Formation of 13,14-dihydro-prostaglandin E1 during intravenous infusions of prostaglandin E1 in patients with peripheral arterial occlusive disease.

Formation of 13,14-dihydro-prostaglandin (PG) E1 during intravenous infusions of PGE1 in patients with peripheral arterial occlusive disease was investigated. Using both high performance liquid chromatography (h.p.l.c.) combined with radioimmunoassay and gas chromatography/triple stage quadrupole mass spectrometry (GC/MS/MS) basal levels of 13,14-dihydro-PGE1 were found to be close to or below the detection limits of the assay methods. Levels of the PGE1 metabolite increased significantly during the infusion periods and decreased after their end. Since 13,14-dihydro-PGE1, in contrast to its precursors 15-keto-PGE1 and 15-keto-13,14-dihydro-PGE1, is biologically active, its formation could contribute to the beneficial effects of PGE1 administered intravenously in patients with peripheral arterial occlusive disease.     

Prostaglandins and prostaglandin metabolites in human gastric juice

Human gastric juice contains higher concentrations of PG metabolites than of unmetabolized PG indicating that local metabolism might play a role in limiting the biological activity of PG in gastric mucosa and has to be considered when investigating endogenous gastric PG. A major fraction of the 15-keto-13,14-dihydro-PGE2 (KH2PGE2) formed in gastric mucosa and released into the gastric lumen seems to be rapidly dehydrated to a compound co-chromatographing with KH2PGA2, while the amounts of the bicyclic degradation product 11-deoxy-13,14-dihydro-15-keto-11,16-cyclo-PGE2 (11-deoxy-KH2-cyclo-PGE2), as measured by radioimmunoassay, in freshly extracted gastric juice are negligible. Stimulation of secretion with pentagastrin does not influence significantly the concentrations of PG and PG metabolites in human gastric juice, but total output tends to increase parallel to the increase in secretion volume. Levels of immunoreactive 6-keto-PGF1 alpha in human gastric juice are much lower than those of PGE2. Since human gastric mucosa synthesizes conciderable amounts of PGI2 and 6-keto-PGF1 alpha in vitro, the low levels of 6-keto-PGF1 alpha in gastric juice might indicate that PGI2 formed by gastric mucosa in vivo is, like PGE2 and PGF2 alpha, rapidly metabolized and/or removed preferentially via the blood stream.     

Prostaglandin 9-hydroxydehydrogenase activity in the adult rat kidney. Identification, assay, pathway, and some enzyme properties.

Prostaglandin F2alpha is converted to 15-keto-13,14-dihydroprostaglandin E2 by adult rat kidney homogenates. A variety of substrates labeled as either the 9beta position alone or at several other positions in the prostaglandin molecule were used to define the step at which the crossover from the F type to the E type prostaglandins takes place. Time course studies further confirmed that 15-keto-13,14-dihydroprostaglandin F2alpha is the immediate substrate for this enzyme which we have termed prostaglandin 9-hydroxydehydrogenase. An assay system based on specific loss of tritium from 9beta-tritiated prostaglandin F2alpha is described. Enzyme activity with prostaglandin F2alpha as substrate is linear with time up to 10 min, stimulated by NAD+, saturable at low concentrations of substrate, stable to storage at minus 25 degrees in phosphate buffer (up to 3 weeks), and has a broad pH optimum around 7.5. The product, 15-keto,13,14-dihydroprostaglandin E2 was identified by mass spectrometry through a sodium borohydride-sodium borodeuteride reduction method.     

On the metabolism of prostaglandin E1 administered intravenously to human volunteers.

We have demonstrated recently the formation of a biologically active metabolite of prostaglandin (PG) E1, 13,14-dihydro-PGE1, during intravenous infusions of PGE1 in patients with peripheral arterial occlusive disease. We have now investigated the levels of the immediate precursor of 13,14-dihydro-PGE1, the biologically inactive 15-keto-13,14-dihydro-PGE1, during intravenous administration of 20 micrograms, 40 micrograms or 80 micrograms PGE1 over a period of 60 min to human volunteers. It was found that levels of 15-keto-13,14-dihydro-PGE1, but not those of PGE1 itself, increased in a dose-dependent manner. Thus, increased formation of 13,14-dihydro-PGE1 from 15-keto-13,14-dihydro-PGE1 with increasing doses of PGE1 can be expected to occur. It remains to be investigated, to which extent formation of small amounts of 13,14-dihydro-PGE1 during intravenous infusion of PGE1 could contribute to the therapeutic effects of PGE1 in patients with peripheral arterial occlusive disease.     

Responsiveness of the lamb ductus arteriosus to prostaglandins and their metabolites

The relative potencies of the prostaglandins A1, A2, E1, E2, F2alpha and their 15-keto-, 15-keto-13,14-dihydro-, and 13,14-dihydro-metabolites were investigated on isolated lamb ductus arteriosus preparations contracted by exposure to elevated PO2. All the prostaglandins (except PGF2alpha and its 15-keto-metabolites) relaxed the tissue. However, only PGE1, E2, and their 13,14-dihydro-metabolites, were effective at concentrations below 10(-8) M. Therefore, events that alter metabolism of circulating PGs in the perinatal period may have significant effects on the relative patency or closure of the ductus arteriosus.     

Release of PGF(2alpha) during parturition and the postpartum period in the ewe

Peripheral plasma levels of 15-keto-13, 14-dihydro-PGF(2alpha) were determined from one week before parturition until five weeks postpartum in six ewes. Starting at approximately 1 nmol/l one week before parturition, the prostaglandin metabolite levels rose successively during the week preceding parturition and peaked at 70 to 125 nmol/l during parturition. During the first three days postpartum the concentrations of the 15-keto-13, 14-dihydro-PGF(2alpha) decreased to 0.5 to 1 nmol/l. These levels were maintained for three weeks and low levels of 50 to 100 pmol/l were reached around four weeks postpartum. The ewe, as well as other ruminants, has a sustained release of elevated concentrations of PGF(2alpha) postpartum. It seems likely that PGF(2alpha) plays a role in uterine involution.     

Estradiol-17 beta and 2-hydroxyestradiol-17 beta-induced differential production of prostaglandins by cells dispersed from human intrauterine tissues at parturition

Prostaglandin (PGE, 6-keto PGF1 alpha) output by cells dispersed from human amnion and decidua in the presence of increasing levels (0-5000 ng/ml) of estradiol-17 beta (E2) or 2-hydroxyestradiol-17 beta (2-OH E2) was studied in relation to parturition. Tissues were obtained from women at term either before (CS) or after (SL) spontaneous labor and vaginal delivery. In the absence of estrogens, the output of both PGs from amnion increased significantly with labor. No significant increase in decidua PG output occurred with labor. Neither estrogen influenced CS amnion PG output. However, both E2 and 2-OH E2 stimulated SL amnion PGE output (2-OH E2 greater than E2) while having no affect on 6-keto PGF1 alpha output. Only the highest dose of 2-OH E2 stimulated PGE output in CS decidua, but both estrogens significantly inhibited 6-keto PGF1 alpha output in this tissue. In SL decidua only 2-OH E2 significantly stimulated PGE, and neither estrogen affected 6-keto PGF1 alpha output. These results might suggest that estrogens modulate PG biosynthesis at the level of endoperoxide to primary PG conversion.     

Determination of prostaglandin F2 alpha, E2, D2 and 6-keto-F1 alpha in human cerebrospinal fluid.

Prostaglandin (PG)F2 alpha, E2, D2 and 6-keto-F1 ALha were determined in human cerebrospinal fluid by a mass spectrometric technique. The samples were obtained from 12 patients with suspected intracranial disease. A 64 fold variation in PG levels was observed. The major PG was 6-keto-F1 alpha (0.12--15 ng/ml). PGF2 alpha and PGE2 were present in lower concentrations PGD2 was below the level of detection (0.05 ng/ml) except in one patient with extremely high total levels of PGs.     

Stimulation of prostaglandin synthesis in rabbit gastric antral mucosal slices by desferrioxamine in vitro.

Desferrioxamine is an iron-chelating agent used in the treatment of iron overload. It is a powerful inhibitor of iron-dependent radical reactions. The effect of desferrioxamine of prostaglandin (PG) synthesis and metabolism in rabbit gastric antral mucosal slices has been examined. Desferrioxamine significantly enhanced the production of PGE2 and PGF2 alpha. The formation of 13,14-dihydro-15-keto PGE2 and 13,14-dihydro-15-keto PGF2 alpha was also increased slightly by desferrioxamine. The addition of Fe3+ or Al3+ blocked the stimulatory action of desferrioxamine on PGE2 and PGF2 alpha production. Desferrioxamine appears to be stimulating the activity of PG cyclooxygenase through the removal of endogenous antral mucosal iron. These results suggest that desferrioxamine has the potential to increase the PG levels in gastric mucosa by primarily stimulating PG biosynthesis. The possibility that desferrioxamine may be of therapeutic value in the treatment of ischemic injury in the stomach is discussed.     

Blood levels of 15-keto-13, 14-dihydroprostaglandin F(2alpha) during the postpartum period in primiparous cows

Plasma levels of the PGF(2alpha) metabolite 15-keto-13, 14-dihydroprostaglandin F(2alpha) were determined postpartum in 51 primiparous Black and White Lowland cows. The highest geometric mean was 1702 pmol/l on day 3 and lowest 190 pmol/l on day 21. It should be noted that variation between animals in the concentration of the metabolite is high. For instance, on days 4, 10, 16 and 22, concentration of metabolite ranged from 775-2500, 209-2450, 45-851 and 30-398 pmol/l, respectively. The duration of the massive postpartum release of PGF(2alpha) could be determined in only 29 cows. Significant correlations were found between the duration of elevated PGF(2alpha) metabolite levels and the time required for completion of uterine involution (r = -0.41, P < 0.05) and between the duration of increased PGF(2alpha) metabolite levels and the interval from parturition to occurrence of the first ovulation followed by a normal luteal phase length (r = -0.37, P < 0.05). The occurrence of the first ovulation followed by a normal luteal phase length in the 29 cows was positively correlated with the time needed for completion of uterine involution (r = 0.54, P < 0.01).     

Effects of prostaglandin E2 and F2 alpha on peri-implantation development of mouse embryos in vitro.

The effects of exogenous prostaglandin (PG) E2 and F2 alpha on the morphology and lactate dehydrogenase (LDH) activities of pre-implantation mouse embryos in vitro were studied. A 24-hour exposure from 0.01 to 10 micrograms/ml of PGE2 at the 4-cell or morula stages had no effect on the morphology of embryos during the 144 hours in culture. Exposure to 10 micrograms/ml PGE2 at the blastocyst stage accelerated and enhanced spreading of the trophoblast in vitro. Embryos treated at 0.01 to 10 micrograms/ml PGE2 at various stages all showed a more rapid decline in LDH activity from morula to blastocysts. Treatment with 50 or 100 micrograms/ml PGE2 led to abnormal morphology of embryos in vitro. In contrast, continuous treatment with 0.01 to 100 micrograms/ml PGF2 alpha from 4-cell to early post-implantation (day 8) had no effect on the morphology of embryos, although breakdown of LDH was again accelerated. These results suggest that the peak of PGE2 secretion on day 4 of pregnancy in mice may enhance trophoblastic outgrowth, and the lower levels of PGE2 and PGF2 alpha secreted earlier in pregnancy modulate the development of pre-implantation mouse embryos.     

Anti-apoptotic roles of prostaglandin E2 and F2alpha in bovine luteal steroidogenic cells

Production of prostaglandins (PGs) and expression of their receptors have been demonstrated in bovine corpus luteum (CL). The aim of the present study was to determine whether PGE2 and PGF2alpha have roles in bovine luteal steroidogenic cell (LSC) apoptosis. Cultured bovine LSCs obtained at the midluteal stage (Days 8-12 of the cycle) were treated for 24 h with PGE2 (0.001-1 microM) and PGF2alpha (0.001-1 microM). Prostaglandin E2 (1 microM) and PGF2alpha (1 microM) significantly stimulated progesterone (P4) production and reduced the levels of cell death in the cells cultured with or without tumor necrosis factor alpha (TNF)/interferon gamma (IFNG), in the presence and absence of FAS ligand (P < 0.05). Furthermore, DNA fragmentation induced by TNF/IFNG was observed to be suppressed by PGE2 and PGF2alpha. Prostaglandin E2 and PGF2alpha also attenuated mRNA expression of caspase 3 and caspase 8, as well as caspase 3 activity (P < 0.05) in TNF/IFNG-treated cells. FAS mRNA and protein expression were decreased only by PGF2alpha (P < 0.05). A specific P4 receptor antagonist (onapristone) attenuated the apoptosis-inhibitory effects of PGE2 and PGF2alpha in the absence of TNF/IFNG (P < 0.05). A PG synthesis inhibitor (indomethacin) reduced cell viability in PGE2- and PGF2alpha-treated cells (P < 0.05). A specific inhibitor of cyclooxygenase (PTGS), PTGS2 (NS-398), also reduced cell viability, whereas an inhibitor of PTGS1 (FR122047) did not affect it. The overall results suggest that PGE2 and PGF2alpha locally play luteoprotective roles in bovine CL by suppressing apoptosis of LSCs.     

Release of prostaglandins from healthy and sensitized guinea-pig lung and trachea by histamine.

The effects of histamine and its antagonists on the release of prostaglandin E and F2alpha (PGE and PGF2alpha) and the 15-keto-13,14-dihydro PGF2alpha/E (metabolites) were examined in minced and whole perfused guinea pig lung. Lung fragments released considerable amounts of prostaglandins into the incubation media with time alone: parenchyma more PGF2alpha than PGE, trachea more PGE than PGF2alpha. The levels of PGF2alpha found in the filtrates of both tissues on per gram basis were about the same, whereas the concentrations of PGE were several fold higher in the media of incubated trachea. In contrast to lung, trachea released only trace amounts of metabolites. These differences in synthesis and turnover are probably of importance for maintenance of the adequate ventilation-perfusion ratios. The process of sensitization caused a significant increase in the outflows of PGF2alpha and metabolites from the lung fragments. The PGE to PGF2alpha ratio was decreased in both parenchymal and tracheal tissues. Increased spontaneous release of prostaglandins was also found in whole perfused sensitized lung. This was consistent with the hypothesis that sensitization with antigen alters the biochemical properties of the organism. Incubation of lung fragments with histamine had only a small additional effect on the liberation of prostaglandins, since the baseline release was high due to the trauma of mincing. However, histamine perfusion of whole lung caused severalfold increase in the outflows of prostaglandins. Pretreatment with pyrilamine (histamine receptor 1 antagonist) decreased the subsequent release of PGF2alpha by histamine. On the other hand, pretreatment with metiamide (histamine receptor 2 antagonist) diminished the subsequent release of PGE. It is suggested that stimulation of histamine receptor 1 is predominantly (but not solely) related to the synthesis of PGF2alpha, and stimulation of the receptor 2 is related to the synthesis of PGE.     

Metabolism of prostaglandins E2 and F2 alpha by human fetal membranes.

Prostaglandin E2 (PGE2) is important in the early stages of human labour, leading particularly to cervical ripening and dilatation. The source of PGE2 is thought to be either the amnion or the decidua, but the chorion interposes between the amnion and the target tissues, namely the myometrium and cervix. In order to investigate the role of the chorion in modulating prostanoid production, [3H]PGE2 was added to the amnion side of fetal membranes, and the production of metabolites on both sides of the fetal membrane followed by HPLC. The major metabolite was 13,14-dihydro-15-oxo-PGE2 with smaller amounts of 13,14-dihydro-15-oxo-PGA2 and PGB2. The production of all metabolites of PGE2 was time dependent. [3H]PGF2 alpha, which is normally produced by the decidua, was also added to fetal membranes and found to be metabolised to 13,14-dihydro-15-oxo-PGF2 alpha and PGE2. These results suggest that the metabolic enzymes in the chorion may determine intra-uterine levels of prostaglandins, and may also determine the identity of the eicosanoids released by intact fetal membranes.     

Oleic acid lung injury increases plasma prostaglandin levels

To determine whether lung injury causes increased plasma prostaglandin (PG) levels, 35 rabbits received oleic acid and 35 served as controls. Half of each group also received 4 ml/kg of Intralipid over one hour and at least five in each subgroup received indomethacin 7.5 mg/kg. Arterial and venous plasma concentrations of PGE2, 6-keto-PGF1 alpha, and PGF2 alpha-M were measured. Venous PGE2 was significantly higher in the oleic acid-injured than in the normal lung group, 1560 +/- 270 (Mean +/- SEM) versus 880 +/- 140 pg/ml (p less than .05). Plasma levels were reduced by 50% with indomethacin, but PGE2 levels remained significantly higher than in the normal lung group, 850 +/- 180 versus 480 +/- 60 for arterial (p less than .05) and 820 +/- 140 versus 480 +/- 80 for venous (p less than .05), respectively. PGF2 alpha-M levels were significantly higher in the lung injury group, 240 +/- 50 versus 50 +/- 40 pg/ml for arterial (p less than .05) and 220 +/- 50 versus 95 +/- 40 for venous (p less than .05), respectively. These lung injury-related increases in PGE2 and PGF2 alpha-M appear related both to increased pulmonary production and to decreased pulmonary clearance. With Intralipid infusion, however, arterial PGE2 increased by 500 +/- 260 pg/ml compared to baseline (p less than .05) with no change in venous PGE2, indicating in this instance that the increase in arterial PGE2 levels is related to increased pulmonary production.     

Activity of prostaglandin biosynthetic pathways in rat pancreatic islets

Isolated pancreatic islets of the rat were either prelabeled with [3H]arachidonic acid, or were incubated over the short term with the concomitant addition of radiolabeled arachidonic acid and a stimulatory concentration of glucose (17mM) for prostaglandin (PG) analysis. In prelabeled islets, radiolabel in 6-keto-PGF1 alpha, PGE2, and 15-keto-13,14-dihydro-PGF2 alpha increased in response to a 5 min glucose (17mM) challenge. In islets not prelabeled with arachidonic acid, label incorporation in 6-keto-PGF1 alpha increased, whereas label in PGE2 decreased during a 5 min glucose stimulation; after 30-45 min of glucose stimulation labeled PGE levels increased compared to control (2.8mM glucose) levels. Enhanced labelling of PGF2 alpha was not detected in glucose-stimulated islets prelabeled or not. Isotope dilution with endogenous arachidonic acid probably occurs early in the stimulus response in islets not prelabeled. D-Galactose (17mM) or 2-deoxyglucose (17mM) did not alter PG production. Indomethacin inhibited islet PG turnover and potentiated glucose-stimulated insulin release. Islets also converted the endoperoxide [3H]PGH2 to 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and PGD2, in a time-dependent manner and in proportions similar to arachidonic acid-derived PGs. In dispersed islet cells, the calcium ionophore ionomycin, but not glucose, enhanced the production of labeled PGs from arachidonic acid. Insulin release paralleled PG production in dispersed cells, however, indomethacin did not inhibit ionomycin-stimulated insulin release, suggesting that PG synthesis was not required for secretion. In confirmation of islet PGI2 turnover indicated by 6-keto-PGF1 alpha production, islet cell PGI2-like products inhibited platelet aggregation induced by ADP. These results suggest that biosynthesis of specific PGs early in the glucose secretion response may play a modulatory role in islet hormone secretion, and that different pools of cellular arachidonic acid may contribute to PG biosynthesis in the microenvironment of the islet.     

Plasma levels of 15-keto-13,14-dihydro-prostaglandin E2 in patients with bronchogenic carcinoma

Plasma levels of the circulating metabolite of prostaglandin (PG) E2, 15-keto-13,14-dihydro-PGE2 (KH₂PGE₂), were determined radioimmunologically after conversion to the stable degradation product 11-deoxy-15-keto-13,14-dihydro-11, 16-cyclo-PGE2 (DKH2-cyclo-PGE₂). In healthy volunteers a plasma level of 25 + 2 pg/ml (mean ± S.E.M., n=24) was found. The plasma level of KH₂PGE₂ was significantly decreased after administration of acetylsalicylic acid (4 × 1 g/24 hours). A significant elevation of the plasma levels of the circulating metabolite of PGE₂ was observed in patients with bronchogenic carcinoma as compared to healthy controls, while no elevation was found in patients with chronic myeloid leukemia, lymphatic leukemia and non-Hodgkin lymphoma. The increased plasma levels of KH₂PGE₂ in the patients with bronchogenic carcinoma were independent of the clinical condition, histological type of tumor, tumor spread and therapeutic regimen. The results indicate that the elevated plasma level of the circulating PGE2 metabolite in patients with bronchogenic carcinoma is not an expression of malignant disease in general. On the other hand, the results do not suggest that the increase in the plasma level of KH₂ PGE₂ is a biochemical tumor marker closely related to a particular clinical feature of patients with bronchogenic carcinoma.     

Inhibition of uterine prostaglandin-F2 alpha production by bovine conceptus secretory proteins

The effect of bovine conceptus secretory proteins (CSP) on uterine prostaglandin (PG)-F2 alpha production was evaluated in dairy cattle following injection of estradiol-17 beta. Intrauterine injections of dialyzed serum proteins (Control, n = 5) or CSP (n = 5) were administered from days 15 through 18 post-estrus. Following intrauterine treatments on day 18, all cows were injected with E2 (3 mg) to stimulate uterine PGF2 alpha production. Plasma concentrations of progesterone (P4) and 15-keto-13,14-dihydro-PGF2 alpha (PGFM) were determined by RIA. The PGFM responses following E2 challenge were decreased (p less than 0.01) for cows receiving CSP versus serum proteins into the uterine lumen. Individual PGFM, P4 and cycle length responses are discussed. Data suggest that proteins secreted by the bovine conceptus suppress uterine PGF2 alpha production during pregnancy recognition in the cow.     

Patterns of prostaglandin synthesis and degradation in isolated superficial and proliferative colonic epithelial cells compared to residual colon

Prostaglandin (PG) synthesis and degradation were examined in different regions (epithelial versus non-epithelial structures) of the rat distal colon by both HPLC analysis of [14C] arachidonate (AA) metabolites and by specific radioimmunoassays. Intact isolated colonic epithelial cells synthesized mainly PGF2 alpha and TXA2, as monitored from the formation of its stable degradation product TXB2 (PGF2 alpha greater than TXB2 greater than 6-keto-PGF1 alpha, the stable degradation product of PGI2 = PGD2 = PGE2 = 13,14-dihydro-15-keto-PGF2 alpha). The profile of PG products of isolated surface epithelial cells was identical to that of proliferative epithelial cells. However, generation of PGs by surface epithelium was 2 to 3-fold higher than by proliferative cells both basally and in the presence of a maximal stimulating concentration (0.1 mM) of AA. The latter implied a greater synthetic capacity of surface epithelium, rather than differences due to endogenous AA availability. The major sites of PG synthesis in colon clearly resided in submucosal structures; the residual colon devoid of epithelial cells accounted for at least 99% of the total PGs produced by intact distal colon. The profile of AA metabolites formed by submucosal structures also differed markedly from that of the epithelium. The dominant submucosal product was PGE2. PGE2 and its degradation product 13,14-dihydro-15-keto-PGE2 accounted for 63% of the PG products formed by submucosal structures (PGE2 much greater than PGD2 greater than 13,14-dihydro-15-keto-PGE2 greater than PGF2 alpha = TXB2 = 6-keto-PGF1 alpha greater than 13,14-dihydro-15-keto-PGF2 alpha). By contrast, epithelial cells, and particularly surface epithelium, contributed disproportionately to the PG degradative capacity of colon, as assessed from the metabolism of either PGE2 or PGF2 alpha. When expressed as a percentage, epithelial cells accounted for 71% of total colonic PGE2 degradative capacity but only 23% of total colonic protein. Approximately 15% of [3H] PGE2 added to the serosal side of everted colonic loops crossed to the mucosal side intact. Thus, at least a portion of the PGE2 formed in the submucosa reaches, and thereby can potentially influence functions of the epithelium.     

Stimulation of the formation of 13,14-dihydroprostaglandin F2 alpha by gonadotropin in rat ovary

Effects of pregnant mare serum gonadotropin and human chorionic gonadotropin on the formation of 13,14-dihydroprostaglandin F2 alpha, a biologically active compound, were investigated in rat ovarian homogenate. The mass number of the compound, which was formed prostaglandin F2 alpha via 13,14-dihydro-15-ketoprostaglandin F2 alpha in rat ovarian homogenate but was not produced in rat homogenate, accorded with that of the authentic 13,14-dihydroprostaglandin F2 alpha by negative ion chemical ionization mass spectrometry. In the present experiment, the radioactivity of [3H]prostaglandin F2 alpha added to ovarian homogenate was decreased linearly and immediately until the incubation time of 10 min. The formation of 13,14-dihydroprostaglandin F2 alpha was increased up to 60 min. The formation of 13,14-dihydroprostaglandin F2 alpha from prostaglandin F2 alpha was markedly increased by pregnant mare serum gonadotropin and human chorionic gonadotropin. However, there was no additive or synergistic effect of these hormones. The formation of 13,14-dihydroprostaglandin F2 alpha from 13,14-dihydro-15-ketoprostaglandin F2 alpha weas also greatly stimulated by pregnant mare serum gonadotropin and human chorionic gonadotropin. The formation of 13,14-dihydro-15-ketoprostaglandin F2 alpha steeply declined until 24 h after treatment with human chorionic gonadotropin in pregnant mare serum gonadotropin-primed rats. In contrast, the formation of 13,14-dihydroprostaglandin F2 alpha was markedly increased until 24 h after human chorionic gonadotropin treatment, and the level was about 2.5-fold higher than that at 0 h, 48 h after injection of pregnant mare serum gonadotropin.