Influence of adenosine on the vascular responses to sympathetic nerve stimulation in the canine subcutaneous adipose tissue

Adenosine appears to regulate resting blood flow in canine subcutaneous adipose tissue. Sympathetic nerve stimulation has been shown to enhance the adenosine production in this tissue. This study therefore tested the possibility that adenosine may influence the vascular responses to sympathetic nerve stimulation. Intraarterial infusion of adenosine (5-20 microM in arterial blood) increased the resting vascular conductance (from 0.048 +/- 0.007 to 0.095 +/- 0.013 ml . min-1 . 100 g-1. mmHg-1) and the percental reduction in vascular conductance due to sympathetic nerve stimulation (4 HZ) by 34 per cent (p less than 0.05) and to i.a. noradrenaline by 27 per cent (p less than 0.05). The vasodilator response due to nerve stimulation after alpha-blockade was reduced by adenosine. Dipyridamole (0.5-1.5 microM) + EHNA (3-10 microM), which increases plasma adenosine levels, had similar effects to adenosine, while theophylline (30-80 microM) decreased the vasoconstrictor response. The vasoconstrictor escape was enhanced by EHNA alone and in combination with dipyridamole, but was reduced by theophylline. On the other hand, the poststimulatory hyperemia was unaffected by adenosine, dipyridamole and EHNA, and theophylline. The results show that adenosine does not reduce the magnitude of the initial vasoconstrictor response in proportion to the increase in resting blood flow. The autoregulatory escape in adipose tissue during nerve stimulation appears to be mediated both by adenosine and by noradrenaline acting on beta-adrenoceptors. Poststimulatory hyperemia does not seem to be greatly influenced by exogenous or endogenous adenosine.