Cardiovascular effects of adenosine and the adenosine A 1 Receptor antagonist NPC 205 are altered with age in guinea pigs

Responsiveness of the cardiovascular system to the effects of vasoactive agents can vary with age. The endogenous metabolite adenosine has negative chronotropic, inotropic, and hypotensive effects. The purpose of this study was to determine if the effects of exogenously administered adenosine and the adenosine A 1 receptor antagonist 1,3‐di‐n‐propyl‐8‐(hydroxyphenyl) xanthine (NPC 205) vary with age. The effects of adenosine on mean arterial blood pressure (MABP), heart rate, and cardiac contractility (LV dP/dt) were investigated in two groups of guinea pigs: a young group (3–4 weeks) and an older group (72–75 weeks). In vivo, the older animals were shown to be significantly more sensitive to the negative inotropic, chronotropic, and hypotensive effects of adenosine, whereas the responses to R‐N 6 ‐phenylisopropyladenosine (R‐PIA), a metabolically stable analog of adenosine, were similar in both age groups. In vitro, right atria from young (3–4 weeks) and old (72–75 weeks) guinea pigs exhibited no age‐related differences in the sensitivity to the negative chronotropic effects of adenosine or R‐PIA. Younger animals were more sensitive to the positive inotropic effects of the adenosine A 1 receptor antagonist, NPC 205. In addition, basal heart rates were significantly lower in the older group of animals. It may therefore be concluded that there age‐related effects of adenosine. Furthermore, comparison of the effects of adenosine to the effects of the stable analog R‐PIA and the adenosine antagonist NPC 205 suggests that these differences may be due to changes in adenosine metabolism with age. © Wiley‐Liss, Inc.