Inhibitory action of lanthanum(La) on PGF2α- induced contraction of guinea-pig stomach muscle

The effects of lanthanum(La) on contractions induced by prostaglandin F_2α(PGF_2α) or isotonic K⁺ were investigated in the isolated stomach muscle of guinea-pig.Low concentrations of La(0.1–1 μM) inhibited the contraction to PGF_2α 1 μM in a dose-dependent manner, without affecting the tonic contraction to isotonic K⁺.0.1 and 1 μM La shifted the dose-response curve for PGF_2α(0.001 – 1 μM) to the right and reduced the maximum response.The IC₅₀ of La against PGF_2α and K⁺ were 0.6 μM and 30 μM, respectively.These results support the suggestion that PGF_2α -induced contraction in the stomach muscle depends mainly on the intracellular release of sequestered Ca, which would be depleted or immobilized by La.     

Structure and Antiviral Activity of the Galactofucan Sulfates Extracted from Undaria Pinnatifida (Phaeophyta)

The galactofucan sulfate extract (GFS) obtained from the brown seaweed Undaria pinnatifida by extraction with dilute acid is a potent inhibitor of the herpes viruses HSV-1, HSV-2 and HCMV, with IC₅₀ values determined in vitro of 1.1, 0.2 and 0.5 μgmL⁻¹, respectively. Fractionation of GFS by anion exchange chromatography gave three fractions which differed in their uronic acid and sulfate contents and in their antiviral activity, as well as in having somewhat reduced molecular weights compared to GFS. The low uronic acid/high sulfate fraction (F2M), obtained in 63% yield, had similar molar proportions of galactopyranosyl and fucopyranosyl residues, little associated protein and was equipotent with GFS (IC₅₀ values of 1.1, 0.1 and 0.5 μgmL⁻¹, respectively). The high uronic acid/low sulfate fraction (F1M), obtained in 18% yield, had a much lower proportion of galactopyranosyl residues and was less active (IC₅₀ values of 4.6, 1.0 and 4.0 μgmL⁻¹, respectively). The minor low uronic acid/high sulfate fraction (F4M) had a significant amount of associated protein and was also less active (IC₅₀ = 3.1, 1.0 and 2.0 μgmL⁻¹, respectively). The structure of the major fraction (F2M) was shown to be complex by glycosyl linkage analysis before and after solvolytic desulfation, with many component sugar residues being identified, although 3-linked fucopyranosyl 2,4-disulfate residues were a prominent feature.     

Prejunctional Inhibitory Effects of Isoprostanes on Dopaminergic Neurotransmission in Bovine Retinae,In vitro

We investigated the effect of isoprostanes (IsoPs) on potassium (K⁺)-depolarization-evoked release of [³H]dopamine from isolated bovine retinae. Isolated retinae were preloaded with [³H]dopamine and then prepared for studies of [³H]dopamine release using the superfusion method. 8-iso(15R)PGF_2α, 8-isoPGE₂, 8-isoPGE₁ and 8-isoPGF_2α attenuated [³H]dopamine release from isolated bovine retinae. At a concentration of 1 μM, the rank order of activity displayed by IsoP agonists was: 8-iso(15R)PGF_2α > 8-isoPGE₂ > 8-isoPGE₁ > 8-isoPGF_2α. Inhibition of cyclooxygenase (COX) with flurbiprofen reversed the effects caused by 8-isoPGE₂ (10 nM and 10 μM), 8-iso(15R)PGF_2α (1 μM) and 8-isoPGE₁ (1 μM). Although the EP1/EP2 antagonist, AH 6809 (10 μM) had no significant effect on K⁺-induced [³H]dopamine release, it blocked the inhibitory effect of both 8-isoPGE₁ (10 μM) and 8-isoPGE₂ (10 μM). In conclusion, IsoPs attenuate K⁺-induced [³H]dopamine release in isolated bovine retinae, presumably via an indirect action on COX pathway leading to the production of prostanoids, which in turn, activates EP receptors.     

M1 Muscarinic Receptors Contribute to, whereas M4 Receptors Inhibit, Dopamine D1 Receptor-Induced [3H]-Cyclic AMP Accumulation in Rat Striatal Slices

In rat striatal slices labelled with [³H]-adenine and in the presence of 1 mM 3-isobutyl-1-methylxantine (IBMX), cyclic [³H]-AMP ([³H]-cAMP) accumulation induced by the dopamine D₁ receptor agonist SKF-81297 (1 μM; 177±13% of basal) was inhibited by the general muscarinic agonist carbachol (maximum inhibition 72±3%, IC₅₀ 0.30±0.06 μM). The muscarinic toxin 7 (MT-7), a selective antagonist at muscarinic M₁ receptors, reduced the effect of SKF-81297 by 40±7% (IC₅₀ 251±57 pM) and enhanced the inhibitory action of a submaximal (1 μM) concentration of carbachol (69±4% vs. 40±7% inhibition, IC₅₀ 386±105 pM). The toxin MT-1, agonist at M₁ receptors, stimulated [³H]-cAMP accumulation in a modest but significant manner (137±11% of basal at 400 nM), an action additive to that of D₁ receptor activation and blocked by MT-7 (10 nM). The effects of MT-7 on D₁ receptor-induced [³H]-cAMP accumulation and the carbachol inhibition were mimicked by the PKC inhibitors Ro-318220 (200 nM) and Gö-6976 (200 nM). Taken together our results indicate that in addition to the inhibitory role of M₄ receptors, in rat striatum acetylcholine stimulates cAMP formation through the activation of M₁ receptors and PKC stimulation.     

Pharmacological properties of the potassium-activated inward current in pyramidal hippocampal neurons

Elevation of the external potassium concentration induced a two-phase inward current in freshly isolated pyramidal hippocampal neurons. This current was voltage-dependent and demonstrated strong inward rectification. The current consisted of a leakage current and a time-dependent current (τ=40–50 msec at 21°C); the latter was designated asI _ΔK. As was shown earlier, K⁺ is a major charge carrier in the development of slow potassium-activated current. The pharmacological properties ofI _ΔK were studied using a patch-clamp technique.I _ΔK was completely blocked by external 10 mM TEA or 5 mM Ba²⁺ (IC₅₀=480±90mM) and exhibited low sensitivity to extracellular Cs⁺ (2 mM). This current was not affected by 1 mM 4-aminopyridine and was insensitive to a muscarinic agonist, carbachol (50 μM), and to 1 mM extracellular Cd²⁺. Elevation of external Ca²⁺ from 2.5 mM to 10 mM did not changeI _ΔK. Our data indicate that the pharmacological properties ofI _ΔK differ from those of other voltage-gated potassium currents, but more specific blockers must be used to make this evidence conclusive.     

Action of 7-oxa-13-prostynoic acid on rat uterine contractility and sensitivity to PGF2α and angiotensin II

The action of 7-oxa-13-prostynoïc acid on spontaneous contractions and on PGF_2α and angiotensin II elicited contractions has been studied on rat uteri excised during pro and metaoestrus At the concentration of 5 × 10⁻⁶M, the compound does not alter the spontaneous contractions of proestrus uteri and suppresses the phasic component of PGF_2α-elicited contractions. At the concentration of 5 × 10⁻⁵M, 7-oxa-13-prostynoïc acid inhibits spontaneous contractions and inhibits PGF_2α-elicited contractions. In metaoestrus uteri, the inhibitory effect is not competitive. 7-oxa-13-prostynoïc acid is also able to inhibit non competitively the contractor effect of angiotensin II in proestrus uteri. This result, together with those of previous investigations performed using other prostaglandin inhibitors, suggest that the contractor effect of angiotensin II on the uterus is partially mediated by endogenous prostaglandins.     

In Vitro evaluation of the cytotoxic and anti-proliferative properties of resveratrol and several of its analogs

Resveratrol (RES), a component of red wine, possesses anti-inflammatory properties. The studies described in the present work were aimed at evaluating the potential for RES and related stilbene analogs (piceatannol, PIC; pterostilbene, TPS; trans-stilbene, TS; and trans-stilbene oxide, TSO) to exhibit toxicity towards RAW 264.7 mouse macrophages. The effect of TS, TSO, RES and TPS on RAW 264.7 macrophage viability was determined by two standard methods: (a) the MTT assay and (b) the trypan blue dye exclusion test. Whereas macrophages were more sensitive to PIC (LC_{50 trypan} ∼ 1.3 μM) and to TPS (LC_{50 trypan} ∼ 4.0 μM and LC_{50 MTT} ∼ 8.3 μM) than to RES (LC_{50 trypan} ∼ 8.9 μM and LC_{50 MTT} ∼ 29.0 μM), they were relatively resistant to TSO (LC_{50 trypan} ∼ 61.0 μM and LC_{50 MTT} > 100 μM) and to TS (LC_{50 trypan} ≥ 5.0 μM and LC_{50 MTT} ≥ 5.0 μM). The ability of selected stilbenes (RES, TPS and PIC) to exhibit growth inhibitory effects was also examined. Although RES and TPS were observed to inhibit cell proliferation in macrophages (IC₅₀ ≤ 25 μM), these cells were resistant to growth inhibition by PIC (IC₅₀ ≥ 50 μM). The data obtained in the present analysis demonstrate that substituted stilbene compounds such as RES have the capacity to exhibit cytotoxic and anti-proliferative activities in macrophages.     

Effects of Cd2+, Mn2+, and Al3+ on rat brain synaptosomal uptake of noradrenaline and serotonin

Cd²⁺, Mn²⁺, and Al³⁺ inhibited synaptosomal amine uptake in a concentration-dependent and time-dependent manner. In the absence of Ca²⁺, the rank order of inhibition of noradrenaline uptake was: Cd²⁺ (IC₅₀ = 250 μM) > Al³⁺ (IC₅₀ = 430 μM) > Mn²⁺ (IC₅₀ = 1.50 mM), the IC₅₀ being the concentration of metal ions that gave rise to 50% inhibition of uptake. In the presence of 1 mM Ca²⁺, the rank order of inhibition of uptake was: Al³⁺ (IC₅₀ = 330 μM) > Cd²⁺ (IC₅₀ = 540 μM) > (IC₅₀ = 1.5 mM). The rank order of inhibition of serotonin uptake without Ca²⁺ was: Al³⁺ (IC₅₀ = 370 μM) > Cd²⁺ (IC₅₀ = 610 μM) > Mn²⁺ (IC₅₀ = 3.4 mM) and the rank order in the presence of 1 mM Ca²⁺ was: Al³⁺ (IC₅₀ = 290 μM) > Cd²⁺ (IC₅₀ = 1.5 mM) > Mn²⁺ (IC₅₀ = 4.0 mM). Ca²⁺, at 1 mM, definitely antagonized the inhibitory actions of Cd²⁺ on noradrenaline and serotonin uptake. Al³⁺ stimulated noradrenaline uptake at concentrations around 20–250 μM but inhibited this uptake at concentrations exceeding 300 μM in a dose-related fashion. Ca²⁺, at 1 mM, enhanced both the stimulatory and inhibitory effects of Al³⁺. Ca²⁺ also enhanced the inhibitory actions of Al³⁺ on seotonin uptake. These results, in conjunction with those we have previously published, suggest that Cd²⁺, Mn²⁺, and Al³⁺ exert differential and selective effects on the structure and function of synaptosomal membranes.     

Inhibition of human platelet aggregation and membrane lipid peroxidation by food spice, saffron

The inhibitory activity of saffron extract was studied on human platelets. Platelet aggregation and lipid peroxidation were evaluated with platelet rich plasma (PRP) and platelet membranes respectively obtained from blood of healthy human volunteers. Human platelets were subjected to stimulation with a variety of agonists like ADP (61 μM), epinephrine (76 μM), collagen (11 μg/ml), calcium ionophore A 23187 (6 μM) and ristocetin (1.25 μg/ml) in the presence and absence of saffron extract with IC₅₀ being 0.66, 0.35, 0.86 and 0.59 mg respectively and no inhibition with ristocetin. The inhibitory effect was dose dependent with concentrations varying between 0.16 to 0.80 mg and time dependent at IC₅₀. A significant decrease was observed in malondialdehyde (MDA) formed, one of the end products of arachidonic acid metabolism and of serotonin released from dense granules of platelets at respective IC₅₀. Lipid peroxidation in platelet membranes induced by iron-ascorbic acid system was inhibited by saffron extract significantly with IC₅₀ of 0.33 mg. Hence, it may be said that aqueous extract of saffron may have component(s), which protect platelets from aggregation and lipid peroxidation. (Mol Cell Biochem 278: 59–63, 2005)     

Tetraethylammonium and 4-aminopyridine block calcium-dependent chloride current in rat cerebellum Purkinje cells

Using patch-clamp method (whole cell configuration), it was shown that tetraethylammonium (TEA) and 4-aminopyridine (4-AP) block calcium-dependent chloride currents in the membrane of freshly isolated cerebellar Purkinje cells of rats (12–15 days). In the concentration range studied (50 μM–10 mM TEA and 100 μM–1 mM 4-AP), both compounds blocked the chloride current at IC₅₀ 130 μM for TEA and 110 μM for 4-AP. TEA blockade was reversible after washing. The effect of 4-AP at concentrations greater than 100 μM was irreversible: both outward and inward chloride currents were blocked even after the removal of 4-AP from the incubation medium.     

Interactions between tachykinins and diverse,human nicotinic acetylcholine receptor subtypes

Nicotinic acetylcholine receptors (nAChR) are diverse members of the ligand-gated ion channel superfamily of neurotransmitter receptors and play critical roles in chemical signaling throughout the nervous system. Reports of effects of substance P (SP) on nAChR function prompted us to investigate interactions between several tachykinins and human nAChR subtypes using clonal cell lines as simple experimental models. Acute exposure to SP inhibits carbamylcholine- or nicotinestimulated function measured using⁸⁶Rb⁺ efflux assays of human ganglionic (α3β4) nAChR expressed in SH-SY5Y neuroblastoma cells (IC₅₀∼2.3 μM) or of human muscle-type (α1β1γδ) nAChR expressed in TE671/RD clonal cells (IC₅₀∼21 μM). SP also acutely blocks function of rat ganglionic nAChR expressed in PC12 pheochromocytoma cells (IC₅₀∼2.1 μM). Neurokinin A and eledoisin inhibit function (extrapolated IC₅₀ values between 60 and 160 μM) of human muscle-type or ganglionic nAChR, but neurokinin B does not, and neither human nAChR is as sensitive as PC12 cell α3β4-nAChR to eledoisin or neurokinin A inhibition. At concentrations that produce blockade of nAChR function, SP fails to affect binding of [³H]acetylcholine to human muscle-type or ganglionic nAChR. SP-mediated blockade of rat or human ganglionic nAChR function is insurmountable by increasing agonist concentrations. Collectively, these results indicate that tachykinins act noncompetitively to inhibit human nAChR function with potencies that vary across tachykinins and nAChR subtypes. They also indicate that tachykinin actions at nAChR could further contribute to complex cross-talk between nicotinic cholinergic and tachykinin signals in regulation of nervous system activity.     

State-Dependent Block of Na<Superscript>+</Superscript> Channels by Articaine Via the Local Anesthetic Receptor

Articaine is widely used as a local anesthetic (LA) in dentistry, but little is known regarding its blocking actions on Na⁺ channels. We therefore examined the state-dependent block of articaine first in rat skeletal muscle rNav1.4 Na⁺ channels expressed in Hek293t cells. Articaine exhibited a weak block of resting rNav1.4 Na⁺ channels at −140 mV with a 50% inhibitory concentration (IC₅₀) of 378 ± 26 μM (n = 5). The affinity was higher for inactivated Na⁺ channels measured at −70 mV with an IC₅₀ value of 40.6 ± 2.7 μM (n = 5). The open-channel block by articaine was measured using inactivation-deficient rNav1.4 Na⁺ channels with an IC₅₀ value of 15.8 ± 1.5 μM (n = 5). Receptor mapping demonstrated that articaine interacted strongly with a D4S6 phenylalanine residue, which is known to form a part of the LA receptor. Thus the block of rNav1.4 Na⁺ channels by articaine is via the conserved LA receptor in a highly state-dependent manner, with a ranking order of open (23.9×) > inactivated (9.3×) > resting (1×) state. Finally, the open-channel block by articaine was likewise measured in inactivation-deficient hNav1.7 and rNav1.8 Na⁺ channels, with IC₅₀ values of 8.8 ± 0.1 and 22.0 ± 0.5 μM, respectively (n = 5), indicating that the high-affinity open-channel block by articaine is indeed preserved in neuronal Na⁺ channel isoforms.     

Physiological and antioxidant responses of <Emphasis Type="Italic">Mentha pulegium</Emphasis> (Pennyroyal) to salt stress

Mentha pulegium L. is a medicinal and aromatic plant belonging to the Labiatae family present in the humid to the arid bioclimatic regions of Tunisia. We studied the effect of different salt concentrations on plant growth, mineral composition and antioxidant responses. Physiological and biochemical parameters were assessed in the plant organs after 2 weeks of salt treatment with 25, 50, 75 and 100 mM NaCl. Results showed that, growth was reduced even by 25 mM, and salt effect was more pronounced in shoots (leaves and stems) than in roots. This growth decrease was accompanied by a restriction in tissue hydration and K⁺ uptake, as well as an increase in Na⁺ levels in all organs. Considering the response of antioxidant enzymes to salt, leaves and roots reacted differently to saline conditions. Leaf and root guaiacol peroxidase activity showed an increase by different concentration of NaCl, but superoxide dismutase activity in the same organs showed a slight modification in NaCl-treated leaves and roots. Moreover, polyphenol contents and antioxidant activity were analysed in M. pulegium leaves and roots under salt constraint. The analysis showed an increase of total polyphenol content (2.41–8.17 mg gallic acid equivalent g⁻¹ dry weight) in leaves. However, methanol extract of leaves at 100 mM NaCl displayed the highest DPPH· scavenging ability with the lowest IC₅₀ value (0.27 μg ml⁻¹) in comparison with control which exhibited IC₅₀ equal to 0.79 μg ml⁻¹.     

Biochemical controls of citrate synthase in chickpea bacteroids

Bacteroids formed by Mesorhizobium ciceri CC 1192 in symbiosis with chickpea plants (Cicer arietinum L.) contained a single form of citrate synthase [citrate oxaloacetate-lyase (CoA-acetylating) enzyme; EC 4.1.3.7], which had the same electrophoretic mobility as the enzyme from the free-living cells. The citrate synthase from CC 1192 bacteroids had a native molecular mass of 228 ± 32 kDa and was activated by KCl, which also enhanced stability. Double reciprocal plots of initial velocity against acetyl-CoA concentration were linear, whereas the corresponding plots with oxaloacetate were nonlinear. The K _m value for acetyl-CoA was 174 μM in the absence of added KCl, and 88 μM when the concentration of KCl in reaction mixtures was 100 mM. The concentrations of oxaloacetate for 50% of maximal activity were 27 μM without added KCl and 14 μM in the presence of 100 mM KCl. Activity of citrate synthase was inhibited 50% by 80 μM NADH and more than 90% by 200 μM NADH. Inhibition by NADH was linear competitive with respect to acetyl-CoA (K _is = 23.1 ± 3 μM) and linear noncompetitive with respect to oxaloacetate (K _is = 56 ± 3.8 μM and K _ii = 115 ± 15.4 μM). NADH inhibition was relieved by NAD⁺ and by micromolar concentrations of 5′-AMP. In the presence of 50 or 100 mM KCl, inhibition by NADH was apparent only when the proportion of NADH in the nicotinamide adenine dinucleotide pool was greater than 0.6. In the microaerobic environment of bacteroids, NADH may be at concentrations that are inhibitory for citrate synthase. However, this inhibition is likely to be relieved by NAD⁺ and 5′-AMP, allowing carbon to enter the tricarboxylic acid cycle. Received: 14 July 1999 / Accepted: 20 September 1999     

Nutrient regulation of bacterial growth and production of anti-tumor metabolites in <Emphasis Type="Italic">Stigmatella</Emphasis> WXNXJ-B fermentation

The metabolites produced by Stigmatella WXNXJ-B inhibited the growth of tumor cells. The aims of this research were to evaluate the inhibition potency to different tumor cell lines and to study the effects of ammonium, phosphate and iron salts on bacterial growth and production of bioactive metabolites in Stigmatella WXNXJ-B fermentation. The results showed that the chloroform extract (CE-ME) showed the strongest growth inhibition bioactivity on mouse melanoma cell line (B16), murine colon carcinoma cell line (CT-26), human liver carcinoma cell line (HepG2) and human breast cancer cell line (MDA-MB231) in vitro and the IC₅₀ values were 9.94, 7.33, 11.34 and 11.66 μg ml⁻¹ respectively. The IC₅₀ value was above 700 μg ml⁻¹ on normal mouse spleen cells. Morphology happened changes in B16 cells treated with CE-ME. The anti-tumor metabolites were mainly produced during the stationary phase of the bacterial growth. Cell growth was stimulated at the phosphate concentration below 5 mM, but it was inhibited partly with 10 mM phosphate. The production of bioactive substances was inhibited by the phosphate. Ammonium increased the cell growth by 250% at 5 mM addition. The inhibition rate to B16 cells was increased to 89% at the concentration of 40 mM ammonium. The bacteria showed the best growth with 4 mM iron. Iron had little effect on the production at 2 mM, but bigger inhibition effect at higher iron concentration.     

Involvement of prostaglandins in the effect of cupric ions on the human uterus

The effect of cupric ions on the human uterus and the involvement of prostaglandins (PGs) in mediating this effect was studied by recording of isometric contractions of isolated myometrial strips and pieces of uterine arteries, and by intrauterine pressure recordings in women before the onset of menstruation. , CuCl₂ in concentrations of 10⁻⁴ M and higher caused a significant inhibition of myometrial contractile activity, but no effect on the artery preparations was seen. Furthermore, the contractile response of myometrial strips to PGF_2α and PGE₂ (10 ng/ml) decreased in the presence of CuCl₂ in concentrations of 5 and 50 μmol. , instillations of 0.3, 1.0 and 2.0 mM of CuCl₂ in 0.7 ml of saline solution into the uterine cavity caused a dose-dependent stimulation of uterine activity, but after pretreatment with naproxen, 500 mg orally, the effect of these substances was abolished. After naproxen treatment, but during infusion of PGF_2α (5 μg/min), the response to the CuCl₂ solutions was partially restored. It is suggested that cupric ions, at high concentrations, have an inhibiting effect on myometrial activity. The stimulatory effect of low doses of CuCl₂ seen after installation into the uterine cavity is largely exerted via initiation of synthesis and release of endometrial PGs.     

The molecular basis for the inhibition of human cytochrome P450 1A2 by oroxylin and wogonin

In our previous kinetics studies the natural products oroxylin and wogonin were shown to have strong biological affinity for, and inhibitory effects against, human cytochrome P450 1A2, with IC₅₀ values of 579 and 248 nM, respectively; this might lead to the occurrence of drug–drug interactions when co-administered clinically. However, their inhibitory mechanisms against 1A2 remain elusive. In this study, molecular docking and molecular dynamics simulations were performed to better understand the molecular basis of their inhibitory mechanisms towards 1A2. Structural analysis revealed that oroxylin has a different binding pattern from wogonin and another very strongly binding inhibitor α-naphthoflavone (ANF, IC₅₀ = 49 nM). The O₇ atom of oroxylin forms hydrogen bonds with the OD1/OD2 atoms of Asp313, which is not observed in the 1A2–wogonin complex. Because of energetically unfavorable repulsions with the methoxy group at the 6 position of the oroxylin ring, significant conformational changes were observed for the sidechain of Thr118 in the MD simulated model. As a result, the larger and much more open binding-site architecture of the 1A2–oroxylin complex may account for its weaker inhibitory effect relative to the 1A2–ANF complex. Energy analysis indicated that oroxylin has a less negative predicted binding free energy of −19.8 kcal/mol than wogonin (−21.1 kcal/mol), which is consistent with our experimental assays. Additionally, our energy results suggest that van der Waals/hydrophobic and hydrogen-bonding interactions are important in the inhibitory mechanisms of oroxylin whereas the former is the underlying force responsible for strong inhibition by ANF and wogonin.     

The GABAA Receptor Complex as a Target for Fluoxetine Action

The clinically important antidepressant fluoxetine is established as a selective serotonin reuptake inhibitor. This study demonstrates that fluoxetine also interacts with the GABA_A receptor complex. At concentrations above 10 M fluoxetine inhibited the binding of both [³H]GABA (IC₅₀ = 2 mM) and [³H]flunitrazepam (IC₅₀ = 132 M ) to the GABA_A receptor complex in brain cortical membranes. Low fluoxetine concentrations (1 nM) enhanced GABA-stimulated Cl^– uptake by a rat cerebral cortical vesicular preparation. At higher concentrations (100 M and 1 mM), however, fluoxetine inhibited GABA-stimulated Cl^– uptake, an effect related to a reduction in E_max. These observations might assist in an explanation of the basis of the antidepressant action of fluoxetine.     

Effect of using calcium-free Krebs' solution on basal and A23187-stimulated prostaglandin output from the day 15 guinea-pig uterus superfused in vitro

The basal outputs of prostaglandin (PG) F_2α and PGE₂ from the Day 15 guinea-pig uterus superfused in vitro were unaffected by omitting Ca²⁺ from the Krebs' solution. In contrast, this omission of Ca²⁺ reduced the basal output of 6-oxo-PGF_1α (which reflects PGI₂ production) from the uterus by an average of 50%. Spontaneous and A23187-stimulated contractions of, and the stimulation by A23187 of PGF_2α, PGE₂ and 6-oxoPGF_1α outputs from the Day 15 guinea-pig uterus were all abolished by superfusing the tissue with Krebs' solution lacking Ca²⁺. It is concluded that the basal output of 6-oxo-PGF_1α, the occurrence of spontaneous contractions, and the effects of A23187 on PG output and contractility of the Day 15 guinea-pig uterus are dependent on extracellular Ca²⁺. However, the increase in PGF_2α output from the guinea-pig uterus on Day 15 compared to days much earlier in the cycle is apparently not dependent upon extracellular Cat+. The implications of these findings regarding the biochemical mechanisms involved in the increased synthesis of PGF_2α (the uterine luteolytic hormone) by the guinea-pig endometrium during the last one-third of the cycle are discussed.