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.     

Prostaglandins have limited actions on abnormalities of beating induced in cultured heart cells

Prostaglandins are antiarrhythmic in a variety of situations including ischaemic arrhythmias, but the mechanisms involved are not known. In view of this, the protective actions of prostaglandins A₂, E₂, F_1α, F_2β, and I₂ against abnormalities of beating induced in cultured heart cells were investigated. Abnormalities of beating were induced in single cells by a variety of agents including ouabain, Ca⁺⁺, K⁺, dinitrophenol (DNP), and toxic material from the jellyfish . Abnormalities were assessed in terms of rate, rate range, subjective arrhythmic behaviour and percent cells beating. The prostaglandins (at 10⁻⁷-10⁻⁵ M) were added with the arrhythmogenic agent to test for their ability to modify agent-induced beating abnormalities and were compared with lidocaine and quinidine. Prostaglandins alone had minimal direct effects on the cells and only minimally reduced responses to arrhythmogenic agents. The most protective prostaglandins, PGE₂ and PGF_1α, tended to normalise beating behaviour most noticeably in DNP-treated cells, unlike lidocaine and quinidine which were effective against Ca⁺⁺-induced changes while worsening those of K⁺. Thus, a general ability to protect disturbed cardiac cells is not seen with high concentrations of prostaglandins.     

The action of prostaglandin E2 and F1α on myocardial ischaemia-infarction arrhythmias in the dog

Prostaglandin E₂ and F_1α infusions have been tested for their ability to reduce the arrhythmias associated with occlusion of the left descending coronary artery in the anaesthetised dog. At 1 μg/kg/min both PGs reduced the incidence of premature ventricular contractions occurring during 25-min occlusions, while not reducing the incidence of ventricular fibrillation occurring on occlusion release. When infused for 5-min periods at 1 to 16 μg/kg/min, neither PGE₂ nor PGF_1α effectively reduced the frequency of ventricular arrhythmias occurring 24 hr after a permanent coronary occlusion.     

Regional and species differences in endogenous prostaglandin biosynthesis by brain homogenates

Endogenously formed prostaglandins (PGs) D₂, E₂ and F_2α were determined in homogenates of brain regions from rat, guinea-pig, rabbit and cat, using gas-chromatography-mass spectrometry. The main PGs formed in the brain regions of the rat were PGD₂, in the guinea-pig PGD₂ and PGF_2α, in the rabbit PGF_2α and in the cat PGE₂. Brain regions from the same animal species showed the same pattern of PG formation. They varied, however, in the amount of total PGs formed, the limbic system and the cerebral cortex being highest and cerebellum lowest.     

Prostaglandins in the isolated testicular capsule of immature and young adult rats

The presence of prostaglandin (PGs) E₁, E₂, F_1α, F_2α and the metabolite 13, 14-Dihydro-15-keto PG Fa (1+2) has been studied in the isolated testicular capsule of Wistar rats (22 to 90 days of age). Handling and homogenization of tissues were controlled and the in vitro synthesis and degradation were prevented by immediated freezing of samples and homogenization in a solution containing of PG synthetase inhibitor. The PGs were measured by specific and sensitive radioimmuoassay. The isolated rat testicular capsule was found to contain mainly PG E₂ and PG_2α at concentrations about 100 times higher than those in decapsuled testes (ng/g of tissue).     

Follicle stimulating hormone and prolactin release induced by prostaglandins in rat

Ten to 60 minutes following a single i.v. injection of PGE₂ (500 μg/rat) into male rats of 30 to 35 days of age FSH concentration in the serum was raised significantly. The rise in FSH was maintained from 10 to 60 minutes after treatment, then at 90 minutes FSH had declined and was not significantly different from that of the control before treatment. Prostaglandin E₁, E₂ or F_2α (670μg/rat) significantly increased the serum prolactin level 10 to 60 minutes after a single i.v. injection in spayed rats primed with estrogen and progesterone. And, rats primed with estrogen and progesterone. And, increases in prolactin in the serum were observed with as little as 2μg of PGE₁ or E₂, and 20μg of PGF_2α. Twenty μg of PGE₂, and 200μg of PGE₁ or F_2α gave the maximum stimulation. These results indicate that release of pituitary hormones is affected by prostaglandins.Prostaglandins (PGs) are widely distributed in mammalian tissues, and they have been reported to have an almost equally wide variety of endocrine and metabolic effects. It was recently postulated that PGs may be involved in the process of ovulation because ovulation was blocked by inhibitors of PG synthesis (1–5).     

Effects of prostaglandins and arachidonic acid on baboon cerebral and mesenteric arteries

Effects of prostaglandins (PGs) E₁, E₂, F_2α and I₂ in a wide range of concentration were examined in mesenteric and cerebral arteries isolated from mature baboons. PGs E₁, E₂ and F_2α at low concentrations (10⁻¹⁰ to 10⁻⁷ M) elicited relaxation in helically cut strips of cerebral arteries precontracted with phenylephrine. In contrast, the PGs did not cause relaxation in the mesentric artery. PGI₂ (10⁻⁹ to 10⁻⁶ M) produced marked relaxation in both arteries. The EC₂₅ for PGI₂ in the mesenteric artery was significantly lower than that in the cerebral artery. During baseline conditions, cerebral arteries contracted in response to high concentrations (greater than 10⁻⁷ M) of PGs E₁, E₂ and F_2α. In mesentric arteries, a large contraction was induced by PGs F_2α and E₂ but not by PGE₁. Arachidonic acid (10⁻⁶ M) produced an aspirin-inhibitable relaxation in both arteries to a similar extent, so that the vasodilator PG(s) formed in the two different arterial walls appear to exert a similar relaxant action. Thus, the baboon mesenteric artery was more sensitive to PGI₂ for the relaxant effect than was the cerebral artery, while PGs F_2α, E₁ and E₂ caused only a contraction in the mesenteric artery but both relaxation and contraction in the cerebral artery.     

Triphasic effect of prostaglandins E1, E2 and F2α on the fluid transport of isolated gall-bladder of guinea-pigs

Prostaglandins (PGs) F_2α, E₁ and E₂ exerted a triphasic influence on the fluid transport of isolated guinea-pig gall-bladders, when applied to the serosal side. PGE₁ and PGE₂ produced these effects in lower concentrations than F_2α. Directly after PG addition to the serosal side a short stimulation of fluid transport to between 200 and 400% was observed. The stimulatory effect of PGs was most distinct in gall-bladders from female guinea-pigs, less pronounced in male and nearly absent in pregnant animals. Since PGs increased intraluminal hydrostatic pressure in gall-bladders by contraction of the smooth muscle, experiments were performed in which hydrostatic pressure was increased by different procedures. These included the addition of imidazole (10⁻² M), raising of K⁺ in the bathing solution and an increase in intraluminal pressure by addition of Ringer's solution into the lumen. All three procedures stimulated fluid reabsorption temporarily in the same way as PGs, hence increase of intraluminal pressure is thought to be the reason for the observed temporary stimulation of fluid transport. Direct evidence for this thesis was obtained when the gall-bladder was mounted as a flat sheet over a chamber; in this preparation no stimulation of fluid transport was obtained. The second phase of the PG influence was characterized by a concentration-related inhibition of fluid reabsorption followed by a significant but small reverse of fluid transport (secretion of fluid). When PGs were applied to the mucosal side, only an inhibition of fluid transport was observed, which was much weaker compared to the addition to the serosal side.     

Sow (Sus scrofa) follicular fluid: Prostaglandin content and effect on the motility of isolated oviducts

The present study provides information regarding the effects of the sow follicular fluid (FF) on the motility of isolated segments of swine and rabbit oviducts. In addition, the concentration of prostaglandins (PGs) F_{2 α}, E₂ and E₁ in the follicular fluid of sow ovaries isolated at different stages of the sex cycle as well as the generation of the same PGs by walls of ovarian follicles in early and late proestrus, in estrus, in metestrus and in diestrus, were explored. The stimulatory contractile effect of proestrous FF in isolated segments of sow fimbria was antagonized by polyphloretin phosphate (PPP), a PG receptor blocker and by indomethacin, an inhibitor of PG synthesis. The positive inotropism evoked by the FF was mimiked by bradykinin and the influences of both interventions were similarly antagonized by PPP. It appears plausible that the inotropic effect of the preovulatory FF on the sow fimbria could be not only by PGs already present in the fluid, but also by the stimulation of the synthesis of tubal PGs by follicular fluid bradykinin. The FF also stimulated the ampullary tubal segments isolated from proestrous sows whereas the same volume of FF depressed significantly the isometric developed tension of rabbit ampulla. The total concentration of the three PGs in the FF from late proestrous follicles was significantly greater than that of the same PGs in the other two stages of the sex cycle (early proestrus and diestrus), whereas the concentration of each PG (PGE₂, PGF_{2 α} or PGE₁), did not differ within any of the stages of the cycle. Furthermore, the total amount of the three PGs produced by the walls of follicles from late proestrous ovaries was also significantly greater than that generated by ovarian follicles from early proestrus, estrus, metestrus and diestrus.     

Role of endogenous and exogenous prostaglandins on the contractile functioning of isolated sow (Sus scrofa) oviducts

The output prostaglandins (PHs) E₁, E₂ and F₂ α, from ampullary and isthmic portions of sow oviducts isolated during proestrus, estrus and metestrus, was explored. Moreover, $\text{in vitro}$ cumulative dose-response curves for the contractile effect of these three PGs, on identical oviductal segments, were constructed. Isthmic preparations form proestrous and metestrous animals released more PGE₁ and PGF₂ α than PGE₂ “like material”. During estrus, the outputs of PGE₁, PGE₂ and PGF₂ α were similar, whereas, oviducts from proestrous and metestrous sows released less PGE₁ and PGF₂ α than during estrus. Although the output of PGE₂ “like material” from isthmic and ampullary segments did not differ significantly during the three stages of the sex cycle, ampullary metestrous preparations released more PGE₁ and PGF₂ α, than estrous or proestrous ones. The addition of PGE₁, PGE₂ α, consistently stimulatedthe amplitude of contractions of isthmic oviductal segments isolated from proestrous and metestrous sows. Within the concentration-range explored, dose-response curves for PGE₂ and PGE₁ were to the left of those for PGF₂ α in the isthmus obtained before ovulation (proestrus) but not in segments isolated at later times (2–3 days) of the cycle (metestrus). The stimulatory dose-response curves for PGE₁, or PGE₂, in isthmic segments of metestrous preparations incubated with phentolamine (10^?6M) were shifted to the right of controls not exposed to the adrenoreceptor blocker, whereas, the curve for PGF₂ α without phentolamine, was identical to that obtained in its presence. PGE₁ and PGE₂ did not evoke significant contractile effects on oviductal ampullary protions from proestrous sows, wherea, PGF₂ α was clearly stimulatory at concentrations of 10^?9M and higher. In ampullary segments isolated after ovulation (metestrus) the threshold for contractile enhancement following PGF₂ α was greater than during proestrus, whereas, PGE₁ elicited a significant inhibition of contractions. The spontaneous contractile pattern exhibited by isthmic and ampullary oviductal regions, prior to and after ovulation, is discussed in terms of tissue PG generation and output and is compared with results regarding tubal motility following the exposure to exogenous PGs.     

Determination of prostaglandin F2α, E2, D2 and 6-keto-F1α in human cerebrospinal fluid

Prostaglandin (PG)F_2α, E₂, D₂ and 6-keto-F_1α were determined in human cerebrospinal fluid by a mass spectrometric technique. The samples were obtained from 12 patients with suspected intracranial disease. A 64 fold variation in PG levels was observed. The major PG was 6-keto-F_1α (0.12–15 ng/ml). PGF_2α and PGE₂ were present in lower concentrations PGD₂ was below the level of detection (0.05 ng/ml) except in one patient with extremely high total levels of PGs.     

Kinetic changes in rat renal 15-hydroxy-prostaglandin dehydrogenase induced by chronic ethanol exposure

Several lines of investigation have suggested that exposure to ethanol may lead to alterations in both the synthesis and degradation of the E and F series of prostaglandins (PG). It has been suggested that these changes in PG metabolism underlie cartain of the pathophysiological consequences of chronic alcoholism but few data re availalbe as to the mechanism resonsible for these changes. We now report that chronic exposure to ethanol in moderate doses (17% total dietary calories as ethanol) and high doses (35% total dietary calories as ethanol) results in a concentration dependent loss of renal 15-hydroxy-prostaglandin dehydrogenase for the NAD mediated reactioins. Soluble fractions of kidney homogenates in teh presnet of > 10 K_m concentratons of NAd exhibited dose dependent loss of specific and total organ PG dehydrogenase activity toward PGE₂ and F_2α. A similar dose dependent decrease in the V_max of the NAD mediated reaction was measured for the oxidation of PGE₁, E₂, and F_2α. Moderate doses of ethanol resulted in an increase in the K_m for PGE₂ and F_2α. K_m values for the NADP mediated reactions were not significantly influenced by exposure to high doses of ethanol other than for PGE₁. These data suggest that chronic ethanol consumption results in a dose dependent, selective inhibition of the metabolism of PGs of the “2” series by the renal PGDH enzyme which utilizes NAD.     

Relative contracting adn relaxing potencies of a series of prostaglandins on isolated canine mesenteric artery strips

The contracting and relaxing potencies of anf interactions between a number of prostaglandins (PGs) were studied $\text{in vitro}$ on spiral strips of small canine mesenteric arteries (outside diameter < mm). PGF₂α and PGE₂, the most potent contracting PGs, were nearly equal in potency (EC₅₀ 4 × 10^?7M) and did not cause relaxation under our experimental conditions. PGI₂ and PGE₁ were equal and the most potent relaxing PGs (EC₅₀ 3 × 10^?9M). PGE₁ also caused contraction, but this effect was not consistent. PGI₂ did not cause contraction in concentrations up to 3 × 10^?6M. In higher concentrations, however, it caused abrupt and near maximal contraction. PGD₂ was weak in both respect, causing incomplete relaxation and contraction or biphasic effects. Interaction studies showed that PGE₁ and PGI₂ mutually excluded the relaxing effects of each other. PGE₁ also reversed the relaxing effect of isoproterenol. However, pre-exposure to PGD₂ did not attenuate the relaxing effect of PGE₁ or PGI₂ nor was the relaxing effect of PGD₂ changed by pre-exposure to PGE₁. Two different orders of potency of PGs suggest two PG receptors subserving contraction and relaxation, respectively. Further, it appears that several PGs can act upon both receptors which may explain unusual interactions between the PGs and some of their atypical effects. Finally, the data also suggest that there may be subtypes of the PG receptors subserving contraction and relaxation.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE₂, PGE₁, PGI₂). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE₁, PGE₂, PGI₂) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maximas. The results suggest that renal PGs (PGE₂ and PGI₂) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.     

Studies of prostaglandins and prostaglandin antagonists on bovine pulmonary vein in vitro

Acetylsalicylic acid (ASA), indomethacin, sodium meclofenamate (FEN), phenylbutazone (PB), phloretin phosphates (PP), SC-19220, and diethylcarbamazine citrate (DECC) were screened against histamine, 5-hydroxytryptamine (5-HT), bradykinin, acetylcholine, and prostaglandins (PG) E₁, E₂, and F_2α to determine their specificity in antagonizing PG's on the bovine pulmonary vein. PG E₂ relaxed the smooth muscle preparation at low concentrations and induced contraction at higher concentrations. PG E₁ consistently evoked dose-related relaxations, whereas PG F_2α contracted the bovine pulmonary vein. Studies with inhibitors suggest that the different actions of prostaglandins could be mediated through different receptors. Sodium meclofenamate and PP dimer blocked PG E₂-induced contractions, whereas relaxations were not blocked. DECC inhibited the relaxant effect of PG E₂. DECC also antagonized histamine, 5-HT, and PG F_2α, suggesting the drug is rather non-specific. Phenylbutazone antagonized the actions of both PG E₂ and PG F_2α on the bovine pulmonary vein. By classifying receptors by antagonism the bovine pulmonary vein appears to contain PG E₂ (PP-type), PG E₂ (FEN-type), PG E₂ (PB-type), and PG F_2α (PB-type) receptors. An absence of SC-type PG-receptors is noted.     

Morphine diminishes the constancy of spontaneous uterine contractions, antagonizes the positive inotropic effects of prostaglandin E2, but not of prostaglandin F2α and inhibits prostaglandin E and F outputs from the uterus of ovariectomized rats

The effects of morphine on the constancy of spontaneous contractions (isometric developed TENSION = IDT and contractile FREQUENCY = CF), in uterine strips isolated from ovariectomized rats and the influence of naloxone, were explored. The inotropic responses to added prostaglandins (PGs) E₂ and F_2α and the influences of morphine and of morphine in the presence of naloxone on PG actions, were also determined. Moreover, the synthesis and outputs of PGs E and F from uteri and the effects of morphine alone and of morphine plus naloxone, were studied. Morphine (10⁻⁶ M) significantly depressed uterine constancy of IDT during the first hours following delivery, but its action on CF did not differ from controls. Naloxone, neither at 10⁻⁸ M nor at 10⁻⁶ M, altered the negative inotropoic influence of morphine on IDT. Exogenous PGs E₂ and F_2α, stimulated uterine inotropism in a concentration-dependent fashion. Morphine altered dose-response curves for exogenous PGE₂, evoking a parallel surmountable shift to the right, but did not affect the inotropic action of added PGF_2α. This antagonistic effect of the opioid was not altered by preincubation with naloxone. Basal synthesis and outputs of PGs E and F in uteri from ovariectomized rats were significantly depressed by morphine (10⁻⁶ M) but not altered by incubating tissues with morphine in presence of naloxone. Results are discussed in terms of a presumptive dual action of morphine on uterine motility, i.e., antagonizing PGE₂ receptors and inhibiting the synthesis of some PGs by the uterus. These influences of morphine do not appear to be subserved by the activation of μ opioid receptors. Moreover, the possibility that endogenous opioids could play a relevant role modulating uterine PG influences, is also discussed.     

Paradoxical endogenous synthesis of a coronary dilating substance from arachidonate

Isolated bovine, canine, and human coronary arteries exhibited dose dependent contractions to prostaglandin (PG) E₂ and F_2α (50 ng/ml to 10 μg/ml). The ED₅₀ value for both PGE₂ and PGF_2α was 500 ng/ml in the bovine and human coronary arteries. Paradoxically, although PGE₂ and PGF_2α are vasoconstrictors, administration of their precursor, arachidonate (100 ng/ml to 10 μg/ml) caused relaxation of the bovine, canine and human coronary arteries. This observation suggests that arachidonate is not being converted by the coronary PG synthetase to PGE₂ or PGF_2α. However, the arachidonate induced coronary relaxation was inhibited by pretreatment with PG synthetase inhibitors, indomethacin, meclofenemate and aspirin. Indomethacin addition to the strips previously relaxed by arachidonate caused contraction. In contrast to other PGs (E₂ and F_2α), PGE₁ (10 ng/ml to 10 μg/ml) caused dose dependent relaxation of the bovine coronary arteries (ED₅₀ = 100 ng/ml). Indomethacin induced further relaxation of the blood vessels previously relaxed by PGE₁. Since PGE₁ cannot arise from arachidonate, the arachidonate coronary dilation and reversal by indomethacin must be independent of PGE₁ formation. Linolenate (100 ng/ml to 10 μg/ml) and oleate (100 ng/ml to 10 μg/ml) also caused relaxation of the bovine coronary blood vessels both before and after indomethacin, thereby eliminating a direct non-specific fatty acid effect as the cause of the arachidonate relaxation. These results suggest that in isolated coronaries, arachidonate undergoes a novel conversion, possibly by PG synthetase, to a dilating substance which exerts different contractile effects than exogenously administered PGE₂, PGF_2α and PGE₁.This work was supported by (USPHS) training grants NS 05221, RCDA (P.N.) HL-19586, HL-11771A, HL-14397 and SCOR grant HL-17646, HL-17646-0.     

Phosphatidylethanolamide derivatives of prostaglandins E1 and E2

Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) have been coupled with the amine group of phosphatidylethanolamine (PE) by means of dicyclohexylcarbodiimide. These complexes basically mimic the relaxant and contractile effects of the corresponding free prostaglandins (PGs) on various smooth muscle preparations, but exhibit a delayed onset of action and a lower affinity for the PG receptors. The complexes are comparable with the free, parent PGs, in their intrinsic activities. The same holds true for the effects on blood pressure and on the motility of the uterus . The PGE₂-PE complex is hydrolysed to release obviously free PGE₂ by cell-free homogenates prepared from various tissues, but not by blood plasma. The PGE₂-PE complex is immunologically indistinguishable from the free PGE₂.     

Effect of prostaglandins on cyclic nucleotide levels in cultured keratinocytes

Guinea pig ear epidermal cells (keratinocytes) were established in primary cultures using trypsin, and treated in their proliferative phase of growth with prostaglandins E₁, D₁, F_1α, E₂, D₂, or F_2α. This phase is induced by the addition of retinoic acid during cell plating. Intracellular content of cAMP and cGMP was measured by radioimmunoassay at various times after treatment.Maximum stimulation of cAMP levels was observed with PGD₂, smaller increases with PGE₂ and relatively transient rises with PGF_2α which were of low significance, but confirm earlier data. Similar results were observed with PGD₁, PGE₁, and PGF_1α with smaller increases. The effects of D and E PGs were biphasic. Significant increases in cGMP were immediately observed with PGD₂ and PGE₂. With PGF_2α, maximum cGMP levels were noted after some delay.All PGs tested showed some effect in elevating cyclic nucleotides in keratinocytes. The most striking result was the increase in cAMP on PGD₂ treatment.     

Prostaglandin-induced enhancement of the in vitro anamnestic response

The ability of various prostaglandins (PGs) to affect the $\text{in vitro}$ anamnestic immune response of keyhole limpet hemocyanin (KLH)-primed rabbit popliteal lymph node cells was investigated. Of the four PGs studied (PGA₁, PGE₂ and PGF_2α), PGE₁ was found to have a stimulatory effect, whereas PGA₁, PGE₂ and PGF_2α were ineffective in stimulating or inhibiting the $\text{in vitro}$ anamnestic response. Under the conditions studied, a 3.5-fold increase in antibody production was obtained in PGE₁-treated, KLH-stimulated cultures. Maximum enhancement was obtained when 0.2 μg of PGE₁ were added at the time of culture initiation and were allowed to remain in contact with the lymph node cells for 24 hours.