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Biomedical subjects

A Fleckenstein

Publications and source records attributed to A Fleckenstein.

At least 19 recordsLinked to original sources
PubMed1999

A PDR5-independent pathway of multi-drug resistance regulated by the SIN4 gene product.

The SIN4 locus encodes a global transcriptional regulator of various yeast genes. In this report, we demonstrate that loss of function mutations in SIN4 create a multi-drug hypersensitive phenotype that is independent of PDR5 mediated resistance. Thus, double sin4, pdr5 mutants are more sensitive than single mutants. Furthermore, SIN4 does not regulate the PDR5 locus. These observations establish that yeast cells have two genetically distinct pathways conferring resistance towards similar substrates.

ATP-Binding Cassette Transporters↗
PubMed1992

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.

Animals↗
PubMed1992

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.

Amlodipine↗
PubMed1991

Calcium--a neglected key factor in arteriosclerosis. The pathogenic role of arterial calcium overload and its prevention by calcium antagonists.

Using specific calcium antagonists as experimental tools, both the physiological messenger and current carrying function of calcium ions as well as their pathogenetic potencies could be elucidated. Notably, excess intracellular calcium signalling and intra- and extracellular calcium overload turned out to be pathogenetic principles of general importance. In this context, progressive calcium overload of arteriosclerotic vascular walls and the antiarteriosclerotic effects of calcium antagonists, deserve particular interest. In fact, with the help of calcium antagonists, arterial calcium overload as decisive component of various types of experimental arteriosclerosis became accessible to a direct therapeutic intervention. According to their responsiveness to calcium antagonists, two pathophysiologically different types of experimental coronary plaques could be characterized: (1) The calcium type, i.e. coronary calcinosis of vitamin D3-intoxicated rats highly sensitive to calcium antagonist treatment, (2) the cholesterol type, represented by coronary atheromata of cholesterol-intoxicated rabbits; this primary coronary cholesterol accumulation could not be inhibited by calcium antagonists. The formation of conventional human coronary artery plaques is characterized from the very early lesion onwards by a progressive local uptake of calcium, finally leading to lethal consequences. Conversely, the analysis of the mural cholesterol does not allow to discriminate arteriosclerotic from normal coronary artery segments. Thereby, conventional human coronary plaques typically represent a calcium-dominated type of human arteriosclerosis and differ widely from plaques produced in cholesterol-fed rabbits. The results indicate the decisive pathophysiological role of calcium and calcium overload in both calcium-dominated types of experimental arteriosclerosis and conventional human coronary artery plaques. Moreover, the antiarteriosclerotic effects of calcium antagonists are demonstrated to be based--in various types of experimental arteriosclerosis--on the inhibition of intra- and extracellular calcium overload of arterial walls evoked by various risk factors (vitamin D3 intoxication, hypertension, nicotine, diabetes).

Animals↗
PubMed1991

Differentiation between calcium- and cholesterol-dominated types of arteriosclerotic lesions: antiarteriosclerotic aspects of calcium antagonists.

In a series of animal studies we have clearly demonstrated since 1970 that calcium overload of the arterial wall is crucially involved in the pathogenesis of arteriosclerotic lesions. Following excessive calcium uptake, vascular stretch compliance and distensibility were lost together with structural integrity. Conversely, calcium antagonists that counteract abundant calcium uptake were found to prevent pathogenic mural calcium accumulation and damage. These effects were realized with light and electron microscopy as well as with measurements of calcium accumulation using atomic absorption spectrometry and radiocalcium. The experiments were carried out on rats exposed to various well-known risk factors such as nicotine, alloxan diabetes, high doses of vitamin D3, or dihydrotachysterol. Another particularly vasotoxic factor appeared to be hypertension, which develops in spontaneously hypertensive Okamoto rats (SHRs), in hypertensive NaCl-loaded salt-sensitive Dahl-S rats, and in rats with nephrogenic Goldblatt hypertension. Interestingly, aging arteries in animals and humans also exhibit, as a characteristic phenomenon, a steady increase in arterial calcium content. This natural age-dependent calcium accumulation is further enhanced in severe diabetics, heavy smokers, and hypertensive patients. However, the most excessive degree of toxic calcium overload, correlated with dramatic structural damage, occurred in human coronary artery plaques. Here, in "fatty streaks" (type I plaques according to World Health Organization classification), the mural calcium content exhibited a rise by 13 times above normal; in type II lesions (fibrous plaques), the increase in calcium was 24-fold; and in type III plaques, i.e., in "complicated lesions of stenosing character," calcium overload amounted to a value greater than 80 times above that found in healthy coronary segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Excessive mural calcium overload--a predominant causal factor in the development of stenosing coronary plaques in humans.

Healthy human coronary artery walls contain, over their entire lifetime, more free and total cholesterol than calcium. However, as soon as arteriosclerotic alterations set in, the calcium content increases. Thus in coronary fatty streaks (arteriosclerotic plaques of WHO stage I), calcium was increased 13 times, in stage II plaques 25 times, and in fully developed stage III plaques 80 times above normal on average. The most dramatic calcium incrustation was found in coronary stage III plaques that had produced massive fatal coronary infarction. Here, the proportion of calcium salts (particularly hydroxyapatite) may amount to almost 50% of dry weight. Thus the most excessive accumulation of calcium seems to be correlated with the highest fatality. In contrast, there is no correlation between mural coronary free or total cholesterol content, and plaque severity. Accordingly, stenosing coronary stage III plaques contain less cholesterol than do fatty streaks. Moreover, in coronary stage III plaques the proportion of free cholesterol was 1.37%, and of total cholesterol only 2.34% of the whole mass, certainly not enough for directly causing coronary occlusion. Thus the calcium-rich plaques of human coronary arteries considerably differ from the well-known cholesterol-rich plaques (stage I and II) of human aortae. Our findings justify a new prophylactic approach with suitable calcium antagonists to interfere with deleterious calcium uptake in coronary plaque development.

Adult↗
PubMed1990

Scope of vasodilatory effects of calcium antagonists.

Specific Ca antagonists of the verapamil, nifedipine, and diltiazem type have become the drugs of choice in the therapy of cardiac hyperkinetic disorders and of vascular hypertonicity (spasms). The specific mechanism of vasodilatation by Ca antagonists was substantiated by electrophysiological, radionuclear and mechanical measurements on rather different types of arterial vasculature, including the systemic resistance vessels, as well as on portal veins. The results indicate that the vasodilator efficacy of these Ca antagonists is mainly based on at least three components: (1) Suppression of the generation of Ca-carried membrane spike potentials; (2) decrease of direct transmembrane supply of activator Ca through potential- or receptor-operated membrane channels, and (3) interference with Ca-triggered intracellular Ca release in an indirect way, in that Ca antagonists block the influx of small amounts of trigger Ca or produce depletion of intracellular Ca stores. In any case, contractile activation practically ceases if transmembrane Ca supply is totally cut off upon addition of Ca antagonists to a Ca-deficient medium.

Animals↗
PubMed1989

Amlodipine, a new 1,4-dihydropyridine calcium antagonist with a particularly strong antihypertensive profile.

The effects of a new 1,4-dihydropyridine derivative amlodipine have been compared with results from our previous work. Application of amlodipine at a concentration of 1.6 X 10(-6) M to isolated guinea-pig papillary muscle for 120 minutes produced a 50% reduction in tension development compared with a concentration of 3.7 X 10(-7) M nifedipine needed to produce the same result under identical conditions. This suggests that amlodipine has even weaker negative inotropic effects than nifedipine. In isolated porcine coronary strips, the K+-induced contractions were approximately 10,000 times more sensitive to the relaxing effects of nisoldipine, nitrendipine and nicardipine than to those of papaverine, whereas nifedipine and amlodipine were 3,000 times more potent than papaverine. However, in comparison with these in vitro actions, the efficacy of amlodipine appears to be greater in vivo: Simultaneous subcutaneous injection of nifedipine (20 mg/kg) and of equimolar doses of nisoldipine and felodipine attenuated the myocardial calcium uptake by rat hearts in situ (stimulated with a single subcutaneous dose of 30 mg/kg isoproterenol) with the same efficacy, whereas the actions of nitrendipine and nimodipine were considerably weaker. In contrast, amlodipine antagonized isoproterenol-stimulated myocardial calcium accumulation more effectively. Furthermore, amlodipine exhibited a high antihypertensive potency combined with rapid onset and long duration of action: Amlodipine (10 mg/kg orally [p.o.]) reduced the blood pressure of spontaneously hypertensive rats almost to the same extent as nifedipine, nitrendipine, verapamil and felodipine administered at the much higher doses of 100 mg/kg p.o. Amlodipine (20 mg/kg/day p.o.) maintained normal blood pressure during the whole life span of Dahl-S rats (5 months), but this dose is considerably lower than that reported for other 1,4-dihydropyridines. The survival of NaCl-loaded Dahl-S rats increased from 20 to 100% after administration of amlodipine (20 mg/kg/day p.o.) over 10 weeks: The effective dose of other calcium antagonists is approximately 5 times higher, but well tolerated as, e.g., demonstrated in long-term studies on Dahl-S rats with nitrendipine over 12 months. Increases in systemic arteriolar tone can be visualized in the ocular fundus of spontaneously hypertensive rats. After amlodipine (10 mg/kg p.o.) arteriolar spasm declines. Prophylaxis with 2 doses of 20 mg/kg amlodipine daily in NaCl-loaded Dahl-S rats abolished the macroscopic and histologic changes that are normally seen in branches of the mesenteric artery. With use of electron microscopy, calcium accumulation in the lamina elastica interna was demonstrated by the potassium-pyr-oantimonate technique.(ABSTRACT TRUNCATED AT 400 WORDS)

Amlodipine↗
PubMed1989

Antihypertensive, anticalcinotic, and antiarteriosclerotic properties of anipamil, a long-acting new derivative of verapamil.

The classical indication for calcium antagonists has for a long time been coronary heart disease. However, more recent experimental data as well as a host of clinical observations now encourage a broader use of these drugs also for antihypertensive purposes and for prevention of concomitant sclerotic vascular injury. Needless to say, for the treatment of hypertensive crises rapidly acting calcium antagonists are required, whereas for chronic therapy of hypertension calcium antagonists with a long duration of action on blood pressure are advantageous. In this context anipamil seems to be particularly suited for long-term control of elevated blood pressure. Thus, anipamil justifies good therapeutic expectations regarding the clinical management of essential or renal hypertension.

Animals↗
PubMed1988

Mechanism of action of calcium antagonists in heart and vascular smooth muscle.

A transmembrane supply of Ca2+ ions is required for active tension development in both vascular smooth musculature and myocardial fibres. Ca2+ antagonists thus not only damp hyperkinetic myocardial dysfunction but also act against practically all vasoconstrictor or spastic responses of extramural coronary smooth muscle. Clinically important targets of Ca2+ antagonists include the pulmonary, cerebral, mesenteric and renal arteries, as well as the peripheral resistance vessels of the systemic circulation. Ca2+ antagonists are used increasingly to treat acute hypertensive crises as well as for long-term antihypertensive therapy. In physiological experiments, Ca2+ antagonists not only neutralize various vasoconstrictor agents but also greatly reduce the sensitivity of the systemic arteries and arterioles to mechanical stimuli such as extension of the vascular wall by a rise in intraluminal pressure. In human arterial walls, at an advanced age, cytotoxic degrees of Ca2+ overload probably play an important role in the pathogenesis of arteriosclerotic lesions. Severe diabetics and heavy smokers exhibit an even faster progression of age-dependent arterial calcinosis. In rats, the Ca2+ antagonist verapamil not only prevented arterial calcinosis due to overdoses of vitamin D and dihydrotachysterol but also counteracted age-dependent Ca2+ accumulation. Spontaneously hypertensive rats also exhibit progressive arterial Ca2+ overload which responds excellently to the Ca2+ antagonists nifedipine, nimodipine, nisoldipine, nitrendipine, as well as to verapamil and diltiazem. Suitable Ca2+ antagonists could possibly retard or even prevent premature arterial calcinosis in humans. Moreover, Ca2+ antagonists exert a direct cardioprotective effect on the myocardium by preventing intracellular Ca2+ overload.

Animals↗