Release of prostaglandins during the contraction of rat aorta induced by ouabain and K+-free solution.

Contractile effects of ouabain and K+-free solution on rat aortic strips were investigated. In the aorta without endothelium, application of ouabain or K+-free solution produced, after a latency period, a slow contraction reaching the maximum after 80-100 min. Pretreatment of the muscle with either indomethacin (20 microM) or verapamil (1 microM) decreased the maximum level of these contractions, whereas verapamil, but not indomethacin, prolonged the latency period. Simultaneous application of these inhibitors showed additive inhibitory effects. In the presence of endothelium, the latency period slightly increased without changing the maximum contractile tension. Methylene blue (5 microM) shortened the latency period only in the aorta with endothelium. These results suggest that the contractions of rat aorta induced by ouabain and K+-free solution are due not only to membrane depolarization and Na+-Ca2+ exchange but also to the release of prostaglandins. Endothelium-derived relaxing factor seems to inhibit a part of these contractions.