Effects of prazosin and alphamethyldopa on blood lipids and lipoproteins in hypertensive patients

Metabolic effects of antihypertensive agents: role of sympathoadrenal and renin-angiotensin systems

Reports of beneficial, neutral and adverse impacts of antihypertensive drug classes on glucose and lipid metabolism can be found in human data. Furthermore, mechanisms for these diverse effects are often speculative and controversial. Clinical trial data on the metabolic effects of antihypertensive agents are highly contradictory. Comparisons of clinical trials involving different agents are complicated by differences in the spectrum of metabolic disturbances that accompany hypertension in different groups of patients. Two physiological systems are predominant at the interface between metabolic and cardiovascular regulation: the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). These two systems are major targets of antihypertensive drug actions, and also mediate many of the beneficial and adverse effects of antihypertensive agents on glucose and lipid metabolism. Thiazides and beta-adrenergic antagonists can adversely affect glucose and lipid metabolism, which are frequently compromised in human essential hypertension, and increase the incidence of new cases of diabetes. Laboratory studies confirm these effects, and suggest that compensatory activation of the SNS and RAS may be one mechanism. Other antihypertensives directly targeting the SNS and RAS may have beneficial effects on glucose and lipid metabolism, and may prevent diabetes. Resolution of the controversies surrounding the metabolic effects of antihypertensive agents can only be resolved by further laboratory studies, in addition to controlled clinical trials.

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.

Clinical experience with doxazosin in general medical practice

The antihypertensive efficacy, lipid effects, and safety of doxazosin, a selective alpha 1-inhibitor for the reduction of coronary heart disease (CHD) risk in hypertensive patients, was assessed in a general medical practice setting. Seven hundred seventy-one patients were entered into the study, which involved three phases: (1) a 2-week baseline period, (2) an 8-week period in which patients received doxazosin, 1 to 8 mg once daily, and (3) a 4-week maintenance period. From baseline to final visit there was a highly significant 27% reduction (p less than 0.001) in calculated CHD risk based on the Framingham equation as a consequence of doxazosin's favorable effects on both blood pressure and serum lipid levels. Efficacy and toleration of doxazosin therapy were good to excellent in most patients. The investigators' global assessment of efficacy of once-daily doxazosin therapy was excellent or good for 82% of patients and fair or poor for only 18% of patients. After 12 weeks, 83% of the patients were considered therapy successes (sitting diastolic blood pressure either less than or equal to 90 mm Hg or greater than or equal to 10 mm Hg reduction not reaching less than or equal to 90 mm Hg) at a mean daily dose of 3.5 mg. Seventy-one percent achieved "normalized" blood pressure control (sitting diastolic less than or equal to 90 mm Hg with a decrease of greater than or equal to 5 mm Hg) at a mean dose of 3.1 mg once daily. By the final treatment visit, systolic/diastolic blood pressures of efficacy evaluable patients were reduced by 20.6/15.3 and 21.0/15.4 mm Hg from a mean baseline of 166/104 and 165/104 mm Hg in the sitting and standing positions, respectively (p less than 0.05). Total cholesterol was significantly decreased (p less than 0.01). Most side effects were mild or moderate and disappeared with or were tolerated on continued therapy. The investigators' global assessment of patient toleration of doxazosin treatment was excellent or good for 89% of the 763 patients evaluated and fair or poor for only 11% of patients. The most commonly reported side effects were headache (8%) and dizziness (7%). No clinically significant laboratory changes were apparent, and no trends were observed with regard to organ systems or correlations with dose or duration of treatment.

Methyldopa-induced autoantibodies against red blood cells

Methyldopa therapy results in the formation of red cell autoantibodies in 10-20% of patients taking the drug for longer than 4 months. These red cell antibodies are true autoantibodies, that is they are directed against an autoantigen on the red blood cell membrane and not against the drug or against a drug-altered antigen. The target membrane antigen is usually within the Rhesus system, although often the antibody specificity cannot be defined. Red cell antibody is usually detectable in the patient's sera as well as on the red cells. The autoantibody is usually a warm reacting IgG antibody. Most patients who develop these autoantibodies do not go on to develop hemolytic anemia in spite of high titres of antibodies on their red cells. In addition, these patients do not tend to develop hemolysis if methyldopa therapy is continued. Rarely patients develop hemolytic anemia which can be severe. Differences in antibody characteristics, including subclass restriction, complement-binding ability, or titre do not explain why some patients with autoantibody hemolyze while most do not. One group of investigators found that hemolyzing patients had IgM on their red cells while those who did not had IgG only. But while this observation could explain why some patients (IgM-sensitized red cells) hemolyze, it does not explain why most patients with IgG-sensitized red cells do not hemolyze. Why the autoantibody forms is not known but some investigators have proposed that the drug may directly affect B or T cells with resulting impairment of immune tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

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.