In-vitro production of prostaglandin E, F and 6-oxo-prostaglandin F1 alpha by the uterine and ovarian tissues of pseudopregnant rabbits

Abstract

The production of prostaglandin (PG) E, PGF and 6-oxo-PGF1 alpha by the uterine and ovarian tissues of pseudopregnant rabbits was investigated at the various stages of pseudopregnancy. The production of PGE, PGF and 6-oxo-PGF1 alpha in the tissues tested was expressed as mean (+/-S.E.M.) ng/mg protein per 6h. The production of PGE by endometrial tissue was found to be slightly raised with levels ranging from 2.15 to 2.92 on days 13 - 19 compared with values on day 5 (P less than 0.01). Subsequently PGE production declined on day 22 to the same level as that on day 5. In the myometrial tissue the same tendency in PGE production was observed as in the endometrial tissue. A significant increase in PGF production in the endometrial tissues was observed on day 13 (4.08 +/- 0.56) compared with that on day 12 (1.28 +/- 0.17) (P less than 0.001). The highest activity was detected on day 19 (7.19 +/- 0.29). An abrupt decrease occurred on day 20. In the myometrial tissues there was a slight and gradual increase in PGF production from day 12 (1.88 +/- 0.18) until day 16 (3.22 +/- 0.21). A sudden decline in the activity was detected after day 17. A marked increase of the 6-oxo-PGF1 alpha production activity in the myometrial tissues was observed on days 12 - 20 ranging from 14.60 to 19.25 compared with that on day 5 (P less than 0.001). The maximum activity was detected on day 16 (19.25 +/- 2.76). In the endometrium significant increase ranging from 4.85 to 8.31 occurred continuously from days 14 - 20 compared with that of day 12 (P less than 0.01). The myometrial tissue was shown to be significantly more potent in 6-oxo-PGF1 alpha production than endometrial tissue (P less than 0.01). No significant increase of PGE and PGF production activity was detected in the ovarian tissues throughout pseudopregnancy. The corpora lutea were shown to have very low 6-oxo-PGF1 alpha production activity. The 6-oxo-PGF1 alpha production activity of the remaining ovarian tissue was demonstrated to be significantly (P less than 0.01) more potent than the corpus luteum. The endometrial tissue of pseudopregnant rabbits has marked PGF2 alpha production activity in the late stage of pseudopregnancy, whereas the myometrial tissue is remarkably potent in 6-oxo-PGF1 alpha synthesis. Conversely, ovarian tissues showed much lower PG production activity than the uterine tissues. These experiments suggest that the main site of PGF production in luteolysis may be the endometrium and not the ovary itself. The physiological significance of PG production in relation to luteolysis is discussed.