Time-course of LPS-induced ATP (A), ADP (B) and ADO (C) levels in rats of different age groups. ADO, ADP and ATP were determined in serum of adult (black circles), 1middle-aged (grey circles) and 23 mo (open circles) old rats at various times after LPS challenge as shown, LPS was administered at 0 h time point. †,*, # indicate significant differences (p < 0.05) between adults (6 mo) and middle aged (15 mo), adults and aged (23 mo), or middle aged and aged, respectively. Each point was studied in 3–5 animals from the different age groups. Values, Means ± SEM.