PGE2 is a more potent vasodilator of the lamb ductus arteriosus than is either PGI2 or 6 keto PGFα

It has been shown in vitro that the lamb ductus arteriosus forms prostaglandins PGE₂, PGF_2α, 6 keto PGF_1α (and its unstable precursor PGI₂). In this study the relative potencies of these endogenous prostaglandins were investigated on isolated lamb ductus arteriosus preparations contracted by exposure to elevated PO₂ and indomethacin. All the prostaglandins (except PGF_2α) relaxed the vessel. This is consistent with the hypothesis that endogenous prostaglandins inhibit the tendency of the vessel to contract in response to oxygen. Only PGE₂, however, relaxed the vessel at concentrations below 10⁻⁸M. PGI₂ and 6 keto PGF_1α had approximately 0.001 and 0.0001 times the activity of PGE₂. Although PGE₂ has been observed to be a minor product of prostaglandin production in the lamb ductus arteriosus, the tissue's marked sensitivity to PGE₂ might make it the most significant prostaglandin in regulating the patency of the vessel.     

Endothelin is a potent constrictor of the lamb ductus arteriosus

Endothelin was tested on isolated ductus arteriosus preparations from mature fetal lambs. At low PO2 (18-24 Torr; 1 Torr = 133.3 Pa), the compound constricted the vessel dose-dependently over the range from about 10(-10) to 10(-7) M. The contraction was sustained and did not subside even after an extended period of washing. Endothelin was also effective on tissues (PO2,217-231 Torr; indomethacin, 2.8 X 10(-6) M) that had been completely relaxed with CO (CO/O2 ratio, 0.28). CO treatment interferes with a cytochrome P-450 mechanism, which is considered crucial for the contractile response of the vessel to oxygen. These findings are consistent with a role of endothelin in the closure of the ductus arteriosus at birth.     

Prostaglandin I2 is less relaxant than prostaglandin E2 on the lamb ductus arteriosus.

Prostaglandin (PG) I2 and its stable metabolite, 6-keto-PGF1alpha, were tested on the isolated ductus arteriosus from mature fetal lambs. PGI2 relaxed the ductus in high doses (threshold 10(-6)M) and its activity disappeared on standing at room temperature for 30 minutes. 6-keto-PGF1alpha was inactive at all doses. By contrast, PGE2 produced a dose-dependent relaxation over a range between 10(-10) and 10(-6)M. These findings confirm that PGE2 is the most potent ductal relaxant among the known derivatives of arachidonic acid. PGE2 probably maintains ductus patency in the fetus and, together with PGE1, remains the compound of choice in the management of newborns requiring a viable ductus for survival.     

Characterization of PGE2 receptors in fetal and newborn lamb ductus arteriosus

Although the role of PGE2 in maintaining ductus arteriosus (DA) patency is well established, the specific PGE2 receptor subtype(s) (EP) involved have not been clearly identified. We used late gestation fetal and neonatal lambs to study developmental regulation of EP receptors. In the fetal DA, radioligand binding and RT-PCR assays virtually failed to detect EP1 but detected EP2, EP3D, and EP4 receptors in equivalent proportions. In the newborn lamb, DA total density was one-third of that found in the fetus and only EP2 was detected. Stimulation of EP2 and EP4 increased cAMP formation and was associated with DA relaxation. Though stimulation of EP3 inhibited cAMP formation, it surprisingly relaxed the fetal DA both in vitro and in vivo. This EP3-induced relaxation was specifically diminished by the ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide. In conclusion, PGE2 dilates the late gestation fetal DA through pathways that involve either cAMP (EP2 and EP4) or K(ATP) channels (EP3). The loss of EP3 and EP4 receptors in the newborn DA is consistent with its decreased responsiveness to PGE2.     

6-Keto-PGE1 is a potent relaxant of the fetal ductus arteriosus

6-Keto-PGE₁ is nearly as potent as PGE₂ in relaxing the ductus arteriosus of fetal lambs. This finding raises the possibility that 6-keto-PGE₁, if occuring naturally as a by-product of PGI₂ transformations, may contribute to prenatal patency of the vessel.     

The effects of prostaglandins PGE1, PGE2, PGF1a, and PGF2alpha on canine synovial perfusion.

In these experiments we have examined the effects of PGE1, PGE2, PGF1alpha and PGF2alpha on synovial perfusion in the normal canine synovial microcirculation. The effects of the drugs on synovial perfusion were determined indirectly from the changes produced in the rate of clearance of 133Xenon from the joint by their intra-articular injection. Prostaglandins PGE1 and PGE2 were found to be strongly vasodilator with PGE1 being the more active. PGF1alpha appeared to have little or no vasoactive properties in doses up to 1 ugm. (2.8 times 10(-5M)) in our preparation while PGF2alpha was vasodilator at this high dosage only. Neither SC19920 nor diphloretin phosphate antagonished the effects of PGE1 in these experiments.     

Basal level of human platelet prostaglandins: PGE1 is more elevated than PGE2.

Radioimmunoassays of platelet prostaglandins E1 and F1 alpha in platelet rich plasma or platelet suspension, demonstrate that both PGE1 and PGF1 alpha are present at higher concentrations than prostaglandins E2 and F2 alpha. Gas chromatography--mass spectrometry determinations of prostaglandins E1 and E2 in resting washed platelets confirm this difference. Lastly, there is a greater incorporation of [1--14C] acetate into prostaglandins E1 and F1 alpha compared to that into prostaglandins E2 and F2 alpha.     

Developmental response to indomethacin: a comparison of isometric tension with PGE2 formation in the lamb ductus arteriosus

We studied the effects of oxygen and indomethacin on the isometric contractile response and the production of PGE2 in isolated rings of lamb ductus arteriosus from animals of different gestational ages (100 to 144 days; term is 150 days). Rings of ductus arteriosus from animals less than 110 days released significantly less PGE2 than did rings from animals greater than 120 days. The indomethacin-induced increase in muscle tension in relation to the decrease in endogenous PGE2 production in preparations from animals less than 110 days gestation was greater than in animals older than 120 days. These findings do not support the hypothesis that immature animals have a larger indomethacin-induced contraction due to an increased production of PGE2 earlier in gestation. They are, however, consistent with a decreased sensitivity to PGE2 in the more mature animals; they also support the hypothesis that the decreased effectiveness of indomethacin on the ductus arteriosus from later gestation animals reflects primarily a decrease in the sensitivity of the vessel to PGE2 during development.     

The intrafusion platelet rebound during and following PGE1-infusion is faster and more intensive than that with PGI2

During continuous long-term prostacyclin infusion an intra- and post-infusion rebound of platelets has been reported. During the present study 8 patients suffering from peripheral vascular disease in stage IIb according to Fontaine have been infused intravenously at a constant rate of 5ng/kg/minute for seven days. Throughout this time the platelet function parameters were followed daily in the morning. An intrainfusion platelet rebound occurs using PGE₁ as well. In comparison to the data for PGI₂ published earlier it is noteworthy that the rebound for PGE₁ occurs faster and more intensive. We conclude that for both the antiaggregatory prostaglandins PGE₁ and PGI₂, an intermittent treatment scheme seems to be optimal at the moment.     

Prostaglandin I2 is less relaxant than prostaglandin E2 on the lamb ductus arteriosus

Prostaglandin(PG) I₂ and its stable metabolite, 6-keto-PGF_1α, were tested on the isolated ductus arteriosus from mature fetal lambs. PGI₂ relaxed the ductus in high doses (threshold 10⁻⁶M) and its activity disappeared on standing at room temperature for 30 minutes. 6-keto-PGF_1α was inactive at all doses. By contrast, PGE₂ produced a dose-dependent relaxation over a range between 10⁻¹⁰ and 10⁻⁶ M. These findings confirm that PGE₂ is the most potent ductal relaxant among the known derivatives of arachidonic acid. PGE₂ probably maintains ductus patency in the fetus and, together with PGE₁, remains the compound of choice in the management of newborns requiring a viable ductus for survival.     

Adenosine facilitates the response to HCG, PGE1 or PGE2 and inhibits the response to PGF2 alpha by HCG-stimulated ovine luteal cells in vitro.

Dispersed ovine luteal cells collected on day 7 or 16 postestrus were incubated in vitro with hCG, PGE1 or PGE2 in the presence or absence of adenosine, dipyridamole (inhibitor of adenosine uptake) or PGF2 alpha in two separate experiments. Secretion of progesterone was increased by hCG, PGE1 or PGE2 when incubated with day 7 luteal cells (P less than or equal to 0.05) which was increased further when co-incubated with adenosine (P less than or equal to 0.05). PGF2 alpha alone or in the presence of hCG decreased (P less than or equal to 0.05) the secretion of progesterone by day 7 luteal cells, PGF2 alpha decreased post treatment cell viability with or without hCG (P less than or equal to 0.05) and adenosine reduced (P less than or equal to 0.05) the inhibitory effect of PGF2 alpha on hCG actions and luteal cell viability. Day 16 luteal cells were not functional based on jugular progesterone (P less than or equal to 0.05) and did not respond to hCG, PGE1, or PGE2 in the presence of adenosine or PGF2 alpha (P greater than or equal to 0.05). It is concluded that adenosine enhances the response of functional luteal cells to the luteotropins hCG, PGE1 or PGE2 and adenosine reduces the luteolytic response to PGF2 alpha by hCG-stimulated ovine luteal cells in vitro.     

Influence of 15-keto-metabolites and 13,14-dihydro-15-keto-metabolites of PGE2 and PGF2 alpha as well as of 6-keto-PGF1 alpha as a metabolite of PGI2 on aconitine induced cardiac arrhythmia in rats

The 15-keto-metabolites of PGE2 and PGF2 alpha produced an antiarrhythmic effect on aconitine induced arrhythmias in rats. The ED50 values of these metabolites were approximately 2.0 micrograms/kg. The 13,14-dihydro-15-keto-metabolites of PGE2 and PGF2 alpha had no statistically significant antiarrhythmic effect. PGI2 (0.25-1.00 micrograms/kg) produced an antiarrhythmic effect between 15-54% (ED50 0.75 micrograms/kg), whereas 6-keto-PGF1 alpha, a metabolite of PGI2, showed no significant antiarrhythmic effect. The results suggest a participation of 15-keto-metabolites in the antiarrhythmic effects of PGE2 and PGF2 alpha.     

Receptor binding in various tissues of PGE2, PGF2 alpha and sulprostone, a novel PGE2-derivative.

Sulprostone is a tissue-specific PGE2-derivative with high abortifacient activity in various species including man. The dissociation constant KD of the receptor binding of this compound was compared with PGE2 and PGF2 alpha in various tissue preparations of different species. A structure-binding relationship was developed from competition curves after a logit/log transformation. It is demonstrated that the relative affinities of Sulprostone, PGE2 and PGF2 alpha remain essentially constant in all the tissues investigated. It is concluded that the tissue-specificity of Sulprostone cannot be ascribed to structural differences of the receptor molecule.     

ACTH1-17 is a more potent agonist at the human MC1 receptor than alpha-MSH.

The melanocortin receptor MC1 is expressed on melanocytes and is an important control point for melanogenesis and other responses. Alpha-MSH, which is considered to be the major ligand at the human melanocortin (MC)1 receptor (hMC1R), is produced from proopiomelanocortin (POMC) in the pituitary and in the skin by melanocytes and keratinocytes. Other POMC peptides are also produced in the skin and their concentrations exceed those of alpha-MSH by several fold. One of the most abundant is ACTH1-17. We have shown that adrenocorticotrophic hormone (ACTH)1-17 is more potent than alpha-MSH in stimulating melanogenesis in human melanocytes and unlike alpha-MSH produces a biphasic dose response curve. In this study we have examined the ability of ACTH1-17 to function as a ligand at the hMC1R. Competitive binding assays with [125I]Nle4 DPhe7 alpha-MSH as labelled ligand were carried out in HEK 293 cells transfected with the hMC1R. ACTH1-17 showed high affinity for the hMC1R with a Ki value of 0.21 +/- 0.03 nM which was slightly higher than that of 0.13 +/- 0.005 nM for alpha-MSH. ACTH1-17 was, however, more potent than alpha-MSH in increasing cAMP and IP3 production in the transfected cells. Our results demonstrate that ACTH1-17 is a potent agonist at the hMC1R. It is therefore possible that ACTH1-17, which is found in the skin in greater concentrations than alpha-MSH, has an important role in the regulation of human melanocytes and other cell types that express the hMC1R.     

Interleukin-1 beta is more potent than interleukin-1 alpha in suppressing follicle-stimulating hormone-induced differentiation of ovarian granulosa cells

Most studies have shown that the immune and inflammatory actions of interleukin-1 alpha and beta exhibit the identical biological spectrums of activity with similar dose-response curves. We have previously demonstrated that interleukin-1 beta suppresses follicle-stimulating hormone-induced differentiation of ovarian granulosa cells. In these experiments, we show that although the human recombinant preparations of interleukin-1 alpha and beta exhibit a similar directional inhibition of ovarian granulosa cell differentiation, there is a significant difference in the dose-response relationships between the two forms. Interleukin-1 beta was 31 times and 18 times more potent than interleukin-1 alpha in suppressing follicle-stimulating hormone-induced luteinizing hormone receptor development and progesterone secretion, respectively, from rat granulosa cells. However, there was no difference in the dose-dependent activities of interleukin-1 alpha and beta in stimulating murine thymocyte proliferation. These results suggest that interleukin-1 beta is more effective in influencing ovarian granulosa cell function than interleukin-1 alpha.     

Involvement of intramural prostaglandin E2 in prenatal patency of the lamb ductus arteriosus

Release of prostaglandin E2 (PGE2) was studied in isolated ductus arteriosus preparations from immature (103 or 104 days gestation; term, 147 days) and near-term fetal lambs. Mature preparations produced measurable amounts of the compound in most cases and the release rate was 19 +/- 2 pg/(100 mg wet weight X min) at a PO2 of 3-8 Torr (1 Torr = 133.3 Pa). PGE2 release increased with the PO2 of the medium, peak values (about 125 pg/(100 mg X min)) being attained at 106-276 Torr when the oxygen-induced contraction was still submaximal. Experiments in which tissues were either contracted with excess potassium or relaxed with CO proved that PGE2 formation is independent from the contractile state. PGE2 was also released from ductus preparations lacking the adventitia, the intima, or both; however, release values were maximal when the adventitia was preserved. The magnitude of the intrinsic tone in these stripped preparations was inversely related to the rate of PGE2 formation. Reduced glutathione increased PGE2 release from the mature ductus, whole or stripped, and also relaxed hypoxic preparations; both effects were reversed by concomitant treatment with indomethacin. PGE2 synthesis tended to be greater in the immature than the mature ductus, maximal values (115 +/- 27 pg/(100 mg X min)) being observed at 6-8 Torr. We conclude that the ductus arteriosus is endowed with an enzyme system for the synthesis of PGE2 whose function accords with an effector role of the compound in the regulation of tone. These findings, together with the potent relaxation exerted by PGE2 at low PO2, indicate that the locally generated prostaglandin is well suited for keeping the ductus patent in the fetus.