypertensive drugs. This is probably owing to the multifactorial nature of atherosclerosis, the main cause of coronary heart disease. For example, dyslipidemias and other risk factors are very common among hypertensive patients. Prevention of coronary heart disease among hypertensive subjects is possible only by intervening in the many contributory risks. Non-pharmacological hypolipidemic treatments such as adequate nutrition and exercise are positive steps in the treatment of all hypertensive patients. The role of various antihypertensive agents should also be carefully considered. The associations between hypertension, several metabolic abnormalities, development of organ complications and various antihypertensive drugs should be explored in detail.

Doxazosin therapy in the treatment of diabetic hypertension

The incidence of cardiovascular disease in non-insulin-dependent diabetes mellitus (NIDDM) has not been reduced by the control of hyperglycemia alone. Hypertension and dyslipidemia may be the major determinants of macrovascular disease in these patients. With the high prevalence of hypertension in NIDDM, antihypertensive drugs are likely to be important determinants of an atherogenic lipid profile. To date, there is no completed major randomized controlled trial of antihypertensive treatment outcome in a diabetic population, and as such, drug choice for the treatment of diabetic hypertension is often based on evidence extrapolated from studies in nondiabetic groups. However, two short-term studies have assessed the effects of doxazosin antihypertensive therapy in subjects with NIDDM. Both studies showed that the significant reduction in blood pressure with doxazosin treatment was associated with favorable effects on the serum lipid profile. In one study, contrasting adverse effects of atenolol treatment on glycemic control, lipids, and lipoproteins were observed. Doxazosin therapy was associated with a trend toward correcting the disturbances of lipoprotein metabolism characteristic of NIDDM. These metabolic effects, combined with effective lowering of blood pressure by doxazosin, may be important determinants of cardiovascular disease in the long term.

Effect of alpha-adrenergic blockade on blood pressure, glucose, and lipid metabolism in hypertensive patients with non-insulin-dependent diabetes mellitus

To clarify the long-term effects of alpha-adrenergic blockade on blood pressure, glucose, and lipid metabolism, a selective alpha 1-adrenergic inhibitor (prazosin, 1.0 to 2.0 mg/day in divided doses) was administered as a single antihypertensive agent to 10 (four men and six women, aged 52 to 76 years) hypertensive patients (systolic blood pressure [SBP] greater than or equal to 150 mm Hg or diastolic blood pressure [DBP] greater than or equal to 90 mm Hg) with non-insulin-dependent diabetes mellitus (NIDDM) for up to 20 weeks. Blood pressure, glucose tolerance and immunoreactive insulin (IRI) response to 75 gm oral glucose load, hemoglobin A1 (Hb A1), serum lipid profile, and serum apolipoprotein were examined before and after treatment. SBP and DBP were significantly reduced at 20 weeks after treatment with the selective alpha 1-adrenergic inhibitor (SBP 167 +/- 6 mm Hg versus 152 +/- 7 mm Hg; DBP 81 +/- 3 mm Hg versus 76 +/- 3 mm Hg, (p less than 0.05 and p less than 0.01, respectively). Glucose tolerance and IRI response to glucose load were not significantly changed at 4 and 12 to 20 weeks after selective alpha 1-inhibitor treatment compared with the baseline data before treatment; the level of Hb A1 was not significantly changed at 4 and 20 weeks after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperlipidaemia and hypertension

Hyperlipidaemia and hypertension are commonly found in the population and are independent risk factors for cardiovascular complications. The combined presence of hypertension and hypercholesterolaemia increases considerably the risk for cardiovascular complications. These high-risk patients have to be identified early and treated appropriately in order to avoid complications. The goal of antihypertensive therapy is to reduce the average levels of diastolic pressure to below 90 mm Hg and the systolic pressure to below 140 mm Hg. The goals set for lipid levels in these patients are total cholesterol less than or equal to 200 mg/dl, LDL cholesterol less than or equal to 135 mg/dl and triglycerides less than or equal to 200 mg/dl. The first step in the treatment of patients with both hyperlipidaemia and hypertension is to seek underlying causes and to take appropriate therapeutic measures for both diseases. Non-pharmacological treatment of these high-risk patients includes weight reduction, appropriate dietary measures including alcohol and salt restriction, cessation of smoking and increasing physical activity. If pharmacological antihypertensive treatment is needed, drugs without adverse effects on lipid and lipoprotein levels should be preferred. If, in addition to dietary measures, drug treatment is necessary to reduce high cholesterol levels, bile acid sequestrants are the drug of first choice at present. If long-term safety can be established for HMG CoA reductase inhibitors, these drugs will represent a major advance in the therapy of hypercholesterolaemia.

Alpha-adrenergic blockers: mechanism of action, blood pressure control, and effects of lipoprotein metabolism

The sympathetic nervous system plays a major role in the pathogenesis of essential hypertension and is mediated by the alpha and beta receptors. The alpha receptor is divided into two types, alpha 1 and alpha 2, based on response to epinephrine and norepinephrine. alpha 1-Adrenergic receptors have a high affinity for drugs such as prazosin, doxazosin, and terazosin, which act to reduce blood pressure by selective blockade of the receptor. These agents provide a rational approach to the treatment of hypertension by correcting elevated total peripheral resistance, the fundamental hemodynamic abnormality in essential hypertension. In contrast, early alpha-adrenergic receptor blockers nonselectively blocked both alpha 1 and alpha 2 receptors and were unsuitable as antihypertensive agents because they induced tachycardia and patients developed a tolerance to them rapidly. alpha 1-Adrenergic blockers also have beneficial effects on plasma lipoproteins, tending to decrease levels of triglycerides and cholesterol and increase levels of high-density lipoprotein (HDL) cholesterol and the HDL cholesterol/total cholesterol ratio. beta-Adrenergic blockers, such as propranolol and atenolol, have been shown to have an adverse effect on the lipid profile by tending to increase levels of triglycerides and decrease HDL cholesterol. A number of mechanisms contribute to these effects, in particular, adrenergic modulation of lipoprotein lipase and the triglyceride secretion rate. Doxazosin has been shown to increase the activity of LDL receptors, which may be partly responsible for its beneficial effect on plasma lipids and lipoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective alpha 1-adrenergic blockade, lipids, and coronary heart disease risk. Considerations in the treatment of mild hypertension

The importance of hypertension and hyperlipidemia as independent and interactive risk factors for the development of premature cardiovascular disease, and particularly for the development of atherosclerotic coronary heart disease, is becoming increasingly apparent both from epidemiologic data and from therapeutic trials. Nevertheless, therapeutic trials of patients with mild hypertension have not demonstrated benefits from lowering arterial pressure, in terms of reduced mortality rates from coronary events. This may, in part, be due to the fact that many of the antihypertensive agents used in these trials adversely influence lipid and lipoprotein levels. Thus, agents that are lipid-neutral or that favorably influence the lipid profile, such as selective alpha 1-inhibitors, are receiving increasing attention for the treatment of mild hypertension. Recent insights into these issues are considered.

Alpha-1 blockers. A new generation of antihypertensive agents

Alpha-1 blockers have certain disadvantages over conventional and antihypertensive therapies in their haemodynamic profile and metabolic effects. This paper reviews the development of alpha-blockade, the therapeutic efficacy of prazosin, the prototype alpha-1 blocker, and the rationale for the once-daily antihypertensive compounds, terazosin and doxazosin. These drugs offer a useful alternative to first- or second-line therapy in suitable hypertensive patients, particularly with their potentially beneficial effects on serum lipids.

The relevance of plasma lipid changes with cardiovascular drug therapy

Evidence is reviewed that thiazide diuretics increase plasma levels of triglycerides and LDL-cholesterol, and that most beta-blockers increase triglycerides and depress HDL-cholesterol. By contrast, indapamide, pindolol, and calcium channel blockers have little effect, and alpha 1-blockers and alpha 2-stimulants may improve the HDL- to LDL-cholesterol ratio.

Adrenergic blocking agents and lipoprotein lipase activity

Lipoprotein lipase activity, total serum cholesterol and triglycerides, HDL cholesterol were determined before and after two weeks of treatment with a low dose of an alpha 1-blocking agent (prazosin) or of a beta-adrenergic-blocking drug (metoprolol). Lipoprotein lipase activity was almost doubled after prazosin (p less than 0.02) and practically unchanged after metoprolol, at a time and at a drug dosage when only minor changes in blood pressure and serum lipids were detectable. HDL cholesterol was slightly but significantly increased after prazosin (p less than 0.05). Heart rate was increased after prazosin (p less than 0.05) and decreased after metoprolol (p less than 0.01).

Effect of alpha- and selective beta-blockade for hypertension control on plasma lipoproteins, apoproteins, lipoprotein subclasses, and postprandial lipemia

Fourteen male patients (mean age +/- SD, 52 +/- 11 years) with a history of hypertension (systolic blood pressure, 148 +/- 10 mm Hg; diastolic blood pressure, 99 +/- 2 mm Hg) were enrolled in a cross-over trial of prazosin and atenolol, with a minimum of eight weeks of treatment with each drug. Measures of lipoprotein metabolism included levels of: total plasma cholesterol, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and high-density lipoprotein2 cholesterol. Lipoprotein mass was measured by analytical ultracentrifugation in low-density to very low-density lipoprotein flotation rate intervals of 0 to 12, 12 to 20, and 20 to 400, and high-density lipoprotein flotation rate intervals of 0 to 3.5 and 3.5 to 9.0. Apolipoproteins A1 and B, postheparin lipoprotein and hepatic lipase activities, and magnitude of postprandial lipemia also were determined. Mass of intermediate-density lipoproteins (flotation rate, 12 to 20) was significantly lower (p = 0.05) following prazosin therapy compared with atenolol therapy. Other lipid parameters, including triglycerides and low- and high-density lipoprotein cholesterol, were not significantly different for the two drug treatments.

Effects of prazosin on hemodynamics, hemostasis, and serum lipid and lipoprotein levels in normal and hypercholesterolemic monkeys

The effect of prazosin on hemodynamics, hemostasis, and serum lipid and lipoprotein levels was investigated in normal and hypercholesterolemic rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) monkeys. Administration of prazosin (2 mg/kg bodyweight, orally, twice a day) for three weeks caused significant reductions in plasma cholesterol, including low- plus very low-density lipoprotein cholesterol, apolipoprotein B, and triglyceride levels. Drug therapy was associated with increased high-density lipoprotein cholesterol levels, although in one group of monkeys this rise also was associated with a reduction in apolipoprotein A1. Prazosin treatment significantly decreased mean arterial pressure in normal and hypercholesterolemic monkeys. As was expected, acute administration of phenylephrine caused mean arterial pressure to rise, with animals receiving normal- or high-cholesterol-containing diets showing similar responses. After prazosin treatment, however, a greater inhibition in the phenylephrine pressor response was observed in hypercholesterolemic monkeys compared with normal animals. Platelet aggregation in response to adenosine 5'-diphosphate, prothrombin time, and activated partial thromboplastin time were not altered by prazosin. Thus, in our nonhuman primate models of hypercholesterolemia, administration of prazosin resulted in reduction in lipid and apoprotein levels with no change in hemostasis.

Effects of prazosin on blood pressure and diabetic control in patients with type II diabetes mellitus and mild essential hypertension

The effects of prazosin treatment on blood pressure and diabetic control were assessed in 22 patients with stable non-insulin-dependent diabetes mellitus and hypertension. After an initial six-week baseline period, patients were titrated to optimal therapeutic doses of prazosin (mean daily dose, 12.9 +/- 6.5 mg). Both sitting and standing systolic and diastolic blood pressures were significantly decreased (p = 0.01) with prazosin therapy from a mean of 152/99 mm Hg sitting and 144/99 mm Hg standing to a mean of 139/84 mm Hg and 133/85 mm Hg, respectively, at the end of titration and throughout the 12-week prazosin maintenance therapy period. Seventy-seven percent of patients achieved the goal sitting diastolic blood pressure of 85 mm Hg or less. Total cholesterol, high-density lipoprotein cholesterol, and triglyceride levels were not significantly altered during prazosin therapy compared with baseline measurements. Diabetic control and renal function were maintained during prazosin treatment with no significant changes from baseline noted. No unexpected adverse experiences were reported. In summary, prazosin treatment effectively reduced blood pressure without compromising diabetic control or renal function in this group of hypertensive patients with concomitant diabetes mellitus.

Effects of alpha- and beta-adrenergic antagonists on plasma apolipoproteins and forearm blood flow in patients with mild hypertension

To study the mechanisms by which adrenergic antagonists affect blood pressure and plasma lipid levels, the effects of alpha-blockade with prazosin were compared with those of beta-blockade with propranolol in 23 normolipidemic, mildly hypertensive patients. Plasma lipoprotein composition, apolipoproteins, and some of the processes involved in lipid synthesis and clearance from plasma were investigated also. Patients entered an eight-week placebo period during which they were free of all antihypertensive medications. They were then randomly assigned under double-blind conditions to treatment with either prazosin (mean dose, 5 mg per day) or propranolol (mean dose, 133 mg per day) for eight weeks. Doses of both drugs were titrated to achieve either a decrease in diastolic blood pressure of 10 mm Hg or more or a reduction of diastolic blood pressure to less than 85 mm Hg, whichever was lower. Total plasma cholesterol decreased by 9 percent during prazosin treatment and increased by 7 percent during propranolol treatment (p less than 0.005 between treatments). Low-density lipoprotein cholesterol decreased by 12 percent with prazosin and increased by 12 percent with propranolol (p less than 0.005). Apolipoprotein B decreased by 17 percent with prazosin and increased by 15 percent with propranolol (p less than 0.005). There were no significant changes in total high-density lipoprotein cholesterol, its subfractions high-density lipoprotein2 or high-density lipoprotein3, or in apolipoprotein A1 and apolipoprotein A2. Plasma very low-density lipoprotein and low-density lipoprotein triglycerides were not significantly affected by either treatment. Plasma post-heparin lipase activities, which clear triglyceride and high-density lipoprotein cholesterol from plasma, were not altered significantly. Since regional blood flow could affect the clearance of plasma lipoproteins, measurements were taken of forearm blood flow, forearm vascular resistance, and maximal forearm vasodilatory potential during reactive hyperemia. The adrenergic antagonists had no effect on these measurements, nor did they affect cellular cholesterol synthesis as measured by the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in blood mononuclear cells. The results of this study demonstrate differing actions between alpha- and beta-adrenergic antagonism. Alpha-blockade produced significantly lower levels of plasma low-density lipoprotein cholesterol and apolipoprotein B than beta-adrenergic antagonism without changes in high-density lipoproteins.

Inhibition of hepatic cholesterol synthesis by the alpha 1-adrenoceptor blocker doxazosin in the hypercholesterolemic golden hamster

The effect of treatment with the alpha 1-specific adrenoceptor blocker, Doxazosin, on lipid parameters was studied in male Golden hamsters fed a cholesterol-enriched diet. Within 1 week the Doxazosin-treated animals had a lower plasma (-12%) and hepatic (-30%) cholesterol content than the cholesterol-fed controls. De novo cholesterol synthesis in the liver was lowered by 39% in the Doxazosin-treated animals. These data indicate that the reported beneficial effect of alpha 1-blockade on plasma cholesterol levels may be due to lowering of the hepatic cholesterol synthesis.

Effects of antihypertensives on plasma lipids and lipoprotein metabolism

There is good epidemiologic evidence that hypertension is associated with a high risk of cardiovascular disease. However, primary intervention trials have failed to demonstrate that a reduction in blood pressure in hypertensive patients reduces morbidity and mortality from cardiac events. Since various antihypertensive drugs adversely affect lipoprotein metabolism, these drugs may increase associated coronary risk and offset the beneficial effects of lowering blood pressure. This article reviews the effects of various antihypertensive drugs on plasma lipids, lipoproteins, and apolipoproteins. They can be summarized as follows: thiazide-type diuretics cause a marked elevation of plasma triglycerides and very low-density lipoprotein (VLDL) and minor increases in total cholesterol and low-density lipoprotein (LDL), but have little effects on high-density lipoprotein (HDL). The nonselective beta-blockers do not significantly affect total cholesterol and LDL, but increase total triglycerides and VLDL and decrease HDL. The changes in plasma lipids and lipoproteins caused by cardioselective beta-blockers and beta-blockers with intrinsic sympathomimetic activity are qualitatively similar but less pronounced. Calcium antagonists and angiotensin-converting enzyme inhibitors appear to have no significant effects on plasma lipids. alpha 1-Inhibitors reduce total triglycerides, total cholesterol, VLDL, and LDL and increase HDL. The possible mechanisms by which antihypertensive drugs affect cellular lipid metabolism (e.g., LDL receptor, lipid synthesis, lipoprotein lipase, lecithin cholesteryl acyltransferase, acylcholesteryl acyltransferase, and cholesteryl ester hydrolase) are described. The clinical significance of changes in blood lipids and cellular lipid metabolism caused by antihypertensive drugs is not yet totally clear. Nevertheless, before antihypertensive drug treatment is initiated, blood lipid levels should be measured to identify preexisting hyperlipidemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of beta-adrenergic blocking agents on blood lipid levels

This review examines the effects of beta-adrenergic blocking agents on blood lipids. These agents have been effective in the treatment of angina and hypertension and in the reduction of recurrence of ischemic cardiac disease, such as myocardial infarction. Many beta blockers, however, have an adverse effect on blood lipids, especially by reducing high-density lipoprotein (HDL) cholesterol and increasing triglycerides. One result is an unfavorable influence on the cholesterol ratio (expressed either as low-density lipoprotein [LDL]/HDL or total cholesterol/HDL). These cholesterol parameters have been shown to have a strong influence on coronary heart disease (CHD) risk. Studies have shown that antihypertensive therapy has reduced the incidence of cerebrovascular disease but, in many instances, has not reduced the incidence of CHD. A hypothesis for this lesser effect on coronary disease is that antihypertensive agents may be adversely affecting blood lipids. Thus, while one major risk factor for CHD is reduced, another may be somewhat enhanced. Pharmacologic properties of some beta blockers such as peripheral alpha blockade (e.g., with labetalol) or intrinsic sympathomimetic activity (ISA) (e.g., with pindolol) may counteract some of these negative lipid effects. An investigational beta blocker, bevantolol, which will be marketed shortly in the United States, has been effective in antihypertensive therapy. Bevantolol has been shown to lower LDL cholesterol and not adversely affect HDL cholesterol; in this way, bevantolol favorably influences the serum lipoprotein profile. Whether this effect will have clinical significance remains to be seen.

Mode of action of lipid-lowering drugs

Following the recent demonstration that both cholestyramine and nicotinic acid decrease mortality from coronary heart disease, there is a new enthusiasm for hypolipidaemic therapy. The agents in current use are, however, insufficiently active or are accompanied by unacceptable side effects. An understanding of the mode of action is necessary, both to optimize treatment guidelines (e.g. regarding combination therapy or use in specific subsets of patients) and to develop new agents with preferred actions on rate-limiting steps. A reduction in LDL cholesterol concentration remains the principal desired action, although an elevation in HDL may also be beneficial. The main categories of commercially available agent comprise the anion exchange resins (inhibitors of bile acid absorption); cholesterol absorption inhibitors; fibrates (probably acting by enhancing lipoprotein lipase); and probucol (affecting LDL clearance). The most interesting of the new agents in clinical trials are the beta-hydroxy-beta-methylglutaryl-CoA reductase inhibitors, but other types of agent are at an earlier stage of evaluation, e.g. acyl-CoA: cholesterol acyltransferase inhibitors and peptide cofactors. It is not yet certain whether all the approaches to cholesterol lowering have equal validity, although an effect on biological endpoints is obtained for a variety of agents. Future evaluation will be aided by the implementation of noninvasive methods to quantify atherosclerosis and by the use of simple, 'dry-chemistry', cholesterol assays to screen populations.

Comparison of effects on lipid metabolism of antihypertensive drugs with alpha- and beta-adrenergic antagonist properties

Elevated blood cholesterol levels are a major cause of coronary heart disease. High-density lipoprotein cholesterol is regarded as a protective cholesterol fraction that is negatively associated with the incidence of coronary heart disease. Thus, the ratio of high-density lipoprotein to total cholesterol levels is an expression of the total atherogenicity--the higher the ratio, the lower the risk of coronary heart disease. There is a sharp contrast between alpha- and beta-adrenergic blockers with regard to their effect on the profile of blood lipids. In most studies, alpha blockers increased high-density lipoprotein cholesterol levels and decreased serum triglyceride levels. In addition, alpha blockers generally reduce total serum cholesterol levels. On the other hand, most beta blockers reduce serum levels of high-density lipoprotein cholesterol and increase serum triglyceride levels. European clinical trials recently investigated the effects of alpha blockers and beta blockers on blood lipids in a total of 104 and 281 patients with hypertension, respectively. On the average, selective alpha blockade increased the high-density lipoprotein cholesterol:total cholesterol ratio by 11.3 percent and reduced serum triglyceride levels by 11.4 percent. In contrast, the selective and nonselective beta-adrenergic blockers atenolol, metoprolol, and propranolol reduced that ratio by 11.7 percent and increased serum triglyceride levels by 25.8 percent. This difference between alpha and beta blockers may significantly influence the risk profile of coronary heart disease and should be given strong consideration when choosing drug therapy for hypertensive patients.