ENHANCED SYMPATHETIC NEUROTRANSMISSION IN THE TAIL ARTERY OF 1,3-DIPROPYL-8-SULPHOPHENYLXANTHINE (DPSPX)-TREATED RATS

1 Sympathetic neurotransmission and noradrenaline content of the tail artery of Wistar rats treated for 7 days with the adenosine antagonist , 1,3-dipropyl-8-sulphophenylxanthine (DPSPX), were examined. 2 Systol ic blood pressure of the DPSPX-treated rats (164.0 +/- 2.9 mmHg; n = 6 ) was significantly greater than saline-treated controls (140.0 +/- 2. 8 mmHg; n = 5) after 7 days treatment. 3 The presser responses of the arterial rings to transmural nerve stimulation (65 V, 0.1 ms, 4-64 Hz, for 1 s) were markedly enhanced in the DPSPX-treated compared with th e saline-treated animals. Both noradrenergic and purinergic components of perivascular sympathetic neurotransmission were enhanced during DP SPX-induced hypertension. 4 Vasoconstrictor responses to exogenous nor adrenaline (0.1-300 mu M) and adenosine 5'-triphosphate (0.01-3 mM) we re unaffected after DPSPX treatment, indicating prejunctional alterati on of sympathetic cotransmission during DPSPX-induced hypertension. 5 Acute exposure to DPSPX (10 mu M) did not modify vasoconstrictor respo nses to transmural nerve stimulation, thus supporting the claim that t he enhancement of sympathetic neurotransmission only results from long -term DPSPX treatment.6 The noradrenaline content of the tail arteries of DPSPX-treated (4.498 +/- 0.26 ng cm(-1); n = 4) was significantly greater than saline-treated (3.440 +/- 0.30 ng cm(-1); n = 5) animals. 7 These findings show that chronic inhibition of the actions of endog enous adenosine by DPSPX results in an elevation of systolic blood pre ssure accompanied by enhanced sympathetic cotransmission and enhanced noradrenaline content of the rat tail artery.