Effect of prostaglandin F2α on propulsive activity of the isolated segmental colon of the guinea-pig

The effects of prostaglandin F_2α (PGF_2α) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated.Using experimental conditions under which spontaneous propulsive activity was negligible, PGF_2α (5×10⁻⁸×1×10⁻⁶M), added to the bathing medium, increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1×10⁻⁷g/ml).The contractions produced by PGF_2α(5×10⁻⁷ − 1×10⁻⁵M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1×10⁻⁷g/ml).From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF_2α may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.     

Prostaglandin synthesis by rat uterine homogenates in the presence of copper ions,and the effects of indomethacin and salicylic acid

While no significant effects on the in vitro production of PGF₂α by homogenates of rat estrous uteri were observed in the presence of 10⁻³ and 10⁻⁶M Cu²⁺, the presence of Cu²⁺ at 10⁻⁴ and 10⁻⁵M was found to stimulate production with maximal synthesis of PGF₂α occurring with 10⁻⁴M Cu²⁺. By contrast, the synthesis of PGE₂ and PGI₂ (determined as 6-keto PGF₁α) were unaffected at all of the different Cu²⁺ concentrations used. When indomethacin and salicylic acid were tested for their effects on the Cu²⁺-mediated levels of PG synthesis by the homogenates, indomethacin (at 20μM) was found to cause similar pronounced decreases in PGF₂α, PGE₂ and 6-keto PGF₁α whereas salicylic acid (400μM) showed preference towards suppressing PGE2 and 6-keto PGF₁α production.     

Apparent differences in tryptophan hydroxylation by cockroach (periplaneta americana) nervous tissue and rat brain

Tryptophan hydroxylation in cockroach (Periplaneta americana) nervous tissue was measured and compared to the hydroxylation of tryptophan in rat brain. Tryptophan hydroxylation in both tissues requires a pterine cofactor, and is inhibited by p-chlorophenylalanine. The molecular weight of the protein responsible for hydroxylation of tryptophan in cockroach nervous tissue obtained from gel filtration was estimated to be 54,000.The pH optima and enzyme kinetics differed greatly between the two hydroxylases. Hydroxylation of tryptophan by the enzyme obtained from cockroach tissues incubated with dimethyltetrahydropterine had a pH optimum of about 5.8–5.9 and a K_m in crude enzyme preparations of 2.6 × 10⁻⁶ M and is activity was substrate inhibited above 10⁻⁴ M tryptophan. Hydroxylation of tryptophan by the enzyme obtained from rat brain incubated with dimethyltetrahydropterine had a pH optimum of about 6.5–7.0, a K_m of about 6.7 × 10⁻⁴ M and exhibited no substrate inhibition at tryptophan concentrations up to 2 × 10⁻³ M.When incubated with biopterin, the presumed natural cofactor, the hydroxylase from cockroach tissues had a K_m of about 6.8 × 10⁻⁵ M and no substrate inhibition occurred at tryptophan concentrations up to 2 × 10⁻³ M. Under the same conditions rat hydroxylase had a K_m of 1.1 × 10⁻⁵M and substrate inhibition occurred above 10⁻⁴ M tryptophan.Unlike the mammalian situation, administration of tryptophan peripherally did not change the 5-hydroxytryptamine concentration in cockroach nervous tissue, but did increase tryptophan levels. The low V_max values of the cockroach hydroxylase and the inability of administered tryptophan to elevate 5-hydroxytryptamine levels suggest that in the cockroach hydroxylation of tryptophan itself may be the limiting factor in the biosynthesis of 5-hydroxytryptamine.     

Production of prostaglandins by cells in vitro: radioimmunoassay measurement of the conversion of arachidonic acid to PGE2 and PGF2 alpha

A specific radioimmunoassay has been applied to the measurement of the conversion of arachidonic acid to PGE₂ and PGF_2α. PGE₂ and PGF_2α biosynthesis was linearly related to the amount of arachidonic acid added and was significantly inhibited by indomethacin in concentrations as low as 10^?10 M. Sonicated Hela, L, and HEp-2 cells synthesized 244.0, 42.3, and 22.6 ng PGE₂ per mg of protein, but made substantially less PGF_2α.     

Abrogation by prostaglandin F2alpha of LH-stimulated cyclic AMP accumulation in isolated rat corpora lutea of pregnancy.

Corpora lutea explanted from rats on the sixth day of pregnancy responded to luteinizing hormone (LH; 5 μg/ml) in vitro with a two- to five-fold increase in cellular cyclic AMP (cAMP) concentration. The maximal cAMP level was reached within 60 min and maintained to the end of the 2 hr-incubation. On incubation with prostaglandin F_2α (PGF_2α) in addition to LH, this rise in cAMP accumulation was prevented. For significant suppression, 1.4 × 10^?5M PGF_2α was required. In the absence of LH, PGF_2α (4.2 × 10^?5M) caused no change in cellular cAMP. Addition of PGF_2α (4.2 × 10^?5M) to the incubation medium after the maximal response to LH was attained, caused the cAMP concentration to return to its basal level within 15 min. This abrogation of LH-stimulated cAMP accumulation represents the earliest and hence possibly the triggering event in PGF_2α-induced luteolysis.     

Inhibition of membrane transport ATPases by halenaquinol,a natural cardioactive pentacyclic hydroquinone from the sponge Petrosia seriata

Halenaquinol, a natural cardioactive pentacyclic hydroquinone from the sponge Petrosia seriata, was found to be a powerful inhibitor of the rat brainstem and of the rat brain cortex Na⁺, K⁺-ATPases and the rabbit muscle sarcoplasmic reticulum Ca²⁺-ATPase with I₅₀ values of 7.0×10⁻⁷, 1.3×10⁻⁶ and 2.5×10⁻⁶ M, respectively. Halenaquinol also inhibited K⁺-phosphatase activity of the rat brain cortex Na⁺, K⁺-ATPase with an I₅₀ value of 3×10⁻⁶ M. Ouabain-insensitive Mg²⁺-ATPase activity of the microsomal fraction of the rat brain cortex was weakly inhibited by halenaquinol. Inhibition was irreversible, dose- and time-dependent. Naphthohydroquinone fragment in structures of halenaquinol, related natural and model compounds was very important for an inhibiting effect.     

Effects of estriol on PGF2α output by cultures of human endometrium and endometrial cells

We have shown that the rate of release of PGF_2α by monolayer cultures of epithelial cells from proliferative endometrium is markedly elevated by addition of estradiol to the medium. In cultures maintained in HAM F-10 medium containing charcoal stripped calf serum, estradiol (10⁻⁸M) increased the levels of PGF_2α several fold during the second and third days in culture. Similar responses were obtained with estradiol at 10⁻¹⁰M concentration.When this system was used to compare the effects of estradiol and estriol at equal concentrations (10⁻⁸M), similar elevation (10–16-fold) of PGF_2α levels were noted during 3 consecutive days in culture. When cultures of epithelial cells derived from secretory endometrium were used for these tests, estriol was as effective as than estradiol in elevating PGF_2α levels in the medium.When the effects of estradiol and estriol were compared using fragments of secretory endometrium in organ culture, the increases in PGF_2α levels noted in the medium were about equal (2- to 10-fold) for the two estrogens at the same concentration (10⁻⁹−10⁻⁸M).Exposure of the tissue to either estradiol or estriol for only 1 h resulted in increases in PGF_2α output for the following 3 days.These results clearly show that estriol is as effective as estradiol in stimulating PGF_2α output by human endometrial tissue.     

Properties of [3H] prostaglandin F2α binding to dispersed bovine luteal cells

Intact viable bovine luteal cell suspensions prepared by collagenase digestion of luteal tissue were used in studying the selected properties of [³H] prostaglandin (PG) F_2α binding and compared with those observed in plasma membranes. [³H]PGF_2α specific binding to luteal cells was a rapid (K₁ = 8.4 × 10⁴M^?12αS^?1), reversible (K_?1 = 1.8 × 10^?4S^?1) and saturable process at 24°. There was a single class of receptors with an apparent dissociation constant of 10.6 nM and 1.8 × 10⁵ receptors per cell. The presence of increasing amounts of unlabeled PGs inhibited [³H]PGF_2α binding in a dose-dependent manner. The potency order for this inhibition was: (15S) 15-methyl-PGF_2α methyl ester > ICI-80,996 > PGF_2α > ICI-81,008 > PGF_1α > PGE₂, (15S) 15-methyl-PGE₂ methyl ester > PGF_2α metabolites > other PGs, PGF_1α metabolites and PGE metabolites. Other than the homegeneous nature of binding and a greater association rate in cells, the rest of the [³H]PGF_2α binding properties in cells were in good agreement with those observed in plasma membranes.     

Role of prostaglandin F2α in modulation of LH-stimulated steroidogenesis in vitro in different types of rat and ewe corpora lutea

An inhibitory effect of PGF_2α at a dose of 7 × 10^?7 M on LH stimulated synthesis of progesterone was observed $\text{in vitro}$ after incubation of pseudopregnant rat ovaries for a period of 2 hours. A similar effect was seen with cyclic and gestant ewe corpora lutea at the same dose of PGF_2α. This effect was observed both in the secretion of progesterone and on the amount of progesterone present in the tissue. This inhibitory effect of PGF_2α on LH stimulated progesterone synthesis may explain the modification in the time course for gonadotropin action in luteal tissue at high and low doses.     

Effects of estradiol and progesterone on uterine prostaglandin levels in the pregnant rat

Prostaglandin D₂ was found to be a potent inhibitor of B-16 melanoma cell replication $\text{in vitro}$. The inhibition was dose-dependent between 3×10^?9M and 3×10^?6M (IC_50～ 0.3 μM after 6 days). On a molar basis, PGD₂ was a better inhibitor than PGA₂ or 16,16-dimethyl-PGE₂-methyl ester (di-M-PGE₂) and in higher concentrations (10^?6?10^?7M), comparable to retinoic acid. In higher concentrations, PGD₂ inhibited DNA, RNA and protein synthesis. The B-16 melanoma cell line which we used synthesized arachidonic acid metabolites which comigrated with PGA₂, PGD₂, PGE₂ and PGF_2α on a thin layer chromatography system.     

Spectral characteristics of human fetal adrenal microsomes.

Investigations of human fetal adrenal gland microsomes indicated that a carbon monoxide binding pigment had an absorption maximum of 446 to 448 nm. This pigment, upon heat treatment at 37°C was degraded to the form of cytochrome p-420. NADPH reduced cytochrome p-450 slowly and completely. Typical concentrations of 0.75 and 0.16 nmoles/mg protein cytochrome P-450 and b₅, respectively, were observed. Reduced ethylisocyanide spectra were similar to those of rat hepatic microsomes with absorption maxima at 430 as well as 454 nm. Typical type I spectral changes were observed with progesterone, 17-α-OH-progesterone, pregnenolone and androstenedione when these steroids were added to the sample cuvettes. Androstenedione exhibited an apparent spectral dissociation constant (K_S) of 5×10⁻⁶M pregnenolone and progesterone exhibited higher affinities with apparent dissociation constants of 1.1×10⁻⁷M and 1.8×10⁻⁷M, respectively. The maximal absorbance change induced by androstenedione was lower (Emax = 0.027 per mg protien) than the changes in absorbance maxima induced by pregnenolone or progesterone (Emax = 0.060 and 0.047 per mg protein, respectively) when saturating concentrations of these steroids were added to the sample cuvettes. Ethylmorphine and aminopyrine (10⁻³M final concentrations) did not exhibit observable spectral changes; however, type II spectra could be elicited with aniline and nicotinamide and apparent dissociation constants of 3.5×10⁻²M and 2.5×10⁻²M, respectively, were obtained.     

Characterization of prostaglandin F2α receptor of mouse 3T3 fibroblasts and its functional expression in Xenopus laevis oocytes

Prostaglandin (PG) F_2α increased [³H]thymidine incorporation into quiescent NIH 3T3 cells, stimulated phosphoinositide breakdown, and raised intracellular Ca²⁺ concentration ([Ca²⁺]_i) in a dose-dependent manner with ED₅₀ values of 2.0 × 10^?8 M, 4.6 × 10^?8 M, and 7.5 × 10^?8 M, respectively. The increase in [³H]thymidine incorporation with PGF_2α was additive with that seen with epidermal growth factor (EGF) or insulin. The peak [Ca²⁺]_i increase with PGF_2α was still obvious in the absence of extracellular Ca²⁺ and was insensitive to islet activating protein (IAP) pretreatment. Membranes prepared from NIH 3T3 cells exhibited a specific binding for PGF_2α, which was sensitive to GTP_γS but not sensitive to IAP pretreatment. Xenopus laevis oocytes injected with NIH 3T3 cell mRNA between 18S and 28S rRNA fractionated by sucrose gradient, expressed a PGF_2α-specific Cl^? current when examined by voltage clamp. This Cl^? current was also insensitive to IAP pretreatment and not affected by extracellular Ca²⁺ concentration ([Ca²⁺]_o). These results indicate 1) that the NIH 3T3 cells expressed a specific PGF_2α receptor which is linked to phosphoinositide-specific phospholipase C (PLC) activation and to mobilization of Ca²⁺ via an IAP-insensitive G-proteins(s), 2) that this PGF_2α receptor may play an active role in the proliferation of NIH 3T3 cells, and 3) that this PGF_2α receptor can be expressed in the oocyte system. © 1993 Wiley-Liss, Inc.     

Prostaglandins of the F series are extremely powerful growth factors for primary neonatal rat hepatocytes

At low concentrations (i.e., 10^?12–10^?9 mol/l), PGF_1α and PGF_2α very intensely stimulated both the DNA-synthetic and mitotic activities of hepatocytes in 4-day-old primary cultures of neonatral rat liver. DNA replication was more intensely enhanced by PGF_2α than by PGF_1α, whereas mitotic activity was nearly equally affected by the two prostaglandins. On the whole, the growth-promoting activity of PGF_1α used by itself or in equimolar mixtures with other prostaglandins ($\text{e}$. $\text{g}$., A₁, E₁, $\text{etc}$.) mimicked that of arachidonic acid we previously reported (1). On a molar basis, PGF_2α by itself stimulated hepatocytes′ DNA synthesis is more powerfully than arachidonate did, and when used in equimolar mixtures with other prostaglandins was at least as potent as arachidonic acid. These observations establish prostaglandins of the F series as quite powerful commitment factors and, though by a lesser degree, also intracycle regulators for neonatal rat hepatocytes in primary culture. However, the understanding of the role(s) of prostaglandins of F and other series in the physiological control of hepatocytes′ proliferative activation must wait the clarification of their interaction(s) with other arachidonate derivative(s) and polypeptide growth factor(s) which also may be involved in the process.     

The effects of prostaglandins E2 and F2α on synaptosomal accumulation and release of 3H-norepinephrine

Prostaglandins (PG) of both the E and F series may serve as modulators of norepinephrine (NE) release from peripheral sympathetic neurons. We have studied the effects of PGE₂ and PGF_2α on the accumulation and release of ³H-NE in the CNS using synaptosomes isolated from rat hypothalami.The release of ³H-NE from synaptosomes superfused with Krebs-Ringer bicarbonate buffer was multiphasic with an initial fast release phase followed by a slower release. Raising KC1 concentration of the superfusion medium to 56mM during the slow release phase is known to stimulate ³H-NE release. PGE₂ (1 × 10^?6M) attenuated ³H-NE release during the fast phase and reduced the amount of ³H-NE released due to KC1 stimulation. At lower concentrations of PGE₂ there was no change in the release profile. PGF_2α was without effect on ³H-NE release at all concentrations tested.The accumulation of ³H-NE was significantly diminished by PGE₂ at a concentration of 1 × 10^?6M, while a lower concentration (1 × 10^?7M) was ineffective. PGF_2α had no effect on ³H-NE accumulation at all concentrations investigated.     

Interactions of prostaglandins with hepatic microsomal cytochrome P-450

The spectral changes associated with the addition of prostaglandins (PGs) to hepatic microsomes from guinea pigs and rats were examined. PGA₁, PGA₂, PGE₁, PGE₂, PGF_1α and PGF_2α when added to guinea pig liver microsomes exhibited type I spectra. The binding affinities as determined from spectral dissociation constants (K_s) were highest with PGA₁ and PGA₂. With liver microsomes from control or 3-methyl-cholanthrene (MC)-treated rats, PGs did not yield type I spectra; however, in this case a $\text{weak}$ spectrum, designated here as type “II” was at times observed, With microsomes from phenobarbital (Pb)-treated rats only PGA₁ and PGA₂ yielded type I spectra; again in absence of type I spectrum, a weak type “II” was occasionally observed. The addition of PGA₁ and PGA₂ to liver microsomes from Pb-treated rats inhibited the microcomal mediated hydroxylation of hexobarbital. The inhibition by PGA₁ was competitive; the K_i = 8.2 × 10^?4 M was found to be similar in magnitude to the K_s = 7.3 × 10^?4 M of PGA₁ observed with rat liver microsomes. These observations suggested that PGs particularly of the A series interact with the hepatic microsomal cytochrome P-450 monooxygenase system.     

The presence of discrete receptors for prostaglandin F2 alpha in the cell membranes of bovine corpora lutea.

The cell membranes isolated from bovine corpora lutea bound ³H-prostaglandin (PG) F₂α with high affinity and specificity. The specific binding of ³H-PGF₂α was detectable at 10^?10M added ³H-PGF₂α and reached saturation at 10^?7M to 10^?6M. Unlabeled PGF₂α, as low as 10^?9M, inhibited the binding of ³H-PGF₂α with complete inhibition occurring at 10^?6M. The Scatchard analysis of equilibrium binding data revealed that the PGF₂α receptors are heterogeneous: Kd₁?5.1 × 10^?9M, n?289 fmoles/mg protein; Kd₂?1.8 × 10^?8M, n?780 fmoles/mg protein. The relative affinities of various other PGs for binding to PGF₂α receptors were (PGF₂α?100%): PGF₁α?17.5; PGE₁?0.8; PGE₂?22.4; PGA₁?0.007; PGB₁?0.01. The specificity and affinity of ³H-PGF₂α binding is consistent with the possibility that this receptor interaction may reflect an initial event in the action of PGF₂α as a luteolytic agent.     

Characteristics of leukotriene (LT) and hydroxy eicosatetraenoic acid (HETE) synthesis in human leukocytes in vitro: Effect of arachidonic acid concentration

Suspensions of human blood leukocytes and platelets were stimulated with the ionophore A23187 in the presence of increasing concentrations of arachidonic acid. Nine metabolites of the 5-,12- and 15-lipoxygenase and the cyclooxygenase pathways were analyzed by high performance liquid chromatography in order to study the rate-limiting steps and other characteristics of their biosynthesis. The data indicate that the LTA₄ hydrolase and the LTA₄ glutathione transferase activities are respectively the limiting factors in the synthesis of LTB₄ and LTC₄. At high substrate concentrations (5 × 10⁻⁵M and above), the 5-lipoxygenase activity was inhibited whereas the synthesis of the 15-HETE (15-lipoxygenase product) increased linearly up to the highest concentration tested (3 × 10⁻⁴M). The data also indicate that contrary to 5-HETE and LTs, 15-HETE is not formed upon stimulation with the ionophore, but only following incubation with exogenous arachidonic acid (20 μM and above), pointing out major differences in the synthesis of 5- and 15-lipoxygenase products.     

Prostaglandin Biosynthesis from Endogenous Precursors in Rabbit Kidney

THIS report describes the biosynthesis of the naturally occurring renal prostaglandins E₂ (PGE₂) and F_2α (PGF_2α)^1,2 by homogenates and slices of rabbit renal medulla, from endogenous precursors. I have confirmed that rabbit renal cortex contains little prostaglandin and cannot synthesize them from endogenous lipids³. Hamberg has reported that arachidonic acid, which is converted to PGE₂ and PGF_2α by enzymes present in ram seminal vesicles⁴, can be efficiently converted to PGE₂ and PGF_2α by homogenates of rabbit renal medulla³. I have now confirmed that arachidonic acid, added to such medullary homogenates, can increase the quantities of prostaglandins synthesized. There was no evidence that the major prostaglandin biosynthesized, PGE2, was further metabolized to inactive products.     

Effect of various prostaglandins on the release of arachidonic acid from cultured fibroblasts

Effect of various prostaglandins on the release of arachidonic acid from [¹⁴C]arachidonic acid labeled fibroblasts was studied. Prostaglandin(PG) F_2α was found to enhance the release of radioactive arachidonic acid from the cells. The stimulatory effect was dose dependent, and was greater than that of bradykinin. The active compounds can be ranked in potency for the release of arachidonic acid from the pre-labeled cells per cent of control: PGF_2α(200.1%)>PGF_1α (141.8%)>PGD₂ (137.1%)>thromboxane B₂ (113.7%)>PGE₂ (109.4%). On the other hand, PGI₂ showed a strong inhibitory effect on the arachidonic acid release from the pre-labeled cells (the value was only 69% of the control), while 6-ketoPGF_1α, an end metabolite of PGI₂, had no effect.     

Prostaglandin biosynthesis by the rat uterus during the oestrus cycle, temporal correlation with plasma oestradiol and progesterone concentrations, identification of 6 keto PGF1α as the major metabolite

Prostaglandin biosynthesis was studied in the rat uterus during the oestrous cycle. Uterine homogenates were incubated for 20 minutes in the presence of exogenous substrate (2.10⁻⁵M). PGF_2α and PGE₂ were measured by R.I.A.. A sharp peak PGF_2α and a smaller peak of PGE₂ were observed at prooestrus, 20 h. Another small PGE₂ peak occurred at dioestrus II, 15 h. The lowest values of both PGs were found on dioestrus, 15 h. Plasma oestradiol concentration were highest at proestrus, 15 h and 20 h. A sharp progesterone peak occurred at prooestrus, 20 h. The PGF_2α peak is next to the oestradiol peak and is superimposable or lags slightly beyond the progesterone peak.Incubation with ¹⁴C arachidonic acid and subsequent analysis of extracts by TLC and scanning showed that the major metabolite is PGI₂, identified as 6 keto PGF_1α. The conversion rate of arachidonic acid into 6 keto PGF_1α is 5 times higher than into PGF_2α. 6 keto PGF_1α was further identified by GC/MS. No significant difference was observed between 6 keto PGF_1α production during oestrus and dioestrus.