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Biomedical subjects

R A Harper

Publications and source records attributed to R A Harper.

At least 55 records · Page 3Linked to original sources
PubMed1978

DNA synthesis among uninvolved and involved psoriatic epidermal cells and normal epidermal cells in vitro.

Epidermal cells from 8 patients with psoriasis (involved and uninvolved areas) and from 7 normal individuals, were propagated in vitro. DNA synthesis was determined autoradiographically by measuring the labeling index (1 hr) and a continuous labeling index (72 hr) on 8-10 day old cell cultures. No differences in these 2 kinetic parameters were obtained with respect to involved and uninvolved psoriatic cells. However, when psoriatic cells (involved and uninvolved) were compared to normal cells, the psoriatic cells exhibited a much higher labeling index and continuous labeling index, 200-300% and 60-70% respectively. These data clearly show that in vitro (1) epidermal cells from clinically uninvolved skin of psoriatics proliferate at a rate equal to that of involved psoriatic cells and (2) psoriatic epidermal cells proliferate at a rate greater than normal cells.

Adolescent↗
PubMed1977

Effects of methotrexate on proliferation of human keratinocytes in vitro.

Normal human keratinocytes, propagated as epithelial outgrowths in vitro, were exposed to different concentrations of methotrexate (MTX) for different periods of time. After a 1-hr exposure, DNA synthesis was inhibited in a reversible manner. No change in the mitotic index was observed. After a 6-hr exposure, both DNA synthesis and mitosis were inhibited, again in a reversible fashion. Prolonged exposure (24 hr) resulted in irreversible mitotic inhibition even when followed by recovery periods of 168 hr. The effective concentrations of MTX in vitro were similar to those described previously in vivo.

Culture Techniques↗
PubMed1977

Collagen fiber orientations in human secondary osteons.

Scanning electron microscopy studies of decalcified human secondary osteons were conducted to determine correlations in fiber orientations in these osteons with their appearance under crossed polaroids. Using a new sample preparation technique, osteons were prepared to expose many of their lamellar interfaces. By studying many such samples, it was concluded that osteons which appear 'dark' under crossed polaroids contain fibers with orientations having little or no transverse component, whereas 'bright' osteons possess fiber orientations with transverse and longitudinal components. 'Intermediate' osteons have been found to contain fiber orientations richer in longitudinal component than in transverse.

Bone and Bones↗
PubMed1976

Effect of prostaglandins on 3H-thymidine uptake into human epidermal cells in vitro.

Prostaglandins A2, B1, E1, E2, F1alpha and F2alpha were added to cultures of human epidermal cells (keratinocytes) for 24 hours at 37 degrees C, and the effects on 3H-thymidine uptake into DNA was measured. At 70 mu/ml all prostaglandins tested except PGF2alpha inhibited the uptake of 3-thymidine greater than 50%. However, at 35 mug/ml, PGA2 and PGB1 were the only two prostaglandins to show significant inhibition, 96% and 51% respectively. At 17.5 mug/ml only PGA2 caused substantial inhibition, 68%. In order to determine if the PGA2 action was mediated by membrane receptors propranolol, phentolamine, metiamide and prostynoic acid were added in conjunction with PGA2. None of the above receptor antagonists were able to reduce the PGA2-induced inhibition of 3H-thymidine uptake. These results indicate that the pre-incubation of human keratinocytes with prostaglandins for 24 hours results in a decrease of 3H-thymidine incorporation in DNA. The precise mechanism of action is unknown at this time.

Cell Division↗
PubMed1976

Isolation of single osteons and osteon lamellae.

Single human osteons were isolated by propagating fractures along their natural boundaries. Furthermore, decalcified osteons were mechanically manipulated to expose their interlamellar interfaces, making possible the study of collagen fibers by means of scanning electron microscopy (SEM). Isolation of single osteons of a wide range of lengths, as described in this paper, makes possible for the first time the study of their mechanical properties in all possible modes. SEM studies of exposed lamellar interfaces reveal that collagen fiber orientations are more complex than previously suggested and suggest further studies in an effort to solve past controversies on collagen fiber orientations in human bone.

Bone and Bones↗
PubMed1976

Rabbit corneal epithelial cells grown in vitro without serum.

Primary outgrowth cultures of normal rabbit corneal epithelium can be initiated and propagated in vitro up to 6 days in serum-free medium. By the eighth day the majority of cells have ceased to divide. Epithelial cells grown without serum show DNA synthetic activity at a level comparable to control cultures grown with added serum.

Animals↗
PubMed1975

Effect of pharmacological agents on human keratinocyte mitosis in vitro. II. Inhibition by catecholamines.

Catecholamines produce mitotic inhibition in primary cell cultures of human keratinocytes probably via a block in the G2 part of the cell cycle. Epinephrine produced significant mitotic inhibition (49%) at a concentration as low as 4.5 X 10(-10) M, while its analog, isoproterenol, produced 47% inhibition at 1 X 10(-10) M. Norepinephrine elicited a 49% inhibitory response at 1 X 10(-8) M. One other catecholamine, dopamine, caused a 53% decrease in mitosis at 1 X 10(-6) M. Other structurally related amines to exhibit mitotic inhibition were phenylephrine, 58% at 1 X 10(-7) M; octopamine, 47% at 1 X 10(-5) M; and tyramine, 52% at 1 X 10(-4) M. Serotonin showed no mitotic inhibition at 1 X 10(-4) M. Various alpha and beta adrenergic blocking agents were added to the cell system. The alpha blocking agent, phentolamine, had no effect on mitosis. When added in conjunction with epinephrine or norepinephrine, no reduction of the catecholamine-induced mitotic inhibition was observed. The beta blocking agent, propranolol, by itself showed slight mitotic inhibition at 1 X 10(-6) M. When added along with epinephrine or noreinephrine, propranolol reduced the catecholamine-induced mitotic inhibition approximately 65%. In addition, propranolol blocked mitotic inhibition caused by phenylephrine, an alpha adrenergic agent. However, another beta blocking agent, dichloroisoproterenol, showed strong mitotic inhibition (53%) when added to the cultures at a concentration of 1 X 10(-8) M. The effect was reduced to zero in the presence of propranolol. These data suggest that while beta receptors may be involved in the catecholamine-induced mitotic inhibition of human keratinocytes in vitro, the nature of the receptor-molecule interaction may be complex.

Catecholamines↗
PubMed1975

Organ culture of human skin in chemically defined medium.

Explants of adult human skin were grown in vitro in a chemically defined medium without serum. Under these conditions the epidermis was well maintained for up to 7 days, during which time new stratum corneum formation was observed. Most often the stratum corneum was orthokeratotic and associated with a prominent granular layer. Parakeratotic regions were also evident and these were not associated with a granular layer. During the first 5 days in culture there was a signficant increase in DNA synthesis (as measured radioautographically) and mitosis.

Culture Media↗
PubMed1975

In vitro analysis of the control of keratinocyte proliferation in human epidermis by physiologic and pharmacologic agents.

Human keratinocytes grown in vitro as epithelial outgrowths or as organ cultures maintain many of their normal functions such as proliferation and keratinization. These in vitro systems have been used to analyze the effect of various agents on proliferation. All adenine nucleotides, including dibutyryl cyclic AMP, blocked mitosis in the G2 part of the cell cycle at concentrations of 1 times 10(-4) M. Some nonadenine nucleotides also showed this effect, but only at higher concentrations, an indication that the effect was specific for adenine nucleotides. Dibutyryl cyclic AMP and theophylline both depressed the incorporation of [3H]thymidine into DNA. Catecholamines such as isoproterenol, epinephrine, and norepinephrine were also potent inhibitors of mitosis (G2 block) at concentrations of 1 times 10(-8) to 1 times 10(-10) M. The fact that the effect could be blocked by the beta-blocking agent, propranolol, suggests the existence of specific membrane receptor sites. However, dichloroisoproterenol, another beta blocker, had distinct inhibitory properties in itself and thus indicated that the mechanism of action of catecholamines in human keratinocytes is complex and may involve more than binding to specific receptor sites. Histamine at a concentration of 2 times 10(-6) M was also a strong mitotic inhibitor. This finding is directly opposed to that in rat skin where mitosis is stimulated. Imidazole acetate, a histamine breakdown product, was found to be a striking mitotic stimulator in organ culture. A water-extractable protein (chalone) from human skin also caused a block in G2. Most of the substances tested occur naturally in the cell or organism and their ability to stimulate or depress proliferation in vitro suggests that they play a regulatory role in vivo.

Adenine Nucleotides↗
PubMed1975

Effect of pharmacologic agents on human keratinocyte mitosis in vitro. III. Inhibition by histamine and methylated analogs.

Keratinocytes from normal human skin were propagated in vitro. Histamine at 2 times 10(-6) M inhibited mitosis 68%. The side-chain methylated analogs, n-methylhistamine and n,n-dimethylhistamine, produced an inhibitory response of 53 and 60%, respectively, at 1 times 10(-6) M. The side-chain acetylated analog, n-acetylhistamine, did not elicit an inhibitory response in concentrations as high as 1 times 10(-4) M. The ring-methylated analogs, 1-methylhistamine and 4-methylhistamine, produced some degree of mitotic inhibition at 1 times 10(-4) M. When the H1-blocking agent, pyrilamine, or the H2-blocking agent, metiamide, was added in conjunction with histamine, the histamine-induced mitotic inhibition was abolished. These data indicate that human keratinocytes may possess receptors for histamine which could play a role in the regulation of human keratinocyte proliferation in vivo.

Histamine↗
PubMed1975

Scanning and transmission electron microscopy of calcified tissues.

Some recent innovations have been utilized to extend studies of the structure of calcified tissues on the ultra- and microstructural levels of organization. The introduction of hydrazine as a replacement for the conventionally used ethylene diamine to deproteinize calcified tissue samples has resulted in the acquisition of previously unobtainable information about the mineral phase as it exists in situ. This enables inference of mineral-organic interrelationships when coupled with the EDTA demineralization technique used to study collagen fiber frameworks. In addition, a method for obtaining whole single osteons and separating them into lamellar constituents permits observations of the collagen-apatite orientation within successive lamellae of compact Haversian bone. The use of the structural information derived to develop a fiber-reinforced model of compact bone as a composite material is outlined and discussed.

Bone and Bones↗