Abstract
Prostacyclin (PGI2) production by rat aortae under various conditions was investigated and activities of the aorta to produce this substance in stroke-prone spontaneously hypertensive rats (SHRSP), stroke-resistant SHR (SHRSR) and normotensive control rats from the Wistar-Kyoto (WK) colony were compared.
Except for some preliminary experiments to establish the test system, only age-matched male animals (6 months) before the development of stroke were utilized (5 animals in each group). The descending aorta was removed from each animal, washed and used immediately or stored at -20°C until use. Fine rings of the aorta were routinely incubated in 0.25-1.0ml of pH 9.0 borate-buffered ered saline for 1hr at 20°C. Volumes (1-10μl) of the buffered saline in which the aortic rings had been incubated were added to 0.2ml human plateletrich plasma (PRP) 1 min before the addition of collagen. Platelet aggregation was monitored in a Sienco dual sample aggregometer. The amount of prostacyclin produced by the aorta was estimated by comparison of its anti-aggregatory activity with thay produced by known amounts of authentic prostacyclin-Na.
Rings of the aorta incubated as described above produced increasing prostacyclin-like activity, as shown by the strong inhibition of ADP-, collagen- and arachidonate-induced platelet aggregation for up to 1hr (Fig. 1) and the activity was dependent on the volume of buffered-saline added as well as on the length of aortae incubated. The activity produced by incubation of the aorta in pH 7.4 Tris-buffered saline for longer than 20 min at 20°C decreased progressively during the incubation and disappeared within 1hr (Fig. 1), confirming the lability of prostacyclin at pH 7.4. Incubation of the aorta boiled for 3 min produced no such activity. The spontaneous generation by the aorta of prostacyclip was inhibited by preincubation of the aorta with indomethacin (cyclo-oxygenase inhibitor), while the generation induced by PGH2 was not (Fig. 2). These results indicate that the aorta has both cyclo-oxygenase and prostacyclin synthetase.
Amounts of prostacyclin generated by the aorta of SHRSP and SHRSR were significantly higher than those of WK rats (Fig. 3). Although the meaning of the enhanced production of prostacyclin by the aorta of these hypertensive rats is not clear at the moment, it could be a physiological defence mechanism against the development of vascular injuries possibly due to hypertension in these animals and stroke might be triggered by the development of any inhibitory mechanisms against prostacyclin synthesis by the vessel of SHRSP.
