Chronic beta-blockade transregulates inhibitory A1 adenosine and muscarinic M2 receptors of the adenylyl cyclase system.
Chronic beta-blockade has evolved to an important therapeutic strategy in medicine. Not all its therapeutic effects may be explained by its direct action on the beta-adrenergic system. We therefore investigated if chronic beta-blockade in vivo or in isolated cell systems may modulate also inhibitory receptors of the adenylyl cyclase system. Chronic treatment with metoprolol for 6 days (10 mg/day) induced an increase of beta-adrenergic receptors in rat cardiac plasma membranes (53 +/- 8 vs 80 +/- 12 fmol/mg protein). Simultaneously the density of cardiac muscarinic M2 receptors decreased significantly from 150 +/- 17 to 110 +/- 12 fmol/mg protein without any change of the affinity of the receptors for their agonists or antagonists. By this mechanism chronic beta-blockade leads to an unexpected impairment of the muscarinic-mediated inhibition of the adenylyl cyclase. This transregulation of inhibitory receptors by chronic beta-blockade was not restricted to the heart but also reduced the muscarinic receptors of rat lung (35 +/- 4 vs 24 +/- 3 fmol/mg protein). Additionally, other inhibitory receptors of the adenylyl cyclase system such as the A1 adenosine receptors of rat brain were reduced by chronic beta-blockade (532 +/- 32 vs 444 +/- 26 fmol/mg protein). This transregulation of A1 adenosine receptors occurred only after chronic beta-blockade with the active stereoisomer (-)-metoprolol whereas the (+)-isomer was ineffective. The ability of the remaining A1 adenosine receptors to form the agonist-promoted high affinity state was unaltered. Their reduction, however, was sufficient to abolish the phenylisopropyl-mediated inhibition of the adenylyl cyclase. To evaluate if this regulation of various inhibitory receptors in different organs may represent a general cellular regulation mechanism, we investigated whether this transregulation also occurred in isolated cells. Isolated smooth muscle cells derived from the vas deferens (DDT1 MF-2) were cultivated in the presence of the beta-blocker atenolol (10(-5) M) for 3 days. Chronic beta-blockade in these isolated cells induced an increase of beta-adrenergic receptors and concomitantly a significant decrease of A1 adenosine receptors (460 +/- 42 vs 368 +/- 18 fmol/mg protein). The affinity of the A1 adenosine receptors for their agonists and antagonists and the ability of the remaining receptors to form the agonist-promoted high affinity state remained unaltered. In contrast, the reduction of receptor density greatly impaired the adenosine-mediated inhibition of the adenylyl cyclase. These data demonstrate that chronic beta-blockade leads to a functionally significant reduction of inhibitory receptors of the adenylyl cyclase system.(ABSTRACT TRUNCATED AT 400 WORDS)
Department of Cardiology, University of Heidelberg, Germany.
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R
Marquetant
B
B
Brehm
R H
RH
Strasser
D000262:Adenylyl Cyclases / Q000187:drug effects* / Q000502:physiology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D006321:Heart / Q000187:drug effects; D008168:Lung / Q000187:drug effects / Q000378:metabolism; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009928:Organ Specificity; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000502:physiology; D011983:Receptors, Purinergic / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects*
D000319:Adrenergic beta-Antagonists; D011976:Receptors, Muscarinic; D011983:Receptors, Purinergic; D000262:Adenylyl Cyclases