A comparison of the bronchodilator activity of (±) 11-deoxy prostaglandin E1 with its 15-methyl analogue, (doxaprost)

The bronchodilator activity of (±) 11-deoxy prostaglandin E₁ was compared to the activity of its (±) 15-methyl analogue, (doxaprost). Both compounds inhibited histamine-induced bronchoconstriction in the anesthetized guinea pig where changes in tracheal pressure were measured. Doxaprost was 73 and 32 times more potent than (±) 11-deoxy PGE₁ by the aerosol and i.v. routes, respectively. Doxaprost also demonstrated a longer duration of effect. Both compounds decreased pulmonary resistance in the 5HT tonal cat. There was no difference in the potency of the two compounds. However, doxaprost had a longer duration of effect. Both compounds caused a fall in mean arterial blood pressure after i.v. administration in the guinea pig but not after aerosol administration in the guinea pig and cat. Both compounds caused relaxation of the isolated guinea pig tracheal strip when tone was induced with carbachol. There was no difference in the potency of the two compounds. The increased activity $\text{in vivo}$ but not $\text{in vitro}$ of the 15-methyl analogue doxaprost is consistent with a lack of enzyme inactivation.     

The bronchodilator acitivity of an 11-deoxyprostaglandin (AY 23 578).

The bronchodilator activity of AY-23 578 was studied in vivo and in vitro techniques. In the conscious guinea pig, aerosols of AY-23 578, prostaglandin (PGE2) E2, and isoproterenol afforded significant protection against histamine-induced convulsions. In the anesthetized guinea pig, where changes in tracheal pressure were taken as an index of bronchoconstriction, AY-23 578, PGE2, and isoproterenol were equipotent in inhibiting the bronchoconstriction induced by histamine. AY-23 578, PGE2, and isoproterenol reduced or prevented neostigmine-, prostaglandin F2alpha- or carbachol-induced increases in pulmonary resistance, and decreases in dynamic compliance in the anesthetized cat. The activities of the former two compounds were qualitatively similar but less potent than isoproterenol. In both the guinea pig and the cat, the aerosol administration of effective bronchodilator doses of AY-23 578 did not exhibit any significant cardiovascular effects. Both AY-23 578 and PGE2 caused relaxation of the isolated guinea pig tracheal strip; PGE2 was about six times more potent than AY-23 578. It is concluded that AY-23 578 is an effective bronchodilator in both the guinea pig and cat.     

2-Decarboxy-2-hydroxymethyl prostaglandin E1 (TR4161), a prostaglandin bronchodilator of low tracheobronchial irritancy

2-Decarboxy 2-hydroxymethyl prostaglandin E₁ (TR4161) relaxed isolated guinea-pig trachea with about double and relaxed human isolated bronchial muscle with about one half the potency of PGE₁. In conscious restrained cats an aerosol of TR4161 was about 100–1000 times less active than PGE₁ in inducing tracheobronchial irritation. When given intravenously or by aerosol to the anaesthetised spontaneously breathing guinea-pig, TR4161 was approximately equipotent with PGE₁ in inhibiting histamine-induced bronchoconstriction and in reducing basal inherent tone. The onset and duration of the bronchodilator effects of TR4161 administered intravenously, however, were significantly longer than those of PGE₁. In conscious guinea-pigs, TR4161 by aerosol was approximately three times more potent than PGE₁ in preventing histamine-induced convulsions, whereas only TR4161 was active in this test system when the test drugs were administered orally. These observations indicate that TR4161 might be therapeutically useful as a non-irritant prostaglandin bronchodilator in conditions of airway obstruction.     

Effects of oral administration of PGE2 on gastric secretion and experimental peptic ulcerations

The anti-secretory and anti-ulcer effects of prostaglandin E₂ (PGE₂) using iso-osmotic buffer as a vehicle have been investigated in several types of laboratory animals. Orally administered PGE₂ was found to be highly effective in preventing formation of ulcers in several experimental models -- pylorus ligated induced ulcers in rats, histamine induced ulcers in guinea pigs, reserpine induced ulcers in rats and pentagastrin induced ulcers in guinea pigs and cats. PGE₂ also suppressed acid secretion but not pepsin activity. It was concluded that the anti-ulcer effects of PGE₂ were due to its anti-secretory activity rather than antipepsin activity. In view of PGE₂'s activity in preventing ulceration induced by histamine and reserpine in addition to pentagastrin, it is suggested that the anti-pentagastrin activity of PGE₂ is not specific.     

The protective effect of thromboxane synthetase inhibitor UK 38485 against bile duct ligation induced liver injury

In order to elucidate the relation between tissue eicosanoids and liver injury due to bile duct obstruction, we have examined the effects of iloprost, a stable analogue of prostaglandin I₂ (PGI₂), and UK 38485 (UK), an inhibitor of thromboxane synthetase, on prostaglandin E₂ (PGE₂) and leukotriene C₄ (LTC₄) in guinea pig liver. 56 male guinea pigs were divided into the following groups: (i) sham operations (SHAM), (ii) bile duct ligated (BDL) group, (iii) guinea pigs given UK (5 μg/kg body wt intraperitoneally 10 min, 8 h and 16 h after bile duct ligation), and (iv) guinea pigs treated with iloprost (ILO) (2 μg/kg body wt intraperitoneally 10 min, 8 h and 16 h after bile duct ligation). Liver damage was assessed by blind quantitation of liver cell necrosis. Bile duct ligation caused an increase in tissue PGE₂-like activity and a decrease LTC₄-like activity. But the most pronounced elevation of PGE₂ was observed in ILO treated group. The LTC₄-like activity level improved significantly in the UK-treated BDL group compared with the BDL only and ILO treated animals. Also, UK was found to be beneficial in preventing the liver cell necrosis due to cholestasis. It is concluded that the ratio of PGE₂/LTC₄ in liver is a valuable marker for cholestatic injury.     

Structure-activity relationships in a series of 11-deoxy prostaglandins

A series of 11-deoxy prostaglandin derivatives and some naturally occurring prostaglandins have been investigated in the anaesthetized artificially respired guinea-pig for their effect on blood pressure, bronchial resistance (overflow pressure at constant volume), tracheal segment pressure, and on intestinal and uterine smooth muscle. The compounds were administered intravenously. Prostaglandins E₁, E₂ and F_2α produced responses that were qualitatively similar to those in the literature. Prostaglandin A₂ (100 μg) was a bronchoconstrictor, although it decreased tracheal segment pressure and blood pressure. Prostaglandin B₂ (100 μg) caused double elevations in blood pressure, tracheal segment pressure and bronchial resistance. The intensity of bronchoconstriction produced by PGB₂ was of the same order as with PGF_2α. A number of structure-activity relationships were found. 11-Deoxygenation lowered the biological activity of the natural prostaglandins PGE₁ and PGF_1α. The vasodepressor and bronchodilator responses of 11-deoxy PGE₁ were converted to vasopressor and bronchoconstrictor by epimerisation at C-15. Introduction of a methyl group at C-15 of 11-deoxy PGF_1α both increased and prolonged vasopressor and bronchoconstrictor activity. At C-9 both the keto and β-hydroxy group imparted vasodepressor and bronchodilator activity, while the α-hydroxy led to vasopressor and bronchoconstrictor activity. Extension of the omega sidechain by two methylene groups radically reduced the activity of 11-deoxy PGF_1α and its derivatives.These experiments indicate that steric differences in the prostaglandin structures studied can result in diametrically opposed profiles of biological activity. Further, small variations in the prostaglandin molecule can lead to differences in potency and/or profile of activity in the guinea-pig.     

Effect of polyamines on prostaglandin synthesis in various cell-free systems

Synthesis of PGF_2α by bovine uterus and guinea pig lung microsomes and that of TXB₂ by human platelet and rat spleen microsomes were stimulated by spermine. PGE₂ synthesis by bovine seminal vesicle and porcine lung microsomes, and 6-keto-PGF_1α synthesis by bovine seminal vesicle and uterus microsomes were inhibited by spermine. When phospholipid-free prostaglandin synthetase from bovine seminal vesicle was used instead of microsomes, the inhibition of PGE₂ synthesis by spermine disappeared. The inhibition of PGE₂ synthesis by spermine gradually appeared with an increase of phospholipid added. Among phospholipids tested, phosphatidylcholine was the most effective for the inhibition of PGE₂ synthesis by spermine.     

Bronchodilator activity of a PGE2 analog in animals and in man

A C-11 substituted PGE₂ analog, DHET-PGE₂ [$\text{?}$-11-deoxy-11α-(2-hydroxyethylthio)-PGE₂ methyl ester], was demonstrated to exert potent bronchodilator activity in three $\text{in vivo}$ models of augmented airway resistance: (1) acute bronchospasms, induced by 5-hydroxytryptamine, histamine and acetylcholine in the anesthetized guinea pig, (2) acute bronchospasm, induced by pilocarpine, in the anesthetized dog, and (3) chronic bronchospasm, induced by SO₂ exposure, in the unanesthetized dog. In acute and 30-day toxicological studies in the dog, no cardiovascular, respiratory or gastrointestinal side effects were observed at aerosol doses at least 1,000 times those required for efficacy. $\text{In vitro}$, DHET-PGE₂ effectively relaxed isolated preparations of dog bronchus that had been contracted with carbachol. In clinical studies, human asthmatics and bronchitics responded consistently to β-agonist bronchodilators but variably to DHET-PGE₂. Overall, increases in pulmonary resistance or decreases in FEV₁ were observed with DHET-PGE₂. Subsequent evaluation in isolated carbachol-contracted human bronchus revealed that, in contrast to the bronchodilator activity of PGE₁ and β-agonists, DHET-PGE₂ and PGE₂ induced contraction. Considered along with results from previous clinical studies on other PGs, these data underscore the difficulties in making extrapolations on this class of compounds from animal models to humans and suggest that human bronchial tissue may provide the only appropriate preclinical test system for predicting the clinical efficacy of PG bronchodilators.     

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.     

Antagonistic Action of Aerosols of Prostaglandins F2α and E2 on Bronchial Muscle Tone in Man

Experiments were carried out in healthy male volunteers to investigate the effect of the inhalation of prostaglandin F₂α (PGF₂α) on airways resistance and the influence of the subsequent inhalation of prostaglandin E₂ (PGE₂). Airways resistance, which reflects the tone of smooth muscle in the larger airways in man, was measured by total body plethysmography.The inhalation of PGF₂α (40-60 μg) caused an increase in airways resistance in all subjects. Both PGE₂ (55 μg) and isoprenaline (550 μg) given by metered aerosol promptly reversed the bronchoconstriction induced by PGF₂α, but isoprenaline was more effective in this respect.A role for these prostaglandins in the control of bronchial muscle tone is discussed.     

Prostaglandins and pacemaker activity in isolated guinea pig SA node

Prostaglandins PGE₂, PGE₁, PGF_2α, and PGA₁ substantially increase automaticity in SA-nodal, right atrial preparations excised from guinea pigs. This natural pacemaker tissue is sensitive to nanomolar doses of PG with, for example, 10⁻⁸ M PGE₂, increasing SA rate by about 20%. If these preparations are pretreated with 2 μM indomethacin, a blocker of endogenous prostaglandin synthesis, then spontaneous rate drops and subsequent rate increases due to PGE₂ administration can be more easily demonstrated. Guinea pig pacemaker tissue differs from similar rabbit tissue not only in that it is directly responsive to PGE₂, but also in that PGE₂ does not depress the absolute response to transmural stimulation (adrenergically mediated rate increase). The positive chronotropic responses to PGE₂ also occur when the guinea pig tissue is pretreated in 0.6 μM propranolol, which causes blockade of beta-adrenergic receptors.The pacemaker myocardium in the guinea pigs thus appears to be directly stimulated by exogenous PGE₂ at very low doses. The observation that 2 μM indomethacin reduces SA-nodal rate suggests the presence of a very sensitive, functionally important, PGE-like system which modulates heart rate in this mammalian species.     

Effects of inhibitors of thromboxane synthesis on reactions of the cat bronchus in situ to prostaglandins

Cats were anesthetized by chloralose, relaxed by suxamethonium, and ventilated. The influence of 3 inhibitors of thromboxane synthesis, N.0096 (±α-benzyl-α-p-chlorobenzyl-4-hydroxyacetophenon phenylhydrogen-phosphonate), imidazole and dipyridamole were studied on bronchial reactions to prostaglandins E₂ and F₂α and arachidonic acid. During a bronchoconstriction maintained by infusion of 5-HT, N.0096 and imidazole dose-dependently potentiated the intensity and duration of the bronchodilator effect of PGE₂. This effect was maximal at a total dose of 17 mg/kg N.0096 or 25–50 mg/kg imidazole, but decreased after higher doses which are supposed to inhibit cyclo-oxygenase also. Bronchoconstrictor reactions to single injections of arachidonic acid were inhibited by N.0096 in the same dose range. Reactions to PGF_2α were unaltered by both drugs. Dipyridamole was devoid of a comparable activity.     

Effects of hypothalamic microinjection of PGE2 on body temperature and sympathetic nervous activities in the rabbit

The febrile response and sympathetic nervous response to hypothalamic microinjections of prostaglandin E₂ (PGE₂) were investigated in anesthetized rabbits. Microninjection of PGE₂ (500–1000 ng) caused an increase in rectal temperature of more than 0.3°C in 13 of 50 loci in the preoptic and anterior hypothalamic area (PO/AH). At 8 of these 13 loci, PGE₂ elicited response patterns in the sympathetic nervous system, such as an increase in cutaneous sympathetic nervous activity and decrease in renal sympathetic nervous activity. This pattern of sympathetic nervous responses was induced with a simultaneous increase in rectal temperature of more than 0.5°C. The 8 loci were distributed in the preoptic area, especially in the vicinity of the supraoptic nucleus. Electrolytic lesions of this region were made bilaterally, and intracerebroventricular injection of PGE₂ (8 µg/kg) was found to inhibit fever and sympathetic activity. The results demonstrate that the action of PGE₂ is responsible for the response patterns of sympathetic twigs during fever. The preoptic area, especially in the vicinity of the supraoptic nucleus, is most sensitive to PGE₂ for the patternized response of sympathetic neurons and fever.     

Prostaglandin endoperoxides. VII. Novel transformations of arachidonic acid in guinea pig lung

The following labeled compounds were isolated and identified after incubation of [1-¹⁴C]arachidonic acid with guinea pig lung homogenates: 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT), the hemiacetal derivative of 8-(1-hydroxy-3-oxopropyl)-9,12-dihydroxy-5,10-heptadecadienoic acid (PHD), 12-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE), PGE₂, PGF_2α, 11-hydroxy-5,8,12,14-eicosatetraenoic acid, and 15-hydroxy-5,8,11,13-eicosatetraenoic acid (in order of decreasing yield). Perfused guinea pig lungs released PHD (654–2304 ng), HHT (192–387 ng), HETE (66–111 ng), PGE₂ (15–93 ng), and PGF_2α (93–171 ng) following injection of 30 μg of arachidonic acid. Thus guinea pig lung homogenates as well as intact guinea pig lung converted added arachidonic acid predominantly into PHD and HHT, metabolites of the prostaglandin endoperoxide PGG₂, and to a lesser extent into the classical prostaglandins PGE₂ and PGF_2α.     

In vivo insulin secretion: Prostaglandin and adrenergic interrelationships

Infusion of prostaglandin (PG) E₁ in anesthetized dogs significantly lowered circulating insulin levels and inhibited insulin responses following intravenous glucose. A similar trend was observed with PGE₂. Alpha adrenergic blockade did not reverse the PGE₁ effect. Epinephrine infusion also inhibited glucose-stimulated insulin secretion, an effect that was not reversed by indomethacin. Therefore, in this investigative model, PGE₁ inhibited insulin secretion but no interdependency of PGE₁ and alpha adrenergic effects were found.     

Prostaglandin-norepinephrine interaction in guinea pig longitudinal muscle

Norepinephrine block of electrically induced contractions of the guinea pig longitudinal muscle-myenteric plexus preparation reverses spontaneously. PGE₁ or E₂ fails to alter rate of reversal in the presence of ascorbic acid but increases the rate in its absence. Using spectrophotometry, it could be demonstrated that PGE₁ or E₂ significantly increases the rate of autoxidation of norepinephrine, thereby accounting for the pharmacological interaction observed.     

Effect of prostaglandins on uterine contractions in the estrous ewe.

Administration of exogenous prostaglandins at the time of mating may improve fertility via their effects on uterine contractility. The present study was undertaken to compare the effects of three prostaglandins that affect either the male or female reproductive uterine contractility. Contractions in the uterine body of anesthetized ewes during estrus were studied before, during and after a 5 min interval of systemic infusion of prostaglandin F_2α-THAM salt (PGF_2α; 5 mg), prostaglandin E₁ (PGE₁; 5 mg), prostaglandin E₂ (PGE₂; 5 mg) or vehicle. Pressure changes were detected by the use of an open-ended intrauterine catheter and a transducer. Each of the three prostaglandins initially caused a single prolonged contraction that lasted about 10 minutes and had a maximum pressure of 50 mm Hg. Prior to the prolonged contraction, PGE₁ and E₂ caused a relaxation for about 1 minute. In addition, PGE₁ and E₂ caused more secondary contractions (15–20) during the prolonged contraction than did PGF_2α (7–9). The effects of prostaglandin (PG) treatment lasted for 20–30 minutes. The authors conclude that with the dose used the three prostaglandins studied do not have greatly different effects on uterine contractility in estrous ewes.     

Prostaglandins and congeners XXIII (1). Synthesis of 15-deoxy-16-hydroxy-16-methylprostaglandins. The importance of the C13-C14 trans double bond for bronchodilator activity

The synthesis and bronchodilator activity in the guinea pig of several 15-deoxy-16-hydroxy-16-methylprostaglandin analogs is described. The E₂ (VIa) and E₁ (VIb) analogs are potent bronchodilators comparable in activity to the natural prostaglandins, but possessing a longer duration of effect. Replacement of the C₁₃-C₁₄ trans double bond by a cis double bond or an ethylene linkage causes a substantial diminishment of this activity.     

The mechanism of action of soluble lymphocyte mediators. IV. Effect of migratio inhibitory factor (MIF) on macrophage cyclic AMP and on responsiveness to adenylate cyclase stimulators.

Intracellular levels of cyclic 3′,5′-adenosine monophosphate (cAMP) in purified guinea pig peritoneal macrophages were elevated following incubation with the adenylate cyclase stimulators prostaglandins E₁ and E₂ (PGE₁, PGE₂), isoproterenol, and cholera toxin. Exposure of macrophages to antigen-stimulated lymphocyte culture supernatants, containing migration inhibitory factor (MIF), resulted in a moderate but consistent decrease in the cAMP level, which was best expressed after 1–2 hr of incubation. Incubation of macrophages with MIF-containing supernatants or partially purified MIF for 1–2 hr resulted in reduced cAMP accumulation in response to PGE₁, PGE₂, isoproterenol, and cholera toxin (nonspecific refractoriness). These findings indicate that MIF-induced inhibition of macrophage migration is not due to an increase in the cellular level of cAMP and that the reduction in cAMP concentration, caused by MIF, is probably a secondary phenomenon unrelated to the inhibition of cellular motility.     

Endogenous formation of the prostaglandin endoperoxine metabolite,thromboxane B2, by brain tissue

Thromboxane B₂ was formed from endogenous precursors during short incubations of guinea pig and rat cerebral cortex. The amount formed by guinea pig brain tissue was 5–6 times the formation of prostaglandin F_2α and E₂. Noradrenalin stimulated and indomethacin and mercaptoethanol inhibited thromboxane B₂ formation. The mass spectrum of the brain compound was identical to thromboxane B₂ formed from arachidonic acid by guinea pig lung and human platelets.