Adenosine receptors, cyclic AMP accumulation, and DNA-synthesis in aortic smooth muscle cell cultures of adult and neonatal rats

The effects of two adenosine analogs on cyclic AMP (cAMP) accumulation and DNA synthesis were studied in cultured smooth muscle cells (SMCs) isolated from adult and neonatal rat arteries. N‐ethylcarboxamido adenosine (NECA) dosedependently increased intracellular cAMP levels and appeared to be more potent in adult than in neonatal SMCs. R‐phenylisopropyl adenosine (R‐PIA), in nanomolar concentrations, counteracted the increase in cAMP evoked by 10 μM forskolin in adult but not in neonatal SMCs, indicating that the enhanced “A2” response seen in adult SMCs was not due to a lack of “A1” receptors in these cultures. Binding experiments performed using the adenosine antagonist XAC did not reveal any differences in the number or affinity of the adenosine receptors between neonatal and adult SMCs. This indicates effects presumably on the G‐protein level. A high capacity to spontaneously synthesize DNA and a weak response to platelet‐derived growth factor (PDGF) were seen in the neonatal SMCs. Furthermore, NECA had no effect on PDGF‐induced DNA synthesis in these cells. In contrast, adelt SMCs presented a low rate of spontaneous DNA synthesis and a marked proliferative response to PDGF, which was inhibited by NECA. This inhibition paralleled the increase in cAMP elicited by NECA. Our findings suggest that neonatal and adult SMCs differ both in their response to growth factors and growth inhibitors. © 1992 Wiley‐Liss, Inc.