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Biomedical subjects

J Hansen

Publications and source records attributed to J Hansen.

At least 343 records · Page 19Linked to original sources
PubMed1978

Influence of the Irradiance on Carbohydrate Content and Rooting of Cuttings of Pine Seedlings (Pinus sylvestris L.).

Seedlings of Pinus sylvestris L. were grown for 6 weeks at an irradiance of either 8 or 40 watts per square meter in a controlled environment room. Cuttings from these plants were rooted in tap water for 75 days at either 8 or 40 watts per square meter. The photoperiod was 17 hours.During the first 30 days of the rooting period quantitative changes in carbohydrates were recorded in cuttings from the different treatments. The carbohydrate contents of the cuttings were mainly regulated by the irradiance during the stock plant stage and generally a higher carbohydrate level was found in cuttings from stock plants grown at 40 watts per square meter.The irradiance during the rooting period had only minor effects on the time course of root formation, whereas the irradiance during the stock plant stage did influence the subsequent root formation. Cuttings from stock plants grown at 8 watts per square meter rooted faster and with higher frequency than those from stock plants grown at 40 watts per square meter. These results are discussed in relation to the mentioned irradiance effects on carbohydrate content.

Journal Article↗
PubMed1978

The DNA . tyrocidine complex and its dissociation in the presence of gramicidin D.

The peptide antibiotic tyrocidine affects transcription in vitro by interfering with the initiation process. The complex formed between tyrocidine and native DNA is stable against nucleolytic enzymes. It is sensitive to variations in the salt concentration. Protection of DNA as a function of the tyrocidine concentration follows a curve suggesting cooperative binding of tyrocidine to DNA. The complex formation at low tyrocidine concentrations is accompanied by the presence of single stranded regions of unknown length. With single-stranded DNA, tyrocidine forms a complex which is relatively insensitive to high salt concentrations. Both native and single-stranded DNAs of the complexes become digestible in the presence of gramicidin D, another peptide antibiotic. Breakdown of the complex as a function of the gramicidin D concentration follows a curve which is the reverse of cooperative binding. Gramicidin D acts more effectively on single-stranded rather than on double-stranded DNA . tyrocidine complexes. The DNA . tyrocidine complex, which is broken down by formamide and dimethyl sulfoxide is stabilized by gramicidin D. The implications of these results are discussed with respect to a possible recognition of DNA sequences by tyrocidine and the interaction between DNA, tyrocidine and gramicidin D.

Bacillus↗
PubMed1978

Time course of vasospasm in man.

Measurements were made at eight predetermined positions on 627 sets of angiograms from 293 patients with aneurysms. A ratio between the sum of the vessel diameters in the subarachnoid space to the sum in the base of skull and neck was calculated and plotted against time. Vasospasm has its onset in man about Day 3 after subarachnoid hemorrhage, is maximal at Days 6 to 8, and is gone by Day 12. There is a tendency for patients in poor clinical grades to have more vasospasm. The patients with most vasospasm have a significantly higher mortality than those with the least.

Carotid Artery, Internal↗
PubMed1977

Spontaneous atherosclerosis: an ultrastructural study in the white Carneau pigeon.

The atheroscleroit lesions, associated with the celiac intimal smooth muscle cushions, of four and five year old White Carneau pigeons were studied with the light and electron microscopes. Light microscopic examination of the spontaneous lesions demonstrated large intimal cushions composed of smooth muscle abundant collagen, clusters of foam cells and cholesterol crystal clefts. Ultrastructural examination of the intimal atheroma revealed dilatations between apposing endothelial cells which contained a flocculent material, similar to that seen in the subendothelial space. The subendothelial compartment contained abundant collagen, extracellular lipid, vesiculated material and cell processes which contained a flocculent matrix and tubular-like elements. In addition, fibroblast-like interlaminar cells were often observed. Numerous intimal smooth muscle cells were seen which displayed varied morphology. Abundant foam cells were also present within the intimal atheromas. The presence of atherosclerotic lesions in preexisting intimal smooth muscle cushions suggests that hemodynamic factors may be important in the progression of these spontaneous lesions. Endothelial cell dilatations may provide an important route of transport for circulating elements which may accumulate withing the subendothelial space. Morphologically, it appears that the smooth muscle cells undergo modification and may represent the precursors of foam cells in this species.

Animals↗
PubMed1976

Aplastic anaemia: Evidence for an immunological mechanism.

The soft agar culture assay (C.F.U.-C) has been used in vitro as a measure of haemopoietic capacity of bone-marrow. In a patient with aplastic anaemia pretreatment of the patient's bone-marrow with horse anti-human-thymocyte globulin and complement (A.T.G. + C) prior to culture led to a dramatic increase in ability to form colonies in the soft agar assay; and co-culturing marrow from a normal donor and from the patient resulted in a distinct reduction in the number of expected C.F.U.-C. These findings point ot an immunological or autoimmune mechanism in this patient by selective destruction of the suppressing cells in the patient's marrow with A.T.G. and by suppression of normal myelopoiesis following addition of the patient's marrow to normal marrow.

Adult↗
PubMed1976

Immunogenetic aspects of allotransplantation.

It now appears unequivocal that three markers exist in a linkage group in chromosome 6 of man: HLA-A, HLA-B and PGM3 (Fig. 1.) Tentatively, two other HLA loci and one Ir gene have been mapped close to HLA-B. The probable map order is HLA-A - HLA-C - HLA-B - HLA-D - Ir. The biological functions of these loci are unknown. However, HLA-A, B and C are important in allograft rejection. Other closely linked loci (HDR, CML) appear to be important in the first events of the allograft rejection (first set) and in generation of killer cells. HLA-D might be important in cellular recognition and graft-versus-host reactions (matching at HLA-D decreases the incidence and severity of graft-versus-host disease), and the Ir genes in the defense against infections. HLA-B and HLA-D loci are important markers in studies of disease susceptibility. HLA-B locus antigens HLA-B27 and HLA-B8 are frequently associated with arthritic or autoimmune disorders. HLA-D determinants have been found in association with multiple sclerosis and C2 deficiency (HLA-DW2); juvenile diabetes and Addison's disease (HLA-DW3) and adult type of rheumatoid arthritis (HLA-DW4).

Alleles↗
PubMed1976

Evolution and utility of a Pseudomonas aeruginosa drug resistance factor.

We describe the addition to the Pseudomonas aeruginosa sex factor, FP2, of carbenicillin resistance encoded by the RP1 plasmid. This occurred in a step-wise manner as detected by variations in the characteristics of the FP2-RP1 plasmid aggregate. The addition of the carbenicillin resistance marker to FP2 facilitates estimates of FP2 transfer. Transfer frequencies for the presumed cointegrate plasmid, using carbenicillin selection, approached 10(-1) per donor bacterium. The chromosomal mobilization properties of the derived plasmid, designated pR0271, resembled those of the progenitor plasmid FP2. Plasmid pR0271 was also observed to mobilize a nontransmissible drug resistance plasmid sharing genetic homology at frequencies corresponding to those observed for chromosomal markers proximal to the origin of transfer.

Anti-Bacterial Agents↗