Effect of Endogenous Prostaglandin E on the Vasoconstrictor Response to Noradrenaline

The effect of the endogenous prostaglandin E (PGE) level in the vascular wall on the vasoconstrictor response to noradrenaline (NA) was examined using the perfused central artery of an isolated rabbit ear. The endogenous PGE level in the ear artery was estimated from that in the venous perfusate, which was measured by radioimmunoassay. Pretreatment with indomethacin, a cyclooxygenase inhibitor, was followed by a significant decrease in the PGE level and a significant increase in the vasoconstrictor response to exogenous NA. In addition, there was a significant correlation between the response to NA and the PGE level in the venous perfusate in combination with the results during perfusion of indomethacin and of PGE1 plus indomethacin, although the former did not correlate with the latter under the basal conditions alone. From these results, it seems possible to draw the conclusion that as far as vasoconstrictor responsiveness is concerned, there is some antagonism between NA and endogenous and/or exogenous PGE in the rabbit ear artery.