Histophysiological studies of prostaglandin F2alpha on isolated organs. I. Effect of prostaglandin F2alpha on the heart.

The physiological and histochemical effects of PGF2alpha on isolated rabbit hearts were examined. The results showed a positive inotropic effect. The coronary flow increased. From the histochemical studies, adenosine triphosphatase (ATP-ase) and succinic dehydrogenase activities were increased while that of alkaline phosphatase was decreased. Glycogen granules were depleted. These findings were discussed on a histophysiological basis.     

A novel effect of indomethacin on prostaglandin F2 alpha synthesis and metabolism by the human prostate

Human prostate tissue has been found to be an excellent organ for synthesizing and metabolizing prostaglandin F₂ alpha. Employing ³H-arachidonic acid as substrate, tritium incorporation into PGF₂ alpha and three different metabolites, namely, 15-keto-PGF₂ alpha, 13, 14-dihydro-PGFP₂ alpha, and 13, 14-dihydro-15-keto-PGF₂ alpha, has been shown. The identity of these substances was corroborated by gas chromatography and chemical ionization mass spectrometry. Indomethacin has been widely reported as an inhibitor of PGF₂ alpha synthesis. In our experiments, upon adding indomethacin, slight to no inhibition of PGF₂ alpha synthesis was seen. Instead, we found a highly significant increase in the incorporation of the tritium of arachidonic acid into 15-keto-PGF₂ alpha. We interpret these findings as evidence that the indomethacin may block not PGF₂ alpha synthetase, but the Δ13-reductase, thus causing the accumulation of this enzyme's substrate, 15-keto-PGF₂ alpha.     

Oxytocin stimulates prostaglandin F2alpha secretion and prostaglandin F synthase protein expression in porcine myometrial tissue

The possibility of PGF(2)alpha production and presence of prostaglandin F synthase (PGFS; PGD(2) 11-ketoreductase) was studied in control and oxytocin (OT)-stimulated myometrial slices isolated from cyclic (Days 14-16) and early pregnant (Days 14-16) sows. Oxytocin (10(-7) M) stimulated (p<0.01) PGF(2)alpha production in both cycling and early pregnant myometrial slices. Prostaglandin F(2)alpha release was higher (p<0.01) in control as well as OT-treated myometrium of early pregnant sows in comparison to cycling myometrium. Prostaglandin F synthase expression at protein level was evident in myometrial slices of cyclic as well as early pregnant sows. The signals of PGFS was stronger (p<0.05) in cycling myometrium exposed to OT compared to that of control. There were no significant differences (p>0.05) in PGFS protein expression between control and OT-stimulated myometrial tissue of early-pregnant sows. The results of this study indicate the local PGF(2)alpha synthesis and the presence of PGFS in porcine cycling and early pregnant myometrial tissue. In addition, OT increased PGD(2) 11-ketoreductase protein expression in myometrium harvested during the porcine estrous cycle. However, the OT-stimulated PGF(2)alpha myometrial secretion was observed in both, cycling and pregnant gilts.     

Effect of prostaglandin F2 alpha on the secretion of human prolactin

This study examines the role of PGF2a (prostaglandin F2alpha) in increasing the secretion rate of human prolactin. 11 women (mean gestational period, 18 weeks) seeking pregnancy termination were divided into 4 groups: 1) Group 1 consisted of 6 women who received 30 mg initially of PGF2a injected intramuscularly and an additional 15 mg after 24 hours if abortion had not occured; mean induction to termination period was 38 hours; 2) Group 2 comprised of 3 women who received PGF2a (500-1500 ug) via the transcervical route at 1 to 2 hourly interval; average number of injections was 20; mean induction to termination period, 24 hours; 3) Group 3 had 2 women receiving hypertonic saline by intraamniotic injection; mean induction to termination period was 51 hours; 4) Group 4 had 4 women who served as controls; mean observation period, 20 hours. Venous blood samples were heparinized in tubes at intervals of 2 to 3 hours. A homologous radioimmunoassay using highly purified human prolactin (for iodination and standards) plus rabbit antihuman prolactin measured serum prolactin. Spikes of serum prolactin up to 550 ng/ml were observed at irregular intervals in 5 women in Group 1; the spikes were less frequent and of smaller amplitude in Groups 3 and 4. The increase in serum prolactin was dramatic and more sustained in Group 2 patients and peaked towards the end of the prostaglandin infusion. Serum prolactin of Group 2 patients were significantly higher than those of Groups 3 and 4 (p0.01). 5 of 9 women whose pregnancies were terminated by PGF2a lactated. However, there was no significant difference between the mean serum prolactin levels in women who lactated (136 ng/ml) and those who did not (120 ng/ml). Although PGF2a is not a lactogenic hormone, this study shows that PGF2a stimulates the secretion of human prolactin during second trimester pregnancy. The fact that the transcervical route caused a significant increase in serum prolactin and the intraamniotic route did not is attributed to the increased systemic absorption of PGF2a following transcervical administration. No correlation was seen between the presence or absence of lactation and the serum prolactin level following pregnancy termination with PGF2a.     

Role of prostaglandin F2alpha in ovulation.

Using radioimmunoassay procedures, the levels of plasma, uterine and ovarian prostaglandin (PG) F2alpha, and those of plasma estradiol and progesterone were measured in intact, hysterectomized or ovariectomized immature female rats pretreated with PMS and subsequent HCG. Occurrence of ovulation was confirmed at 8 hours after the HCG administration not only in the intact rats but also in the hysterectomzied rats. The levels of plasma estradiol and progesterone, and of uterine and ovarian PGF2alpha rose with the PMS injection alone, but they did not reach the peaks before the HCG administration. Both plasma estradiol and uterine PGF2alpha showed a peak at 2 hours after the HCG injection. These peaks were antecedent 2 or 6 hours before the peaks of ovarian and plasma PGF2alpha, respectively. However, such increase of uterine PGF2alpha does not seem to be indispensable for ovulation, because ovulation could occur in the hysterectomized rats. The levels of ovarian PGF2alpha showed a high plateau from 4 to 8 hours after the HCG injection, and then rapidly decreased after ovulation. The levels of plasma PGF2alpha peaked not only in the intact rats but also in the hysterectomized rats at 8 hours after the HCG treatment. But in the ovariectomized rats, this plasma PGF2alpha peak at 8 hours disappeared and there was no statistical change of plasma PGF2alpha throughout the PMS-HCG treatment. Plasma progesterone gradually increased and reached the maximum at 10 hours after the HCG injection. These results conclude that the main source of increased plasma PGF2alpha during the ovulatory process induced with the PMS-HCG treatment is the ovary, and it is strongly suggested that a rapid increase of PGF2alpha in the ovary may play some important role(s) in the ovulatory process.     

Specific binding sites for prostaglandin D2 on human platelets.

³H-PGD₂ was biosynthesized from ³H-arachidonate and used to study the binding of PGD₂ to intact human platelets. The binding of ³H-PGD₂ to platelets was rapid, being essentially complete within two min. Bound ³H-PGD₂ PGD₂. Scatchard analysis of concentration-dependent binding indicated a single class of binding sites with a dissociation constant (K_D) of 4.12 × 10^?7M and a capacity of 760 sites per platelet. The relative ability of PGD₂, PGE₂, PGE₁ and PGI₂ to displace ³H-PGD₂ bound to these sites was 100:2:2<1. We conclude therefore, that these PGD₂ binding sites are specific for PGD₂ and independent of those previously demonstrated to recognize ³H-PGI₂ and ³H-PGE₁.     

Endothelin-1 stimulates prostaglandin F2 alpha release from human endometrium

Despite a key role in the pathogenesis of menorrhagia, the factors controlling the uterine vascular bed are poorly understood. This study has assessed the effects of the potent vasoconstrictor endothelin (ET)-1 on prostaglandin (PG) release from human endometrial explants in short-term culture. There was no significant difference between the production of PGF2 alpha in proliferative and secretory tissue (1709 and 2434 pg/mg/h--median values, range 70,3745 and 219,6700 pg/mg/h). Less PGE was released than PGF2 alpha, and the amount did not vary with the phase of the menstrual cycle (308 and 296 pg/mg/h (range 65,387 and 105,429) for proliferative and secretory tissue). ET-1 (10 and 100 nM) and arachidonic acid (AA, 30 microM), stimulated PGF2 alpha release from proliferative, but not secretory endometrium, by 78%, 86% (P less than 0.01) and 80% respectively, compared with control tissue. No effect was seen on PGE release. ET-1 may play a role in the local control of the endometrial vascular bed either directly, or via the release of PGF2 alpha.     

Lack of negative cooperativity among binding sites for prostaglandin F2alpha in bovine corpus luteum cell membranes.

The Scatchard analysis of equilibrium prostaglandin (PG) F₂α binding revealed that the binding was heterogeneous. The Hill plot of the same data had a slope of 0.68. This suggested that the heterogeneous nature of [³H] PGF₂α binding was either due to the presence of negative cooperativity or to the presence of two groups of independent binding sites. The kinetic experiments revealed that the presence of excess unlabeled PGF₂α in a diluting medium had no effect on dissociation rates at 25 fold dilution and it even retarded dissociation at higher dilutions. Furthermore, the observations that the low affinity PGF₂α binding sites can exist in the absence of high affinity binding sites and high affinity binding sites can be selectively abolished by treatment with N-ethylmaleimide suggest that negative cooperativity was not responsible for heterogeneous [³H] PGF₂α binding.     

Peroxisomal chain-shortening of prostaglandin F2 alpha

We have recently reported that prostaglandin F2 alpha can be chain-shortened by isolated rat liver peroxisomes. In the present study it is further established by cell fractionation experiments that the enzymes involved in this reaction are localized to peroxisomes. Under the conditions employed, the highest activity was found in the light mitochondrial fraction. Further fractionation of the light mitochondrial fraction by sucrose density gradient centrifugation showed that the prostaglandin oxidation activity comigrated with peroxisomal marker enzymes. Di(2-ethylhexyl)phthalate treatment resulted in a tenfold increased capacity for the conversion of prostaglandin F2 alpha into tetranorprostaglandin F1 alpha. The reaction was not inhibited by KCN. The reaction was further characterized with respect to cofactor requirements. The prostaglandin oxidation was found to be completely dependent on NAD, CoA, ATP, Mg2+ and was stimulated by FAD. Incubation of prostaglandin E2 with peroxisomes resulted in conversion into several products. After alkaline hydrolysis, one of these was identified as tetranorprostaglandin B1.     

Ability of human plasma to inhibit prostaglandin F2 alpha in asthma

Human plasma has been reported to inhibit the conversion of arachidonic acid into prostaglandin (PG) E2 and PGF2 alpha. In the present study the plasma inhibitory activity was determined in three groups (16 each) of plasma obtained from normal healthy volunteers, treated asthmatics and untreated asthmatic patients. The result showed that plasma from all three groups were equally effective in inhibiting the biosynthesis of PGE2. Plasma of normal volunteers and treated asthmatics also inhibited PGF2 alpha biosynthesis. In contrast the plasma obtained from untreated asthmatics was considerably less active in inhibiting the biosynthesis of PGF2 alpha than plasma from the other two groups.     

The effect of prostaglandin F2 alpha on third stage labor.

The effects of intramyometrially injected PGF2 alpha intravenous Ergometrin and no treatment were compared during 3rd stage labor in 140 patients. In comparison with Ergometrin or no treatment, PGF2 alpha significantly reduced the duration of 3rd stage labor, blood loss, incidence of subinvolution and subfebrility.     

Multiple classes of prostaglandin F2 alpha binding sites in subpopulations of ovine luteal cells

A cryostorage procedure was developed to provide ovine luteal cells throughout the period of seasonal anestrus. Corpora lutea obtained from midluteal phase, superovulated ewes were dispersed enzymatically. Some dispersed cells were fractionated into subpopulations by elutriation. Dimethylsulfoxide (7.5% final concentration) in Hanks' buffered saline was added to cells at 4 degrees C, and dispersed cell preparations were frozen in a programmable cell freezer and stored at -196 degrees C. After recovery from cryopreservation, cell viability and prostaglandin F2 alpha (PGF2 alpha) binding characteristics of thawed cells were not different from those of corresponding fresh cells. Additionally, thawed cells retained the capacity to attach to culture dishes and retained responsiveness of progesterone secretion to prostaglandin E2 (PGE2) and ovine luteinizing hormone (LH), although rates of progesterone secretion were attenuated in thawed compared with fresh cells. The cryopreservation procedure will prove useful to relieve constraints in utilization of ovine luteal cells arising from reproductive seasonality in sheep. Cells retrieved from cryostorage were evaluated by studying PGF2 alpha binding characteristics. From saturation analyses (increasing amounts of radiolabeled PGF2 alpha) of PGF2 alpha binding to unfractionated cells, we detected a single class of high affinity binding sites (Kd = 17.4 +/- 2.3 nM) in addition to the nonspecific binding component. Using displacement analyses (constant radiolabeled PGF2 alpha and increasing amounts of unlabeled PGF2 alpha) and unfractionated cells, we detected additional binding sites of lower affinity (Kd = 409 +/- 166 nM) as well as the nonspecific binding component. Small luteal cells obtained by elutriation, which were essentially devoid of large cell contamination, had only low affinity binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of pregnancy-specific protein B on prostaglandin F2 alpha and prostaglandin E2 release by day 16-perifused bovine endometrial tissue

Five normal estrous cycling multiparous non-lactating Brahman cows were utilized to determine if pregnancy-specific protein B (PSPB) would alter prostaglandin F2 alpha (PGF) and prostaglandin E2 (PGE) synthesis/release by endometrial tissue. The uterine horn ipsilateral to the corpus luteum was excised on Day 16 of the estrous cycle. Endometrial tissue (200 mg wet wt) was cultured in Nutrient Mixture F-10 medium in a perifusion system. The tissue and medium were aerated with 95% O2: 5% CO2 and temperature was maintained at 39 degrees C. The medium flow rate was 100 microliters/min and fractions were collected at 20 min intervals. After a 120 min settling period, tissue culture continued with: 1) control (medium only); 2) 2 micrograms [Asu1,6]-oxytocin/ml medium for 1 h; 3) 4 or 8 micrograms PSPB/ml medium for 2 h; or 4) 4 or 8 micrograms PSPB/ml medium for 2 h plus 2 micrograms oxytocin/ml medium during the second h. Differences in PGF and PGE secretion rate were not found between 4 and 8 micrograms PSPB. Therefore, groups were combined and data were analyzed according to tissue not receiving PSPB (control); receiving PSPB and receiving PSPB plus oxytocin. A nonsignificant rise (p greater than 0.10) in PGF secretion was observed in response to PSPB and PSPB plus oxytocin above the control by the end of the perifusion period (263.7 +/- 41.7, 220.0 +/- 41.7 and 166.1 +/- 41.7 pg/(100 mg tissue/min), respectively). Treatment with PSPB alone elevated (p less than 0.05) PGE secretion rate above control by 100 and 160 min post-removal of PSPB treatment. Treatment with PSPB plus oxytocin elevated (p less than 0.05) PGE release above control by 20 min after starting oxytocin treatment and continued throughout the duration of the perifusion. Pregnancy-specific protein B plus oxytocin-induced PGE release was greater (p less than 0.05) than PSPB alone after initiating the oxytocin treatment until 20 min after removal of the treatments. However, no further differences between PSPB alone and PSPB plus oxytocin treatments were detected throughout the remainder of the perifusion period. It appears that PSPB tends to elevate PGF release and significantly elevates PGE release from Day 16 endometrial tissue.     

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.     

Effects of indomethacin, prostaglandin E2, prostaglandin F2 alpha and 6-keto-prostaglandin F1 alpha on hatching of mouse blastocysts

The present study has been performed to investigate how PGs would participate the hatching process. Effects of indomethacin, an antagonist to PGs biosynthesis, on the hatching of mouse blastocysts were examined in vitro. Furthermore, it was studied that prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) or 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were added to the culture media with indomethacin. The hatching was inhibited by indomethacin yet the inhibition was reversible. In the groups with indomethacin and PGE2, no improvement was seen in the inhibition of hatching and the inhibition was irreversible. In the groups with indomethacin and PGF2 alpha, inhibition of hatching was improved in comparison with the group with indomethacin. In the groups with indomethacin and 6-keto-PGF1 alpha, no improvement was seen. The above results indicated that PGF2 alpha possibly had an accelerating effect on hatching and a high concentration of PGE2 would exert cytotoxic effect on blastocysts.