Non-genomic effects of catecholestrogens in the in vitro rat uterine contraction

• 1.1. The effects of catecholestrogens 2-hydroxyestradiol (2-OH E₂, 0.6–30 μM), 4-hydroxy-estradiol (4-OH E₂, 1–30 μM) and 2-methoxyestradiol (2-MeO E₂, 0.6–30 μM) on rat uterine contraction induced by KCI (60 mM), have been assayed.
• 2.2. All drugs assayed relaxed the tonic-contraction induced by KCI in a concentration-dependent way. The EC₅₀s were: 4.4 ± 0.5, 4.2 ± 0.3 and 8.5 ± 0.7 μM for 2-MeO E₂, 2-OH E₂ and 4-OH E₂, respectively. This relaxing effect was counteracted by CaCl₂ (1–10 mM) but not by the calcium channel agonist Bay k 8644 (1 nM-1 μM).
• 3.3. The effect of 2-MeO E₂ is not modified by propranolol (1 μM), cycloheximide (35 μM), actinomycin D (4 μM), α-difluoromethyl-ornithine (10 μM) or genistein (10 μM). Not did cycloheximide (35 μM) or actinomycin D (4 μM) modify the relaxing effect of 2-OH E₂ and 4-OH E₂. Propranolol (1 μM) significantly increased the effect of 4-OH E₂ but not the effect of 2-OH E₂.
• 4.4. Our results suggest that the relaxing effect of catecholestrogens in the rat uterus is a non-genomic effect and could be related to inhibition of extracellular calcium entry.

     

Involvement of sodium/calcium exchange in the diclofenac-induced spasmolytic effect on rat uterus

• 1.1. The effect of diclofenac (10–100 μM) on rat uterus contraction and its modification by ouabain (0.1 mM), amiloride (0.1 and 1 mM), ouabain (0.1 mM) plus amiloride (1 mM) and the replacement of sodium by choline have been assayed.
• 2.2. Diclofenac produces dose-dependent relaxation of vanadate (0.3 mM)-induced contraction (EC₅₀, 17.3 ± 1.8 μM). This effect is significantly reduced in choline medium (EC₅₀, 49.1 ± 4.5 μM) and by ouabain in sodium-medium (EC₅₀, 52 ± 7 μM).
• 3.3. Amiloride displaces, in a dose-dependent way, the diclofenac-induced relaxant effect. However, ouabain plus amiloride did not produce a sinergic effect.
• 4.4. Our results suggest that diclofenac produces relaxation of vanadate-induced contraction by activation of Na⁺/Ca²⁺-exchange.

     

Mechanisms involved in the spasmolytic effect of extracts from sabal serrulata fruit on smooth muscle

• 1.1. The effects of two extracts from Sabal serrulata fruits [total lipidic (L) and saponifiable (S)] on smooth muscle contractions have been assayed.
• 2.2. Both extracts (0.1–1 mg/ml) relaxed the tonic contraction induced by norepinefrine (30 nM) on rat aorta [EC₅₀, 0.53 ± 0.05 mg/ml (L) and 0.5 ± 0.04 mg/ml (S)] and by KCl (60 mM) on rat uterus. The Sabal extracts (0.3–1 mg/ml) also antagonized the dose-response curve of contractions induced by acetylcholine (0.1–100 μM) on urinary bladder.
• 3.3. dL-Propranolol (1 μM) but not the inactive (R)-(+)-propranolol (1 μM) potentiated the Sabal extracts relaxant effect by lowering the EC₅₀ (0.35 ± 0.2 vs 0.20 ± 0.01 mg/ml for L and 0.43 ± 0.02 vs 0.19 ± 0.02 mg/ml, P < 0.01, for S extract).
• 4.4. Cycloheximide (10 μg/ml) antagonized the effect of extracts from Sabal. However, actinomycin D (5 μg/ml) significantly (P ≤ 0.01) antagonized the effect of the total lipidic extract without modifying that of the saponifiable extract.
• 5.5. The relaxant effect of both extracts was not modified by the tyrosine kinase inhibitor genistein (10 μM) or the ornithine decarboxylase inhibitor α-difluoromethyl-ornithine (10 mM).

     

Mechanism of the potentiating effect of NH4Cl on vasoconstriction in rat aorta

• 1.1. In medium containing 10 or 20 mM KCI, NH₄Cl (10 mM) addition significantly diminished tetraphenylphosphonium bromide (TPP⁺) uptake in A7r5 vascular smooth muscle cells.
• 2.2. Addition of 10 mM NH₄Cl significantly potentiated the ⁴⁵Ca²⁺ uptake of A7r5 cells in medium containing 20 mM KCI; this increased uptake could be reduced to the basal level by pretreatment with 0.1 μM verapamil.
• 3.3. In rat aortic strips, KCI at 10 mM induced a slight contraction, that was greatly potentiated by the simultaneous addition of 10 mM NH₄C1. In this case, also, pretreatment with verapamil (1 μM) completely abolished the NH₄C1-potentiating effect.
• 4.4. The results suggest that ammonium ion amplifies the K⁺-induced contraction of rat aorta by facilitating transmembraneous Ca²⁺ influx through the voltage-dependent calcium channel, which may be due to potentiation of KC1-induced depolarization of the plasma membrane.

     

Possible Stimulation of Na+-K+-ATPase by NO Produced from Sodium Nitrite by Ultraviolet Light in Mouse Gastric Fundal Strip

• 1.In the present study, we investigated the roles of Na⁺-K⁺-ATPase and extracellular Na⁺ or Ca²⁺ ions in ultraviolet (UV) light-induced photorelaxation of methacholine-contracted mouse isolated gastric fundus in the presence of NaNO₂ (50 μM).
• 2.Ouabain (1–500 μM), sodium vanadate (10 μM to 3 mM) and amiloride (1–100 μM) completely inhibited the photorelaxation in a concentration-dependent manner.
• 3.Metabolic inhibitors, sodium azide (10–100 μM), 2,4-dinitrophenol (100 μM to 1 mM) and sodium fluoride (100 μM to 1 mM) significantly reduced photorelaxation.
• 4.Substitution of sucrose, lithium or KCl with extracellular Na⁺ completely abolished the photorelaxant responses.
• 5.Replacement of all extracellular CaCl₂ with BaCl₂ also completely inhibited UV-induced relaxation.
• 6.Verapamil (1–10 μM) decreased UV-induced relaxation significantly.
• 7.These results suggest that nitric oxide produced from NaNO₂ by UV-light in mouse gastric fundus probably stimulates Na⁺-K⁺-ATPase activity, and photorelaxation of gastric smooth muscle is dependent on extracellular Na⁺ and Ca²⁺ ions.

     

Protein kinase A inhibitors selectively inhibit the tonic contraction of the guinea pig ureter to high potassium

• 1.1. We have investigated the effect of various protein kinase A (PKA) inhibitors on the phasic and tonic components of the response to potassium chloride (KCI) in the guinea pig ureter. All experiments were performed in ureters pretreated with capsaicin (10 μM for 15 min) to prevent the release of sensory neuropeptides and in the presence of 1 μM Bay K 8644 to maximize calcium (Ca) entry via voltage-sensitive channels. The addition of 80 mM hypertonic KCI produced maximal shortening of the ureter with distinct phasic and tonic components, the latter further showing a transient and a sustained component. Nifedipine (30 μM for 120 min) totally abolished all the responses to KCI.
• 2.2. The selective PKA inhibitor, H89 (10 μM), abolished the tonic response to KCI in about 30 min with minor inhibitory effect on the phasic contraction. This pattern was unchanged when extending the contact time to 120 min. When added 30 min before the next challenge, H89 (1–30 μM) concentration-dependently inhibited the responses to KCI with a preferential inhibitory effect on the tonic contraction. Another PKA inhibitor, H8, produced similar effects at tenfold higher concentrations (10–300 μM) than H89, consistent with the known potency ratio of these isoquinoline derivatives in inhibiting PKA.
• 3.3. The potent and nonselective protein kinase inhibitor, staurosporine (10–100 nM) produced an even depression of the various phases of the response to KCI. The selective protein kinase G inhibitor, KT 5823 (10 μM for 60 min) produced only a slight reduction of the sustained tonic response to KCI. The selective protein kinase C inhibitor GF 109,203X (1–3 μM) and the cAMP analog, Rp-cAMPS (300 μM for 60 min) had no effect on the three components of the response to KCI.
• 4.4. In the presence of Bay K 8644, electrical field stimulation (10 Hz for 1 sec, 60 V, pulse width 5 ms) produces direct myogenic phasic contractions (twitches) of the ureter which are suppressed by nifedipine (10–30 μM). H8 (up to 30 μM) and H89 (up to 300 μM) had minor effect on the amplitude of twitches, consistent with their poor inhibitory activity on the phasic responses to KCI.
• 5.5. In sucrose gap, superfusion with 80 mM hypertonic KCI produced action potentials followed by a sustained depolarization of the membrane: the two electrical responses underlie the phasic and tonic components of contraction to KCI, respectively. H89 (10 μM for 30 min) did not affect the resting membrane potential nor the KCl-evoked action potentials and sustained depolarization. H89 had no effect on the phasic contraction to KCl but markedly depressed (about 65% inhibition) the tonic contraction.
• 6.6. The present findings are consistent with the view that phosphorylation by PKA increases the availability of L-type Ca channels in the ureter smooth muscle. Blockade of PKA dissociates the electromechanical coupling between the sustained membrane depolarization produced by KCI and the corresponding sustained increase in tension. The L-type Ca channel responsible for generating action potentials and phasic contractions to KCI are less sensitive to PKA inhibitors than those responsible for the tonic contraction.

     

H-7, A protein kinase C inhibitor,inhibits spontaneous tone and spasmogenic responses in normal and sensitized guinea pig trachea

• 1.1. H-7, a protein kinase C inhibitor, fully inhibited the spontaneous and stimulated (KC120 mM or histamine 0.5 mM) tone of trachea from normal and sensitized guinea pig.
• 2.2. H-7 depressed the concentration-contraction curves to KCI, histamine or 5-hydroxytryptamine in epithelium-denuded, indomethacin-treated, trachea from normal and sensitized guinea pigs while responses to CaCI₂ (in Ca²⁺-free, K⁺-depolarized tissues) and acetylcholine were not affected.
• 3.3. H-7 (100 gM) did not depress Ca²⁺ (20 μM)-induced contraction of Triton X-100 skinned trachea.
• 4.4. These results suggest the involvement of PKC in the maintenance of spontaneous tone and spasmogenic responses of guinea pig trachea.

     

High potassium-evoked release of ATP from rabbit pulmonary artery via endogenous noradrenaline

• 1.1. High potassium 30 mM and noradrenaline at 10 μM significantly evoked the release of ATP and produced remarkable vasoconstriction in the rabbit pulmonary artery.
• 2.2. Phentolamine and prazosin at 0.1 μM inhibited ATP release but not vasoconstriction by 30 mM potassium.
• 3.3. 30 mM potassium significantly evoked the release of noradrenaline.
• 4.4. There was a significant positive correlation between the amounts of release of total purines, sum of ATP, ADP, AMP and adenosine, and noradrenaline evoked by 30 mM potassium.
• 5.5. 30 mM potassium-evoked ATP release was significantly reduced by denudation of endothelium.

     

Modulatory effect of 8-iso-PGE2 on platelets

• 1.1. 8-Iso-PGE₂ induced either reversible or irreversible aggregation of platelets in human platelet-rich plasma (PRP) or in the suspension of washed platelets (WP). The values of EC₅₀ for irreversible aggregation in PRP and WP were 4 and 2 μM, respectively.
• 2.2. In rabbit PRP, 8-iso-PGE₂ (0.1-100 μM) itself did not induce or induced only reversible aggregation.
• 3.3. 8-Iso-PGE₂ (0.1-20μM) potentiated adenosine diphosphate-(ADP) induced platelet aggregation in both human and rabbit. The same effect also was found for adrenaline-induced platelet aggregation in rabbit.
• 4.4. The lower concentrations (0.2-0.5 μM) of 8-iso-PGE₂ decreased, and higher concentrations (1–2 μM) increased platelet aggregating factor- (PAF) induced aggregation in human PRP. In rabbit PRP, 8-iso-PGE₂ (0.02–200 μM) had only a decreasing effect on PAF-induced aggregation.
• 5.5. The results suggest that low concentrations of 8-iso-PGE₂ can amplify or weaken platelet aggregation induced by various aggregatory agents.

     

Effects of nicotine on spontaneous activity and underlying ionic currents in rabbit sinoatrial nodal cells

• 1.1. Effects of nicotine on the spontaneous action potentials and the underlying ionic currents in rabbit sinoatrial (SA) nodal cells were investigated using current-clamp and whole-cell voltage-clamp modes.
• 2.2. Nicotine (30 μM to 1 mM) produced a negative chronotropic effect in a concentration-dependent manner (at 1 mM by 10.6±2.8%, n=9, p<0.01). Nicotine at 300 μM significantly decreased the maximum rate of depolarization by 9.8±1.3% (n=9, p<0.05). Other action potential parameters were not affected to any significant extent.
• 3.3. Pretreatment with atropine (1 μM) and hexamethonium (1 mM) did not modify the nicotine-induced effects. After washout, these responses were reversible.
• 4.4. Isoprenaline decreased the responses induced by nicotine, but ACh increased them.
• 5.5. Nicotine at 100 μM did not affect the L-type Ca²⁺ current (I_Ca), but at 300 μM inhibited it at +10 mV by 21.6±2.9% (n=6, p<0.05). The fast time constant (τ_f) of the inactivation phase for I_Ca was not affected, but the slow one (τ₅) significantly increased from 36.8±1.9 ms to 41.2±2.8 ms (n=6) at 300 μM nicotine. The activation and inactivation kinetics (d_∞ and f_∞) for I_Ca were not modified.
• 6.6. Nicotine also did not affect the delayed rectifier K⁺ current (I_K) and its activation kinetic (P_∞)
• 7.7. These results suggest that nicotine depresses the action potentials and causes a negative chronotropic effect due to inhibitions of the ionic currents in the SA nodal cells.

     

Influence of hormonal status in relaxant effect of diethylstilbestrol and nifedipine on isolated rat uterus contraction

• 1.1. The effects of diethylstilbestrol (DES, 10⁻⁷-10⁻⁵ M) and nifedipine (10⁻¹⁰-10⁻⁷ M) on KCl (60 mM)-induced tonic contraction in the uterus of ovariectomized and 17β-estradiol (0.1 mg/kg/day, s.c.)-, 17α-estradiol (0.1 mg/kg/day, s.c.)-, or progesterone (2 mg/kg/day, s.c.)-treated rats have been assayed.
• 2.2. The dose-dependent relaxation produced by nifedipine in ovariectomized rats (EC₅₀ = 5.59 ± 1.25 × 10⁻⁹ M) is potentiated in uterus of rats treated with 17β-estradiol and progesterone (EC₅₀ = 0.59 ± 0.1 and 0.49 ± 0.1 × 10⁻⁹ M, respectively) but not in the 17α-estradiol-treated rats (3.01 ± 0.6 × 10⁻⁹ M).
• 3.3. The relaxation produced by DES on ovariectomized rats (EC₅₀ = 0.84 ± 0.14 × 10⁻⁶ M) is reduced when the rats are treated with 17β-estradiol (EC₅₀ = 2.22 ± 0.2 × 10⁻⁶ M) or progesterone (EC₅₀ = 1.24 ± 0.08 × 10⁻⁶ M), but unmodified by 17α-estradiol (EC₅₀ = 0.58 ± 0.01 × 10⁻⁶ M).
• 4.4. The nifedipine-induced relaxation is reversed with Bay K 8644 (10⁻¹⁰-10⁻⁶ M) in all experimental conditions. However, Bay K 8644 counteracted the relaxation of DES at 45.7% on ovariectomized rats but this was lower than 30% in the other groups.
• 5.5. Our results suggest that in ovariectomized rats the effects of both nifedipine and DES are similar, but 17β-estradiol and progesterone produce a contrary effect on the relaxation induced by nifedipine and DES (by increasing the nifedipine and decreasing the DES effects).
• 6.6. The modifications produced by 17α-estradiol are similar to those produced by the ovariectomy and this suggests that 17α-estradiol is a drug lacking estrogenic activity.

     

The role of endothelium in the calcium-induced reduction of the contractile response of the rabbit aorta

• 1.1. Increase of Ca²⁺ concentration in the bath solution diminishes the contractile response of isolated rabbit aorta rings to α₁-adrenoceptor agonists and KCI.
• 2.2. In intact preparations the contractions of methoxamine and phenylephrine were maximal when a 0.3- to 0.6-mM Ca²⁺ bath solution was used, and those of KCI were maximal with a 2.5-mM Ca²⁺ concentration.
• 3.3. The contractions of methoxamine and phenylephrine also were decreased by increasing the Ca²⁺ concentration above 1.25 mM in disrupted endothelium preparations and in those incubated in indomethacin (10⁻⁵ M), N^ω-nitro-L-arginine methyl ester (10⁻⁴ M), or methylene blue (10⁻⁶ M).
• 4.4. High organ bath Ca²⁺ concentrations also caused a decrease in KCI contractions using endotheliumdenuded and the treated preparations, the responses being similar with 1.25 mM and 2.5-mM Ca²⁺ in the methylene blue-treated preparations, whereas they were greater with 1.25 mM Ca²⁺ in the others.

     

A comparison of the relaxant effects of pinacidil in rabbit renal and mesenteric artery

• 1.1. The relaxant effects of pinacidil were compared in isolated rabbit renal and mesenteric artery.
• 2.2. Pinacidil (10 nm–300 μM) relaxed renal and mesenteric arterial rings precontracted with phenylephrine with pD₂ values of 5.11 ± 0.03 and 6.27 ± 0.04, respectively.
• 3.3. The inhibitory effect of pinacidil on the rabbit mesenteric artery was competitively antagonized by glibenclamide (1–10 μM). The calculated pK_B value was 6.37 ± 0.04. On the renal artery, glibenclamide (2–20 μM) did not significantly affect pinacidil-induced relaxation (P > 0.05).
• 4.4. Tetraethylammonium (TEA, 1–10 mM) competitively antagonized the pinacaidil induced relaxation of the rabbit renal artery. The pK_B value was 3.22 ± 0.08. On the mesenteric artery TEA antagonized the effect of pinacidil in a noncompetitive manner.
• 5.5. The concentration-response curves for pinacidil on the rabbit renal and mesenteric artery were not affected by apamin (0.1 μM).
• 6.6. It is concluded that ATP-sensitivie K⁺ channels (K_ATP) are not involved in pinacidil action on the rabbit renal artery. On the contrary, K_ATP are probably major sites of pinacidil action on the rabbit mesenteric artery.

     

Comparative effects of the Dihydropyridine-type calcium-agonists (−)-S-Bay K 8644, (±)-Bay-W 5035 and (±)-Bay-T 5006 on human platelet aggregability

• 1.1. Human platelet aggregation induced by collagen is concentration-dependently inhibited by dihydropyridine (DHP)-type calcium(Ca)-agonists.
• 2.2. There was no significant difference between the maximal anti-aggregatory effects or the anti-aggregatory potencies of (−)-S-Bay-K 8644 (EC₅₀: 5.3 ± 1.5 × 10^-5 M), (±)-Bay-W 5035 (EC₅₀: 14.9 ± 8.8 × 10^-5 M) or (±)-Bay-T 5006 (EC₅₀: 2.7 ± ± 10^-5 M) (P > 0.05).
• 3.3. Antiaggregatory effects of DHP-type Ca-agonists seem to be independent of Ca-channel activation.

     

Cardiac mechanical and electrophysiologic modulations of guinea-pig by caffeine and thapsigargin

• 1.1. The effects of caffeine and thapsigargin on the contractile force and the action potential in guinea-pig papillary muscles were examined.
• 2.2. Caffeine (1 to 10 mM) initially increased contractile force in a concentration-dependent manner. Subsequently, 1 mM caffeine decreased it as compared with precaffeine level (but not significantly). At 5 mM or 10 mM, caffeine also decreased contractile force, but the decrease was still positive as compared with control level.
• 3.3. Exchange to low [Ca]_o(0.9 mM) or high[k]_o(8 mM) decreased steady-state value during exposure to 1 mM caffeine. Addition of 1 μM thapsigargin (TG) decreased the steady-state value during exposure to 1 mM caffeine, but enhanced it with 5 mM and 10 mM caffeine. TG (1 μM) alone increased the force.
• 4.4. In electrophysiologic studies, caffeine shortened the action potential duration (APD) in a concentration-dependent manner. In the presence of caffeine (1 mM), high[K]_o shortened APD and decreased the action potential amplitude and resting potential.
• 5.5. These results suggest that in the presence of caffeine and/or thapsigargin calcium overload might not occur in the left ventricular papillary muscles of the guinea-pig heart.

     

Xanthonolol: A calcium channel and beta-adrenoceptor blocker with vasodilating properties

• 1.1. Xanthonolol (0.1–0.5 mg/kg, i.v.) reduced the blood pressure, heart rate, and l-isoproterenol (0.05 μg/kg, i.v.)-induced tachycardia in rats.
• 2.2. In the isolated guinea-pig right atrium, xanthonolol (10⁻⁶−3 × 10⁻⁴ M) produced long-lasting negative, inhibited l-isoproterenol-induced positive chronotropic effects, prevented the rate-increasing effects of increased extracellular Ca²⁺ (3.0–9.0 mM), and inhibited Ca²⁺ (3.0–9.0 mM)-induced heart rate-increase.
• 3.3. In the isolated guinea-pig thoracic aorta, the contractions induced by CaCl₂ (0.1–5.0 mM) were inhibited by xanthonolol (10⁻⁶–10⁻⁴ M).
• 4.4. Xanthonolol is suggested to have a calcium channel and beta adrenergic blocking effect with vasodilating properties.

     

The effect of Lithium on endothelial-dependent relaxation in rat isolated aorta

• 1.1. In endothelium-containing rings of rat aorta, precontracted by phenylephrine, addition of acetylcholine (Ach), resulted in a concentration-dependent relaxation through the release of endothelial dependent relaxing factors, including nitric oxide (IC₅₀ = 8.41 μM).
• 2.2. Pretreatment of the tissues with 20 μM indomethacin, significantly decreased the relaxation.
• 3.3. Preincubation of the preparations in medium solution in which sodium has been partially replaced by 0.5 mM lithium, significantly reduced Ach-induced endothelial dependent relaxation (EDR).
• 4.4. Lithium (2 mM) in medium, significantly increased Ach-induced relaxation.
• 5.5. As is shown in this study, lithium has two opposite actions on EDR, with the dose of 0.5 mM inhibiting, while the dose of 2 mM potentiates EDR. Thus it seems that the action of lithium on EDR is mediated through two separate mechanisms.

     

Purine and pyrimidine nucleotide metabolism of vascular smooth muscle cells in culture

• 1.1. Cultures of vascular smooth muscle cells accumulate extracellular breakdown products of purine and pyrimidine nucleotides that, over 9 hr, represent 60±7 and 78±17%, respectively, of the intracellular nucleotide content.
• 2.2. The accumulation is stimulated during contracture with 20 mM KCl or 70 μM carbachol, consistent with the notion that both pyrimidine and purine nucleotides are involved in the energetics of smooth muscle contracture.
• 3.3. Because the intracellular levels of pyrimidine and purine nucleotides remain constant, it appears likely that rates of synthesis match the rates of release.
• 4.4. Ectonucleotidases are present that can degrade ATP, UTP, and CTP. High-energy nucleotides may be the primary products released.

     

Influence of diethylcarbamazine and mefloquine on PGI2 synthesis by the rat thoracic aorta and myometrial tissues

• 1.1. The influence of the antifilarial drug diethylcarbamazine citrate (D) and dl-erythro mefloquine hydrochloride (Mf) on PGI₂ synthesis by the male rat thoracic aorta and day-20 pregnant rat myometrium was investigated in vitro using a rat platelet antiaggregatory bioassay method.
• 2.2. Pretreatment of the tissues with D (25.5–204 μM) or Mf (24–192 μM) for 30 min at 37°C significantly inhibited PGI₂ synthesis in a concentration-dependent manner.
• 3.3. D exhibited its inhibitory effect even in presence of exogenous arachidonic acid (AA) (16.6 μM) whereas Mf lost its inhibitory effect in presence of AA.
• 4.4. Pretreatment of urethane-anaesthetized rats with D (32 μmol kg⁻¹) but not Mf (7.5 μmol kg⁻¹) for 30 min significantly antagonized AA (4 nmol kg⁻¹)-induced hypotension
• 5.5. Furthermore, D (0.25–0.5 μM) antagonized AA-induced aggregation in rabbit platelet-rich plasma without affecting that of ADP.
• 6.6. D seemed to interfere with the action of the PG endoperoxide synthase (PG cyclooxygenase) whereas Mf seemed to interfere with the action of phospholipase A₂ (PLA₂) enzyme.
• 7.7. D may have exerted its effect via release of toxic O₂ radicals whereas Mf effect may have been due to an interaction with PLA₂ substrate phospholipids.
• 8.8. The demonstrated inherent property of these two drugs to inhibit the synthesis of the potent vasodilator, platelet antiaggregatory, anticonvulsant and antiinflammatory mediator PGI₂ may partly contribute towards better understanding of the biochemical mechanisms that underly some of the previously known but poorly understood actions of these drugs.