Direct evidence for the local generation of vascular angiotensin II and its prostaglandin-mediated release from isolated hind legs in the rat

We examined the effect of prostaglandin synthesis inhibitors (indomethacin and meclofenamate) on the release of immunoreactive angiotensins I (irAng I) and II (irAng II) from isolated perfused rat hind-leg vasculature in order to delineate the possible relevance of prostaglandins to the vascular renin-angiotensin system in vitro. Isolated rat hind-legs were perfused with Krebs-Ringer solution and release of irAng I and irAng II into the perfusate was directly measured by using a Sep-Pak C18 cartridge connected to the perfusion system. The spontaneous release of irAng I and irAng II was as high as 600-700 pg per 30 min and was stable for at least 3 h. Addition of indomethacin and meclofenamate (10(-8) to 2 X 10(-6) mol/l) to the perfusion medium suppressed the release of both irAng I and irAng II to a similar extent in a dose-dependent fashion (P less than 0.001); the maximal percentage inhibition of irAng II release that was evoked by these inhibitors (2 X 10(-6) mol) was 60 +/- 6% (P less than 0.001) for indomethacin and 50 +/- 4% (P less than 0.001) for meclofenamate. There was a highly significant positive correlation between the amount of irAng I released and the amount of irAng II that was altered by indomethacin (r = 0.91) or meclofenamate (r = 0.94). These results provide direct proof of the local generation and subsequent release of Ang II by peripheral vascular tissue and suggest that prostaglandin plays an important role in the regulation of vascular Ang II release.