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 μg/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 situation than d1-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.     

Catecholamine release and ventricular arrhythmias during coronary occlusion and reperfusion in the dog

In anesthetized dogs, 60-min occlusions of either the proximal (n = 14), distal (n = 8) left circumflex (LCX), or left anterior descending (LAD, n = 10) arteries were followed by reperfusion. Coronary sinus and aortic norepinephrine and epinephrine plasma concentrations were measured. The ventricular arrhythmias were ventricular premature depolarizations (VPDs), unsustained ventricular tachycardia (VT) (greater than or equal to 3 and less than 20 VPDs), sustained VT (greater than or equal to 20 VPDs), and ventricular fibrillation (VF). A gradual twofold increase (p less than 0.05) in myocardial norepinephrine overflow followed occlusion in all three groups. The increases in the amounts of norepinephrine released in the coronary sinus blood during reperfusion were significant and proportional to the size of the occluded area: proximal LCX, from 0.236 +/- 0.038 to 1.528 +/- 0.490 ng/mL of plasma (p less than 0.001); LAD, from 0.180 +/- 0.027 to 0.795 +/- 0.286 ng/mL (p less than 0.05); distal LCX, from 0.215 +/- 0.039 to 0.404 +/- 0.110 ng/mL (p less than 0.05). Aortic epinephrine concentrations were significantly increased only by LAD occlusion; at 15 min, the value had increased to 0.187 +/- 0.053 ng/mL from an initial value of 0.069 +/- 0.029 ng/mL (p less than 0.001). Two phases of ventricular arrhythmias followed both occlusion and reperfusion. Phase 1 postocclusion was characterized by VPDs and phase 2 by VPDs and unsustained VT. Sustained VT was seen only in phase 1 postreperfusion, whereas unsustained VT was seen in phase 2. VF was seen in 50, 35, and 25% of the dogs with proximal LCX, LAD, and distal LCX occlusion and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the effects of prostaglandins E1 and A1 on coronary occlusion induced arrhythmia.

The present study compares the effects of PGE1 and PGA1 on ventricular arrhythmias following coronary artery occlusion. The left anterior descending coronary artery (LAD) was occluded abruptly in 55 cats anesthetized with alpha-chloralose. Lead II of the ECG along with arterial blood pressure were monitored for one hour after occlusion. Either vehicle or prostaglandin was infused into the left atrium (LA) or femoral vein (IV) 15 min prior to and for 1 hour after LAD occlusion at a rate of 0.15 ml/min. Prostaglandin was infused at either a high dose (1.0 microgram/kg/min) or a low dose (0.1 microgram/kg/min). Infusion of either PGE1 or PGA1 produced a marked fall in blood pressure and heart rate which returned toward control before occlusion. Abrupt occlusion of the LAD produced ventricular arrhythmia in all cats ranging from ventricular premature beats to ventricular fibrillation (VF). The control animals had a 38% incidence of VF. VF occurred in 75% of the animals in which PGE1 was administered into the LA at either the high or low dose while the occurrence in those administered PGA1 was 67% and 50%, respectively. Intravenous administration of the high dose of PGE1 or PGA1 resulted in VF in 13% and 67% of the animals after LAD occlusion, respectively. These data indicate that the IV administration of PGE1 may protect the heart from VF while the infusion of PGE1 or PGA1 into the LA may enhance VF after LAD occlusion.     

Ventricular arrhythmias following coronary artery occlusion in the streptozotocin diabetic rat

The following investigation was designed to assess whether or not streptozotocin diabetes has an influence on the number and severity of ventricular arrhythmias following coronary artery occlusion in the conscious rat. In addition, electrocardiogram and haemodynamic data were compared between streptozotocin groups and control. Diabetes was induced in male Sprague-Dawley rats with streptozotocin (55 mg/kg iv) and left anterior descending coronary artery ligation was performed either 6 or 9 weeks later. Rats were allowed to recover from preparative surgery for 1 week prior to ligation. Streptozotocin diabetes (untreated or insulin controlled) appeared to have little influence on the variables tested. When exposed to equivalent degrees of ischaemia (the rat is a microangiopathy-resistant species), the streptozotocin diabetic rat heart was not appreciably more prone to arrhythmias of any type compared with control.     

The action of prostaglandins on GA3 controlled responses I. Induction of barley endosperm acid phosphatase activity by prostaglandins E1 and E2

The effect of PGE₁ and PGE₂ on the induction of acid phosphataseactivity in embryoless barley half-seeds was examined. Thesecompounds were found to promote the total amount of enzyme synthesizedas well as the amount released into the medium to nearly thesame levels obtainable when these seeds are incubated in GA₃or cyclic AMP. The enzyme induction by PGE₁ and PGE₂ was inhibited by cycloheximide,ABA, 6-methyl purine and acetylsalicyclic acid, but not by AMO-1618.A time course for the induction of acid phosphatase activityby PGE₁ and PGE₂ lagged behind by 9 hr a similar time courseobtained when seeds were incubated in GA₃ or cyclic AMP. Someof the implications of these results are discussed. (Received May 6, 1973; )     

Interactions of prostaglandins with subpopulations of ovine luteal cells. I. Stimulatory effects of prostaglandins E1, E2 and I2

Preparations of small and large steroidogenic cells from enzymatically dispersed ovine corpora lutea were utilized to study the in vitro effects of luteinizing hormone (LH) and prostaglandins (PG) E1, E2 and I2. Cells were allowed to attach to culture dishes overnight and were incubated with either LH (100 ng/ml), PGE1, PGE2, or PGI2 (250 ng/ml each). The secretion of progesterone by large cells was stimulated by all prostaglandins tested (P less than 0.05) while the moderate stimulation observed after LH treatment was attributable to contamination of the large cell population with small cells. Prostaglandins E1 and E2 had no effect on progesterone secretion by small cells, while LH was stimulatory at all times (0.5 to 4 hr) and PGI2 was stimulatory by 4 hr. Additional studies were conducted to determine if the effects of PGE2 upon steroidogenesis in large cells were correlated with stimulated activity of adenylate cyclase. In both plated and suspended cells PGE2 caused an increase (P less than 0.05) in the rate of progesterone secretion but had no effect upon the activity of adenylate cyclase or cAMP concentrations within cells or in the incubation media. Exposure of luteal cells to forskolin, a nonhormonal stimulator of adenylate cyclase, resulted in marked increases in all parameters of cyclase activity but had no effect on progesterone secretion. These data suggest that the actions of prostaglandins E1, E2 and I2 are directed primarily toward the large cells of the ovine corpus luteum and cast doubt upon the role of adenylate cyclase as the sole intermediary in regulation of progesterone secretion in this cell type.     

Effect of angiotensin ii and norepinephrine on release of prostaglandins E2 and I2 by the perfused rat mesenteric artery

Prostaglandin E2 (PGE2) and 6 keto-PGF1 alpha, the stable metabolite of prostacyclin (PGI2), have been measured in the effluent of perfused rat mesenteric arteries by the use of a sensitive and specific radioimmunoassay (RIA) method. The PGE2 and 6 keto-PGF1 alpha were continuously released by the unstimulated mesenteric artery over a period of 145 min. After 100 min of perfusion the release of PGE2 and 6 keto-PGF1 alpha was 45.1 +/- 8.4 pg/min and 254 +/- 75 pg/min respectively, which is in accord with the general belief that PGI2 is the major PG synthesized by arterial tissue. Angiotensin II (AII) (5 ng/ml) induced an increase of PGE2 and 6 keto-PGF1 alpha release without changing the perfusion pressure. The effect of norepinephrine (NE) injections on release of PGs depended on the duration of the stabilization period. The changes of perfusion pressure induced by NE were not related to changes in release of PGs. Thus, it seems that the increase of PG release induced by AII and NE was due to a direct effect of the drugs on the vascular wall. This may represent an important modulating mechanism in the regulation of vascular tone.     

The biosynthesis of the 3-series prostaglandins in rat uterus after alpha-linolenic acid feeding: Mass spectroscopy of prostaglandins E and F produced by rat uteri in tissue culture

The abnormal uterine activity associated with dietary n-3 fatty acids may result from competitive inhibition of PG2 production. Uterine synthesis of 2- and 3-series prostaglandins F(PGF) and E(PGE) was studied using mass spectrophotometry in rats fed diets containing predominantly n-3 fatty acid, n-6 fatty acid, or control pelleted diet. Mass spectra of PGF (Me, TMS and Me, TBDMS derivatives) synthesised by uteri of n-3 fed rats were characterised by 8 ions containing the n-3 double bond, and m.i.d. of the 651/653 ions of PGF-Me, TBDMS indicated PGF3 alpha synthesis (44 +/- 8% and 13 +/- 2% of PGF release by uteri incubated + or -5 micrograms/ul calcium ionophore A23187 respectively). In uteri from the control diet group incubated with ionophore, PGF3 alpha ions were detected and PGF 3 alpha represented 9.5 +/- 1.0% of PGF alpha release. Similarly, analysis of PGE from uteri of n-3 fed rats indicated that PGE3 (16 +/- 6% of PGE) was released in the presence of ionophore A23187. Synthesis of 3-series PG by rat uteri was detected after only 3 weeks of n-3 diet. The capacity to synthesise 3-series PG increased at intracellular calcium concentrations which mimicked cell calcium during decidual autolysis at parturition. These experiments suggest that uterine synthesis of 3-series PG is regulated by the specifity of enzymes incorporating fatty acids, rather than by the cyclooxygenase enzyme.     

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.     

Interactions of prostaglandins with subpopulations of ovine luteal cells. I. Stimulatory effects of prostaglandins E1, E2 and I21

Preparations of small and large steroidogenic cells from enzymatically dispersed ovine corpora lutea were utilized to study the $\text{in}$$\text{vitro}$ effects of luteinizing hormone (LH) and prostaglandins (PG) E₁, E₂ and I₂. Cells were allowed to attach to culture dishes overnight and were incubated with either LH (100 ng/ml), PGE₂, PGE₂, or PGI₂ (250 ng/ml each). The secretion of progesterone by large cells was stimulated by all prostaglandins tested (P < 0.05) while the moderate stimulation observed after LH treatment was attributable to contamination of the large cell population with small cells. Prostaglandins E₁ and E₂ had no effect on progesterone secretion by small cells, while LH was stimulatory at all times (0.5 to 4 hr) and PGI₂ was stimulatory by 4 hr. Additional studies were conducted to determine if the effects of PGE₂ upon steroidogenesis in large cells were correlated with stimulated activity of adenylate cyclase. In both plated and suspended cells PGE₂ caused an increase (P < 0.05) in the rate of progesterone secretion but had no effect upon the activity of adenylate cyclase or cAMP concentrations within cells or in the incubation media. Exposure of luteal cells to forskolin, a nonhormonal stimulator of adenylate cyclase, resulted in marked increases in all parameters of cyclase activity but had no effect on progesterone secretion. These data suggest that the actions of prostaglandins E₁, E₂ and I₂ are directed primarily toward the large cells of the ovine corpus luteum and cast doubt upon the role of adenylate cyclase as the sole intermediary in regulation of progesterone secretion in this cell type.     

Reflex tracheal contraction evoked in dogs by bronchodilator prostaglandins E2 and I2

Bronchodilator prostaglandins E2 and I2 may cause airway irritation and bronchoconstriction in human subjects. These experiments were designed to test the hypothesis that this paradoxical bronchoconstriction is a vagal reflex triggered by stimulation of airway afferents. We recorded smooth muscle tension in an innervated upper tracheal segment in anesthetized dogs and injected prostaglandins into the general circulation or into a bronchial artery or administered them as aerosol to the lungs. Prostaglandins usually caused tracheal contraction, which survived vagal cooling to 5-7 degrees C but was abolished at 0 degrees C. Vagally mediated tracheal contraction was also evoked when prostacyclin was injected into the pulmonary circulation of dogs whose pulmonary and systemic circulations were independently pump perfused. Recordings of afferent vagal impulses indicated that bronchial arterial injection of prostaglandins stimulated bronchial C-fibers; aerosols of prostaglandin stimulated pulmonary and bronchial C-fibers and C-fibers in extrapulmonary airways. We postulate that in susceptible human subjects concentrations of these prostaglandins too low to have direct bronchodilator effects may cause reflex bronchoconstriction by stimulating afferent vagal C-fibers in the lower airways.     

The immunomodulatory actions of prostaglandin E2 on allergic airway responses in the rat

PGE(2) has been reported to inhibit allergen-induced airway responses in sensitized human subjects. The aim of this study was to investigate the mechanism of anti-inflammatory actions of PGE(2) in an animal model of allergic asthma. BN rats were sensitized to OVA using Bordetella pertussis as an adjuvant. One week later, an aerosol of OVA was administered. After a further week, animals were anesthetized with urethan, intubated, and subjected to measurements of pulmonary resistance (R(L)) for a period of 8 h after OVA challenge. PGE(2) (1 and 3 micro g in 100 micro l of saline) was administered by insufflation intratracheally 30 min before OVA challenge. The early response was inhibited by PGE(2) (3 micro g). The late response was inhibited by both PGE(2) (1 and 3 micro g). Bronchoalveolar lavage fluid from OVA-challenged rats showed eosinophilia and an increase in the number of cells expressing IL-4 and IL-5 mRNA. These responses were inhibited by PGE(2). Bronchoalveolar lavage fluid levels of cysteinyl-leukotrienes were elevated after OVA challenge and were reduced after PGE(2) to levels comparable with those of sham challenged animals. We conclude that PGE(2) is a potent anti-inflammatory agent that may act by reducing allergen-induced Th2 cell activation and cysteinyl-leukotriene synthesis in the rat.     

Effects of prostaglandins E2 and F2 alpha on progesterone metabolism by rat granulosa cells

Rat granulosa cells were cultured with or without PGE2 and/or PGF2 alpha. Accumulation of endogenous progesterone and 20 alpha-hydroxy-4-pregnen-3-one was determined. Additionally, [4-14C]progesterone metabolism was assessed. PGE2 increased progesterone accumulation, in part, by decreasing progesterone catabolism to 20 alpha-reduced progestins. In contrast, PGF2 alpha stimulated 20 alpha-hydroxysteroid dehydrogenase activity, thus increasing progesterone catabolism. Combined treatment with PGE2 and PGF2 alpha augmented progesterone accumulation to levels above controls but below those attained with PGE2 alone. These data indicate that PGE2 and PGF2 alpha exert opposite effects on progesterone production and catabolism and that the ratio of PGE2 to PGF2 alpha in the local granulosa cell milieu may be of importance in determining overall progesterone output.     

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.     

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 in situ. 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.     

Interactions between prostaglandins E2 and F2alpha and isoprenalin in the dog heart in situ]

The effects of PGE2 and PGF2alpha on the isoprenaline induced elevation of myocardial contractility were studied on hearts of anesthetized dogs. The steady state effects were determined after single or simultaneous infusion of the substances. Two indices of contractility were used for the quantification of inotropic effects. PGE2 but not PGF2alpha showed positivinotropic effects. PGE2 significantly inhibited the inotropic responses induced by isoprenaline (p less than 0,01); whereas PGF2alpha was without any effect in this direction. The results are discussed with respect of a postjunctional action of PGE2.     

Decreased levels of prostaglandins I2 and E2 in acute gastric mucosal lesions induced by hypoxia

We have observed that the contents of prostaglandin (PG) D2 and 6-keto-PGF1 alpha were five times higher than those of PGE2 and PGF2 alpha in rat gastric mucosa. In order to elucidate the role of PGs in the function of gastric mucosa, we studied the effect of hypoxia on the levels of PGs in relation to the degree of gastric mucosal lesions. 6-Keto-PGF1 alpha levels were significantly decreased only by severe and long-term hypoxia (10% O2, 18 hours) when severe ulcerative lesions were observed. PGE2 levels were significantly decreased even by mild and short-term hypoxia (13% O2, 4 hours) when slight ulcerative lesions were observed. PGF2 alpha and PGD2 levels were significantly decreased by mild and short-term hypoxia; however, there was no significant difference from the control group under severe and long-term hypoxia. These results suggest that each of the PGs plays a different role in the pathogenesis of acute gastric mucosal lesions induced by hypoxia.