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Biomedical subjects

L Johnson

Publications and source records attributed to L Johnson.

At least 577 records · Page 32Linked to original sources
PubMedDate not supplied

Leydig cell cytoplasmic content is related to daily sperm production in men.

The relationship between the abundance of specific Leydig cell organelles and daily sperm production (DSP) was determined. Testes from 10 men (26-53 years of age) were obtained at autopsy within 10 h of traumatic death or heart failure and fixed by vascular perfusion. Testicular tissue was processed for light and electron microscopy. DSP/testis and Leydig cell cytoplasmic volume/testis were determined by stereology of histologic sections. The Leydig cell organelle content was determined by point counting electron micrographs for smooth endoplasmic reticulum (SER), rough endoplasmic reticulum, mitochondria, lipofuscin pigment, lipid, Golgi bodies, and Reinke crystals. Men were divided equally into two groups based on DSP/testis. Men with low DSP/testis had less SER volume density (P less than 0.01) and lower SER volume per testis (P less than 0.05) than men with high DSP. Other organelles were unrelated to DSP. When all men were combined, the volume density of SER (r = 0.80; P less than 0.01), the volume SER per testis (r = 0.69; P less than 0.05), and the volume SER per Leydig cell (r = 0.84; P less than 0.01) were significantly related to DSP. Hence, there appears to be a significant relationship between Leydig cell SER and the level of spermatogenesis in men.

Adult↗
PubMedDate not supplied

Disposition of benzo(f)quinoline in male rats.

The absorption, distribution, metabolism, and excretion of 14C-benzo(f)quinoline (BQ), an air pollutant and component of cigarette smoke, was studied in male Fischer 344 rats. BQ was completely absorbed after oral exposure over a dose range from 1 to 100 mg/kg. Rats were treated iv with 1 mg/kg and total radioactivity was examined at sacrifice from 15 min to 3 days after dosing. BQ was rapidly distributed throughout the body and excreted in approximately equal amounts in the urine and via the bile into the feces. Metabolism to several compounds more polar than BQ occurred prior to excretion. Most of the radioactivity in blood and half of that in liver was due to metabolites of BQ, while only parent compound could be detected in other tissues. No parent BQ was present in the excreta. By 3 days after treatment, less than 2% of the 14C-BQ remained in the rats. Given the rapid metabolism and excretion of this compound it is unlikely that low dose, repeated exposure would result in its accumulation in the body.

Animals↗
PubMedDate not supplied

Wounded warrior.

Explore the source record for details and available documents.

Emergency Medical Services↗
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Disposition of 4,4'-thiobis(6-t-butyl-m-cresol) in rats.

The absorption, distribution, metabolism, and excretion of 14C-labeled 4,4'-thiobis(6-t-butyl-m-cresol) (TBBC) was studied in male rats. Oral treatment showed a dose-related decrease in the rate of absorption due to a dose-related increase in retention time in the stomach. TBBC was incompletely absorbed after oral treatment, although the rate of absorption was proportional to the dose once the compound reached the small intestine. TBBC was rapidly distributed throughout the body with the liver being the major tissue depot. Significant amounts of the compound were also present in blood, muscle, skin, and adipose tissue. TBBC was initially rapidly cleared from all tissues except adipose, although a small percentage of the total dose tended to persist in liver and skin. Over half of the compound was excreted the first day, primarily via the bile into the feces. Little TBBC-derived radioactivity appeared in the urine. Metabolites of TBBC were present in the tissues at early times after administration, but were rapidly excreted. The major metabolite(s) appeared to be glucuronide conjugates of the parent compound. Thus, TBBC, an important antioxidant in the rubber and plastic industries, would tend to accumulate in liver and lipid-rich tissues upon chronic exposure, which if by the oral route, could also result in direct damage to the gastrointestinal tract.

Animals↗
PubMedDate not supplied

Vertical guided bone-graft augmentation in a new canine mandibular model.

Using the mandibular inferior border of four fox hounds from an extraoral approach, six high-profile Brånemark implants were placed in each animal and bone grafted. Graft materials studied included demineralized freeze-dried allograft with and without irradiation sterilization (3.8 x 10(4) Gy), corticocancellous iliac autograft, blood clot, and a control. Corticocancellous grafts were studied with and without expanded polytetrafluoroethylene (EPTFE) barriers. The barrier function improved both graft volume incorporated and bone-implant interface contact. The autograft performed better than the allograft. Irradiation of the allograft did not appear to affect graft performance. The barrier functioned to improve graft incorporation for augmentation and interface contact and gives credence to the use of barriers in conjunction with vertical augmentation grafting of jawbone.

Alveolar Bone Loss↗
PubMedDate not supplied

Dental caries risk in hereditary epidermolysis bullosa.

Epidermolysis bullosa (EB) is a clinically diverse group of conditions characterized by skin fragility and, in certain types, marked dental involvement. The purpose of this study was to determine the prevalence of dental caries in EB and control populations. Healthy individuals and participants from the Southern Clinical Center of the National EB Registry were examined with artificial light and a #23 dental explorer. Caries levels were evaluated by chi-square analysis, regression analyses, and ANOVA (P < 0.05 being significant). The study included 252 individuals with EB, aged 2.3-71 years, and 57 similarly aged controls. The prevalence of dental caries, scored as DMFS (decayed, missing, filled surfaces), was significantly higher in the junctional (mean = 58.6) and recessive dystrophic (mean = 37.6) EB types than controls (mean = 23.2). The simplex (mean = 25.6) and dominant dystrophic (mean = 21.6) EB groups had DMFS levels similar to the control group. Individuals with recessive dystrophic EB had the most severe oral blistering and scarring and did not have generalized enamel hypoplasia. In contrast, junctional EB always was associated with generalized enamel hypoplasia yet the intraoral blistering rarely involved scarring. This study shows that dental caries is increased in dystrophic and junctional EB compared with unaffected individuals or other EB types. While rampant caries appears related to the soft tissue and enamel involvement in these two EB types, other as yet unclear cofactors also must be involved.

Adolescent↗
PubMedDate not supplied

A new approach to study the architectural arrangement of spermatogenic stages revealed little evidence of a partial wave along the length of human seminiferous tubules.

Although evidence of the spermatogenic wave in humans has been reported, little is known about the architectural arrangement of stages along the length of tubules in men with varied rates of sperm production. To conduct these studies, methodology is needed to stage relatively long lengths of straight portions of tubules in several men. Testes obtained at autopsy were glutaraldehyde perfused. Six men representing a range of daily sperm production were selected for this study. Wedges composed of groups of seminiferous tubules attached to the rete testis and separated by testicular septa were teased apart from the remaining testicular tissue, fixed in osmium, and oriented during Epon embedding. This orientation allowed for sections to be cut perpendicular to the length of the group of tubules, beginning at the end near where the tubules had been attached to the rete testis. Also, a tubule isolated away from the rete testis was oriented for perpendicular sectioning for one of the men. Several serial sections were cut at a setting of 22 microns, and each was optically sectioned approximately at 7 microns and photographed using Nomarski optics. Because many cytoplasmic and nuclear features of spermatogonia, spermatocytes, and spermatids were distinguished in photomicrographs produced by Nomarski optics, this optical system facilitated the identification of stages of the spermatogenic cycle in human seminiferous tubules.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMedDate not supplied

Animal model of human disease: lymphocytic gastritis.

Gastric specimens from 102 belonging to 11 different species were reviewed. Of the 11 species, only the gastric mucosa of pigs contained a large number of lymphocytes in the surface and in the foveolar epithelium (mean 82 lymphocytes/1000 epithelial cells, range 62-128 lymphocytes. The gastric specimens of the remaining 10 species revealed none or occasional lymphocytes in the surface or the foveolar epithelium. The occurrence of intraepithelial lymphocytes in the gastric mucosa of pigs mimics the human disease known as "lymphocytic gastritis". Since the etiology of this disease remains unknown, the apparently endemic nature of lymphocytic gastritis in pigs offer an alternative to investigate the possible cause(s), as well as the mechanism of, this disease.

Animals↗