Effect of bisenoic prostaglandins on the uterine vasculature of the nonpregnant sheep

The effects of the bisenoic prostaglandins on the uterine vasculature and uterine contractile activity have been evaluated in an unanesthetized chronically catheterized nonpregnant sheep preparation. Changes in uterine blood flow were monitored with electromagnetic flow probes while uterine contractile activity and tone were determined via an intra-uterine balloon connected to a pressure transducer. Prostaglandins A₂, D₂, E₂, and prostacyclin (PGI₂) were all found to be vasodilators. PGD₂ and PGI₂ were much more potent than PGA₂ and PGE₂ in dilating the uterine vasculature. The prostacyclin breakdown product 6-keto PGF_1α, PGF_2α, thromboxane B₂, and the endoperoxide analogues U44069 and U46619 produced vasoconstriction of the uterine vasculature. Prostaglandins A₂, D₂ and F_2α increased while PGI₂ decreased uterine contractile activity. PGF_2α also increased uterine tone suggesting that a portion of its vasoconstrictor activity may be due to mechanical compression of the uterine vasculature.     

The effect of locally administered PGF2α on the contractility of the nonpregnant human uterus in vivo

The effect of locally administered prostaglandin F_2α on the sensitivity and reactivity of the nonpregnant human uterus during the menstrual cycle was studied. An increase in uterine contractility in response to as little as 1.0 μg PGF_2α could be observed in all patients during both the early and late portions of the menstrual cycle, but at the time of ovulation a marked decrease in sensitivity was noted. Endogenous prostaglandin normally occurs in the secretory endometrium in levels compatible with the amount of exogenous prostaglandin which elicited increased uterine activity. These findings support the hypothesis that PGF_2α plays an important physiological role in the cyclical regulation of uterine motility during the human menstrual cycle.     

Prostacyclin induces a surprising long-lasting motility in quiescent uterine strips (indomethacin-treated) isolated from ovariectomized rats

Dose-response curves for several prostaglandins (PGI₂; PGD₂; PGF₂ and PGE₂); BaCl₂ or prostaglandin metabolites (15-keto-PGF_2α; 13, 14-diOH-15-keto-PGF_2α; 6-keto-PGF_1α and 6-keto-PGE₁ in quiescent (indomethacin-treated) uterine strips from ovariectomized rats, were constructed. All PGs tested as well as BaCl₂, triggered at different concentrations, evident phasic contractions. Within the range of concentrations tested the portion of the curves for the metabolites of PGF_2α was shifted to the right of that for PGF_2α itself; the curve for 6-keto-PGF_1α was displaced to the right of the curve for PGI₂ and that for 6-keto-PGE₁ to the left.It was also demonstrated that the uterine motility elicited by 10⁻⁵ M PGF_2α and its metabolites was long lasting (more than 3 hours) and so it was the activity evoked by PGI₂; 6-keto-PGF_1α and BaCl₂, but not the contractions following 6-keto-PGE₁, which disappeared much earlier. The contractile tension after PGF_2α; 15-keto-PGF_2α; 13, 14-diOH-15-keto-PGF_2α and PGI₂, increased as time progressed whilst that evoked by 6-keto-PGF_2α or BaCl₂ fluctuated during the same period around more constant levels.The surprising sustained and gradually increasing contractile activity after a single dose of an unstable prostaglandin such as PGI₂, on the isolated rat uterus rendered quiescent by indomethacin, is discussed in terms of an effect associated to its transformation into more stable metabolites (6-keto-PGF_1α, or another not tested) or as a consequence of a factor which might protects prostacyclin from inactivation.     

Effects of prostaglandins E2, I2 and F2α, arachidonic acid and indomethacin on pressor responses to norepinephrine in conscious rats

The effects of prostaglandins E₂ (PGE₂), I₂ (PGI₂) and F₂α (PGF₂α), arachidonic acid and indomethacin on pressor responses to norepinephrine were examined in conscious rats. Intravenously infused PGE₂ (0.3, 1.25 μg/kg/min), PGI₂ (50, 100 ng/kg/min), PGF₂α (1.8, 5.4 μg/kg/min) and arachidonic acid (0.7, 1.4 mg/kg/min) did not change the basal blood pressure. Both PGE₂ and PGI₂ significantly attenuated pressor responses to norepinephrine, whereas PGF₂α significantly potentiated them. Arachidonic acid, a precursor of the prostaglandins (PGs), significantly attenuated pressor responses to norepinephrine. Since the attenuating effect of arachidonic acid was completely abolished by the pretreatment with indomethacin (5 mg/kg), arachidonic acid is thought to exert an effect through its conversion to PGs. On the contrary, intravenously injected indomethacin (0.2–5.0 mg/kg) facilitated pressor responses to norepinephrine in a dose-related manner without any direct effect on the basal blood pressure. These results suggest that endogenous PGs may participate in the regulation of blood pressure by modulating pressor responses to norepinephrine in conscious rats.     

Reversal of indomethacin-induced inhibition of tubuloglomerular feedback by prostaglandin infusion

Experiments were performed in rats to study the effect of infusion of PGI₂, PGE₂, and PGF_2α on tubuloglomerular feedback responses (i.e. the change of SNGFR in response to a change of loop of Henle flow rate) in the presence and absence of simultaneous inhibition of endogenous PG synthesis with indomethacin. Infusion of PGI₂ or PGE₂ at rates that did not alter arterial blood pressure did not significantly modify the magnitude of feedback responses (PGI₂) 8.5 μg/hr, PGE₂ 85 μg/hr). Some inhibition of feedback responses was seen when PGI₂ and PGE₂ were administered at higher rates were associated with a reduction of blood pressure (PGI₂ 20 μg/hr, PGE₂ 200 μg/hr). PGI₂ (8.5 μg/hr) and PGE₂ (85 μg/hr) largely prevented feedback inhibition induced by indomethacin. When given subsequent to indomethacin PGI₂ and PGE₂ restored feedback responsiveness almost to normal. In contrast, PGF_2α did not influence feedback inhibition caused by indomethacin. Infusion of PGI₂ induced partial restoration of feedback responses in DOCA-salt treated animals in which the feedback system is virtually completely inactive. Our results indicate that availability of PGI₂ or PGE₂ is necessary for the normal operation of the tubuloglomerular feedback mechanism for control of nephron filtration rate.     

Effect of prostaglandin F3α on gastric mucosal injury by ethanol in rats: Comparison with prostaglandin F2α

In humans eicosapentaenoic acid can be converted to 3-series prostaglandins (PGF_3α, PGI₃, and PGE₃). Whether 3-series prostaglandins can protect the gastric mucosa from injury as effectively as their 2-series analogs is unknown. Therefore, we compared the protective effects of PGF_3α and PGF_2α against gross and microscopic gastric mucosal injury in rats. Animals received a subcutaneous injection of either PGF_3α or PGF_2α in doses raning from 0 (vehicle) to 16.8 μmol/kg and 30 min later they received intragastric administration of 1 ml of absolute ethanol. Whether mucosal injury was assessed 60 min or 5 min after ethanol, PGF_3α was significantly less protective against ethanol-induced damage than PGF_2α. These findings indicate that the presence of a third double bond in the prostaglandin F molecule between carbons 17 and 18 markedly reduces the protective effects of this prostaglandin on the gastric mucosa.     

Prostaglandin production from homogenates of separated glandular epithelium and stroma from human endometrium

The biosynthesis of prostaglandins by isolated epithelial glandular and stromal cells was studied after collagenase digestion of endometrium collected from women at various stages of the menstrual cycle. Homogenates of the separate cell types were incubated for 60 minutes with 2.08 μg 1¹⁴C arachidonic acid and the products separated by thin layer chromatography. Both glandular and stromal homogenates synthesised PGF_2α. More PGF_2α was synthesised by glandular epithelium separated from both proliferative and secretory endometrium than by stroma. The ratio of PGF_2α/PGE₂ was greater in glands and stroma isolated from secretory than proliferative endometrium. Small but significant amounts of 6-keto-PGF₁α were produced by all cell types. These results suggest that the increased synthesis of PGF₂α from secretory endometrium is due, at least in part, to increased activity of cyclo-oxygenase enzyme in the glandular epithelium.     

Effect of prostaglandin F2α on pulmonary rapidly-adapting-receptors in the guinea pig

Pulmonary rapidly-adapting-receptors (RARs) are sensory nerve endings whose afferent fibers can be recorded in the vagus nerve. RARs may play a role in reflex bronchoconstriction as seen in anaphylaxis. They can be stimulated by chemical mediators of anaphylaxis, such as prostaglandin F_2α (PGF_2α). PGF_2α aerosol was administered to saline and bovine serum albumin (BSA)-treated guinea pigs while recording the activity of RARs. PGF_2α (250 μg/ml) given for 7–13 minutes increased both tracheal pressure and nerve activity over that produced by saline exposure in untreated guinea pigs. PGF_2α administered for three minutes (5–100 μg/ml) increased RAR nerve activity in a dose-related manner in the first five minutes of the experiment only in the BSA treated guinea pigs. Since changes in tracheal pressure did not show a significant dose-response relationship, the RARs responding to PGF_2α seemed to be stimulated by a direct mechanism. No correlation was shown between tracheal pressure and RAR nerve activity during PGF_2α treatment. Whereas, a significant correlation was found between tracheal pressure and RAR nerve activity during histamine aerosol treatment (r=0.985). Histamine aerosol (1 to 1000 μg/ml, 3 min.) increased intratracheal pressure for 3 out of 4 doses. RAR nerve activity increased significantly only at the highest dose. Therefore, a possible direct effect of PGF_2α upon RARs exists while the effect of histamine seems dependent upon changes in airway pressure in the guinea pig.     

Effect of prostaglandin F2α on ovarian and pituitary function in the mid-luteal phase

The effects of PGF_2α infusion in a dose of 25 μg/min for 5 hours on serum levels of estradiol-17β, progesterone, LH, FSH, TSH and prolactin, and on the pituitary hormone responsiveness to LRH and TRH were studied in 10 apparently healthy cycling women in the mid-luteal phase. No systematic alteration was seen in the pituitary and ovarian hormone levels during PGF_2α infusion, and the pituitary hormone responses to releasing hormones were unaffected. Ovarian steroid production increased in response to increased gonadotropin levels after LRH injection during PGF_2α administration. These results confirm that PGF_2α is not luteolytic in humans and no apparent relationship between PGF_2α and pituitary hormone secretion exists.     

Effect of PGI2, PGE2 and 6-keto PGF1α on canine gastric blood flow and acid secretion

Prostaglandins (PG)I₂, PGE₂ and 6-keto PGF₁α were infused directly into the gastric arterial supply at 10⁻⁹, 10⁻⁸ and 10⁻⁷ g/kg/min during an intra-gastric artery pentagastrin infusion in anesthetized dogs. 6-keto PGF₁α was also infused at 10⁻⁶ g/kg/min. Gastric arterial blood flow was measured continuously with a non-cannulating electromagnetic flow probe and gastric acid collected directly from the stomach. PGI₂ and PGE₂ produced similar dose-dependent increases in blood flow with an increase of more than four-fold at the highest dose. Both PGs inhibited acid output over this dose range with PGE₂ having 10 times the potency of PGI₂. 6-keto PGF₁α was at least 1000 times less active than PGI₂ or PGE₂ at increasing blood flow and failed to inhibit acid output even at 10⁻⁶ g/kg/min.     

Interaction between uterine PGE and PGF2α production and the nitridergic system during embryonic implantation in the rat

Embryonic implantation is a complex process in which both maternal andembryonic signals are involved. In the present study, we evaluated changes in uterine prostaglandins production and nitric oxide synthase (NOS) activity during the course of early pregnancy and their interaction during implantation in rats. Uterine phospholipase A₂ (PLA₂) activity is increased on days 5 (day of ovoimplantation) and 6, compared to preimplantation days (3 and 4). This enhanced activity might be responsible for the observed increase in uterine PGE and PGF_2α production observed on day 5 of pregnancy, which induces endometrial vascular permeability and decidualization. When embryo access to the uterus is impaired, the increase of PG production is suppressed. During postimplantation, PGE levels return to preimplantation values, while PGF_2α decreased with respect to preimplantation values. Uterine NOS activity is also increased on day 4 and reaches a maximum on day 5, with a profile similar to PGE and PGF_2α Dexamethasone administered in vivo decreased uterine NOS activity on day 4 of pregnancy but not on day 5, suggesting the presence of at least two types of NOS enzymes in the early days of pregnancy. A competitive inhibitor of NOS, L-NAME (600 and 1000 μM) induced a decrease in PGE and PGF_2α production in uterine tissue on day 5 of pregnancy. These results suggest the existence of a physiologically relevant nitridergic system which modulates prostaglandin production in the rat uterus during embryonic implantation.     

The lack of involvement of central nervous system in the antiarrhythmic effects of prostaglandins E2, F2α, and I2 in cat

The role of the central nervous system (CNS) in the antiarrhythmic effects of prostaglandins (PGs) E₂, F_2α, and I₂ was studied by administering each agent into the left lateral cerebral ventricle (i.c.v. administration) of chloralose-anesthetized cats. The cardiac arrhythmias were produced by intravenous (i.v.) infusion of ouabain (1 μg/kg/min). The PGs E₂, F_2α and I₂ on i.c.v. administration in the dose range of 1 ng to 10 μg failed to inhibit ouabain-induced cardiac arrhythmias. However, when infused i.v., PGE₂ (1 μg/kg/min), PGF_2α (5 μg/kg/min), and PGI₂ (2 μg/kg/min) effectively suppressed these arrhythmias. The standard antiarrhythmic drug propanolol (0.5–8.0 mg)oni.c.v.administration also significantly reduced the ouabain-induced cardiac arrhythmias. It is suggested that the CNS is not the site of action of PGs E₂, F_2α, and I₂ in antagonising the ouabain-induced cardiotoxicity in cats.     

Is the epithelium-derived inhibitory factor in guinea-pig trachea a prostanoid?

To examine further the possible prostanoid involvement in the influence of the epithelium on guinea-pig tracheal smooth muscle responsiveness, we have analyzed the effects of LTD₄, methacholine and histamine on the level of airway smooth muscle tone and on the amounts of PGE_2α and PGI₂ (determined by radioimmunoassay) in the presence and absence of the epithelium. Removal of the epithelium increased the sensitivity of guinea-pig trachea to the contractile effects of LTD₄, methacholine and histamine. LTD₄ (3–100 nM), methacoline (0.1–10 μM) or histamine (0.3–30 μM) did not increase prostanoid release above control values in either the presence or absence of the epithelium. The unstimulated release of PGE₂ and PGF_2α but not PGI₂, was decreased in tissues lacking epithelium. Indomethacin (1 μM) reduced the baseline tone to a smaller extent in the absence of epithelium. In the presence but not the absence of the epithelium, indomethacin increased the sensitivity of preparations to the contractile effect of methacholine. The results support the postulate of an epithelium-derived inhibitory factor modulating guinea-pig tracheal smooth muscle responsiveness. The identity of this factor is not known but is not PGI₂ and is unlikely to be PGF_2α or PGE₂. However, the possibility remains that the basal release of PGE₂ and/or PGF_2α derived from the epithelium may markedly affect the responsiveness of guinea-pig tracheal smooth muscle. Furthermore, the epithelium is a significant source of PGE₂ and PGF_2α which may be involved in the maintenance of baseline tone.     

Effects of hydrocortisone, oestradiol and progesterone on A23187-stimulated prostaglandin output from the guinea-pig uterus superfused in vitro

Hydrocortisone (10 μg/ml) had no effect on the basal outputs and A23187-stimulated outputs of PGF_2α, PGE₂ and 6-keto-PGF_1α from the Day 15 guinea-pig uterus superfused . These findings indicate that the high output of PGF_2α from the guinea-pig uterus during the last one-third of the oestrous cycle is not modulated by the adrenal glucocorticoid hormones. Progesterone (10 gmg/ml) had no effect on the A23187-induced increases in PG output from the Day 15 guinea-pig uterus. However, oestradiol (10 gmg/ml but not 1 μg/ml) significantly reduced the increases in outputs of PGF_2α, PGE₂ and 6-keto-PGF_1α induced by A23187 from the Day 15 guinea-pig uterus, without affecting basal PG outputs. The increase in uterine tone induced by A23187 in the Day 15 guinea-pig uterus was reduced by 20–50% by oestradiol (10 μg/ml). The addition of oestradiol (10 μg/ml) and progesterone together (10 gmg/ml) produced the same effects on the Day 15 guinea-pig uterus as oestradiol alone. Oestradiol (10 μg/ml) also reduced the A23187-induced increases in PG output from the Day 7 guinea-pig uterus, but did not reduce the increase in uterine tone. Oestradiol (10 gmg/ml) reduced the increases in outputs of PGF_2α, PGE₂ and 6-keto-PGF_1α induced by exogenous arachidonic acid from the Day 7 and Day 15 guinea-pig uterus. Previous studies have shown that oestradiol is not a cyclo-oxygenase inhibitor. The present findings suggest that oestradiol, at a relatively high concentration, may interfere with the access of arachidonic acid to the cyclo-oxygenase enzyme. This action of oestradiol may explain its anti-luteolytic action when administered to guinea-pigs in large doses after Day 9 of the cycle.     

Involvement of prostaglandins in the effect of cupric ions on the human uterus

The effect of cupric ions on the human uterus and the involvement of prostaglandins (PGs) in mediating this effect was studied by recording of isometric contractions of isolated myometrial strips and pieces of uterine arteries, and by intrauterine pressure recordings in women before the onset of menstruation. , CuCl₂ in concentrations of 10⁻⁴ M and higher caused a significant inhibition of myometrial contractile activity, but no effect on the artery preparations was seen. Furthermore, the contractile response of myometrial strips to PGF_2α and PGE₂ (10 ng/ml) decreased in the presence of CuCl₂ in concentrations of 5 and 50 μmol. , instillations of 0.3, 1.0 and 2.0 mM of CuCl₂ in 0.7 ml of saline solution into the uterine cavity caused a dose-dependent stimulation of uterine activity, but after pretreatment with naproxen, 500 mg orally, the effect of these substances was abolished. After naproxen treatment, but during infusion of PGF_2α (5 μg/min), the response to the CuCl₂ solutions was partially restored. It is suggested that cupric ions, at high concentrations, have an inhibiting effect on myometrial activity. The stimulatory effect of low doses of CuCl₂ seen after installation into the uterine cavity is largely exerted via initiation of synthesis and release of endometrial PGs.     

Metabolism of prostacyclin. III. Urinary metabolite profile of 6-keto PGF1α in rat

The in vivo metabolism of 6-keto PGF_1α was investigated in rats. Following continuous intravenous infusion for 14 days the urinary metabolites were isolated and identified. A substantial amount of unchanged 6-keto PGF_1α was recovered in the urine. The metabolic pattern very closely resembles that of PGI₂ in rats. Metabolites were found which represented 15-dehydrogenation, β-oxidation, ω and ω-1-hydroxylation and oxidation.Previous work showed that 6-keto PGF_1α is very poorly oxidized by 15-PGDH. We administered 15-[H³]-PGI₂ and 15-[H³]-6-keto PGF_1α to rats and measured urinary tritiated water as an index for in vivo 15-PGDH activity. The results showed that PGI₂ and 6-keto PGF_1α were both oxidized to the 15-keto product, although the rate of oxidation of PGI₂ was greater than that of 6-keto PGF_1α. We concluded that the administered PGI₂ was oxidized by 15-PGDH before hydrolysis to 6-keto PGF_1α. A portion of the dose is probably hydrolyzed before 15-dehydrogenation.     

Influences of prostaglandins on electrophoretic mobility and aggregation of rabbit platelets

Influences of prostaglandin(PG)s on electrophoretic mobilities and aggregation of rabbit platelets were studied. The PGs studied (PGI₂, PGE₁, PGD₂, PGE₂, PGF_2α, PGA₂ and PGA₁) had no effect on platelet electrophoretic mobility. However, both PGE₁ and PGI₂ in 0.3 and 3.0 μM inhibited ADP-induced aggregation and ADP-induced decrease in the mobility. PGD₂ in 0.3 and 3.0, and PGE₂ in 30 μM inhibited the aggregation but did not depress the ADP-induced decrease in the mobility. PGF_2α, PGA₂ and PGA₁ had no effect on the decrease in electrophoretic mobility and on the aggregation caused by ADP.     

Plasma 13, 14-dihydro-15-keto-PGF2 (PGFM) in pregnant and nonpregnant heifers prior to and during surgery and following intrauterine injection of PGF2

On day 17 postestrus or postmating, heifers were given intrauterine injections of saline (2 pregnant, 2 non-pregnant) or 200 μg PGF₂α (7 pregnant, 6 nonpregnant) through cannulae installed surgically into the uterine horn ipsilateral to the corpus luteum bearing ovary. Jugular blood samples were collected prior to the laparotomy at which the cannulae were installed during surgery, and for 90 min following the intrauterine injection. Plasma was assayed for progesterone and 13,14-dihyro-15-keto-PGF₂α )PGFM). Laparotomies were reopened to confirm proper cannula placement and to determine if blastocysts were present in mated heifers. Concentrations of PGFM were higher in pregnant compared to nonpregnant heifers during the presurgery (68 26 24 26 pg/ml; P < 0.25) and surgery (186 47 65 17 pg/ml; P < .05) periods. Pregnancy status did not alter the mean concentrations of PGFM (pregnant, 554 70 pg/ml; nonpregnant, 422 81 pg/ml) or the half-life of its decline in concentration (18 min) following intrauterine injection of PGF₂α. Pregnancy at 17 days in cattle does not appear to influence PGF₂α transport from the uterine lumen or its metabolism in the uterus or elsewhere in response to an acute intrauterine injection.     

Effect of in vivo prostaglandin treatment on H-PGF2α uptake in hamster corpora lutea

Pregnant hamsters were administered (SC) prostaglandin or vehicle on the morning of the 4th day of pregnancy. Serum progesterone was significantly depressed (p<.01) at 0.5, 2, and 6 hours after treatment with 100 μg PGF_2α. Serum progesterone levels were unchanged 2 hours and 6 hours after treatment with 100 μg PGF_2β and 2 hours after treatment with 1 mg PGF_2β. Progesterone levels were depressed to less than 1 ng/ml 6 hours after treatment with 1 mg PGF_2β. The specific uptake of ³H-PGF_2α in whole hamster corpora lutea was significantly depressed 2 hours and 6 hours following 100 μg PGF_2α treatment. A 15% depression in specific uptake occurred 0.5 hour post-treatment. Treatment with 100 μg PGF_2β resulted in no change. Administration of 1 mg PGF_2β resulted in depressed ³H-PGF_2α uptake at both 2 and 6 hours post-treatment.Prostacyclin (PGI₂) treatment resulted in no change in either ³H-PGF_2α specific uptake or serum progesterone 2 hours after 100 μg treatment SC. These parameters were both reduced approximately 30% 6 hours post-treatment. Treatment with 6-keto-PGF_1α resulted in a complete lack of measurable ³H-PGF_2α uptake and serum progesterone levels less than 1 ng/ml at both 2 and 6 hours after treatment with 1 mg SC.     

Enhanced formation of PGI2, a potent hypotensive substance, by aortic rings and homogenates of the spontaneously hypertensive rat

Intact rings and homogenates of aorta from spontaneously hypertensive rats (SHR) contain enhanced capacity over normal rats (NR) to convert arachidonic acid into PGI₂. The PGI₂ synthetic system in SHR is stimulated to a greater extent than NR by norepinephrine. Indomethacin blocks this stimulation. PGE₂ and PGF_2α were detected in much smaller amounts in homogenates (undetected in rings) but their formation was not enhanced by the hypertensive tissue. The identity of PGI₂ was based on 1) direct pharmacological assay on the rat blood pressure. In this system identical vasodepressor responses to PGI₂ are observed after intracarotid and intrajugular administration 2) indirectly as 6-keto PGF_1α isolated after incubation of aortic homogenates with tritiated arachidonic acid and 3) indirectly by GC-MS assay of PGE₂, PGF_2α and 6-keto PGF_1α formed during incubation of aortic homogenates with excess unlabeled arachidonic acid. These results provide additional support to our recent hypothesis that PGI₂, of aortic origin, might actively participate in the regulation of systemic blood pressure. Its enhanced formation by intact hypertensive vascular tissue reflects an increase in the number of enzyme molecules immediately available to the substrate. This could probably be an adaptive response to the elevated levels of catecholamines in the circulation.