Effect of prostaglandins A1, A2, B1, B2, E2 and F2 alpha on human umbilical cord vessels

Human umbilical blood vessels have the ability to close spontaneously following delivery at term. It has been suggested that prostaglandins may have a possible physiological role in its closure. This study investigates the effects of 6 naturally occurring prostaglandins (A1, A2, B1, B2, E2, F2a) on the umbilical blood vessels. Umbilical cords were collected from cases of normal spontaneous vaginal deliveries and cesarian section at term. A total of 41 strips of umbilical arteries and 26 strips of umbilical veins from 24 cords were used. A 4-point bioassay method was used to compare the potency of prostaglandins A1, A2, B1 and F2a with PGE2. The effect of Polyphloretin Phosphate (PPP) on prostaglandin-induced contractions was studied on umbilical artery strips from 12 cords. The 6 prostaglandins exerted a stimulant effect on the isolated strips of human umbilical arteries. Prostaglandin B2 was the most potent compound on the umbilical vein, followed by PGA2. PPP in the concentration range of 10 to 40 mcg/ml completely eliminated the responses of PGE2, F2a, A1, A2, and B1. Responses to PGB2 were considerably but not completely abolished. PPP (up to 40 mcg/ml) did not affect contractions induced by 5-hydroxytryptamine, suggesting the presence of discrete receptor sites in the blood vessels for different pharmacologically active compounds. This is the first report of the constrictor effect of PGA and PGB compounds. These naturally occuring prostaglandins with high potencies (compared with other prostaglandins and other vasoactive substances) may play a role in spontaneous closure of umbilical vessels. PGE1, E2, F1 and F2a are found in umbilical blood vessels obtained at term.     

Effect of prostaglandins A1, A2, B1, B2, E2 and F2α on human umbilical cord vessels

The effect of six naturally occurring prostaglandins on isolated umbilical arteries and veins has been studied. All six prostaglandins had a constricting effect on the umbilical vessels. On the umbilical artery preparations the potencies in decreasing order were A₂>B₂>F_2α>B₁>E₂>A₁. Prostaglandin B₂ was more potent than PGA₂ on the umbilical vein. Polyphloretin phosphate (PPP) antagonised the constricting effect of all six prostaglandins without altering responses to 5-hydroxytryptamine.     

Fetal-maternal secretion of prostaglandins in the cow

A study was conducted to measure the blood plasma concentrations of prostaglandin F₂α (PGF₂α), 13,14-dihydro-15-keto-prostaglandin F (PGFM), 6-keto-prostaglandin F₁α (6-keto), prostaglandin E₂ (PGE₂), and thromboxane B₂ (TBX₂) in the ovarian vein, uterine artery, uterine vein, umbilical artery and umbilical vein in 24 cows from days 80 to 260 of pregnancy. Blood was collected during surgery and all prostaglandins were measured using specific radioimmunoassay procedures. Results indicate that PGF₂α blood levels are higher in the umbilical vessels and uterine vein than in the ovarian vein and uterine artery. PGFM and PGE₂ showed a trend towards higher values in the umbilical than in the maternal vessels, but the levels of 6-keto and TBX₂ were not different among the vessels studied. No differences across time couls be observed in any of the prostaglandins measured, partly due to the great variability in blood levels among animals during the same stage of pregnancy.     

Effect of calcium on in vitro contractility of human umbilical artery

The action of calcium on human umbilical artery was studied by an in vitro perfusion method. An increase in tonus and intense spontaneous activity were observed in the preparations at high calcium concentrations. A marked relaxation of the umbilical artery occurred in the absence of calcium. Estriol had a relaxing effect on the umbilical vessels which was more intense at calcium concentrations near physiological levels. Estriol also abolished spontaneous contractions. In the absence of calcium, estriol showed no relaxing effect. The results suggest a participation of calcium in the mechanism of action of estriol on human umbilical artery in vitro.     

The effect of prostacyclin on the human umbilical artery

Prostacyclin was tested on human umbilical artery obtained after spontaneous delivery or by Cesarean section. Isometric and isotonic responses were measured on spiral preparations in Krebs-bicarbonate buffer at 37°C equilibrated with 95% O₂ and 5% CO₂. Spiral artery strips, whether superfused or mounted in organ baths isometrically or isotonically, responded in a dose-dependent manner to both prostacyclin and serotonin; the PGI₂ response was biphasic in that low doses (2.5 × 10^-8 M - 1.0 × 10^-6 M) elicited a dose-dependent relaxation which changed with higher concentrations (1.0 × 10^-6 M - 2.53 × 10⁵ M) to a contractile response. The maximum tension exerte was 50% less than that elicited by serotonin. The data indicate that the human umbilical artery is responsive to prostacyclin and may be involved in the regulation of fetal placenta blood flow.     

The development of tone in the smooth muscle of guinea-pig isolated tracheal preparations may be influenced by prostanoids released from the adjacent airway cartilage

Guinea-pig tracheal strip preparations containing cartilage, placed under an applied load , develop tone spontaneously. The finding that spontaneous tone is reduced by indomethacin suggests that one or more prostanoids are involved in the development of spontaneous tone in this species. In this study we examined the effects of removing the cartilage component of the preparations on changes in tone induced by indomethacin and isoproterenol. In contrast to preparations containing cartilage, tissues devoid of cartilage, did not develop tone after the application of an initial 1 g resting load. Indomethacin (1 μM) reduced resting tone by 0.62 ± 0.14 g in cartilage-containing tissues but, in contrast, reduced tone by only 0.03 ± 0.01 g in tissues devoid of cartilage. Furthermore, relaxation responses (0.38 ± 0.05 g) to isoproterenol (1 μM) could be produced in cartilage-containing preparations but not in cartilage-free preparations. Radioimmunoassays indicated that the release of PGE₂, PGF_2α and 6-keto PGF_1α, the end-product of PGI₂ breakdown, was diminished in preparations lacking cartilage. Thus, in guinea-pig airway preparations cartilage is apparently a source of sufficient prostanoids to induce spontaneous tone     

Effect of ethanol on thromboxane and prostacyclin synthesis by fetal platelets and umbilical artery

The effect of ethanol (10-500 mmol/l) on platelet thromboxane production and on vascular thromboxane and prostacyclin was studied in human fetal tissues. The release of thromboxane B2 (a metabolite of thromboxane A2) during thrombin-induced spontaneous aggregation of fetal platelets was inhibited by ethanol concentrations of 50 mmol/l or higher. Ethanol at concentration from 100 mmol/l also inhibited umbilical artery production of thromboxane B2 and that of 6-keto-prostaglandin F1 alpha (a metabolite of prostacyclin). However, it stimulated the conversion of exogenous arachidonic acid to thromboxane B2 in fetal platelets and to 6-keto-prostaglandin F1 alpha in the umbilical artery. This suggests that ethanol inhibits phospholipase A2, but stimulates the enzymes distal from phospholipase A2 in the prostaglandin-synthesizing enzyme cascade.     

Stimulatory effect of prostaglandin E1 on thyroliberin-induced α-melanotropin release from perifused neuro-intermediate lobes of frog pituitary gland

A possible direct effect of prostaglandins on α-melanotropin (α-MSH) release at the level of the intermediate lobe of the frog pituitary was investigated $\text{in vitro}$ using a perifusion system technique. The effect of prostaglandins was studied on both spontaneous and TRH-stimulated α-MSH secretion. No significant effect of PGE₁, PGE₂, PGF_1α or PGF_2α on basal release of α-MSH could be detected. Indomethacin did not alter the α-MSH release induced by TRH. Conversely a significant increase in TRH-induced α-MSH secretion was observed in the presence of 1 x 10^?6M PGE₁. This magnifying effect was directly related to the concentration of TRH for doses ranging from 1 x 10^?8M to 1 x 10^?6M.     

Fetal-maternal secretion of prostaglandins in the cow

A study was conducted to measure the blood plasma concentrations of prostaglandin F2 alpha (PGF2 alpha), 13,14-dihydro-15-keto-prostaglandin F (PGFM), 6-keto-prostaglandin F1 alpha (6-keto), prostaglandin uterine artery, uterine vein, umbilical artery and umbilical vein in 24 cows from days 80 to 260 of pregnancy. Blood was collected during surgery and all prostaglandins were measured using specific radioimmunoassay procedures. Results indicate that PGF2 alpha blood levels are higher in the umbilical vessels and uterine vein than in the ovarian vein and uterine artery. PGFM and PGE2 showed a trend towards higher values in the umbilical than in the maternal vessels, but the levels of 6-keto and TBX2 were not different among the vessels studied. No differences across time could be observed in any of the prostaglandins measured, partly due to the great variability in blood levels among animals during the same stage of pregnancy.     

The effects of prostaglandins, prostaglandin inhibitors, and oxygen on the closure of the ductus arteriosus, pulmonary arteries and umbilical vessels in vitro

Three prostaglandins (PGF₂α and PGE₁, PGE₂) have been found in maternal and fetal circulation during labour. Two of these prostaglandins (PGF₂α and PGE₂) are present in elevated levels in maternal circulation during labour and their presence in fetal vessels has been shown.These three prostaglandins have been tested for their effects on fetal vessels in vitro (umbilical artery and vein, ductus arteriosus, and smaller pulmonary artery). These vessels were selected as being crucial in the conversion from fetal to extra-uterine circulation in mammalian species. Responses of these vessels to the prostaglandins under varying oxygen regimes have been examined as well as their responses to prostaglandin inhibitors. Activity of vessels of varying gestational ages exposed to PGF₂α was also examined. The following results were obtained:

1. All vessels, with the exception of pulmonary arteries, contracted in the presence of oxygen over the range 20–100mmHg pO₂. At a pO₂ of < 20mmHg the ductus arteriosus remained inactive or dilated. Pulmonary arteries dilated at high pO₂.

2. All vessels contracted in response to exogenous PGF₂α with the exception of the pulmonary arteries which dilated. In the presence of PGF₂α, the umbilical veins dilated under low (< 20mmHg) pO₂ and contracted at higher levels. Contraction also occurred at lower levels after a period of time.

3. Although PGF₂α was capable of causing contraction in the ductus arteriosus at near zero pO₂, oxygen, (or possibly the products of oxygenation), appear to be required for continued contraction in the presence of PGF₂α. A synergistic relationship between oxygen and PGF₂α responses was found as oxygen tensions increased. A synergistic response between PGF₂α and oxygen with umbilical arteries which did not increase with increased pO₂ was also found. Oxygen tension appeared to have little effect on the response of other vessels to PGF₂α.

4. PGE₁ caused dilations in all vessels examined. Such dilations appearing to be independent of the oxygen regime prevailing. However, an increase in oxygen during experiments reversed any dilation caused by the prostaglandins.

5. PGE₂ caused contractions in umbilical vessels which were independent of oxygen. PGE₂ caused contraction of pulmonary arteries. However, in the ductus arteriosus, PGE₂ caused an initial contraction followed by a strong dilation. This dilation became weaker as pO₂ increased.

6. Additions of prostaglandin inhibitors (Naproxen and Indomethacin) to the bathing solution in which the ductus arteriosus and umbilical arteries were contracting (in response to PGF₂α, or oxygen alone) caused a decrease in contractions, and sometimes a slight decrease when the vessel had been pretreated with PGF₂α suggesting a possible need for endogenously synthesised prostaglandins for the maintenance of oxygen mediated contractions (in vivo).

7. Vessels responsed to PGF₂α at an early gestational age. A role for prostaglandins and oxygen in the closure of fetal vessels is discussed.

     

Effects of analogues of prostaglandins E2 and F2α on uterine luminal fluid accumulation in the estrogen-treated ovariectomized rat: An indirect measure of cervical tone

Experiments were performed to determine if prostaglandins were able to reduce cervical tone in the rat. Cervical tone was assessed indirectly by measuring uterine luminal fluid accumulation in ovariectomized rats implanted subcutaneously with Silastic capsules containing crystalline estradiol-17β. When given subcutaneously in separate experiments, 16,16-dimethyl-prostaglandin E₂, methyl ester, and 15(S)-15-methyl-prostaglandin F_2α, analogous of prostaglandins E₂ and F_2α, respectively, caused the loss of uterine luminal fluid. Fluid accumulation in uterine horns ligated at the cervical end did not differ in control and treated rats, whereas in non-ligated horns the prostaglandin analogues reduced fluid accumulation, suggesting the cervix as their site of action. For both prostaglandin analogues, the effects on uterine luminal fluid accumulation were seen within 45 min of administration and were related to the dose administered. The effects of submaximal doses of the analogues were additive. These results suggest that prostaglandins are able to reduce cervical tone in the estrogen-treated rat.     

Synthesis of prostaglandins by subpopulations of human peripheral blood monocytes

The ability of monocytes/macrophages to regulate various aspects of immunologic responses may in part depend on their release of soluble substances such as prostaglandins. Using quantitative gas-liquid chromatography/mass spectrometry, prostaglandin E₂ was found to be the major prostaglandin synthesized in culture by human peripheral blood monocytes. Subjecting these cells to discontinuous density gradient fractionation demonstrated significant differences in the synthesis of prostaglandins E₂ and E₁ among the resulting monocyte subpopulations.     

Differential inhibition of fetal vascular prostacyclin and platelet thromboxane synthesis by monsteroidal anti-inflammatory drugs in humans

To study the synthesis of proaggregatory, vasoconstricting thrombone A₂ (TxA₂) by human fetal platelets we evaluated the formation of its stable metabolite thromboxane B₂ (TxB₂) during thrombin-induced spontaneous clotting of blood from the umbilical vein of 13 healthy infants. We further compared the effects of acetylsalicyclic acid, indomethacin, naproxen sodium and diclofenac sodium on platelet TxA₂ production in response to thrombin-induced aggregation during spontaneous clotting, and on prostacyclic (PGI₂) production by umbilical arteries in a superfusion system by measuring the 6-keto-prostaglandin F_1α (6-keto-PGF_1α) concentration in the superfusate. For every drug four concentrations covering the clinically significant range were studied. The basal production of TxB₂ by fetal platelets (181.5±22.5 ng/ml, mean±SEM) was comparable with that of adults (216.1±11.5 ng/ml). The concentrations of the drugs needed for 50 % inhibition of TxB₂ generation were 19.0 umol/1 for acetylsalicylic acid, 0.09 umol/1 for indomethacin, 0.06 umol/1 for diclofenac sodium and 4.2 umol/1 for naproxen sodium. The basal production of 6-keto-PGF_1α by umbilical arteries was 24.5±3.2 ng/min/g. The concentrations of the drugs needed for 50 % inhibition of 6-keto-PGF_1α production were 360.0 umol/1 for acetylsalicylic acid, 4.0 umol/1 for indomethacin, 2.3 umol/1 for diclofenac sodium and 15.0 umol/1 for naproxen sodium. Thus fetal platelet cyclo-oxygenase was 4–44 times more sensitive to these prostaglandin synthesis inhibitors than umbilical artery cyclo-oxygenase.     

Endothelial cells cultured from human umbilical vein release ATP, substance P and acetylcholine in response to increased flow.

Cultured human umbilical vein endothelial cells superfused with Krebs' solution were used to investigate release of ATP, substance P and acetycholine with shear stress. ATP was consistently released when the cells were exposed to increased flow rate; release was rapid, had declined by 1 min and occurred upon a second exposure. Release of substance P and acetylcholine was more varied; increased shear stress led to release of substance P from 4 out of 16 endothelial-cell columns, whereas acetylcholine was released in 4 out of 12 columns. This is the first time that unequivocal evidence has been presented for release of these neurotransmitter substances from vascular endothelial cells. These findings have important implications about the mechanisms of local regulation of vascular tone.     

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 F_2α (PGE and PGF_2α) and the 15-keto-13,14-dihydro PGF_2α/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 PGF_2α than PGE, trachea more PGE than PGF_2α. The levels of PGF_2α 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 PGF_2α and metabolites from the lung fragments. The PGE to PGF_2α 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 PGF_2α 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 PGF_2α, and stimulation of the receptor 2 is related to the synthesis of PGE.     

Prostaglandins and enzyme secretion from dispersed rat pancreatic acinar cells

The role of prostaglandins in exocrine pancreatic enzyme secretion was studied. The effects of three inhibitors of prostaglandin and thromboxane syntheses, were evaluated on release of amylase from dispersed rat pancreatic acinar cells. Mepacrine inhibited, while indomethacin and imidazole had no effect on basal or carbachol or cholecystokinin stimulated enzyme release. Exogenous arachidonic acid or various prostaglandins (E₁, E₂, F_2α, I₂), also did not affect the secretory process. Acinar cells actively incorporated radioactive arachidonic acid, principally into phospholipids (especially phosphatidylcholine), however release of the free fatty acid and subsequent synthesis of radioactive endogenous prostaglandins was not stimulated by the presence of different pancreatic stimulants. Pancreatic microsomes were found to be lacking in cyclo-oxygenase, an enzyme involved in endegenous synthesis of prostaglandins. The data suggest that prostaglandins are not involved directly in excitation-secretion coupling in the exocrine pancreas.     

The effect of prostacyclin on the human umbilical artery.

Prostacyclin was tested on human umbilical artery obtained after spontaneous delivery or by Cesarean section. Isometric and isotonic responses were measured on spiral preparations in Krebs-bicarbonate buffer at 37 degrees C equilibrated with 95% O2 and 5% CO2. Spiral artery strips, whether superfused or mounted in organ baths isometrically or isotonically, responded in a dose-dependent manner to both prostacyclin and serotonin; the PGI2 response was biphasic in that low doses (2.5 x 10(-8) M -1.0 x 10(-6) M) elicited a dose-dependent relaxation which changed with higher concentrations (1.0 x 10(-6) M -2.53 X 10(-5) M) to a contractile response. The maximum tension exerted was 50% less than that elicited by serotonin. The data indicate that the human umbilical artery is responsive to prostacyclin and may be involved in the regulation of fetal placenta blood flow.     

Synthesis and release of prostaglandins by rat brain synaptosomal fractions.

Abstract— Particulate fractions from rat brain homogenate containing the synaptosomes synthesize and release prostaglandins F and E on aerobic incubation. The prostaglandin of the F-typc released could be further identified as proslaglandin F_2α using specific radioimmunoassays for prostaglandins F_1α, and F_2α-. The metabolite 13,14-dihydro-15-keto-prostaglandin F_2α could not be detected. The amount of prostaglandins released is dependent on incubation time and temperature as well as pH and osmolarity of the incubation medium. Total brain homogenate released more prostaglandins than purified synaptosomes per mg protein, indicating that synaptosomes are probably not a main source of prostaglandins when compared with other subcellular brain fractions. While prostaglandin synthesis was only moderately increased by the addition of the precursor fatty acid arachidonic acid, anti-inflammatory drugs like indomethacin, high concentrations of some local anaesthetics and Δ¹-tetrahydrocannabinol inhibited prostaglandin release. The neurotransmitters noradrenaline, dopamine and 5-hydroxytryptamine did not influence prostaglandin release from the synaptosomal rat brain fractions.     

Effects of thrombin,PAR-1 activating peptide and a PAR-1 antagonist on umbilical artery resistance in vitro

Background  

The non-thrombotic effects of thrombin in cardiovascular tissues, as mediated via the protease activated receptors (PARs), and particularly PAR-1, have been the focus of much recent research. The aims of this study were to evaluate the effects of thrombin, a specific PAR-1 activating peptide (PAR1-AP), and a PAR-1 antagonist on human umbilical artery tone in vitro.     

Human recombinant lipocortin 1 inhibits prostacyclin production by human umbilical artery

Submicromolar concentrations of human recombinant Lipocortin 1 inhibit the release of prostacycin from human umbilical artery rings in a dose-dependent fashion. This is the first demonstration that the recombinant protein is effective in human cells.