Subsensitivity of presynaptic adenosine A 1-receptors in caudal arteries of spontaneously hypertensive rats

Abstract

(-)-N 6-(R-phenylisopropyl)-adenosine (R-PIA) depressed tritium overflow and vasoconstriction evoked by electrical stimulation to a similar extent in isolated tail arteries of Wistar rats (WR) preincubated with [ 3H]noradrenaline. The inhibitory effects of adenosine, 5'-N-ethylcarboxamidoadenosine (NECA) and R-PIA were determined on the constrictor responses of tail arteries obtained from WR, as well as spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY). In WR and WKY, the rank order of agonist potency (R-PIA > NECA > adenosine) was compatible with the presence of adenosine A 1-receptors. Whereas adenosine, NECA and R-PIA were equiactive in WR and WKY, they produced no or only slight changes in SHR. The left renal arteris of some WR were partially occluded to induce hypertension. R-PIA had the same effect in the tail arteries of these animals as in preparations obtained from sham-operated WR. The above results suggest that the subsensitivity of presynaptic A 1-receptors in the blood vessels of SHR is genetically determined. This could contribute in vivo to enhanced transmitter release from terminals of perivascular nerves and subsequent increases in vascular resistance.