Diminished purinergic modulation of the vascular adrenergic neurotransmission in spontaneously hypertensive rats

The inhibitory effects of adenosine and ATP on the pressor response of the perfused mesenteric vascular bed to perivascular adrenergic nerve stimulation were compared between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKR). Both adenosine and ATP inhibited the neurogenic vasoconstriction in a dose-dependent manner in WKR, in which the inhibitory effect of adenosine was approximately eight times greater than that of ATP on the basis of 50% inhibitory doses (ID50). In the same preparation isolated from SHR, the inhibitory effects of both adenosine and ATP were significatly smaller than that in WKR. The ID50 values in the SHR for both agonists were approximately six times those found in WKR. These compounds also inhibited the pressor response to norepinephrine (0.3 microgram/ml) infusion, but the degrees of inhibition were markedly less than those with the neurogenic pressor response, and were not significantly different between WKR and SHR. These results suggest that presynaptic inhibition of vascular adrenergic neurotransmission by purine compounds is reduced in SHR.