ISSN:
1432-1750
Keywords:
Key words: 3′,5′-Cyclic adenosine monophosphate—Adrenergic—Pulmonary circulation—Vasodilation.
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract. To determine whether functional atypical β-adrenoceptors (β3-adrenoceptors) are present in pulmonary vascular smooth muscle, we studied isolated canine pulmonary arterial rings under isometric conditions in vitro. Addition of β-adrenoceptor agonists produced a concentration-dependent relaxation of noradrenaline-precontracted tissues, a rank order potency being isoproterenol (1) 〉 salbutamol (0.95) 〉 selective β3-adrenoceptor agonists, CL 316243 (0.85), and BRL 37344 (0.83). A marked desensitization to salbutamol occurred by pretreatment with salbutamol but not with CL 316243. When β1-adrenoceptors had been blocked, the relaxant responses to salbutamol were competitively antagonized by the β2-adrenoceptor antagonist ICI 118551 with a pA2 value of 7.67 ± 0.21 (mean ± S.E.), but the response to CL 316243 was weekly antagonized by ICI 118551 only at a high concentration of 10−5 M, where an apparent pA2 value was 5.24. In contrast, cyanopindolol, a nonselective β-adrenoceptor antagonist, antagonized CL 316243–induced relaxation in a competitive manner with a pA2 of 6.10 ± 0.11. This pA2 value was lower than that when salbutamol was used as an agonist (6.69 ± 0.14, p 〈 0.01). Intracellular 3′,5′-cyclic adenosine monophosphate (cAMP) levels were increased by CL 316243 in a concentration-dependent fashion, an effect that was not altered by ICI 118551. These results suggest that β3-adrenoceptors may exist in canine pulmonary artery smooth muscle and that stimulation of this atypical receptor causes vasodilation through a cAMP-dependent pathway.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/PL00007650
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