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Biomedical subjects

R Sivakumar

Publications and source records attributed to R Sivakumar.

At least 19 recordsLinked to original sources
PubMed2002

Indoor gamma dose measurements in Gudalore (India) using TLD.

Indoor gamma radiation dose rates were measured inside residential buildings in Gudalore using a CaSO4:Dy thermoluminescent dosimeter for 1 year. Significant seasonal variations are observed. The highest dose rate is observed during summer and the lowest in winter. The dose rates observed are between 77.9 and 229.3 nGy h(-1) and may be attributed to the type of building materials used in the dwellings monitored. The calculated mean annual effective dose equivalent rates range between 477.6 microSv y(-1), for the inhabitants of mud houses to 1406.3 microSv y(-1), for those living in terrace houses made of cement and brick.

Air Pollution, Indoor↗
PubMed2001

Identification of a new class of molecules, the arachidonyl amino acids, and characterization of one member that inhibits pain.

In mammals, specific lipids and amino acids serve as crucial signaling molecules. In bacteria, conjugates of lipids and amino acids (referred to as lipoamino acids) have been identified and found to possess biological activity. Here, we report that mammals also produce lipoamino acids, specifically the arachidonyl amino acids. We show that the conjugate of arachidonic acid and glycine (N-arachidonylglycine (NAGly)) is present in bovine and rat brain as well as other tissues and that it suppresses tonic inflammatory pain. The biosynthesis of NAGly and its degradation by the enzyme fatty acid amide hydrolase can be observed in rat brain tissue. In addition to NAGly, bovine brain produces at least two other arachidonyl amino acids: N-arachidonyl gamma-aminobutyric acid (NAGABA) and N-arachidonylalanine. Like NAGly, NAGABA inhibits pain. These findings open the door to the identification of other members of this new class of biomolecules, which may be integral to pain regulation and a variety of functions in mammals.

Alanine↗
PubMed2001

Nested polymerase chain reaction in the diagnosis of congenital cytomegalovirus infection.

OBJECTIVE: Human cytomegalovirus infection is highly prevalent in Indian population. It is the commonest congenitally acquired infection causing various anomalies. The diagnosis of infection in neonates is difficult as IgM may not be detected in all cases. The polymerase chain reaction is reported as alternative and better option in these patients. However, there is lack of data to substantiate this preference in a resource poor country like India. METHODS: Blood samples from 930 neonates/fetuses were first tested for specific anti-CMV IgM antibodies using mu-capture enzyme linked immunosorbent assay, Mac-ELISA. Nested PCR was first standardised on clinically and therapeutically confirmed cases of CMV disease. In the second phase blood samples randomly from 20 babies suspected of CMV infection were collected for serology and PCR and both tests were run independently. Twenty healthy controls were also included. IgM ELISA and PCR were performed on these samples and results of these 20 samples were compared to evaluate the sensitivity and specificity of each method. RESULTS: Out of 930 serum samples of suspected congenital CMV infection 188 (20.2%) were found positive for CMV specific IgM antibodies. While comparing the results of 40 paired samples, PCR was found to be highly specific (100%) but less sensitive than Mac-ELISA (95%) with negative predictive value of 100% and positive predictive value of 95%. Thus in congenital CMV infection Mac-ELISA was less costly, less cumbersome and more user friendly. CONCLUSION: The Mac-ELISA seem to have parallel sensitivity and specificity as PCR for diagnosing congenital CMV infection.

Case-Control Studies↗
PubMed2001

A quantitative structure-activity relationship study on some HIV-1 protease inhibitors using molecular connectivity index.

A quantitative structure-activity relationship (QSAR) study has been made on two different series of tetrahydropyrimidinones acting as HIV-1 protease inhibitors. A structural parameter, the first order valence molecular connectivity index ((1)chi(v)), has been used to account for the variation in the activity. The protease inhibition activity as well as the antiviral potency of the compounds are found to be significantly correlated with (1)chi(v) of P(2)/P(2') substituents attached to the two nitrogens N1 and N3, suggesting that substituents containing less electronegative and more saturated atoms, meaning thereby the less polar or more hydrophobic substituents, will be more advantageous. Further, if P(2) and P(2') are dissimilar, the former is found to be more effective than the latter. This difference is attributed to a conformational change in the enzyme that may be more favorable to P(2) binding than to P(2') binding.

Anti-HIV Agents↗
PubMed2001

Quantitative structure-activity relationship of some HIV-1 protease inhibitors: a Fujita-Ban type analysis.

A Fujita-Ban type analysis has been made on a few series of HIV-1 (human immunodeficiency virus of type 1) protease inhibitors and the activity contributions of various substituents obtained. From these activity contributions, a compound is predicted that may have better activity than ritonavir, presently prescribed for the treatment of patients suffering from HIV-1. A few other compounds are also suggested.

Animals↗
PubMed2001

Evaluation of the sharpness of concentric needle electrodes by a penetration test.

This paper deals with a method to evaluate the sharpness of the concentric needle electrode (CNE) and the consistency of sharpness on repeated penetration. An aluminum foil of standard thickness and properties was used as the penetration medium. A load profile was obtained as a function of time, and has been correlated with the shape and quality of grinding of the tip of the CNE. This load profile can be used as a quality evaluation method. This method is utilized for the assessment of the impairment of the needle tip on repeated penetration and hence for comparison of different needle electrode models.

Aluminum↗
PubMed2000

Chronic administration of corticosterone impairs LH signal transduction and steroidogenesis in rat Leydig cells.

The mechanism involved in the inhibitory actions of chronic corticosterone treatment on Leydig cell steroidogenesis was studied in adult Wistar rats. Rats were treated with corticosterone-21-acetate (2 mg/100 g body weight, i.m., twice daily) for 15 days and another set of rats was treated with corticosterone plus ovine luteinizing hormone (oLH) (100 microg/kg body weight, s.c., daily) for 15 days. Chronic treatment with corticosterone increased serum corticosterone but decreased serum LH, testosterone, estradiol and testicular interstitial fluid (TIF) testosterone and estradiol concentrations. Administration of LH with corticosterone partially prevented the decrease in serum and TIF testosterone and estradiol. Leydig cell LH receptor number, basal and LH-stimulated cAMP production were diminished by corticosterone treatment which remained at control level in the corticosterone plus LH treated rats. Activities of steroidogenic enzymes, 3beta- and 17beta-hydroxysteroid dehydrogenase (3beta-HSD and 17beta-HSD) were significantly decreased in corticosterone treated rats. LH plus corticosterone treatment did not affect 3beta-HSD activity but decreased 17beta-HSD activity, indicating a direct inhibitory effect of excess corticosterone on Leydig cell testosterone synthesis. The indirect effect of corticosterone, thus, assume to be mediated through lower LH which regulates the activity of 3beta-HSD. Basal, LH and cAMP-stimulated testosterone production by Leydig cells of corticosterone and corticosterone plus LH treated rats were decreased compared to control suggesting the deleterious effect of excess corticosterone on LH signal transduction and thus steroidogenesis.

Animals↗
PubMed2000

Natural radionuclide distribution in soils of Gudalore, India.

The concentration of primordial radionuclides in soil samples of Gudalore Taluk in the Udagamandalam district has been measured from the gamma ray spectrum of the soil. The mean activities of 232Th, 238U and 40K are 75.3 +/- 44.1, 37.7 +/- 10.1 and 195.2 +/- 85.1 Bq kg-1 dry weight, respectively. The average outdoor absorbed dose rate in air at a height of 1 m above ground is 74.3 +/- 27.8 nGy h-1, corresponding to an annual effective dose equivalent of 455.6 microSv. The dose equivalent ranges from 168.3 to 1250.5 microSv. The results have been compared with other global radioactivity measurements and evaluations.

Gamma Rays↗
PubMed2000

Growth hormone directly stimulates testosterone and oestradiol secretion by rat Leydig cells in vitro and modulates the effects of LH and T3.

The modulatory effect of GH on basal, LH and T3 mediated secretion of testosterone and oestradiol by purified rat (60 day old) Leydig cells was studied in vitro. Percoll gradient purified Leydig cells (1 x 10(3)) were cultured for 48 hours at 34 degrees C in a medium containing different concentrations of rat GH (5-400 ng/mL), after an initial culture for 24 hours at 37 degrees C. GH increased testosterone and oestradiol secretions in a dose dependent manner. While testosterone secretion reached the saturation point with 50 ng GH, oestradiol secretion reached the saturation point with 150 ng GH, followed by diminished secretions. Co-administration of minimum (10 ng) effective does of GH with minimum (25 ng) or maximum (100 ng) effective doses of oLH significantly decreased the testosterone secretion. However, an increased secretion of testosterone was observed when maximum effective doses of rGH (50 ng) and oLH (100 ng) were co-administered. Minimum effective (25 ng) or maximum effective (50 ng) doses of T3 inhibited GH mediated secretion of testosterone in vitro. Oestradiol concentration in the culture medium increased when either dose of rGH was co-administered with the minimum or maximum effective doses of oLH. T3 50 ng augmented the secretion of oestradiol by Leydig cells in the presence of GH. These results indicate that GH acts as a gonadotrophin to stimulate testosterone and oestradiol secretions by Leydig cells, and that it modulates LH or T3 induced secretion of these steroids, depending on the intensity of their stimulation.

Animals↗