Acute renal effects of doxazosin in man

The Effects of Verapamil, Hydralazine, and Doxazosin on Renin, Aldosterone, and the Ratio Thereof

PURPOSE

Hydralazine, doxazosin, and verapamil are currently recommended by the Endocrine Society as acceptable bridging treatment in those in whom full cessation of antihypertensive medication is infeasible during screening for primary aldosteronism (PA). This is under the assumption that they cause minimal to no effect on the aldosterone-to-renin ratio, the most widely used screening test for PA. However, limited evidence is available regarding the effects of these particular drugs on said ratio.

METHODS

In the present study, we retrospectively assessed the changes in aldosterone, renin, and aldosterone-to-renin values in essential hypertensive participants before and after treatment with either hydralazine (n = 26) or doxazosin (n = 20) or verapamil (n = 15). All samples were taken under highly standardized conditions.

RESULTS

Hydralazine resulted in a borderline significant rise in active plasma renin concentration (19 vs 25 mIU/L, p = 0.067) and a significant fall in the aldosterone-to-renin ratio (38 vs 24, p = 0.017). Doxazosin caused declines in both plasma aldosterone concentration (470 vs 330 pmol/L, p = 0.028) and the aldosterone-to-renin ratio (30 vs 20, p = 0.020). With respect to verapamil, we found no statistically significant effect on any of these outcome variables.

CONCLUSION

We conclude that the assumption that these drugs can be used with little consequence to the aldosterone-to-renin cannot be substantiated. While it is possible that they are indeed the best option when full antihypertensive drug cessation is infeasible, the potential effects of these drugs must still be taken into account when interpreting the aldosterone-to-renin ratio.

alpha-Adrenergic regulation of human renal function

Pharmacological and molecular cloning techniques have identified six human subtypes of alpha-adrenoceptors which are designated alpha 1A, alpha 1D, alpha 2A, and alpha 2C. At the protein level human kidney expresses predominantly alpha 2A-adrenoceptors while other alpha 2-adrenoceptor subtypes or alpha 1-adrenoceptors have not been detected consistently in radioligand binding studies. However, the presynaptic receptors, which inhibit noradrenaline release in the human kidney, appear to belong to the alpha 2C-subtype. Intrarenal infusion of the nonselective alpha-adrenoceptor antagonist, phentolamine, and of the selective alpha 2-adrenoceptor antagonist, yohimbine, but not of the selective alpha 1-adrenoceptor antagonist, doxazosin, increase renal blood flow and renin release in hypertensive patients undergoing diagnostic renal angiography. Thus, alpha 2- but not alpha 1-adrenoceptors appear to mediate a tonic renal vasoconstriction and inhibition of renin release. Effects of systemically given alpha 1-adrenoceptor agonists and antagonists are difficult to interpret on a mechanistic level since direct effects in the kidney and indirect effects due to baroreflex activation and peripheral presynaptic and central sympatholytic actions may at least partially offset each other. Moreover, some of these drugs may additionally act independent of alpha-adrenoceptors, for example, via imidazoline recognition sits. The net result in a given subject may depend on the endogenous sympatho-adrenal tone. Thus, for each target population of interest, effects have to be described empirically for each drug.

Doxazosin. An update of its clinical pharmacology and therapeutic applications in hypertension and benign prostatic hyperplasia

Doxazosin is a long-acting alpha 1-adrenoceptor antagonist structurally related to prazosin and terazosin. Its antihypertensive effect is produced by a reduction in the smooth muscle tone of peripheral vascular beds resulting in a decrease in total peripheral resistance without significant effect on cardiac output or heart rate. In benign prostatic hyperplasia, doxazosin's effect of relieving bladder outflow obstruction is produced through a reduction in prostatic tone mediated via alpha 1-adrenoceptor blockade. In most comparative trials doxazosin has proven to be equally effective as the comparator drug in the treatment of mild to moderate hypertension. It has been used in a variety of patient populations including the elderly, Blacks, smokers, and patients with concomitant disease states such as renal dysfunction, hypercholesterolaemia, non-insulin dependent diabetes mellitus (NIDDM) and respiratory disease. Doxazosin has also been used successfully in combination with beta-adrenoceptor antagonists, diuretics, calcium channel antagonists, and angiotensin-converting enzyme inhibitors in patients with hypertension that is uncontrolled with monotherapy. Doxazosin has a beneficial effect on some of the risk factors associated with coronary heart disease including elevated serum lipid levels, impaired glucose metabolism, insulin resistance and left ventricular hypertrophy. Modest decreases in total cholesterol, low density lipoprotein cholesterol and triglycerides are seen with doxazosin therapy while small increases in high density lipoprotein cholesterol and the high density lipoprotein cholesterol/total cholesterol ratio are consistently reported. Some studies have reported an improvement in glucose tolerance although this effect has been more consistently seen in nondiabetic patients than in patients with NIDDM. Additionally, doxazosin produces a similar reduction in left ventricular hypertrophy to other antihypertensive agents. Modelling-based calculations suggest that doxazosin significantly reduces the risk of developing coronary heart disease in patients with mild to moderate hypertension, although this remains to be confirmed in long term prospective studies. Doxazosin appears to be a promising agent in the treatment of urinary symptoms associated with benign prostatic hyperplasia. Similar to other alpha 1-adrenoceptor antagonists, doxazosin treatment produces increases in peak and mean urinary flow rates and improves other objective and symptomatic measures.(ABSTRACT TRUNCATED AT 400 WORDS)

Alpha 2-adrenoceptor activation inhibits noradrenaline release in human and rabbit isolated renal arteries

The aim of the present study was to investigate alpha 2-adrenoceptor modulation of noradrenaline release in superfused strips of human and rabbit renal arteries. The arteries were field-stimulated after incubation with [3H]noradrenaline. The stimulation-induced outflow of radioactivity was taken as an index of noradrenaline release. At a high stimulation frequency (4 Hz), the alpha 2-adrenoceptor agonist clonidine (0.1 mumol/l) failed to inhibit stimulation-induced outflow of radioactivity in human and rabbit renal arteries whereas the alpha 2-adrenoceptor agonist UK 14304 (0.1 mumol/l) did inhibit stimulation-induced outflow. The inhibitory effect of UK 14304 in human renal arteries was blocked by the alpha 2-adrenoceptor blocking drug rauwolscine (1 mumol/l). At a lower stimulation frequency (2 Hz), both clonidine and UK 14304 inhibited stimulation-induced outflow of radioactivity from rabbit renal arteries; both effects were blocked by rauwolscine. Rauwolscine by itself enhanced stimulation-induced outflow of radioactivity in both preparations. The results suggest that activation of prejunctional alpha 2-adrenoceptors in human and rabbit renal arteries inhibits noradrenaline release. Neuronally released noradrenaline exerts inhibitory feed-back modulation of its own release through activation of prejunctional alpha 2-adrenoceptors. At a higher stimulation frequency most of the prejunctional alpha 2-adrenoceptors are already occupied by endogenous noradrenaline and clonidine fails to inhibit noradrenaline release since it seems to act as a partial agonist at these prejunctional alpha 2-adrenoceptors.

An evaluation of the efficacy and safety of doxazosin in hypertension associated with renal dysfunction. The Japanese Doxazosin Study Group

Doxazosin was administered once daily to 26 patients with renal hypertension or hypertension associated with renal dysfunction. Doxazosin produced a significant reduction in blood pressure that was stable throughout the treatment period. A significant change was not observed in heart rate. Blood pressure was "markedly decreased" or "decreased" in 80% of patients receiving doxazosin monotherapy, 78.6% of patients receiving combined therapy, and 79.2% of all the patients. The cumulative efficacy ratio according to final daily dose was 62.5% with 1 to 4 mg/day and 75.0% to 79.2% with 8 to 16 mg/day. Side effects were observed in three patients (12.0%), none of them severe, and all side effects disappeared with continued administration of doxazosin. Abnormal laboratory values in six items were observed in four patients. Serum creatinine and blood urea nitrogen values, which were regarded as renal function parameters, did not show significant changes, and no negative influence was observed with respect to doxazosin therapy. Overall clinical usefulness was considered "very useful" or "useful" in 80% of patients receiving doxazosin monotherapy, 78.6% of patients receiving combination therapy, and 79.2% of all patients. In conclusion, once-daily administration of doxazosin was considered a useful antihypertensive therapy for renal hypertension and hypertension associated with renal dysfunction.

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)

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.

Doxazosin versus atenolol: a randomized comparison of calculated coronary heart disease risk reduction

Doxazosin is a selective alpha 1-inhibitor for the reduction of calculated coronary heart disease (CHD) risk in hypertensive patients. Atenolol, although a widely used beta-blocker, appears to adversely affect blood lipids by increasing triglycerides and decreasing high-density lipoprotein (HDL) cholesterol. The aim of our study was to compare doxazosin and atenolol for their therapeutic efficacy in reducing CHD risk (decrease in blood pressure and effect on lipid distribution) and toleration. Patients with mild-to-moderate hypertension were randomized into two groups of 20 patients to receive once-daily atenolol (100 mg) or doxazosin (2 to 8 mg) for 8 weeks. Doxazosin was as effective as atenolol in reducing supine and standing blood pressure. Unlike atenolol, doxazosin did not produce a marked bradycardia. Doxazosin therapy produced favorable modifications in plasma lipid profiles by decreasing triglycerides and total cholesterol and by increasing HDL cholesterol and HDL/total cholesterol ratio. A reverse in this lipid profile was seen with atenolol. Therefore doxazosin may reduce calculated CHD risk more effectively than atenolol, based on the Framingham equation.

New alpha 1-adrenergic receptor antagonists for the treatment of hypertension: role of vascular alpha receptors in the control of peripheral resistance

The pharmacology, clinical efficacy and safety of new alpha-adrenergic receptor antagonists for the treatment of hypertension was reviewed (Table XIV). Although all these agents block alpha 1 receptors, some of them have additional effects on histamine, serotonin, dopamine, and alpha 2 receptors. These other actions account for the differences in the side effect profiles observed, i.e., increased incidence of central nervous system side effects found with indoramin, ketanserin, and urapidil, as well as for some additional beneficial effects of ketanserin (i.e., antiplatelet aggregation activity). The magnitude of BP reduction observed with antagonists of alpha 1-adrenergic receptors is modest. In most studies, the degree of BP reduction is comparable to that of prazosin, but less than that achieved with thiazide diuretics, beta-receptor antagonists, or methyldopa. Studies on the comparative efficacy and safety of new alpha 1 antagonists with converting enzyme inhibitors or calcium-channel blockers are not available. In general, alpha 1 antagonists produce greater reductions in standing than in supine BP, an effect due to the venodilatory action of these drugs. New alpha 1 antagonists appear to have equal efficacy in black and white hypertensive individuals. Their comparative efficacy and safety in young vs elderly hypertensive individuals requires further investigation. No information about the possible development of tolerance during treatment with new alpha 1 blockers was encountered. The effects of alpha 1 antagonists on HR are variable and depend on how long after the oral dose the measurements were obtained. In most studies, no significant HR changes are noticed for readings obtained 24 hours post dose; whereas tachycardia has been observed at the time of peak hypotension. Since alpha 1 antagonist-induced tachycardia is most likely of reflex nature, i.e., mediated to an increase in sympathetic activity, the increased HR may be associated with increases in myocardial contractility and in myocardial oxygen consumption. Consequently, a 24-hour HR monitoring during treatment with alpha 1 antagonists should be required for evaluation of new agents. The hemodynamic, humoral, and hormonal effects of the newer alpha 1-receptor antagonists are comparable to those of prazosin. The most consistent finding is a reduction in total peripheral resistance associated with either no change or with only small increases in cardiac index. These agents have been shown either not to change or to increase renal blood flow.(ABSTRACT TRUNCATED AT 400 WORDS)

Doxazosin. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in mild or moderate hypertension

Doxazosin is a long-acting selective alpha 1-adrenoceptor antagonist structurally related to prazosin. Like prazosin, doxazosin exerts its antihypertensive effect by reducing total peripheral resistance by selective postsynaptic alpha 1-blockade, without reducing cardiac output, and similarly, doxazosin appears to have a negligible effect on heart rate. Doxazosin differs from prazosin in that its long half-life enables once-a-day oral administration. Doxazosin significantly lowers both standing and supine blood pressure and appears to maintain this antihypertensive effect over a 24-hour dosing interval. Doxazosin 1 to 16 mg once daily has been found to be comparable in efficacy to atenolol 50 to 100 mg and prazosin 1 to 20 mg daily. Characteristic of alpha 1-adrenoceptor antagonists, doxazosin also has favourable effects on the plasma lipid profile in that it decreases total cholesterol and triglycerides, and increases high density lipoprotein (HDL) cholesterol as well as the HDL/total cholesterol ratio. Although further long term trials are needed to clarify the role of doxazosin in multidrug regimens in more severe hypertension, it appears to be a suitable drug for consideration as first-line therapy in mild to moderate essential hypertension.