ABSTRACT
AIM: In failing myocardium the mechanical response to beta-adrenoceptor stimulation is attenuated. Alternative signalling systems might provide inotropic support when the beta-adrenoceptor system is dysfunctioning. Accordingly, the inotropic responses to alpha 1- and beta-adrenoceptor stimulation by the endogenous adrenoceptor agonist noradrenaline in non-failing and failing rat hearts were compared. METHODS: Chronic heart failure was induced in male Wistar rats by coronary artery ligation. Corresponding sham groups were prepared. After 6 weeks, papillary muscles from non-failing and failing hearts were isolated. Receptor binding studies were performed in the corresponding myocardium. The alpha 1-adrenoceptor-mediated inotropic response was not changed while the beta-adrenoceptor-mediated response was substantially reduced in failing compared with non-failing myocardium. RESULTS: No change in potency for the agonists was observed at the alpha 1-adrenoceptors, while an increased potency for the agonists at the beta-adrenoceptors was found during heart failure. The lusitropic response to beta-adrenoceptor stimulation was intact during heart failure. No over all change in affinity or number of either adrenoceptor type was observed in receptor binding studies. The alpha 1-adrenoceptor-mediated inotropic response became dominating compared with the beta-adrenoceptor-mediated one in failing rat myocardium in contrast to the dominating role of the latter in non-failing myocardium. The attenuation of the beta-adrenoceptor-mediated inotropic response in rat failing myocardium was not because of a reduced number of receptors. CONCLUSION: Increasing contractility through stimulation of alpha 1-adrenoceptors in situ by the endogenous agonist may be an alternative way of inotropic support during heart failure and even more so during beta-adrenoceptor blockade.
Subject(s)
Adrenergic alpha-Agonists/pharmacology , Heart Failure/physiopathology , Myocardial Contraction/drug effects , Norepinephrine/pharmacology , Receptors, Adrenergic/physiology , Vasoconstrictor Agents/pharmacology , Adrenergic beta-Agonists/pharmacology , Animals , Cardiotonic Agents/pharmacology , Dose-Response Relationship, Drug , Isoproterenol/pharmacology , Male , Phenylephrine/pharmacology , Rats , Rats, Wistar , Receptors, Adrenergic, alpha-1/physiology , Receptors, Adrenergic, beta/physiologyABSTRACT
The present study was undertaken to develop an improved and stabilized method for isolating cardiomyocytes from perfused rat heart. Different lots of the commercial collagenases used for isolating cardiomyocytes give variable results both with respect to the total cell yield and the percentage of elongated cells obtained. When trypsin was present both before and during collagenase treatment of the tissue, the performance of the collagenases was improved and stabilized, and a high and stable cell yield (7.5 x 10(6) cells per heart), and a high percentage of elongated cells (about 70%) was regularly obtained. The cells possessed alpha 1-adrenergic binding sites with binding properties (Bmax = 43.5 fmol/mg protein and Kd = 125.5 pmol/l) in agreement with values previously reported. The cells were able to respond functionally, as the cellular uptake of 86Rb+ increased by 18% after alpha 1-adrenoceptor stimulation with phenylephrine. These criteria indicate that the cells were well preserved during the isolation procedure.
Subject(s)
Cell Separation/methods , Collagenases , Myocardium/cytology , Trypsin , Animals , In Vitro Techniques , Male , Myocardium/metabolism , Rats , Rats, Wistar , Receptors, Adrenergic, alpha-1/metabolism , Rubidium/metabolismABSTRACT
A sensitive radioimmunoassay (limit of detection 7 +/- 1 fmol per tube) for cyclic AMP (cAMP) based on acetylation of both 3H-cAMP and unlabeled ligand was developed. Rabbit anti-cAMP antibodies had an apparent Ka for the acetylated ligand of 2 x 10(10) l/mol. When the unlabeled ligand only was acetylated an increased sensitivity was obtained without loss of specificity.
