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Biomedical subjects

M Steinfath

Publications and source records attributed to M Steinfath.

13 recordsLinked to original sources
PubMed1992

Isoprenaline-induced increase in the 40/41 kDa pertussis toxin substrates and functional consequences on contractile response in rat heart.

Chronic beta-adrenoceptor stimulation leads to desensitization of the myocardial adenylyl cyclase signalling pathway which includes beta-adrenoceptor downregulation and upregulation of Gi-protein alpha-subunits. However, these investigations have mainly been done in cellular preparations. In this study we report that isoprenaline infusion in vivo leads to an increase in myocardial Gi alpha and present evidence for functional consequences of this increase. Rats were treated by a 4-day subcutaneous infusion with isoprenaline (2.4 mg/kg.d), propranolol (9.9 mg/kg.d) and triiodothyronine (T3, 0.5 mg/kg.d) for comparison. Isoprenaline treatment increased the pertussis toxin-sensitive amount of Gi alpha by 22 +/- 6% and decreased beta 1- and beta 2-adrenoceptor density from 35 +/- 4 to 23 +/- 6 fmol/mg protein and 24 +/- 4 to 8 +/- 6 fmol/mg protein, respectively. Contraction experiments on electrically driven papillary muscles revealed that the negative inotropic potency of the M-cholinoceptor agonist carbachol in the presence of isoprenaline was increased as compared to control (mean EC50-values: 0.04 mumol/l vs. 0.28 mumol/l). All isoprenaline-induced effects were antagonized by simultaneously administered propranolol. T3 treatment had no influence on the parameters investigated. The results suggest that chronic beta-adrenoceptor stimulation desensitizes myocardial adenylyl cyclase by at least two mechanisms: beta-adrenoceptor downregulation leading to diminished signal transduction in the stimulatory pathway and Gi alpha upregulation leading to sensitization of the inhibitory pathway. Such adaptation might protect the heart from chronic exposure to catecholamines in heart diseases with elevated plasma catecholamine levels.

Adenosine Diphosphate Ribose↗
PubMed1992

Regional distribution of beta 1- and beta 2-adrenoceptors in the failing and nonfailing human heart.

Total beta-adrenoceptor density and beta 1- and beta 2-subtype distribution in right and left atria and in different ventricular regions from 14 failing and seven nonfailing human hearts have been compared. End-stage heart failure was due to idiopathic dilated cardiomyopathy (n = 8) or ischaemic cardiomyopathy (n = 6). In nonfailing hearts the total beta-adrenoceptor density was similar in the right and left atria and in all the ventricular regions studied (about 70 to 80 fmol/mg protein). The beta 1:beta 2-adrenoceptor ratio in both nonfailing atria was similar (about 70:30%) and was significantly smaller than in the different regions of both ventricles (about 80:20%). The beta 1-subtype density was similar in nonfailing atria and ventricles (about 55 fmol/mg protein). The beta 2-subtype density was significantly higher in the right and left atrium (about 25 fmol/mg protein) than in both ventricles (about 15 fmol/mg protein). In patients with end-stage heart failure due to idiopathic dilated cardiomyopathy or ischaemic cardiomyopathy the total beta-adrenoceptor density was reduced by 50-60% in all regions. On the other hand, the beta 1- and beta 2-subtype distribution differed with the cause of heart failure. In patients with idiopathic dilated cardiomyopathy, the beta 1-adrenoceptor density was not significantly reduced. In patients with ischaemic cardiomyopathy both beta 1- and beta 2-adrenoceptors were reduced in all regions. It is concluded that downregulation of beta-adrenoceptors in patients with end-stage idiopathic dilated cardiomyopathy or ischaemic cardiomyopathy occurs uniformly throughout the heart. The results support the hypothesis that changes in beta-adrenoceptor subtypes may be related to the cause of heart failure.

Adult↗
PubMed1992

Changes in cardiac beta 1- and beta 2-adrenoceptor densities after human cardiac transplantation: relation to transplant coronary vasculopathy and pretransplantation disease.

In 100 patients 12 to 60 months after cardiac transplantation, the influence of transplant coronary vasculopathy and of the pretransplantation disease (end-stage heart failure caused by coronary artery disease or dilated cardiomyopathy) on the beta-adrenergic receptor (AR) numbers and beta 1/beta 2-AR ratio of right ventricular biopsies was determined. Patients with coronary vasculopathy (CVP) after cardiac transplantation had lower absolute numbers of beta 1-AR compared with patients without CVP. Since patients with CVP had increased left ventricular (LV) end-diastolic pressure and LV muscle mass, it is suggested that decreased beta 1-AR may be the result of an altered hemodynamic situation of the transplanted heart after development of CVP. Patients with dilated cardiomyopathy (DCM) before cardiac transplantation showed a decrease in total beta-AR and of the beta 1/beta 2-AR ratio as a result of an increase in beta 2-AR and a decrease in beta 1-AR numbers. The decreased beta 1/beta 2-AR ratio in patients with previous DCM may indicate that the beta-AR system of the transplanted heart might be influenced (at least in part) by pathophysiologic factors that are characteristic of the pretransplantation disease ultimately leading to cardiac transplantation and persisting after cardiac transplantation.

Adult↗
PubMed1992

Decrease in beta 1- and increase in beta 2-adrenoceptors in long-term follow-up after orthotopic cardiac transplantation.

Total beta 1- and beta 2- subtype distribution were examined in right ventricular biopsies taken from 100 patients 1-60 months after orthotopic cardiac transplantation and from eight prospective transplant donor hearts serving as controls. The patients were classified into eight groups depending on the time after transplantation that the biopsies were taken: 1-3 (n = 15), 4-7 (n = 15), 8-11 (n = 6), 12 (n = 15), 24 (n = 15), 36 (n = 12), 48 (n = 12) and 60 months (n = 10). The non-selective beta-adrenoceptor antagonist (-)-[125I]-iodocyanopindolol (ICYP) was used as a radioligand to assess total beta-adrenoceptor density. The beta 1- and beta 2-subtype distribution was determined with a beta 1-adrenoceptor saturating concentration of the selective beta 1-adrenoceptor antagonist CGP 20712A (300 nmol/l). In transplant donor hearts the total beta-adrenoceptor density was found to be 70.8 +/- 7.1 fmol/mg protein including a beta 1:beta 2-adrenoceptor ratio of about 80:20%. Until 36 months after cardiac transplantation the total number of beta-adrenoceptors showed no significant change. A slight but insignificant decrease was observed after 48 (16.2%) and 60 (21.2%) months. In contrast, from 12 to 60 months after cardiac transplantation the beta 1:beta 2-adrenoceptor ratio was shifted significantly (66:33% to 61:39%) as compared with transplant donor hearts which was due to an increase in beta 2- and a decrease in beta 1-adrenoceptor number. Thus, the surgically denervated, transplanted human heart exhibits a beta 2-adrenoceptor up-regulation during long-term follow-up. It is suggested that this up-regulation of the beta 2-adrenoceptor subtype could be owing to an increased importance of circulating catecholamines in modulating positive chronotropic and inotropic effects.

Adult↗
PubMed1992

Binding of beta-adrenergic receptors in human skin.

Radioligand-binding experiments were performed with crude membrane homogenates (CMH) from human skin in order to investigate the epidermal beta-adrenergic receptor (beta AR) density. CMH were prepared from leftovers of split-thickness skin grafts by sequential homogenization and centrifugation procedures to yield essentially epidermal fragments. Saturation experiments with the non-selective beta-adrenoceptor antagonist (-)-[125I]-iodocyanopindolol (ICYP) as radioligand showed saturable specific binding isotherms. Scatchard transformation of the data demonstrated high-affinity binding of ICYP to a single class of beta AR (Bmax = 80 +/- 10 fmol/mg protein; KD = 8 pM +/- 0.9; n = 8). beta AR antagonists displaced ICYP in a monophasic displacement pattern. The IC50 values were (nmol/1) propranolol (non-selective) 24.8; ICI 118,551 (beta 2 selective) 14.7; CGP-12177 (non-selective) 28.9; bisoprolol (beta 1 selective) 1500; CGP-20712A (beta 1 selective) 8990. beta AR agonists displaced ICYP with a potency ranking isoprenaline greater than adrenaline greater than noradrenaline. We conclude that epidermal crude membrane homogenates prepared from human split-thickness skin contain a high population of beta 2-adrenergic receptors. These receptors may be studied to further investigate the nature of human epidermal beta-adrenergic mechanisms.

Adult↗
PubMed1992

Reduced alpha 1- and beta 2-adrenoceptor-mediated positive inotropic effects in human end-stage heart failure.

1. alpha 1-Adrenoceptor (phenylephrine in the presence of propranolol) and beta 2-adrenoceptor (fenoterol)-mediated positive inotropic effects were investigated in human ventricular preparations isolated from five non-failing (prospective organ donors) and from eight explanted failing hearts with end-stage idiopathic dilative cardiomyopathy (NYHA IV). 2. For comparison, the nonselective beta-adrenoceptor agonist isoprenaline, the phosphodiesterase (PDE) inhibitor 3-isobutyl-1-methylxanthine (IBMX), the cardiac glycoside dihydroouabain, and calcium were studied. 3. Furthermore, the influence of IBMX on adenosine 3':5'-cyclic monophosphate (cyclic AMP) PDE activity as well as total beta-adrenoceptor density, beta 1- and beta 2-adrenoceptor subtype distribution, and alpha 1-adrenoceptor density were compared in nonfailing and failing human heart preparations. The radioligands (-)-[125I]-iodocyanopindolol for beta-adrenoceptor binding and [3H]-prazosin for alpha 1-adrenoceptor binding were used. 4. The inotropic responses to calcium and dihydroouabain in failing human hearts were unchanged, whereas the maximal alpha 1- and beta 2-adrenoceptor-mediated positive inotropic effects were greatly reduced. The inotropic effects of the other cyclic AMP increasing compounds, i.e. isoprenaline and IBMX, were also reduced to about 60% of the effects observed in nonfailing controls. The potency of these compounds was decreased by factors 4-10. 5. The basal PDE activity and the PDE inhibition by IBMX were similar in nonfailing and failing preparations. 6. The total beta-adrenoceptor density in nonfailing hearts was about 70 fmol mg-1 protein. In failing hearts the total number of beta-adrenoceptors was markedly reduced by about 60%. The betal/beta2-adrenoceptor ratio was shifted from about 80/20% in nonfailing to approximately 60/40% in failing hearts which was due to a selective reduction of beta1-adrenoceptors. The beta2-adrenoceptor population remaining unchanged. alpha-Adrenoceptor density was increased from about 4 fmol mg-' protein in nonfailing to 10 fmol mgprotein in failing hearts.7. Changes in PDE activity and adrenoceptor downregulation cannot completely explain the reduced positive inotropic effects of alpha 1- and beta 2-adrenoceptor agonists in failing human hearts. This supports the hypothesis that impairment of other processes such as the coupling between receptor and effector system, i.e. the respective G-proteins, are equally important in end-stage heart failure.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1992

Cardiac alpha 1-adrenoceptor densities in different mammalian species.

1. alpha 1-Adrenoceptor densities were studied in cardiac membrane preparations from several mammalian species including human failing hearts under identical experiment conditions; the alpha 1-adrenoceptor antagonist, [3H]-prazosin, was used as radioligand. End-stage heart failure (NYHA IV) in human hearts was due to idiopathic dilated cardiomyopathy. 2. The ventricular alpha 1-adrenoceptor densities were not significantly different in guinea-pig, mouse, pig, calf, and man (11 to 18 fmol mg-1 protein) but about 5 to 8 fold smaller than in rat (about 90 fmol mg-1 protein). Right and left ventricular receptor densities were similar in these species. 3. A sufficient amount of right and left atrial tissue was obtained from rabbit, pig, calf, and man only. The alpha 1-adrenoceptor densities in both atria of these species were found to be at the detection limit of the method used (less than 8 fmol mg-1 protein). 4. The equilibrium dissociation constant (KD) was similar in all species studied ranging from 0.047 +/- 0.006 to 0.063 +/- 0.007 nmol l-1. 5. It is concluded that differences in alpha 1-adrenoceptor density between atria and ventricles may exist in mammalian species. The exceptionally high density of these receptors in rat ventricles seem to be a particular feature in these animals.

Animals↗
PubMed1991

Distinct down-regulation of cardiac beta 1- and beta 2-adrenoceptors in different human heart diseases.

Cardiac beta-adrenoceptor density and beta 1- and beta 2-subtype distribution were examined in human left ventricular myocardium from transplant donors serving as controls and from patients with mitral valve stenosis, aortic valve stenosis, idiopathic dilated cardiomyopathy, and ischaemic cardiomyopathy respectively. The total beta-adrenoceptor density was similar in transplant donors and patients with moderate heart failure (NYHA II-III) due to mitral valve stenosis, but was markedly reduced in all forms of severe heart failure (NYHA III-IV) studied. A reduction of both beta 1- and beta 2-adrenoceptors was found in patients with severe heart failure due to mitral valve stenosis or ischaemic cardiomyopathy. In contrast, a selective down-regulation of beta 1-adrenoceptors with unchanged beta 2-adrenoceptors and hence a relative increase in the latter was observed in idiopathic dilated cardiomyopathy and aortic valve stenosis. It is concluded that the extent of total beta-adrenoceptor down-regulation is related to the degree of heart failure. Selective loss of beta 1-adrenoceptors is not specific for idiopathic dilated cardiomyopathy but also occurs in aortic valve stenosis. Changes in beta 1- and beta 2-subtype distribution are rather related to the aetiology than to the clinical degree of heart failure.

Adult↗
PubMed1991

High density of beta 2-adrenoceptors in a human keratinocyte cell line with complete epidermal differentiation capacity (HaCaT).

A non-tumorigenic keratinocyte cell line with complete epidermal differentiation capacity (HaCaT) was used in radioligand binding experiments to determine the number of beta-adrenoceptors. Intact cells were saturated with 3H-labelled (-)CGP-12177 (CGP), a hydrophilic non-selective beta-adrenergic antagonist as radioligand. In order to investigate the beta-adrenergic subtype selectivity, displacement experiments were performed with different antagonists and agonists. Binding of CGP to keratinocytes has been shown to be reversible and saturable and to have high affinity (Bmax = 114.0 +/- 8.8 fmol/10(7) cells with 6866 receptors/cell, KD = 0.095 +/- 0.017 nmol/l; n = 11). Beta-adrenergic antagonists inhibited binding yielding monophasic displacement curves. IC50-values (nmol/l) were: propranolol (non-selective) 1.68; CGP-12177 (non-selective) 1.08; ICI 118,551 (beta 2-selective) 2.92; bisoprolol (beta 1-selective) 1230; and CGP-20712 (beta 1-selective) 24,980. Agonists displaced CGP in the order isoprenaline greater than adrenaline greater than noradrenaline. We conclude that HaCaT cells express a high density of beta2-adrenoceptors providing a good model system to study adrenergic receptor mechanisms under reproducible experimental conditions in keratinocytes.

Binding, Competitive↗
PubMed1988

Alpha-1 adrenoceptor-mediated positive inotropic effect and inositol trisphosphate increase in mammalian heart.

The positive inotropic effect of the alpha-1 adrenoceptor agonist phenylephrine was accompanied by a concentration-dependent increase in inositol trisphosphate (IP3) in electrically driven left auricles isolated from rat hearts. Further analysis of the myocardial phosphoinositide pathway revealed an additional increase in inositol phosphate and inositol bisphosphate with a concomitant decrease in phosphatidylinositol phosphate and phosphatidylinositol bisphosphate. The decrease in phosphatidylinositol bisphosphate and increase in IP3 preceded the increase in force of contraction. All effects were antagonized by the alpha-1 adrenoceptor antagonist prazosin. For comparison the effects of the beta adrenoceptor agonist isoprenaline were studied. Isoprenaline produced a positive inotropic effect similar to that of phenylephrine but all phosphoinositide products remained unaffected. The influence of lithium and calcium ions were studied systematically. The stimulatory effect of phenylephrine on inositol phosphates was lithium-dependent. Without lithium phenylephrine did not detectably affect the phosphoinositide turnover. Phenylephrine caused a maximal increase in inositol phosphate, inositol bisphospate and IP3 at 10 mmol/l of lithium. Lithium itself had a concentration-dependent positive inotropic effect. However, lithium did not enhance the positive inotropic effect of phenylephrine. Variation of the extracellular concentration of calcium did not influence the stimulatory effect of phenylephrine on inositol phosphates indicating that inositol phosphate turnover does not require the presence of extracellular calcium. It is concluded that the stimulation of myocardial phosphoinositide breakdown generating an increased IP3 turnover may be involved in the mechanism(s) whereby alpha-1 adrenoceptor stimulation exerts an increase in myocardial force of contraction.

Animals↗