Biological membranes in hypertension: is control of intracellular calcium and other ions mediated by a membrane defect?

Blood and tissue zinc levels in spontaneously hypertensive rats

Zinc (Zn) determinations were performed on blood plasma and red cells, liver, heart, adrenals, and spleen of spontaneously hypertensive (SHR) and control normotensive (WKY) male rats, 20 weeks of age. SHR revealed higher red cell (p = 2 x 10(-5)) and heart (p = 0.007) Zn levels than WKY rats. The water content of organs was the same in the two strains. When compared with published data, these results suggest an association between high cell Zn levels and hypertension, the meaning of which is briefly discussed.

Ultracytochemical localisation of Na+, K(+)-ATPase in cerebral endothelium in acute hypertension

This ultracytochemical study was undertaken to determine whether increased arteriolar permeability in acute hypertension is accompanied by altered localisation of the ouabain-sensitive, K(+)-dependent p-nitrophenyl-phosphatase (K(+)-NPPase), a component of the Na+, K(+)-ATPase system. Rats were injected with horseradish peroxidase (HRP) intravenously and acute hypertension was induced by a 2-min infusion of angiotensin amide. Rats were killed at 3 and 15 min, following which brains were sliced and reacted for demonstration of K(+)-NPPase and HRP reaction product. Vessels of normotensive and hypertensive rats that were nonpermeable to HRP showed discontinuous distribution of K(+)-NPPase on the outer plasma membranes of endothelial and adventitial cells of arterioles and endothelial cells and pericytes of capillaries. Arterioles of the hypertensive rats which were permeable to HRP showed marked reduction of K(+)-NPPase localisation in their walls at 3 min while at 15 min when the blood pressure had returned to resting levels the enzyme localisation was similar to controls. This study demonstrates transient alteration of the NA+, K(+)-ATPase system during increased endothelial permeability in acute hypertension. The implication of this finding and our previous observation of reduced Ca2(+)-ATPase localisation in endothelial plasma membranes in acute hypertension has been discussed.

Calcium channel antagonists. Part III: Use and comparative efficacy in hypertension and supraventricular arrhythmias. Minor indications

The major antihypertensive mechanism of calcium antagonists is by decreasing the systemic vascular resistance, modified by the counter-regulatory responses of the baroreflexes and the renin-angiotensin-aldosterone system. In severe hypertension, the concept that calcium overload of the vascular myocyte could precipitate or aggravate peripheral vasoconstriction provides a logical basis for the use of these agents as first choice therapy; nifedipine, especially, has been well tested. As monotherapy for mild to moderate hypertension each of the three first-generation agents compares well with beta-blockers. Calcium antagonists may have a special role in the therapy of certain patient groups (elderly, black) or in those subjects whose life style involves intense physical or mental exertion (hemodynamics better maintained than with beta-blockade) or in patients with early end-organ damage such as left ventricular hypertrophy or renal insufficiency. However, the goal blood pressure may not be reached during monotherapy so that drug combinations may be required. Further indications for these compounds are as follows. Verapamil and diltiazem are frequently used in supraventricular tachycardias including acute and chronic atrial fibrillation. In the arrhythmias of the Wolff-Parkinson-White syndrome, there is the potential danger of provocation of anterograde conduction. Further indications for calcium antagonists, still under evaluation, include congestive heart failure (controversial), hypertrophic cardiomyopathy (verapamil), primary pulmonary hypertension (high doses required), Raynaud's phenomenon (nifedipine and diltiazem effective), peripheral vascular disease (proof not yet documented), cerebral insufficiency and subarachnoid hemorrhage (nimodipine promising), migraine, exertional bronchospasm, renal disease, atherosclerosis (experimental), and primary aldosteronism (nifedipine inhibits aldosterone release). Second-generation agents include dihydropyridines, such as nitrendipine, nicardipine, felodipine, amlodipine, nisoldipine, nimodipine, and isradipine. From these will be selected agents that are longer acting and provide higher vascular selectivity. New preparations of existing agents include slow-release formulations of nifedipine, verapamil, and diltiazem. Minor side effects include those caused by vasodilation (flushing and headaches), constipation (verapamil), and ankle edema. Serious side effects are rare and result from improper use of these agents, as when intravenous verapamil is given to patients with sinus or atrioventricular nodal depression from drugs or disease, or nifedipine to patients with aortic stenosis. The potential of a marked negative inotropic effect is usually offset by afterload reduction, especially in the case of nifedipine. Yet caution is required when calcium antagonists, especially verapamil, are given to patients with myocardial failure unless caused by hypertensive heart disease. Drug interactions of calcium antagonists occur with other cardiovascular agents such as alpha-adrenergic blockers, beta-adrenergic blockers, digoxin, quinidine, and disopyramide.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium channel antagonists, Part I: Fundamental properties: mechanisms, classification, sites of action

Ca2+ channel antagonists are agents that interact with the voltage-dependent Ca2+ channel in a highly specific way. The prototype agents of cardiovascular importance are verapamil, nifedipine, and diltiazem, in historical order of appearance. These agents all have different molecular structures and bind separately with receptor sites located in or near the calcium channel, at molecular sites still to be fully identified. There are probably three distinct receptor sites (V, N, D) which stand in relation to the "gate" of the long-acting "L" calcium channel. There is probably overlap among the receptor sites, especially between the V and D sites to explain their common properties. All three agents inhibit the voltage-dependent calcium channel in vascular smooth muscle and also myocardial slow calcium channels. The ratio of the arterial to the myocardial effect is an index of the arterial selectivity, generally held to be a desirable property because the negative inotropic effect is usually a liability. The general clinical impression that nifedipine is the agent most active in vascular tissue in relation to the myocardial effect is supported by data on the relative potencies of these three agents on blood perfused dog preparations and by a comparison of the potency on rat vascular (portal vein) versus myocardial effects. Nonetheless all three agents are highly active in the inhibition of K(+)-induced vascular contractions (nifedipine 10(-9) M to 10(-8) M; verapamil 10(-7) M to 10(-6) M; and diltiazem 5 x 10(-7) M to 10(-6) M; concentrations for 50% inhibition of K(+)-induced vascular contractions in rat or rabbit aorta; comparative data for resistance vessels not available). The clinical impression that verapamil and diltiazem are more active on nodal tissue is also supported by a comparison of potencies on blood perfused dog nodal preparations in comparison with effects on coronary flow, with verapamil and diltiazem being approximately 10x more potent on the AV node than increasing coronary blood flow, so that the nodal effect is first detected. These basic pharmacological properties explain why all these three agents have clinical effects relevant to inhibition of vascular contraction (antihypertensive and antianginal effects) and only verapamil and diltiazem have clinically relevant inhibitory effects on the AV node (inhibition of supraventricular tachycardias). The comparative potencies of verapamil, diltiazem, and nifedipine in angina and hypertension will be examined in Parts II and III of this review.