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.     

Bronchopulmonary and cardiovascular effects of prostaglandin D2 in the dog

The effects of intravenously administered prostaglandin D₂ (PGD₂) on bronchopulmonary and cardiovascular functions were examined in the dog. PGD₂ (0.03–1.0 μg/kg) was shown to be more active than PGF_2α, a known bronchoconstrictor, in decreasing dynamic lung compliance, tidal volume, and expiratory airflow rate, as well as in elevating lung resistance. PGD₂ demonstrated a potency approximately 4–6 times that of PGF_2α on pulmonary mechanics. Atropine sulfate infusions reduced significantly the resistance and compliance responses to PGF_2α, but only the resistance responses to PGD₂, thereby suggesting that part of the bronchoconstrictor activities of these agents involved a cholinergic component.In another series of anesthetized dogs, PGD₂ (0.1–10.0 μg/kg) increased pulmonary arterial pressure (comparable to PGF_2α) and heart rate (greater than PGF_2α, but less than PGE₂), while concomitantly decreasing systemic arterial pressure in a dose-related manner ( that of PGE₂). Qualitatively similar alterations in cardiovascular parameters were obtained for PGD₂ in conscious dogs.Therefore, potent biologica activity of PGD₂ has been shown in the dog. No physiologic or pathologic role for PGD₂ has yet been demonstrated, but nonetheless, since it is a naturally occurring PG derived from arachidonic acid, further studies are warranted.     

Biological activities of 17-phenyl-18,19,20-trinorprostaglandins

In a number of assay ssytems, some 17-phenyl-trinor prostaglandins were similar in activity and potency to the corresponding parent prostaglandin. In others, the 17-phenyl analogs appeared several times more potent. In the hamster antifertility assay, which is considered to measure luteolytic activity, 17-phenyl-18,19,20-trinor prostaglandin F_2α was about 90-times PGF_2α in potency.Rat blood pressure responses to 17-phenyl analogs were significant. The 17-phenyl-trinor PGF_2α pressor potency was 5 times that of PGF_2α. The 17-phenyl-trinor PGE₂ blood pressure response was atypical since a pressor rebound phenomenon followed the expected depressor response. Lastly, 17-phenyl-trinor PGF_2α was more potent than PGF_2α in synchronizing the estrous cycle in beef cows.     

Synthesis and antifertility activity of 13-aza 14-oxo-prostaglandins

Some 13-aza-14-oxo prostaglandin analogues of PGF_2α, PGE₂ and PGA₂, have been synthetized in optically active form, starting from Corey's intermediate and evaluated for antifertility activity in the hamster. The C-15 absolute configuration was established and found critical for the biological activity, but unexpectedly the highest potency was always associated with the 15 epi derivatives.Among the PGF_2α analogues the 15 epi derivatives was about one tenth as potent as PGF_2α.The preparation of a few 16-phenoxy 17,18,19,20 tetranor-derivatives led to more potent compounds with the p-fluorophenoxy analogue having the same potency as PGF_2α.     

Prostaglandin F2α increases responsiveness of pulmonary airways in dogs

We studied the effect of prostaglandin F_2α (PGF_2α) on the responsiveness of pulmonary airways in dogs. Airway responsiveness was assessed by determining the bronchoconstrictor response to increasing concentrations of acetylcholine aerosol delivered to the airways. In each of five dogs, we determined responsiveness during treatment with physiologic saline, histamine, or PGF_2α aerosols. The doses of histamine and PGF_2α were determined by establishing the largest dose of each which could be given to the dog without causing bronchoconstriction (subthreshold doses). We found that airway responsiveness was not significantly different during histamine treatment than after saline, however, responsiveness increased during treatment with PGF_2α. In addition, the hyperresponsiveness induced by PGF_2α was prevented by pretreatment with the ganglion blocking drug hexamethonium (5 mg/kg given intravenously). The results show that PGF_2α specifically increases the responsiveness of pulmonary airways in doses that do not cause bronchoncostriction, and suggest that the hyperresponsiveness involves a neural mechanism such as increased responsiveness of airway sensory nerves.     

Prostaglandin IX - synthesis of (±)-15-methyl-11-deoxy PGE1 (doxaprost) - a potent bronchodilator - and its C-15-epimer

The communication describes the total synthesis of (±)-15-methyl-11-deoxy PGE₁ and its C-15-epimer. The synthesis of (±)-15-methyl-11-deoxy PGF₁ and (±)-15-methyl-11-deoxy PGF_1β is also reported. Preliminary data for the bronchodilator activity is presented.     

Radioimmunoassays of prostaglandin F2α and prostaglandin F2α-main urinary metabolite with prostaglandin-I-tyrosine methylester amide

Radioimmunoassays for measuring prostaglandin F_2α (PGF_2α) and 5α, 7α-dihydroxy-11-keto tetranorprosta-1,16-dioic acid, PGF_2α-main urinary metabolite (PGF_2α-MUM), with ¹²⁵I-tyrosine methylester amide (TMA) of PGF_2α and PGF_2α-MUM were developed.Antibody to PGF_2α was produced in rabbits immunized with conjugates of PGF_2α coupled to bovine serum albumine. Antibody to PGF_2α-MUM was also produced in rabbits immunized with conjugates of PGF_2α-MUM coupled to bovine serum albumin.PGF_2α-¹²⁵I-TMA had an affinity to antiserum to PGF_2α. PGF_2α-MUM-¹²⁵I-TMA also responded to antiserum to PGF_2α-MUM.     

Radioimmunoassay of main urinary metabolite of prostaglandin F2α

Radioimmunoassay of 5α,7α-dihydroxy-11-keto-tetranorprosta-1,16-dioic acid, main urinary metabolite of prostaglandin F₂α (PGF₂α), was performed using an antiserum produced in the rabbit.The antibody in 100 μ1 of 1,600-fold diluted antiserum binds with 60 picograms of metabolite.The main urinary metabolite level fell when flufenamic acid, a prostaglandin synthetase inhibitor, was given to rats. In contrast, it was significantly elevated when PGF₂α was administered.     

Is prostaglandin F2α involved in the increased myometrial contractility of primary dysmenorrhoea?

The concentrations of prostaglandin F₂α (PGF₂α) and E₂ (PGE₂) in menstrual fluid collected daily from 13 women with primary dysmenorrhoea and 11 matched controls, were compared with the pattern of uterine contractility during the hour following the menstrual fluid collection. The intra-uterine pressure (IUP) was measured using a micro-transducer catheter and the tracings analysed.On Day 2 the concentration of PGF₂α correlated with the peak area, but not with amplitude, duration or rate of contraction. These findings add additional support to the hypothesis that increased production of PGF₂α could contribute to the increased uterine contractility in primary dysmenorrhoea.     

Serum prostaglandin F2α concentration in the carcinoid syndrome

Using specific radioimmunoassay procedures we measured prostaglandin F₂α (PGF₂α) and 13, 14-dihydro-15-keto prostaglandin F₂α (PGF₂α metabolite) in 12 patients with carcinoid tumors. Although PGF₂α and PGF₂α metabolite were each modestly elevated in 17% of the patients the magnitude of the elevation did not correlate with the symptoms of the carcinoid syndrome. The 24 hour urinary 5-hydroxyindoleacetic acid excretion showed a good correlation with carcinoid symptoms while the serum serotonin concentration showed a fair correlation with carcinoid symptoms. We conclude that serum elevation of PGF₂α is not a frequent occurrence in patients with the carcinoid syndrome.     

Anandamide-derived Prostamide F2α Negatively Regulates Adipogenesis

Lipid mediators variedly affect adipocyte differentiation. Anandamide stimulates adipogenesis via CB₁ receptors and peroxisome proliferator-activated receptor γ. Anandamide may be converted by PTGS2 (COX2) and prostaglandin F synthases, such as prostamide/prostaglandin F synthase, to prostaglandin F_2α ethanolamide (PGF_2αEA), of which bimatoprost is a potent synthetic analog. PGF_2αEA/bimatoprost act via prostaglandin F_2αFP receptor/FP alt4 splicing variant heterodimers. We investigated whether prostamide signaling occurs in preadipocytes and controls adipogenesis. Exposure of mouse 3T3-L1 or human preadipocytes to PGF_2αEA/bimatoprost during early differentiation inhibits adipogenesis. PGF_2αEA is produced from anandamide in preadipocytes and much less so in differentiating adipocytes, which express much less PTGS2, FP, and its alt4 splicing variant. Selective antagonism of PGF_2αEA receptors counteracts prostamide effects on adipogenesis, as does inhibition of ERK1/2 phosphorylation. Selective inhibition of PGF_2αEA versus prostaglandin F_2α biosynthesis accelerates adipogenesis. PGF_2αEA levels are reduced in the white adipose tissue of high fat diet-fed mice where there is a high requirement for new adipocytes. Prostamides also inhibit zebrafish larval adipogenesis in vivo. We propose that prostamide signaling in preadipocytes is a novel anandamide-derived antiadipogenic mechanism.     

Evaluation of the role of the F prostaglandins in canine bile flow

Prostaglandin F_2α (PGF_2α) has been shown to be an effective stimulant of hepatic bile flow producing a specific chloride rich bile. Subsequent evaluation by radioimmunoassay has shown that prostaglandin F compounds are present in relatively large amounts in canine hepatic bile. This study evaluates the effect of PGF_2α administration and of prostaglandin synthetase inhibition by aspirin and indomethacin on bile flow and radioimmunoassayable prostaglandin F (iPGF) secretion. Chronic, canine bile fistula preparations were utilized and the enterohepatic circulation was maintained by intravenous bile salts. Bile volume and composition were evaluated by standard techniques as well as bile PGF concentration by radioimmunoassay during bile salt infusion and during bile salt and PGF_2α, aspirin and indomethacin infusion in varying doses. Both aspirin and PGF_2α were potent stimulatns of hepatic bile flow with aspirin producing a chloride rich bile similar to that produced by PGF_2α. PGF_2α produced dose related increases in bile iPGF concentration and output indicating that as the systemic concentration increases during infusion of PGF_2α the lipid appears in bile. Aspirin in the highest dose administered, decreased iPGF concentration in bile while output was unchanged. Indomethacin was ineffectual in consistently altering bile flow or iPGF secretion. This study demonstrates that iPGF is present in canine bile, that its concentration can be altered by prostaglandin infusion while prostaglandin synthetase inhibition has minimal effects on bile iPGF secretion.     

Bronchopulmonary effects of prostaglandin F2α and three of its metabolites in the dog

The airway and lung dynamics of prostaglandin F_2α (PGF_2α) and three of its metabolites were examined in the spontaneously-ventilated, pentobarbital anesthetized dog. Changes in expiratory flow rate, tidal volume, respiration rate, lung resistance and dynamic lung compliance were evaluated and compared quantitatively. In a dose range of 0.3–3.0 μg/kg i.v., PGF_2α and its 13,14-dihydro metabolite were found to be exceptionally potent agents. This metabolite was approximately twice as potent as PGF_2α on most parameters studied. Two other metabolites, 15-keto-PGF_2α and 15-keto-13,14-dihydro-PGF_2α, were only slightly effective, even in a dose range of 1.0–30.0 μg/kg i.v. These latter two metabolites produced dose-response curves with significantly shallower slopes than PGF_2α and were shown to be at least thirty-five times less potent than the parent compound. Therefore, oxidation of PGF_2α at the carbon-15 position by 15-hydroxy prostaglandin dehydrogenase appears to produce compounds with minimal bronchopulmonary activity.     

Gardiovascular responses to prostaglandin f2α in spontaneously hypertensive rats

To test the hypothesis that abnormal prostaglandin reactivity may be a characteristic of essential hypertension, cardiovascular responses to prostaglandin F_2α (PGF_2α) were measured in young spontaneously hypertensive (SHR) and Wistar normotensive rats (NR). PGF_2α(1 sec injection; 50 l/100 g.; .05, .5, 5, 50 g salt/kg) was injected retrograde into the femoral artery. Maximum changes were measured with respect to: 1) four different diameter categories of cremaster muscle arterioles, 2) mean arterial pressure (MAP), 3) pulse pressure (PP) and 4) heart rate. PGF_2α at 5 and 50 g/kg significantly increased NR and SHR blood pressure. SHR MAP increased significantly more than NR MAP with the 50 g dose (P <. 001). PGF_2α increased NR PP at the 50 g/kg dose and increased SHR PP at the .5, 5 and 50 g/kg dose. SHR PP response was significantly greater than that of the NR with the .5, 5 and 50 g/kg dose (P < .05, .01, .001 respectively). The mean SHR arteriolar constriction was greater than that of NR with the 50 g dose. The only change in heart rate was a 3% decrease from control in both NR and SHR during the pressor response to 50 g/kg. These results show an increased cardiovascular reactivity to PGF_2α in SHR and may further suggest prostaglandin involvement in hypertensive disease.     

Luteolytic action of 15-keto prostaglandin F2α in the rhesus monkey

The naturally-occurring metabolite of prostaglandin F_2α, 15-keto prostaglandin F_2α (15-keto PGF_2α), elicited rapid and sustained declines in serum progesterone concentrations when administered to rhesus monkeys beginning on day 22 of normal menstrual cycles. Evidence for luteolysis of a more convincing nature was obtained in studies where a single dose of 15-keto PGF_2α was given on day 20 of ovulatory menstrual cycles in which intramuscular injections of hCG were also given on days 18–20; serum progesterone concentrations fell precipitously in monkeys within 24 hours following intramuscular administration of 15-keto PGF_2α. However, corpus luteum function was impaired in only 4 of 11 early pregnant monkeys when 15-keto PGF_2α was administered on days 30 and 31 from the last menses, a time when the ovary is essential for the maintenance of pregnancy. Gestation failed in 2 additional monkeys 32 and 60 days after treatment with 15-keto PGF_2α, but progressed in an apparently normal manner in the remaining 5 animals. Two pregnant monkeys treated with 15-keto PGF_2α on day 42 from the last menstrual period, a time when the ovary is no longer required for gestation, continued their pregnancies uneventfully. Corpus luteum function was not impaired in 9 control monkeys which received injections of vehicle or hCG at appropriate times during the menstrual cycle or pregnancy.     

Tracheobronchial irritancy of inhaled prostaglandins in the conscious cat

A novel test was developed to measure the tracheobronchial irritant activity of inhaled prostaglandins. Conscious restrained cats were challenged with seperate aerosols of PGE₁, PGF_2α, acetylcholine or isoprenaline. All of the aerosols except isoprenaline caused coughing in a concentration related manner. Tolerance developed very quickly to the tracheobronchial irritation and lasted 1–2 days for PGE₁ and less than 1 day for PGF_2α and acetylcholine. When a 3 day interval between each aerosol challenge was used, PGF_2α was approximately 700 times more potent than acetylcholine as a tracheobronchial irritant. The highest PGE₁ aerosol concentration (500 μg/ml) also caused sedation, diarrhoea and salivation. This test probably provides a useful method for evaluating the tracheobronchial irritant activity of potential prostaglandin bronchodilator analogues and for investigating the mechanism of action of prostaglandin induced tracheobronchial irritancy.     

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.     

Comparison of three subcutaneous modes of prostaglandin F2α administration for pregnancy termination in the hamster

Dose response relationships for pregnancy termination in hamsters following administration of prostaglandin F_2α (PGF_2α by three subcutaneous methods were determined in 526 hamsters. The median effective dose (ED₅₀) for PGF_2α given as a single subcutaneous injection in 500 μl of saline was 22.2 μg. Administration of the prostaglandin with an Alzet® osmotic minipump (subcutaneous insertion for 24 hours) required 1.35 times more PGF_2α (ED₅₀ = 30.0 μg). The least effective method of prenancy termination in the hamster involved administration of PGF_2α by a single subcutaneous injection in 20.4 μl of saline (the same volume delivered by the minipump in 24 hours); the ED₅₀ for this method of administration was 41.3 μg of PGF_2α.     

The identification of prostaglandins E(2), F(2alpha) and A(2) from rabbit kidney medulla

Rabbit kidney medulla (10kg.) was homogenized in 5mm-disodium hydrogen phosphate and deproteinized with ethanol, and the concentrated supernatant solution was extracted at pH8 with light petroleum and at pH2 with chloroform. The acidic lipids present in the chloroform phase were separated on silicic acid columns into three biologically active fractions. The first fraction contained only vasodepressor activity; the second fraction contained both vasodepressor and non-vascular-smooth-muscle-stimulating activity; the third fraction contained both vasopressor and non-vascular-smooth-muscle-stimulating activity. Purification of each fraction by reversed-phase partition and thick-layer chromatography yielded three pure acids. Thin-layer chromatographic, spectroscopic and mass-spectral analysis of the acids and their methyl esters established their structures as prostaglandins E₂, F_2α and A₂. Evidence is presented demonstrating that part or all of the prostaglandin A₂ is formed during the isolation procedures from endogenous prostaglandin E₂.     

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.