Population Pharmacokinetics of Levofloxacin in Plasma and Bone of Patients Undergoing Hip or Knee Surgery

Patients undergoing hip or knee replacement therapy are routinely pretreated with antibiotics before they enter the operation theater. This treatment intends to reduce the incidence of peri- or postsurgical infections. Here, we calculated the uptake kinetics of levofloxacin into bone to see whether levofloxacin could be obtained from the trabecular and cortical bone and at what time concentrations are sufficiently high to inhibit the usual hospital infections. Patients (n = 42) undergoing routine surgery were treated with 500 mg levofloxacin intravenously immediately prior to the operation. Plasma samples were taken before and at 3 points after termination of drug infusion. After replacement of the bones, extracts were obtained from them. Levofloxacin was quantified using high-performance liquid chromatography. The kinetics of levofloxacin and its distribution into bone were analyzed using a population approach (ADAPT5). Clearance was 14.0 L/h, and distribution volume was 77 L. Bone uptake t½ was calculated as 4.2 and 5.4 hours for cortical bone and trabecular bone, respectively. In knee samples (but not in hip samples), we noted that the cortical bone contained higher levels of levofloxacin than the trabecular bone. From our data, we can conclude that levofloxacin might be useful for prophylactic use in bone surgery.

Pharmacokinetics of ceftriaxone in plasma and bone of patients undergoing hip or knee surgery

OBJECTIVES

Patients undergoing hip or knee replacement therapy are routinely pretreated with antibiotics before surgery. It is controversial in which antibiotic is the treatment of choice for this purpose. One possibility is the cephalosporin ceftriaxone. Here, we wanted to know if effective tissue concentrations are reached.

METHODS

We studied plasma and bone kinetics of ceftriaxone in orthopaedic patients (n = 22) treated with ceftriaxone (2 g) immediately prior operation. Plasma samples were withdrawn before and at three time points after ceftriaxone infusion. After bone replacement, extracts from cancellous bone or cortical bone were obtained, and ceftriaxone was quantified using column chromatography.

KEY FINDINGS

The plasma kinetics of ceftriaxone and distribution into bone were analysed using a population approach (ADAPT 5). The population mean of the area under the curve (AUC) was 140 mg h/l. A cancellous bone to plasma concentration ratio of 1.12 ± 1.29 was achieved 5 h after start of infusion. The half-life of uptake into the cortical bone was less (8.4 h) than into cancellous bone (12.1 h, P < 0.05).

CONCLUSIONS

Under these experimental conditions, concentrations of ceftriaxone in cancellous and cortical bone should be adequate to protect the patients against usual ceftriaxone-sensitive nosocomial infections and are substantially lower than the plasma concentrations.

Catecholamines are the key for explaining the biological relevance of insulin-melatonin antagonisms in type 1 and type 2 diabetes

In this paper, we analyze the biological relevance of melatonin in diabetogenesis. As has recently been demonstrated, melatonin decreases insulin secretion via specific melatonin receptor isoforms (MT1 and MT2) in the pancreatic β-cells. In addition, type 2 diabetic rats, as well as patients, exhibit decreased melatonin levels, whereas the levels in type 1 diabetic rats are increased. The latter effects were normalized by insulin substitution, which signifies that a specific receptor-mediated insulin-melatonin antagonism exists. These results are in agreement with several recent genome-wide association studies, which have identified a number of single nucleotide polymorphisms in the MTNR1B gene, encoding the MT2 receptor, that were closely associated with a higher prognostic risk of developing type 2 diabetes. We hypothesize that catecholamines, which decrease insulin levels and stimulate melatonin synthesis, control insulin-melatonin interactions. The present results support this assertion as we show that catecholamines are increased in type 1 but are diminished in type 2 diabetes. Another important line of inquiry involves the fact that melatonin protects the β-cells against functional overcharge and, consequently, hinders the development of type 2 diabetes. In this context, it is striking that at advanced ages, melatonin levels are reduced and the incidence of type 2 diabetes is increased. Thus, melatonin appears to have a protective biological role. Here, we strongly repudiate misconceptions, resulting from observations that melatonin reduces the plasma insulin level, that the blockage of melatonin receptors would be of benefit in the treatment of type 2 diabetes.

On the presence of serotonin in mammalian cardiomyocytes

Pleiotropic effects of serotonin (5-HT) in the cardiovascular system are well documented. However, it remains to be elucidated, whether 5-HT is present in adult mammalian cardiomyocytes. To address this issue, we investigated the levels of 5-HT in blood, plasma, platelets, cardiac tissue, and cardiomyocytes from adult mice and for comparison in human right atrial tissue. Immunohistochemically, 5-HT was hardly found in mouse cardiac tissue, but small amounts could be detected in renal preparations, whereas adrenal preparations revealed a strong positive immunoreaction for 5-HT. Using a sensitive HPLC detection system, 5-HT was also detectable in the mouse heart and human atrium. Furthermore, we could identify 5-HT in isolated cardiomyocytes from adult mice. These findings were supported by detection of the activity of 5-HT-forming enzymes-tryptophan hydroxylase and aromatic L-amino acid decarboxylase-in isolated cardiomyocytes from adult mice and by inhibition of these enzymes with p-chlorophenylalanine and 3-hydroxybenzyl hydrazine. Addition of the first intermediate of 5-HT generation, that is 5-hydroxytryptophan, enhanced the 5-HT level and inhibition of monoamine oxidase by tranylcypromine further increased the level of 5-HT. Our findings reveal the presence and synthesis of 5-HT in cardiomyocytes of the mammalian heart implying that 5-HT may play an autocrine and/or paracrine role in the heart.

Cardiac overexpression of the human 5-HT4 receptor in mice

Serotonin (5-HT) exerts pleiotropic effects in the human cardiovascular system. Some of the effects are thought to be mediated via 5-HT(4) receptors, which are expressed in the human atrium and in ventricular tissue. However, a true animal model to study these receptors in more detail has been hitherto lacking. Therefore, we generated, for the first time, a transgenic (TG) mouse with cardiac myocyte-specific expression of the human 5-HT(4) receptor. RT-PCR and immunohistochemistry revealed expression of the receptor at the mRNA and protein levels. Stimulation of isolated cardiac preparations by isoproterenol increased phospholamban phosphorylation at Ser(16) and Thr(17) sites. 5-HT increased phosphorylation only in TG mice but not in wild-type (WT) mice. Furthermore, 5-HT increased contractility in isolated perfused hearts from TG mice but not WT mice. These effects of 5-HT could be blocked by the 5-HT(4) receptor-selective antagonist GR-125487. An intravenous infusion of 5-HT increased left ventricular contractility in TG mice but not in WT mice. Similarly, the increase in contractility by 5-HT in isolated cardiomyocytes from TG mice was accompanied by and probably mediated through an increase in L-type Ca(2+) channel current and in Ca(2+) transients. In intact animals, echocardiography revealed an inotropic and chronotropic effect of subcutaneously injected 5-HT in TG mice but not in WT mice. In isolated hearts from TG mice, spontaneous polymorphic atrial arrhythmias were noted. These findings demonstrate the functional expression of 5-HT(4) receptors in the heart of TG mice, and a potential proarrhythmic effect in the atrium. Therefore, 5-HT(4) receptor-expressing mice might be a useful model to mimic the human heart, where 5-HT(4) receptors are present and functional in the atrium and ventricle of the healthy and failing heart, and to investigate the influence of 5-HT in the development of cardiac arrhythmias and heart failure.

Pineal melatonin synthesis is decreased in type 2 diabetic Goto-Kakizaki rats

AIMS

It is not well understood why the amplitude of melatonin rhythms is reduced in diabetic animals and humans. This paper addresses the differences in the pineal melatonin synthesis of type 2 diabetic Goto-Kakizaki (GK) rats compared to non-diabetic Wistar rats (8 and 50 weeks old).

MAIN METHODS

Plasma melatonin concentrations and the pineal content of melatonin and its precursors (tryptophan, 5-hydroxytryptophan, serotonin, and N-acetylserotonin) were quantified at the middle of the day and night. Additionally, the expression of melatonin synthesizing enzymes, pineal noradrenaline content, and pineal protein content were considered, and the melatonin secreting capacity of pineal glands was studied in vitro.

KEY FINDINGS

The pineal glands of diabetic GK rats have a different expression pattern of melatonin synthesizing enzymes. The amount of all precursors of melatonin is reduced in pineal glands of diabetic GK rats. The pineal glands of diabetic GK rats contain less noradrenaline, indicating a reduced stimulation of nighttime melatonin synthesis. The pineal glands of diabetic GK rats produce less melatonin in reaction to noradrenaline in vivo and in vitro. The pineal glands of diabetic GK rats contain less protein, probably a consequence of diabetic neuropathy.

SIGNIFICANCE

This is the first time that melatonin synthesis is examined in a type 2 diabetic rat model. The present data unveiled several reasons for a reduced melatonin secretion in diabetic animals and presents an important link in the interaction between melatonin and insulin.

Increased melatonin synthesis in pineal glands of rats in streptozotocin induced type 1 diabetes

It is well-documented that melatonin influences insulin secretion. The effects are mediated by specific, high-affinity, pertussis-toxin-sensitive, G protein-coupled membrane receptors (MT(1) as well MT(2)), which are present in both the pancreatic tissue and islets of rats and humans, as well as in rat insulinoma cells (INS1). Via the Gi-protein-adenylatecyclase-3',5'-cyclic adenosine monophosphate (cAMP) and, possibly, the guanylatecyclase-cGMP pathways, melatonin decreases insulin secretion, whereas, by activating the Gq-protein-phospholipase C-IP(3) pathway, it has the opposite effect. For further analysis of the interactions between melatonin and insulin, diabetic rats were investigated with respect to melatonin synthesis in the pineal gland and plasma insulin levels. In this context, recent investigations have proven that type 2 diabetic rats and humans display decreased melatonin levels, whereas type 1 diabetic IDDM rats or those with diabetes induced by streptozotocin (STZ) of the present study show increased plasma melatonin levels and elevated AA-NAT-mRNA. Furthermore, the mRNA of pineal insulin receptors and beta1-adrenoceptors, including the clock genes Per1 and Bmal1 and the clock-controlled output gene Dbp, increases in both young and middle-aged STZ rats. The results therefore indicate that the decreased insulin levels in STZ-induced type 1 diabetes are associated with higher melatonin plasma levels. In good agreement with earlier investigations, it was shown that the elevated insulin levels observed in type 2 diabetes, are associated with decreased melatonin levels. The results thus prove that a melatonin-insulin antagonism exists. Astonishingly, notwithstanding the drastic metabolic disturbances in STZ-diabetic rats, the diurnal rhythms of the parameters investigated are maintained.

Agonist-specific activation of the beta2-adrenoceptor/Gs-protein and beta2-adrenoceptor/Gi-protein pathway in adult rat ventricular cardiomyocytes

In rat ventricular cardiomyocytes beta2-adrenoceptors (AR) couple to Gs- and Gi-protein, and evidence has accumulated that beta2-AR agonists can differentially activate either Gs- or Gs- and Gi-protein. In this study, in isolated adult rat ventricular cardiomyocytes, we assessed the effects of pertussis toxin (PTX) on beta2-AR agonist (terbutaline (TER), salbutamol (SAL) and fenoterol (FEN)) evoked inhibition of phenylephrine (PE)-induced increase in the rate of protein synthesis (assessed as [3H]phenylalanine incorporation) to find out which beta2-AR agonist activates selectively Gs- or Gs- and Gi-protein. PE (1 microM) increased the rate of protein synthesis from 100% to 130+/-2% (n = 34). FEN, TER and SAL (1 nM-10 microM) inhibited PE-induced increase in the rate of protein synthesis concentration-dependently. FEN inhibited PE effects almost completely (from 132+/-3 to 101+/-1%), whereas TER and SAL caused only partial inhibition (from 131+/-2 to 114+/-2 and 129+/-1 to 111+/-2%, respectively). Pretreatment of cardiomyocytes with PTX (250 ng ml(-1) for 16 h at 37 degrees C) did not affect FEN effects, but converted TER- and SAL-evoked partial inhibition into complete inhibition. Inhibitory effects of the three beta2-AR agonists were markedly attenuated by beta1-AR selective antagonist CGP 20712A (CGP) (300 nM); in contrast, beta2-AR selective antagonist ICI 118,551 (55 nM) inhibited the inhibitory effects of the three beta2-AR agonists only in PTX-pretreated cardiomyocytes,with beta1-AR blocked by CGP. We conclude that, in adult rat ventricular cardiomyocytes, FEN activates selectively the Gs protein-pathway, while TER and SAL activate the Gs- and Gi-protein pathways. Part of the effects of these three beta2-AR agonists appears to be mediated by beta1-AR.

?2-Adrenoceptor-mediated intrinsic sympathomimetic activity of carteolol: an in vivo study

The intrinsic sympathomimetic activity (ISA) of a beta-adrenoceptor blocker can be mediated by beta(1)- or beta(2)-adrenoceptors. The aim of this study was to characterize the ISA of the beta-adrenoceptor blocker carteolol in healthy volunteers. Two approaches were employed. First, we assessed the effects of carteolol (20, 40 or 80 mg p.o.) on blood pressure, heart rate and heart-rate corrected duration of electromechanical systole (QS(2)c, a measure of cardiac contractility) in the volunteers. Carteolol dose-dependently increased systolic blood pressure, heart rate and contractility and decreased diastolic blood pressure. The beta(1)-adrenoceptor blocker bisoprolol did not attenuate these carteolol effects, but rather enhanced the effects on heart rate and systolic blood pressure. Second, we treated volunteers for 7 days with 1 x 20 mg/day carteolol and assessed lymphocyte beta(2)-adrenoceptor density (by (-)-[(125)I]-iodocyanopindolol binding) and functional responsiveness (by 10 muM isoprenaline-induced increase in lymphocyte cyclic AMP content). Carteolol significantly reduced lymphocyte beta(2)-adrenoceptor density and function. After withdrawal of carteolol lymphocyte beta(2)-adrenoceptor density and function recovered only very slowly and had not returned to control levels 11 days after carteolol withdrawal. In conclusion, the fact that, on the one hand, the cardiovascular effects of carteolol were not attenuated by the beta(1)-adrenoceptor blocker bisoprolol and, on the other, carteolol significantly decreased lymphocyte beta(2)-adrenoceptor density and function is in favour of the idea that the ISA of carteolol is mediated by beta(2)-adrenoceptors. Involvement of an additional receptor site (e.g. the propranolol-resistant state of the beta(1)-adrenoceptor), however, cannot be excluded.

Effect of a beta 2-adrenoceptor stimulation on hyperglycemia-induced endothelial dysfunction

To investigate whether beta(2)-adrenoceptors exist on endothelial cells and whether a beta(2)-adrenoceptor stimulation might prevent the development of hyperglycemia-induced endothelial dysfunction, porcine aortic endothelial cells (PAECs) were cultured and chronically exposed to either 5 mM D-glucose ("normoglycemia") or 20 mM D-glucose ("hyperglycemia"), with or without 100 nM salbutamol in absence or presence of beta(2)-adrenoceptor antagonist ICI 118,551 [1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxyl]-3-[(1-methylethyl)-amino]-2-butanol] or beta(1)-antagonist metoprolol. For osmotic control, PAECs were exposed to 15 mM L-glucose. We measured nitric oxide release using the met-hemoglobin assay and assessed beta-adrenoceptor density and subtypes by radioligand binding. Furthermore, we determined intracellular NADH and NADPH using high-performance liquid chromatography. High D-glucose concentrations but not L-glucose led to significantly reduced basal and stimulated nitric oxide release. Chronic salbutamol treatment significantly antagonized the impairment of the nitric oxide response, which was inhibited by ICI 118,551 but not by metoprolol. The number of giant cells was significantly increased in hyperglycemia, which could be prevented by salbutamol. Binding of the radioligand (-)-[(125)I]iodocyanopindolol revealed a total beta-adrenoceptor density of 29.8 +/- 3.7 (normoglycemic) and 30.3 +/- 3.6 (hyperglycemic) fmol/mg protein. Displacement by ICI 118,551 revealed beta-adrenoceptor subtype distribution with 30.3 +/- 4.4 (normoglycemic) and 29.1 +/- 3.8% beta(2)-adrenoceptors. NADH production increased in hyperglycemia, which was completely prevented by salbutamol. We conclude that hyperglycemia in PAEC induces endothelial dysfunction with impaired nitric oxide release and that this can be prevented by beta(2)-adrenoceptor stimulation.

Role of beta 1- and beta 2-adrenoceptors in hypertrophic and apoptotic effects of noradrenaline and adrenaline in adult rat ventricular cardiomyocytes

In adult rat ventricular cardiomyocytes alpha1-adrenoceptor (AR) stimulation causes increases in protein synthesis. On the other hand beta1-AR stimulation inhibits protein synthesis, and evokes apoptotic cell death. We studied, in adult rat ventricular cardiomyocytes, effects of noradrenaline (NA), adrenaline (ADR) and phenylephrine (PE) on protein synthesis (assessed by [3H]-phenylalanine incorporation into the cardiomyocytes) in relation to effects on early apoptosis (measured by Annexin V/propidium iodide staining). PE (10(-9)-10(-5) M) induced protein synthesis was not affected by the beta1-AR blocker CGP 20712A (CGP, 300 nM) or beta2-AR blocker ICI 118,551 (ICI, 55 nM). ADR (10(-9)-10(-5) M) induced protein synthesis was enhanced by CGP and decreased by ICI. Pretreatment of the cardiomyocytes with pertussis toxin (PTX) decreased NA- and ADR- induced protein synthesis, but did not affect PE-effects. NA (10(-5) M) and ADR (10(-5) M) caused a significant increase in the number of apoptotic cells; these effects were enhanced by PTX-treatment, abolished by CGP, but not significantly affected by ICI. Furthermore, there was a significant negative correlation between catecholamine-evoked apoptosis and catecholamine-induced hypertrophic effects. We conclude that, in ventricular cardiomyocytes of adult rats, growth-promoting effects of NA and ADR are composed of alpha1A-AR mediated increase in protein synthesis and beta1-AR mediated apoptosis that counteracts increases in protein synthesis. The role of beta2-adrenoceptor appears to be a balance of antiapoptotic effects via a PTX-sensitive pathway and proapoptotic effects via a GS-adenylyl cyclase pathway.

Cardiac beta-adrenoceptor changes in monocrotaline-treated rats: differences between membrane preparations from whole ventricles and isolated ventricular cardiomyocytes

In monocrotaline (MCT)-treated rats the beta-adrenoceptor-G-protein-adenylyl cyclase system-determined in crude membrane preparations from whole ventricular tissue-was desensitized not only in right (RV) but also in left ventricles (LV). This study aimed to assess the specific contribution of cardiomyocytes to these beta-adrenoceptor changes. Six-week-old male Wistar rats were treated with 60 mg/kg body weight MCT intraperitoneally; within 4-6 weeks, rats developed marked RV hypertrophy. Cardiomyocytes were isolated from RVs and LVs. In RV cardiomyocytes of MCT-treated rats, beta-adrenoceptor density was significantly reduced whereas it was unaltered in LV cardiomyocytes. Reduction of RV cardiomyocyte beta-adrenoceptors was due to a selective beta(1)-adrenoceptor reduction. Isoprenaline (100 microM)-induced cAMP increase was significantly reduced in RV but not in LV cardiomyocytes of MCT-treated rats. G protein-coupled receptor kinase activity was increased in RV but not in LV cardiomyocytes. alpha(1)-Adrenoceptor density and noradrenaline-induced increase in inositol phosphate formation were significantly reduced only in RV but not in LV cardiomyocytes from MCT-treated rats. It is concluded that in cardiomyocytes of MCT-treated rats, cardiac beta-adrenoceptors and alpha -adrenoceptors are chamber-specifically desensitized only in the RV. Thus, changes in cardiac beta-adrenoceptors determined in membrane preparations from whole tissue homogenates do not correctly reflect changes occurring in cardiomyocytes.

Demonstration of functional M3-muscarinic receptors in ventricular cardiomyocytes of adult rats

1 Muscarinic receptors (M-receptors) in the mammalian heart are predominantly of the M(2)-subtype. The aim of this study was to find out whether there might exist an additional myocardial non-M(2)-receptor. 2 For this purpose, we assessed, in adult rat isolated ventricular cardiomyocytes, carbachol-induced [(3)H]-inositol phosphate (IP) formation, and its inhibition by M-receptor antagonists. 3 Carbachol (10(-7)-10(-3) mol l(-1)) increased IP-formation (maximal increase: 14+/-3% above basal, n=6). This increase was significantly enhanced by pretreatment with pertussis toxin (PTX, 250 ng ml(-1) for 20 h): maximal increase was 31+/-5%, pEC(50)-value was 5.08+/-0.33 (n=6). 4 In PTX-pretreated cardiomyocytes 100 micromol l(-1) carbachol-induced IP-formation was inhibited by atropine (pK(i)-value: 8.89+/-0.10) and by the M(3)-receptor antagonist darifenacin (pK(i)-value: 8.67+/-0.23) but was not significantly affected by the M(1)-receptor antagonist pirenzepine (1 micromol l(-1)) or the M(2)-receptor antagonists AF-DX 116 and himbacine (1 micromol l(-1)). 5 In conclusion, in adult rat cardiomyocytes there exists an additional, non-M(2)-receptor, that is coupled to activation of the phospholipase C/IP(3)-pathway; this receptor is very likely of the M(3)-subtype.

The ageing heart: influence of cellular and tissue ageing on total content and distribution of the variants of elongation factor-2

The involvement of elongation factor-2 (EEF-2), a key-protein of peptide-chain elongation, in the slowing down of protein synthesis during cardiac ageing was addressed. EEF-2 was measured in rat heart extracts and isolated rat cardiomyocytes (CM) from newborn and adult rats using sodium-dodecylsulphate polyacrylamide gel electrophoresis after specific labeling with [32P]ADP-ribosylation or immunoblot. The age-dependent proportional content of several eucaryotic elongation factor-2 (eEF-2) subtypes in rat CM and rat heart extracts was compared using one-dimensional isoelectric focusing. EEF-2 was considerably reduced in the hearts of adult compared to neonatal rats (P<0.01). EEF-2 was also significantly decreased in isolated CM from adult versus newborn rats and during prolonged cultivation of neonatal CM. Cellular ageing was combined with reduced protein synthesis. During adolescence the eEF-2 variants shifted to acidic subtypes. Young adult and old rats revealed similar amounts and subtype distribution of cardiac eEF-2. Only the more acidic eEF-2 variants appeared to contain phosphorylated eEF-2. We concluded that total cardiac eEF-2 and its subtype pattern might play an important role in developmental and age-related proteomic changes.

Ventricular hypertrophy plus neurohumoral activation is necessary to alter the cardiac beta-adrenoceptor system in experimental heart failure

Treatment of rats with monocrotaline (MCT) leads to pulmonary hypertension, right ventricular (RV) hypertrophy, and finally to RV heart failure. This is associated with characteristic changes in right ventricular beta-adrenoceptors (beta-AR), neuronal noradrenaline transporter (NAT) density and activity (uptake1), and G protein-coupled receptor kinase (GRK) activity. This study aimed to find out factors that determine beta-AR, uptake1, and GRK changes. Thus, 6-week-old rats were treated with 50 mg/kg MCT subcutaneous or 0.9% saline. Within 13 to 19 days after MCT application (group A), RV weight (222+/-6 versus 147+/-5 mg) and RV/left ventricular (LV) weight ratio (0.42+/-0.01 versus 0.29+/-0.01) were significantly increased, whereas plasma noradrenaline, RV beta-AR density, RV NAT density and activity, and RV GRK activity were not significantly altered. Twenty-one to twenty-eight days after MCT (group B), however, not only RV weight (316+/-4 versus 148+/-2 mg) and RV/LV weight ratio (0.61+/-0.01 versus 0.3+/-0.01) were markedly increased but also plasma noradrenaline (645+/-63 versus 278+/-18 pg/mL); now, RV beta-AR density (13.4+/-1.3 versus 26.5+/-1.1 fmol/mg protein), RV NAT density (50.9+/-11.3 versus 79.6+/-2.9 fmol/mg protein), and RV NAT activity (65.4+/-7.4 versus 111.8+/-15.9 pmol [3H]-NA/mg tissue slices/15 min) were significantly decreased and RV-membrane GRK activity (100+/-15 versus 67+/-6 [32P]-rhodopsin in cpm) significantly increased. LV parameters of MCT-treated rats were only marginally different from control LV. We conclude that in MCT-treated rats ventricular hypertrophy per se is not sufficient to cause characteristic alterations in the myocardial beta-AR system often seen in heart failure; only if ventricular hypertrophy is associated with neurohumoral activation beta-ARs are downregulated and GRK activity is increased.

Differential effects of bucindolol and carvedilol on noradenaline-induced hypertrophic response in ventricular cardiomyocytes of adult rats

In adult rat ventricular cardiomyocytes, noradrenaline exerts dual effects on protein synthesis: increases via alpha(1)-adrenoceptors and decreases via beta(1)-adrenoceptors. Carvedilol and bucindolol are beta-blockers with additional alpha(1)-adrenoceptor blocking activities. We studied the effects of carvedilol and bucindolol on noradrenaline-induced protein synthesis (assessed by [(3)H]phenylalanine incorporation) in adult rat ventricular cardiomyocytes. Radioligand binding studies with [(125)I]iodocyanopindolol and [(3)H]prazosin revealed that carvedilol had a much higher affinity to alpha(1)-adrenoceptors than bucindolol (beta(1)-/alpha(1)-adrenoceptor ratio for carvedilol, 1:2.7; for bucindolol, 1:43). Noradrenaline-evoked increases in protein synthesis were enhanced by propranolol (1 microM) and beta(1)-adrenoceptor-selective antagonists bisoprolol (1 microM) and CGP 20712A [1-[2-((3-carbamoyl-4-hydroxy)phenoxy)-ethyl-amino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propranol methanesulfonate] (300 nM). Carvedilol (100 pM-10 microM) inhibited 1 microM noradrenaline-induced increase in protein synthesis with monophasic concentration-inhibition curves independent of whether CGP 20712A was present or not; K(i) values for carvedilol were 5 to 6 nM. In contrast, bucindolol (100 pM-10 microM) inhibited l microM noradrenaline-induced increase in protein synthesis with a bell-shaped concentration-inhibition curve; it increased noradrenaline-induced protein synthesis at 10 nM, although at concentrations >100 nM it was inhibited. In the presence of 300 nM CGP 20712A or 1 microM propranolol, however, bucindolol inhibited 1 microM noradrenaline-induced increase in protein synthesis with monophasic concentration-inhibition curves; K(i) values were 40 to 75 nM. On the other hand, both carvedilol and bucindolol inhibited 1 microM phenylephrine-induced protein synthesis with monophasic concentration-inhibition curves; K(i) values were 4 (carvedilol) and 45 nM (bucindolol). These results indicate that, at low (beta-adrenoceptor blocking) concentrations, bucindolol can enhance noradrenaline-induced protein synthesis whereas it is inhibited by carvedilol.

Cardiac beta-adrenoceptor desensitization due to increased beta-adrenoceptor kinase activity in chronic uremia

Patients with chronic renal failure develop an autonomic dysfunction with impaired baroreflex control and attenuated cardiovascular beta-adrenoceptor response to noradrenaline. In rats that underwent 5/6-nephrectomy (SNX), cardiac beta-adrenoceptor responsiveness was reduced as well. Therefore, the aim of this study was to further investigate the mechanism underlying cardiac beta-adrenoceptor desensitization in SNX rats. For this purpose, right and left ventricular beta-adrenoceptor density, activity of the G-protein-coupled receptor kinase, and activity and density of the neuronal noradrenaline transporter (uptake1) were assessed in SNX rats. Seven weeks after SNX, rats had developed left heart hypertrophy. Plasma creatinine, urea, and noradrenaline levels were significantly increased; left and right ventricular noradrenaline content was significantly decreased when compared with sham-operated control rats. In these SNX rats, left, but not right, ventricular beta-adrenoceptor density was significantly reduced, and membrane-associated G-protein-coupled receptor kinase activity was significantly increased compared with sham-operated rats. Although right and left ventricular activity of uptake1 was unchanged, the neuronal noradrenaline transporter density was significantly reduced in both ventricles of SNX versus sham-operated rats. An increase in left ventricular G-protein-coupled receptor kinase activity, possibly triggered by enhanced cardiac noradrenaline release, might be responsible for the decrease in left ventricular beta-adrenoceptor responsiveness in SNX rats.

The impact of insulin-like growth factor-1 on the pattern of cardiac elongation factor-2 variants in a model of overload

Because of its key role in proteosynthesis, the total content of elongation factor-2 (EF-2) and the distribution of six main EF-2 variants were investigated after Pseudomonas Exotoxin A catalyzed [37P]ADP-ribosylation using 1D-PAGE and isoelectric focusing (IEF) in a rat model of hemodynamic overload with variable degrees of cardiac hypertrophy: Chronic NO-synthase inhibition by L-NAME (N-omega-nitro-L-arginine-methyl-ester; 0.75 mg/ml drinking water) induced arterial hypertension without hypertrophy but myocardial apoptosis; additional treatment with IGF-1 (osmotic micropumps) did not modify hypertension but reduced apoptosis allowing moderate hypertrophy of the left ventricles. Total EF-2 did not significantly increase in rats with hemodynamic overload with or without IGF-1 supplementation. A positive correlation was found between an acidic EF-2 variant and apoptosis (p = 0.01). Hypertrophy under additional IGF-1 was combined with a shift of the EF-2 variants to basic subtypes (p < 0.01). This finding may be indicative of the trophic potency of IGF-1.

Noradrenaline-induced increase in protein synthesis in adult rat cardiomyocytes: involvement of only alpha1A-adrenoceptors

Adult rat ventricular cardiomyocytes contain alpha1A- and alpha1B-adrenoceptors (ARs, 20%:80%, assessed by [3H]prazosin binding). We studied which alpha1-AR subtype mediates noradrenaline (NA)-induced increase in rate of protein synthesis, and which signalling pathway is involved. NA (10-9-10-4 M) concentration-dependently increased inositol phosphate (IP) formation (pEC50-value=6.1+/-0.1, n=5) and protein synthesis (assessed as [3H]phenylalanine incorporation; pEC50-value=6.6+/-0.1, n=6). NA-induced IP-formation was partly inhibited by the alpha1B-AR antagonist chloroethylclonidine (CEC, 30 microM; 33+/-9% inhibition, n=5); following CEC-treatment the alpha1A-AR-selective 5-methyl-urapidil (5-MU) inhibited NA-induced IP-formation with a pKi-value of 9.2+/-0.2 (n=6); the alpha1D-AR-selective BMY 7378 was only a weak antagonist (pKi-value <7). NA-induced increase in protein synthesis was insensitive to CEC whereas 5-MU inhibited it with a pKi-value of 9.1+/-0.2 (n=6). NA (1 microM)-induced increase in protein synthesis was inhibited by the protein kinase C (PKC) inhibitor bisindolylmaleimide (IC50-value: 206 nM), the PI 3-kinase inhibitors wortmannin (IC50=3.4 nM) and LY 294002 (IC50=10 microM), and p70s6-kinase inhibitor rapamycin (IC50=123 pM) but not by the p38 MAP-kinase inhibitor SB 203580 (10 microM) or the MEK-inhibitor PD 98059 (25 microM). Moreover, 5-MU (30 nM) but not CEC inhibited NA-induced activation of p70s6-kinase. We conclude that, in adult rat cardiomyocytes, alpha1A- and alpha1B-AR mediate NA-induced IP-formation but only alpha1A-ARs mediate increase in protein synthesis. Alpha1A-AR-mediated increase in protein synthesis involves activation of a PKC, PI 3-kinase and p70s6-kinase but not of ERK- or p38 MAP-kinase.

Impaired beta-adrenergic control of immune function in patients with chronic heart failure: reversal by beta1-blocker treatment

BACKGROUND

In patients with chronic heart failure (CHF) and heightened sympathetic activity alterations in immune function have been described.

OBJECTIVES

To find out whether, in CHF patients, beta-blocker treatment might beneficially affect immune function.

METHODS

We studied activation of circulating lymphocytes (assessed as concanavalin A (CON A)-induced inositol phosphate (IP) formation and proliferation ([3H]-thymidine incorporation) from 8 CHF patients on standard medication (Group A, mean age 54 +/- 6 yrs, NYHA class II - IV, mean 3.1 +/- 0.3) and in 9 CHF patients on standard medication and additional treatment with the beta1-blocker metoprolol (Group B, mean age: 56 +/- 3 yrs, NYHA class II - IV, mean 2.9 +/- 0.2); 8 age-matched healthy volunteers (mean age 49 +/- 3 yrs) served as controls.

RESULTS

Compared to controls, in group A isoprenaline-induced lymphocyte cyclic AMP-increase was reduced, CON A-evoked IP formation significantly enhanced and isoprenaline-induced inhibition of CON A-evoked IP formation and proliferation almost abolished. In group B, however, all these parameters were not significantly different from controls.

CONCLUSION

In CHF patients lymphocyte cyclic AMP response to beta-adrenoceptor stimulation is blunted and the inhibitory effect of cyclic AMP on lymphocyte activation is almost abolished; this could result in a non-regulated increased production and release of proinflammatory cytokines that might contribute to the progression of the disease. Chronic treatment of CHF patients with the beta1-blocker metoprolol (at least partly) restores lymphocyte cyclic AMP responses to beta-adrenoceptor stimulation and the inhibitory effects of cyclic AMP on lymphocyte activation; the resulting "normalization" of the immune function might contribute to the beneficial effects of beta1-blockers in treatment of CHF.

ET-receptor function in relation to blood pressure in spontaneously hypertensive and aortic-banded rats

Endothelin-1 (ET-1), a potent endogenous vasoconstrictor, has been proposed to play a pathophysiologic role in hypertension. The aim of this study was to find out whether changes in ET-receptor function are cause or consequence of blood pressure elevation in hypertension. For this purpose, we assessed ET-receptor function [as ET-1-induced [3H]inositol phosphate (IP) accumulation] in slices of left ventricle and renal cortex and in rings of thoracic and abdominal aorta from spontaneously hypertensive rats (SHR) at the age of 8 weeks (i.e. developing hypertension), 12 and 24 weeks (established hypertension) vs. normotensive age-matched Wistar-Kyoto (WKY) rats, and from supra-renal aortic-banded (AOB) rats at the age of 8, 12 and 24 weeks (i.e. 4, 8 and 20 weeks after AOB) vs. sham-operated (SOP) age-matched WKY rats. In the SHR with established hypertension ET-1-induced IP formation was altered in all tissues investigated: it was significantly increased vs. WKY rats in left ventricle, and significantly decreased in renal and aortic tissues. Similarly, in AOB rats at all ages ET-1-induced IP formation was changed in those tissues that were under pressure load [heart (increase) and thoracic aorta (decrease)] vs. SOP rats, whereas in those tissues not under pressure load (kidney and abdominal aorta) ET-1-induced IP formation was not different between AOB and SOP rats. Moreover, in 8-week-old SHR (where hypertension is not yet established) ET-1-induced IP formation was not significantly different compared to WKY rats (with the exception of thoracic aorta). We conclude that, at least in SHR and AOB rats, changes in ET-1 signalling are secondary to the elevation in blood pressure.

Inositolphosphate formation in thoracic and abdominal rat aorta following Gq/11-coupled receptor stimulation

Although thoracic and abdominal rat aorta are often used as a classical pharmacological preparation for the assessment of vascular drug effects, little is known on regional differences among these two parts of the aorta with regard to their reaction to Gq/11-coupled receptor activation. Thus, we determined, in rings from thoracic and abdominal aorta from 12-week-old male Wistar rats, the effects of noradrenaline (NA; 10(-8)-10(-4) M), endothelin-1 (ET-1; 10(-10)-10(-6) M) and the thromboxane A2 mimetic U 46619 (10(-8)-10(-5) M) on inositolphoshate (IP) formation (assessed as accumulation of total [3H]IPs in [3H]myoinositol prelabelled rings). NA, ET-1 and U 46619 concentration-dependently increased IP formation; maximum increases were, however, significantly more pronounced in thoracic than in abdominal aorta. Similarly, NA, ET-1 and U 46619 evoked significantly larger maximum contractions in thoracic than in abdominal aorta. NA-induced [3H]IP formation could be inhibited with BMY 7378 (10(-9)-10(-4) M) and with 5-methyl-urapidil (5-MU; 10(-9)-10(-5) M) both exhibiting biphasic concentration-inhibition curves. The pKi-values for BMY 7378 at the high affinity site were in thoracic aorta 8.93+/-0.28 (n=5), and in abdominal aorta 8.76+/-0.35 (n=4) and at the low affinity site 6.45+/-0.2 (thoracic aorta) and 6.55+/-0.27 (abdominal aorta). pKi-Values for 5-MU in thoracic aorta at the high affinity site were 8.25+/-0.34 (n=4), and at the low affinity site 6.61+/-0.39 . In abdominal aorta reliable pKi-values could not be calculated for 5-MU due to a low signal-to-noise ratio. On the other hand, in both preparations the ETA-receptor antagonist BQ-123 (10(-9)-10(-5) M) and the TP-receptor antagonist SQ 29548 (10(-9)-10(-5) M) inhibited ET-1- and U 46619-induced IP formation, respectively, with monophasic concentration-inhibition curves: pKi-values for BQ-123 were: 8.16+/-0.24 (thoracic aorta) and 8.10+/-0.35 (abdominal aorta) and for SQ 29548: 8.2+/-0.3 (thoracic aorta) and 8.5+/-0.3 (abdominal aorta). The amount of immunodetectable Gq/11-protein was similar in both tissues. We conclude that responses to NA, ET-1 and U 46619 (IP formation and contractile force) are larger in thoracic than in abdominal aorta. ET-1 effects on IP formation are mediated by ETA-receptors and U 46619 effects by TP-receptors. NA effects are mediated by alpha1D- and alpha1A-adrenoceptors; alpha1B-adrenoceptors seem to play a minor role.

Beta-adrenoceptor stimulation attenuates the hypertrophic effect of alpha-adrenoceptor stimulation in adult rat ventricular cardiomyocytes

OBJECTIVES

The study investigated whether beta-adrenoceptor antagonists augment the hypertrophic response of cardiomyocytes evoked by norepinephrine.

BACKGROUND

In adult ventricular cardiomyocytes, stimulation of alpha- but not beta-adrenoceptors induces myocardial hypertrophy. Natural catecholamines, like norepinephrine, stimulate simultaneously alpha- and beta-adrenoceptors. We investigated whether beta-adrenoceptor stimulation interferes with the hypertrophic response caused by alpha-adrenoceptor stimulation.

METHODS

Adult ventricular cardiomyocytes isolated from rats were used as an experimental model. Hypertrophic parameters under investigation were stimulation of phenylalanine incorporation and protein mass, stimulation of 14C-uridine incorporation and RNA mass, and increases in cell shape.

RESULTS

Norepinephrine (0.01 to 10 micromol/liter) increased concentration-dependent phenylalanine incorporation; pEC50 value was 5.9 +/- 0.1 (n = 8). The alpha1-adrenoceptor antagonist prazosin (0.1 micromol/liter) suppressed norepinephrine-induced increase in rate of protein synthesis. Conversely, propranolol (1 micromol/liter) and the beta1-adrenoceptor selective antagonists CPG 20712A (300 nmol/liter) or atenolol (1 micromol/liter) augmented increases in phenylalanine incorporation caused by norepinephrine. Addition of the beta2-adrenoceptor antagonist ICI 118,551 (55 nmol/liter) did not influence the hypertrophic effect of norepinephrine. Atenolol augmented the norepinephrine-induced increases of all hypertrophic parameters investigated (i.e., protein mass, uridine incorporation, RNA mass, cell volume, and cross-sectional area). In the presence of norepinephrine, inhibition of beta1-adrenoceptors increased the amount of protein kinase C-alpha and -delta isoforms translocated into the particulate fraction. The effect of pharmacological inhibition of beta1-adrenoceptors could be mimicked by Rp-cAMPS (adenosine-3', 5'-cyclic phosphorothiolate-Rp). The inhibitory effect of beta1-adrenoceptor stimulation on the alpha-adrenoceptor-mediated effect persisted in cardiomyocytes isolated from hypertrophic hearts of rats submitted to aortic banding.

CONCLUSIONS

In isolated ventricular cardiomyocytes from rats, beta1-adrenoceptor stimulation attenuates the hypertrophic response evoked by alpha1-adrenoceptor stimulation.

The cardiac beta-adrenoceptor-G-protein(s)-adenylyl cyclase system in monocrotaline-treated rats

In rats, injection of the alkaloid monocrotaline (MCT) causes right ventricular hypertrophy and cardiac failure. In order to study whether, in MCT-treated rats, changes in the cardiac beta -adrenoceptor-G-protein(s)-adenylyl cyclase system might be comparable to those found in human primary pulmonary hypertension, we assessed in right and left ventricles from MCT-treated rats the components of the beta -adrenoceptor system: the receptor number and subtype distribution (by (-)-[(125)I]iodocyanopindolol binding), the G-proteins (by quantitative Western blotting), and the activity of adenylyl cyclase. A single injection of 60 mg/kg i.p. MCT caused in rats right ventricular hypertrophy (RVH); part of the rats developed cardiac failure (RVF). In these rats the cardiac beta -adrenoceptor-G-protein(s)-adenylyl cyclase system was markedly changed beta -adrenoceptors were desensitized due to a decrease in receptor number, an uncoupling of the receptor from the G(s)-adenylyl cyclase system, a decrease in G(s)and a decrease in the activity of the catalytic unit of adenylyl cyclase. In general, these changes were more pronounced in right ventricles v left ventricles, and in rats with RVF v rats with RVH. On the other hand, cardiac muscarinic receptors and G(i)appeared not to be altered. We conclude that in MCT-treated rats changes in the cardiac beta -adrenoceptor-G-protein(s)-adenylyl cyclase system occur that resemble those observed in human primary pulmonary hypertension. Thus, MCT-treated rat appears to be a suitable animal model to study in more detail the pathophysiology of the development of right heart failure, and to identify new therapeutic possibilities.

Heterogeneity of cardiac rat and human elongation factor 2

Elongation factor 2 (EF-2) catalyses the last step of the elongation cycle, translocation, in the course of protein biosynthesis. A system for analyzing post-translational modifications of EF-2, which is a single polypeptide of 857 amino acids, is reported and its application to cytosolic extracts of cultured neonatal rat heart myocytes, neonatal and adult rat cardiac tissue, and extracts of human left ventricular myocardium is described. Comparing different pH ranges in immobilized pH gradient-isoelectric focusing (IPG-IEF), a range of pH 3 - 10 and 4 - 9 resulted in a highly defined and reproducible resolution of six different EF-2 variants of all extracts in the first dimension. These six variants were detected by the "imaging plate" (phosphor radiation image sensor) after specific labeling with Pseudomonas exotoxin A catalyzed [32P]ADP-ribosylation. This finding could be confirmed in Western blot analysis with a specific polyclonal rabbit antibody. Using two-dimensional polyacrylamide gel electrophoresis (2-D-PAGE), five to six EF-2 variants could be demonstrated in all extracts. By application of a second IPG indicator strip to the 2-D gel, they could be aligned with corresponding spots in a silver-stained 2-D separation of human myocardial tissue, revealing that the EF-2 variants belong to the group of low-abundance proteins.

FP-receptor mediated trophic effects of prostanoids in rat ventricular cardiomyocytes

The aim of this study was to characterize the receptor subtype involved in cardiac effects of prostanoids. For this purpose we determined in neonatal and adult rat cardiomyocytes effects of prostanoids on inositol phosphate (InsP)-formation (assessed as accumulation of total [(3)H]-InsP's in myo-[(3)H]-inositol pre-labelled cells) and on rate of protein synthesis (assessed as [(3)H]-phenylalanine incorporation), and on contractile force in left ventricular strips of the rat heart. For comparison, effects of prostanoids on InsP-formation and contractile force were determined in rat thoracic aorta, a classical TP-receptor containing tissue. Prostanoid increased InsP-formation and rate of protein synthesis in neonatal as well as adult rat cardiomyocytes; the order of potency was in neonatal (PGF(2alpha)>PGD(2)> or =PGE(2)> or =U 46619>PGE(1)) and adult (PGF(2alpha)>PGD(2)> or =PGE(2)>U 46619) rat cardiomyocytes well comparable. Moreover, in electrically driven left ventricular strips PGF(2alpha) caused positive inotropic effects (pD(2) 7.5) whereas U 46619 (up to 1 microM) was uneffective. In contrast, in rat thoracic aorta U 46619 was about 100 times more potent than PGF(2alpha) in increasing InsP-formation and contractile force. The TP-receptor antagonist SQ 29548 only weakly antagonized prostanoid-induced increases in rate of protein synthesis (pK(B) about 6) in rat cardiomyocytes but was very potent (pK(B) about 8-9) in antagonizing prostanoid-induced increases in InsP-formation and contractile force in rat aorta. We conclude that, in cardiomyocytes of neonatal and adult rats, the prostanoid-receptor mediating increases in InsP-formation and rate of protein synthesis is a FP-receptor. Moreover, stimulation of these cardiac FP-receptors can mediate increases in contractile force.

Gq/11-coupled receptors and protein synthesis in rat cardiomyocytes: role of Gi-proteins and protein kinase C-isozymes

Our recent findings indicate that, in rat neonatal ventricular cardiomyocytes, endothelin-1 (ET-1) induces increases in the rate of protein synthesis in a partly pertussis toxin (PTX)-sensitive manner, and that angiotensin II-evoked increases in the rate of protein synthesis are brought about via local secretion of ET-1. The aim of this study was to find out: (1) whether noradrenaline (NA) and the thromboxane A2 (TXA2)-mimetic U 46619-induced increases in the rate of protein synthesis may be also partly PTX-sensitive and/or mediated by ET-1, and (2) whether the growth-promoting effects of NA and U 46619 as well as ET-1 might involve activation of the same set of protein kinase C (PKC) isozymes. For this purpose we first studied the effects of NA and U 46619 on inositol phosphate (IP)-formation (assessed as accumulation of total [3H]IPs in myo-[3H]inositol prelabelled cells) and on the rate of protein synthesis (assessed as [3H]phenylalanine incorporation) (1) in the presence and absence of the ET(A)-receptor antagonist BQ-123, and (2) in nontreated and PTX-pretreated cells. Second, we assessed the effects of the PKC-inhibitors bisindolylmaleimide I and Gö 6976 and of phorbol-12-myristate-13-acetate (PMA; 1 microM overnight)-pretreatment on U 46619-, NA- and ET-1-induced increases in the rate of protein synthesis. NA (0.01-10 microM) concentration-dependently increased IP-formation (maximum increase: 115-/+23% above basal, n=4) and [3H]phenylalanine incorporation (maximum increase: 40+/-3% above basal, n=20). Both responses were antagonized by the alpha1-adrenoceptor antagonist prazosin (1 microM), but were not significantly affected by BQ-123 (1 microM). U 46619 (0.01-100 microM) concentration-dependently increased IP-formation (maximum increase: 89+/-12% above basal, n=8) and [3H]phenylalanine incorporation (maximum increase: 33+/-4% above basal, n=16). Both responses were slightly but significantly antagonized by the TP-receptor antagonist SQ 29548 (1 microM), but were not affected by BQ-123 (1 microM). Pretreatment of the cardiomyocytes with 250 ng ml(-1) PTX overnight did not significantly affect NA- and U 46619-evoked increases in IP-formation and [3H]phenylalanine incorporation. The PKC-inhibitor bisindolylmaleimide I (5 microM) as well as pretreatment of the cells with PMA (1 microM) significantly reduced the effects of NA, U 46619 and ET- I on the rate of protein synthesis; in contrast, the PKC-inhibitor Gö 6976 (5 microM) was without any effects. We conclude that, in rat neonatal ventricular cardiomyocytes, stimulation of Gq/11-coupled receptors increases the rate of protein synthesis; this involves activation of the same PKC-isozymes (very likely PKC-delta and/or -epsilon). NA and U 46619 cause their growth-promoting effects in a PTX-insensitive manner; ET-1 is not involved in their effects.

Muscarinic receptors in the failing human heart

In the human heart, as in the heart of several other species, muscarinic receptors are predominantly of the M2-subtype that couple via a pertussis toxin-sensitive Gi-protein to inhibit adenylyl cyclase. However, it is not clear whether an additional muscarinic receptor subtype exists in the human heart. In human right atrium, stimulation of muscarinic M2 receptors causes direct negative inotropic and chronotropic effects; in human ventricular myocardium, however, the negative inotropic effect can be only achieved when basal force of contraction has been pre-stimulated by cyclic AMP-elevating agents such as beta-adrenoceptor agonists, forskolin or phosphodiesterase inhibitors (indirect effect); this has been shown in various in vitro and in vivo studies. Evidence has accumulated that in chronic heart failure vagal activity is decreased. Cardiac muscarinic M2 receptor density and functional responsiveness (inhibition of adenylyl cyclase activity and negative inotropic effects), however, are not considerably changed when compared with non-failing hearts although cardiac Gi-activity is increased.

Cardiac effects of beta-adrenoceptor antagonists with intrinsic sympathomimetic activity in humans: beta1- and/or beta2-adrenoceptor mediated?

The aim of this study was to find out whether cardiac responses to the beta-adrenoceptor antagonists with intrinsic sympathomimetic activity (ISA) xamoterol and celiprolol are mediated by cardiac beta1- or beta2-adrenoceptors or both. For this purpose we assessed, in six healthy male volunteers, the effects of xamoterol (100 and 200 mg, p.o.) and celiprolol (200, 600, and 1,200 mg, p.o.) on blood pressure, heart rate, and heart rate-corrected duration of the electromechanical systole (QS2c, as a measure of inotropism). Xamoterol, in both doses, increased systolic blood pressure and heart rate, transiently decreased diastolic blood pressure, and shortened QS2c; all these effects were attenuated after pretreatment of the volunteers with the beta1-adrenoceptor antagonist bisoprolol. Celiprolol, in all three doses, increased heart rate, decreased diastolic blood pressure, and shortened QS2c but only marginally increased systolic blood pressure. Bisoprolol did not attenuate these celiprolol effects but rather enhanced celiprolol effects on systolic blood pressure and heart rate. In a further set of experiments, we studied cardiovascular effects of celiprolol in six healthy volunteers whose beta2-adrenoceptors had been desensitized by a 2-week treatment with 3x5 mg/day terbutaline. Under these conditions, celiprolol failed to increase heart rate or to shorten QS2c. We conclude that, under resting conditions, in healthy volunteers, beta-adrenoceptor antagonists with ISA can exert increases in heart rate and contractility that are mediated by either cardiac beta1-adrenoceptor (xamoterol) or cardiac beta2-adrenoceptor (celiprolol) stimulation. Thus in the human heart, the ISA of beta-adrenoceptor antagonists can be a beta1- or beta2-adrenoceptor agonistic component.

Mechanism of ET(A)-receptor stimulation-induced increases in intracellular Ca2+ in SK-N-MC cells

The mechanism underlying endothelin-1 (ET-1)-induced increases in intracellular Ca2+ concentrations in the human neuroblastoma cell-line SK-N-MC was investigated. ET-receptor agonists increased inositol phosphate (IP)-formation (assessed as accumulation of total [3H]-IPs in [3H]-myo-inositol prelabelled cells) and intracellular Ca2+ (assessed by the FURA-2 method) with an order of potency: ET-1 > sarafotoxin 6b (S6b)> ET-3 = S6c; the ETA-receptor antagonist BQ-123 inhibited both responses with apparent pKi-values of 8.3 and 8.6, respectively, while the ETB-receptor antagonist BQ-788 did not. Pretreatment of the cells with pertussis toxin (PTX, 500 ng ml(-1) overnight) reduced ET-1-induced Ca2+ increases by 46+/-5%, but rather enhanced ET-1-induced IP-formation. Chelation of extracellular Ca2+ by 5 mM EGTA did not affect ET-1-induced IP-formation. However, in the presence of 5 mM EGTA or SKF 96365, an inhibitor of receptor mediated Ca2+ influx (1.0-3.0 x 10(-5) M) ET-1-induced Ca2+ increases were inhibited in normal, but not in PTX-treated cells. [125I]-ET-1 binding studies as well as mRNA expression studies (by RT-PCR) detected only ETA-receptors whereas expression of ETB-receptor mRNA was marginal. ET-1 (10(-8) M) inhibited isoprenaline-evoked cyclic AMP increases; this was antagonized by BQ-123, not affected by BQ-788 and abolished by PTX-treatment. We conclude that SK-N-MC cells contain a homogeneous population of ETA-receptors that couple to IP-formation and inhibition of cyclic AMP formation. Stimulation of these ETA-receptors increases intracellular Ca2+ by at least two mechanisms: a PTX-insensitive IP-mediated Ca2+ mobilization from intracellular stores and a PTX-sensitive influx of extracellular Ca2+.

Terbutaline-induced desensitization of human cardiac beta 2-adrenoceptor-mediated positive inotropic effects: attenuation by ketotifen

BACKGROUND

In patients with chronic heart failure cardiac beta 1-adrenoceptors are desensitized whereas beta 2-adrenoceptors are only marginally affected. The mechanism underlying this differential regulation is not known.

OBJECTIVES

To find out whether or not human cardiac beta 2-adrenoceptors might be 'resistant' to agonist-induced desensitization and whether or not the antiallergic drug ketotifen might attenuate possible desensitization.

METHODS

We investigated, in a single blinded, randomised, placebo-controlled, cross-over study of ten healthy male volunteers (mean age, 25.3 +/- 0.7 years), the effects of two weeks treatment with the beta 2-adrenoceptor agonist terbutaline (3x5 mg/day p.o.) with and without simultaneous treatment with ketotifen (2x1 mg/day p.o. for three weeks) or placebo on beta-adrenoceptor-mediated cardiovascular effects. Cardiovascular effects were assessed as isoprenaline (3.5-35 ng/kg/min)- and terbutaline (25-150 ng/kg/min)-infusion-induced increases in heart rate and systolic blood pressure, decreases in diastolic blood pressure and shortening of the systolic time intervals (STIs), heart rate corrected duration of electromechanical systole (QS2c) and pre-ejection period (PEP; as a measure of inotropism).

RESULTS

Ketotifen did not significantly affect basal haemodynamics in the volunteers. Isoprenaline- and terbutaline-infusion caused dose-dependent increases in systolic blood pressure and heart rate, decreases in diastolic blood pressure and shortening of QS2c and PEP, whereby isoprenaline effects were more pronounced. After two weeks of treatment with terbutaline p.o., isoprenaline- and terbutaline-infusion-induced increases in heart rate, shortening of QS2c and PEP were significantly reduced whereby terbutaline-infusion effects were markedly more attenuated than isoprenaline-infusion effects. Ketotifen significantly reduced terbutaline p.o. treatment-induced attenuation of all terbutaline-infusion effects (largely beta 2-adrenoceptor-mediated) and the isoprenaline-infusion-induced increase in heart rate (beta 1- and beta 2-adrenoceptor-mediated), but did not (or only marginally) affect reduction in isoprenaline-induced shortening of QS2c and PEP (largely beta 1-adrenoceptor-mediated).

CONCLUSION

Human cardiac beta 2-adrenoceptors are not 'resistant' to agonist-induced desensitization: Ketotifen might prevent such beta 2-adrenoceptor-agonist-evoked desensitization.

Effects of uremic plasma on alpha- and beta-adrenoceptor subtypes

Responsiveness of adrenergic receptors is decreased in patients on maintenance hemodialysis. In this study we investigated whether uremic plasma might affect adrenergic receptors. For this purpose we determined the effects of uremic plasma obtained from 10 patients on hemodialysis treatment (mean age 61 +/- 3 years, dialysis frequency 3 x 4 h/week, duration of treatment 3 +/- 1 years) before and at the end of the 4-hour dialysis treatment on binding of radioligands to beta1- and beta2- as well as alpha1- and alpha2-adrenoceptors. Plasma from 6 healthy volunteers served as control; the plasmas were studied in three dilutions: undiluted, 1:1 (v/v) and 1:4 (v/v) with saline diluted. Plasma from healthy control did not significantly affect the number of beta1- and beta2- or alpha1- and alpha2-adrenoceptors. On the other hand, uremic plasma significantly decreased the number of beta1- and beta2-adrenoceptors; this inhibitory effect was also observed when plasma obtained at the end of the 4-hour dialysis treatment was investigated. On the other hand, uremic plasma did not significantly decrease the number of alpha1- and alpha2-adrenoceptors. We conclude that in patients on maintenance hemodialysis, the presence of inhibitory substance(s) in uremic plasma could be - at least partly - responsible for the beta-adrenoceptor hyporesponsiveness; the mechanism leading ot alpha-adrenoceptor hyporesponsiveness, however, remains to be elucidated.

[Histamine in tears in allergic rhinoconjunctivitis]

The classic clinical symptoms of allergic conjunctivitis (type I allergy)--itching and lacrimation--are the effect of histamine. Determination of histamine levels in tears may be useful in evaluating the dynamics of local histamine release in connection with the clinical findings.

PATIENTS AND METHODS

Between 1.7.1994 and 31.6.1995 we analyzed the histamine levels in tears and investigated the clinical symptoms (score of 0-3) of 32 hyposensitized pollen-sensitive patients (14 males and 18 females, aged 18-45 years, group I) and of 32 controls (group II) without any allergic disease, performed in each case once in season and once out of season. Tear production and composition were measured by Schirmer's test and tear break-up time at the same time. The histamine levels of the tear samples (obtained by microcapillary method) were analyzed by electrochemical determination.

RESULTS

In group I there was a highly significant increase of the mean histamine level from 0.89 +/- 2.22 ng/ml (out of season) to 7.71 +/- 7.51 ng/ml (in season) for the right eye and from 0.73 +/- 2.36 ng/ml (out of season) to 9.51 +/- 9.07 ng/ml (in season) for the left eye (P = 0.0000). The histamine level in tears of the controls (group II) was below the detection limit in all samples. The seasonal histamine level were higher with the severity of atopy (Erlangen atopy score). There was no significant influence of age and gender. The reduction of allergic symptoms during hyposensitization was not comparable to the degree of seasonal histamine level. Compared with the clinical findings, the histamine level in tears did not correlate with the symptoms of lacrimation, itching and conjunctival hyperemia.

CONCLUSION

The histamine level in tears alone is not useful as a marker for the clinical severity of this atopyassociated disorder and for the efficacy of the anti-allergic therapy. After standardization of the determination method and the identification of other soluble mediators simultaneously, the histamine level in tears can be used as one part of a profile of mediators to evaluate the clinical symptoms.

Endothelin receptors in the failing and nonfailing human heart

BACKGROUND

In patients with chronic heart failure (CHF), plasma endothelin-1 (ET-1) levels are increased. We studied whether the cardiac ET-receptor system is altered in CHF patients.

METHODS AND RESULTS

We assessed ET-evoked inositol phosphate (IP) formation in slices from right atria and left ventricles from 6 potential heart transplant donors (NFH) and 15 patients with end-stage CHF; in membranes from the same tissues, we studied ET-induced inhibition of isoprenaline- and forskolin-stimulated adenylyl cyclase and ET-receptor density. ET (10[-9] to 10[-6] mol/L, ET-1 >>> ET-3) increased IP formation in right atria and left ventricles through ET(A)-receptor stimulation in a concentration-dependent manner; no difference in potency or efficacy between NFH and CHF hearts was observed. ET-1 (10[-10] to 10[-6] mol/L), via ET(A)-receptor stimulation, inhibited isoprenaline- and forskolin-stimulated adenylyl cyclase in right atria but not in left ventricles, whereas carbachol inhibited adenylyl cyclase in both tissues; again, the potency and efficacy of ET- or carbachol-induced adenylyl cyclase inhibition was not different between NFH and CHF hearts. [125I]ET-1 binding revealed the coexistence of ET(A) and ET(B) receptors in both tissues; however, the density of ET(A) receptors was not significantly different between NFH and CHF hearts. Finally, the immunodetectable amount of left ventricular Gq/11 protein did not differ between NFH and CHF hearts.

CONCLUSIONS

In the human heart, ET(A) and ET(B) receptors coexist; however, only ET(A) receptors are of functional importance. In right atria, ET(A) receptors couple to IP formation and inhibition of adenylyl cyclase; in left ventricles, they couple only to IP formation. In end-stage CHF, the functional responsiveness of the cardiac ET(A)-receptor system is not altered.

Influence of atropine on the cardiovascular effects of noradrenaline and tyramine in elder volunteers

The aim of this study, carried out in six elder healthy volunteers (mean age: 61 years), was to determine the influence of muscarinic receptor blockade with atropine (15 microg/kg i.v. loading dose followed by 0.15 microg/kg/min by i.v. infusion) on the effects of i.v. infusions of noradrenaline (5 incremental doses of 10-120 ng/kg/min) or tyramine, that releases endogenous noradrenaline (4 incremental doses of 5-20 microg/kg/min), on blood pressure, heart rate and systolic time intervals (STI's, as a measure of positive inotropism). These results were compared with those recently published for young healthy volunteers (mean age: 26 years; Schäfers et al. 1997). Noradrenaline caused increases in systolic and diastolic blood pressure, decreases in heart rate and a shortening of STI's that were not different from those in young volunteers. Atropine did not significantly affect these hemodynamic responses to noradrenaline, while in young volunteers it significantly enhanced noradrenaline-induced blood pressure increases and converted the heart rate decrease into an increase. In the present study in elder volunteers, tyramine caused a smaller increase in systolic blood pressure than in the previous study in young volunteers; in addition, it slightly increased diastolic blood pressure while it decreased diastolic blood pressure in young volunteers. Atropine did not significantly affect the hemodynamic effects of tyramine in the elder volunteers, while in the young volunteers it enhanced the increase in systolic blood pressure and converted the decreases in diastolic blood pressure and heart rate into increases. These results indicate a) that ageing is accompanied by a blunted baroreflex-mediated parasympathetic activation resulting in reduced cholinergic vasodilation and decreases in heart rate, and b) that ageing is associated with a decreased responsiveness of (cardiac) beta-adrenoceptors and (vascular) alpha1-adrenoceptors which is only unmasked when the counterregulatory action of parasympathetic activation is removed.

Trophic effect of angiotensin II in neonatal rat cardiomyocytes: role of endothelin-1 and non-myocyte cells

1. Angiotensin II (AII) and the endothelins (ET) are known to be potent trophic stimuli in various cells including cardiomyocytes. In order to characterize further these effects we studied, in neonatal rat ventricular cardiomyocytes, the effects of several endothelin-receptor antagonists and the AT1-receptor antagonist losartan on AII- and endothelin-induced inositol phosphate (IP)-formation (assessed as accumulation of total [3H]-IPs in myo-[3H]-inositol prelabelled cells) and increase in rate of protein synthesis (assessed as [3H]-phenylalanine incorporation). 2. Endothelin (10 pM-1 microM) concentration-dependently increased IP-formation (max. increase at 100 nM ET-1: 130 +/- 14% above basal, n = 25) and [3H]-phenylalanine incorporation (max. increase at 1 microM: 52 +/- 4% above basal, n = 16) with an order of potency: ET-1 > > ET-3. Both effects were antagonized by the ETA/ETB-receptor antagonist bosentan and the ETA-receptor antagonist BQ-123, but not affected by the ETB-receptor antagonist IRL 1038 and the AT1-receptor antagonist losartan. 3. Pretreatment of the cells with 500 ng ml-1 pertussis toxin (PTX) overnight that completely inactivated PTX-sensitive G-proteins did not attenuate but rather enhance ET-1-induced IP-formation. On the other hand, in PTX-pretreated cardiomyocytes ET-1-induced [3H]-phenylalanine incorporation was decreased by 39 +/- 5% (n = 5). 4. All (1 nM-1 microM) concentration-dependently increased IP-formation (max. increase at 1 microM: 42 +/- 7% above basal, n = 16) and [3H]-phenylalanine incorporation (max. increase at 1 microM: 29 +/- 2%, n = 9). These effects were antagonized by losartan, but they were also antagonized by bosentan and BQ-123. 5. In well-defined cultures of cardiomyocytes (not contaminated with non-myocyte cells) All failed to increase [3H]-phenylalanine incorporation: addition of non-myocyte cells to the cardiomyocytes restored All-induced increase in [3H]-phenylalanine incorporation. 6. We conclude that, in rat neonatal ventricular cardiomyocytes, (a) the ET-1-induced increase in rate of protein synthesis (through ETA-receptor stimulation) involves at least two signalling pathways: one via a PTX-insensitive G-protein coupled to IP-formation, and the other one via a PTX-sensitive G-protein, and (b) the trophic effects of All are brought about via local ET-1 secretion upon AT1-receptor stimulation in neonatal rat ventricular non-myocyte cells.

Influence of adrenoceptor and muscarinic receptor blockade on the cardiovascular effects of exogenous noradrenaline and of endogenous noradrenaline released by infused tyramine

This study aimed firstly to compare the in vivo cardiovascular effects of exogenously administered and of endogenously released noradrenaline; secondly to characterize the adrenoceptors mediating these responses; thirdly to assess the influence of parasympathetic tone on the cardiovascular effects of noradrenaline. In two randomised placebo-controlled studies, healthy, young, male volunteers received intravenous (i.v.) infusions of noradrenaline at six incremental doses of 10-160 ng/kg/min and-in order to release endogenous noradrenaline-tyramine at four incremental doses of 5-20 micrograms/kg/min. Noradrenaline and tyramine were administered in the absence and presence of alpha 1-adrenoceptor blockade with doxazosin (2 mg p.o.), alpha 2-adrenoceptor blockade with yohimbine (15 mg p.o.), selective beta 1-adrenoceptor blockade with bisoprolol (15 mg p.o.) and muscarinic receptor blockade with atropine (1.5 micrograms/kg i.v. loading dose followed by 0.15 microgram/kg/min by i.v. infusion). Vasoconstrictor effects were assessed by measurement of diastolic blood pressure (Pdiast) and myocardial effects by measurement of systolic time intervals, namely the duration of electromechanical systole corrected for heart rate (QS2c). I.v. noradrenaline increased Pdiast (delta max 17 mmHg) and this was nearly completely suppressed by doxazosin but only slightly blunted by yohimbine. Noradrenaline also slightly shortened QS2c (delta max -22 ms), and this was potentiated by both doxazosin and yohimbine and completely blocked by biosprolol. I.v. tyramine reduced Pdiast (delta max -7 mmHg), which was not affected by alpha 1-adrenoceptor blockade, and profoundly shortened QS2c (delta max -104 ms) which was significantly correlated with a marked increase in systolic blood pressure (Psyst) (delta max 57 mmHg). The shortening of QS2c and the rise in Psyst were not influenced by alpha-adrenoceptor blockade but were antagonized by bisoprolol. Atropine potentiated the blood pressure rise and the shortening of QS2c induced by i.v. noradrenaline and converted the fall in Pdiast induced by i.v. tyramine into an increase. Thus the cardiovascular effects of exogenous noradrenaline are mainly characterized by alpha 1-adrenoceptor-mediated vasoconstriction and the actions of endogenous noradrenaline (released by i.v. tyramine) by beta 1-adrenoceptor-mediated positive inotropic effects. The rise in Psyst with i.v. tyramine most likely reflects positive inotropism and not a vascular "pressor' response.

Age-dependent changes in cardiac muscarinic receptor function in healthy volunteers

OBJECTIVES

This study was conducted to determine possible age-dependent changes in the responsiveness of human cardiac muscarinic receptors.

BACKGROUND

It is well known that the baroreflex activity decreases with aging. However, the mechanisms underlying this phenomenon are not completely understood at present.

METHODS

In six healthy young (mean [+/-SEM] age 26 +/- 2 years) and six healthy older volunteers (mean age 60 +/- 2 years), we determined 1) the effects of graded doses of atropine (bolus application, six doses, each for 20 min, range 0.03 to 0.96 mg) and the M1-cholinoceptor selective antagonist pirenzepine (bolus application, eight doses, each for 20 min, range 0.04 to 10 mg) on heart rate, blood pressure and systolic time intervals (as measure of inotropism); and 2) the baroreflex activity by assessing the bradycardic response to phenylephrine.

RESULTS

Atropine and pirenzepine caused biphasic effects on heart rate: At lower doses (< 0.12 mg for atropine, < 5 mg for pirenzepine) they decreased heart rate, whereas at higher doses they increased heart rate. Heart rate decreases induced by both antimuscarinic drugs were significantly larger in the young volunteers than in the older volunteers, whereas heart rate increases were not significantly different for both drugs. Atropine and pirenzepine did not significantly affect blood pressure and systolic time intervals. Infusion of graded doses of phenylephrine (four doses ranging from 0.1 to 1.0 microgram/kg body weight per min for 15 min each) caused a higher increase in systolic blood pressure and a smaller decrease in heart rate at each dose in the older volunteers than in the young volunteers. The slopes of the regression lines were 16 +/- 2.3 ms/mm Hg for the young and 6 +/- 0.5 ms/mm Hg for the older volunteers (p < 0.01).

CONCLUSIONS

Human cardiac muscarinic receptor activity is diminished with increasing age; such decreased cardiac muscarinic receptor activity could contribute to the decrease in baroreflex activity with aging. In contrast, antimuscarinic drugs seem to have no effect on human cardiac contractility.

Pharmacokinetics of trapidil in patients with chronic liver disease

The pharmacokinetics of trapidil were studied in 15 patients with chronic liver disease (12 with hepatic cirrhosis, 2 with alcoholic fatty liver, 1 with liver fibrosis). Trapidil was administered intravenously as a 100-mg bolus. Serum samples were analyzed for trapidil by means of high-performance liquid chromatography. Mean pharmacokinetic parameters were compared with those found in a previous study of 12 healthy volunteers. Total plasma clearance was decreased significantly in patients with hepatic cirrhosis (96 mL/ min versus 258 mL/min in healthy individuals and 252 mL/min in patients with noncirrhotic liver disease). No difference in clearance was observed between patients with compensated or decompensated cirrhosis, and portal hypertension did not affect this clearance of trapidil. It can be concluded that trapidil clearance is a parameter that is very sensitive to alterations in hepatic clearance caused by liver cirrhosis, and that the dosage of trapidil should be adjusted accordingly in such patients.

Dose-dependent separation of dopaminergic and adrenergic effects of epinine in healthy volunteers

Epinine (N-methyl-dopamine, the active metabolite of ibopamine), is a full agonist at dopamine (DA)-receptors and alpha- and beta-adrenoceptors. To study whether in vivo DA-receptors mediated effects can be separated from alpha- and beta-adrenoceptor effects we compared in 10 male volunteers the effects of i.v. epinine (0.5; 1; 2; 4 micrograms/kg/min for 15 min each) on DA-receptor (changes in serum prolactin)- and alpha- and beta-adrenoceptor (changes in systolic [Psyst] and diastolic blood pressure [Pdiast] and heart rate)-mediated effects with those of dopamine before and after propranolol (5 mg i.v. 45 min pre-infusion), bisoprolol (15 mg p.o. 2 h pre-infusion) and domperidone (10 mg p.o. 1 h pre-infusion). At the 0.5 and 1 microgram doses of dopamine and epinine did not effect Psyst, Pdiast and heart rate but significantly decreased prolactin levels. At the higher dose both dopamine and epinine significantly increased Psyst and heart rate, while only epinine significantly increased Pdiast. In addition, both dopamine and epinine significantly increased diuresis and natriuresis; in contrast, only dopamine, but not epinine dose-dependently increased plasma noradrenaline levels. Domperidone did not affect dopamine- and epinine-evoked blood pressure- and heart rate-changes, but antagonized their prolactin-effects (at least at the lower doses). Bisoprolol and propranolol significantly reduced dopamine-induced Psyst- and heart rate-increases to about the same extent. Propranolol enhanced epinine-induced Psyst- and Pdiast-increases while bisoprolol reduced epinine-evoked Psyst-increase but not Pdiast-increase. Epinine-induced heart rate-increase was abolished by bisoprolol and was converted into heart rate-decrease by propranolol. We concluded that in 0.5 and 1 microgram doses (plasma levels of 20-80 nmol/l)epinine acts only at DA-receptors. Thus, ibopamine in therapeutically recommended doses (3 x 100 mg/day with peak plasma epinine-levels of 50-80 nmol/l) very likely activates only DA-receptors. In higher doses, however, epinine-like dopamine-activates alpha- and beta-adrenoceptors whereby epinine has a stronger alpha-adrenoceptor agonistic activity than dopamine. Moreover, part of the dopamine-effects are indirect via release of endogenous noradrenaline whereas epinine-effects do not appear to include an indirect component.

PAF effects on eicosanoid release in neonatal rat cardiomyocytes

The aim of this study was to find out whether, in neonatal rat cardiomyocytes, platelet-activating factor (PAF) can stimulate eicosanoid formation. For this purpose neonatal cardiomyocytes were incubated for 60 min at 37 degrees C in HANKS buffer with PAF (10-1000 nM), and the eicosanoids thromboxane A2 (TXA2) and prostacyclin (PGI2) were assessed in the supernatant as TXB2 and 6-keto-PGF1 alpha, respectively, by an enzyme immunoassay. PAF caused concentration-dependent release of PGI2; TXA2, however, was significantly released only at the highest concentration of PAF (1000 nM). Acetylsalicylic acid (556 microM) and the PAF antagonist WEB 2086 (10 microM) significantly attenuated PAF-induced eicosanoid formation. We conclude that in neonatal rat cardiomyocytes PAF can induce eicosanoid formation and this effect is brought about by activation of a specific PAF receptor.

Effects of PAF on cardiac function and eicosanoid release in the isolated perfused rat heart: comparison between normotensive and spontaneously hypertensive rats

The aim of this study was (a) in isolated perfused rat heart to characterize the effects of platelet-activating factor (PAF) on coronary flow, ventricular contractility, and eicosanoid release and (b) to determine whether PAF effects are altered in hearts from spontaneously hypertensive rats (SHR). PAF (10(-10)-10(-7) mol) dose-dependently decreased coronary flow and ventricular contractility; concomitantly, coronary effluent concentrations of thromboxane (TX)B2 and prostaglandin F2 alpha (PGF2 alpha) were elevated but not those of prostacyclin. The PAF receptor antagonist WEB 2086 (10(-7)-10(-5) mol/l) concentration-dependently antagonized these PAF effects. In addition; the cyclo-oxygenase inhibitor indomethacin (5 x 10(-5) mol/l) prevented PAF (10(-9)-10(-7) mol) induced eicosanoid release; in the presence of indomethacin PAF caused coronary constriction and ventricular depression only at the highest dose (10(-7) mol) but had no effect at 10(-9) or 10(-8) mol. Moreover, the TXA2 antagonist SQ29,548 (10(-6) mol/l) completely inhibited 10(-8) mol PAF induced ventricular depression but did not effect coronary constriction. In SHR PAF (10(-9)-10(-7) mol) evoked decreases in coronary flow and ventricular contractility did not differ from those in normotensive Wistar-Kyoto rats while PAF induced TXA2 and PGF2 alpha release was markedly enhanced. In addition, decreases in coronary flow and ventricular contractility induced by the TXA2 agonist U 46619 (10(-7) mol/l) were markedly depressed in SHR. We conclude that in isolated perfused rat heart PAF causes coronary constriction and depression of ventricular function mainly indirectly through released TXA2 and/or PGF2 alpha. Moreover, the fact that in SHR the PAF effects on coronary flow and ventricular function are not altered despite markedly enhanced TXA2 and PGF2 alpha release supports the view that in the SHR the receptors mediating TXA2 and/or PGF2 alpha effects are desensitized.

Relevance of mediators to cardiac parameters of isolated anaphylactic guinea-pig heart

The release of histamine, eicosanoids and catecholamines were measured after induction of anaphylaxis in isolated guinea-pig hearts. The concentration-time profile of these mediators was compared with changes of cardiac parameters. The histamine and catecholamine levels of the coronary effluent were determined at 10 s intervals; thromboxane and prostacyclin levels at 60 s intervals. The release of histamine and norepinephrine were maximum between 20 and 30 s after the antigen challenge and decreased rapidly within 60 s. Thromboxane and prostacyclin increased to a maximum after 3 min and declined slowly within 10 min. The rise in histamine release was correlated with tachycardia. The release of thromboxane was correlated with the increase of coronary perfusion pressure. Cimetidine inhibited the tachycardia and clemastine reduced bradyarrhythmia. The inhibition of lipoxygenase and cyclooxygenase also reduced the rise in the perfusion pressure. These data suggest that different mediators are time-dependently involved in anaphylaxis-induced cardiac changes.

Pharmacokinetics of trapidil (Rocornal) in patients with chronic liver disease

The pharmacokinetics of trapidil (Rocornal, Deutsches Hydrierwerk Rodleben GmbH) were studied in 15 patients with chronic liver disease (12 patients with hepatic cirrhosis, 2 patients with alcoholic fatty liver, one patient with liver fibrosis). Trapidil was given orally (200 mg, Rocornal dragees 100 mg) as well as intravenously (100 mg) in random order. Serum samples were analyzed for trapidil by HPLC. The pharmacokinetic parameters were compared with the parameters of 12 healthy volunteers, investigated by Weiss [1991]. Total plasma clearance was decreased significantly in patients with hepatic cirrhosis (99.6 ml/min vs 273.1 ml/min in controls and 255.3 ml/min in patients with non cirrhotic liver disease). However, there was no difference in clearance between patients with compensated and patients with decompensated cirrhosis. Clearance and aspartate aminotransferase activity correlated inversely. In addition, in some of the patients suffering from portal hypertension delayed absorption was observed, but the difference did not reach statistical significance. The volumes of distribution were significantly lower in patients with non alcoholic cirrhosis (19.9 l vs 36.8 l in controls and 41.0 l in patients with alcoholic cirrhosis). It might be concluded from this study, that dosage adjustments are necessary in treatment of patients with cirrhosis. In patients suffering from portal hypertension an intravenous administration should be prefered.

Bioavailability of trapidil tablets

Trapidil was given orally (200 mg, Rocornal dragees 100 mg) and intravenously (100 mg) to 12 healthy volunteers. Serum samples were analyzed for trapidil by HPLC. Complete bioavailability was obtained and a mean absorption time of 66.4 min was calculated using the method of curve moments.

Stimulation of aggregation and thromboxane A2 formation of human platelets by hypoxia

The influence of hypoxia on the spontaneous platelet aggregation (SPA) and thromboxane formation was studied. The analysis of aggregation curve was carried out according to Breddin. The hypoxia enhanced the aggregability from Q2norm = 2.46 +/- 0.40 (normoxia) to Q2hyp = 4.39 +/- 0.39 (hypoxia), n = 52, p less than 0.001. 10 samples of those showed no SPA under equilibration with air but the hypoxic stimulus provoked SPA (Q2norm = 0, Q2hyp = 1.19 +/- 60, n = 10, p less than 0.001). When the results were arranged according to the degree of the stimulation of SPA, two groups could be separated with low and high response to hypoxia. The hypoxia caused also an augmentation of the TXB2 level in comparison to normoxia. The stronger enhancement of the TXB2 formation during the incubation under hypoxic conditions was independent of the fact whether SPA took place or not. The present study suggests that hypoxic conditions alone may be a reason for a stimulated TXA2 formation of the platelets and that the enhanced TXA2 formation caused by hypoxia is possibly inducing or reinforcing the SPA.

The stoichiometry of oxygen uptake and conjugated diene formation during the dioxygenation of linoleic acid by the pure reticulocyte lipoxygenase. Evidence for aerobic hydroperoxidase activity

Simultaneous measurements of oxygen uptake and conjugated diene formation (increase in the absorbance at 234 nm) during the dioxygenation of linoleic acid by the pure reticulocyte lipoxygenase gave a nearly theoretical stoichiometry of 1.1 in a temperature range from 5 to 30 degrees C and a wide range of concentrations of both oxygen and linoleic acid. At low concentrations of either oxygen or linoleic acid or both, secondary processes occurred such as linoleic acid-supported lipohydroperoxidase reactions leading to the disappearance of conjugated dienes and to the formation of oxodienes, linoleic acid dimers and epoxyhydroxy derivatives. Under these conditions marked deviations of the stoichiometry between oxygen uptake and conjugated diene formation appeared. The formation of conjugated oxodienoic fatty acids absorbing at 285 nm occurred only under conditions of high concentrations of linoleic acid and limiting oxygen supply. The results indicate that lipohydroperoxidase reactions catalyzed by the pure reticulocyte lipoxygenase do not only take place under strictly anaerobic conditions but also under conditions of limiting concentrations of either linoleic acid or oxygen or both.