Progesterone and pregnanolone derivatives relaxing effect on smooth muscle

• 1.1. The effect of gestagens, 5α-hydroxyprogesterone (10⁻⁶−6 × 10⁻⁵ M), 5β-hydroxyprogesterone (10⁻⁶−3 × 10⁻⁵ M), progesterone (6 × 10⁻⁶−10⁻⁴ M), pregnanolone (10⁻⁶−10⁻⁵ M), allopregnanolone (10⁻⁶−10⁻⁴ M) and epipregnanolone (10⁻⁶−6 × 10⁻⁵ M) on rat uterine contractions induced by KCl (60 mM), has been assayed.
• 2.2. All drugs assayed relaxed the tonic-contraction induced by KCl in a concentration-dependent way. The respectives IC₅₀ were 31.3 ± 4.1 × 10⁻⁶ M (progesterone), 8.9 ± 0.8 × 10⁻⁶ M (5α-hydroxyprogesterone 3.8 ± 0.3 × 10⁻⁶ M (5β-hydroxyprogesterone), 3.1 ± 0.1 × 10⁻⁶ M (pregnanolone), 21.2 ± 3.1 × 10⁻⁶ M (allopregnanolone) and 6.3 ± 1.3 × 10⁻⁶ M (epipregnanolone). This relaxing effect was partially or totally counteracted by CaCl₂ (1–10 mM)
• 3.3. Cycloheximide (10 μg/ml) significantly shifted to the right the effect of allopregnanolone but not the effect of the other drugs. Actinomycin D (5 μg/ml) did not modify the effect of allopregnanolone.
• 4.4. Our results suggest that the relaxing effect of gestagens in the rat uterus could be related to inhibition on calcium influx and mainly occur through non-genomic mechanisms.

     

Lymphokines production by concanavalin A-stimulated mouse splenocytes: modulation by Met-enkephalin and a related peptide

Methionine-enkephalin (ME) and its synthetic congener Tyr-D-Ala-Gly-Me-Phe-Gly-NH.C₃H₇-iso (82/205), in a concentration-dependent biphasic manner modulated the concanavalin A (Con A)-stimulated phagocytosis-promoting (PP)-activity elaboration in the culture supernatants of mouse splenocytes in vitro. Both these peptides at 1 × 10⁻⁵ and 1 × 10⁻⁶ M inhibited the production of PP activity; conversely, at 1 × 10⁻⁷−1 × 10⁻⁹ M they augmented it. Peptide 82/205 was nearly 1.2-fold more inhibitory and approximately 1.8-fold more potent in augmenting the PP activity elaboration. The PP activity appeared to be due to lymphokines (LK) gamma interferon and interleukin-4 as the neutralizing concentrations of monoclonal antibodies against these LK significantly (p<0.05) inhibited it. Cycloheximide (50.0 μg/ml) completely inhibited the production of LK indicating their de novo synthesis. The peptides appeared to exert their inhibitory and augmenting effects via δ-and μ-opioid receptors, respectively, as pretreatment of splenocytes with 100-fold higher (1 × 10⁻³ M) concentration of naloxone was required to block their inhibitory effect; the augmenting effect was blocked by 1 × 10⁻⁵ M only. None of the peptides or naloxone could directly stimulate the splenocytes for PP-LK elaboration.     

Effects of Ro 5-4864 and PK 11195 in rat duodenum and vas deferens

Ro 5-4864 and PK 11195 inhibit in a concentration-dependent manner carbachol-induced contractions in rat duodenum (IC₅₀: 1.56 ± 0.07 × 10⁻⁵ M and 1.18 ± 0.07 × 10⁻⁵ M respectively). The antagonism is non-competitive and is not mediated by peripheral-type benzodiazepine receptors. The Ro 5-4864 effect is modulated by the calcium concentration of the Tyrode-Ringer solution. In the presence of 1 mM NaF/10 μM AlCl₃, Ro 5-4864 and PK 11195 do not inhibit carbachol-induced contractions. Moreover, Ro 5-4864 and PK 11195 significantly relax AlF₄⁻-induced contractions, with IC₅₀ values of 2.01±0.12×10⁻⁵ M and 1.28 ± 0.11 × 10⁻⁵ M respectively. This effect is also modulated by the calcium concentration of the medium. Pertussis toxin potentiates the antagonist effects of Ro 5-4864 and PK 11195 on carbachol-induced contractions, but cholera toxin does not affect them. Ro 5-4864 and PK 11195 inhibit ⁴⁵Ca²⁺ uptake induced by KCl (120 mM) in rat vas deferens, but do not affect either basal ⁴⁵Ca efflux or noradrenaline-induced ⁴⁵Ca²⁺ efflux. Only high doses of PK 11195 (above 5 × 10⁻⁵ M) are able to produce a slight reduction of the accumulation of inositol phosphates induced by methoxamine in rat vas deferens, while Ro 5-4864 has no significant effect. Finally, Ro 5-4864 and PK 11195 reduce calcium influx, but do not seen to be the only mechanism of the antagonistic effect on carbachol-induced contractions. An alteration of other second messengers. probably cyclic monophosphate nucleotides, may be involved.     

Effects of cirsiliol,a flavone isolated from Achillea fragrantissima,on rat isolated ileum

• 1.1. In concentrations from 10⁻⁸ M to 3 × 10⁻⁴ M, cirsiliol caused concentration-dependent relaxation of rat isolated ileum.
• 2.2. Phentolamine (10⁻⁶ M) or phentolamine and propranolol (10⁻⁶ M) had no significant effects on the concentration-effect curves or on the EC₅₀ of cirsiliol on the ileum.
• 3.3. Cirsiliol shifted to the right the acetylcholine (Ach) concentration-effect curves on ileum and significantly inhibited the maximum contractions induced by Ach.
• 4.4. In Ca²⁺-free, depolarizing solution, cirsiliol shifted to the right the CaCl₂ concentration-effect curves and inhibited the maximum contractions induced by CaCl₂ on ileum.
• 5.5. Large concentrations (10⁻⁴ M, 3 × 10⁻⁴ M) of cirsiliol induced relaxation followed by contraction of the ileal segments incubated in Ca²⁺-free solution.
• 6.6. In Ca²⁺-free solution, cirsiliol (10⁻⁴ M, 3 × 10⁻⁴ M) caused concentration-dependent potentiation of the ileal contractions induced by 3 × 10⁻³ M Ach when the latter was added 2–3 min after cirsiliol. When Ach was added 15–20 min after cirsiliol, the latter compound inhibited the Ach-induced contractions.
• 7.7. These observations suggest that cirsiliol inhibits Ca²⁺ influx but stimulates Ca²⁺ release from intracellular stores. Furthermore, they suggest that cirsiliol utilizes the same Ca²⁺ source used by acetylcholine in Ca²⁺-free solution.

     

The effects of BAY-K-8644 on the contraction of cat middle cerebral and femoral arteries

The effects of BAY-K-8644 on the reactivity of cylindrical segments of cat middle cerebral and femoral arteries were studied. BAY-K-8644 induced dose-dependent contractile responses in cerebral arteries up to 10⁻⁶M; higher concentrations tended to cause relaxation of the segments. The dihydropyridine elicited contractions in femoral arteries only when these vessels were previously exposed to 15 mM K⁺ Nifedipine (3 × 10⁻⁷M) produced a parallel shift to the right of the dose-response curve to BAY-K-8644, whereas 5 × 10⁻⁶ M verapamil markedly reduced the responses evoked by all concentrations of this drug. The removal of Ca²⁺ from the medium abolished the response evoked by the Ca²⁺-channel activator at 10⁻⁷M in both kinds of arteries. Under these conditions Ca²⁺ addition induced vasoconstriction, which was blocked by nifedipine (3 × 10⁻⁷M). Preincubation of femoral arteries with 10⁻⁷ M BAY-K-8644 potentiated the effects evoked by 25, 50, 75 and 125 mM K⁺, but did not modify those produced by 10⁻⁵ M noradrenaline. Nifedipine (10⁻⁷ M and 3 × 10⁻⁷ M) blocked the potentiation caused by this drug in a dose-dependent manner. Both the increase of the response elicited by BAY-K-8644 and the inhibitory effects of nifedipine were greater at 25 mM K⁺ than at 125 mM. These results suggest that (1) BAY-K-8644 facilitates Ca²⁺ influx into smooth muscle through Ca²⁺ channels that are possibly voltage sensitive and (2) the voltage independence of the drug-induced contractions in cerebral arteries.     

Effect of a New Vasodilator,Pinacidil (P 1134), on Potassium,Noradrenaline and Serotonin Induced Contractions in Rabbit Vascular Tissues

Abstract: Ring preparations of rabbit aorta were contracted by potassium (127 mM). Pinacidil (P 1134), a new vasodilator (2.3×10⁻⁵ M), the calcium antagonists verapamil (3.4×10⁻⁷ M), nifedipine (3.4×10⁻⁹ M) and hydralazine (1.9×10⁴ M) relaxed the preparation by 50%. 50% relaxation of noradrenaline-contracted tissues was obtained with pinacidil, 6.8×10⁻⁵ M, verapamil, 2.4×10⁻⁴ M and hydralazine, 1.9×10⁻³ M. At 2×10⁻⁷ M concentration nifedipine was almost inactive. In ring preparations of rabbit aorta exposed to calcium-free medium and then depolarized with potassium (127 mM), pinacidil, 5×10⁻⁵ M and nifedipine, 10⁻⁸ M significantly inhibited the contractions by cumulative addition of calcium. Hydralazine, 10⁻³ M had no effect. Noradrenaline-induced contractions in calcium-free medium or in presence of increasing amounts of calcium were significantly inhibited by nifedipine, 10⁻⁸ M and hydralazine, 10⁻³ M. Pinacidil, 10⁻⁴ M had no effect. Pinacidil, 1.3×10⁻⁵ M and verapamil, 2.0×10⁻⁵ M inhibited by 50% the serotonin-induced increase of perfusion pressure of isolated rabbit ear artery. The noradrenaline effect in this preparation were 50% inhibited by pinacidil, 2.4×10⁻⁴ M and by verapamil, 8.8×10⁻⁵ M. Hydralazine, 10⁻³ M exerted minor inhibitory effect. It is suggested that interference with calcium influx contributes to the vasodilator activity of pinacidil.     

Characterization of 5-Hydroxytryptamine receptors in goat cerebral arteries

• 1.1. In isolated goat middle cerebral artery segments, 5-hydroxytryptamine (5-HT, 10⁻⁸-3 × 10⁻⁵ M) elicited concentration-dependent contractions with EC₅₀ = 2.1 (1.9−2.5) × 10⁻⁷ M and E_max = 64 ± 2% of 50 mM KCl-induced contraction.
• 2.2. Several 5-HT receptor agonists were used: (a) the agonist of 5-HT₂ receptors α-methyl-5-hydroxytryptamine (10⁻⁷ -3 × 10⁻⁴ M) induced strong contraction (51± 6%); (b) the selective agonists of 5-HT_1A receptors sumatriptan (10⁻⁸ - 10⁻⁵ M) and 5-carboxamidotryptamine (10⁻⁹ - 10⁻⁴ M) and the agonist of 5-HT_1A receptors 8-hydroxy-2-(di-n-propylamino)tetralin (10⁻⁷ - 3 × 10⁻⁵ M) induced weak contractions (8, 18 and 14%, respectively); and (c) the agonist of 5HT₃ receptors 2-methyl-5-hydroxytryptamine (3 × 10⁻⁶ - 10⁻⁴ M) induced almost negligible contraction.
• 3.3. Pretreatment with the antagonist of 5-HT_1A and 5-HT_1B receptors cyanopindolol (10⁻⁸, 10⁻⁶ M), the antagonist of 5-HT₁/5-HT₂ receptors methysergide (10⁻¹¹, 10⁻⁹ M) and the antagonist of 5-HT₂ receptors ketanserin (10⁻¹¹, 10⁻⁹ M) induced non-competitive inhibition of the concentration-response curve to 5-HT. The antagonist of 5-HT₃ receptors 3-trophanyl-3,5-dichlorobenzoate (10⁻⁷, 10⁻⁵ M) did not inhibit the contractile curve to 5-HT.
• 4.4. These results suggest that 5-HT contracts the goat middle cerebral artery by acting mainly on 5-HT₂ receptors.

     

Effect of naringin and naringenin on contractions induced by noradrenaline in rat vas deferens—I. Evidence for postsynaptic alpha-2 adrenergic receptor

• 1.1. Naringin at all doses (2 × 10⁻⁶, 5 × 10⁻⁷, and 1 × 10⁻⁷ M) significantly increased contractions induced by noradrenaline in rat vas deferens but the increments of maximal contraction were not concentration-dependent.
• 2.2. In a medium containing 1 × 10⁻⁶ M yohimbine (a selective blocker of α₂-adrenoceptor) and naringin, the curve constructed with noradrenaline decreased below the control curve.
• 3.3. Naringenin (aglycone of naringin) (2 × 10⁻⁶ and 1 × 10⁻⁷ M) increased the contractile effect of noradrenaline and the maximal effect evoked was related to the maximal dose of naringenin.
• 4.4. The α₂ antagonism produced by yohimbine in the naringenin-noradrenaline association were retained at two doses of naringenin tested and we noticed a similar behaviour when we used clonidine-noradrenaline.

     

Inhibition of ATP-Induced Contraction in the Guinea-pig Urinary Bladder in Vitro and in Vivo

Abstract Contractions were elicited by adenosine 5′-triphosphate (ATP) in the guinea-pig urinary bladder in vitro and in vivo. In isolated detrusor strips, tetrodotoxin (3.1 × 10^-6-4.4 × 10^-5M) did not affect contractions induced by a submaximum concentration (10^-3M) of ATP, nor did atropine (1.7 × 10^-6 - 2.1 × 10^-4M), or the anticholinergic agent PR 197 within the concentration range 2.6 × 10^-8 - 2.6 × 10^-5M. In higher concentrations (5.2 × 10^-5-2.6 × 10^-4M), PR 197 inhibited the ATP-response by 60-70% in a way that was not clearly concentration-related. Isoprenaline (10^-7-2.0 × 10^-5M) and noradrenaline (2.5 × 10^-6-10^-4M) reduced the ATP-induced contractions by up to 79%. The effects of the amines were abolished by propranolol (5.2 × 10^-6-3.8 × 10^-5M). Adenosine, 1.0-2.0 × 10^-2M, reduced the ATP-response by about 50%; in lower concentrations, it had no effect. Nifedipine, 7.8 × 10^-7-1.2 × 10^-5M, reduced the responses by 15-795%. Indomethacin (≤2.0 × 10^-4M), and theophylline (2.0 × 10^-4M) had no consistent effects on ATP-induced contractions. Exposure of the preparations to a calcium-free medium reduced and abolished the ATP-response within 60 min. Intravenous injection of ATP (1 -20 mg/kg) caused a rapid and transient increase in intravesical pressure in the anaesthetized guinea-pig. The effect of ATP (3mg/kg) was reduced by atropine(5-10 mg/kg) by approximately 35%. PR 197 (2.5-5 mg/kg) abolished the ATP-response. Isoprenaline (5-100 pg/kg) caused a 53-95% inhibition that could be blocked by propranolol (1 mg/kg). The inhibiting effect of noradrenaline (10-100,μg/kg) could not be blocked by propranolol (1 mg/kg). Adenosine (1.5-3.0 mg/kg) given immediately before ATP completely inhibited the ATP-response. Nifedipine, 0.1-0.2 mg/kg, reduced the ATP-induced contraction by 34 to 100%. It is concluded that the ATP-induced contraction is elicited by a direct effect on the smooth muscle cell. It can be inhibited non-specifically by drugs with different modes of action.     

No evidence for dopamine-induced relaxation in isolated human mesenteric arterial strips from elderly patients

• 1.1. We investigate the effects of dopamine in isolated mesenteric artery from elderly patients.
• 2.2. Noradrenaline (10⁻¹¹ to 10⁻⁴ M) and dopamine (2.7 × 10⁻⁶ to 1.4 × 10⁻³ M) induced a concentrationdependent contraction that was antagonized by prazosin. Fenoldopam (10⁻⁸ to 10⁻⁴ M) and clonidine (10⁻⁹ to 10⁻⁴ M) did not produce any contractile effects.
• 3.3. Potassium chloride (80 mM) produced a well-maintained plateau contraction and dopamine-induced contraction in these conditions, which was decreased by prazosin (10⁻⁸ M). Neither fenoldopam nor isoprenaline (10⁻¹⁰ to 10⁻⁵ M) modified the well-maintained plateau.
• 4.4. Our results suggest that post-synaptic dopamine receptors are not present in this preparation but α₁-adrenoceptors are present.

     

Comparison of various calcium channel blockers on guinea-pig isolated common bile duct

• 1.1. The inhibitory effects of various calcium channel blockers; nifedipine, verapamil, diltiazem and a heterogenous compound, dantrolene, have been investigated on isolated common bile duct from guinea-pig.
• 2.2. All the compounds tested induced a concentration-dependent reduction of the amplitude of contractile response to electrical stimulation or increasing the calcium concentration of the bathing media.
• 3.3. Nifedipine was the most potent compound whereas the least potent was dantrolene; verapamil and diltiazem had intermediate potency.
• 4.4. The IC₅₀ values for these compounds were calculated as: nifedipine 3.68 × 10⁻⁹M; verapamil, 4.93 × 10⁻⁸M; diltiazem, 4.2 × 10⁻⁷M; and dantrolene 5.51 × 10⁻⁵M.
• 5.5. All the compounds displaced the concentration-response curve of calcium chloride to the right in a concentration-dependent manner. Among the compounds studied, nifedipine had the highest and dantrolene had the lowest potency.
• 6.6. These results indicate the striking pharmacological effects of the calcium channel blockers on the common bile duct and may indicate a possible role for these compounds in the treatment of biliary colic.

     

Effects of Cholinoceptor Blocking Drugs,Adrenoceptor Stimulants,and Calcium Antagonists on the Transmurally Stimulated Guinea-pig Urinary Bladder in Vitro and in Vivo

Abstract The effects of different drugs on the response to transmural electrical stimulation of the guinea-pig urinary bladder were studied in vitro and in vivo. In vitro, atropine (3.0 × 10^-8-5.9 × 10^-4M) did not influence the contractions. When used in high concentrations (>5.2 × 10^-5M), PR 197, another anticholinergic compound, reduced the responses by 25-40%, probably by a non-specific action. Noradrenaline (2.0×10^-6-2.0 × 10^-4M) and isoprenaline (2.0 × 10^-8-2.0 × 10^-4M) had concentration-related inhibitory effects that could be blocked by propranolol (5.2 × 10^-6M). Adenosine (2.0 × 10^-2M) inhibited the response by 27±3% (mean±S.E.M., n = 9). Theophylline (2.0 × 10^-3-6.0 × 10^-4M) had no consistent effects. The calcium antagonist nifedipine (1.2 × 10^-6-1.7 × 10^-5M) reduced the contractions by 25-50%; verapamil (2.2 × 10^-5-4.4 × 10^-4M) was little effective. In vivo, atropine (10 mg/kg) reduced the contractions by 55±5 % (n= 10), whereas PR 197 (5 mg/kg) almost completely suppressed the responses. Noradrenaline (20-100 μg/kg) and isoprenaline (20-300 μg/kg) also caused a marked inhibition that could be blocked by propranolol (0.25-2.0 mg/kg). Theophylline (5 and 10 mg/kg) had a weak (10-20%) inhibitory effect. Adenosine (3.0 mg/kg) reduced the contractions by 47±4% (n= 14); in guinea-pigs pretreated with atropine (10 mg/kg), adenosine produced a further 10 to 20% decrease of the responses. Verapamil (0.5-2.0 mg/kg) had no consistent effect, whereas nifedipine (0.1-0.2 mg/kg) caused an inhibition of 20-50%. The results suggest that β-adrenoceptor stimulants, and drugs with a combined anticholinergic and non-specific action, can effectively suppress the electrically evoked contractions in the guinea-pig urinary bladder.     

Effects of S-adenosyl-L-methionine on platelet thromboxane and vascular prostacyclin

We therefore designed the present study to evaluate the effect of S-adenosyl-L-methionine (SAMe) on the synthesis of platelet thromboxane and vascular prostacyclin. The experimental materials were human blood and aortic rings from untreated Wistar rats; and platelets and aortic rings from Wistar rats treated for 7 days with SAMe at 5 or 10 mg/kg/day s.c. The administration of 10 mg/Kg/day of SAMe to rats significantly increased vascular production of 6-keto-PGF_1α. In vitro vascular production of 6-keto-PGF_1α increased in a concentration-dependent manner when SAMe was incubated in the range of 10⁻⁷ to 10⁻⁴ M. The greatest increase was 167 ± 15%, obtained in samples incubated with 5 × 10⁻⁵M SAMe. In aortic rings, lipid peroxidase production was inhibited in a concentration-dependent manner in the SAMe range of 10⁻⁷ to 10⁻⁵ M. Maximum inhibition (75.3 ± 6.2%) was obtained with SAMe at 1.5 × 10⁻⁵M. Vascular 6-keto-PGF_1α production showed a significant inverse linear correlation with vascular lipid peroxide production (Y = −0.04 × + 18.1, r = 0.7309, P < 0.0001).     

Signal transduction in endothelin-induced contraction of rabbit pulmonary vein

The effect of porcine endothelin (endothelin 1) on rings of isolated rabbit pulmonary vein was studied using tissue bath techniques. Endothelin was found to be a potent constrictor of these vessels, producing concentration-dependent contractions with an EC₅₀ value of 3.2 ± 0.6 × 10⁻⁹ M. Contractions were not significantly affected by the Ca²⁺ channel antagonists verapamil, nifedipine, or nicardipine. Contractions were greatly attenuated by 3 mM LaCl₃ (85.8 ± 8.0% relaxation) and were diminished in Ca²⁺-free media (51 ± 9% of control). The protein kinase C (PKC) inhibitor H7 (20 μM) potently and reversibly inhibited endothelin-induced contractions by 82 ± 6% when used as a post-treatment. Incubation of tissues with 20 μM H7 did not significantly affect either the strength of contractions induced with endothelin or the time required for contraction to reach plateau, but these contractions were poorly sustained compared to controls. The phospholiphase C (PLC) inhibitor neomycin (10 mM) inhibited endothelin-induced contractions and it also affected the rate of force development. The phopholipase A₂ (PLA₂) inhibitor quinacrine had no significant effect on endothelin-induced contractions. Thus, both extracellular and intracellular Ca²⁺ are required for full development of endothelin-induced contractions. Extracellular Ca²⁺ appears to enter the cell via non-potential dependent channels that can be blocked by La³⁺. Moreover, the potent vasoconstrictor properties of endothelin on rabbit pulmonary veins involves activation of both PLC and PKC, but not PLA₂. PKC is intimately associated with maintaining the tonic phase of smooth muscle contraction.     

Estrogen and antiestrogen non-genomic effect in rat uterus contraction in calcium-free solution

1. The effects of estrogens estradiol (E₂, 10^-6-10^-4M) and diethylstilbestrol (DES, 10^-6-10^-4M) and the antiestrogens nafoxidine (N, 10^-6-10^-4M), tamoxifen (T, 10^-6-6 × 10^-4M), tamoxifen ethyl bromide (TEB, 10^-4M) and ICI 164,384 (ICI, 10^-5M) on tonic contractions induced by oxytocin (2 × 10^-8M) or vanadate (3 × 10^-4M) in rat uterus incubated in calcium-free EDTA treated solution have been assayed.2. E₂ and DES relaxed the tonic contraction induced by oxytocin in a dose dependent way (EC₅₀: 1.11 ± 0.01 × 10^-4M and 1.5 ± 0.07 × 10^-5M). The vanadate-induced contraction only was relaxed with DES (57.62 ± 2.38% at 10^-3M).3. The effect of DES on oxytocin contraction was unmodified by the protein synthesis inhibitor cycloheximide (10 μg/ml) and by the cycloxygenase inhibitor indomethacin (3 × 10^-6M), but enhanced by the intracellular calcium release inhibitor TMB-8 (10^-5M). The antiestrogen tamoxifen (3 × 10^-5M) promotes the relaxing effect of DES.4. The antiestrogens N, and T, but not ICI, relaxed the oxytocin-induced contraction (EC₅₀: 4.51 ± 0.43 × 10^-5M and 2.27 ± 0.05 × 10^-4M). TEB (10^-4M) produces a relaxation of 74.5 ± 2.11%. The vanadate contraction is also relaxed by T (EC₅₀: 6.03 ± 0.04 × 10^-4M).5. The effect of T on oxytocin contraction was unmodified with cycloheximide or TMB-8 but decreased with indomethacin.     

The Role of Cyclooxygenase and 5-Lipoxygenase Metabolites in Potentiated Endothelin-1-evoked Contractions in Bovine Bronchi

We have previously shown that angiotensin II (AII) potentiates responses evoked by endothelin-1 (Et-1). In the present study, the additional ability of hypoxia or phorbol 12, 13-dibutyrate (PDBu) to evoke hyperreactivity was examined. In addition, the role of cyclooxygenase and 5-lipoxygenase metabolites of arachidonic acid in the potentiation evoked by AII, hypoxia or PDBu was studied, using indomethacin and nordihydroguaiaretic acid (NDGA). The involvement of protein kinase C in the enhanced response was examined using staurosporine. Contractions were measured isometrically from rings of bovine bronchi. Contractions evoked by Et-1 alone were unaltered by indomethacin (10⁻⁶m), NDGA (10⁻⁵m) or staurosporine (3×10⁻⁸m). AII (3×10⁻⁷m), hypoxia (4% O₂) or PDBu (10⁻⁸m) each significantly potentiated the contractions evoked by Et-1. Indomethacin (10⁻⁶m) virtually abolished the effect of AII, hypoxia or PDBu. NDGA (10⁻⁵m) reversed the potentiating effect of both AII and hypoxia and partially reversed PDBu-evoked enhancement of Et-1-mediated responses. Staurosporine (3×10⁻⁸m) abolished the ability of AII or PDBu, but not hypoxia, to enhance Et-1-mediated contractions. In conclusion, AII, hypoxia and PDBu evoke hyperresponsiveness which is mediated by prostanoids and/or leukotrienes, the precise nature of which remains to be elucidated. Differences in the ability of staurosporine to reverse AII- and hypoxia-induced hyperreactivity suggests, however, that these conditions may generate different eicosanoids.     

Involvement of catecholamines in the effect of U-50,488H on isolated left atria of the rat

• 1.1. The present study examined the effect of U-50,488H on auricular contraction of isolated left atria of the rat.
• 2.2. The negative inotropic action induced by the к-agonist was antagonized in the presence of propranolol (10⁻⁸ or 5 × 10⁻⁸ M), yohimbine (5 × 10⁻⁷ or 10⁻⁶ M) or in reserpinized rats (5 mg/kg i.p. 24 hr before the experiments).
• 3.3. These results suggest that catecholaminergic mechanisms are involved in the cardiac depressant effect induced by U-50,488H.

     

The effect of stercuronium on cardiac muscarinic receptors

In the electrically stimulated guinea-pig left atrium preparation stercuronium (10^?6?3 × 10^?4 M) a short-acting neuromuscular blocking drug, was found to produce parallel displacement of concentration-response curves for negative inotropic responses to acetylcholine, carbachol, methacholine and pilocarpine but not those to ATP or K⁺. The effect of stercuronium was not modified in the presence of mecamylamine (2 × 10^?5 M) or propranolol (3 × 10^?6 M). It was concluded that stercuronium possesess antimuscarinic activity but in contrast to the competitive antagonist homatropine (2 × 10^?6?3 × 10^?4 M) the degree of antagonism of cholinomimetics tended towards a limiting value at high concentrations of antagonist being more marked with acetylcholine than with carbachol and the other cholinomimetics. Pretreatment of guinea pigs with dyflos (1.2 mg/kg s.c. daily for 3 days) reduced but did not abolish the difference between acetylcholine and carbachol. Using acetylcholine as the agonist in atria obtained from dyflos-pretreated guinea pigs combination of stercuronium and homatropine produced dose ratios which were significantly less than expected for combination of 2 competitive antagonists. It is suggested that the antimuscarinic activity of stercuronium is due to a non-competitive antagonism of the metaffinoid type whereby interaction at an allosteric site may modify the bining of agonists and of competitive antagonists for the receptor.     

Effects of an extract of Ginkgo biloba and diverse substances on the phasic and tonic components of the contraction of an isolated rabbit aorta

• 1.1. The effects of phentolamine, propranolol, D 600, theophylline, papaverine and an extract of Ginkgo biloba were studied with respect to the two phases of the contractile response induced by norepinephrine in an isolated rabbit aorta.
• 2.2. Phentolamine (3 × 10⁻⁶ M) inhibits the rapid phase of the contraction of the rabbit aorta brought on by norepinephrine (NE) 10⁻⁵ M more strongly than the tonic phase. Propranolol (10⁻⁶ M) potentiates this rapid phase.
• 3.3. D 600 inhibits the slow phase with an EC₅₀ = to 3.8 × 10⁻⁸ M.
• 4.4. Papaverine and theophylline increase the relaxation that follows the rapid phase of contraction. The slow phase is inhibited only by papaverine.
• 5.5. The extract of Ginkgo biloba (Gb) at a concentration of 3 mg/ml has the same type of effect as papaverine 3 × 10⁻⁵ M.

     

Inhibition of superoxide anion production in macrophages by anti-inflammatory drugs.

The inhibition by anti-inflammatory drugs of the production of Superoxide anions (O₂^?) by isolated guinea pig macrophages was studied spectrophotometrically using NADH and lactate dehydrogenase. id₅₀ values were: 4 × 10^?7M (diclophenac sodium), 1 × 10^?6M (oxyphenbutazone), 1 × 10^?5M (indomethacin), 4 × 10^?5M (phenylbutazone), 7 × 10^?5M (mefenamic acid), 8 × 10^?5 M (flufenamic acid), 8 × 10^?5M (colchicine), 3 × 10^?4M (aspirin), 3 × 10^?4M (benzydamine), 10^?3M < (dexamethasone) and 10^?3M < (gold sodium thiomalate). They seemed to block the cell membrane-associated mechanism to produce Superoxide anions, since most of them did not abolish the generation of superoxide anions from the xanthine oxidase plus hypoxanthine system. Cytochalasin B, pyrogallol, ascorbate, NEM, l-epinephrine and chlorpromazine also inhibited, the production of Superoxide anion, but many non anti-inflammatory drugs were ineffective. This technique was evaluated as a screening method in vitro for nonsteroidal anti-inflammatory drugs.