Synthesis and SAR of Benzisothiazole- and Indolizine-β-d-glucopyranoside Inhibitors of SGLT2

d-glucopyranoside inhibitors of human SGLT2 are described. The synthesis of the C-linked heterocyclic glucosides took advantage of a palladium-catalyzed cross-coupling reaction between a glucal boronate and the corresponding bromo heterocycle. The compounds have been evaluated for their human SGLT2 inhibition potential using cell-based functional transporter assays, and their structure−activity relationships have been described. Benzisothiazole-C-glucoside 16d was found to be an inhibitor of SGLT2 with an IC₅₀ of 10 nM.     

The effects of PGE2 and PGF2α on rhythmic contractions of sphincter of Oddi

• 1.1. Spontaneous rhythmic activity observed in some of the guinea-pig sphincter of Oddi preparations was completely abolished by PGE₂ (10⁻⁸ M) but not altered by PGF_2α (10⁻⁶ M).
• 2.2. Indomethacin (10⁻⁵ M), a cyclooxygenase inhibitor, elicited long-lasting rhythmic contractions in 50% of the preparations tested, which did not show any spontaneous activity. PGE₂ (10⁻⁸ M) completely inhibited, however PGF_2α (10⁻⁸-10⁻⁶ M) did not change the rhythmic contractions induced by indomethacin.
• 3.3. Both initial phasic contraction and the frequency and amplitude of peristaltic waves induced by ACh (10⁻³ M) were increased by indomethacin (10⁻⁵ M), decreased by PGE₂ (10⁻⁷ M) and not altered by PGF_2α (10⁻⁷ M).

     

Cellular pharmacology of multi- and duplex drugsconsisting of ethynylcytidine and 5-fluoro-2′-deoxyuridine

Prodrugs can have the advantage over parent drugs in increased activation and cellular uptake. The multidrug ETC-L-FdUrd and the duplex drug ETC-FdUrd are composed of two different monophosphate-nucleosides, 5-fluoro-2′deoxyuridine (FdUrd) and ethynylcytidine (ETC), coupled via a glycerolipid or phosphodiester, respectively. The aim of the study was to determine cytotoxicity levels and mode of drug cleavage. Moreover, we determined whether a liposomal formulation of ETC-L-FdUrd would improve cytotoxic activity and/or cleavage. Drug effects/cleavage were studied with standard radioactivity assays, HPLC and LC-MS/MS in FM3A/0 mammary cancer cells and their FdUrd resistant variants FM3A/TK⁻. ETC-FdUrd was active (IC₅₀ of 2.2 and 79 nM) in FM3A/0 and TK⁻ cells, respectively. ETC-L-FdUrd was less active (IC₅₀: 7 nM in FM3A/0 vs 4500 nM in FM3A/TK⁻). Although the liposomal formulation was less active than ETC-L-FdUrd in FM3A/0 cells (IC₅₀:19.3 nM), resistance due to thymidine kinase (TK) deficiency was greatly reduced. The prodrugs inhibited thymidylate synthase (TS) in FM3A/0 cells (80–90%), but to a lower extent in FM3A/TK⁻ (10–50%). FdUMP was hardly detected in FM3A/TK⁻ cells. Inhibition of the transporters and nucleotidases/phosphatases resulted in a reduction of cytotoxicity of ETC-FdUrd, indicating that this drug was cleaved outside the cells to the monophosphates, which was verified by the presence of FdUrd and ETC in the medium. ETC-L-FdUrd and the liposomal formulation were neither affected by transporter nor nucleotidase/phosphatase inhibition, indicating circumvention of active transporters. In vivo, ETC-FdUrd and ETC-L-FdURd were orally active. ETC nucleotides accumulated in both tumor and liver tissues. These formulations seem to be effective when a lipophilic linker is used combined with a liposomal formulation.     

Effect of catecholamic acid on detoxication and distribution of NiCl_2 in mice and rats

目的：研究双酚胺酸（ＣＢＭＩＤＡ）对氯化镍的解毒作用．方法：ＮｉＣｌ２中毒后，立即给予ＣＢＭＩＤＡ，记录动物存活数；小鼠ｉｖ６３ＮｉＣｌ２后给药，测定２４ｈ组织中６３镍；用整体放射自显影术，显示小鼠体内６３镍分布．结果：ｓｃＣＢＭＩＤＡ０５－１５ｇ·ｋｇ－１对ｉｐＮｉＣｌ２５００ｍｇ·ｋｇ－１有解毒作用；小鼠ｉｐＮｉＣｌ２ＬＤ５０为８２８ｍｇ·ｋｇ－１，给药１５或２５ｇ·ｋｇ－１，ＬＤ５０分别为７８９和８２０ｍｇ·ｋｇ－１；大鼠ｉｍＣＢＭＩＤＡ５００ｍｇ·ｋｇ－１使ＮｉＣｌ２的ＬＤ５０提高８倍；组织中６３镍测定和定位显示，ＣＢＭＩＤＡ减少肺和血液中６３镍，增加了骨中６３镍，２４ｈ尿、粪６３镍排出与对照组无明显差异．结论：ＣＢＭＩＤＡ有效地解除镍毒性，提高动物存活率，降低镍在肺部的滞留．     

β1 and β2 Stimulatory effects of prenalterol

Summary Prenalterol, previously characterized as a functionally cardioselective partial -adrenoceptor agonist, was shown to relax K⁺-elicited contractures in the uterine muscle from progesterone pretreated rats (pD ₂ 7.7) and to increase beating rate in the rat right atrium (pD ₂ 8.0) at about the same concentrations with maximal effects corresponding to 94 and 82% respectively of those of isoproterenol. Terbutaline, with equal maximal effects as isoproterenol, was 50 times more potent in the uterus (pD ₂ 7.8) than in the right atrium (pD ₂ 6.1). Both tissues displayed a high sensitivity to isoproterenol (pD ₂ 9.1 in both tisues) indicating large receptor reserves for the full agonist.The maximal relaxing effect of prenalterol in the uterus was obtained at about a three-fold increase of the cyclic AMP content, which is similar to that obtained with isoproterenol at a corresponding relaxation.The effects in the uterine muscle of all three agonists were mediated through ₂-adrenoceptors since ₂-adrenoceptor blockers (ICI 118,551 and IPS 339) antagonized the effects in concentrations which had only marginal effects on the atrial responses of the agonists. The ₁-antagonists pafenolol and pamatolol in concentrations higher than those, which blocked the effects of the agonists on beating rate, were devoid of inhibitory effects in the uterus.These results indicate that prenalterol possesses the ability to elicit a functional response by stimulation of either ₁- or adrenoceptors provided that the tissue has a large spare receptor reserve for full agonists.     

Effects of β2-agonist- and dexamethasone-treatment on relaxation and regulation of β-adrenoceptors in human bronchi and lung tissue

1. Long-term treatment with β₂-adrenoceptor agonists can lead to a decreased therapeutic efficacy of bronchodilatation in patients with obstructive pulmonary disease. In order to examine whether or not this is due to β-adrenoceptor desensitization, human bronchial muscle relaxation was studied in isolated bronchial rings after pretreatment with β₂-adrenoceptor agonists. Additionally, the influence of pretreatment with dexamethasone on desensitization was studied.
2. The effect of β₂-agonist incubation alone and after coincubation with dexamethasone on density and affinity of β-adrenoceptors was investigated by radioligand binding experiments.
3. In human isolated bronchi, isoprenaline induces a time- and concentration-dependent β-adrenoceptor desensitization as judged from maximal reduction in potency by a factor of 7 and reduction of 73±4% in efficacy of isoprenaline to relax human bronchial smooth muscle.
4. After an incubation period of 60 min with 100 μmol l⁻¹ terbutaline, a significant decline in its relaxing efficacy (81±8%) and potency (by a factor 5.5) occurred.
5. Incubation with 30 μmol l⁻¹ isoprenaline for 60 min did not impair the maximal effect of a subsequent aminophylline response but led to an increase in potency (factor 4.4).
6. Coincubation of dexamethasone with isoprenaline (120 min; 30 μmol l⁻¹) preserved the effect of isoprenaline on relaxation (129±15%).
7. In radioligand binding experiments, pretreatment of lung tissue for 60 min with isoprenaline (30 μmol l⁻¹) resulted in a decrease in β-adrenoceptor binding sites (B_max) to 64±1.6% (P<0.05), while the antagonist affinity (K_D) for [³H]-CGP-12177 remained unchanged.
8. In contrast, radioligand binding studies on lung tissue pretreated with either dexamethasone (30 μmol l⁻¹) or isoprenaline (30 μmol l⁻¹) plus dexamethasone (30 μmol l⁻¹) for 120 min did not lead to a significant change of B_max (160±22.1% vs 142.3±28.7%) or K_D (5.0 nmol l⁻¹ vs 3.5 nmol l⁻¹) compared to the controls.
9. In conclusion, pretreatment of human bronchi with β-adrenoceptor agonists leads to functional desensitization and, in lung tissue, to down-regulation of β-adrenoceptors. This effect can be counteracted by additional administration of dexamethasone. Our model of desensitization has proved useful for the identification of mechanisms of β-adrenoceptor desensitization and could be relevant for the evaluation of therapeutic strategies to counteract undesirable effects of long-term β-adrenoceptor stimulation.

     

Pharmacokinetics of flutamide and its metabolite 2-hydroxyflutamidein normal and hepatic injury rats

目的：建立一新的高压液相色谱法用来研究氟他胺（Ｆｌｕ）及其活性代谢产物２羟基氟他胺（ＨＦ）的药物动力学．方法：正常及肝损伤大鼠灌胃Ｆｌｕ５０ｍｇ·ｋｇ－１．采用反相高压液相色谱法，以甲基睾丸素为内标，流动相为甲醇∶乙腈∶水∶乙醚＝４０∶２０∶３５∶１（体积比），检测波长为２３４ｎｍ．结果：Ｆｌｕ的Ｋ与Ｃｌ分别由０６２±０１６ｈ－１及６０±１０Ｌ·ｋｇ－１·ｈ－１减小到０１６±００３ｈ－１及０６３±０２９Ｌ·ｋｇ－１·ｈ－１（Ｐ＜００１），ＡＵＣ与Ｃｍａｘ分别由８６±１３ｍｇ·Ｌ－１·ｈ及２４±０７ｍｇ·Ｌ－１增加到１００±４４ｍｇ·ｋｇ－１·ｈ及６７±２８ｍｇ·Ｌ－１（Ｐ＜００１）．ＨＦ的Ｋ（ｍ）由００７±００１ｈ－１减小到００５±００１ｈ－１（Ｐ＜００１）．结论：在肝损伤大鼠，Ｆｌｕ与ＨＦ消除受到显著抑制．     

Effects of Sr2+ and Mg2+ on the phospholipase A and the presynaptic neuromuscular blocking actions of β-bungarotoxin,crotoxin and taipoxin

1.beta-Bungarotoxin, crotoxin and taipoxin, presynaptic neurotoxins of snake venom origin, have about the same phospholipid-splitting activities as a much less toxic cobra phospholipase A2 in the presence of Ca2+ and deoxycholate. 2. Sr2+ was a much less effective activator of the enzymes than is Ca2+, the activation by Sr2+ being only 3-6% for beta-bungarotoxin and crotoxin and 12% for taipoxin. 3. Sr2+ also inhibited the Ca2+ -activated enzymes by 80% in the cases of beta-bungarotoxin and crotoxin, but only 16% in the case of taipoxin. 4. Mg2" had no significant effect on beta-bungarotoxin or crotoxin, but activated taipoxin in the presence or absence of Ca2". 5. In Sr2+ -Tyrode lacking Ca2+ all three toxins exhibited the same immediate depression followed by facilitation in the rat and mouse diaphragms, but the final blocking activity was only 3-10% with beta-bungarotoxin and crotoxin and was 30% with taipoxin. 6. In Sr2+ -Tyrode, increasing in the rate of nerve stimulation had less accelerating effect on the development of neuromuscular block than in Ca2+ -Tyrode for any of the toxins. 7. Removal of Mg2+ from Sr2+ -Tyrode did not diminish the potency of taipoxin in blocking neuromuscular transmission, suggesting that enzyme activity at the outer surface of the axolemma does not contribute to the neuromuscular blocking action. 8. All of the results indicate that there are close correlations between the presynaptic activities of these toxins and their phospholipid-splitting activities in the cationic environment prevailing in the axoplasm. Apparently the final blocking effect of these toxins is due to phospholipase A action within the nerve terminal.     

Glucuronidation and Methylation of Procyanidin Dimers B2 and 3,3″-Di-O-Galloyl-B2 and Corresponding Monomers Epicatechin and 3-O-Galloyl-Epicatechin in Mouse Liver

Purpose  

The 3,3″-di-O-galloyl ester of procyanidin B2 (B2G2) is a component of grape seed extract that inhibits growth of human prostate carcinoma cell lines. In preparation for studies in mice, its hepatic metabolism was examined in vitro and compared to B2 and the corresponding monomers, epicatechin (EC) and 3-O-galloyl-epicatechin (ECG).     

Synthesis and pharmacological activity of derivatives of 3-aminomethylene-1-(2′,6′-dichlorophenyl)oxindole and 2-aminomethyleneindoxyl

Derivatives of 3-aminomethylene-1-(2,6-dichloro)phenyloxindole and 2-aminomethyleneindoxyl were synthesized. The¹H and¹³C NMR spectra and pharmacology of the compounds were studied.     

Isolation and Characterization of a Monomethioninesulfoxide Variant of Interferon α-2b

Purpose. To isolate and characterize a monomethioninesulfoxide variant of the commercially available therapeutic protein interferon -2b. Methods. The methionine (Met)-oxidized variant was isolated by reverse-phase high performance liquid chromatography and characterized by SDS-PAGE, peptide mapping and mass spectrometric analysis of the trypsin/V8-generated peptide fragments. The biological and immunological activities of the isolated variant were also evaluated. Results. The rHuIFN -2b variant was found to contain a Met sulfoxide residue at position 111 of the rHuIFN -2b molecule. The far-UV CD spectra showed a slight loss of -helical content and an increase in the -sheet contribution. The CD spectra indicate that both chromatographic conditions and Met oxidation contribute to the observed secondary structure changes. Both interferon -2b main component and its methionine-oxidized variant showed different reactivity to monoclonal antibodies employed in immunoassays for the protein. Conclusions. A monomethioninesulfoxide rHuIFN -2b variant was found to be present in the rHuIFN -2b bulk drug substance in solution. The Met¹¹¹ residue was identified as Met sulfoxide by comparative tryptic/V8 mapping and mass spectrometric analysis. Nevertheless, the oxidation of the Met¹¹¹ residue did not seem to have a detectable effect on the biological activity of the molecule.     

Effects of intracerebroventricular administration of prostaglandin D2 on behaviour,blood pressure and body temperature as compared to prostaglandins E2 and F2α

The present work examined some central nervous actions of prostaglandin D₂ (PGD₂), which is the most prevalent prostaglandin in rodentorain. The effects of PGD₂ were compared with those of PGE₂ and PGF₂. The prostaglandins were administered intracerebroventricularly (ICV) to conscious rats using the method of Herman (1970). All three prostaglandins studied produced depressive behavioral effects, causing obvious sedation at doses of 2.0 g and 20.0 g ICV. PGD₂ and PGE₂ significantly reduced spontaneous motor activity at doses of 2.0 g and 20.0 g ICV. PGF₂ was less effective; only 20.0 g significantly inhibited motor activity. At a dose of 20.0 g ICV all three compounds were shown to block convulsions induced by pentylenetetrazol. PGD₂, the most effective prostaglandin in this respect, was still slightly anticonvulsive at a dose of 2.0 g ICV. PGF₂ hat the weakest anticonvulsive potency. PGE₂ and PGF₂ (2.0 g and 20.0 g ICV) caused a marked hypertensive effect, whereas PGD₂ at the same dose levels only produced a small increase in blood pressure. PGE₂ and PGF₂ (2.0 g and 20.0 g) also exerted marked pyrogenic actions. The effects of PGD₂ on body temperature were variable. When given at a dose of 20.0 g ICV, it caused slight hyperthermia whereas a lower dose (2.0 g ICV) induced a moderate fall in body temperature. These findings suggest a relationship between the actions of the different prostaglandins on blood pressure and body temperature.A preliminary report was given at the Spring Meeting of the Deutsche Pharmakologische Gesellschaft, March 1983 (Förstermann and Heldt, 1983)     

The effects of chronic dosing on the β1 and β2-adrenoceptor antagonism of betaxolol and atenolol

Summary Six normal subjects were given once daily treatment for 15 days with placebo (PL), betaxolol 10 mg (B10), 40 mg (B40); atenolol 100 mg (A100); and nadolol 40 mg (N40). Measurements of ₁-adrenoceptorblockade (reduction of exercise heart rate) and of ₂-adrenoceptor-blockade (attenuation of isoprenaline induced finger tremor) were made after the first, eighth and fifteenth doses of each drug.Plasma concentrations showed dose related increases between 10 mg and 40 mg doses of betaxolol, and there was significant drug accumulation at steady state compared with after single dosing. The reduction in exercise heart rate (EHR) with B10 was less in comparison with all other treatments.There were no significant differences in effects between single and chronic-dosing for any of the treatments (% reduction EHR compared with placebo, on days 1 and 15): B10 (18.2, 19.0), B40 (28.6, 26.5); A100 (22.7, 23.1); N40 (26.6, 23.8). Dose-ratios for attenuation of isoprenaline-induced finger tremor (IT₁₀₀) were significantly greater with B40 compared with B10 or A100 (no dose-ratio for finger tremor could be calculated for N40).There were no differences between single and chronic-dosing (IT₁₀₀ dose-ratios on days 1 and 15): B10 (3.0, 2.5), B40 (4.4, 5.3); A100 (3.0, 3.0). The attenuation of isoprenaline-induced chronotropic response (IH₂₅) by N40 was significantly greater in comparison with all other treatments. IH₂₅ dose-ratios (on days 1 and 15) were as follows: B10 (2.8, 3.6), B40 (5.1, 5.8); A100 (3.6, 3.6); N40 (19.0, 17.4).Thus, despite drug accumulation after chronic-dosing, there was no evidence of any increase in either ₁ or ₂-adrenoceptor antagonism at steady-state in comparison with after single-dosing. The apparent dissociation between plasma concentration and -adrenoceptor antagonism after chronic-dosing my be a consequence of -adrenoceptor up-regulation, resulting in partial attenuation of -blockade.     

Binding sites of α1- and α2-adrenoreceptors

Conclusions The models constructed for the binding sites of rat brain ₁-AR and ₂-AR satisfy all the steric requirements and energy characteristics of interaction with known ligands, cited in [5–7, 14]. The differences detected in the arrangement and orientation of the functional groups of the binding sites permit an explanation of a whole series of typical differences in the interaction of adrenoactive substances with both subtypes of-AR.Our analysis showed that the greatest contribution to the interaction with the receptor is made by ionic, donor-acceptor, and hydrophobic bonds. The role of van der Waals forces in the interactions examined is evidently extremely negligible. The most effective and specific preparations prove to be compounds that not only form the maximum number of donor-acceptor bonds with the receptor but also orient their own hydrophobic fragments in such a way that the ionic and donor-acceptor bonds formed between the molecule and the receptor are shielded from contact with the aqueous phase. The energy effects of hydrophobic interactions of this type may be rather substantial (3.9–3.12).The production of new synthetic preparations, for which the conditions of complementarity to the-AR will be most fully satisfied, can be carried out taking the requirements of structural correspondence of the topography of the binding sites into account.Translated from Khimiko-farmatsevticheskii Zhurnal, Vol. 18, No. 8, pp. 904–912, August, 1984.     

Anti-tumor efficacy and pre-clinical immunogenicity of IFNα2a-NGR

Previously studies have shown that tumor-homing peptide NGR enhances the therapeutic efficacy of human interferon α2a (IFNα2a) against tumors. Here we investigated in vivo anti-tumor effect of recombinant human IFNα2a-NGR (rhIFNα2a-NGR) against human lung adenocarcinoma cell line SPC-A-1, A549 and murine Lewis lung carcinoma (LLC) subcutaneously xenografted tumors and further assessed the immunogenicity of rhIFNα2a-NGR in Sprague Dawley (SD) rats and rhesus monkeys. We found that rhIFNα2a-NGR significantly inhibited the growth of SPC-A-1, A549 and LLC cells-xenografted tumors in a dose-dependent manner. Although the antibodies to rhIFNα were detected in the serum of SD rats and rhesus monkeys treated with rhIFNα2a-NGR, these antibodies did not cause obvious pathological consequence. Taken together, these data demonstrate that rhIFNα2a-NGR has obvious anti-tumor efficacy in vivo, perhaps due to the tumor-homing peptide NGR. Thus rhIFNα2a-NGR represents a promising novel drug for effective treatment of cancer.     

Involvement of α2- and β2-adrenoceptors on breast cancer cell proliferation and tumour growth regulation

BACKGROUND AND PURPOSE

β-Adrenoceptors are expressed in human and experimental animal breast cancer cells. However, the effect of the agonists and antagonists reported on cell proliferation and tumour growth was paradoxical, precluding their utilization as possible adjuvant therapy, mainly in the cases of refractory tumours.

EXPERIMENTAL APPROACH

β-Adrenoceptor expression was analysed by immunofluorescence and RT-PCR. Cell proliferation was assessed by [³H]-thymidine incorporation, tumour growth by measuring with a calliper and ERK 1/2 phosphorylation by Western blotting.

KEY RESULTS

β₂-Adrenoceptor expression was confirmed in the mouse and human cells tested. Cell proliferation was increased by adrenaline (by α₂-adrenoceptor action) and decreased in every tested cell line by the β-adrenoceptor agonist isoprenaline and the β₂-adrenoceptor agonist salbutamol. Isoprenaline and salbutamol reduced tumour growth in every tumour tested (mouse C4-HD and CC4-3-HI and human IBH-4, IBH-6 and MDA-MB-231 cell lines growing as xenografts in nude mice). These effects were reversed by the β-adrenoceptor antagonist propranolol. The α₂-adrenoceptor antagonist rauwolscine and the β₂-adrenoceptor agonist salbutamol were equally effective in diminishing tumour growth. ERK 1/2 activation analysed in IBH-4 tumours correlated with tumour growth, with the β-adrenoceptor agonists decreasing its activation. Inhibition of ERK 1/2 phosphorylation in vitro was mainly mediated by the PKA pathway.

CONCLUSIONS AND IMPLICATIONS

In our experimental models, the β-adrenoceptor agonists inhibited breast cancer cell proliferation and tumour growth, probably mediated by inhibition of ERK 1/2 phosphorylation. The β-adrenoceptor agonists were as effective as the α₂-adrenoceptor antagonist rauwolscine, providing possible novel adjuvant treatments for breast cancer.     

Solubility and stability of melatonin in propylene glycol and 2-hydroxypropyl-β-cyclodextrin vehicles

The physicochemical properties of melatonin (MT) in propylene glycol (PG) and 2-hydroxypropyl-beta-cyclodextrin (2-HPbetaCD) vehicles were characterized. MT was endothermally decomposed as determined by differential scanning calorimetry (DSC). Melting point and heat of fusion obtained were 116.9+/-0.24 degrees C and 7249+/-217 cal/mol, respectively. MT as received from a manufacture was very pure, at least 99.9%. The solubility of MT in PG solution increased slowly until reaching 40% PG and then steeply increased. Solubility of MT increased linearly as concentration of 2-HPbetaCD without PG increased (R(2)=0.993). MT solubility in the mixtures of PG and 2-HPbetaCD also increased linearly but was less than the sum of its solubility in 2-HPbetaCD and PG individually. The MT solubility was low in water, simulated gastric or intestinal fluid but the highest in the mixture of PG (40 v/v%) and 2-HPbetaCD (30 w/v%) although efficiency of MT solubilization in 2-HPbetaCD decreased as the concentration of PG increased. MT was degraded in a fashion of the first order kinetics (r(2)>0.90). MT was unstable in strong acidic solution (HCl-NaCl buffer, pH 1.4) but relatively stable in other pH values of 4 approximately 10 at 70 degrees C. In HCl-NaCl buffer, MT in 10% PG was more quickly degraded and then slowed down at a higher concentration. However, the degradation rate constant of MT in 2-HPbetaCD was not changed significantly when compared to the water. The current studies can be applied to the dosage formulations for the purpose of enhancing percutaneous absorption or bioavailability of MT.     

Dalargin and [Cys-(O2NH2)]2 analogues of enkephalins and their selectivity for μ opioid receptors

• 1.1. Effects of the enkephalins Met-enk (M) and Leu-enk (L), of two newly synthesized analogues—[Cys-(O₂NH₂)]²-Met-enk (CM) and [Cys-(O₂ NH₂)]²-Leu-enk (CL)-and of a hexapeptide—d-Ala²-Leu⁵-Arg⁶ (Dalargin; DL) on the spontaneous and electrically stimulated activity were examined with respect to their selectivity for the μ opioid receptors in the longitudinal layer of guinea pig ileum.
• 2.2. M and CM exerted relaxing and contractile effects on the spontaneous contractile activity while L, CL and DL produced only relaxation. The order of potency towards the relaxatory phase was DL > M > CM > L > CL and towards the contractile phase CM > M.
• 3.3. The effects of enkephalins on the spontaneous activity were naloxone and TTX sensitive except for the contractile phase of M and CM which persisted in the presence of TTX. NO was not involved in the neurotransmission of the relaxatory responses, while the blockade of α and β adrenoceptors showed the participation of adrenergic mechanisms. Relaxation and contraction induced by enkephalins could not be directly attributed to cholinergic neurotransmission.
• 4.4. The naloxone-sensitive and concentration-dependent inhibitory effects of enkephalins and their analogues on the electrically stimulated cholinergic contractions were established. The order of the relative potency of opioids was: DL—3.8; M—1.0; L-0.4; CM-0.01; CL—0.005.
• 5.5. These data indicated that the D-Ala² substitution and lengthening of the peptide chain by Arg⁶ in the molecule of L increased the potency at the μ opiate receptors, while the substitution in position 2 with Cys-(O₂NH₂) in the molecule of M and L yielded a less potent and selective μ agonists.