The rat and human pregnant myometrium and human placenta, when chopped and incubated in Tris-buffered saline (25%, 50% & 50% w/v respectively) released materials with anti-aggregatory activity. The myometrial activities were stable at pH 12.0, and unstable at pH 4.0. Optimum conditions for the release of the anti-aggregatory activities were 15, 30 and 15 minutes incubation respectively at 20°C at pH 8.0. The release of anti-aggregatory activity by human myometrium was stimulated by arachidonic acid and phospholipase A2 (PLA2) and inhibited by indomethacin. Human myometrial incubate did not possess adenosine- diphosphatase activity. This anti-aggregatory activity released by pregnant rat and human myometria was attributed to prostacyclin (PGI2). Human placental anti-aggregatory activity was unstable at both pH 12.0 and pH 4.0, was not inhibited by administration of indomethacin and had the ability to degrade adenosine diphosphate. PGI2 synthesis by human pregnant myometrium was low up to week 37 of pregnancy and then increased progressively to a maximum at week 40 (term). Two patients who did not progress to labour by week 42 had a low capacity to release PGI2. Incubation of human myometrial tissue with oxytocin and ergometrine did not alter PGI2 synthesis. PGI2 inhibited the spontaneous contractility of human pregnant myometrium bathed in Krebs' solution in 3/4 samples and reduced basal tone in 2/4. Studies on pregnant rat myometrial PGI2 synthesis showed that removal of the deciduum by scraping with a microscope slide resulted in greatly increased synthesis of PGI2 compared to teasing. Chopping increased the rate of synthesis of the scraped samples, and maximal synthesis of the teased samples. Pre-incubation of scraped myometrial tissue with uterine stimulant drugs (oxytocin, angiotensin & 5-hydroxytryptamine [5-HT]) stimulated PGI2 synthesis in a dose related fashion. Methysergide, whilst reducing synthesis, inhibited the stimulant effect of 5-HT. The uterine relaxant salbutamol inhibited synthesis by day 21 but not day 19 pregnant myometerium, and was antagonised by propranolol. The adenylate cyclase stimulant, forskolin, reduced PGI2 synthesis. Rat uterine homogenate, when incubated in HEPES buffer (pH 8.0; + Triton X-100) released H-oleic acid from I'-oleoyl, 2'-[3H]-oleoyl- phosphatidylcholine (H-dPC). Two methods were assessed for the separation of released oleic acid from the 3H-dPC. Thin layer chromatography was found to be the method of choice. The release of 3H-oleic acid by late pregnant rat uterine homogenate acid was Ca++ dependent, protein dependent, had a pH optimum at pH 8.0 and was inhibited by mepacrine and tetracaine. This activity was attributed to PLA2. Perfusion of the uterine vascular bed with Krebs' solution to remove blood elements increased activity as measured by this method.
|Date of Award||1983|