Ca(2+) entry into primary cultured pig coronary smooth muscle cells after previous store depletion by repetitive P2Y purinoceptor stimulation.

Store-operated Ca(2+) entry, stimulated by depletion of intracellular Ca(2+) pools, has not been fully elucidated in vascular smooth muscle cells of pig coronary arteries. Therefore, [Ca(2+)](i) was measured in cultured cells derived from extramural pig coronary arteries using the Fura-2/AM fluorometry. Divalent cation entry was visualized with the Fura-2 Mn(2+)-quenching technique. Ca(2+) stores were depleted either by repetitive stimulation of P2Y purinoceptors with ATP (10 micromol/L), or by the sarcoendoplasmic Ca(2+)-ATPase inhibitor 2,5-Di-(tert-butyl)-1,4-benzohydroquinone (BHQ; 1 micromol/L) in Ca(2+)-free medium (EGTA 1 mmol/L). Addition of Ca(2+)(1 mmol/L) induced refilling of ATP-sensitive Ca(2+) stores and an increase in [Ca(2+)](i) in the presence of BHQ. Both could be significantly diminished by Ni(2+)(5 and 1mmol/L), La(3+)(10 micromol/L), Gd(3+)(10 micromol/L), and Mg(2+)(5.1 mmol/L). In contrast to the BHQ-mediated rise in [Ca(2+)](i), refilling of ATP-depleted stores was affected by neither flufenamate (0.1 mmol/L), nor by nitrendipine, nifedipine, and nisoldipine (each 1 micromol/L). The data suggest that after store depletion in pig coronary smooth muscle cells ATP and BHQ may converge on a common, Ni(2+)-, La(3+)-, Gd(3+)-, and Mg(2+)- sensitive Ca(2+) entry pathway, i.e. on a store-operated Ca(2+) entry. An additional contribution of the Na(+)/Ca(2+) exchanger cannot be excluded. Flufenamate-sensitive non-selective cation channels and dihydropyridine-sensitive L-type Ca(2+) channels are not involved in refilling of Ca(2+) stores after previous depletion by repetitive P2Y purinoceptor stimulation. The store-operated Ca(2+) entry in-between repetitive purinoceptor stimulation, i.e. in the absence of the agonist, may be responsible for the maintenance of agonist-induced rhythmic Ca(2+) responses.

Extracellular ATP increases [Ca2+]i in primarily cultured pig coronary smooth muscle cells via a P2Y purinoceptor subtype.

In primarily cultured pig coronary smooth muscle cells, extracellular adenosine triphosphate (ATP; 10(-9) to 10(-3) M) dose-dependently increases intracellular calcium ([Ca2+]i). The [Ca2+]i transients measured by fura-2 fluorescence consist of peak and plateau phases with [Ca2+]i values of 191.84 +/- 5.67 nM (n = 10) and 91.67 +/- 1.89 nM, respectively. In Ca(2+)-free solution, the peak phases persisted, but there was a loss of the plateau response, indicating an initial ATP-stimulated intracellular Ca2+ release and a subsequent transarcolemmal Ca2+ entry. Various agonists have been used to characterize the P2 purinoceptor subtype involved in the ATP-induced Ca2+ transients. The rank order of potency was uridine triphosphate (UTP) > ATP >> 2-meSATP > beta,gamma-meATP = alpha,beta-meATP = adenosine = 0. To examine the refilling of ATP-sensitive stores, four repetitive 60-s ATP responses were produced throughout with a 5-min recovery period in between. Now the ATP peaks gradually declined in Ca(2+)-free solution, indicating the emptying of the stores. If, however, Ca2+ entry was allowed in the "refilling period" (i.e., between the ATP pulses), the Ca2+ peaks could be maintained or restored, respectively. The data suggest that the ATP-dependent [Ca2+]i transients may be mediated via a UTP > ATP-activated P2Y purinoceptor subtype, mediating both an intracellular Ca2+ release and a transarcolemmal Ca2+ influx. The refilling of Ca2+ stores may occur through the unstimulated membrane after agonist stimulation. A putative pathway may be a "capacitative" Ca2+ entry induced on depletion of intracellular Ca2+ stores.

Voltage dependence of the pharmacological Mg2+ block of the Ca2+ entry into vascular smooth muscle cells.

We studied the voltage dependence of the inhibitory effects of the Ca2+ antagonist Mg2+, compared to nifedipine, on the transsarcolemmal Ca2+ uptake into primary monolayers of smooth muscle cells obtained from pig coronary arteries. The cellular Ca incorporation was analyzed by liquid scintillation. Depolarization was produced by elevation of K+0. The data suggest that depolarization known to improve the inhibition by organic Ca2+ antagonists of L-type voltage-gated Ca2+ channels attenuates the Ca2+ antagonism of Mg2+ at vascular smooth muscle cells.

Synthesis and evaluation of azole-substituted tetrahydronaphthalenes as inhibitors of P450 arom, P450 17, and P450 TxA2.

In search of potential drugs for the treatment of estrogen- and androgen-dependent cancer as well as the prophylaxis of metastases, tetralones, tetralins, and dihydronaphthalenes bearing a OCH3 substituent at the benzene nucleus and an imidazol-4-yl, imidazol-1-yl, or 1,2,4-triazol-1-yl substituent in 2-position were synthesized with and without C1-spacer between the rings (compounds 2-26). The compounds were tested in vitro for inhibition of the three targets enzymes P450 arom (human placental microsomes), P450 17 (rat testicular microsomes), and P450 TxA2 (citrated human whole blood). To examine selectivity, some compounds were further tested in vitro for inhibition P450 18 (bovine adrenal mitochondria), P450 scc (bovine adrenal mitochondria) and corticoid formation (aldosterone, corticosterone; ACTH stimulated rat adrenal tissue). In vitro, selected compounds were examined in Sprague Dawley rats regarding P450 TxA2 inhibition, reduction of plasma testosterone concentration, antiuterotrophic activity (inhibition of the uterotrophic activity of androstenedione), reduction of plasma estradiol concentration (pregnant mares' serum gonadotropin-primed rats), and mammary tumor inhibiting activity (dimethylbenzanthracene-induced tumor; pre-and postmenopausal model). In the series of imidazol-4-yl compounds, which represent a novelty in the field of azole inhibitors of steroidogenic P450 enzymes, strong inhibitors of P450 arom and/or P450 17 were found; 7-OCH3-2-(imidazol-4-ylmethylene)-1-tetralone (4) and 7-OCH3-2-(imidazol-4-ylmethyl)-tetralin (12) are among the most potent inhibitors of P450 arom in vitro known so far. Compound 4 is a selective inhibitor, whereas 12 shows in addition strong inhibition of P450 17. In contrast to 12, the 6-OCH3 derivative (compound 11) is a selective inhibitor of P450 17, being 50 times more potent than ketoconazole. Some imidazol-1-yl compounds show a marked inhibition of P450 TxA2: 2-(imidazol-1-ylmethyl)-1-tetralone (13) is a selective inhibitor of P450 TxA2, whereas 7-OCH3-2-(imidazol-1-ylmethyl)-tetralin (17) as well 2-(imidazol-1-ylmethyl)-tetralin (16) and 7-OCH3-2-imidazol-1-yl-3, 4-dihydronaphthalene (25) additionally show strong inhibition of P450 arom and P450 17. Regarding the other steroidogenic P450 enzymes as well as corticosterone formation, the compounds show only little inhibitory activity. Aldosterone formation, however, is inhibited at low concentrations. Nevertheless, 4 and 12 are more selective, i.e. inhibit aldosterone synthesis less than the well known inhibitor of P450 arom fadrozole. The compounds show activity in the aforementioned in vivo tests.

Tetrahydronaphthalenes: influence of heterocyclic substituents on inhibition of steroid enzymes P450 arom and P450 17.

In search of new leads for selective inhibition of estrogen and androgen biosynthesis, respectively, heterocyclic substituted 2-(arylmethylene)-1-tetralones (1-4, 9-17), 2-(aryl-hydroxymethyl)-1-tetralones (5-8), exo-1a,2,3,7b-tetrahydro-1H-cyclopropa[alpha] naphthalenes (18-24), and 3-alkyl substituted 4,5-dihydronaphtho[1,2-c]pyrazoles (25-27) were synthesized and tested for inhibitory activity toward four steroidogenic enzymes (P450 arom, P450 17, P450 18, and P450 scc, as well as another P450 enzyme, thromboxane A(2) (TXA(2)) synthase. The test compounds inhibited human placental P450 arom, showing a wide range of inhibitory potencies. (Z)-4-Imidazolyl compound 17 was the most potent inhibitor, with a relative potency (rp) of 110 [rp of aminoglutethimide (AG) = 1), rp of fadrozole = 359]. A competitive type of inhibition was shown by the (E)-4-imidazolyl compound 16(rp = 71). On the other hand some of these compounds inhibited rat testicular P450 17. Maximum activity was shown by the 3-pyridyl compound 20 (rp = 10, ro of ketoconazole = 1). 20 was the only compound which exhibited a marked inhibition of TXA(2) synthase (IC(50) = 14.5 microM; IC(50) of dazoxiben = 1.1 microM). Regarding selectivity toward the steroidogenic enzymes, compound 16 was relatively selective toward P450 arom, whereas compound 20 was relatively selective toward P450 17. (P450 arom: K(m) testosterone = 42 nM, K(i)16 = 33 nM, K(i)20 = 3 microM. P450 17: K(m)progesterone = 7 microM, K(i)16 = 9 microM, K(i)20 = 80 nM). 17 and 24 were not selective since they showed strong inhibition of P450 arom (K(i)17 = 26 nM, K(i)24 = 0.12 microM) and P450 17 (K(i) 17 = 0.7 microM, K(i)24 = 0.11 microM).

Calcium antagonism in vascular smooth muscle cells.

Ca2+ ions play critical roles in physiological and pathological signal transduction in vascular smooth muscle cells (VSMC). The control of Ca2+ homeostasis is an important means for modulating excitability and response. A pathological increase of Ca(2+)-dependent vascular tone causes vasospasm and arterial hypertension. Moreover, Ca(2+)-mediated migration, proliferation, matrix production and necrotization of VSMC are important components of atherogenic plaque formation. At least two physiological Ca2+ antagonists are known that compete for Ca2+ binding sites at VSMC: H+ and Mg2+. Effective pharmacological control of Ca2+ homeostasis is exerted by organic Ca2+ antagonists. The prototypical compounds verapamil, nifedipine and diltiazem and their derivatives represent three separate structural categories of drugs that block transsarcolemmal Ca2+ influx by specific interaction at a set of binding sites associated with the alpha 1-subunit of the L-type, voltage-gated Ca2+ channel protein. Selectivity of action of the Ca2+ antagonists may arise from pharmacokinetics, class and subclass of the Ca2+ channel activated, state-dependent interactions or pathological alterations. In human therapy they are the drugs of choice in the treatment of arterial spasms and hypertension. The extent to which their antiatherogenic properties are related to Ca2+ channel antagonism at VSMC remains to be elucidated further.

Progression and regression by verapamil of vitamin D3-induced calcific medial degeneration in coronary arteries of rats.

Vitamin D3-induced mural calcification represents an animal model for investigating experimental calcium (Ca) overload and calcification of arterial walls. In this study, long-term progression of calcific degeneration in coronary arteries of rats after one intoxication with vitamin D3 was examined, as well as possible regression of preestablished mural Ca overload with the Ca antagonist verapamil. Sprague-Dawley rats were treated with one intramuscular (i.m.) overdose of vitamin D3 [300,000 IU/kg body weight (b.w.)]. Oral verapamil therapy (100 mg/kg/day b.w. for 24 weeks) was initiated 14 days after the vitamin D3 intoxication. Arteriosclerotic alterations were verified by microchemical analyses of tissue Ca and of cholesterol contents with atomic absorption spectroscopy (special graphite tube technique) and gas chromatography, respectively, and by standard histological techniques. Serum lipids were determined by sequential ultracentrifugation. Between week 3 and week 26 after the vitamin D3 injection, a progressive Ca incorporation from 448.8 +/- 110 to 1,310 +/- 166.3% of control values (i.e., coronary Ca content in 32-week-old untreated control rats = 100%) was observed, associated with calcific morphological lesions, and reactive intimal plaque formation. Verapamil prevented this progression and induced a regression of preestablished mural Ca overload. Therefore, the coronary Ca content after 24 weeks of verapamil treatment amounted to only 146.3 +/- 53.8% of controls. The data indicate that an initial calcific lesion of coronary arteries may serve as crystallization nucleus for advancing Ca overload and morphological alterations.(ABSTRACT TRUNCATED AT 250 WORDS)

Pyridyl-substituted tetrahydrocyclopropa[a]naphthalenes: highly active and selective inhibitors of P450 arom.

The synthesis and biological evaluation of substituted exo-1-(4-pyridyl)-1a,2,3,7b-tetrahydro-1H-cyclopropa[a]naphthalene s as inhibitors of estrogen biosynthesis is described [H (1); 4-OCH3 (2); 5-OCH3 (3); 6-OCH3 (4); 1-CH3, 6-OCH3 (5); 4-OCH3, 7-Br (6); 6-OCH3, 5-Br (7); 4-OH (8); 5-OH (9); 6-OH (10)]. The synthetic key step--the formation of the cyclopropyl ring--was accomplished using the conditions of a modified Wolff-Kishner reduction (N2H5OH/KOH; delta T) and yielded exclusively the exo-configurated diastereomers. The racemic compounds 1-10 showed an inhibition of human placental aromatase (P450 arom) exhibiting relative potencies (rp) from 3.7 to 303 (compounds 8 and 4, respectively; rp of aminoglutethimide (AG) identical to 1, fadrozole = 359). The enantiomers of 4 and 7 were separated by LPLC on tribenzoyl cellulose and by crystallization of the diastereomeric tartrates (4). (1aS,2S,7bS)-(+)-4 (absolute configuration determined by X-ray crystallographic analysis) is the active P450 arom inhibiting enantiomer of 4 and shows a rp value of 617. Compound 4 is a reversible inhibitor showing a competitive type of inhibition and a type II difference spectrum. In vitro 4 influenced other steroidogenic P450 enzymes either not at all (bovine adrenal P450 scc) or only marginally (rat testicular P450 17, bovine adrenal P450 18). In ACTH-stimulated rat adrenal tissue, 4 was less active, inhibiting corticosterone and aldosterone formation compared to AG and fadrozole, respectively. In vivo 4 was not superior to AG as far as the inhibition of the uterotrophic activity of androstenedione (juvenile SD rats) and the reduction of the plasma estradiol concentration (pregnant mares' serum gonadotropin-primed SD rats) are concerned. Compound 4 shows marked antitumor activity in the dimethylbenzanthracene-induced mammary carcinoma of the SD rat: in the postmenopausal model it is at least as active as AG; in the premenopausal experiment it is clearly superior to AG. No induction of hepatic P450 enzymes was observed in the latter experiment. The rp value of 4 toward rat ovarian P450 arom, i.e., 23 (rp of AG identical to 1), is markedly decreased compared to the human enzyme (rp value of 303). From this fact it must be concluded that 4 should be more active in the human than in the rat.

Evaluation of 6,7-aziridinyl steroids and related compounds as inhibitors of aromatase (P-450arom).

Inhibitors of human placental aromatase (P-450arom) may be useful in treating estrogen-dependent diseases (e.g., breast cancer). Some 6,7-aziridinyl steroids and related compounds (fused steroidal oxiranes, azidohydrins and an azide) were evaluated as inhibitors of this enzyme. Although the 6,7-aziridines and their N-derivatives are poor inhibitors of the enzyme (IC50 values 3.0-15.0 microM), while 6 beta-azido-7 alpha-acetoxyandrost-4-ene-3,17-dione (10) is a potent inhibitor of the enzyme (IC50 value = 0.4 microM, Ki = 14 nM). The difference in inhibitory potency between 10 and the parent compound, 6 beta-azido-7 alpha-hydroxyandrost-4-ene-3,17-dione (9), (IC50 value = 47 microM, Ki = 294 nM) is striking and unexpected. The inhibitory potency of 10 is comparable to that of formestane (4-hydroxyandrost-4-ene-3,17-dione, 4-OHA, 16) (IC50 value = 0.6 microM, Ki = 9 nM), an inhibitor of aromatase which recently has been approved for clinical use in breast cancer treatment. Our most active inhibitors, 10 and 7 alpha-azido-6 beta-hydroxyandrost-4-ene-3,17-dione (11) (at concentrations of 125 microM each) did not inhibit the rat 17 alpha-hydroxylase/C17,20-lyase (17 alpha-lyase) enzyme.

Aromatase inhibitors. Syntheses and structure-activity studies of novel pyridyl-substituted indanones, indans, and tetralins.

The (E)-2-(4-pyridylmethylene)-1-indanones(E)-1-(E)-5[(E)-1,H;(E)-2,4- OCH3; (E)-3,5-OCH3; (E)-4,4-OH;(E)-5,5-OH] were obtained by aldol condensation of the corresponding 1-indanones with 4-pyridinecarboxaldehyde, and in case of the OH compound (E)-4 subsequent ether cleavage of (E)-2. The synthesis of the (Z)-isomers (Z)-1-(Z)-3[(Z)-1,H;(Z)-2,4-OCH3; (Z)-3,5-OCH3] was accomplished by UV irradiation of the corresponding (E)-isomers. Catalytic hydrogenation of (E)-1-(E)-3 gave the 2-(4-pyridylmethyl)-1-indanones 6-8 (6, H; 7,4-OCH3; 8,5-OCH3). The 2-(4-pyridylmethyl)-substituted indans 11-13 (11,H; 12,4-OCH3; 13,5-OCH3) and the tetralins 16-19 (16,H;17,5-OCH3;18,6-OCH3;19,7-OCH3) were obtained by reduction of the corresponding ketones using N2H4/KOH. The 2-(4-pyridylmethyl)-substituted indanones 9 (4-OH) and 10 (5-OH), indans 14 (4-OH) and 15 (5-OH), and tetralins 20-22 (20,5-OH; 21,6-OH; 22,7-OH) were synthesized by ether cleavage of the corresponding OCH3 compounds. All compounds showed inhibition of human placental aromatase exhibiting relative potencies from 0.9 [(E)-4] to 163 [18; aminoglutethimide (AG) potency identical to 1]. Compounds 13 and 18 showed competitive type of inhibition and a type II difference spectrum, indicating the interaction of the pyridyl-N with the central Fe(III) ion of the cytochrome P450 heme component.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of calcium in arteriosclerosis--experimental evaluation of antiarteriosclerotic potencies of Ca antagonists. Study Group for Calcium Antagonism.

Chemical microanalyses of conventional human coronary artery plaques (stages I-III [WHO]) revealed the correlation between progressive mural Ca overload up to excessive degrees, and the severity of plaque formation, whereas only small amounts of cholesterol were found, even in complicated lesions. The pathogenetic role of Ca was tested in three types of experimental arteriosclerosis and atheromatosis, using Ca antagonists (verapamil, nitrendipine, diltiazem) as research tools: 1) The Ca type, in vitamin D3 plus nicotine-treated rats; 2) the cholesterol type, in cholesterol-fed New Zealand rabbits; 3) mixed types, in SHRs and NaCl-fed Dahl-S rats. Types (1) and (3) were demonstrated to be governed by a progressive arterial Ca uptake that could be established already in early lesions. The increased mural Ca supply promoted cellular necroses, migration, and proliferation, as well as calcification and degradation of elastic fibers. Ca antagonists prevented the increased Ca incorporation into arterial walls and inhibited the development of experimental arterioscleroses of types (1) and (3). Ca antagonists did not protect coronary arteries of cholesterol-fed rabbits (type [2]) from occlusive cholesterol accumulation. The data suggest an important pathogenetic role of Ca and pronounced antiarteriosclerotic potencies of Ca antagonists in Ca-dominated types of experimental arteriosclerosis. The significance of the present results for pathophysiology and therapy of conventional human arteriosclerosis remains to be clarified.

Experimental vasoprotection by calcium antagonists against calcium-mediated arteriosclerotic alterations.

According to chemical analyses, the development of conventional human coronary artery plaques from "fatty streaks" to "fibrous plaques" and "complicated lesions" is dominated by progressive mural calcium (Ca) incorporation. The atherogenic significance of Ca ions and arterial Ca overload was examined under the influence of nicotine, oxidatively modified low-density lipoproteins, spontaneous hypertension, and an elevated extracellular Ca concentration or vitamin D3. Experiments were carried out either in vitro on cultured medial cells of rats or in vivo on various types of experimental arteriosclerosis of rats. Suitable Ca antagonists (verapamil, diltiazem, nifedipine, or nitrendipine) prevented experimental Ca overload of arterial walls and transmembrane Ca uptake into cultured medial cells produced by risk factors. Thus they protected, in vivo and/or in vitro, against the atherogenic potential of Ca ions, i.e., migration, proliferation, matrix production and intracellular Ca overload of vascular smooth-muscle cells, as well as calcification of elastic fibers. The data indicate that various Ca-consuming processes demand a progressive uptake of Ca into arterial walls if Ca-dominated types of arteriosclerosis develop. Under experimental conditions, specific Ca antagonists inhibit Ca-mediated arteriosclerotic alterations by preventing progressive mural Ca incorporation.

Protective effects of various calcium antagonists against experimental arteriosclerosis.

Arterial walls altered by sclerotic processes accumulate lipids (particularly cholesterol) and calcium. Whereas the accumulation of lipids has long been incriminated as the major pathogenic factor involved in arteriosclerosis, concomitant arterial calcium overload has been considered of secondary importance. Using various animal models and specific calcium antagonists as experimental tools, we have shown the crucial role of excessive calcium uptake into arterial walls in the pathogenesis of arteriosclerotic lesions. Anticalcinotic vasoprotection with calcium antagonists has been demonstrated using light and electron microscopy, radiocalcium uptake experiments and calcium analyses with atomic absorption spectroscopy. The new 1,4-dihydropyridine calcium antagonist amlodipine has been shown to inhibit calcium accumulation in the internal elastic membrane of abdominal arteries of NaCl-loaded salt-sensitive Dahl-S rats, and consequently also exerts protective effects against arteriosclerotic lesions, shown particularly in the distal mesenteric artery branches. Formation of human coronary plaques is marked by a substantial local uptake of calcium, whereas there is a large overlap in the mural cholesterol content of healthy coronary arteries and plaques. Experimental findings in animals and with human tissue indicate that calcium antagonists such as amlodipine may provide a new approach to the prophylaxis of coronary artery lesions.

Evaluation of the racemate and the enantiomers of a new highly active and selective aromatase inhibitor of the aminoglutethimide type.

Compound 1 [3-(4-aminophenyl)-3-cyclohexylpiperidine-2,6-dione] is a highly potent nonsteroidal aromatase inhibitor of the aminoglutethimide (AG)-type containing an asymmetric carbon atom. 1 and its enantiomers (+)-1 and (-)-1 inhibited human placental aromatase by 50% at 0.3, 0.15, and 4.6 microM, respectively (IC50 AG = 37 microM). A competitive type of inhibition was observed for 1 and (+)-1 (Ki 1 = 3.9 nM, Ki (+)-1 = 2.0 nM, Ki AG = 408 nM). Using solubilized high spin aromatase, 1 showed a type II difference spectrum indicating the interaction of the amino nitrogen with the central Fe(III)-ion of the cytochrome P450 heme component. 1 and (+)-1 inhibited cholesterol side chain cleavage enzyme (desmolase) by 50% at 67 and 82 microM, respectively (IC50 AG = 29 microM). In ACTH-stimulated rat adrenal tissue in vitro, 1 was less active in inhibiting aldosterone and corticosterone production compared to AG (IC50s, 1, 130 and 140 microM, AG, 80 and 50 microM, respectively). In vivo, 1 was superior to AG, too: it showed a stronger inhibition of the plasma estradiol concentration of pregnant mares' serum gonadotropin-primed SD rats, the activity residing mainly in the (+)-enantiomer [ovarian vein: (+)-1, 0.31 mg/kg: 81% inhibition, (-)-1, 0.31 mg/kg: 6%, AG, 1.25 mg/kg: 35%]. Furthermore 1 was much more active in inhibiting the testosterone-stimulated tumor growth of the ovariectomized 9,10-dimethyl-1,2-benzanthracene tumor-bearing SD rat (postmenopausal model). Up to a dose of 600 mg/kg of 1 no central nervous symptom depressive effects were observed in the motility test and the rotarod experiment, whereas AG exhibited ED50s of 62 and 164 mg/kg, respectively.

Calcium overload--an important cellular mechanism in hypertension and arteriosclerosis.

Arterial hypertension and arteriosclerosis are dramatic consequences of vascular calcium overload. Acute intracellular calcium overload of vascular smooth muscle cells produces hypercontractility. Hypertension develops if a general increase in systemic arteriolar tone leads to a rise in peripheral flow resistance. Moreover, progressive elevation of calcium destroys the structural integrity of the arterial and arteriolar walls. Thus, in various animals models, calcium overload initiates lesions of an arteriosclerotic character. Interestingly, conventional human coronary plaques also represent a calcium-dominated type of arteriosclerosis. With the advent of specific calcium antagonists, the pathogenic effects of calcium overload and its deleterious consequences have become, for the first time, accessible to therapeutic intervention. Accordingly, adequate treatment with calcium antagonists prevents calcium overload and can thereby protect arteries and arterioles from functional disturbances and structural damage. In spontaneously hypertensive rats, specific calcium antagonists of the verapamil, nifedipine and diltiazem type normalise blood pressure (BP) by reducing transmembrane calcium influx into vascular smooth muscle cells. However, in addition to controlling BP, these drugs also act as tissue protective agents. The long term effects of calcium antagonists such as verapamil in experimental hypertension include the prevention of severe arteriosclerosis, myocardial hypertrophy, and malignant nephrosclerosis. In humans, the antihypertensive efficacy of verapamil is well documented. Further clinical studies have yet to evaluate the antiarteriosclerotic and tissue protective potential of verapamil in humans.

Gallopamil: cardiovascular scope of action of a highly specific calcium antagonist.

According to Fleckenstein's original classification, gallopamil represents a prototype of highly specific calcium antagonists of Group A. Its large scope of cardiovascular effects is lastly based on one and the same mechanism of action: inhibition of transmembrane calcium influx into myocardial, cardiac pacemaker, and vascular smooth muscle cells. Thereby, in experimental studies that use electrophysiological, biochemical, isotopic, and histological techniques, gallopamil reduced calcium-dependent myocardial contractility and oxygen consumption; dampened nomotopic and ectopic cardiac pacemaker activity; exerted pronounced vasodilator effects; and protected myocardial cells from calcium overload-induced necrotization. The effects of gallopamil on myocardium, cardiac pacemakers, and vasculature are quantitatively comparable, surpassing those of verapamil by approximately one order of magnitude. Further clinical studies must demonstrate to what extent humans will benefit from the experimentally proven cardiovascular potential of gallopamil.