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Biomedical subjects

L B Johnson

Publications and source records attributed to L B Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1985

Effects of photic history and illuminance levels on male golden hamsters.

Four-week-old male hamsters, born and raised in total darkness or in LD 14:10 (hr) were exposed to several low levels of illumination for 14 weeks. Analyses showed that testicular weights were significantly affected by both photic history and illuminance levels. Animals born in the dark possessed larger testes than those born in LD cycles and, further, displayed less responsiveness to levels of illumination below those required to suppress pineal function. While gonadal responses to photic duration may be said to be "all or none," those resulting from insufficient illuminance levels are seemingly graded. Thus, the pineal gland may act indirectly as a photodosimeter at low illuminance levels.

Adrenal Glands↗
PubMed1985

The effects of spectral power distribution and illuminance levels on key parameters in the male golden hamster and rat with preliminary observations on the effects of pinealectomy.

Three different light sources were used to determine the effects of spectral power distribution (SPD) and illuminance levels on growth and organ weights of male golden hamsters and rats. SPD had little effect on organ weights or measurements of either rats or hamsters. However, responses to illuminance levels were quite apparent, provided they were equalized for the scotopic eye sensitivity curve characteristic of nocturnal animals. Under seven illuminance levels from 0 to 3.9 scotopic fc, hamsters demonstrated graded responses in gonadal weights and presumed function from 0 to 0.02 scotopic fc. Above this level, photopic saturation was apparent. The neuroendocrine system of pinealectomized animals failed to show sensitivity to illuminance levels. The suggestion is made that the pineal gland acts to monitor illuminance levels (below about 0.02 scotopic fc) as well as photic duration. While the latter appears to be an "all or none" effect, the former appears to be graded.

Animals↗
PubMed1985

Interaction of diet and photoperiod on growth and reproduction in male golden hamsters.

Two basic diets (commercial rodent pellets or seeds) with or without supplements of carbohydrate were tested for growth and development, and effects on organ weights and serum calcium in male golden hamsters. The additional influence of photoperiod was measured. The data suggest that a seed diet alone is not adequate for growth. Addition of seeds and/or carbohydrate to the pellet diet increases growth rates substantially compared to the pellet diet alone. There are significant interaction effects on reproduction between diet and photoperiod indicating that diet can modify responses to short photic input. While reproduction remains essentially normal in seed-fed animals in long photoperiods, the rate of reproductive involution in short photoperiods is greatly enhanced. Added carbohydrate appears to offer some protection against the adverse effect of short photoperiods on reproduction. Even though calcium supplements to the diet increase serum calcium levels toward normal, growth rates are not improved. Addition of Tenebrio (grain beetle) larvae to the seed diet induces growth rates comparable to those of control animals, yet serum calcium levels remain significantly lower.

Adrenal Glands↗
PubMed1980

Management of acute asthma in childhood. A randomized evaluation of beta-adrenergic agents.

We examined the efficacy of several beta-adrenergic agents commonly used to treat asthma and evaluated the optimum route of administration. Two hundred and sixty-nine persons aged 5 to 21 years who came to the emergency ward while suffering from acute asthma were treated with either (1) inhalation isoetharine hydrochloride or (2) subcutaneous epinephrine or terbutaline sulfate. Patients were evaluated using clinical scores and pulmonary function tests and were monitored for adverse side effects. Regardless of mode of therapy, the acute attack was either treated successfully, terminated in hospital admission, or required further therapy within 24 hours in a comparable number of patients. Adverse side effects were more common with terbutaline sulfate than with either epinephrine or isoetharine in the doses used. Thus, inhalation of beta-adrenergic agents is as effective as subcutaneous administration in the treatment of acute asthma in childhood.

Acute Disease↗
PubMed1980

The role of zinc in dental amalgams.

Twenty-five AG-Sn alloys containing various additions of Zn were amalgamated and the amalgams tested for physical properties pertinent to dental restoration use. The mercury retained, dimensional change, compressive strength, and creep were all functions of the Zn content.

Corrosion↗
PubMed1978

The effect of the cooling rate of dental alloys on their amalgamation properties.

Silver-tin alloys of various compositions (60-80 atomic % Ag) have been prepared from the melt using cooling rates from about 50 degrees C/hr to about 10(6) degrees C/sec. Structural differences due to the different cooling rates were shown by metallographic and x-ray diffraction techniques. From each composition and cooling rate, powders were then prepared and amalgamated. The amalgams were tested for Hg content, dimensional change during setting, and tensile strength. Changes in cooling rates had some effect on the relative amounts of phases present but primarily affected the grain sizes. In general, the faster the cooling rate, the smaller the grain size; the smaller the grain size, the faster and more uniform the amalgamation; the more uniform the amalgamation, the stronger the amalgam. Storage of the alloy powders at room temperatures slowed their amalgamation rates, destroyed their uniformity,and resulted in weaker amalgams. However, no phase changes were observed by x-ray diffraction in the freshly comminuted alloys after aging at room temperature for two months.

Dental Amalgam↗
PubMed1977

Progress in splat-cooling of dental alloys.

Improved techniques in preparing and sizing dental alloy powders containing Ag, Sn, and Cu have led to amalgams with higher strengths and less spread in dimensional change but very poor shelf life. Since maximum strengths occurred for amalgams containing about 15% more Sn than previously reported, and consequently presumably more of the weak gamma2 phase, the higher strengths are difficult to understand. The poor shelf life may be explained by oxidation of the highly reactive splat-cooled alloy or possibly by the existence of highly reactive metastable phases which transform fairly rapidly to the less reactive equilibrium ones.

Copper↗
PubMed1976

Effects of inhibitors of RNA and protein synthesis on aspartate transcarbamylase activity in etiolated plant tissue.

Aspartate transcarbamylase (ATCase) activity declines in etiolated cowpea (Vigna unguiculata L. Walp.) and soybean (Glycine max L. Merr.) hypocotyls between 3 and 11 days after planting. Treating cow-pea hypocotyls with cycloheximide (CH), actinomycin D (AMD), 6-methyl purine (6-MP), or cordycepin increases ATCase activity up to 740, 350, 465, and 305%, respectively, over water-treated controls 48 to 72 hours after treatment. In contrast erythromycin had no effect, and d-threo-chloramphenicol (CHL) reduced ATCase activity nearly 40%. CH, AMD, and CHL, whose effects were further characterized, each markedly reduced total RNA synthesis and protein synthesis. Respiration was stimulated by CH and AMD and reduced by CHL. In soybean, CHL-treated tissues and water-treated controls had comparable ATCase activities 48 hours after treatment, while AMD, 6-MP, and CH treatments reduced activities 29, 37, and 78%, respectively. The results suggest that the level of ATCase activity in etiolated cowpea hypocotyls is regulated by a mechanism or mechanisms that are interfered with by inhibition of RNA and protein synthesis. Possibly the mechanism is absent from etiolated soybean hypocotyls.

Journal Article↗
PubMed1974

Splat-cooled alloys in the Ag-Sn-Cu system.

Strength, dimensional change during setting, and corrosion resistance have been measured for amalgams prepared from splat-cooled alloys of different compositions in the Ag-Sn-Cu system. The amalgam with optimum values of these properties was made from the alloy containing 60 at. % Ag, 25 at. % Sn, and 15 at.% Cu. Tensile strengths for amalgams from this alloy were about 8000 psi, dimensional change during setting near zero, and corrosion resistance was good. X-Ray diffraction showed that the gamma1 and gamma2 phases had essentially disappeared after about 24 hr. At the latter time Cu6Sn5 was present.

Copper↗
PubMed1973

Asparate transcarbamylase activity in etiolated cowpea hypocotyls treated with 2,4-dichlorophenoxyacetic Acid.

Treating etiolated cowpea (Vigna unguiculata) seedlings with 2,4-dichlorophenoxyacetic acid resulted in 2.5-, 3.9-, and 6.5-fold increases in DNA, soluble protein, and RNA, respectively, over untreated controls 84 hours after treatment. Aspartate transcarbamylase activity increased within 12 hours after treatment, and by 84 hours it was almost 12-fold greater than that in the untreated controls. During that time, activity in untreated controls dropped 60%. The assay used (14)C-aspartate, which was then separated from the (14)C-ureidosuccinate product by Dowex 50 (H(+) form) column chromatography. Thin layer chromatography of the reaction product indicated that most of the carbamyl-phosphate-dependent radioactivity co-chromatographed with ureidosuccinate. The reaction has a pH optimum near 10.0 and is inhibited by uridine 5'-phosphate and succinate. The data suggest that aspartate transcarbamylase is important in pyrimidine biosynthesis in 2,4-dichlorophenoxyacetic acid-treated seedlings.

Journal Article↗