ADENOSINE INHIBITS GROWTH OF HUMAN AORTIC SMOOTH-MUSCLE CELLS VIA A(2B) RECEPTORS

Adenosine inhibits rat vascular smooth muscle cell (SMC) growth. Howev er, the effects of adenosine on human vascular SMC proliferation and s ynthesis of extracellular matrix proteins, such as collagen, are unkno wn. The objective of this study was to characterize the effects of exo genous and endogenous (SMC-derived) adenosine on human aortic SMC prol iferation and collagen synthesis. Growth-arrested SMCs were stimulated with 2.5% fetal calf serum (FCS) in the presence and absence of adeno sine, 2-chloroadenosine (stable adenosine analogue), and with agents t hat increase endogenous adenosine levels, including erythro-9-(2-hydro xy-3-nonyl) adenine (EHNA), dipyridamole, and iodotubericidin. All of these agents inhibited in a concentration-dependent manner FCS-induced SMC proliferation as assessed by DNA synthesis (H-3-thymidine incorpo ration) and cell counting, as well as collagen synthesis (H-3-proline incorporation). EHNA, dipyridamole, and iodotubericidin increased extr acellular levels of adenosine by 1.7-fold to 18-fold when added separa tely to SMCs, and EHNA+iodotubericidin and EHNA+iodotubericidin+dipyri damole increased extracellular adenosine levels by more than 392-fold. Both KF17837 (selective A(2) antagonist) and DPSPX (A(1)/A(2) antagon ist), but not DPCPX (selective A(1) antagonist), blocked the antimitog enic effects of 2-chloroadenosine, EHNA, and dipyridamole on DNA and c ollagen synthesis, suggesting the involvement of A(2A) and/or A(2B), b ut excluding the participation of A(1), receptors. The lack of effect of CGS21680 (selective A(2A) agonist), excluded involvement of A(2A) r eceptors and suggested a major role for A(2B) receptors. A comparison of the inhibitory potencies of 2-chloroadenosine, N-6-cyclopentyladeno sine (selective A(1) agonist), NECA (A(1)/A(2) agonist), and MECA (A(1 )/A(2) agonist) were consistent with an A(2B) receptor subtype mediati ng the inhibitory effects of adenosine on human aortic SMC proliferati on. In conclusion, human aortic SMCs synthesize adenosine, and exogeno us as well as endogenous (SMC-derived) adenosine inhibits SMC prolifer ation and collagen synthesis via activation of A(2B) receptors.