Blockers hypotensive action

The relevance of either the experimentally demonstrated central hypotensive action of the 3-blockers, or their ability to antagonise sympathetically mediated renin release remains to be proven. While it is still possible that the mechanism of the anti-hypertensive action of the 3-blocking drugs could contain both a central and a renin-inhibitary component, the clinical evidence would appear to rule against the possibility of either being a major component of the mode-of-action. 

Most types of smooth muscle are dependent on transmembrane calcium influx for normal resting tone and contractile responses. These cells are relaxed by the calcium channel blockers (Figure 12-3). Vascular smooth muscle appears to be the most sensitive, but similar relaxation can be shown for bronchiolar, gastrointestinal, and uterine smooth muscle. In the vascular system, arterioles appear to be more sensitive than veins orthostatic hypotension is not a common adverse effect. Blood pressure is reduced with all calcium channel blockers. Women may be more sensitive than men to the hypotensive action of diltiazem. The reduction in peripheral vascular resistance is one mechanism by which these agents may benefit the patient with angina of effort. Reduction of coronary artery tone has been demonstrated in patients with variant angina. 

Beta-blockade in brain, kidney, and peripheral adrenergic neurons has been proposed as contributing to the antihypertensive effect observed with 13-receptor blockers. In spite of conflicting evidence, the brain appears unlikely to be the primary site of the hypotensive action of these drugs, because some 6-blockers that do not readily cross the blood-brain barrier (eg, nadolol, described below) are nonetheless effective antihypertensive agents. 

BETA-BLOCKERS SYMPATHOMIMETICS -INDIRECT 1 hypotensive efficacy of beta-blockers The hypertensive effect of sympathomimetics opposes the hypotensive actions of beta-blockers Monitor BP at least weekly until stable watch for poor response to beta-blockers... 

CALCIUM CHANNEL BLOCKERS PHOSPHODIESTERASE TYPE 5 INHIBITORS t hypotensive action particularly with sildenafil and vardenafil Additive effect phosphodiesterase type S inhibitors cause vasodilatation Warn patients of the small risk of postural 1 BP... 

Ketanserin appears to act principally to block serotonin vasoconstrictor (subtype 5-HTj) receptors but also has significant a-adrenoceptor blocking activity (its affinity ratio for the two receptors is 1 5). The latter explains its hypotensive action and use in Raynaud s disease. It is not available in many countries and offers no advantages over pure a-blockers such as doxazosin. 

Finally, experimental studies have established that nipradilol, another NO-releasing beta-adrenergic blocker, enhances postischemic recovery and limits infarct size (100a). Moreover, there is a clear involvement of NO in the ocular hypotensive action of nipradilol (100b). These studies should be carried out in humans before a conclusion is made. 

The mechanism of the clinical hypotensive action of p-blockers remains contentious, but several papers29 have demonstrated further the... 

Antihypertensive Vasodilators - A common characteristic of hypertensive patients, regardless of the etiology of their disease, is abnormally high peripheral vascular resistance. Drugs that act directly on peripheral vasculature to decrease resistance are, therefore, logical agents for the treatment of hypertension. Unfortunately, sympathetic reflex actions leading to cardiac stimulation, hyperreninemia and fluid retention limit the hypotensive action of vasodilators and they are used mainly in combination with 6-blockers and diuretics for the treatment of more severe hypertension. A vasodilator that may not cause undesirable reflex... 

The manufactrrrer of indoramin states that concurrent use with beta blockers may enhance their hypotensive action, and that titration of the dose of the beta blocker may be needed when initiating therapy. ... 

Isoflurane is a respiratory depressant (71). At concentrations which are associated with surgical levels of anesthesia, there is Htde or no depression of myocardial function. In experimental animals, isoflurane is the safest of the oral clinical agents (72). Cardiac output is maintained despite a decrease in stroke volume. This is usually because of an increase in heart rate. The decrease in blood pressure can be used to produce "deHberate hypotension" necessary for some intracranial procedures (73). This agent produces less sensitization of the human heart to epinephrine relative to the other inhaled anesthetics. Isoflurane potentiates the action of neuromuscular blockers and when used alone can produce sufficient muscle relaxation (74). Of all the inhaled agents currently in use, isoflurane is metabolized to the least extent (75). Unlike halothane, isoflurane does not appear to produce Hver injury and unlike methoxyflurane, isoflurane is not associated with renal toxicity. 

Terazosin is selective a -adrenoceptor blocker having hypotensive efficacy equal to that of prazosin. Terazosin has a longer duration of action and better gastrointestinal absorption profile than prazosin. 

Mollusca and Arthropoda. A variety of pharmacological actions are induced by the toxins found in molluscs (17). For example, surugatoxin is a potent mydriatic (5J), ganglion blocker (84), and a potent hypotensive agent in cats. 

Antihypertensive drugs can be divided into eight classes based on the mechanism of action diuretics, )3-adrenoblockers, centrally acting sympatholytics, peripherally acting sympatholytics, calcium channel blockers, myotropic hypotensive drugs, angiotensin-con-verting enzyme inhibitors, and calcium channel activators. 

Benazepril (Lotensin) [Antihypertensive/ACEI] Uses HTN DN, CHF Action ACE inhibitor Dose 10 0 mg/d PO Caution [C (1st tri), D (2nd 3rd tri), +] Contra Angioedema, Hx edema, bilateral RAS Disp Tabs 5, 10, 20, 40 mg SE Symptomatic i BP w/ diuretics dizziness, HA, nonproductive cough Interactions T Effects W/ a-blockers, diuretics, capsaicin effects W/ NSAIDs, ASA T effects OF insulin, Li T risk of hyperkalemia W/ trimethoprim K-sparing diuretics EMS Monitor EGG for signs of hyperkalemia angioedema is rare but can occur persistent cough /or taste changes may develop OD Profound hypotension treat w/ IV fluid... 

Prazosin was the first example of a selective O -blocker. Its main application is hypertension, usually in combination with a -blocker and/or a diuretic. Orthostatic hypotension readily occurs as a result of venous dilatation. The problem may be avoided by a gradual increase of the dosage. The drug has a short duration of action and must be administered 2-3 times daily in order to achieve adequate control of blood pressure. 

Doxazosin, also a selective a i-blocker, resembles prazosin in most aspects, but it has a better pharmacokinetic profile, at least for long-term use as in essential hypertension. Owing to its slow onset of action, doxazosin causes far less orthostatic hypotension and reflex tachycardia than prazosin. As a result of its long duration of action, it can be administered once daily in the long-term treatment of essential hypertension. 

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