The effect of circulating prostaglandin antibodies on reproduction in rabbits with special reference to the placenta

Effects of indomethacin, NS-398 (a selective prostaglandin H synthase-2 inhibitor) and protein synthesis inhibitors on prostaglandin production by the guinea-pig placenta

The outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)were similar from the day 22 guinea-pig placenta and sub-placenta in culture, except for PGE2 output from the sub-placenta which was lower. Between days 22 and 29 of pregnancy, the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)during the initial 2 h culture period increased 6.9-, 1.1- and 3.2-fold, respectively, from the placenta, and 2.1-, 1.4- and 2.2-fold, respectively, from the sub-placenta. Therefore, there was a relatively specific increase in PGF(2 alpha)production by the guinea-pig placenta between days 22 and 29 of pregnancy. The output of PGFM from the cultured placenta also increased between days 22 and 29, indicating that the increase in PGF(2 alpha)output was due to increased synthesis rather than to decreased metabolism. By comparing the amounts of prostaglandins produced by tissue homogenates during a 1 h incubation period, it appears that there is approximately a 2-fold increase in the amount of prostaglandin H synthase (PGHS) present in the guinea-pig placenta between days 22 and 29. NS-398 (a specific inhibitor of PGHS-2) and indomethacin (an inhibitor of both PGHS-1 and PGHS-2) both inhibited prostaglandin production by homogenates of day 22 and day 29 placenta. Indomethacin was more effective than NS-398, except for their actions on PGF(2 alpha)production by the day 29 placenta where indomethacin and NS-398 were equiactive. Indomethacin and NS-398 were both very effective at inhibiting the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)from the day 22 and day 29 placenta and sub-placenta in culture, indicating that prostaglandin production by the guinea-pig placenta and sub-placenta in culture is largely dependent upon the activity of PGHS-2. The high production of PGF(2 alpha)by the day 29 placenta is not dependent on the continual synthesis of fresh protein(s), as inhibitors of protein synthesis did not reduce PGF(2 alpha)output from the day 29 guinea-pig placenta in culture.

Prostaglandin production by guinea-pig placenta and other uterine tissues during mid-pregnancy

Prostaglandin (PG) output from cultured placenta, sub-placenta, endometrium and fetal membranes of guinea-pigs was measured on days 22, 29 and 36 of pregnancy to establish the source of increased PGF2alpha production during mid-pregnancy. PGF2alpha and 6-keto-PGF1alpha were produced in larger quantities than PGE2 by the placenta, sub-placenta and endometrium; 6-keto-PGF1alpha was in the major prostaglandin produced by the fetal membranes. The initial outputs of PGF2alpha, PGE2 and 6-keto-PGF1alpha from the sub-placenta, fetal membranes and endometrium either decreased or remained fairly constant between days 22 and 36. In contrast, the initial outputs of PGF2alpha, PGE2 and 6-keto-PGF1alpha from the placenta increased 14.7-, 2.5- and 2.0-fold, respectively, between days 22 and 36, indicating that the placenta is the tissue responsible for the increase in PGF2alpha output from the mid-pregnant guinea-pig uterus. Aristolochic acid (a phospholipase A2 inhibitor) inhibited prostaglandin output from the endometrium, but had a more variable effect in prostaglandin output from the other tissues. Thimerosal (an arachidonic acid uptake inhibitor) inhibited PGF2alpha and PGE2 outputs from the endometrium, but generally potentiated 6-keto-PGF1alpha output and prostaglandin output from the other tissues. Arachidonic acid release for prostaglandin synthesis in the endometrium, but not the placenta, sub-placental or fetal membranes, is apparently dependent upon a constant level of phospholipase A2 activity.

Detection of acyl-CoA synthetase, acyl-CoA:lysophospholipid acyltransferase and phospholipase A2 activities in non-pregnant and pregnant guinea-pig uterine tissues

Acyl-CoA synthetase (ACS), acyl-CoA:lysophospholipid acyltransferase (ACLAT) and phospholipase (PL) A2 activities were detected in guinea-pig endometrium on days 7 and 15 of the cycle, and on days 15, 29 and 36 of pregnancy. Ovariectomy of non-pregnant animals resulted in an increase in the apparent activities of these three enzymes which was reversed by treatment with oestradiol and/or progesterone. ACS, ACLAT and PLA2 activities were detected in day 15 conceptuses, and in the placenta, sub-placenta, chorion and amnion on days 29 and 36 of pregnancy. Apparent activities of the enzymes were generally higher in the fetal membranes than in the placental tissue. This study has established that the enzymes involved in turnover of arachidonic acid in phospholipids are present in tissues in the non-pregnant and pregnant guinea-pig uterus. The higher apparent activities of enzymes (ACS and ACLAT) involved in arachidonic acid uptake compared to the enzyme (PLA2) involved in arachidonic acid release is in agreement with there being very low concentrations of free arachidonic acid in tissues.

The control of prostaglandin production by the endometrium in relation to luteolysis and menstruation

Oestradiol acting on a progesterone-primed uterus stimulates prostaglandin (PG) F2 alpha synthesis by the endometrium. In some species (notably the sheep, cow and goat) oxytocin released from the ovary also forms part of the physiological stimulus for increased endometrial PGF2 alpha production. The corpus luteum contains high concentrations (> 1 microgram/g tissue) of this peptide in these species. The intracellular mechanisms by which these three hormones control endometrial PGF2 alpha synthesis and release are far from clear. Oxytocin stimulates the synthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial PGF2 alpha synthesis is still open to question. There is evidence that increased endometrial PGF2 alpha synthesis is dependent upon increased endometrial protein synthesis but, apart from the recorded effects of steroid hormones on the concentrations of phospholipase A2, prostaglandin H synthase and oxytocin receptors, it is not known what other endometrial proteins are involved. Some disorders of menstruation are associated with abnormal PG production by the endometrium, but the reasons for this abnormality are not clear. During early pregnancy an increase in PGF2 alpha synthesis by the endometrium is prevented, except in the pig where the PGF2 alpha produced is directed from the venous drainage to the uterine lumen. In those species in which endometrial PGF2 alpha synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named trophoblast protein-1) which prevents oestradiol and oxytocin acting on a progesterone-primed uterus from stimulating endometrial PGF2 alpha synthesis. The identities of the factors produced by the conceptus which prevent endometrial PGF2 alpha synthesis during early pregnancy in other species are not known, although it is clear that they are not interferons.

Dietary deprivation induces fetal loss and abortion in rabbits

We assessed the effects of a pared diet (20, 60 or 150 g/day for days 6-20 after coitus) on the course of pregnancy in rabbits. Dams receiving 20 g/day manifested a marked weight loss, 5 of 6 animals aborted and in the remaining dam, the litter size, fetal and placental weight were significantly lower than in the controls. In the 60 g/day group, the maternal body weight remained stable throughout the observation period; the number of dead embryos on fetuses was significantly higher, that of liver fetuses lower, than in he controls. Feedings on the 150 g/day group did not markedly differ from the controls, indicating that pregnant rabbits require at least 150 g of food/day.

[Prostaglandins in reproductive physiology (author's transl)]

Up to the present time, the most extensive knowledge in prostaglandin research has been achieved in the field of reproductive physiology. It seems now certain that prostaglandins are involved in each phase of the reproductive process although their precise physiological functions cannot yet be completely explained. For example they are thought to play an important role in the hypothalamic -- pituitary system in the liberation of LHRH and in the ovary in steroid genesis, ovulation and luteolysis; also, in the non-pregnant uterus in the onset of menstruation while at conception both sperm and ovum transport are influenced by prostaglandins. In pregnancy, a prostaglandin function has been demonstrated in the uterus in initiating labour in cases of abortion and in birth at term. Further, they appear to be involved in regulating the blood circulation in placenta, cord and fetus. Already, because of their established physiological functions, the prostaglandins have been introduced successfully into clinical use.