Different response of vascular fibrinolysis to adrenergic stimulation in young and aged rats

We have studied the vascular response to epinephrine infusion in an experimental model of vascular perfusion in young (3 ± 1 months) and old (18 ± 3 months) rats. Five min epinephrine infusion induced a dosedependent (0.15-25 μM) increase in t-PA release and in perfusion pressure in both young and old rats. However, in old rats, the basal levels of t-PA were higher than in young rats (0.24 ± 0.06 vs 0.08 ± 0.01 IU/ml; p < 0.01, means ± SE, n = 6) and epinephrine infusion induced a significantly higher increase in t-PA activity levels (0.78 ± 0.06 vs 0.47 ± 0.08 IU/ml, p < 0.01, for 625 μM epinephrine). The response, however, was characterized by a delayed onset. An opposite tendency was observed in the increase of the perfusion pressure, which was significantly lower in old than in young rats. In young rats venous stasis induced in young rats, a rapid and significant increase in t-PA activity (from 020 ± 0.03 to 0.68 ± 0.02 IU/ml; p < 0.01; n = 6). The response rapidly decreased, reaching the basal level at 5 minutes of wash-out. In aged rats, however, the increase in t-PA activity triggered by thirty minute venous stasis was less pronounced, delayed and long-lasting. Our data show a different vascular response to adrenergic stimulation in young and aged rats. © 1992.