Modulatory effects of endothelin-1 on purinergic and adrenergic components of sympathetically-mediated contractile activity of rabbit saphenous artery.

1. The present study has been performed to evaluate the modulatory effects of endothelin-1 (ET-1) on the purinergic and adrenergic components of sympathetically-mediated contractile responses of endothelium-free rabbit saphenous artery preparations. 2. ET-1 increased the smooth muscle tone, the pD2 value being 7.77 +/- 0.05. 3. Postjunctionally, ET-1 enhanced the responses to exogenous adenosine 5'-triphosphate (ATP) and did not influence those to exogenous noradrenaline (NA). 4. ET-1 increased the contractile responses to short-lasting and to long-lasting electrical field stimulation at a frequency of 5 or 10 Hz, showing a tendency towards decreasing the prazosin-sensitive component and increasing the mATP-sensitive component of the contractile responses. 5. In prazosin-treated preparations ET-1 increased the residual mATP-sensitive responses and this effect was more pronounced after yohimbine. 6. In mATP-treated preparations ET-1 increased the residual electrically-induced contractions and this increase was abolished after yohimbine. 7. It is suggested that ET-1 modulates co-transmission in the rabbit saphenous artery by potentiating postjunctionally the purinergic component of the contractile responses to both exogenous ATP or electrical stimulation.