Abstract
The modulation of cAMP contents of rat peritoneal macrophages by β-adrenergic stimulants and blocking agents were studied. The maximum increase of cAMP contents induced by isoproterenol, epinephrine, norepinephrine and hexoprenaline (a selective β 2-adrenergic stimulant) was about 170 ~ 200 per cent and about 100 per cent by salbutamol (a selective β 2-adrenergic stimulant) above the basal level. The activity of phenylepherine, a α-adrenergic stimulant, was very weak. The concentration giving a half maximum stimulation was as follows: isoproterenol; 6.3 × 10 −8 M, hexoprenaline; 8.9 × 10 −8 M, salbutamol; 3 × 10 −7 M, epinephrine; 5.6 × 10 −7 M, and norepinephrine; 5.6 × 10 −6 M. Taking propranolol as a standard for comparison, antagonists of the isoproterenol induced increase in cAMP in macrophages ranged in their minimum effective concentrations as follows: bufetolol; 1. metoprolol (a selective β 1-adrenergie blocking agent); 1000, practolol (a selective β 1-adrenergic blocking agent); > 1000, while in rat hearts bufetolol; 1, metoprolol and practolol; 100. The increase of cAMP by 10 −5 M epinephrine or 10 −5 M hexoprenaline in rat peritoneal macrophages was blocked by bufetolol at a concentration of 10 −7 M or 10 −6 M, but not by practolol at a concentration of 10 −4 M. Phentolamine, a α-adrenergic blocking agent, showed no antagonistic activity against isoproterenol in rat peritoneal macrophages. These observations suggest that the increases in cAMP in rat peritoneal macrophages by catecholamines are mediated by β 2-adrenergic receptors.
Published Version
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