The effects of adrenaline, noradrenaline and isoprenaline on inhibitory alpha- and beta-adrenoceptors in the longitudinal muscle of the guinea-pig ileum

Use of inotropes and vasopressor agents in critically ill patients

Inotropes and vasopressors are biologically and clinically important compounds that originate from different pharmacological groups and act at some of the most fundamental receptor and signal transduction systems in the body. More than 20 such agents are in common clinical use, yet few reviews of their pharmacology exist outside of physiology and pharmacology textbooks. Despite widespread use in critically ill patients, understanding of the clinical effects of these drugs in pathological states is poor. The purpose of this article is to describe the pharmacology and clinical applications of inotropic and vasopressor agents in critically ill patients.

Effects of Opioid and α2-Adrenoceptor Agonists on the Isolated Ileum of Morphine-dependent Guinea-pigs During Withdrawal and After Clonidine Treatment

The present study was undertaken to investigate the effect of clonidine administration to opiate-dependent guinea-pigs after morphine withdrawal on subsequent twitch responses of the longitudinal muscle-myenteric plexus preparations to electrical field stimulation. The results indicate that clonidine, administered immediately after morphine removal, causes tolerance to the inhibition exerted by opioid and α2-adrenoceptor agonists on the electrically-evoked twitches. Such a finding suggests that the mechanism of action of clonidine involves not only its well-known effects on locus coeruleus neurons but also that it has specific actions on the myenteric plexus. This work shows the existence of interactions between opioid and α-adrenoceptor on the cholinergic neurons present in the isolated ileum.

The host-defence skin peptide profiles of Peron's Tree Frog Litoria peronii in winter and summer. Sequence determination by electrospray mass spectrometry and activities of the peptides

Positive and negative ion electrospray mass spectrometry together with Edman sequencing (when appropriate) has been used to sequence the host-defence peptides secreted from skin glands of the tree frog Litoria peronii. The peptide profiles are different in winter and summer. In winter, the frog produces small amounts of the known caerin 1.1 [GLLSVLGSVAKHVLPHVVPVIAEHL-NH(2)] (a wide-spectrum antibiotic) and caerin 2.1 [GLVSSIGRALGGLLADVVKSKQPA-OH], a narrow-spectrum antibiotic and an inhibitor of neuronal nitric oxide synthase. The major peptides produced throughout the year are the pGlu-containing peroniins 1.1 to 1.5 (e.g. peroniin 1.1 [pEPWLPFG-NH(2)], a smooth muscle contractor from 10(-7) M), and caerulein [pEQDY(SO(3)H)TGWMDF-NH(2)], a known and potent smooth muscle contractor from 10(-10) M. There are also some precursors to the peroniin 1 peptides, only detected in the skin secretion in summer, which are inactive and appear to be all (or part) of the spacer peroniin 1 peptides, e.g. peroniin 1.1b [SEEEKRQPWLPFG-NH(2)]. There are three members of the Litoria peronii Group of tree frogs classified in Australia, namely, L. peronii, L. rothii and L.tyleri. A comparison of the skin peptide profiles of L. peronii with those reported previously for L. rothii suggests that either these two species of tree frog are not as closely related as determined previously on morphological grounds, or that skin peptide divergence in tree frogs of this Group is more extensive than in others that have been studied.

Skin peptides from anurans of the Litoria rubella Group: sequence determination using electrospray mass spectrometry. Opioid activity of two major peptides

Many species of frogs of the genus Litoria secrete bioactive peptides from their skin glands. These peptides are normally host-defence compounds and may have one, or more of the following activities; smooth muscle contraction, analgesic, antimicrobial, antiviral, lymphocyte proliferator (immunomodulator) and neuronal nitric oxide synthase (nNOS) inactivation. Two frog species of the Litoria rubella Group that have been studied before, namely, Litoria electrica and Litoria rubella, are different from other species of the genus Litoria in that they produce small peptides that show neither membrane, lymphocyte nor nNOS activity. In this study we have used electrospray mass spectrometry together with Edman sequencing to identify eight skin peptides of the third member of this Group, Litoria dentata: surprisingly, none of these peptides show activity in our biological screening program. However, two major peptides (FPWL-NH(2) and FPWP-NH(2)) from L. electrica and L. rubella are opioids at the micromolar concentration.

beta-endorphin: synthesis and morphine-like activity of analogs with D-amino acid residues in positions 1, 2, 4, and 5

The solid-phase syntheses of [D-Tyr1]-, [D-Ala2]-, [D-Phe4]- and [D-Met5]-beta c-endorphins are described. A comparison of certain methods of purification and criteria of homogeneity is made with the use of these compounds. Bioassay of these synthetic analogs both in vitro and in vivo show that [D-Ala2]-beta c-endorphin possesses significant opiate activity whereas the other analogs have minimal activity.

Synthesis of biological activity of human beta-endorphin analogs with disulfide bridges

Three analogs of human beta-endorphin containing internal cystine bridges have been synthesized and their biological activities have been determined. It was found that the analogs with disulfide bridges between positions 17 and 26 or 11 and 26 retained full opiate activity as estimated by guinea ileum assay, whereas the analog with a cystine bridge between positions 7 and 26 showed reduced opiate activity. None of the analogs retained significant immunoactivity as revealed by radioimmunoassay.

Development of highly potent and selective dynorphin A analogues as new medicines

Dynorphin A (Dyn A), a 17 amino acid peptide H-Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys-Trp-Asp-Asn-Gln-OH, is a potent opioid peptide which interacts preferentially with kappa-opioid receptors. Research in the development of selective and potent opioid peptide ligands for the kappa-receptor is important in mediating analgesia. Several cyclic disulphide bridge-containing peptide analogues of Dyn A, which were conformationally constrained in the putative message or address segment of the opioid ligand, were designed, synthesized and assayed. To further investigate the conformational and topographical requirements for the residues in positions 5 and 11 of these analogues, a systematic series of Dyn A(1-11)-NH2 cyclic analogues incorporating the sulphydryl-containing amino acids L- and D-Cys and L- and D-Pen in positions 5 and 11 were synthesized and assayed. Cyclic lactam peptide analogues were also synthesized and assayed. Several of these cyclic analogues, retained the same affinity and selectivity (vs. the mu- and delta-receptors) as the parent Dyn A(1-11)-NH2 peptide in the guinea-pig brain (GPB), but exhibited a much lower activity in the guinea-pig ileum (GPI), thus leading to centrally vs. peripherally selective peptides. Studies of the structure-activity relationship of Dyn A peptide provide new insights into the importance of each amino acid residue (and their configurations) in Dyn A analogues for high potency and good selectivity at kappa-opioid receptors. We report herein the progress towards the development of Dyn A peptide ligands, which can act as agonists or antagonists at cell surface receptors that modulate cell function and animal behaviour using various approaches to rational peptide ligand-based drug design.

Mu-opioid receptor desensitization in mature rat neurons: lack of interaction between DAMGO and morphine

Mu-opioid receptors (MORs) exhibit rapid desensitization and internalization during exposure to various opioid agonists. In some studies, however, morphine has been observed to produce little MOR desensitization or internalization. We examined desensitization in mature rat locus ceruleus (LC) neurons and confirmed that morphine is a very poor desensitizing agent, whereas [D-Ala2,N-MePhe4,Gly-ol5]enkephalin (DAMGO), a high-efficacy agonist, and methadone, an agonist we observed to be of equivalent efficacy to morphine, produced profound rapid desensitization. Similarly, by measuring plasma membrane receptor levels in HEK293 cells stably expressing T7-epitope-tagged rat MOR1 at near physiological levels (HEK293-MOR1 cells), DAMGO and methadone but not morphine caused rapid MOR internalization. It has been reported that a low concentration of DAMGO, coapplied with morphine, caused morphine to induce MOR internalization. We examined whether this interaction occurred in mature mammalian neurons at the level of receptor desensitization. Coapplication of low concentrations of DAMGO did not increase morphine-induced desensitization in LC neurons but caused a lesser degree of desensitization than DAMGO alone. We also failed to observe an enhancement by DAMGO of morphine-induced desensitization in the electrically stimulated guinea pig ileum myenteric plexus-longitudinal muscle preparation. In HEK293-MOR1 cells, low concentrations of DAMGO did not convert morphine into a receptor-internalizing agent. The data presented here fail to support the theory that low concentrations of DAMGO can increase morphine-induced MOR desensitization or internalization.

Mu-opioid receptor desensitization in mature rat neurons: lack of interaction between DAMGO and morphine

Mu-opioid receptors (MORs) exhibit rapid desensitization and internalization during exposure to various opioid agonists. In some studies, however, morphine has been observed to produce little MOR desensitization or internalization. We examined desensitization in mature rat locus ceruleus (LC) neurons and confirmed that morphine is a very poor desensitizing agent, whereas [D-Ala2,N-MePhe4,Gly-ol5]enkephalin (DAMGO), a high-efficacy agonist, and methadone, an agonist we observed to be of equivalent efficacy to morphine, produced profound rapid desensitization. Similarly, by measuring plasma membrane receptor levels in HEK293 cells stably expressing T7-epitope-tagged rat MOR1 at near physiological levels (HEK293-MOR1 cells), DAMGO and methadone but not morphine caused rapid MOR internalization. It has been reported that a low concentration of DAMGO, coapplied with morphine, caused morphine to induce MOR internalization. We examined whether this interaction occurred in mature mammalian neurons at the level of receptor desensitization. Coapplication of low concentrations of DAMGO did not increase morphine-induced desensitization in LC neurons but caused a lesser degree of desensitization than DAMGO alone. We also failed to observe an enhancement by DAMGO of morphine-induced desensitization in the electrically stimulated guinea pig ileum myenteric plexus-longitudinal muscle preparation. In HEK293-MOR1 cells, low concentrations of DAMGO did not convert morphine into a receptor-internalizing agent. The data presented here fail to support the theory that low concentrations of DAMGO can increase morphine-induced MOR desensitization or internalization.

Discriminative disulfide-bonding affinity labeling of opioid receptor subtypes

The affinity-labeling technique is an extremely important method in receptor biochemistry. The 3-nitro-2-pyridinesulfenyl (Npys) group, attached to a mercapto group, can react only with a free thiol group (the beta-mercapto group of cysteine residue) of the target receptor molecules, forming a disulfide bond. This disulfide bonding is mediated through the thiol-disulfide exchange reaction. Unlike other labeling methods, the approach utilizing such chemically activated thiol-containing ligands is able to reproduce an unlabeled protein by treatment with dithiothreitol, a reducing reagent. This provides several unique aspects for the studies elucidating the structure-function relationships between the peptide and the receptor. Based on the SNpys affinity technique, we have achieved the discriminative disulfide-bonding affinity labeling of the three different subtypes of opioid receptors: mu, delta and kappa. This article reviews our novel affinity techniques in the in vitro receptor biochemistry.

Analgesic activity and opioid receptor selectivity of stereoisomers of ohmefentanyl isothiocyanate

Ohmefentanyl is a very potent and highly selective agonist for mu-opioid receptors. We now study analgesia, in vitro activity and opioid receptor affinity of the stereoisomers of ohmefentanyl isothiocyanate. We found that some isomers of ohmefentanyl isothiocyanate had a potent analgesic effect and that all isomers except (3R,4S,2'S)-ohmefentanyl isothiocyanate had a more potent inhibitory action on the electrically evoked contractions of mouse vas deferens than of guinea pig ileum. The inhibitory actions could be antagonized by naloxone. However, compared with the activity of the corresponding stereoisomers of ohmefentanyl, these ohmefentanyl isothiocyanates had significantly reduced analgesia and in vitro activity. They also inhibited the binding of [3H]DPDPE ([D-Pen(2),D-Pen(5)]enkephalin) and [3H]DAGO ([D-Ala(2),Mephe(4),Gly-ol(5)]enkephalin) to opioid receptors in mouse brain membranes. The inhibitory effect of stereoisomers of ohmefentanyl isothiocyanate at mu-opioid receptors was markedly lower than that of their parent compounds. The affinity of stereoisomers of ohmefentanyl isothiocyanate for delta-opioid receptors was, however, greater than or equal to that of their corresponding stereoisomers of ohmefentanyl. The results showed that the introduction of an isothiocyanato group into the phenyl ring in position-1 of ohmefentanyl reduced bioactivity and affinity to mu-opioid receptors but that the selectivity of these compounds for delta-opioid receptors was enhanced. Isomer (3R,4S,2'R)-ohmefentanyl isothiocyanate showed highest selectivity for delta-opioid receptors (K(i)(mu)/K(i)(delta)=13.6) and potent analgesic activity (ED(50)=0.25 mg/kg).

An apparatus to assay opioid activity in the infused lumen of the intact isolated guinea pig ileum

A modified apparatus is described that provides for the simultaneous bathing of the serosa of an intact piece of isolated guinea pig ileum while allowing infusion of the isolated lumen. The comparative compartmental potency of the opioid agonists morphine, casomorphins, and enkephalins to inhibit electrically driven contractions are described in this system. The rank-order potency for serosally applied opioid agonists was (IC(50) values, nM): [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]-enkephalin (DAMGO) (15)>[D-Ala(2),D-Leu(5)]-enkephalin (DADLE) (35)> or =morphine (46)> or =[D-Ala(2)]-met-enkephalinamide (55)>[D-Ala(2)]-beta-casomorphin[1--4] amide (122)>beta-casomorphin[1--4] amide (940)>met- and leu-enkephalin (>6000). This contrasted to the rank-order potency for the luminally applied opioid agonists: DADLE (63)>DAMGO (135)>[D-Ala(2)]-met-enkephalinamide=morphine (4700)>[D-Ala(2)]-beta-casomorphin[1--4] amide (29000). beta-Casomorphin[1--4] amide, leu-enkephalin and met-enkephalin are mostly inactive when applied luminally. Furthermore, the opioid antagonists, casoxin 4 and [D-Ala(2)]-casoxin 4, when infused into the lumen, significantly overcame the inhibitory effect of morphine added to the serosal side. This model provides an assay and screening system to differentiate between the effects of chemical agents applied via the blood stream (serosa) or food side (lumen) on quiescent or electrically driven gut activity of the nervous plexi or receptor systems of the ileum.

Opiate aromatic pharmacophore structure-activity relationships in CTAP analogues determined by topographical bias, two-dimensional NMR, and biological activity assays

Topographically constrained analogues of the highly mu-opioid-receptor-selective antagonist CTAP (H-D-Phe-c[Cys-Tyr-D-Trp-Arg-Thr-Pen]-Thr-NH(2), 1) were prepared by solid-phase peptide synthesis. Replacement of the D-Phe residue with conformationally biased beta-methyl derivatives of phenylalanine or tryptophan (2R,3R; 2R,3S; 2S,3R; 2S,3S) yielded peptides that displayed widely varying types of biological activities. In an effort to correlate the observed biological activities of these analogues with their structures, two-dimensional (1)H NMR and molecular modeling was performed. Unlike the parent (1), which is essentially a pure mu antagonist with weak delta agonist activities in the MVD bioassay, the diastereomeric beta-MePhe(1)-containing peptides exhibited simultaneous delta agonism and mu antagonism by the (2R,3R)-containing isomer 2; mu antagonism by the (2R,3S)-containing isomer 3; weak mu agonism by the (2S,3R)-containing isomer 4; and delta agonism by the (2S,3S)-containing isomer 5. Incorporation of beta-MeTrp isomers into position 1 led to peptides that were mu antagonists (2R,3R), 8; (2R,3S), 9, or essentially inactive (<10%) in the MVD and GPI assays (2S,3R), 10; (2S,3S), 11. Interestingly, in vivo antinociceptive activity was predicted by neither MVD nor GPI bioactivity. When D-Trp was incorporated in position 1, the result (7) is a partial, yet relatively potent mu agonist which also displayed weak delta agonist activity. Molecular modeling based on 2D NMR revealed that low energy conformers of peptides with similar biological activities had similar aromatic pharmacophore orientations and interaromatic distances. Peptides that exhibit mu antagonism have interaromatic distances of 7.0-7.9 A and have their amino terminal aromatic moiety pointing in a direction opposite to the direction that the amino terminus points. Peptides with delta opioid activity displayed an interaromatic distance of <7 A and had their amino terminal aromatic moiety pointing in the same direction as the amino terminus.

Adrenoceptors and colocolonic inhibitory reflex

The colocolonic inhibitory reflex is characterized by inhibition of proximal colonic motility induced by distal colonic distension. The aim of this study was to investigate the underlying neural mechanisms of this reflex, in vivo, using an isolated loop of canine colon. In five beagle dogs, motility was recorded from an exteriorized colonic loop via a serosal strain gauge connected to a digital data logger and chart recorder. Inflation of a balloon in the distal colon resulted in inhibition of motility in the isolated loop. Inhibition of motor activity persisted following injection of propranolol (100 microg/kg intravenously), a beta-adrenoceptor antagonist, but was abolished following administration of the alpha2-adrenoceptor antagonist yohimbine (200 microg/kg intravenously). This study confirms that the colocolonic inhibitory reflex is mediated via the extrinsic nerves to the colon. As the reflex was abolished by alpha2-, but not beta-adrenoceptor blockade, this indicates that the reflex pathway involves alpha2-adrenoceptors.

Cross-tolerance and convergent dependence between morphine and cannabimimetic agent WIN 55,212-2 in the guinea-pig ileum myenteric plexus

The cross-tolerance and convergent dependence between morphine and the cannabimimetic agent R(+)-[2,3-dihydro-5-methyl-3[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-+ ++benzoxazin-yl]-(1-naphthalenyl) methanone mesylate (WIN 55,212-2) were assessed in vitro on guinea-pig ileum. To induce tolerance and dependence the myenteric plexus-longitudinal muscle was incubated at 37 degrees C for 5 h with a fixed concentration representing the IC50 for each compound. Myenteric plexus-longitudinal muscle exposed to WIN 55,212-2 (5 x 10(-8) M) was less sensitive to its inhibitory effect on electrically evoked contractions than naive myenteric plexus-longitudinal muscle. The exposure to cannabinoid induced a parallel rightward shift in the lower part of the concentration-response curve of WIN 55,212-2 and a marked reduction in the maximal inhibitory effect of the drug. Myenteric plexus-longitudinal muscle tolerant to WIN 55,212-2 was subsensitive to the inhibitory effect of morphine on the twitch response. The cross-tolerance between WIN 55,212-2 and morphine was bidirectional. In fact, after 5 h the morphine (10(-7) M)-incubated myenteric plexus-longitudinal muscle was less sensitive to the inhibitory effect of WIN 55,212-2. The tissue tolerant to morphine or WIN 55,212-2 was tested for the presence of physical dependence. Naloxone (10(-5) M) produced a typical withdrawal contracture in morphine-tolerant myenteric plexus-longitudinal muscle which could be reduced by a 15-min pretreatment with WIN 55,212-2 (5 X 10(-8) M). In contrast, SR141716 (10(-6) M) [N-(piperidino)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyr azole-carboxamide], a concentration which fully antagonized the inhibitory effect of WIN 55,212-2 (10(-7) M) in control preparations, did not produce significant contracture in WIN 55,212-2-tolerant myenteric plexus-longitudinal muscle. The mechanisms underlying the cross-tolerance and convergent dependence remain to be ascertained.

Beta-funaltrexamine discriminates between two subtypes of mu2-opioid receptors in electrically stimulated longitudinal muscle of guinea pig ileum

1. Morphine inhibited twitch responses of the longitudinal muscle of the guinea pig to electrical stimulation. A concentration-response curve of morphine was partly inhibited by a 60-min pretreatment of ileal strip with 10(-10) M of beta-funaltrexamine (beta-FNA). However, the 60-min pretreatment with a higher concentration (10(-9) M) of beta-FNA had no further significant inhibitory effect on the curve of morphine, suggesting that beta-FNA discriminated between two subtypes of mu2 receptors, beta-FNA-sensitive and -resistant receptors. 2. The mu2 receptors in synaptosomal fraction were selectively labeled by [3H]naloxone, and the labeled receptors were competitively inhibited by morphine. The competitive-inhibition curve of morphine showed the presence of high- and low-affinity sites. Beta-FNA eliminated the high-affinity site only when endogenous GTP or GTPgamma-S was present. 3. Beta-FNA discriminated between two subtypes of mu2 receptors.

Opioid activity of alkaloids extracted from Picralima nitida (fam. Apocynaceae)

Extracts of the seeds of Picralima nitida (fam. Apocynaceae) have been reported to have opioid analgesic activity. In this investigation, isolated tissue bioassays and radioligand binding assays have been used to determine the opioid activity of five alkaloids--akuammidine, akuammine, akuammicine, akuammigine and pseudoakuammigine--extracted from the seeds of P. nitida. Akuammidine showed a preference for mu-opioid binding sites with Ki values of 0.6, 2.4 and 8.6 microM at mu-, delta- and kappa-opioid binding sites, respectively. The agonist actions of akuammidine in the mouse-isolated vas deferens were antagonised by naloxone and the mu-opioid receptor selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) confirming an action at mu-opioid receptors. In contrast, akuammine also showed highest affinity for mu-opioid binding sites (Ki 0.5 microM) but was an antagonist at mu-opioid receptors with a pK(B) of 5.7 against the selective mu-opioid receptor agonist [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAMGO). Akuammicine has the highest affinity for kappa-opioid binding sites (Ki 0.2 microM) and was a full agonist at kappa-opioid receptors in the guinea pig ileum preparation but a partial kappa-opioid receptor agonist in the vasa deferentia of the mouse and the rabbit. Akuammigine and pseudoakuammigine showed little or no efficacy in the opioid bioassays. None of the alkaloids had significant activity for opioid receptor-like binding sites (ORL1-binding sites) with Ki values >> 10 microM. These data show that some alkaloids extracted from the medicinal plant P. nitida possess varying degrees of agonist and antagonist activity at opioid receptors but possess neither high affinity nor selectivity for mu-, delta- or kappa-opioid receptors or the ORL1-receptor.

Pharmacological studies on the "orphan" opioid receptor in central and peripheral sites

We have exploited the availability of the "orphan" opioid receptor (referred to here as ORL1) in its "natural state" to investigate the effect of nociceptin (orphanin FQ), the endogenous agonist for the ORL1 receptor in the brain, vas deferens, and myenteric plexus of the small intestine. Nociceptin was a potent agonist in electrically stimulated preparations of vasa deferentia (rat and rabbit) and myenteric plexus (guinea-pig) (IC50 ranging from 18 to 31 nM) and susceptible to enzymic cleavage as addition of a cocktail of peptidase inhibitors to the organ bath produced a leftward shift in concentration-response curves (IC50 ranging from 2.1 to 4.9 nM). In radioligand binding experiments using brain membranes from rat, rabbit, and guinea-pig, [3H]nociceptin bound a single population of binding sites with high affinity (KD values ranging from 0.049 to 0.124 nM) and capacity (Bmax ranging from 143 to 254 fmol ·mg-1 protein). However, the response to nociceptin in functional studies and in radioligand binding inhibitory assays was resistant to antagonism/displacement by naloxone and a range of other opioid receptor antagonists, thus displaying a very different pharmacological profile from that of the "classical" opioids. Therefore, we conclude that the effect of nociceptin in these studies is not via an action at µ, delta , or kappa opioid receptors but rather at an orphan opioid receptor, ORL1.Key words: nociceptin, orphanin FQ, vas deferens, myenteric plexus, "orphan" opioid receptor.

Intracellular recording from myenteric neurons of the guinea-pig ileum that respond to stretch

1. Isolated longitudinal muscle-myenteric plexus preparations from guinea-pig ileum were used to investigate the activity of myenteric neurons when the tissue was stretched in the circumferential direction. Membrane potentials were recorded via flexibly mounted intracellular recording electrodes containing Neurobiotin in 1 M KCl. The preparations were stretched to constant widths (+20% and +40% beyond slack width). 2. Multipolar neurons (Dogiel type II morphology) discharged spontaneous action potentials and proximal process potentials during maintained stretching, three of twenty-one at +20% stretch and seven of nine at +40% stretch. At the maximum extent of stretch tried, +40% beyond slack tissue width, action potentials in Dogiel type II neurons occurred at 10-33 Hz. Neurons with other morphologies were all uniaxonal. Some displayed spontaneous fast EPSPs or action potentials, three of forty one at +20% stretch and seven of nineteen at +40% stretch. 3. In seven of eight Dogiel type II neurons, action potentials or proximal process potentials persisted when membrane hyperpolarization was imposed via the recording electrode. Action potential discharge was abolished by hyperpolarization in seven of nine uniaxonal neurons; the exceptions were two orally projecting neurons. 4. Dogiel type II and uniaxonal neurons were classified as rapidly accommodating if they discharged action potentials only at the beginning of a 500 ms intracellular depolarizing pulse and slowly accommodating if they discharged for more than 250 ms. For Dogiel type II neurons, three of thirteen were slowly accommodating at +20% stretch and two of four at 40% stretch. For uniaxonal neurons the corresponding data were twelve of twenty-six and fifteen of nineteen neurons. The slowly accommodating state was associated with increased cell input resistance in uniaxonal neurons. 5. The spontaneous action potential discharge in Dogiel type II and uniaxonal neurons ceased when the muscle was relaxed pharmacologically by nicardipine (3 microM) or isoprenaline (1 microM), although the applied stretch was maintained. At the same time, evoked spike discharge became rapidly accommodating. 6. We conclude that many Dogiel type II neurons, and possibly some orally projecting uniaxonal neurons, are intrinsic, stretch-sensitive, primary afferent neurons that respond to muscle tension with sustained action potential discharge.

Organic solvent extraction associated with HPLC in the preparation of hemorphins from bovine hemoglobin peptic hydrolysate

Hemorphins extraction by organic solvents from a hemoglobin peptic hydrolysate was investigated. About thirteen solvents were used and only the aliphatic alcohols displayed selectivity for hemorphins. The resulting extracted phases, analyzed by SE-HPLC, RP-HPLC, and mass spectrometry, proved 1-butanol and 2-butanol to be the best extracting solvents towards hemorphins. The opioid activity test was carried out following each step of extraction and the obtained results were in agreement with a purification.

Investigation of inhibition angiotensin-converting enzyme (ACE) activity and opioid activity of two hemorphins, LVV-hemorphin-5 and VV-hemorphin-5, isolated from a defined peptic hydrolysate of bovine hemoglobin

Two peptides, LVV-hemorphin-5 and VV-hemorphin-5, were isolated from a defined peptic bovine hemoglobin hydrolysate by reversed-phase HPLC. These peptides were identified as 31-38 and 32-38 fragments of beta chain of bovine hemoglobin. Their inhibitory activity towards angiotensin-converting enzyme and opioid potency were determined. Since their amino acid sequences show close homology with spinorphin, which is found in human cerebrospinal fluid and in the bovine spinal cord, the possible physiological role in vivo of these peptides was discussed.

Identification of casoxin C, an ileum-contracting peptide derived from bovine kappa-casein, as an agonist for C3a receptors

Casoxin C (Tyr-Ile-Pro-Ile-Gln-Tyr-Val-Leu-Ser-Arg) is a bioactive peptide that was isolated from a tryptic digest of bovine kappa-casein as an anti-opioid peptide in longitudinal strips of guinea pig ileum. Casoxin C also evokes contraction of the ileal strips, and we found that this process was biphasic with rapid and slow components. The contractile profile was very similar to that of human complement C3a(70-77), which is the COOH-terminal octapeptide of C3a and has, although less potent, qualitatively the same biological activities as C3a. Casoxin C also has homology with C3a(70-77). The rapid contraction was mediated by histamine release and the slow contraction was mediated by a prostaglandin E2-like substance, judging from the effects of various pharmacological inhibitors and antagonists on the ileal contraction. Casoxin C had affinity for C3a receptors (IC50 = 40 microM) in the radioreceptor assay. In addition, casoxin C showed phagocyte-stimulating activities. Casoxin C is therefore the first milk-derived peptide identified, that acts through complement C3a receptors.

Opioid peptides: simultaneous delta agonism and mu antagonism in somatostatin analogues

Four isomers of the Somatostatin analogue H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) were made with beta-MePhe in position 1 and assayed for opioid binding in rat brain, biological activity in MVD and GPI bioassays, and antinociception in mouse warm-water tail flick assays. The analogues displayed varying potencies and biological activities including: simultaneous delta receptor agonism/mu receptor antagonism, mu receptor antagonism, and delta receptor agonism. These analogues demonstrated that the N-terminal residue is important for receptor potency/selectivity and signal transduction. These analogues my represent leads to therapeutic agents that yield analgesia via delta agonist effects, yet lack side effects associated with mu activity.

The cysteinyl-leukotriene receptor antagonist BAY u9773 is a competitive antagonist of leukotriene C4 in the guinea-pig ileum

Two main classes of receptors exist for leukotrienes C4, D4 and E4, collectively named cysteinyl-leukotrienes (CysLTs). The CysLT1 receptor is blocked by currently available leukotriene antagonists, and the CysLT2 receptor is defined by the absence of selective antagonists. The contractile response to leukotriene C4 in guinea-pig ileum longitudinal muscle is resistant to CysLT1 receptor antagonists. However, the leukotriene E4 analogue BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z), 14(Z)-eicosatetraenoic acid) has recently been reported to inhibit CysLT2 responses. Therefore BAY u9773 was evaluated for antagonism of the effect of leukotriene C4 in the guinea-pig ileum longitudinal muscle. We found that BAY u9773 (0.3-10 microM) did not contract the preparation, but produced a concentration-dependent rightward shift in the concentration-response relation for leukotriene C4. Schild plot analysis yielded a slope which was not significantly different from unity and a pA2 value of 6.1. The inhibition of leukotriene C4 by BAY u9773 was not altered by antagonism of CysLT1 receptors by ICI 198,615 {[1-[[2-methoxy-4-[[(phenylsulfonyl)amino]carbonyl]-phenyl] methyl]-1H-indazol-6-yl]carbamic acid cyclopentyl ester}(100 nM). The CysLT1 receptor agonist, leukotriene E4 (1 microM), contracted the preparation but did not inhibit the contraction induced by leukotriene C4. Taken together, the antagonism exerted by BAY u9773 appeared unrelated to actions on CysLT1 receptors. In conclusion, BAY u9773 was a useful selective competitive antagonist of leukotriene C4, and the findings support the classification of the receptors for leukotriene C4 in the guinea-pig ileum as CysLT2.

Depressant effects of hypoxia and hypoglycaemia on neuro-effector transmission of guinea-pig intestine studied in vitro with a pharmacological model

1. Since intermittent ischaemia may play an important role in the aetiology of Inflammatory Bowel Disease, particularly Crohn's Disease, a pharmacological model of neuronal ischaemia was applied to guinea-pig isolated intestinal preparations to mimic the acute effects of reduced blood flow on intestinal motility. 2. Neuro-effector transmission and smooth muscle performance were examined in myenteric plexus-longitudinal muscle preparations of guinea-pig ileum exposed to sodium cyanide (NaCN), in order to inhibit oxidative phosphorylation, or to iodoacetic acid (IAA), to block glycolysis. Comparisons were made with the effects due to simple deprivation of oxygen or glucose. 3. Depression of cholinergic neuro-effector transmission induced by hypoxia or NaCN (effective concentration range 0.1-3 mM), given as separate treatments, singly or repetitively over 60-90 min, were apparent within 30 s and were reversible. The maximum inhibition was 90% and the IC50 for NaCN was 0.3 mM. A conspicuous component of these inhibitions was prejunctional. 4. Non-cholinergic neuro-effector contractions were inhibited by up to 90% by anoxia or NaCN but recovery was incomplete and slower than with cholinergic contractions. 5. Glucose-free solutions also caused a reversible failure of cholinergic neuro-effector transmission but of slower onset. In contrast, IAA (0.06-1 mM) abolished contractions irreversibly, apparently by a direct depressant effect on smooth muscle contraction. Unlike NaCN, IAA caused an initial potentiation of electrically-induced contractions, partly by a prejunctional potentiation of cholinergic neuro-effector transmission. 6. It is concluded that a disruption of intestinal activity in pathological conditions associated with intestinal ischaemia may result from disturbances in the function of enteric neurones.

Effects of catecholamines on isolated human colonic smooth muscle

1. The effects of catecholamines and some adrenoceptor agonists and antagonists on isolated preparations of human colonic smooth muscle obtained from surgical resections were examined. 2. Strips of circular smooth muscle displayed rhythmic myogenic spontaneous contractions which were inhibited by catecholamines with an order of potency of isoprenaline (1.0) > noradrenaline (0.32) > adrenaline (0.2). Phentolamine (0.7 microM) significantly shifted the noradrenaline concentration-response curve (CRC) to the right but had no significant effect on isoprenaline or adrenaline. Propranolol (1 microM) significantly shifted the isoprenaline to the right but had no significant effect on noradrenaline or adrenaline. 3. Salbutamol (30 microM) had no inhibitory effect on the spontaneous activity and ICI 118,551 (1 microM) had no effect on inhibitory responses to isoprenaline. Betaxolol (1 microM) significantly shifted the CRC to isoprenaline to the right. BRL 37344 had no effect on spontaneous activity. 4. Responsiveness of circular strips to catecholamines was not affected by age of the patient and no consistent differences between males and females were shown. 5. Strips of taenia coli exhibited little or no spontaneous phasic activity. Noradrenaline and isoprenaline relaxed KCl-induced tone. The effects of noradrenaline and isoprenaline were antagonized by propranolol but not by phentolamine. BRL 37344 had no effect on KCl-induced tone. 6. In conclusion, catecholamines relaxed spontaneous activity of human colon circular smooth muscle through an action on both alpha- and beta-adrenoceptors. The alpha-adrenoceptors were of the alpha 1-subtype. The beta-adrenoceptor-mediated relaxation appeared to be primarily beta 1. In taenia coli, catecholamines relaxed KCl-induced tone via beta-adrenoceptors only.

Design, synthesis, and biological activities of cyclic lactam peptide analogues of dynorphine A(1-11)-NH2

We previously have reported four possible binding conformation of dynorphin A (Dyn A) for the central kappa opioid receptors, induced by the address sequence, using a molecular mechanics energy minimization approach. The lowest energy conformation was found to exhibit an alpha-helical conformation in the cyclized address sequence. It was suggested that an alpha-helical conformation in the cyclized address sequence or a helical conformation induced by the conformational characteristics of the message sequence may be important for binding potency and kappa opioid receptor selectivity. Side chain to side chain lactam bridges between the i and i + 4 positions have been shown to stabilize alpha-helical conformation. Thus, a series of cyclic lactam analogues of dynorphin A(1-11)-NH2 have been designed, synthesized and evaluated by the guinea pig brain (GPB) binding assay and guinea pig ileum (GPI) bioassay to evaluate the conformational analysis prediction and, further, to investigate the conformational requirements for high potency and selectivity for kappa opioid receptors. Positions 2-6, 3-7, and 5-9 were chosen as the sites for incorporating cyclic conformational constraints. Cyclization between D-Asp(2) and Lys(6) in c[D-Asp(2),Lys(6)]Dyn A(1-11)-NH2 led to an analogue with pronounced potency and selectivity enhancement for the mu opioid receptor, whereas cyclization between D-Asp(3) and Lys(7) in c[D-Asp(3),Lys(7)]Dyn A(1-11)-NH2 led to a potent ligand (IC(50) 4.9 nM) with kappa receptor selectivity. The other analogues in the series proved to be less selective. The biological results led to the suggestion that the binding conformation for the kappa receptor may have structural requirements that are distinct from those of mu and delta receptors. Interestingly, analogues with a D-Asp at position 2, 3, or 9 were found to be more potent for the kappa receptor than analogues with an L-Asp at the same positions. It is suggested that the incorporation of D-Asp into position 2, 3, or 9 of Dyn A(1-11)-NH2 may have stereochemical and conformational effects on the nearby amino acids which can help discriminate the preference between kappa, mu, and delta receptors.

Studies on the ileum-contracting mechanisms and identification as a complement C3a receptor agonist of oryzatensin, a bioactive peptide derived from rice albumin

Oryzatensin (Gly-Tyr-Pro-Met-Tyr-Pro-Leu-Pro-Arg) is an ileum-contracting and immunostimulating peptide derived from rice albumin. The mechanisms for the ileal contraction that it induces, consisting of rapid and slow components, were examined. The rapid contraction was mediated by histamine release and the slow contraction by a prostaglandin E2-like substance, judging from the effects of various pharmacological inhibitors and antagonists on ileal contraction and titration of histamine release. The contractile profile was very similar to that of human complement C3a(70-77), which is the COOH-terminal octapeptide of C3a and has, although less potent, qualitatively the same biological activities as C3a. Oryzatensin showed homology with C3a(70-77) and affinity for C3a receptors (IC50 = 44 microM) by radioreceptor assay. This is the first report of a food-derived bioactive peptide acting through complement C3a receptors.

The sea anemone purine, caissarone: adenosine receptor antagonism

Caissarone, a sea anemone iminopurine, produced an increase in the twitch response of the electrically stimulated guinea-pig ileum-myenteric plexus. In the same assay, caissarone reduced the inhibitory response to the endogenous neuromodulator, adenosine, the A1 adenosine receptor agonist, R-phenylisopropyladenosine (R-PIA), and the A2 agonist, 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA) in a dose-dependent manner. Schild plot analysis of antagonism by caissarone yielded slopes of near unity, indicating that caissarone acts as a simple competitive antagonist at the adenosine receptor. The dissociation constants (KB) for caissarone ranged from 0.53 mM to 0.78 mM. In functional nicotinic receptor assays in two human cell lines, caissarone failed either to potentiate or to reduce carbamylcholine-mediated 86Rb+ efflux. Thus, the enhancing activity of caissarone on the gut could not be attributed to activity at the ganglionic nicotinic receptor. Based on structure and pharmacological activity, caissarone appears to be the first marine product described as an adenosine receptor antagonist.

Smooth muscle relaxing and hypotensive activities of synthetic calciseptine and the homologous snake venom peptide FS2

The biological activities of synthetic calciseptine and FS2, a homologous peptide from snake venom, were determined using in vitro and in vivo preparations. Calciseptine and FS2 produced dose-dependent relaxation in pre-constricted rat aorta, pulmonary artery and trachea. The onset and duration pattern of these relaxing effects were similar to those caused by nifedipine, an L-type Ca2+ channel blocker. Calciseptine relaxed the contraction of rat aorta provoked by an L-type channel agonist, Bay K 8644. This relaxation was not affected by NG-nitro-L-arginine, indomethacin or propranolol. Calciseptine and FS2 inhibited the contraction caused by acetylcholine in guinea pig ileal longitudinal muscle. In case of in vivo study using anesthetized rats, calciseptine, FS2 and nifedipine showed depressor effects. The hypotensive effects of the two peptides were more potent and sustained than that of nifedipine. These findings show that both synthetic calciseptine and FS2 have similar biological activities like nifedipine, an L-type Ca2+ channel blocker. In addition, these two peptides with large molecular weights may be unique and useful tools for studying the Ca2+ channel.

VV-hemorphin-7 and LVV-hemorphin-7 released during in vitro peptic hemoglobin hydrolysis are morphinomimetic peptides

Two opioid peptides were generated by in vitro pepsin treatment of bovine hemoglobin. These peptides were identified using a GPI test and purified using HPLC chromatographic techniques. They correspond to fragments 31-40 (LVV-hemorphin-7) and 32-40 (VV-hemorphin-7) of the beta-chain of bovine hemoglobin. Binding experiments strongly confirm that VV-hemorphin-7 and LVV-hemorphin-7 are opioid peptides since they inhibited [3H]naloxone binding to rat brain membranes. Our results indicate that VV-hemorphin-7 and LVV-hemorphin-7 exhibit a lesser potency both in GPI and binding tests. Selectivity and affinity of these purified peptides and synthetic hemorphin-7 for opioid receptors is discussed.

Peptic hemoglobin hydrolysis in an ultrafiltration reactor at pilot plant scale generates opioid peptides

Two hemorphins, peptides with opioid activity, have been isolated from a pepsin hydrolysate of bovine hemoglobin, by use of gel permeation (GP) and reverse phase (RP) high-performance liquid chromatography (HPLC). Their primary structure and accurate molecular weights, determined by amino acid analysis and fast atom bombardment (FAB) mass spectrometry, were identical to fragments 31-40 (LVV-hemorphin-7) and 32-40 (VV-hemorphin 7) of the beta-chain of bovine hemoglobin. Two other peptides, 34-40 (hemorphin-7) and 34-41 (hemorphin-8) of the beta-chain of bovine hemoglobin, have been synthesized and studied. The opioid potency of these peptides, exhibited by the use of electrically stimulated muscle of isolated guinea pig ileum (GPI), were significant and comparable with some others previously described. Studies of opioid activities and primary structure of hemorphins led us to postulate the important role of arginine and phenylalanine in opioid potency.

Isolation of cholinergic active ingredients in aqueous extracts of Mareya micrantha using the longitudinal muscle of isolated guinea-pig ileum as a pharmacological activity marker

In our attempt to isolate the pharmacologically active ingredients in the aqueous extracts of Mareya micrantha, we have selected the contractions of the longitudinal muscle of the isolated guinea-pig ileum preparation as a pharmacological marker to monitor retention of pharmacological activity during the chromatographic separation. The aqueous extracts of Mareya micrantha elicited concentration-dependent contractions of the preparation. The maximum response elicited by the aqueous extracts was 50% of the maximum response elicited by the maximum dose of acetylcholine (ACh), 10(-7) M. Mepenzolate (10(-8)-10(-5) M), a specific muscarinic receptor antagonist, similarly antagonized contractions elicited by the aqueous extracts suggesting that the cholinergic ingredient(s) in the extract are acting at the muscarinic receptors of the preparation. Fraction 2-4, which was separated from the aqueous extracts by Sephadex gel chromatography, dose-dependently elicited contractions of the preparation. The maximum response was 80% of the maximum response elicited by the maximum dose of ACh suggesting that separation has enhanced the cholinergic activity of the content in the extract.

Conserved delta-activity in reverse enantiomeric opioid peptide

A reverse enantiomeric peptide has a reversed amino acid sequence with enantiomeric amino acid residues compared with its parent peptide. In most cases the random change of amino acid sequence or chirality might be expected to bring about significant changes in peptide activity. However, the reverse enantiomeric peptides of Leu-enkephalin and Tyr-D-Ala-Gly-Phe-D-Leu (DADLE) have shown affinity for the opioid delta-receptor, but not for mu- or kappa-receptors. This suggests that delta-opioid receptor recognition occurs primarily through interaction with the peptide side chains, since the native opioid peptide and its reverse enantiomer are able to have similar side-chain conformation.

Syntheses, opioid binding affinities, and potencies of dynorphin A analogues substituted in positions, 1, 6, 7, 8 and 10

Structural, stereochemical, stereoelectronic and conformational requirements for biological activity of dynorphin A1-11-NH2 analogues at opioid receptors were explored by substitution of Tyr1, Arg6, Arg7, Ile8 and Pro10 with other amino acid residues. Interestingly, substitution of Tyr1 with N alpha-Ac-Tyr1, D-Tyr1, Phe1 or p-BrPhe1 led to analogues that were quite potent at kappa opioid receptors, and additional substitution of Ile8 with D-Ala8 and/or Pro10 with D-Pro10 retained high potency in brain binding assay: [N alpha-Ac-Tyr1]- (1), [D-Tyr1]-(2) [Phe1]- (3), [Phe1,D-Ala8]- (5), [-BrPhe1, D-Ala8]- (6), [Phe1, D-Pro10]- (7) and [Phe1,D-Ala8, D-Pro10]- Dyn A1-11-NH2 (8) had IC50 (nM) binding affinities of 13.2, 18.6, 1.64, 1.26, 1.84, 2.44 and 1.62 nM, respectively. The D-Phe1 analogue 4, however, was only weakly active (610 nM). All of the analogues except 4 were modestly selective for kappa vs. mu guinea pig brain opioid receptor (11- to 88-fold) and quite selective for kappa vs. delta receptors (65-576). However, all of the analogues appeared to have very low or essentially no activity in the guinea pig ileum and mouse vas deference functional bioassays, and one analogue, 5, appeared to have weak antagonist activities. On the other hand, if constrained amino acids such as beta-methylphenylalanine or 1,2,3,4-tetrahydroisoquinoline carboxylic acid, and hydroxyproline were placed in the 1 position, inactive analogues or analogues with greatly reduced potency and biological activity were obtained (compounds 12-14). It had previously been suggested that the Arg6 and Arg7 residues were critical for biological activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Unexpected antinociceptive potency of cyclic [D-Tca1]CTAP: potential for a novel mechanism of action

This study tested the hypothesis that compounds which may bind simultaneously to delta and mu receptors may be more potent antinociceptive agents than would be predicted from their binding affinities at individual mu and delta opioid receptors. D-Tca-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 ([D-Tca1]CTAP) (where D-Tca is a cyclic D-tryptophan analogue) was synthesized and evaluated in radioligand competition assays, opioid bioassays, and in an antinociceptive assay (the tail-flick test in mice). Additionally, the metabolic stability of [D-Tca1]CTAP was evaluated in striatal and cerebellar tissue slices. In rat brain in vitro, [D-Tca1]CTAP competed weakly for sites labelled by [3H]D-Phe-Cys-Tyr-D-Trp-Om-Thr-Pen-Thr-NH2 ([3H]CTOP) (mu-ligand), and [3H][D-Pen2,pCl-Phe4,D-Pen5]enkephalin (delta-ligand); [D-Pen2,D-Pen5]enkephalin (DPDPE) (delta-agonist) was 6.5-fold less and 230-fold more potent, respectively, against these ligands. Additionally, in mouse isolated vas deferens and guinea pig isolated ileum smooth muscle preparations, [D-Tca1]CTAP proved to be weak as either a delta (IC50 of approximately 2 microM) or mu (IC50 > 8 microM) receptor agonist. Surprisingly, however, i.c.v. [D-Tca1]CTAP produced antinociception with potency similar to DPDPE. The antinociceptive actions of [D-Tca1]CTAP were apparently not due to a metabolite or the release of endogenous opioids, as this compound proved stable in both striatal and cerebellar tissue slices and its antinociceptive actions were not enhanced by the 'enkephalinase' inhibitor thiorphan. The suggestion that [D-Tca1]CTAP might be acting by binding simultaneously to mu and delta receptors to produce its antinociceptive effect is supported by the demonstrated antagonism resulting from mu receptor blockade with either beta-funaltrexamine (beta-FNA) or naloxonazine, or by delta receptor blockade by ICI 174,864 ([N,N-diallyl-Tyr1,Aib2,3,Leu5] enkephalin). Furthermore, the antinociceptive properties of [D-Tca1]CTAP were antagonized by (naltrindole-5'-isothiocyanate) (5'-NTII), an antagonist at the delta 2 opioid receptor subtype, but not by the delta 1 antagonist [D-Ala2,D-Leu5,Cys6]enkephalin (DALCE). Additionally, no antagonism was produced by nor-binaltorphimine (nor-BNI), a kappa antagonist. From these data, [D-Tca1]CTAP appears to bind to mu, and 5'-NTII-sensitive delta 2, opioid receptors, and may represent the first of a class of compounds which may act at an opioid receptor complex via 'self-potentiation'.

Pharmacological evidence for the presence of a beta-adrenoceptor-like agonist in the amphinoid polychaete Eurythoe complanata

1. Methanolic extracts from the body wall of Eurythoe complanata (ExEc) were tested for biological activity on the isolated rat ileum. 2. ExEc produced either relaxation or relaxation followed by contraction of the rat ileum in a concentration-dependent manner. 3. The predominant relaxation response to ExEc was completely blocked by the beta-adrenoceptor antagonist propranolol and was unaffected by the alpha-adrenoceptor antagonist phenoxybenzamine. 4. The results indicate that the relaxation induced by ExEc is mediated by beta-adrenoceptors. The presence of a myorelaxing substance in E. complanata that selectively activates the beta-adrenoceptors is suggested.