Long-term results of electrical stimulation of the lower esophageal sphincter for the treatment of gastroesophageal reflux disease.

BACKGROUND AND STUDY AIMS: In patients with gastroesophageal reflux disease (GERD), temporary electrical stimulation of the lower esophageal sphincter (LES) increases LES pressure without interference with LES relaxation. The aim of the current study was to investigate the safety and efficacy of long term LES electrical stimulation therapy (LES-EST), using a permanently implanted stimulator for the treatment of GERD. PATIENTS AND METHODS: Patients with GERD who were at least partially responsive to proton pump inhibitors (PPIs) and who had hiatal hernia of ≤ 3 cm and esophagitis of Los Angeles Grade A, B, or C were included in the study. Stimulation electrodes were placed in the LES and a pulse generator (EndoStim LES Stimulation System; EndoStim BV, The Hague, The Netherlands) was implanted laparoscopically. LES stimulation was delivered at 20 Hz, 215 µs, 3 - 8 mA in multiple 30-minute sessions. Patients were evaluated at follow-up using the GERD Health-Related Quality of Life (HRQL) questionnaire, daily symptom and medication diaries, the SF-12 Health Survey, esophageal pH testing, and high resolution manometry. RESULTS: A total of 24 patients (mean age 53 ± 12 years; 14 men) were implanted and 23 completed the 12-month evaluation. No serious implantation or stimulation-related adverse affects or sensations were reported. Median composite GERD-HRQL score at 12 months was 2.0 (interquartile range [IQR] 0 - 3.0), which was significantly better than baseline scores both on PPI therapy (median 9.0, IQR 6.0 - 10.0; P = 0.002) and off PPIs (median 23.5, IQR 21 - 25.75; P < 0.001). The median percentage of the 24-hour period with esophageal pH < 4.0 at baseline was 10.1 % (IQR 7.7 - 15.5), which was reduced to 3.3 % (1.8 - 6.9) at 12 months (P < 0.001), with 69 % of patients showing either normalization or > 50 % improvement in their distal esophageal pH. At 12 months, 96 % of patients (22/23) were completely off PPI medication. CONCLUSION: During the long term follow-up of 12 months, LES - EST was safe and effective for the treatment of GERD. There was a significant and sustained improvement in GERD symptoms, reduction in esophageal acid exposure with elimination of daily PPI usage, and no stimulation-related adverse effects.

Juvenile polyposis syndrome: A case report.

INTRODUCTION: Juvenile polyposis syndrome it is an uncommon autosomal dominant inherited condition. Hamartomatous polyps can affect the entire gastrointestinal tract but usually predominates in the colon. We introduce a case of juvenile polyposis syndrome presented with massive gastric polyposis that requires a total gastrectomy. CASE PRESENTATION: A 22-year-old man presented symptoms of chronic upper gastrointestinal bleeding. Gastroscopy showed massive gastric polyposis. Initially endoscopic polypectomy was performed, but due to the progressive symptoms, a total gastrectomy was then performed. Histology confirmed massive gastric juvenile polyposis. CONCLUSION: Massive gastric polyposis it is an uncommon manifestation of juvenile polyposis syndrome.

Oral ulcers produced by mycophenolate mofetil in two liver transplant patients.

Oral ulcers are a frequent problem in transplant medicine. It is important to consider infectious etiologies, exacerbated by the immunosuppressive treatment, but other etiologies are also possible, like adverse drug reactions. Mycophenolate mofetil (MMF) is an immunosuppressive medication that has been used in combination with calcineurin inhibitors and steroids. Reports of renal transplant patients with oral ulcers related to MMF have appeared lately and herein we have described 2 cases in liver transplant patients. Their oral ulcers resolved quickly after suspension of the medication. Our 2 cases in liver transplant patients represented a unique setting for this type of complication.

Cardiomyocyte apoptosis induced by Galphaq signaling is mediated by permeability transition pore formation and activation of the mitochondrial death pathway.

Expression of the wild-type alpha subunit of Gq stimulates phospholipase C and induces hypertrophy in cardiomyocytes. Addition of Gq-coupled receptor agonists additionally activates phospholipase C, as does expression of a constitutively active mutant form of Galphaq. Under these conditions, hypertrophy is rapidly succeeded by apoptotic cellular and molecular changes, including myofilament disorganization, loss of mitochondrial membrane potential, alterations in Bcl-2 family protein levels, DNA fragmentation, increased caspase activity ( approximately 4-fold), cytochrome c redistribution, and nuclear chromatin condensation in approximately 12% of the cells. We used various interventions to define the molecular relationships between these events and identify potential sites at which these features of apoptosis could be rescued. Treatment with caspase inhibitors prevented DNA fragmentation and promoted myocyte survival; however, cytochrome c release and loss of mitochondrial membrane potential still occurred. In contrast, treatment with bongkrekic acid, an inhibitor of the mitochondrial permeability transition pore, not only prevented DNA fragmentation and reduced nuclear chromatin condensation but also preserved mitochondrial membrane potential and limited cytochrome c redistribution to only approximately 2% of cells. These data demonstrate the central role of mitochondrial membrane potential in initiation of caspase activation and downstream apoptotic events and suggest that preservation of mitochondrial integrity is crucial for prolonging the life and function of cardiomyocytes exposed to pathological levels of stress.

Functional interactions between colony-stimulating factors and the insulin family hormones for human myeloid leukemic cells.

We investigated functional interactions between granulocyte-monocyte-colony-stimulating factor (GM-CSF) and the insulin family hormones using the GM-CSF- and insulin-dependent human acute myeloid leukemia cell line AML-193. Recombinant human GM-CSF and insulin enhanced AML-193 cell proliferation 3- and 5-fold, respectively, and showed a synergistic 10-fold increase when added in combination. Insulin-like growth factors I and II (IGFI and IGFII) increased AML-193 cell proliferation 4-fold and 2-fold, respectively, and also demonstrated synergy when combined with GM-CSF. Blocking experiments with monoclonal antibodies against the insulin and IGFI receptors indicated that the proliferative effects of insulin and IGFI were mediated through both their homologous and heterologous receptors. Pertussis toxin and cholera toxin, which ADP ribosylate GTP-binding proteins (G proteins), and the cyclic AMP analogue, dibutyryl cyclic AMP, decreased the proliferation induced by GM-CSF or insulin. Specific receptor binding of 125I-insulin, -IGFI, and -GM-CSF to AML-193 cells was demonstrated and not affected by preincubation with pertussis toxin or cholera toxin. Radiolabeled GM-CSF, insulin, and IGFI did not cross-compete with the heterologous ligands for receptor binding. These studies demonstrate (a) association between receptor binding and proliferative effects of GM-CSF and the insulin family hormones, (b) involvement of the G proteins in signal transduction provoked by these hormones which occurs at a postreceptor-binding level, and (c) synergistic mitogenic interactions between GM-CSF and the insulin family hormones, suggesting that their receptors are linked to divergent signaling mechanisms in addition to sharing G protein-coupled pathways.

Analysis of tandospirone (SM-3997) interactions with neurotransmitter receptor binding sites.

The interactions of tandospirone (formerly called SM-3997) with 5-HT and other neurotransmitter receptor binding sites were determined in brain homogenates. Tandospirone is most potent at the 5-HT1A receptor, displaying a Ki value of 27 +/- 5 nM. The agent is approximately two to three orders of magnitude less potent at 5-HT2, 5-HT1C, alpha 1-adrenergic, alpha 2-adrenergic, and dopamine D1 and D2 receptors (Ki values ranging from 1300 to 41000 nM). Tandospirone is essentially inactive at 5-HT1B receptors; 5-HT uptake sites; beta-adrenergic, muscarinic cholinergic, and benzodiazepine receptors. This pharmacological profile differs slightly from that of other novel anxiolytics such as buspirone, ipsapirone, and gepirone. Saturation and competition studies using 3H-tandospirone also suggest that the drug interacts with 5-HT1A receptor binding sites in rat cortical membranes (KD = 4.5 +/- 0.8 nM; Bmax = 2.2 +/- 0.6 pmol/g tissue). Based on adenylate cyclase studies which measure 5-HT1A receptor-mediated effects, tandospirone displays approximately 60% of the agonist effect of 8-OH-DPAT, a selective 5-HT1A agonist. Thus, the primary pharmacological effect of tandospirone appears to be partial agonism at the 5-HT1A receptor, an activity similar to other pyrimidinyl-piperazines which are being developed as novel anxiolytic agents.

Antagonism of 5-hydroxytryptamine1A (5-HT1A) receptor-mediated modulation of adenylate cyclase activity by pindolol and propranolol isomers.

The interactions of the stereoisomers of pindolol and propranolol with 5-hydroxytryptamine1A (5-HT1A) binding sites and adenylate cyclase activity were examined in rat hippocampus. (-)Pindolol and (-)propranolol displayed high affinity for 5-HT1A binding sites, and their affinities were not affected significantly by the addition of 10(-4) M GTP to the radioligand assay. The selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) decreased forskolin-stimulated adenylate cyclase activity. The (-)isomers of pindolol and propranolol did not affect basal or forskolin-stimulated activity but, at a concentration of 10(-5) M, they reversed the 8-OH-DPAT inhibition of the forskolin-stimulated cyclase activity. The (+)isomers were less potent in producing this effect. These data suggest that (-)pindolol and (-)propranolol are potent antagonists at 5-HT1A receptors in rat hippocampus.

Inhibition of tumoral cell respiration and growth by nordihydroguaiaretic acid.

The effects of nordihydroguaiaretic acid (NDGA), best known as an inhibitor of lipoxygenase activities, on the culture growth, oxygen consumption, ATP level, viability, and redox state of some electron carriers of intact TA3 and 786A ascites tumor cells have been studied. NDGA inhibited the respiration rate of these two tumor cell lines by preventing electron flow through the respiratory chain. Consequently, ATP levels, cell viability and culture growth rates were decreased. NDGA did not noticeably inhibit electron flow through both cytochrome oxidase and ubiquinone-cytochrome b-c1 complex. Also, the presence of NDGA changed to redox state of NAD(P)+ to a more reduced level, and the redox states of ubiquinone, cytochrome b and cytochromes c + c1 changed to a more oxidized level. These observations suggest that the electron transport in the tumor mitochondria was inhibited by NDGA at the NADH-dehydrogenase-ubiquinone level (energy-conserving site 1). As a consequence, mitochondrial ATP synthesis would be interrupted. This event could be related to the cytotoxic effect of NDGA.

5-Hydroxytryptamine1A receptors are linked to a Gi-adenylate cyclase complex in rat hippocampus.

The ability of 5-hydroxytryptamine (5-HT) and the 5-HT1A selective agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) to modulate adenylate cyclase activity was measured in rat hippocampus. In vitro ADP ribosylation of GTP-binding proteins by pertussis toxin in this tissue abolished both 5-HT- and 8-OH-DPAT-induced inhibition of forskolin-stimulated adenylate cyclase activity. These findings indicate that 5-HT1A receptors are linked a pertussis-sensitive Gi protein in rat hippocampus.

Transcriptional expression patterns triggered by chemically distinct neuroprotective molecules.

Glutamate-mediated excitotoxicity has been purported to underlie many neurodegenerative disorders. A subtype of glutamate receptors, namely N-methyl-d-aspartate (NMDA) receptors, has been recognized as potential targets for neuroprotection. To increase our understanding of the mechanisms that underlie this neuroprotection, we employed a mouse model of glutamate receptor-induced excitotoxic injury. Primary cortical neurons derived from postnatal day-0 CD-1 mice were cultured in the presence or absence of neuroprotective molecules and exposed to NMDA. Following a recovery period, whole genome expression was measured by microarray analysis. We used a combination of database and text mining, as well as systems modeling to identify signatures within the differentially expressed genes. While molecules differed in their mechanisms of action, we found significant overlap in the expression of a core group of genes and pathways. Many of these molecules have clear links to neuronal protection and survival, including ion channels, transporters, as well as signaling pathways including the mitogen-activated protein kinase (MAPK), the Toll-like receptor (TLR), and the hypoxic inducible factor (HIF). Within the TLR pathway, we also discovered a significant enrichment of interferon regulatory factor 7 (IRF7)-regulated genes. Knockdown of Irf7 by RNA interference resulted in reduced survival following NMDA treatment. Given the prominent role that IRF7 plays in the transduction of type-I interferons (IFNs), we also tested whether type-I IFNs alone functioned as neuroprotective agents and found that type-I IFNs were sufficient to promote neuronal survival. Our data suggest that the TLR/IRF7/IFN axis plays a significant role in recovery from glutamate-induced excitotoxicity.

Wolff Award presentation 1993. Anti-migraine drug interactions with cloned human 5-hydroxytryptamine1 receptor subtypes.

Multiple 5-hydroxytryptamine (5-HT) receptors have been identified in humans. A subgroup of these receptors (designated 5-HT1 receptors) have been hypothesized to be involved in the mechanism of action of acute anti-migraine drugs. At present, this hypothesis cannot be tested directly in human tissues due to technical limitations. However, recent molecular biological advances have allowed for the development of assays employing cloned human 5-HT1 receptors expressed in cells by DNA transfection. This study analyzed the ability of ergotamine, dihydroergotamine, and 5-HT and sumatriptan to interact with the four known human 5-HT1 receptor subtypes. The four acute anti-migraine agents interacted with all 4 human 5-HT1 receptor subtypes with less than 1 microM affinity. However, drug affinities for the human 5-HT1B and 5-HT1D receptors correlate most closely with the rank order of clinical dosages used to treat a migraine attack. Therefore, these data indicate that human 5-HT1B and/or 5-HT1D receptors are likely to mediate the therapeutic efficacy of acute anti-migraine drugs.

The third intracellular loop of the 5-hydroxytryptamine2A receptor determines effector coupling specificity.

5-Hydroxytryptamine (5-HT) receptors contain seven putative transmembrane domains and couple via different guanine nucleotide binding proteins to specific effector enzymes. Studies with other receptors identify the second and third intracellular loops or the C-terminus of the receptor as important for selective effector coupling. However, it is not known which regions of the 5-HT receptor determine effector coupling specificity. To address this question, we constructed a chimeric 5-HT receptor in which the third intracellular (i3) loop is derived from the 5-HT2A receptor, which is coupled to activation of phospholipase C, and the rest of the sequence is derived from the 5-HT1B receptor, which is coupled to inhibition of adenylyl cyclase. The chimeric receptor exhibited ligand binding properties similar to those of the 5-HT1B receptor and distinct from those of the 5-HT2A receptor. This suggests that the i3 loop is not critical for the unique pharmacology of the 5-HT1B receptor. In contrast, the chimeric receptor exhibited signaling properties similar to those of the 5-HT2A receptor and distinct from those of the 5-HT1B receptor. This indicates that the i3 loop determines the effector coupling specificity of the 5-HT2A receptor.

Cyclic adenosine 3',5'-monophosphate metabolism in activated T-cell clones.

The role of cAMP in lymphocyte proliferation was investigated in the response of a monoclonal T-cell population to a specific antigen and compared to the response to interleukin-2 (IL-2) and allogeneic cells. Myelin basic protein (MBP)-reactive and encephalitogenic T-cell clones were established from long-term lines derived from SJL/J (H-2s) mice. The clone 4b.14a recognizes the peptide sequence 89-101 of the MBP molecule in association with 1-As products of the major histocompatibility complex (MHC). Incubation of 4b.14a cells with syngeneic antigen-presenting cells, previously pulsed with the 89-101 synthetic peptide or with 80 U/ml of IL-2, or allogeneic H-2Ik cells, resulted in a significant increase in the accumulation of intracellular cAMP. This increase was preceded by a peak in membranal adenylate cyclase (AC) activity. Parallel time kinetics but significantly higher cAMP production and AC activity were observed when the cells were treated with pertussis toxin. At the same concentrations the toxin inhibits cellular proliferative responses, assayed by [3H]thymidine incorporation. Our results indicate the involvement of cAMP as a positive signal in the activation of the 4b.14a clone.

[heparin and insulin treatment of acute pancreatitis caused by hypertriglyceridemia. Experience of 5 cases]. / Heparina e insulina en el tratamiento de la pancreatitis aguda por hipertrigliceridemia. Experiencia en 5 casos.

BACKGROUND: Hypertriglyceridemia over 1,000 mg/dl can provoke acute pancreatitis and its persistence can worsen the clinical outcome. On the contrary, a rapid decrease in triglyceride level is beneficial. Plasmapheresis has been performed in some patients to remove chylomicrons from the circulation, while heparin and/or insulin have been administered in some other cases to rapidly reduce blood triglycerides. Heparin and insulin stimulate lipoprotein-lipase activity and accelerate chylomicron degradation. AIM: To report five patients with acute pancreatitis treated with heparin and insulin. PATIENTS AND METHODS: Five patients (4 females and 1 male) seen in the last two years, who suffered acute pancreatitis induced by hypertriglyceridemia are reported. Initial blood triglyceride levels were above 1,000 mg/dl (range 1,590-8,690 mg/dl). Besides the usual treatment of acute pancreatitis, heparin and/or insulin were administered intravenously in continuous infusion. Heparin dose was guided by usual parameters of blood coagulation, and insulin dose, by serial determinations of blood glucose. Pancreatic necrosis was demonstrated in 4 patients. RESULTS: Serum triglyceride levels decreased to < 500 mg/dl within 3 days in all cases. No complication of treatment was observed and all patients survived. Early and late complications of pancreatitis occurred in one patient. CONCLUSION: Administration of heparin and/or insulin is an efficient alternative to reduce triglyceride levels in patients with acute pancreatitis and hypertriglyceridemia.

A single amino-acid difference confers major pharmacological variation between human and rodent 5-HT1B receptors.

Neuropsychiatric disorders such as anxiety, depression, migraine, vasospasm and epilepsy may involve different subtypes of the 5-hydroxytryptamine (5-HT) receptor. The 1B subtype, which has a unique pharmacology, was first identified in rodent brain. But a similar receptor could not be detected in human brain, suggesting the absence in man of a receptor with equivalent function. Recently a human receptor gene was isolated (designated 5-HT1B receptor, 5-HT1D beta receptor, or S12 receptor) which shares 93% identity of the deduced protein sequence with rodent 5-HT1B receptors. Although this receptor is identical to rodent 5-HT1B receptors in binding to 5-HT, it differs profoundly in binding to many drugs. Here we show that replacement of a single amino acid in the human receptor (threonine at residue 355) with a corresponding asparagine found in rodent 5-HT1B receptors renders the pharmacology of the receptors essentially identical. This demonstrates that the human gene does indeed encode a 1B receptor, which is likely to have the same biological functions as the rodent 5-HT1B receptor. In addition, these findings show that minute sequence differences between homologues of the same receptor from different species can cause large pharmacological variation. Thus, drug-receptor interactions should not be extrapolated from animal to human species without verification.

[Comparison of the efficacy of intraarticular and intraarterial injections of two betamethasone preparations in patients with osteoarthritis or epicondilytis]. / Comparación de la eficacia clínica de una inyección intraarticular o intralesional de dos preparados de betametasona en pacientes con artrosis o epicondilitis.

BACKGROUND: Local infiltration with corticoids is a simple therapy for rheumatic disorders devoid of systemic adverse reactions. AIM: To compare the efficacy of two betametasone preparations from two different pharmaceutical laboratories in the treatment of patients with osteoarthritis or epicondylitis. PATIENTS AND METHODS: Fourty patients with knee osteoarthritis and 12 patients with epicondylitis were studied. Using a double blind protocol, one of the two betametasone preparations was used for local infiltration of the lesions. The change in a global score of clinical variables including pain and disability was assessed after 30 days of the infiltration. RESULTS: In patients with osteoarthritis, the global score decreased significantly with both preparations, but no differences were observed between preparations (7.3 +/- 1.8 to 3.9 +/- 2.3 with preparation A and 7.8 +/- 1.9 to 3.6 +/- 2.3 with preparation B). In patients with epicondylitis, pain was also significantly reduced but no differences between preparations was observed (7 +/- 2.1 to 1.4 +/- 2.5 for preparation A and 4.6 +/- 2.8 to 1.2 +/- 1.6 for preparation B). CONCLUSIONS: Local infiltration with both betametasone preparations was equally effective in the treatment of patients with knee osteoarthritis or epicondilytis.

Small bowel motility in primary biliary cirrhosis.

OBJECTIVE: Previous studies have shown small bowel motor activity abnormalities in patients with liver cirrhosis of different etiologies, but motility has not been studied in patients with primary biliary cirrhosis. Our aim was to investigate proximal small bowel motility in these patients. METHODS: Twenty-five female patients presenting clinical, biochemical, serological, and histological findings compatible with primary biliary cirrhosis, 10 female patients with nonalcoholic liver cirrhosis, and 10 normal female controls were studied. Motility of the upper small bowel was measured in the fasted state by means of perfused manometric catheters, connected to external transducers and positioned in the small bowel under fluoroscopy. RESULTS: The average amplitude of contractions was significantly decreased in patients with primary biliary cirrhosis compared with other liver cirrhosis (20.2+/-1.0 vs 32+/-2.9 mm Hg). Also, a significantly increased frequency of cluster of contractions and an increased duration of phase II of the migrating motor complex as seen in liver cirrhosis was observed when compared with normals. CONCLUSION: We conclude that primary biliary cirrhosis patients present motor abnormalities of the small intestine similar to those of patients with liver cirrhosis of other etiologies. In addition, a decrease in the amplitude of small bowel contractions was also found in these patients, suggesting a myogenic involvement.

Heterocycle-peptide hybrid compounds. Aminotriazole-containing agonists of the thrombin receptor (PAR-1).

The thrombin receptor PAR-1 is activated by alpha-thrombin to stimulate cells, including platelets, through the tethered-ligand sequence SFLLRN. We have discovered a novel series of heterocycle-peptide hybrids comprised of a tripeptide segment, such as Cha-Arg-Phe, and an N-terminal heterocyclic group, many of which behave as full PAR-1 agonists. Certain compounds with an aminotriazole group, such as 4 and 16, are nearly as potent as SFLLRN-NH2 in inducing platelet aggregation. Also, some arylethenoyl "N-capped" compounds, such as 52 and 57, exhibit mixed PAR-1 agonist-antagonist activity.

Thrombin receptor-activating peptides (TRAPs): investigation of bioactive conformations via structure-activity, spectroscopic, and computational studies.

The thrombin receptor (PAR-1) is an unusual transmembrane G-protein coupled receptor in that it is activated by serine protease cleavage of its extracellular N-terminus to expose an agonist peptide ligand, which is tethered to the receptor itself. Synthetic peptides containing the agonist motif, such as SFLLRN for human PAR-1, are capable of causing full receptor activation. We have probed the possible bioactive conformations of thrombin receptor-activating peptides (TRAPs) by systematic introduction of certain conformational perturbations, involving alpha-methyl, ester psi(COO), and reduced-amide psi(CH2N) scans, into the minimum-essential agonist sequence (SFLLR) to probe the importance of the backbone conformation and amide NH hydrogen bonding. We performed extensive conformational searches of representative pentapeptides to derive families of putative bioactive structures. In addition, we employed 1H NMR and circular dichroism (CD) to characterize the conformational disposition of certain pentapeptide analogues experimentally. Activation of platelet aggregation by our pentapeptide analogues afforded a structure-function correlation for PAR-1 agonist activity. This correlation was assisted by PAR-1 receptor binding data, which gauged the affinity of peptide ligands for the thrombin receptor independent of a functional cellular response derived from receptor activation (i.e. a pure molecular recognition event). Series of alanine-, proline-, and N-methyl-scan peptides were also evaluated for comparison. Along with the known structural features for PAR-1 agonist peptides, our work adds to the understanding of peptide topography relative to platelet functional activity and PAR-1 binding. The absolute requirement of a positively charged N-terminus for strong agonist activity was contradicted by the N-terminal hydroxyl peptide psi(HO)S-FLLR-NH2. The amide nitrogen between residues 1 and 2 was found to be a determinant of receptor recognition and the carbonyl groups along the backbone may be involved in hydrogen bonding with the receptor. Position 3 (P3) of TRAP-5 is known to tolerate a wide variety of side chains, but we also found that the amide nitrogen at this position can be substituted by an oxygen, as in SF-psi(COO)-LLR-NH2, without diminishing activity. However, this peptide bond is sensitive to conformational changes in that SFPLR-NH2 was active, whereas SF-NMeL-LR-NH2 was not. Additionally, we found that position 3 does not tolerate rigid spacers, such as 3-aminocyclohexane-1-carboxylic acid and 2-aminocycloalkane-1-carboxylic acid, as analogues 1A, 1B, 2A, 2B, 3, 4, 5A and 5B lack agonist activity. On the basis of our results, we suggest that an extended structure of the agonist peptide is principally responsible for receptor recognition (i.e. binding) and that hydrophobic contact may occur between the side chains of the second (Phe) and fourth (Leu) residues (i.e. P2-P4 interaction).