Search PubMed⌕ Search

Biomedical subjects

E B Harris

Publications and source records attributed to E B Harris.

At least 37 records · Page 2Linked to original sources
PubMed1989

Regulation of insulin and glucose plasma levels by central nervous system beta-endorphin in preweanling rats.

Recently, our laboratory has reported that central administration of beta-endorphin to rat pups decreases hepatic and renal ornithine decarboxylase activity, a sensitive biochemical index of tissue metabolic activity. Since these organs are the major sites of insulin catabolism, it seemed possible that the plasma levels of this hormone could be altered by changes in central nervous system (CNS) beta-endorphin levels. In the current study we tested this hypothesis by administering beta-endorphin to rat pups intracisternally (ic), followed by insulin sc, and then analyzing for plasma levels of insulin and glucose at various times after the second injection. We found that the apparent biological half-life of administered insulin markedly increased in 6-day-old rats pretreated with beta-endorphin ic. Similarly, this neuropeptide prolonged the half-life of endogenous insulin, as indicated by a small but significant increase in the plasma levels of this hormone in animals given only beta-endorphin. As expected, hypoglycemia in rats injected with beta-endorphin and insulin was more pronounced than in animals given insulin alone. Naloxone administered ic reversed both actions of beta-endorphin, indicating the involvement of opioid receptors in the response. beta-Endorphin also altered insulin and glucose plasma levels in 2-, 10-, and 18-day-old rats, but there were no effects in 30-day-old animals at any of the doses used in these studies. Peripheral administration of beta-endorphin had no effect, indicating that CNS beta-endorphin's influences on insulin and glucose metabolism occur through brain-based mechanisms. The results from these studies suggest that CNS beta-endorphin may be an important modulator of insulin and glucose metabolism in preweanling rats. In as much as insulin is a major regulator of somatic growth, our findings further suggest that CNS beta-endorphin may have a major role in the control of growth during early postnatal development by influencing insulin homeostasis.

Animals↗
PubMed1988

Biophysical optima for metabolism of Mycobacterium leprae.

The metabolic response of freshly harvested, nude-mouse-derived Mycobacterium leprae to biophysical parameters was studied to facilitate an understanding of axenic culture requirements. Quantitation of intracellular ATP and the rate of [U-14C]palmitic acid incorporation into phenolic glycolipid I (PGL-I) were used as metabolic indicators after axenic incubation in modified Dubos medium under various biophysical conditions. PGL-I synthesis was optimal at 33 degrees C, whereas ATP was optimally maintained at less than or equal to 33 degrees C. Both metabolic indices showed sharp reductions at 37 degrees C. After 5 days of incubation, PGL-I synthesis and ATP maintenance showed pH optima of 5.1 to 5.6, with the higher value appearing optimal for ATP maintenance after extended incubation. Metabolic activity was negatively affected by strong reducing agents, and ATP maintenance was optimal when the gaseous environment was maintained at 2.5 to 10% oxygen. The results may partially explain the failure to cultivate the leprosy bacillus in vitro.

Adenosine Triphosphate↗
PubMed1988

Inhibition of phenolic glycolipid-I synthesis in extracellular Mycobacterium leprae as an indicator of antimicrobial activity.

The effects of 22 antimicrobial agents on the incorporation of [U14C] palmitic acid ([U14C] PA) into the unique phenolic glycolipid-I (PGL-I) antigen of Mycobacterium leprae were studied. Nude-mouse-propagated M. leprae were incubated in a modified Dubos medium in the presence of antimicrobial agents for 4 days. [U14C] PA was then added and incubation was continued for 8 days. The antileprosy agents dapsone, rifampin, and clofazimine (2 micrograms/ml each) caused a significant reduction in [U14C] PA incorporation into PGL-I. Among other agents, the most active were erythromycin, chloramphenicol, and cerulenin. Low concentrations of ethionamide, tetracycline, and minocycline stimulated label incorporation. This system may prove useful in the evaluation of antileprosy agents.

Anti-Bacterial Agents↗
PubMed1987

Beta-lactamase synthesis in Mycobacterium leprae.

Beta-lactam antibiotics are not active against Mycobacterium leprae. The enzyme beta-lactamase mediates the most common form of bacterial resistance to penicillins and cephalosporins. Cell-free extracts of purified suspensions of M. leprae were examined for beta-lactamase. The bacteria were prepared from the tissues of experimentally-infected nine-banded armadillos. Most of the suspensions were inactive. However, the bacteria obtained from the tissues of armadillos treated with penicillin G benzathine (bicillin) 6 months or more prior to sacrifice had beta-lactamase. If the organisms had been exposed to the antibiotic only for a few days, they were negative. Attempts to induce beta-lactamase in the bacteria in vitro did not succeed. Interestingly M. leprae separated from untreated armadillos, infected with the bacilli derived from treated animals contained the enzyme activity. Apparently, the M. leprae genome contains the operon for beta-lactamase, and once it is stimulated to express the enzyme, it continues to do so, even after the inducer is withdrawn.

Animals↗
PubMed1987

N alpha-acetyl-beta-endorphin stimulates ornithine decarboxylase activity in preweanling rat pups: opioid- and non-opioid-mediated mechanisms.

Our laboratory has demonstrated recently that administration of beta-endorphin to rat pups results in profound changes in the levels of the growth-related enzyme ornithine decarboxylase (ODC) in both brain and peripheral tissues. These findings are consistent with accumulated evidence indicating that, in addition to their analgesic and behavioral effects in the adult, endogenous opioid peptides and opioid receptors may be involved as mediators of tissue growth and function in the neonate. This study examines the effects of N alpha-acetyl-beta-endorphin on tissue ODC activity to determine whether post-translational acetylation of beta-endorphin at the N alpha-terminus affects its capability to alter ODC activity and, consequently, tissue development. Intracisternal administration of N alpha-acetyl-beta-endorphin evoked profound increases in brain ODC activity in 6- and 9-day-old rats, whereas normal ODC levels were observed in 25-day-old animals and in adult rats. Centrally administered N alpha-acetyl-beta-endorphin had no effect on ODC in peripheral tissues. In contrast, s.c. administration of this peptide to 6-day-old animals resulted in marked increases in ODC activity in the heart, liver and brain. Naloxone inhibited the stimulatory actions of N alpha-acetyl-beta-endorphin on brain ODC completely, indicating the involvement of opioid receptors in that process. On the other hand, the increases in liver ODC were not prevented by naloxone, suggesting that these effects are not mediated through opioid-sensitive structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1986

A random survey of leprosy in wild nine-banded armadillos in Louisiana.

On the basis of the finding that lepromatous granulomas were almost always seen in the ears of armadillos with disseminated leprosy, a random survey of the prevalence of the disease among wild armadillos in the state of Louisiana, U.S.A., was conducted by examining histopathologically both ears of armadillos killed on the roads by automobiles. Ten (2%) of the 494 animals examined had disseminated leprosy. If a killed lepromatous armadillo releases up to 10 Mycobacterium leprae into the environment, the importance of the event to the epidemiology of leprosy must be considered.

Animals↗
PubMed1986

Thorns in armadillo ears and noses and their role in the transmission of leprosy.

Both ears from 494 wild nine-banded armadillos (Dasypus novemcinctus) and nose specimens from 224 animals were collected and histopathologically studied. Lepromatous granulomas were present in the ear specimens of ten of 494 animals. There were thorns in the ears of 22.5% of animals, and in 36.6% of the nose specimens. In one armadillo, there was evidence to suggest that Mycobacterium leprae entered the tissue through the thorn pricks. In the normal habitat of the armadillo in Louisiana there are thorny bushes consisting mostly of the green briar and the southern dewberry. Thorn pricks as a means of transmission of leprosy in the wild armadillos is suggested.

Animals↗
PubMed1986

Ganglioside patterns in normal and lepromatous armadillo tissues.

Gangliosides derived from tissues of normal and lepromatous armadillos were examined by thin-layer chromatography. The ganglioside patterns produced by the Mycobacterium leprae-infected tissues varied from that of the normal tissue. Although increased levels of several gangliosides were observed in the infected tissues, there was an apparent preferential increase in GM3 gangliosides as determined by column chromatography and enzymatic hydrolysis.

Animals↗
PubMed1985

A possible metabolic role for o-diphenoloxidase in Mycobacterium leprae.

Among mycobacteria, Mycobacterium leprae is unique in its ability to oxidize a variety of diphenols to quinones in vitro. What physiologic role o-diphenoloxidase has in the organism remained unknown. Reducing substrates like NADPH, NADH and ascorbic acid reacted with the quinone formed from dopa (3,4-dihydroxyphenylalanine); the substrates were oxidized and the quinone was reduced back to diphenol in the process. Since the quinone undergoes reversible oxidation-reduction, diphenoloxidase might serve as an alternative respiratory mechanism in M. leprae for the utilization of other substrates, as has been reported in plants.

Animals↗
PubMed1985

Temperature-induced changes in viability, diphenoloxidase and permeability of Mycobacterium leprae.

Among mycobacteria secretion of the enzyme diphenoloxidase has been established as a property of Mycobacterium leprae. The antileprosy drug dapsone (DDS), which completely inhibits the enzyme from plant and mammalian sources, does not readily penetrate intact M. leprae. When the drug is complexed with polylysine, it easily permeates the bacteria and produces 100% inhibition of its diphenoloxidase, suggesting a permeability barrier of the cytoplasmic membrane of M. leprae to dapsone. In this study: (1) when the organisms, purified from fresh tissues of experimentally infected armadillos, were treated with dilute alkali or exposed to warmer temperatures, DDS penetrated the bacteria and inhibited the diphenoloxidase. Washing with trypsin had no effect. Dapsone easily permeated the bacilli, purified from tissues stored at 0 degrees C or at -80 degrees C. (2) Diphenoloxidase of freshly-prepared M. leprae was stimulated when the bacteria were exposed to 50 degrees C for 10 min; at 60 degrees C the activity decreased, and at 100 degrees C the enzyme was completely inactivated. When the enzyme was assayed at temperatures below 37 degrees C, the activity was considerably lower, indicating that M. leprae may not be a psychrophilic organism in this respect. (3) The bacteria exposed to 50 degrees C failed to multiply in mouse footpads. M. leprae remained viable in tissues stored at 0 degrees C or -80 degrees C; but when the bacteria purified from these tissues were frozen, they lost their viability. On the other hand, the organisms separated from fresh tissues remained viable when frozen at -80 degrees C. The inhibition of diphenoloxidase of M. leprae by dapsone could serve as an indirect method to assess the integrity of the bacterial cell membrane and to predict whether the bacteria would retain their viability on freezing.

Catechol Oxidase↗
PubMed1984

An alternative route for infecting armadillos with Mycobacterium leprae.

A nine-banded armadillo was inoculated with Mycobacterium leprae in both hind footpads. The animals were usually inoculated intravenously, or intradermally in the abdominal skin. Profuse multiplication of the bacilli occurred at the injection sites after more than two years. Eventually bacteraemia developed, and large numbers of the organisms were found in skin biopsies and in lymph nodes. There was limited dissemination of the bacteria into the spleen and the liver, and peripheral nerve invasion by the bacilli was also detected. M. leprae remained viable in the liver tissue, kept frozen at -80 degrees C for three years. This experimental system would be useful in testing the effects of certain immunological and chemotherapeutic agents against M. leprae by injecting them directly at the infection site.

Animals↗
PubMed1983

Glutamic acid decarboxylase in Mycobacterium leprae.

Suspensions of Mycobacterium leprae purified from the organs (mostly spleen) of experimentally-infected armadillos (Dasypus novemcinctus, Linn) decarboxylated 1-(14C) glutamic acid liberating 14CO2. The reaction was pyridoxal phosphate-dependent and was inhibited by hydroxylamine, suggesting that it is a true amino acid decarboxylase. Loss of the activity at higher temperatures indicated the enzymatic nature of the reaction. Excess substrate or substrate analogs inhibited the decarboxylase whereas alpha-ketoglutarate and glutarate stimulated it. The activity was four times higher at pH 4.5 than at pH 6.8, suggesting that the enzyme is of microbial origin and not derived form the host cells. Armadillo spleen did not decarboxylate the amino acid. The Km value of the enzyme in the organisms was similar to that in Escherichia coli. The results reported here show that glutamate decarboxylase (EC 4.1.1.15) is an inherent metabolic activity of M. leprae, and might explain its unusual neural affinity. Glutamic acid is the most abundant amino acid occurring in the nerve tissue.

Carboxy-Lyases↗
PubMed1981

Permeability of Mycobacterium leprae to dapsone: alteration by purification procedures.

Permeability of Mycobacterium leprae to dapsone in vitro was determined by the ability of the drug to inhibit o-diphenoloxidase of the bacilli. Dapsone showed little effect on the enzyme activity of the intact organisms. When the M. leprae preparations were washed with trypsin, NaOH, or acetone and ether, DDS penetrated the bacillus to inhibit its o-diphenoloxidase. The method might be useful in studying the utilization of added metabolites by purified M. leprae suspensions.

Animals↗
PubMed1980

A possible method for improving the efficacy of dapsone.

The antileprosy drug dapsone is unable to penetrate intact Mycobacterium leprae in vitro, as determined by its effect on o-diphenoloxidase in the bacilli. When combined with the peptide polylysine, the sulfone drug passes through the bacterial cell membranes, and penetrates the enzyme protein, resulting in a 100% inhibition of its activity.

Catechol Oxidase↗
PubMed1979

Metabolic inhibitors of host-tissue origin in Mycobacterium leprae.

It is not clear why host-derived bacteria are metabolically inert, compared to organisms grown in vitro. o-Diphenoloxidase is the only metabolic property proven to be present in Mycobacterium leprae separated from infected human as well as animal (mouse and armadillo) tissues. However, highly concentrated suspensions of M. leprae obtained from the organs of experimentally infected armadillos showed little or extremely low o-diphenoloxidase, while the organisms bound 14C-labeled dopa. When these preparations were diluted, they readily oxidized D-dopa to pigment. The activity remained unaltered by washing the suspensions with dilute alkali or acetone and ether, indicating that it is an intrinsic property of the bacilli. Treatment with different proteases relieved the inhibition, and resulted in a 100% stimulation of O-diphenoloxidase in the bacilli. Evidently, the M. leprae suspensions obtained from infected tissues contain an inhibitory material which is protein in nature, and the metabolic inertness sometimes observed in host-grown bacteria may not be due to loss of enzymes or metabolites from the organisms.

Animals↗