Modulation of adrenergic receptors during left ventricular hypertrophy development and after regression by captopril.

The objective of this study was to analyze adrenergic receptors during cardiac hypertrophy development, after establishment of cardiac hypertrophy and after regression of cardiac hypertrophy by an angiotensin-converting enzyme inhibitor. Left ventricular hypertrophy (LVH) was induced by abdominal aortic stenosis. After surgery, plasma norepinephrine concentrations (PNE) and left ventricular adrenergic receptors from rat hearts subjected to aortic stenosis were assessed during cardiac hypertrophy development (at 3, 7, 15, and 30 days of aortic stenosis), once cardiac hypertrophy had been established (7 and 14 weeks after the stenosis) and after regression of cardiac hypertrophy by an antihypertensive dose (200 mg/kg/day) of captopril. The presence of LVH was observed from day 7 after stenosis. PNE had significantly increased after 15 days but returned to control values 30 days after surgery. The density of alpha1-adrenoceptors was found to decrease with development of hypertrophy. Once hypertrophy had been established, 7 weeks from stenosis, PNE was not different from control; however, the density of alpha1-adrenoceptors continued to diminish, whereas PNE and the density of beta-adrenoceptors were no different from control values. Fourteen weeks after stenosis, a significant decrease in PNE was recorded, and no change in alpha1- but an increase in beta-adrenoceptors was observed. LVH was reversed by treatment with captopril; PNE was similar in control and stenosed treated animals. The density of alpha1-adrenoceptors was decreased when compared with control animals, and no change in the density of beta-adrenoceptors was observed with treatment. In conclusion, a decrease of alpha1-adrenoceptors was associated with LVH development and earlier stages of established cardiac hypertrophy. Later stages of established cardiac hypertrophy were characterized by no change in alpha1- and an increase in beta-adrenoceptors. Treatment with captopril induced LVH regression and decreased the number of alpha1-adrenoceptors without any change in beta-adrenoceptors.     

Inotropic response to DPI 201-106 in the failing human heart.

1. The present study was designed to characterize the positive inotropic response to DPI 201-106 in isolated papillary muscle strips obtained from heart failure patients undergoing surgery. 2. The positive inotropic responses to isoprenaline and milrinone and cardiac beta-adrenoceptor density were also determined. 3. DPI 201-106 increased the force of contraction in papillary muscle strips from patients with moderate (NYHA II-III) and severe (NYHA IV) heart failure, in a concentration-dependent manner. This positive inotropic effect was more pronounced in tissues from NYHA IV patients. Furthermore, these responses were greater than those produced by milrinone or isoprenaline. The positive inotropic effects of isoprenaline and milrinone were reduced in NYHA IV compared to NYHA II-III. Consistently, there was also a smaller density of beta-adrenoceptors in myocardium from NYHA IV than in NYHA II-III. The positive inotropic effect of Ca2+ was similar in tissues from both groups of patients. 4. The positive inotropic effect of DPI 201-106 was not antagonized by adenosine or carbachol, whereas both compounds reduced the positive inotropic effect of isoprenaline. 5. DPI 201-106 did not increase the Ca2+ -sensitivity of chemically skinned ventricular fibres, whereas a significant increase of the Ca2+ -sensitivity was obtained with trifluoperazine. 6. It is concluded that DPI 201-106 produces significant positive inotropic effects in tissue excised from the failing human heart. The lack of inhibition by adenosine and carbachol might contribute to its greater effectiveness in NYHA IV than NYHA II-III and indicates that its mechanism of action is cyclic AMP-independent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inotropic effects of l-lysine in the mammalian heart

We studied the effects of l-lysine in cardiac preparations of mice and men. Of note, l-lysine increased force of contraction in a concentration- and time-dependent manner in isolated electrically paced left atrium of mouse and in human right atrium. It further increased heart rate and left ventricular pressure in the isolated perfused mouse heart. In isolated adult mouse cardiomyocytes, the contractility as assessed by edge detection was increased as well as the Ca²⁺ transients after electrically pacing by field stimulation. However, using the patch clamp technique, no effect of l-lysine on action potential duration from a constant holding potential or on current through l-type calcium channels could be observed. However, l-lysine led to a depolarization of unclamped cells. Furthermore, effects of l-lysine were stereospecific, as they were not elicited by d-lysine. The inotropic effects of l-lysine were not abrogated by additionally applied l-ornithine or l-arginine (known inhibitors of lysine transport). However, l-lysine (5 mM) shifted the concentration–response curve for a positive inotropic effect of 5-hydroxytryptamine (5-HT; serotonin) in atrium of transgenic mice (with cardiac specific overexpression of 5-HT₄ receptors) to higher concentrations. In summary, we describe a novel positive inotropic effect of an essential amino acid, l-lysine, in the mammalian heart. One might speculate that l-lysine treatment under certain conditions could sustain cardiac performance. Moreover, l-lysine is able to block, at least in part, cardiac 5-HT₄ receptors.     

Inotropic effects of ivabradine in the mammalian heart

Ivabradine represents a novel heart-rate-lowering agent that acts on the sino-atrial node supposedly by selectively inhibiting the 'funny' current (I(f) current). In clinical studies, it was reported that ivabradine effectively reduced resting heart rate and was well tolerated. The aim of this study was to evaluate potential effects of ivabradine on cardiac contractility. Contractile effects of ivabradine were studied in isolated electrically driven atrial preparations from patients undergoing cardiac bypass surgery and for comparison in isolated spontaneously beating right atria and electrically driven left atria from mice. In human trabeculae, a concentration-dependent negative inotropic effect was noted in 7 from 10 patients. However, in 3 patients from 10, a pronounced positive inotropic effect of ivabradine was noted. As expected, in spontaneously beating mouse right atria ivabradine exerted a concentration-dependent negative chronotropic effect. Unexpectedly, contractile effects in mouse and man seem to disagree. In mouse left atria, ivabradine and cilobradine, another hyperpolarization-activated cyclic-nucleotide-gated blocker, always exerted a pronounced positive inotropic effect. These positive inotropic effects were converted to negative inotropic effects in the additional presence of the L-type Ca2+ channel blocker verapamil. The present study demonstrates that ivabradine at high concentrations can affect the force of contraction in atrial preparations from the human heart.     

Inotropic actions of adenosine derivatives in the mammalian heart

The effects of adenosine receptor (AR) stimulation on contractile parameters as well as inositol phosphates, cAMP content, and phospholamban-phosphorylation was studied in cardiac preparations. In guinea-pig papillary muscles adenosine increased inositol trisphosphate formation and also slightly elevated force of contraction. In the presence of isoprenaline, however, adenosine still enhanced inositol trisphosphate formation but reduced force of contraction. In isolated electrically driven guinea-pig ventricular cardiomyocytes the A₁-AR agonist R-PIA and the A₁/A₂-AR agonist NECA reduced isoprenaline-stimulated contractility but only R-PIA decreased isoprenaline-enhanced cAMP content. The selective A₂-AR agonist CGS 21680 increased isoprenaline-stimulated cAMP content. This effect of CGS 21680 was antagonized by the A₂-AR antagonist CGS 15943A and was increased after pertussis toxin-pretreatment. Furthermore, R-PIA and NECA decreased via A₁-ARs the isoprenaline-stimulated phospholamban-phosphorylation in guinea-pig ventricular cardiomyocytes. © 1993 Wiley-Liss, Inc.     

Behavior of caveolae and caveolin-3 during the development of myocyte hypertrophy

Recent studies have indicated that caveolae are enriched in a variety of signaling molecules, some of which are associated with cardiomyocyte hypertrophy. Caveolin-3, a major constituent of cardiac caveolae, has been suggested to interact with several signaling molecules. We investigated the morphologic changes of caveolae and caveolin-3 expression in hypertrophied cardiomyocytes induced by an alpha1-adrenergic agonist. Cultured rat neonatal cardiomyocytes were used for the experiments. Phenylephrine induced cellular hypertrophy associated with an increase of the number of caveolae and an up-regulation of caveolin-3. Although PMA increased the number of caveolae and the caveolin-3 expression, the extent of these up-regulations was less than that by phenylephrine. Moreover, ionomycin increased the number of caveolae and up-regulated caveolin-3 as much as phenylephrine. Phenylephrine-induced up-regulations of caveolae and caveolin-3 expression were inhibited by BAPTA, suggesting that the intracellular Ca2+ is involved in those regulations. Inhibitors of calcineurin and Ca2+calmodulin-dependent kinase II attenuated the phenylephrine-induced up-regulation of caveolin-3. In pressure-overloaded rat hearts, caveolin-3 protein levels were increased compared with sham-operated rats. In conclusion, the number of caveolae and the expression of caveolin-3 were up-regulated in rat hypertrophied cardiomyocytes, possibly via the alterations of intracellular Ca2+ and protein kinase C.     

Inotropic responsiveness in hypertensive left ventricular hypertrophy: impaired inotropic response to glucagon and vasoactive intestinal peptide in renal hypertensive rats

Previous studies have shown that left ventricular (LV) hypertrophy in renal hypertensive rats (RHR) is associated with reduced responsiveness to beta-adrenergic stimulation (isoproterenol) but not to calcium or cardiac glycosides. To determine whether this impairment is restricted to beta-receptor agonists or extended to include other stimulants of the adenylate cyclase system, inotropic responses to glucagon and to vasoactive intestinal peptide (VIP) were determined in isolated paced hearts (Langendorff preparation) from RHR and strictly matched sham-operated controls. The response (delta peak LV +dP/dt) to both agonists was significantly reduced in RHR, whether expressed in absolute value or in percent of baseline. It averaged 59.3 +/- 19.3 (SE) mm Hg X s-1 in RHR at the highest dose of VIP (15 micrograms) and a perfusion pressure (PP) of 50 mm Hg as compared with 255 +/- 68.4 in controls (p less than 0.01). The responses to glucagon were determined at two levels of perfusion pressure--50 and 80 mm Hg--to determine the influence, if any, of possible alterations in myocardial perfusion on differences between the normal and hypertrophied hearts. At both PP levels the LV +dP/dt response was significantly lower in RHR--+ 374 +/- 103 vs. + 1,026 +/- 166 mm Hg X s-1 (p less than 0.005) or + 120 +/- 5 vs. + 143 +/- 7% of baseline value (p less than 0.02) for PP of 50 mm Hg; and 392 +/- 154 vs. + 1,732 +/- 251 mm Hg X s-1 (p less than 0.01) or + 112 +/- 4 vs. + 160 +/- 2% (p less than 0.001) for PP of 80 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction by beta-adrenoceptor blockade of hypoxia-induced right heart hypertrophy in the rat.

1. The study was undertaken to assess the role of beta-adrenoceptors in the induction of compensatory cardiac hypertrophy in an in vivo model. 2. In the rat, exposure to severe hypoxia (6% inspired oxygen for 8 h day) caused a 51% increase in right heart weight and a 75% increase in haematocrit. 3. The hypoxia-induced right ventricular hypertrophic response was reduced by 65% by oral treatment with a high dose of the non-selective beta-adrenoceptor antagonist, propranolol (80 mg kg-1 body weight); the drug treatment caused only a minor reduction (6%) in secondary polycythaemia. 4. With a less severe degree of hypoxia (7% inspired oxygen) there was only minimal secondary polycythaemia (+15%), and a lesser degree of compensatory right ventricular hypertrophy in untreated rats (+33%). 5. Treatment with the beta 1-adrenoceptor antagonist, atenolol, in a dose of 80 mg kg-1 body weight abolished right ventricular hypertrophy in response to 7% inspired oxygen, without affecting haematocrit and caused a small reduction in the ratio of heart weight to body weight in normoxic rats. 6. The results show that the effect of propranolol on hypoxic right ventricular hypertrophy is not secondary to any effect on secondary polycythaemia as has previously been suggested and that a marked reduction of compensatory cardiac hypertrophy can be obtained by a beta 1-selective adrenoceptor antagonist. Thus these findings support the view that noradrenaline released from cardiac sympathetic nerve terminals exerts a trophic effect on myocardial cells and demonstrates that in vivo, this trophic effect can be reduced by beta 1-adrenoceptor blockade.     

Inotropic and chronotropic effect of glycerol formal on the isolated rabbit heart.

Glycerol formal (CAS 5464-28-8), an organic solvent used to vehicle drugs to target cells, has been shown to possess its own toxicopharmacological properties. The present work was undertaken to study its direct effect on the isolated rabbit heart. At 2.3 and 4.6 mmol/l (bolus) glycerol formal exerted a positive inotropic effect. Upon a perfusion of 4.5 mmol/l/h, the left ventricular pressure and the coronary flow were increased, while at 11 mmol/l/h these two parameters showed a tendency to decrease. Glycerol formal upon a perfusion at 11 mmol/l/h decreased mildly the positive inotropic effect of noradrenaline, and strongly that produced by acetylcholine at a nicotinic dose, while it accentuated the bradycardia induced by acetylcholine at a muscarinic dose. On the contrary it potentiated the stimulant effect of nicotine. The positive inotropic effects of tyramine, dimethylphenylpiperazinium and potassium chloride were decreased showing an inhibition of noradrenaline liberation induced by glycerol formal at the doses used. The action of glycerol formal on agents inducing a positive inotropic effect, except nicotine, and its cardiodepressant effect are probably partly due to its action on the Ca2+ ion.     

Change of the sex-dependent response to clofibrate in F344 rat liver during postnatal development

Although it has been reported that male rats are more responsive than females to peroxisome proliferation induced by clofibrate, these sex differences have been confirmed in young adult rats. Using 4-, 8-, and 12-week-old F344 rats, postnatal change of the sex-dependent response to clofibrate was investigated. These animals were administered 200 mg/kg body wt./day clofibrate by gavage for 7 days. In 4-week-old rats clofibrate-dependent changes (hepatomegaly, induction of hepatic microsomal and peroxisomal enzymes, proliferation of smooth endoplasmic reticulum and peroxisomes of hepatocytes) were slight in both sexes. In 8- and 12-week-old rats clofibrate-induced changes of males were moderate, whereas those of females were slight. These results suggest that the responsiveness of immature rat to clofibrate is weak and in males the susceptibility is gradually strong during postnatal development.     

The adenine nucleotide translocator: regulation and function during myocardial development and hypertrophy

1. The present review focuses on the adenine nucleotide translocator (ANT), which facilitates exchange of cytosolic ADP for mitochondrial ATP. This protein serves a central role in regulating cellular oxidative capacity. 2. The ANT, a nuclear-encoded mitochondrial protein, is developmentally regulated and, thus, accumulates within the mitochondrial membrane during maturation. 3. Accumulation of ANT parallels changes in kinetics of myocardial respiration determined from 31P magnetic resonance spectroscopy studies. 4. Thyroid hormone modulates developmental transitions in ANT content, as well as respiratory control patterns. These transitions are linked to quantitative ANT changes, not to alterations in functionality at individual exchanger sites. 5. Developmental programming for ANT and parallel alterations in oxidative phosphorylation kinetics are relevant to the heart, which exhibits remodelling in response to pathological processes. Maladaptive hearts exhibiting ANT deficits demonstrate ADP-dependent respiratory kinetics similar to the newborn heart. Thus, ANT deficits and alterations in mitochondrial respiratory function may contribute to the pathogenesis of myocardial remodelling and heart failure.     

Protein kinase C zeta regulation of hypertrophic and apoptotic events occurring during rat neonatal heart development and growth

The development and growth of the rat heart implies hyperplasia, which stops at birth, and hypertrophy, allowing cardiac mass to grow in response to programmed genetic events along with to haemodynamic overload. Moreover, hypertrophy is accomplished to apoptosis which controls the final number of myocardial cells, deletes vestigial structures, and takes part in remodelling the organ. Since at the basis of all these processes, which lead to the complete development of the heart, the activation of specific signalling pathways underlies, attention has been addressed to the role played in vivo by Protein Kinase C zeta (PKC zeta) in regulating NF-kB signalling system and intrinsic mitochondrial apoptotic route at days 1, 4, 10 and 22 of rat life. In fact, a role has been assigned to PKC zeta in indirectly phosphorylating IKBa, which peaks between 10 and 22 days, through a IKK determining, in turn, NF-kB activation, concomitantly to cytochrome c/Apaf 1 co-localization in the cytoplasm and caspase-9/caspase-3 activation, which leads to the occurrence of apoptosis. Thus a key role for PKC zeta in regulating the hypertrophic and apoptotic events leading to establishment of complete function in rat neonatal heart is here suggested.     

Lovastatin prevents angiotensin II-induced cardiac hypertrophy in cultured neonatal rat heart cells.

Angiotensin II activates p21ras, and mediates cardiac hypertrophic growth through the type 1 angiotensin II receptor in cardiac myocytes. An inhibitor of 3-hydroxy-3-methyglutaryl-coenzyme A (HMG-CoA) reductase has been shown to block the post-translational farnesylation of p21ras and inhibit protein synthesis in several cell types. Primary cultures of neonatal cardiac myocytes were used to determine whether HMG-CoA reductase inhibitors, lovastatin, simvastatin and pravastatin inhibit the angiotensin II-induced hypertrophic growth. Angiotensin II (10(-6) M) significantly increased protein-DNA ratio, RNA-DNA ratio, ratios of protein synthesis and mitogen-activated protein (MAP) kinase activity. Lipid-soluble HMG-CoA reductase inhibitors, lovastatin (10(-6) M) and simvastatin (10(-6) M) partially and significantly inhibited the angiotensin II-induced increases in these parameters, but a water-soluble HMG-CoA reductase inhibitor, pravastatin (10(-6) M) did not. Mevalonate (10(-4) M) overcame the inhibitory effects of lovastatin and simvastatin on angiotensin II-induced increases in these parameters. A selective protein kinase C inhibitor, calphostin C (10(-6) M) partially and significantly prevented angiotensin II-induced increases in these parameters, and treatment with both lovastatin and calphostin C inhibited completely. Angiotensin II increased p21ras activity and membrane association, and lovastatin inhibited them. These studies demonstrate that a lipid-soluble HMG-CoA reductase inhibitor, lovastatin, may prevent angiotensin II-induced cardiac hypertrophy, at least in part, through p21ras/MAP kinase pathway, which is linked to mevalonate metabolism.     

Chronic inhibition of the Na+/H+ - exchanger causes regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling

BACKGROUND AND PURPOSE: Increased activity of the Na+/H+ -exchanger (NHE-1) in heart failure underlies raised [Na+]i causing disturbances of calcium handling. Inhibition of NHE-1, initiated at the onset of pressure/volume overload, prevents development of hypertrophy, heart failure and remodelling. We hypothesized that chronic inhibition of NHE-1, initiated at a later stage, would induce regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling. EXPERIMENTAL APPROACH: Development of heart failure in rabbits was monitored electrocardiographically and echocardiographically, after one or three months. Cardiac myocytes were also isolated. One group of animals were treated with cariporide (inhibitor of NHE-1) in the diet after one month. Cytoplasmic calcium, sodium and action potentials were measured with fluorescent markers and sarcoplasmic reticulum calcium content by rapid cooling. Calcium after-transients were elicited after rapid pacing. Sodium channel current (INa) was measured using patch-clamp techniques. KEY RESULTS: Hypertrophy and heart failure developed after one month and progressed during the next two months. After one month, dietary treatment with cariporide was initiated. Two months of treatment reduced hypertrophy and heart failure, duration of action potential QT-interval and QRS, and restored sodium and calcium handling and the incidence of calcium after-transients. In cardiac myocytes, parameters of INa were not changed by cariporide. CONCLUSION AND IMPLICATIONS: In rabbit hearts with hypertrophy and signs of heart failure one month after induction of pressure/volume overload, two months of dietary treatment with the NHE-1 inhibitor cariporide caused regression of hypertrophy, heart failure and ionic and electrophysiological remodelling.