The central nervous effect of prostaglandins I2, E2 and F2 alpha on aconitine-induced cardiac arrhythmia in rats.

Intracerebroventricular administration of PGI2 or PGE2 reduced aconitine-induced cardiac arrhythmia in rats. PGF2 alpha had no antiarrhythmic effect under the same conditions. The ED50 values of PGI2 and E2 were 0.25 microgram/kg and 1.1 microgram/kg, respectively. Central mechanisms may participate in the antiarrhythmic effect of these PGs.     

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.     

Characterization of prostaglandin (PG)-binding sites expressed on human basophils. Evidence for a prostaglandin E1, I2, and a D2 receptor.

Recent data suggest that prostaglandins (PGs) are involved in the regulation of basophil activation. The aim of this study was to characterize the basophil PG-binding sites by means of radioreceptor assays using 3H-labeled PGs. Scatchard analysis for pure (greater than 95%) chronic myeloid leukemia (CML) basophils revealed two classes of PGE1-binding sites differing in their affinity for the natural ligand (Bmax1 = 217 +/- 65 fmol/10(8) cells; Kd1 = 0.5 +/- 0.2 nM; Bmax2 = 2462 +/- 381 fmol/10(8) cells; Kd2 = 47 +/- 20 nM; IC50 = PGE1 less than PGI2 less than PGD2 less than PGE2 less than PGF2 alpha) as well as two classes of PGI2 (iloprost)-binding sites (Bmax1 = 324 +/- 145 fmol/10(8) cells; Kd1 = 0.5 +/- 0.3 nM; Bmax2 = 2541 +/- 381; Kd2 = 27 +/- 6 nM; IC50 = PGI2 less than PGE1 less than PGD2 less than PGE2 less than PGF2 alpha. In addition, CML basophils exhibited a single class of PGD2-binding sites (Bmax = 378 +/- 98 fmol/10(8) cells; Kd = 13 +/- 4 nM; IC50: PGD2 less than PGI2 less than PGE1 less than PGE2 less than PGF2 alpha). In contrast, we were unable to detect specific saturable PGE2-binding sites. Primary and immortalized (KU812) CML basophils revealed an identical pattern of PG receptor expression. Basophils (KU812) expressed significantly (p less than 0.001) lower number of PGE1 (PGI2)-binding sites (Bmax1: 9% (20%) of control; Bmax2: 36% (50%) of control) when cultured with recombinant interleukin 3 (rhIL-3), a basophil-activating cytokine, whereas rhIL-2 had no effect on PG receptor expression. Functional significance of binding of PGs to basophils was provided by the demonstration of a dose-dependent increase in cellular cAMP upon agonist activation, with PGE1 (ED50 = 1.7 +/- 1.1 nM) and PGI2 (ED50 = 2.8 +/- 2.3 nM) being the most potent compounds. These findings suggest that human basophils express specific receptors for PGE1, PGI2 as well as for PGD2.     

The lack of involvement of central nervous system in the antiarrhythmic effects of prostaglandins E2, F2 alpha, and I2 in cat

The role of the central nervous system (CNS) in the antiarrhythmic effects of prostaglandins (PGs) E2, F2 alpha, and I2 was studied by administering each agent into the left lateral cerebral ventricle (i.c.v. administration) of chloralose-anaesthetized cats. The cardiac arrhythmias were produced by intravenous (i.v.) infusion of ouabain (1 microgram/kg/min). The PGs E2, F2 alpha and I2 on i.c.v. administration in the dose range of 1 ng to 10 micrograms failed to inhibit ouabain-induced cardiac arrhythmias. However, when infused i.v., PGE2 (1 microgram/kg/min), PGF2 alpha (5 micrograms/kg/min), and PGI2 (2 micrograms/kg/min) effectively suppressed these arrhythmias. The standard antiarrhythmic drug propranolol (0.5-8.0 mg) on i.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, F2 alpha, and I2 in antagonising the ouabain-induced cardiotoxicity in cats.     

Effect of oestradiol 17 beta on prostaglandin biosynthesis by the uterus of ovariectomized rat and guinea pig

In vitro prostaglandin biosynthesis by uteri of ovariectomized rats and guinea pigs treated or untreated with oestradiol 17 beta, administered subcutaneously, was measured by R.I.A. of PGF2 alpha and PGE2. Incubations with [1-14C] arachidonic acid were also performed and labelled metabolites were analyzed by TLC. The main metabolite in rats was 6 keto PGF1 alpha and in decreasing order of magnitude, PGF2 alpha and PGE2. In guinea pig PGF2 alpha was the main product. Ovariectomy in rats completely changed the pattern of synthetized prostanoids : PGI2 production was doubled when compared to cycling rats and PGE2 increased 10 fold. PGF2 alpha values were similar to the mean value measured during the cycle. OE2 treatment almost completely inhibited PGI2 synthesis and reduced PGE2 by half. Total PG synthesis in OE2 treated animals was decreased by 5 fold when compared to spayed rats. Endogenous PGF2 alpha synthesis was slightly stimulated. In the guinea pig OE2 treatment of ovariectomized animals increased the total synthesis from 50 per cent. PGF2 alpha was always the main metabolite. In conclusion OE2 regulation of uterine PG synthesis is depending on the animal species and cannot be explained by a unique effect on the cyclooxygenase, but rather by an interplay on the various enzymes of the arachidonic acid cascade.     

Effects of intracerebroventricular administration of prostaglandins I2, E2, F2 alpha and indomethacin on blood pressure in the rat.

The effects of intraventricularly administered prostaglandins I2 (PGI2), E2 (PGE2), F2alpha (PGF2 alpha) and indomethacin on systemic blood pressure were investigated in conscious rats. PGI2 (1.25--10 micrograms/kg) decreased blood pressure in a dose-related manner, whereas PGE2 (100--1000 mg/kg) dose-dependently increased blood pressure. Both PGF2 alpha (0.31--20 micrograms/kg) and indomethacin (0.625--40 micrograms/kg) had no effects on blood pressure. These results indicate that intraventricular injection of PGI2 or PGE2 can induce significant changes in blood pressure, while endogenous prostaglandins synthesized in the brain seem to play a minor role in direct regulation of systemic blood pressure in the rat.     

Prostaglandin synthesis by the cochlea of the guinea pig. Influence of aspirin, gentamicin, and acoustic stimulation

This study describes the synthesis of prostaglandins (PGs) by the vascular structures of the inner ear (lateral wall = stria vascularis and spiral ligament) in vitro. The main PGs produced were PGI2, PGF2 alpha and PGE2. PGI2 and PGF2 alpha were also found in the perilymph. A 350 mg/kg ip injection of aspirin decreased PG synthesis by the lateral wall and PG levels in perilymph. This effect was reversed after 3 days. Gentamicin (10(-9) to 10(-5) M) decreased significantly and reversibly PG synthesis in vitro, as did 100 mg/kg ip injection. Acoustic stimulation increased ex vivo PGI2 and PGE2 synthesis without modifying PG levels in perilymph. Results suggest that PGs could be one humoral mediator of the cochlear microcirculation homeostasis, and, possibly, of the circulatory disturbances reported after acoustic stimulation. The decreased PG synthesis after gentamicin treatment could account for the angiotoxic component observed in aminoglycoside ototoxicity.     

Production of prostaglandins by fetal rat lung type II pneumonocytes and fibroblasts

The output of prostaglandins I2, E2, F2 alpha and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) from third passage day 20 rat fetal fibroblasts and type II alveolar pneumonocytes was studied. In 2 h incubations, the output levels for each cell type were: PGI2 greater than PGE2 much greater than PGF2 alpha = PGFM when cells were incubated with Ca2+ ionophore A23187 (10 microM) or arachidonic acid (1 microgram/ml).     

The actions of prostaglandins I2 and E2 on arrhythmias produced by coronary occlusion in the rat and dog.

Prostaglandins E2 and I2 were compared with known antiarrhythmics for their actions against arrhythmias produced by occlusion of the left anterior descending coronary artery in the anaesthetised rat while PGI2 was also examined in the dog. PGI2 in the dog suppressed early arrhythmias produced during occlusion but did not influence those produced by occlusion-release or those occurring 24 hours after a permanent occlusion; none of the A,B,C or D series prostaglandins tested markedly reduced 24 hour arrhythmias. In the rat PGE2 was antiarrhythmic against early occlusion arrhythmias (30 minutes occlusion) in a dose related manner (infusions of 1-4 microgram/kg/min) whereas PGI2 infusions potentiated the arrhythmogenic effect of occlusion. PGE2 was as effective an antiarrhythmic as 10mg/kg Org. 6001 which was more effective in this test situtation than dl-propranolol. No obvious mechanisms for the actions of PGE2 or PGI2 were apparent although both agents lowered blood pressure and reduced the size of the occluded zone produced by ligation.     

Intraluteal infusions of prostaglandins of the E, D, I, and A series prevent PGF2 alpha-induced, but not spontaneous, luteal regression in rhesus monkeys

A luteotropic role for prostaglandins (PGs) during the luteal phase of the menstrual cycle of rhesus monkeys was suggested by the observation that intraluteal infusion of a PG synthesis inhibitor caused premature luteolysis. This study was designed to identify PGs that promote luteal function in primates. First, the effects of various PGs on progesterone (P) production by macaque luteal cells were examined in vitro. Collagenase-dispersed luteal cells from midluteal phase of the menstrual cycle (Day 6-7 after the estimated surge of LH, n = 3) were incubated with 0-5,000 ng/ml PGE2, PGD, 6 beta PGI1 (a stable analogue of PGI2), PGA2, or PGF2 alpha alone or with hCG (100 ng/ml). PGE2, PGD2, and 6 beta PGI1 alone stimulated (p less than 0.05) P production to a similar extent (2- to 3-fold over basal) as hCG alone, whereas PGA2 and PGF2 alpha alone had no effect on P production. Stimulation (p less than 0.05) of P synthesis by PGE2, PGD2, and 6 beta PGI1 in combination with hCG was similar to that of hCG alone. Whereas PGA2 inhibited gonadotropin-induced P production (p less than 0.05), that in the presence of PGF2 alpha plus hCG tended (p = 0.05) to remain elevated. Second, the effects of various PGs on P production during chronic infusion into the CL were studied in vivo. Saline with or without 0.1% BSA (n = 12), PGE2 (300 ng/h; n = 4), PGD2 (300 ng/h; n = 4), 6 beta PGI1 (500 ng/h; n = 3), PGA2 (300 ng/h; n = 4), or PGF2 alpha (10 ng/h; n = 8) was infused via osmotic minipump beginning at midluteal phase (Days 5-8 after the estimated LH surge) until menses. In addition, the same dose of PGE, PGD, PGI, or PGA was infused in combination with PGF2 alpha (n = 3-4/group) for 7 days. P levels over 5 days preceding treatment were not different among groups. In 5 of 8 monkeys receiving PGF2 alpha alone, P declined to less than 0.5 ng/ml within 72 h after initiation of infusion and was lower (p less than 0.05) than controls. The length of the luteal phase in PGF2 alpha-infused monkeys was shortened (12.3 +/- 0.9 days; mean +/- SEM, n = 8; p less than 0.05) compared to controls (15.8 +/- 0.5). Intraluteal infusion of PGE, PGD, PGI, or PGA alone did not affect patterns of circulating P or luteal phase length.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antiabortifacient action of dibenzyloxyindanpropionic acid in mice

To evaluate the details of the adrenergic stimulation of urinary prostaglandins in man, ten normal volunteers were given various agonists and antagonists. The effect of 4 hour IV infusions of norepinephrine (NE), NE + phentolamine (PHT), NE + phenoxybenzamine (PHB), NE + prazosin (PZ), isoproterenol (ISO), and PHT alone on urinary PGE2 and PGI2 (6 keto PGF1 alpha) were determined. PGE2 and 6 keto PGF1 alpha were measured by radioimmunoassay from 4 hour urine samples. NE stimulated both PGE2 (196 +/- 40 to 370 +/- 84 ng/4 hrs/g creatinine and 6 keto PGF1 alpha (184 +/- 30 to 326 +/- 36), both p less than 0.01. In contrast, ISO had no effect on either PGE2 or 6 keto PGF1 alpha excretion. Alpha blockade with PHT. PHB, or PZ inhibited the NE induced systemic pressor effect. However, the effect of the alpha blockers on the NE induced stimulation of PGE2 and 6 keto PGF1 alpha varied. PHT did not alter the NE stimulated PGE2 or 6 keto PGF1 alpha release (370 +/- 84 vs. 381 +/- 80) PGE2 and (326 +/- 50 vs. 315 +/- 40) 6 keto PGF1 alpha both p greater than 0.2). PHT alone stimulated only 6 keto PGF1 alpha. PHB and the specific alpha 1 antagonist PZ similarly eliminated the NE induced prostaglandin release. These results suggest that adrenergically mediated urinary prostaglandin release in man is via an alpha receptor with alpha 1 characteristics.     

Biosynthesis of prostaglandins and thromboxane B2 by fetal lung homogenates

The conversion of arachidonic acid to prostaglandins (PG's) and thromboxane B2 (TXB2) was investigated in homogenates from fetal and adult bovine and rabbit lungs. Adult bovine lungs were very active in converting arachidonic acid (100 microgram/g tissue) to both PGE2 (10.7 microgram/g tissue) and TXB2 (6.2 microgram/g tissue. Smaller amounts of PGF2alpha (0.9 microgram/g) and 6-oxoPGF1alpha were formed. Homogenates from fetal calf lungs during the third trimester of pregnancy were quite active in converting arachidonic acid to PGE2, but formed very little TXB2, PGF2alpha or 6-oxoPGF1alpha. Homogenates from rabbit lungs converted arachidonic acid (100 microgram/g) mainly to PGE2, both before and after birth. The amount of PGE2 formed increased during gestation to a maximum of about 6 microgram/g tissue at 28 days of gestation. It then decreased to a minimum (1.5 microgram/g) which was observed 8 days after birth, followed by an increase to about 4 microgram/g in older rabbits.     

The effects of prostanoids on estrogen-dominated rat myometrial longitudinal muscle in vitro

The purpose of these experiments was to characterize the contractile response of longitudinal muscle from the estrogen-dominated rat uterus to natural and synthetic prostanoids. The biological significance is 1) to provide evidence for or against a physiological role for each natural prostanoid in the regulation of myometrial activity, 2) to determine if each prostanoid has pharmacological potential for the manipulation of myometrial activity, and 3) to understand the structural requirements for prostanoid action on the myometrium. All analogs tested produced excitation of the myometrium in vitro through what appeared to be a direct action on the muscle. The order of potency of the natural prostanoids was prostaglandin (PG) F2 alpha = PGD2 = PGE2 = PGE1 greater than PGA2 = PGB2 = 6-keto-PGF1 alpha. This order of potency was not consistent with any single currently recognized prostanoid receptor. Furthermore, PGF2 alpha had an EC50 (effective concentration that produces 50% of the maximal response) of 0.5 microM, which was low in comparison to other PGF2 alpha-sensitive tissues. There were large differences in the maximum tension developed in response to the prostanoids tested, only PGF2 alpha, PGE2 and 6-keto PGF1 alpha were full agonists. Although the simplest explanation of these data was that the rat uterus contains a single novel type of prostanoid receptor, the existence of multiple receptor subtypes could not be disproved. Evidence from the effect of synthetic analogs suggested that neither thromboxane A2 nor PGI2 are physiological regulators of activity in this tissue.     

Prostacyclin (PGI2) effects on anterior pituitary hormones in the rat in vivo.

Intravenous injection of 600 microgram PGE2 or PGI2 significantly increased serum LH and prolactin levels in estradiol treated ovariectomized rats. There was no effect on serum FSH concentration. PGE2 and PGI2 stimulated LH release in a non-dose dependent manner, while prolactin levels were positively correlated with the dose administered following PGI2 treatment. 6-keto-PGF1 alpha at a comparable dose had no effect on pituitary hormone levels. Subcutaneous administration of 1 mg/kg or 60 mg/kg PGI2 for seven days significantly depressed serum LH level both in male and female rats. These doses had no effect on serum FSH or prolactin levels.     

The effects of prostacyclin (PGI2) on tissues which detect prostaglandins (PG'S).

The effects of prostacyclin (PGI2) and its stable metabolite 6-oxo-PGF1alpha on various bioassay tissues are compared with those of PGE2 and PGF2alpha, using the cascade superfusion method. On vascular smooth muscle, PGI2 caused relaxation of all tissues tested except the rabbit aorta. PGE2 relaxed rabbit coeliac and mesenteric artery but contracted bovine coronary artery and had no effect on rabbit aorta. 6-oxo-PGF1alpha was ineffective at the concentrations tested. On gastro-intestinal smooth muscle, PGI2 contracted strips of rat and hamster stomach and the chick rectum. It was less potent than PGE2 or PGF2alpha. None of these substances contracted the cat terminal ileum. 6-oxo-PGF1alpha was inactive on these tissues at the doses tested. PGI2 was less active than PGE2 or PGF2alpha in contracting guinea-pig trachea and rat uterus; 6-oxo-PGF1alpha was active only on the rat uterus. Thus, PGI2 can be distinguished from the other stable prostaglandins using the cascade method of superfusion.     

Effects of prostaglandins on the cerebral circulation in the coat

The role of prostaglandins in producing cerebrovasodilation during hypercapnia was tested in goats. Cerebral blood flow (CBF) changes with increasing arterial PCO2 were measured before and after prostaglandin synthesis inhibition with indomethacin or ibuprofen. Both drugs produced significant decreases in CBF under control anesthetized conditions but had no significant effect on the cerebrovascular response to increased arterial PCO2. The effects of direct intracerebrovascular infusion of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) and prostacyclin were also measured. In the dose range tested (0.1-1) microgram/min) PGF2 alpha had no significantly greater than that produced by PGE2. The effectiveness of each compound in producing cerebrovascular changes is consistent with the endogenous distribution of prostaglandins within the brain. These results suggest that prostaglandins, particularly PGI2, may be important in modulating cerebrovascular tone but have no role in increasing CBF during hypercapnia.     

Prostaglandins as reducing agents: a model of adenylate cyclase activation?

It has been suggested that adenylate cyclase activation involves reduction of a disulfide linkage. Prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), prostaglandin I2 (PGI2) and prostaglandin F2 alpha (PGF2 alpha) were tested for their ability to act as reducing agents with either cytochrome c, or the disulfide 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), the latter with a catalytic amount of ferric chloride. PGE1, PGE2, and PGI2 significantly reduced cytochrome c while PGF2 alpha did not. PGE1, PGE2 and PGI2 reduced DTNB while PGF2 alpha did not. The results are consistent with the postulate that prostaglandins which are effective in activating adenylate cyclase can act as reducing agents and might be involved in reductive activation of adenylate cyclase.     

Pertussis toxin abolishes the inhibitory effects of prostaglandins E1, E2, I2 and F2 alpha on hormone-induced cAMP accumulation in cultured hepatocytes

Several prostaglandins inhibit the cAMP response to glucagon and beta-adrenergic stimulation in hepatocytes. To probe the mechanism of this inhibition, we have examined in primary hepatocyte cultures how pretreatment with pertussis toxin (islet-activating protein) influences the ability of the cells to respond to hormones and prostaglandins. Pertussis toxin augmented the effects of glucagon, epinephrine and isoproterenol, and also markedly enhanced the cAMP response to prostaglandin E1 (PGE1). Furthermore, whereas PGE1, PGE2, PGI2 and PGF2 alpha attenuated the cAMP responses to glucagon in control cultures, this inhibition was abolished in cells pretreated with pertussis toxin. A more detailed comparison was made of the effects of PGE1 and PGF2 alpha. In cells not treated with pertussis toxin, both these prostaglandins at high concentrations reduced the cAMP response to glucagon and isoproterenol by approximately 50%, but dose-effect curves showed that PGE1 was about 100-fold more potent as an inhibitor than PGF2 alpha. Pertussis toxin abolished the inhibitory effects of PGE1 and PGF2 alpha with almost identical time and dose requirements. The results obtained with PGE1, PGE2, PGI2 and PGF2 alpha suggest that prostaglandins of different series attenuate hormone-activable adenylate cyclase in hepatocytes through a common mechanism, dependent on the inhibitory GTP-binding protein.     

The mechanism of cytoprotective effect of CHINOIN-127.

According earlier, investigations nitrogen bridgehead compounds make a representative group of non-prostaglandin type gastroprotective agents. One member of this group is CHINOIN-127 (1,6-dimethyl-4-oxo-1, 6, 7, 8, 9, 9a-hexahydro-4H-pyrido-(1, 2a)-pyrimidine-3-carbox-amide). CHINOIN-127 is a potent non-narcotic analgesic and antiinflammatory agent and has a remarkable protective effect on indomethacin induced ulcer (ED50 = 25 mg/kg p.o.) and on acidified ethanol induced ulcer (ED50 = 26 mg/kg p.o.). In this study we examined the mechanism of action of cytoprotective effect of this drug and we made a comparison between the cytoprotective effect of 20% ethanol and 25 mg/kg CHINOIN-127. In the gastric mucosa of control rats we observed a balance between TxA2 and PGI2 (PGI2/TxA2 = 3.8) and between the cytoprotective prostaglandins (PGI2 and PGE2) and ulcerogen eicosanoids (TxA2 and leukotrienes) (PGI2 + PGE2/TxA2 + LTs = 3.9). 100% ethanol treatment causes disintegration of this balance, shifting the synthesis towards the ulcerogen eicosanoids production. CHINOIN-127 and 20% ethanol pretreatment improves the deranged balance between cytoprotective prostaglandins and ulcerogen eicosanoids. Our results demonstrate that CHINOIN-127 and 20% ethanol have a similar mechanism of cytoprotective action on ethanol induced ulcer in rats.     

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 PGE2, PGF2 alpha 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), methacholine (0.1-10 microM) or histamine (0.3-30 microM) did not increase prostanoid release above control values in either the presence or absence of the epithelium. The unstimulated release of PGE2 and PGF2 alpha, but not PGI2, was decreased in tissues lacking epithelium. Indomethacin (1 microM) 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 PGF2 alpha or PGE2. However, the possibility remains that the basal release of PGE2 and/or PGF2 alpha 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 PGF2 alpha which may be involved in the maintenance of baseline tone.