Central dopaminergic system plays a role in the analgesic action of paracetamol: Preclinical evidence

Objective:

Even after 100 years of discovery, the exact mechanisms for the analgesic action of paracetamol are under scanner. It was recently proposed that paracetamol may act through different mechanisms, especially altering the serotoninergic system. The main objective of this preclinical study was to verify the role of drugs modulating dopaminergic system (l-dopa, bromocriptine, olanzapine) on the analgesic effect of paracetamol.

Materials and Methods:

Thirty adult male albino mice were divided into five groups: distilled water (0.5 ml/25 g), paracetamol (200 mg/kg), levodopa (10 mg/kg) + paracetamol, bromocriptine (5 mg/kg) + paracetamol (200 mg/kg), and olanzapine (2 mg/kg) + paracetamol (200 mg/kg). All drugs were administered orally for 14 days. Eddy's hot plate and tail immersion tests were used to determine analgesic activity. Tests were conducted 1 h after the drug administration on the 14^th day. After that, animals were sacrificed and brains were dissected out, to measure the levels of dopamine. Statistical comparisons among the groups were performed by one-way analysis of variance followed by Tukey-Kramer test.

Results:

Coadministration of l-dopa and bromocriptine with paracetamol increased the antinociceptive activity of paracetamol significantly, whereas coadministration of olanzapine with paracetamol decreased the analgesic activity of paracetamol in the Eddy's hot plate and tail immersion tests considerably. There was a significant increase (P < 0.001) in the levels of dopamine in the brains of mice, which received levodopa, bromocriptine, and paracetamol. However, it was opposite in the brains of animals which received olanzapine.

Conclusion:

The results suggest that analgesic action of paracetamol is influenced by dopaminergic system.

Evaluation of the efficacy of 2% curcumin gel in the treatment of experimental periodontitis

CONTEXT

Local drug delivery (LDD) systems have been proposed for the treatment of periodontitis. Curcumin could be a suitable agent as LDD for the treatment of periodontitis.

AIM

To formulate, evaluate the anti-inflammatory activity and to assess the duration of the action and the efficacy of 2% curcumin gel in the treatment of experimental periodontitis in Wistar albino rat model.

SETTINGS AND DESIGN

Twenty-one Wistar albino rats were randomly assigned to three groups. Periodontitis was induced using ligature model. Group 1: Control; group 2: Plain gel, and group 3: 2% curcumin gel.

MATERIALS AND METHODS

About 2% curcumin gel was prepared. The anti-inflammatory activity and duration of action was assessed. Silk ligature 5-0 was used to induce periodontitis. Gingival index (GI) and probing pocket depth (PPD) were measured. Treatment was done. The rats were sacrificed. Morphometric analysis was performed using stereomicroscope and ImageJ software.

STATISTICAL ANALYSIS USED

Analysis of variance followed by Bonferroni's test, Wilcoxon's test for inter-group comparison, Mann-Whitney test for P value computation was used. The observations are mean ± standard deviation and standard error of the mean. P < 0.01 when compared to control was considered as statistically significant.

RESULTS

About 2% curcumin gel showed 42.98% inhibition of edema and peak activity was noted at 24 h. There was statistically significant change in the GI and PPD. Morphometric analysis did not show any significant difference between groups. No toxic effects were seen on oral administration of 2000 mg/kg of curcumin.

CONCLUSIONS

About 2% curcumin gel was effective in the treatment of experimental periodontitis.

Preclinical screening of phyllanthus amarus ethanolic extract for its analgesic and antimicrobial activity

BACKGROUND

To discover a new agent which possesses dual property of analgesic and antimicrobial activity, thereby reducing the burden of polypharmacy. Phyllanthus amarus was screened for its analgesic and antimicrobial activities.

OBJECTIVES

The objective was to evaluate the analgesic and antimicrobial activity, of P. amarus ethanolic extract (PAEE).

MATERIALS AND METHODS

The ethanolic extract of P. amarus was prepared using Soxhlet apparatus. An in vivo study using Swiss albino mice was done to screen the central and peripheral analgesic activity of P. amarus extract. The extract was administered at a dose of 100 mg/kg body weight orally. The peripheral analgesic activity was assessed using acetic acid induced writhing test. The central analgesic activity was assessed using Eddy's hot plate apparatus. An in vitro study was carried out to study the antimicrobial activity of the above extract using selected species of Streptococcus mutans, and S. salivarius. The antimicrobial activities were determined using the agar well method.

RESULTS

The ethanolic extract of P. amarus showed significant (P < 0.05) peripheral and central analgesic activity. In vitro antimicrobial screening indicated that the ethanolic extract had shown a zone of inhibition against S. mutans and S. salivarius in the agar wells.

CONCLUSION

This study showed that PAEE exhibited significant analgesic and antimicrobial activities.

A case of organophosphate poisoning presenting with seizure and unavailable history of parenteral suicide attempt

Organophosphate (OP) poisoning is common in India. Only few case reports of parenteral OP poisoning have been described. We report a case of self-injected methyl parathion poisoning, presenting after four days with seizure, altered sensorium, and respiratory distress which posed a diagnostic and therapeutic dilemma. Despite nonavailability of history of OP poisoning, he was treated based on suspicion and showed a good clinical response to treatment trial with atropine and pralidoxime, and had a successful recovery. Atypical presentations may be encountered following parenteral administration of OP poison, and even a slight suspicion of this warrants proper investigations and treatment for a favorable outcome. Persistently low plasma cholinesterase level is a useful marker for making the diagnosis.

Is povidone-iodine a hemostyptic? A clinical study

Povidone-iodine (PVP-I) is an antiseptic agent commonly used on intact skin in preparation for surgery and on open wounds. In oral surgery it is used for irrigating alveolar sockets following extraction. The present authors found by chance that irrigation of extraction sockets with povidone-iodine led to cessation of bleeding in patients without recurrence. Fifty patients were selected and divided equally into treatment and control groups. Povidone-iodine (1%, w/v) was used for irrigation of extraction sockets in the treatment group and saline was used in the control group. In the treatment group, 19 patients showed cessation of bleeding compared to only 5 in the control group. Povidone-iodine significantly (P<0.01) controlled bleeding as compared to saline. Iodine is corrosive due to its oxidizing potential while povidone is a thickening and granulating agent; together they may have a chemocauterizing effect that could be the reason for the cessation of bleeding. These results suggest that povidone-iodine may act as a hemostyptic as well as an antiseptic.

Guillain-Barré syndrome-like presentation in borderline leprosy with type-2 reaction

A 46-year-old man with borderline lepromatous leprosy with type-2 reaction being treated with multi-bacilliary-multiple drug therapy and steroids presented with an acute onset of flaccid quadriparesis. A nerve conduction study and CSF analysis were similar to that seen in Guillain Barre syndrome. Muscle weakness improved considerably with an increased dose of corticosteroid; after 6 months the patient recovered completely.

Co-existence of lepromatous leprosy and myasthenia gravis

Various circulating autoantibodies are known to occur commonly in patients with lepromatous leprosy. However, the association with autoimmune diseases has rarely been reported. One such association of lepromatous leprosy with myasthenia gravis is being reported.

Prediction of organophosphorus acetylcholinesterase inhibition using three-dimensional quantitative structure-activity relationship (3D-QSAR) methods

Neurotoxic organophosphorous compounds are known to modulate their biological effects through the inhibition of a number of esterases including acetylcholinesterase (AChE), the enzyme responsible for the degradation of the neurotransmitter acetylcholine. In this light, molecular modeling studies were performed on a collection of organophosphorous acetylcholinesterase inhibitors by the combined use of conformational analysis and 3D-QSAR methods to rationalize their inhibitory potencies against the enzyme. The Catalyst program was used to identify the structural features in the group of 8 inhibitors whose IC(50) values ranged from 0.34 nM to 1.2 microM. The 3-D pharmacophore models are characterized by at least one hydrogen bond acceptor site and 2-3 hydrophobic sites and demonstrate very good correlation between the predicted and experimental IC(50) values. Our models can be useful in screening databases of organophosphorous compounds for their neurotoxicity potential via the inhibition of acetylcholinesterase. Also, the pharmacophores offer an additional means of designing AChE inhibitors as potential therapeutic agents for central nervous system diseases.

A reconnaissance of 'traffic noise pollution in the city of Patna'

The noise generated from traffic is a major source of environmental pollution, which is substantiated by the results of continuous monitoring of equivalent noise levels (Leq) at a number of sensitive, residential, commercial and industrial areas during day and night in 1999. The existing noise pollution status of Patna urban environment with emphasis on objective measurement is reported. The data were compared with the published data of other towns and cities and the possible factors responsible for change in the noise levels are discussed.

N-Methyl-N-(1-phenylsulfonylindol-2-ylmethyl)aniline

In the title compound, 2-[(methylphenylamino)methyl]-1-(phenylsulfonyl)indole, C22H20N2O2S, the indole system is not strictly planar and the dihedral angle between the fused rings is 2.7 (1) degrees. The angles around the S atom of the sulfonyl substituent deviate significantly from the ideal value for tetrahedral geometry. The pyramidalization at the indole N atom is very small. Of the two C-H...O interactions, one influences the orientation of indole with respect to the sulfonyl group and the other determines the orientation of the phenyl bound to sulfonyl. The phenyl ring of the sulfonyl substituent makes a dihedral angle of 89.6 (1) degrees with the best plane of the indole. The molecular packing is stabilized by C-H...pi and C-H...O hydrogen bonds.

Elimination of cross-talk and modulation of function in an organized heterosupramolecular assembly

A close-packed monolayer of TiO2 nanocrystals was deposited on a conducting glass support using Langmuir-Blodgett (LB) techniques and fired. A close-packed mixed monolayer of eicosyl phosphonic acid (I) and the viologen. 1,1'-dieicosyl-4,4'-bipyridinium dichloride (II) was then deposited on the TiO2 substrate, also using LB techniques. At sufficiently high dilutions of II in II a single viologen molecule is adsorbed with a known orientation at the surface of each nanocrystal. The resulting assembly was incorporated as the working electrode in an electrochemical cell. Under open circuit conditions, bandgap excitation of a TiO2 nanocrystal results in electron transfer to a viologen molecule. No electron transfer between the viologen molecules adsorbed at different nanocrystals is observed. At a positive applied potential, electron transfer following bandgap excitation is largely suppressed. Considered are the implications of these findings for the development of practical devices based on modulatable function addressable on the nanometer scale.

Mutations in the alpha-synuclein gene in Parkinson's disease among Indians

OBJECTIVE

To investigate the prevalence of G88C, G209A and any other mutation(s) in exons 3 and 4 of the alpha-synuclein gene in Indian patients with Parkinson's disease (PD).

METHODS

A total of 169 PD patients comprising 18 familial, 3 juvenile, 48 early onset and 100 sporadic cases were included in this study. Genomic DNA was amplified by PCR using primers specific for Exons 3 and 4. Mutations at G88C and G209A were screened following restriction enzyme digestion of the PCR product. Direct PCR product sequencing of entire exons 3 and 4 was carried out for at least one proband each from the 10 familial cases.

RESULTS

Neither G88C and G209A mutations nor any other mutation in exons 3 and 4 was found in the PD patients analysed.

CONCLUSION

The G88C and G209A mutations do not seem to be the predominant genetic determinant of PD among Indians.

Local anaesthetic for minor oral surgical procedures. Review

Pain following any surgical procedure is difficult to combat by man. Analgesics can be given for some amount of symptomatic relief. The need for a long lasting local anaesthetic is with the intention to reduce the most severe nature of pain, and decrease the analgesic consumption. This study was conducted to compare the efficacy of, Bupivacaine over Lidocaine for minor oral surgical procedures. The popularly used lidocaine works for 3 to 3.9 hours. This is not sufficient since the most severe nature of pain is felt six to eight hours post surgery, where as Bupivacaine has duration of action of seven to eight hours. Hence the post operative pain experienced following administration of bupivacaine was found to be considerably lesser in degree than compared to the lidocaine group. To avoid severe pain and discomfort to the patient following any minor oral surgical, the use of bupivacaine is recommended.

A new nomenclature for oral and maxillofacial surgery that is facial and oral surgery

To assess whether majority of the public and medical professionals do understand the field Oral & Maxillo-Facial Surgery. To find this, a questionnaire was devised based on P. Ammerally et al. 200 members of the public with educated background and 100 general medical practitioners participated in this study. The results revealed that majority of the public needed more information on the field where as the General medical practitioners were aware, but lacked information about the majority of activity in the field.

The effectiveness of a topical antibiotic irrigating solution in a model of staphylococcal keratitis after lamellar keratectomy

PURPOSE

To create a model of Staphylococcus aureus keratitis after lamellar keratectomy; to assess the toxicity of an antibiotic irrigating solution on the corneal stromal bed; and to test the chemotherapeutic effectiveness of a topical antibiotic, both alone and with an antibiotic-containing irrigating solution in preventing S. aureus keratitis after lamellar keratectomy.

METHODS

The right eye of each of 38 rabbits were used in this study. In 18 eyes, a lamellar flap was created with a microkeratome, and an inoculum of S. aureus (either 1,000, 5,000, or 50,000 CFUs) was instilled under each flap; the eyes were examined for signs of infection and inflammation at 24 and 48 hours. In another five eyes, a lamellar flap was created in the same manner and the stromal bed was irrigated with 0.3% ofloxacin; the eyes were assessed for ocular inflammatory changes and evidence of crystalline deposits. Finally, in each of 15 additional eyes, 1,000 CFUs of S. aureus were instilled under a lamellar flap to create experimental infectious keratitis. The keratitis was treated according to three regimens: irrigation of the stromal bed with sterile balanced salt solution; irrigation of the stromal bed with 0.3% ofloxacin, followed by application of topical ofloxacin four times a day; application of topical ofloxacin only, four times a day. Eyes were examined for infection and ocular inflammatory changes at 24 and 48 hours.

RESULTS

Staphylococcus aureus keratitis can consistently be produced under the stromal flap by inoculation of relatively few organisms. Irrigation of the stromal bed with commercial-strength topical ofloxacin does not appear to be toxic to the stromal bed, with no evidence of crystalline precipitates of the antibiotic. In our model of infectious keratitis after lamellar keratectomy, both topical ofloxacin alone and the combination of topical ofloxacin and irrigation of the stromal bed with 0.3% ofloxacin were effective at preventing S. aureus keratitis. However, the combined treatment of antibiotic irrigation plus topical antibiotic was more effective at preventing inflammation than topical ofloxacin alone.

CONCLUSIONS

In this model of S. aureus keratitis after lamellar keratectomy, irrigation of the stromal bed with antibiotic plus topical antibiotic appears to be both safe and effective for preventing infection.

Effect of age on the refractive outcome of myopic photorefractive keratectomy

PURPOSE

To evaluate the effect of age on the outcome of myopic photorefractive keratectomy (PRK).

SETTING

University-based refractive surgery practice.

METHODS

A retrospective analysis of 197 eyes that had PRK for myopia was performed. Four groups of patients were compared: Group 1, patients < 30 years (n=35); Group 2, patients 31 to 40 years (n=56); Group 3, patients 41 to 50 year s (n=47); Group 4, patients > 50 years (n=59). The percentage of eyes with an uncorrected visual acuity of 20/20 or better and 20/40 or better and the percentage of eyes with spherical correction within +/-0.5 and +/-1.0 diopter (D) of the attempted correction were derived for each age group. The percentage of patients overcorrected and undercorrected by 1.0 D or more in each age group was also calculated. The difference between the percentage of patients who achieved a visual acuity of 20/20 or better in Group 4 and in the younger groups was statistically significant at 3 months (P =.02) but not at 6 months (P =.70) and 12 months (P =.55). The difference between the percentage of patients who achieved an acuity of 20/40 or better was not significant at any time. The difference between the percentage of patients who were within +/-0.5 D of intended correction in Group 4 and in the younger groups was statistically significant at 3 months (P =.001), 6 months (P =.006), and 12 months (P =.008); the difference between the percentage of patients who were within +/-1.0 D of intended correction was not significant at any time. The difference between the percentage of patients overcorrected and undercorrected by 1.0 D or more in Group 4 and in the younger groups was not significant at any time. In the 3 younger groups, age did not significantly affect visual outcome or predictability. However, there was a significant difference between Group 4 and the 3 younger groups in predictability of the refractive outcome at 3, 6, and 12 months. Age may play a role in the outcome of refractive surgery.

Errors in the treatment of tuberculosis in Baltimore

BACKGROUND

Incomplete or incorrect antibiotic therapy, especially in the initial phase of antituberculosis (anti-TB) treatment, is a major cause of acquired drug resistance and treatment failure. We determined the extent of errors in anti-TB treatment regimens by way of nonadherence to recommended treatment protocols among patients with TB in Baltimore, MD, a city with declining rates of disease. An error was defined as using too few drugs or the wrong drugs, giving inadequate doses of drugs, or prescribing an inadequate duration of treatment.

METHODS

We reviewed the records of all patients with culture-positive, pulmonary TB reported in the city of Baltimore from January 1, 1994, to December 31, 1995. We determined demographic information, initial anti-TB regimen, doses and duration of therapy, history or presence of resistance to anti-TB drugs, injecting-drug or alcohol abuse, HIV status, and whether treatment was given by a private physician or by the Tuberculosis Clinic of the Baltimore City Health Department (BCHD).

RESULTS

Of the 110 cases of active pulmonary TB, 17 cases (15.4%) had errors in treatment for control of their current disease. Thirteen of 34 privately treated patients (38%) had some error in their initial anti-TB regimen, compared with 4 of 76 patients (5.2%) treated by the Tuberculosis Clinic of the BCHD (p < 0.0001). Patients were otherwise similar as determined by age, sex, HIV status, drug-resistance characteristics, and injecting-drug use, regardless of whether they had erroneous anti-TB regimens.

CONCLUSION

In a low-prevalence area, private physicians make frequent errors in prescribing anti-TB therapy. Additional educational resources for physicians and increased use of expert consultation may contribute to improved TB control.

Effect of dietary fish on antioxidant parameters of normal and cholesterol stressed rats

Feeding fish (Sardinella longiceps) to normal rats increased lipid peroxidation and total and Se-dependent glutathione peroxidase (GSH-px) activity in erythrocytes and manganese dependent superoxide dismutase (Mn-SOD) activity in liver. Feeding fish to cholesterol stressed rats showed a significant increase in the activity of GSH-px and cholesterol feeding alone, resulted in a significant increase in the lipid peroxidation and liver Mn-SOD activity. The results suggest that the high polyunsaturated fatty acid content of S. longiceps, the fish abundantly available in the west coast of India, does not have any deleterious effect by way of free radical generation. The observed lipid peroxidation is not critical as is evident from the results of glutathione level and other scavenging enzymes.

DDT and HCH residues in dairy milk samples collected from different geographical regions of India: a multicentre study

Under a multicentre study conducted by the Indian Council of Medical Research, 2205 samples of dairy milk were collected from rural and urban areas of 12 states representing different geographical regions of India. These samples were analysed for residues of DDT and different isomers of HCH by gas-liquid chromatography. Analytical quality assurance between various participating laboratories was ensured through analysis of check samples. The residues of DDT and HCH were detected in more than 80% of samples analysed. Concentrations of DDT residues, alpha-HCH, beta-HCH, gamma-HCH and delta-HCH exceeded their maximum residue limits prescribed by the Ministry of Health and Family Welfare of the Indian Government in 37, 21, 42, 28 and 4% of the samples, respectively. Median values of DDT and HCH found in dairy milk in India were more than the corresponding values reported from most other countries. The results showed significant variations in the incidence as well as level of these contaminants in dairy milk from different regions of the country.

Molecular mechanics studies on the conformations of 2',3'-dideoxy-2',3'-didehydroguanine nucleoside, D4G

Conformational energy calculations have been presented on guanine nucleoside in which the furanose ring is replaced by 2',3'-dideoxy-2',3'-didehydrofuran using molecular mechanics and conformational analysis. Conformational energies have been evaluated using the MM2 and AMBER94 force field parameters at two different dielectric constants. The results are presented in terms of isoenergy contours in the conformational space of the glycosidic (chi) and C4'-C5' (gamma) bonds torsions. In general, the chi-gamma interrelationships differ from the corresponding plots for unmodified nucleosides and nucleotides, reported previously. Consistency of the calculated preferred conformations with the x-ray data is sensitive to the force field employed.

Functional homodimeric glycoprotein hormones: implications for hormone action and evolution

BACKGROUND

Human chorionic gonadotropin (hCG), lutropin, follitropin, and thyrotropin act as alpha beta heterodimers to control reproduction and thyroid function. The alpha and beta subunits of these proteins are divided into three loops (alpha 1,alpha 2,alpha 3; beta 1,beta 2,beta 3) by cysteine knots and the heterodimer is stabilized by 20 beta-subunit residues wrapped around alpha 2 like a seatbelt. Understanding how these hormones interact with their receptors, a matter of considerable dispute, would facilitate design of pro- and anti-fertility agents.

RESULTS

By swapping alpha 2 for beta 2 and vice versa and, in some cases, adding an amino-terminal coiled-coil dimerization domain, we prepared homodimeric analogs that have the conformation found in each 'half' of hCG. Homodimers containing loops beta 1,alpha 2,beta 3 and none, part, or all of the seatbelt stimulated signal transduction to the same extent as hCG, albeit with lower potency. Those containing alpha 1,beta 2,alpha 3 were inactive.

CONCLUSIONS

The activities of homodimers containing the beta 1,alpha 2,beta 3 groove exceed those of other minimized analogs more than 100-1000-fold, suggesting this portion of the hormone forms the major receptor contact. The discovery that glycoprotein hormone heterodimers can be converted to functional homodimers supports the proposal that this protein family evolved from an active homodimeric ancestor by gene duplication and acquisition of mutations to loop 2 that prevent homodimerization. This approach to protein minimization should be applicable to other proteins composed of architecturally related subunits, including those that might have arisen by gene duplication.

Multiphasic disseminated encephalomyelitis

A forty five year old patient developed a chronic relapsing and remitting disease after receiving fourteen injections of beta propionalactone inactivated sheep brain vaccine. We offer evidence to support the view that this case is an illustration ofmultiphasic disseminated encephalomyelitis rather than multiple sclerosis.

Molecular mechanics studies on dipeptide models of diphenylalanine and its derivatives

As a part of our studies on the structure and conformations of peptidomimetics, we present conformational energy calculations on model peptides with (a) diphenyl alanine and its tricyclic derivatives and (b) triphenyl alanine residues using molecular mechanics and conformational analysis methods. The energies are calculated as a function of the backbone torsions (phi and psi), and the results are presented in terms of isoenergy contours in the phi-psi space. The low-energy models adopt conformations characteristic of a variety of regular structures such as the alpha-helix, gamma-turn and polyproline-II-type three- and four-fold helices. The conformational preferences in the model peptides with diphenyl alanine and its tricyclic derivatives are sensitive to the side-chain torsion, with some similarities to the corresponding preferences of L-Ala dipeptide. The energy profile of the model peptide with triphenyl alanine is similar to that of the model peptide with Tle (tert-leucine) residue. The results of our studies have implications in the design of conformationally constrained peptidomimetics with structures in the beta- and alpha-helical regions.

Circulating immune complexes in intracranial neoplasms

The levels of circulating immune complexes (CIC) were assayed in the sera of 109 patients with intracranial space occupying lesions. The CIC levels were significantly increased in all the brain tumours. After treatment, the CIC levels were still significantly increased when compared to the controls but showed no change when compared to their respective pre-operative values. Further, no change was observed in the CIC levels between the malignant and benign tumour case. Moreover, in brain tumours, 90% of the CIC precipitate consisted of IgG. However, the CIC levels fail to prognosticate the process of the disease in these patients.

Model of human chorionic gonadotropin and lutropin receptor interaction that explains signal transduction of the glycoprotein hormones

The goal of these studies was to devise a model that explains how human chorionic gonadotropin (hCG) interacts with lutropin (LH) receptors to elicit a hormone signal. Here we show that alpha-subunit residues near the N terminus, the exposed surface of the cysteine knot, and portions of the first and third loops most distant from the beta-subunit interface were recognized by antibodies that bound to hCG-receptor complexes. These observations were combined with similar data obtained for the beta-subunit (Cosowsky, L., Rao, S.N.V., Macdonald, G.J., Papkoff, H., Campbell, R.K., and Moyle, W.R. (1995) J. Biol. Chem. 270, 20011-20019), information on residues of hCG that can be changed without disrupting hormone function, the crystal structure of deglycosylated hCG, and the crystal structure of a leucine-repeat protein to devise a model of hCG-receptor interaction. This model suggest that the extracellular domain of the LH receptor is "U-" or "J"-shaped and makes several contacts with the transmembrane domain. High affinity hormone binding results from interactions between residues in the curved portion of the extracellular domain of the receptor and the groove in the hormone formed by the apposition of the second alpha-subunit loop and the first and third beta-subunit loops. Most of the remainder of the hormone is found in the large space between the arms of the extracellular domain and makes few, if any, additional specific contacts with the receptor needed for high affinity binding. Signal transduction is caused by steric or other influences of the hormone on the distance between the arms of the extracellular domain, an effect augmented by the oligosaccharides. Because the extracellular domain is coupled at multiple sites to the transmembrane domain, the change in conformation of the extracellular domain is relayed to the transmembrane domain and subsequently to the cytoplasmic surface of the plasma membrane. While the model does not require the hormone to contact the transmembrane domain to initiate signal transduction, small portions of both subunits may be near the transmembrane domain and assist in initiating the hormonal signal. This is the first model that is consistent with all known information on the activity of the gonadotropins including the amounts of the hormone that are exposed in the hormone-receptor complex, the apparent lack of specific contacts between much of the hormone and the receptor, and the roles of the oligosaccharides in signal transduction.(ABSTRACT TRUNCATED AT 400 WORDS)

The groove between the alpha- and beta-subunits of hormones with lutropin (LH) activity appears to contact the LH receptor, and its conformation is changed during hormone binding

Gonadotropins are heterodimeric glycoprotein hormones that control vertebrate fertility through their actions on gonadal lutropin (luteinizing hormone, LH) and follitropin (follicle-stimulating hormone, FSH) receptors. The beta-subunits of these hormones control receptor binding specificity; however, the region of the beta-subunit that contacts the receptor has not been identified. By a process of elimination we show this contact to be the portions of beta-subunit loops one and three found in a hormone groove created by the juxtaposition of the alpha- and beta-subunits. Most other regions of the beta-subunit can be recognized by antibodies that bind to human chorionic hormone (hCG)-receptor complexes or replaced without disrupting hormone function. Using a series of bovine LH/hCG and human FSH/hCG beta-subunit chimeras we identified key hCG beta-subunit residues in the epitopes of two antibodies that bind to hCG-receptor complexes. These epitopes include the surfaces of beta-subunit loops one and three near residue 74 on the outside of the hormone groove and parts of the C-terminal end of the "seat belt" that holds the two subunits together. The antibody that recognized residue 74 bound to receptor complexes containing most mammalian lutropins better than to the free hormones, an indication that the outside surface of the beta-subunit groove is altered during hormone binding. This region of the beta-subunit is furthest from the alpha-subunit and is recognized equally well in the free beta-subunit and in the heterodimer. Thus, the receptor associated increase in antibody binding appears due to an interaction of this portion of the beta-subunit with the receptor and not to an effect of the receptor on the relative positions of the alpha- and beta-subunits. Unlike most previous studies designed to identify portions of the beta-subunit likely to contact the LH receptor, this indirect approach provides data that are more easily interpreted because it does not rely on the use of mutations that disrupt hormone function. The approach described here should be valuable for studying the receptor interactions of other complex ligands.

Thymomatous myasthenia gravis

Ten cases of thymoma associated myasthenia were seen in the last 7 years. They constitute 17.2% of all cases of Myasthenia gravis seen during the same period. Five of these patients presented in the third decade, all of them presenting with acute generalised Myasthenia (Osserman stage-III). Two patients presented with tumour related symptoms of chest pain, cough and dyspnea both of them having large, invasive and partially resectable tumours. Five patients underwent complete thymectomy and 3 patients underwent partial resection of tumour. Two patients underwent radiotherapy subsequently. Histologically, mixed lymphoepithelial tumours were common (70%). Tumour recurrence was seen in one patient. Two patients died, one in the post operative period. The surviving 8 patients followed up over 1-8 years remained in partial remission, on maintenance dose of steroids. The special problems related to thymomatous MG and practical approach to management are highlighted.

Conformational studies on model peptides with 1-aminocyclobutane 1-carboxylic acid residues

Conformationally constrained peptidomimetics are being increasingly used in the development of 3-D pharmacophores of peptide-based drug candidates and to alter their metabolic stability towards achievements of oral bioavailability. Here we present conformational energy calculations on model compounds containing 1-aminocyclobutane carboxylic acid (ACBC) and its derivatives using molecular mechanics methods. The low-energy models adopt conformations characteristic of a variety of regular structures such as the alpha-helix, 3(10)-helix, gamma-turn and polyproline-II-type three- and fourfold helices. The energetically most favored models adopt the gamma-turn (2.2(7) helix) conformation or alpha-/3(10)-helical conformation, both of either handedness, depending on the substituents on the cyclobutane. These results are qualitatively consistent with the crystal structures of peptide analogs containing ACBC and have implications for the design of peptidomimetics.

Conformational studies on model dipeptides of Gly, L-Ala and their C alpha-substituted analogs

As a part of the development of conformational guidelines for the design of metabolically altered peptidomimetics, we present conformational energy calculations on model dipeptide compounds with glycine (Gly), L-alanine (Ala), alpha-aminoisobutyric acid (Aib), L-tert-butylglycine (Tle), L-phenylglycine (Phg), (alpha, alpha)-diphenylglycine (D phi g), L-2-aminobutyric acid (Abu), 2-amino-2-ethylbutyric acid (Deg), L-2-amino-2-vinylacetic acid (Ava) and (alpha, alpha)-divinylglycine (Dvg). The energy calculations have been made using molecular mechanics methods with a force field derived from MM2. The salient features are expressed in terms of conformational energy plots, drawn as a function of the backbone torsion angles phi(Ci'-1-Ni-Ci alpha i-Ci') and psi(Ni-Ci alpha -C'-N(i+1)). The low-energy structures of these compounds are qualitatively consistent with the X-ray crystal structure analyses of peptides and peptidomimetics. They are also in agreement with the results of the solution-phase studies carried out by NMR and IR techniques. The results obtained have important implications in the design of conformationally restricted peptidomimetics.