[Reduced sensitivity to noradrenaline and electric stimulation of the caudal artery of the aged rat].

UNLABELLED

Whilst arterial noradrenaline (NOR) content decreases with age (Waterson, et al. 1974; Neubauer and Christensen, 1978; Embree, et al., 1981), changes in vasoconstriction induced by NOR are equivocal (Tuttle, 1966; Cohen and Berkowitz, 1976; Scott and Reid, 1982; Duckles, et al., 1985). We have investigated changes in responsiveness to NOR in the NOR-rich rat tail artery. Two cm segments of the proximal tail artery from male Ivanos rats of 6/7, 16/17 or 30/31 months were perfused/superfused with Krebs bicarbonate (4 ml/min). Changes in perfusion pressure (mmHg) were determined after (1) electrical stimulation (1 to 30 Hz, 0.3 msec, 15 sec at supramaximal voltage, ES) followed by (2) perfusion with exogenous NOR (1 nM to 10 microM for 2 min at each concentration). Responses to ES were abolished by pretreatment with reserpine (2.5 mg/kg, i.p. at - 18 h) or perfusion with phentolamine (4 microM). They were produced therefore, by liberation of endogenous NOR. Arterial NOR content was determined by HPLC-EC following perchloric acid digestion (0.1 N).

RESULTS

(Table: see text). Asterisks refer to t-test with 6/7 months age group (p less than 0.05, p less than 0.01 and p less than 0.001]. There were no differences in basal perfusion pressure before stimulation or in plateaux responses to maximal concentrations of NOR. In conclusion our results show a decrease in arterial NOR and in sensitivity to both endogenous and exogenous NOR with age.