Uterotonic Activity Research Articles

Differences in the behavioral effects of oxytocin and carbetocin after their peripheral application to Wistar rats

Event Abstract Back to Event Differences in the behavioral effects of oxytocin and carbetocin after their peripheral application to Wistar rats Vera Klenerova1* and Sixtus Hynie1 1 Charles University , Laboratory of Neuropharmacology, Department of Medical Biochemistry, 1st Faculty of Medicine, Czechia Oxytocin (OXY) is a neurohypophyseal nonapeptide, which has primarily the peripheral effects during parturation and lactation. In the brain OXY acts as a neurotransmitter or neuromodulator and plays, a prominent role in several central functions, like behavior, memory, learning, grooming etc. A number of OXY analogs have been designed as therapeutic substitutes with changed uterotonic activities. Carbetocin (CBT; deamino-1-monocarba-[2-O-methyltyrosine]-oxytocin) was prepared as a long-acting OXY analog to control postpartum bleeding. Peripheral administration of OXY is known to produce behavioral effects; however, there are very limited experimental data on the central effects of CBT. The aim of this study was to compare the length of behavioral effects of OXY and CBT. Male Wistar rats were used. Spontaneous behavior was tested in circular open-field arena with 150 cm diameter. Behavioral parameters were recorded by AnyMaze software (Stoelting Co, USA). OXY and CBT (Polypeptides GmbH, Czech Republic) were given i.p. 60 min before behavioral test and repeatedly tested in several following days. While OXY produced reduction of exploratory activity and increased grooming time, CBT had slight increasing effect on the exploratory activity and revealed no effect on grooming. The exploratory effect of CBT survives for several days while the effect of OXY was not long lasting. Our results support the possibility of using CBT in various psychic disorders like autism etc. Acknowledgements: Supported by MSM 0021620806. Keywords: Behavior, carbetocin, exploration, Grooming, Oxytocin Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Poster Presentation Topic: Cognition Citation: Klenerova V and Hynie S (2009). Differences in the behavioral effects of oxytocin and carbetocin after their peripheral application to Wistar rats. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.140 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Nov 2009; Published Online: 25 Nov 2009. * Correspondence: Vera Klenerova, Charles University, Laboratory of Neuropharmacology, Department of Medical Biochemistry, 1st Faculty of Medicine, Prague, Czechia, vera.klenerova@lf1.cuni.cz Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Vera Klenerova Sixtus Hynie Google Vera Klenerova Sixtus Hynie Google Scholar Vera Klenerova Sixtus Hynie PubMed Vera Klenerova Sixtus Hynie Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Arginine vasopressin and its analogues – The influence of position 2 modification with 3,3-diphenylalanine enantiomers. Highly potent V 2 agonists

Eleven new analogues of arginine vasopressin (AVP) modified in position 2 by 3,3-diphenyl- l-alanine or its d-enantiomer (Dip or d-Dip) were synthesized and pharmacologically evaluated for their pressor, antidiuretic and in vitro uterotonic activities. Both the Dip and d-Dip modifications at position 2 of AVP are sufficient to completely change the pharmacological profile of the peptides. They preserve or increase antidiuretic activity, cause its prolongation, transform uterotonic property in antagonistic one and cancel the effect on blood pressure. Four of the new peptides ([Mpa 1, d-Dip 2]AVP, [Mpa 1, d-Dip 2,Val 4]AVP, [Mpa 1, d-Dip 2, d-Arg 8]VP, [Mpa 1, d-Dip 2,Val 4, d-Arg 8]VP) are exceptionally potent antidiuretic agents with significantly prolonged activities.

Possible mechanism of the uterotonic activity of the ethanolic leaf extract of Newbouldia leavis (Bignoniaceae) I

The aqueous and ethanolic leaf extract of Newbouldia laevis has been shown in a previous study to stimulate and increase contractions in isolated uterine preparations of non – pregnant rats. This study was therefore carried out in sequel to identify the possible mechanism(s) by which the ethanolic leaf extract causes uterine contraction in vitro.

Stimulatory effects of a microbially dechlorinated polychlorinated biphenyl (PCB) mixture on rat uterine contraction in vitro

Microbially mediated reductive dechlorination has been advocated as the first part of a two-stage (anaerobic/aerobic) biotreatment process for polychlorinated biphenyls (PCBs) in sediments, and is generally viewed as a detoxication process. However, previous studies suggest that microbial dechlorination increases the ability to stimulate uterine contractions compared with the original PCB mixtures. Here, we investigate the composition and uterotonic activity of the commercial PCB mixture Aroclor 1260 before and after incubation with microorganisms eluted from PCB-contaminated sediment of the Hudson River. Incubation with microorganisms resulted in a partially dechlorinated mixture (HR1260) dominated by ortho-substituted PCBs with four or fewer chlorines per biphenyl. Aroclor 1260 that had not been incubated with microorganisms had no significant effect on contraction frequency of rat uterine strips (gestation day 10) in vitro, whereas HR1260 dramatically increased contraction frequency to 718±134% of the basal rate at a total PCB concentration of 70 μM ( p<0.05). The microbial dechlorination increased 2,2′,4,4′-tetrachlorobiphenyl and one or more of four congeners that co-eluted during chromatography (2,3,3′,5-tetrachlorobiphenyl, 2,3′,4,5-tetrachlorobiphenyl, 2,2′,4,4′,6-pentachlorobiphenyl and 2,2′,4,5′,6-pentachlorobiphenyl) to 24 and 8 mol%, respectively. However, the uterotonic activities of the latter congeners were modest when evaluated either solely or in a reconstituted mixture and could not fully account for the uterotonic activity of HR1260. Nonetheless, the relative abundance of congeners with three or fewer chlorines increased to 14 mol% as a group in HR1260, suggesting that these congeners collectively contribute to the uterotonic activity even though the abundance of any one congener in this group was less than 5 mol%.

Potential Biochemical Events Associated with Initiation of Labor

Much of our understanding and knowledge of human parturition has been blurred by conjecture and extrapolation. The limited available data on human parturition reflect the inability to directly experiment with pregnant human subjects. In spite of this obvious impediment and the scarcity of longitudinal data on fundamental physiological changes in human pregnancy, recent reports have generated a better understanding of the synchronous activities leading to labor. The purpose of this review was to organize, in an evidence-based format, the current understanding of maternal physiologic phenomena leading from uterine quiescence to uterine labor activity. Recent discoveries have prompted a revision of pre-existing classical theories on the initiation of parturition, such as the progesterone block theory or the prostaglandins stimulation of the uterotonic action of oxytocin. The presence in the circulation of extrahypothalamic corticotrophin-releasing hormone (CRH) produced by the placenta and myometrium is an inciting unique feature of primate pregnancy and a promising field for research. The concept of anatomical regionalization in labor promotion, including the cervical physiological inflammatory reaction, is also discussed in the review, especially in support of the strong link between inflammatory activation and onset of preterm labor. Understanding the intimate chain of events leading to parturition is critical, and elucidating the interplay of signals and processes that initiate normal labor may help us to understand the abnormal variant, spontaneous preterm labor, and devise efficacious interventions against it.

Plant cyclotides disrupt epithelial cells in the midgut of lepidopteran larvae

Several members of the Rubiaceae and Violaceae plant families produce a series of cyclotides or macrocyclic peptides of 28-37 aa with an embedded cystine knot. The cyclic peptide backbone together with the knotted and strongly braced structure confers exceptional chemical and biological stability that has attracted attention for potential pharmaceutical applications. Cyclotides display a diverse range of biological activities, such as uterotonic action, anti-HIV activity, and neurotensin antagonism. In plants, their primary role is probably protection from insect attack. Ingestion of the cyclotide kalata B1 severely retards the growth of larvae from the Lepidopteran species Helicoverpa armigera. We examined the gut of these larvae after consumption of kalata B1 by light, scanning, and transmission electron microscopy. We established that kalata B1 induces disruption of the microvilli, blebbing, swelling, and ultimately rupture of the cells of the gut epithelium. The histology of this response is similar to the response of H. armigera larvae to the Bacillus thuringiensis delta-endotoxin, which is widely used to control these insect pests of crops such as cotton.

Oxytocin analogues with amide groups substituted by tetrazole groups in position 4, 5 or 9.

Eleven oxytocin analogues substituted in position 4, 5 or 9 by tetrazole analogues of amino acids were prepared using solid-phase peptide synthesis method and tested for rat uterotonic in vitro and pressor activities, as well as for their affinity to human oxytocin receptor. The tetrazolic group has been used as a bioisosteric substitution of carboxylic, ester or amide groups in structure-activity relationship studies of biologically active compounds. Replacement of the amide groups of Gln(4) and Asn(5) in oxytocin by tetrazole analogues of aspartic, glutamic and alpha-aminoadipic acids containing the tetrazole moiety in the side chains leads to analogues with decreased biological activities. Oxytocin analogues in which the glycine amide residue in position 9 was substituted by tetrazole analogues of glycine had diminished activities as well. The analysis of differences in rat uterotonic activity and in the affinity to human oxytocin receptors of analogues containing either an acidic 5-substituted tetrazolic group or a neutral 1,5- or 2,5-tetrazole nucleus makes it possible to draw some new conclusions concerning the role of the amide group of amino acids in positions 4, 5 and 9 of oxytocin for its activity. The data suggest that the interaction of the side chain of Gln(4) with the oxytocin receptor is influenced mainly by electronic effects and the hydrogen bonding capacity of the amide group. Steric effects of the side chain are minor. Substitution of Asn(5) by its tetrazole derivative gave an analogue of very low activity. The result suggests that in the interaction between the amide group of Asn(5) and the binding sites of oxytocic receptor hydrogen bonds are of less importance than the spatial requirements for this group.

Misoprostol Versus Oxytocin for the Reduction of Postpartum Blood Loss

A large majority of maternal deaths from postpartum hemorrhage take place in countries with limited resources. Because uterine atony is the usual cause, standard treatment has been to administer oxytocin intravenously in the third stage of labor. Misoprostol, a synthetic analog of prostaglandin El, also has uterotonic activity and, in addition, is inexpensive and thermogenically stable, and may be administered orally, sublingually, vaginally, or rectally. This prospective, randomized, double-blind trial compared the effects of 5 U of oxytocin, given intravenously, with those of 400 μg of orally administered misoprostol in 622 women with a single fetus in cephalic presentation who were in spontaneous or induced labor before planned vaginal delivery. The study drugs were given after delivery of the anterior shoulder or within a minute of delivery. The primary outcome was a decrease in hematocrit of at least 10% when estimated 24 hours after delivery. Secondary outcomes included a drop in hemoglobin of 30 mg/L or more, an estimated blood loss exceeding 1000 mL, blood transfusion, use of additional oxytocic drugs, manual removal of the placenta, and shivering/fever. The 2 treatment groups did not differ significantly with respect to the primary outcome; the hematocrit fell by 10% or more in 3.4% of oxytocin-treated women and 3.7% of the misoprostol group. There also were no significant differences in secondary outcomes except for the more frequent use of additional oxytocin in the misoprostol group (51% versus 41%). The major indication was uterine atony, with or without bleeding. No patient in either group required blood transfusion, underwent hysterectomy, or died. Shivering occurred in 7% of the misoprostol group, but was self-limited and caused no distress. Fever also was more prevalent in misoprostol-treated women, but was not clinically significant. The investigators believe that injectable oxytocic treatment is preferable to misoprostol for preventing postpartum hemorrhage, but that low-dose oral misoprostol therapy could be a practical option in settings where resources are limited.

Efficient preparation of an acyclic permutant of kalata B1 from a recombinant fusion protein with thioredoxin

A new approach to prepare an acyclic permutant of kalata B1, a cysteine-rich plant cyclopeptide with uterotonic activity, is described. The synthetic codon-optimized cDNA sequence encoding this 29-residue peptide was cloned and fused in-frame to the His(6)-tagged thioredoxin gene in the bacterial expression vector pET-32a. The fusion protein was overexpressed in the bacterial host, Escherichia coli strain BL21 (DE3), and isolated by affinity chromatography on a metal-chelating Sepharose column. An enterokinase recognition sequence incorporated immediately upstream of the target peptide allowed the 29-residue peptide to be released without any unwanted residues upon treatment with enterokinase. This peptide was subsequently separated from the larger thioredoxin moiety by ultracentrifugation through a semipermeable membrane. Further purification was achieved using reversed-phase HPLC. Hydrogen peroxide was found to enhance the rate of enterokinase cleavage in a concentration-dependent manner. Thermal stability studies demonstrated that the recombinant acyclic kalata B1 (ac kalata) was exceptionally stable against thermal denaturation. Mass spectrometric analysis revealed that the recombinant ac kalata was obtained in a fully oxidized form, indicating a high reducing potential and a strong tendency of the 29-residue peptide to form a tightly folded structure.

Synthesis and biological activity of oxytocin analogues containing conformationally-restricted residues in position 7

We report the solid-phase synthesis and some pharmacological properties of twenty oxytocin (OT) analogues. Basic modifications at position 7 (introduction of α-aminoisobutyric acid [Aib], l- or d-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid [ l/ d-Tic], l- α- t-butylglycine [Gly(Bu t )] and pipecolic acid [Pip]) were combined with d-Tyr(Et) 2, l/ d-( pEt)Phe 2, d-Tic 2, and Mpa 1 modifications and their various combinations in a total of 14 analogues. Additionally, two analogues having one more modification in position 3, i.e. Gly(Bu t ), and three analogues having glycine in position 9 substituted by d-Tic or Aib, were prepared. The analogues were tested for rat uterotonic activity in vitro, in the rat pressor assay and for binding affinity to human OT receptor. The analogue having the highest antioxytocic activity was [Mpa 1, d-Tyr(Et) 2, d-Tic 7, Aib 9]OT having pA 2 = 8.31 ± 0.19; this analogue was also selective.

New bradykinin analogues acylated on the N-terminus: effect on rat uterus and blood pressure.

Our previous studies suggested that acylation of the N-terminus of several known B2 antagonists with various kinds of bulky acyl groups consistently improved their antagonistic potency in rat blood pressure assay. On the other hand, our earlier observations also seemed to suggest that the effects of acylation on the contractility of isolated rat uterus depended substantially on the chemical character of the acyl group, as we observed that this modification might either change the range of antagonism or even transform it into agonism. Bearing all this in mind, we decided to synthesize seven new analogues of bradykinin by N-terminal acylation with various acyl groups of a moderately potent B2 antagonist, previously synthesized by Stewart's group, D-Arg-Arg-Pro-Hyp-Gly-Thr-Ser-D-Phe-Thi-Arg. The analogues were tested in vitro for their blood pressure-lowering and uterotonic activities. The modifications either preserved or increased the antagonistic potency in the rat blood pressure test. On the other hand, all seven substituents negatively influenced the interaction with the rat uterine receptors. Our results may be helpful for designing new B2 agonists and antagonists.

Regulation of Oxytocin Receptors and Oxytocin Receptor Signaling

The oxytocin (OT) -oxytocin receptor (OTR) system plays a key role in many aspects of mammalian reproduction as well as several other physiological processes such as bond pairing and cardiovascular homeostasis. To manifest these diverse physiological roles, the transcription and expression of the OTR is tightly regulated within reproductive, cardiovascular, and neuronal tissues. The expression of the OTR within the mammalian uterus is regulated during gestation with a peak at the day of delivery. The control of this dramatic increase in expression is mediated in rodent species by a combination of stretch, classical steroid hormone stimulation, and repression. In the human uterus events are less clear, although a prominent role for inflammatory-related rapid-response genes and novel transcription factors such as hMafF (human homologue of chicken musculoaponeurotic fibrosarcoma oncogene family protein F) have been put forward. In the uterus the potent uterotonic actions of OT are mediated by the OTR through G-protein activation to stimulate phospholipase C activity. The activated OTR increases contraction frequency and increases force by sensitizing the contractile apparatus of the myocytes to calcium. This review summarizes the current knowledge of the complex regulation of OTR transcription in the myometrium and the intracellular signaling mechanisms through which OT mediates its potent stimulatory effects.

Oxytocic Activity of Leaf Extract of Spondias mombin.

The oxytocic property of leaf extract of Spondias mombin. Linn. (Anacardiaceae) was evaluated in relation to its folkloric use by traditional birth attendants. The abortifacient effect of the methanol leaf extract (ME) obtained by cold maceration for 48 h, was evaluated in vivo. in pregnant mice and rats at different trimesters of pregnancy. The effect of ME on isolated gravid and non-gravid rat uteri preparations as well as on spontaneous contractile frequency and amplitude were investigated in vitro.. The results showed that ME caused abortion in rats only in the third trimester within 24 h of administration. An effective abortifacient dose (ED50) of 105.33 mg/kg was established in pregnant mice. In vitro., the extract significantly (P < 0.05) increased the amplitude and frequency of spontaneous contraction of isolated uteri preparations, which were sustained for longer periods. The uterine-stimulant effects of acetylcholine, oxytocin, ergometrine, and PGF2α. were all potentiated by ME in a dose-dependent manner. The in vivo. abortifacient activity was well corroborated by the uterotonic activity of ME in vitro.. Acute toxicity tests in mice revealed an intraperitoneal LD50 of 282.44 mg/kg. Phytochemical tests showed the presence of saponins, flavonoids, tannins, glycosides, resins, protein, and triterpenes. These findings justify the use of S. mombin. by traditional birth attendants in labor induction, augmentation, and as postpartum astringent.

Misoprostol for preventing PPH: some lessons learned

During the past decade, The Lancet has led the debate over the use of misoprostol for prevention of postpartum haemorrhage. A letter published in 1996 first suggested the use of misoprostol for the third stage of labour.1 Here was a drug that seemed perfectly designed to reduce blood loss in childbirth. Misoprostol is an inexpensive heat-stable prostaglandin E1 analogue with strong uterotonic activity that can be given without the need for sterile needles and syringes. Huge interest was generated and, in the ensuing 10 years, more than 30 randomised trials in more than 30 000 women2 were done to study misoprostol for prophylaxis of postpartum haemorrhage.

Novel in vitro system for functional assessment of oxytocin action

One of the classical biological actions mediated by the posterior pituitary hormone oxytocin (OT) is contraction of the uterus at parturition. Moreover, premature activation of the OT system is thought to contribute to preterm labor, a major clinical problem in obstetrical practice. However, the molecular mechanisms linking activation of the OT receptor (OTR) to myometrial contractions are not fully understood. Here, we describe an in vitro system that should serve as a useful tool to study this question at a cellular level. The system consists of a collagen lattice contraction assay and two different human myometrial cell lines: a cell clone from a telomerase-immortalized human myometrial cell population (hTERT-C3) as well as a cell line derived from a primary culture of human myometrial cells (M11). Using this approach, we observed that 1 nM OT promoted an almost maximal effect on cell contraction in both cell lines tested. Furthermore, this dose-dependent, OT-induced contraction was antagonized by the specific OTR antagonist d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2)(9)]OVT as well as the clinically used antagonist atosiban. This cell line-based contraction assay enables the application of molecular tools aimed at suppressing or overexpressing specific genes. It is also amenable to high-throughput testing approaches. Therefore, this system represents a powerful and improved experimental model that should facilitate the study of the molecular signal transduction pathways involved in the uterotonic actions of OT.

Structure-biological activity relationship in prostaglandin analogs

A complex of mathematical models for the recognition of antiulcer and uterotonic activity of prostaglandin analogs is developed based on SARD computer system, which provides for the activity recognition on a level of 86–98%. The most significant structural signs related to manifestations of the given biological properties are revealed. The established relationship between structure and biological activity of prostaglandin analogs will be used in the following research for constructing new compounds with preset properties.

Analogues of oxytocin antagonists bearing a ureido group in the amino acid side chain at position 4 or 5

Substitution of the side chain carboxamido group at position 4 in the potent oxytocin antagonist (OTA) [ThiaPmp(1), D-Trp(2), Cys(6), Arg(8)]-OT, PA, in which ThiaPmp = beta,beta-(3-thiapentamethylene)-beta-mercaptopropionic acid, led to [Orn(Car)(4)]-PA, ([Cit(4)]-PA), which had uterotonic antagonistic activity equal to that of PA. The same modification at position 5, leading to [Cit(5)]-PA, resulted in antagonistic potency more than 10 times lower than that of PA. This paper also describes the same substitutions introduced in the highly potent OTA [Pen(6)]-PA (antioxytocic in vitro pA(2) = 8.72). Analogues of the general formula [U(4)-X(5)-Pen(6)]-PA, in which U = Lys, Orn, Dab, Dap or X = Orn, Dab or Dap, were synthesized by SPPS. Each of these analogues was carbamoylated by treatment with KCNO in DMF-H(2)O, yielding the corresponding U(Car)(4) or X(Car)(5) derivatives. In the uterotonic assay, the substitution with the ureido group at Gln(4) results in retention of high antagonistic potency, albeit somewhat lower than that of PA, e.g. [Orn(Car)(4), Pen(6)]-PA and [Dab(Car)(4), Pen(6)]-PA having pA(2) = 8.52 and pA(2) = 8.42 respectively. In the pressor assay, [Lys(Car)(4), Pen(6)]-PA and [Dab(Car)(4), Pen(6)]-PA were somewhat weaker antagonists of arginine vasopressin than [Pen(6)]-PA; [Dap(Car)(4), Pen(6)]-PA showed only a faint trace of pressor agonistic activity. The substitution with the ureido group at position 5 leads to a significant loss of OTA potency in the in vitro uterotonic assay. The [Orn(Car)(5), Pen(6)]-PA was the most potent of the series (pA(2) = 8.05). An interesting finding is that [Dap(Car)(5), Pen(6)]-PA is equipotent with its precursor [Dap(5), Pen(6)]-PA (potency in the uterotonic test in vitro, pA(2) = 7.71 and pA(2) = 7.68, respectively). Furthermore, neither [Dap(5), Pen(6)]-PA nor [Dap(5), Pen(6), Gly(9)]-PA exhibited activity in the antidiuretic or pressor assays. Although these last two analogues show some decrease in antioxytocin potency, they behave as pure oxytocin antagonists, which makes them attractive candidates for further studies on the development of potent and specific OTAs.

Investigation of mechanism of desmopressin binding in vasopressin V2 receptor versus vasopressin V1a and oxytocin receptors: Molecular dynamics simulation of the agonist‐bound state in the membrane–aqueous system

The vasopressin V2 receptor (V2R) belongs to the Class A G protein-coupled receptors (GPCRs). V2R is expressed in the renal collecting duct (CD), where it mediates the antidiuretic action of the neurohypophyseal hormone arginine vasopressin (CYFQNCPRG-NH2, AVP). Desmopressin ([1-deamino, 8-D]AVP, dDAVP) is strong selective V2R agonist with negligible pressor and uterotonic activity. In this paper, the interactions responsible for binding of dDAVP to vasopressin V2 receptor versus vasopressin V1a and oxytocin receptors has been examined. Three-dimensional activated models of the receptors were constructed using the multiple sequence alignment and the complex of activated rhodopsin with Gt(alpha) C-terminal peptide of transducin MII-Gt(alpha) (338-350) prototype (Slusarz, R.; Ciarkowski, J. Acta Biochim Pol 2004 51, 129-136) as a template. The 1-ns unconstrained molecular dynamics (MD) of receptor-dDAVP complexes immersed in the fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) membrane model was conducted in an Amber 7.0 force field. Highly conserved transmembrane residues have been proposed as being responsible for V2R activation and G protein coupling. Molecular mechanism of the dDAVP binding has been suggested. The internal water molecules involved in an intricate network of the hydrogen bonds inside the receptor cavity have been identified and their role in the stabilization of the agonist-bound state proposed.

Is the use of &lt;i&gt;Gunnera perpensa&lt;/i&gt; extracts in endometritis related to antibacterial activ

Rhizome extracts of Gunnera perpensa are used in traditional remedies in South Africa to treat endometritis both in humans and animals. An investigation was undertaken to determine whether this plant possesses antibacterial activity, which may explain its efficacy. Gunnera perpensa rhizome extracts were prepared serially with solvents of increasing polarity and tested for antibacterial activity. Test bacteria included the Gram-positive Enterococcus faecalis and Staphylococcus aureus and the Gram-negative Escherichia coli and Pseudomonas aeruginosa. A moderate to weak level of antibacterial activity in most of the extracts resulted, with the best minimal inhibitory concentration (MIC) value of 2.61 mg ml(-1) shown by the acetone extract against S. aureus. The extracts were also submitted to the brine shrimp assay to detect possible toxic or pharmacological effects. All the extracts were lethal to the brine shrimp larvae at a concentration of 5 mg ml(-1). The acetone extract was extremely toxic at 1 mg ml(-1), with some toxicity evident at 0.1 mg ml(-1). The remainder of the extracts generally displayed little activity at concentrations lower than 5 mg ml(-1). In summary, the results indicate that although the extracts demonstrated a level of pharmacological activity, the relatively weak antibacterial activity is unlikely to justify the use of G. perpensa rhizomes in the traditional treatment of endometritis. Rather, the slightly antibacterial nature of the rhizomes may contribute to an additive effect, along with their known uterotonic activity, to the overall efficacy of the preparation.

Introduction of acis-Prolyl Mimic in Position 7 of the Peptide Hormone Oxytocin Does Not Result in Antagonistic Activity

New insights into the structure-activity relationship of the peptide hormone oxytocin are presented. Incorporation of the novel cis-prolyl mimic 2,2-dimethyl-1,3-thiazolidine-4-carboxylic acid (pseudoproline, PsiPro) at position 7 of the hormone yielded the analogue [Cys(Psi(Me,Me)pro)]7oxytocin (1) that showed a 92-95% induction of the cis peptide bond conformation between Cys6 and PsiPro7, as determined by one- and two-dimensional NMR spectra in water and in DMSO-d6. The impact of the dimethyl moiety regarding conformation and bioactivity was investigated by the synthesis of the corresponding dihydro compound, [Cys(Psi(H,H)pro)]7oxytocin (2). Biological tests of the uterotonic activity, the pressor activity, and the binding affinity to the rat and human oxytocin receptors were carried out. As a most significant result, no antagonistic activities were found for both the cis-constrained analogue 1 and analogue 2, suggesting that a cis conformation between residues 6 and 7 of the molecule does not result in antagonistic activity. However, the about 10-fold reduction in agonistic activity of 1 as compared to oxytocin is consistent with the reduction of the trans conformation from 90% for oxytocin to 5-8% for compound 1. Compound 1 retained a high binding affinity for the oxytocin receptor, with K(i) values of 8.0 and 1.9 nM for the rat and the human receptor, respectively. The correlation between the biological activities and the cis contents obtained from NMR analysis for compounds 1, 2, and oxytocin leads to the hypothesis that a cis/trans conformational change plays an important role in oxytocin receptor binding and activation.