Biomedical subjects

R L Sah

Publications and source records attributed to R L Sah.

14 recordsLinked to original sources

PubMed1995

Integrative repair of articular cartilage in vitro: adhesive strength of the interface region.

The objective of this study was to quantify the strength of the repair tissue that forms at the interface between pairs of cartilage explants maintained in apposition in an in vitro culture system. Articular cartilage explants were harvested from calves and from adult bovine animals, dissected into uniform blocks, and incubated in pairs within a chamber that maintained a 4 x 5 mm area of tissue overlap. Following 1-3 weeks of incubation, integrative repair was assessed by testing samples in a tensile single-lap configuration to estimate adhesive strength. After incubation in medium containing 20% fetal bovine serum, the adhesive strength between pairs of calf cartilage blocks and pairs of adult bovine cartilage blocks increased at a rate of 7.0 and 10.5 kPa/week, respectively. This repair process appeared to be dependent on viable cells, since lyophilization of adult bovine cartilage before incubation completely inhibited the development of an interface with a measurable adhesive strength. The repair process was dependent on serum components in the medium. Incubation of sample pairs for 3 weeks in medium supplemented with 20% fetal bovine serum resulted in a relatively high proteoglycan content as well as a relatively high adhesive strength (34 kPa), whereas incubation in basal medium with or without 0.1% bovine serum albumin resulted in a 54-70% lower proteoglycan content and a 65-88% lower adhesive strength. Samples incubated for 3 weeks with serum also had a 20% higher DNA content than samples maintained in basal medium. Histological analysis indicated some cell division at the free surfaces of the explant and also occasional cells within the interface region between explants.

Analysis of Variance↗

PubMed1994

Mechanical regulation of cartilage biosynthetic behavior: physical stimuli.

The biosynthetic response of calf cartilage disk explants to small-amplitude dynamic compression was studied in radially unconfined compression over a wide range of frequencies. The relative importance of oscillatory fluid flow, hydrostatic pressure, streaming potential, and cell deformation in modulating chondrocyte metabolism was explored by quantifying the frequency dependence and the spatial (radial) distribution of the biosynthetic response within the 3-mm-diameter explant disks. At frequencies greater than 0.001 Hz (cycle/s), dynamic compression increased biosynthesis of proteoglycans and proteins. While compression at frequencies between 0.002 and 0.01 Hz caused a stimulation of biosynthesis that was distributed throughout the disk, compression at 0.1 Hz caused a stimulation that was confined mainly to the outer radial periphery. These distributions were compared to previous estimates of the radial distribution of physical forces and flows within the matrix. The results suggest that the stimulation of chondrocyte biosynthesis by dynamic mechanical compression at amplitudes up to 10% (stresses up to 0.5 MPa) is related to changes in fluid flow and/or cell shape rather than changes in hydrostatic pressure. Since static compression to the original cut thickness caused a slight decrease in biosynthesis in the center of the disks, we also studied the possible role of limited diffusive transport in the marked inhibition of synthesis seen during large displacement static compression. Experiments in which the surface area-to-volume ratio of disks or the concentration of labeling substrate or serum were varied provided no evidence that limited diffusive transport was responsible for the inhibition of biosynthesis by large displacement static compression. Recovery of biosynthesis from static compression and histological analyses of compressed tissue suggested that there was no significant cell damage even during 12 h of 50% static compression.

Animals↗

PubMed1991

Effects of compression on the loss of newly synthesized proteoglycans and proteins from cartilage explants.

The effects of mechanical compression of calf cartilage explants on the catabolism and loss into the medium of proteoglycans and proteins radiolabeled with [35S]sulfate and [3H]proline were examined. A single 2- or 12-h compression of 3-mm diameter cartilage disks from a thickness of 1.25 to 0.50 mm, or slow cyclic compression (2 h on/2 h off) from 1.25 mm to 1.00, 0.75, or 0.50 mm for 24 h led to transient alterations and/or sustained increases in loss of radiolabeled macromolecules. The effects of imposing or removing loads were consistent with several compression-induced physical mediators including fluid flow, diffusion, and matrix disruption. Cyclic compression induced convective fluid flow and enhanced the loss of 35S- and 3H-labeled macromolecules from tissue into medium. In contrast, prolonged static compression induced matrix consolidation and appeared to hinder the diffusional transport and loss of 35S- and 3H-labeled macromolecules. Since high amplitude cyclic compression led to a sustained increase in the rate of loss of 3H- and 35S-labeled macromolecules that was accompanied by an increase in the rate of loss of [3H]hydroxyproline residues and an increase in tissue hydration, such compression may have caused disruption of the collagen meshwork. The 35S-labeled proteoglycans lost during such cyclic compression were of smaller average size than those from controls, but contained a similarly low proportion (approximately 15%) that could form aggregates with excess hyaluronate and link protein. The size distribution and aggregability of the remaining tissue proteoglycans and 35S-labeled proteoglycans were not markedly affected. The loss of tissue proteoglycan paralleled the loss of 35S-labeled macromolecules. This study provides a framework for elucidating the biophysical mechanisms involved in the redistribution, catabolism, and loss of macromolecules during cartilage compression.

Animals↗

PubMed1990

Effects of tissue compression on the hyaluronate-binding properties of newly synthesized proteoglycans in cartilage explants.

The effects of tissue compression on the hyaluronate-binding properties of newly synthesized proteoglycans in calf cartilage explants were examined. Pulse-chase experiments showed that conversion of low-affinity monomers to the high-affinity form (that is, to a form capable of forming aggregates with 1.6% hyaluronate on Sephacryl S-1000) occurred with a t1/2 of about 5.7 h in free-swelling discs at pH 7.45. Static compression during chase (in pH 7.45 medium) slowed the conversion, as did incubation in acidic medium (without compression). Both effects were dose-dependent. For example, the t1/2 for conversion was increased to about 11 h by either (1) compression from a thickness of 1.25 mm to 0.5 mm or (2) medium acidification from pH 7.45 to 6.99. Oscillatory compression of 2% amplitude at 0.001, 0.01, or 0.1 cycles/s during chase did not, however, affect the conversion. Changes in the hyaluronate-binding affinity of [35S]proteoglycans in these experiments were accompanied by no marked change in the high percentage (approximately 80%) of monomers which could form aggregates with excess hyaluronate and link protein. Since static tissue compression would result in an increased matrix proteoglycan concentration and thereby a lower intra-tissue pH [Gray, Pizzanelli, Grodzinsky & Lee (1988) J. Orthop. Res. 6, 777-792], it seems likely that matrix pH may influence proteoglycan aggregate assembly by an effect on the hyaluronate-binding affinity of proteoglycan monomer. Such a pH mechanism might have a physiological role, promoting proteoglycan deposition in regions of low proteoglycan concentration.

Animals↗

PubMed1989

Biosynthetic response of cartilage explants to dynamic compression.

The biosynthetic response of calf articular cartilage explants to dynamic compression was examined over a wide range of amplitudes, waveforms, and frequencies. Glycosaminoglycan synthesis was assessed by 35S-sulfate incorporation, and amino acid uptake and protein synthesis were assessed by 3H-proline incorporation. Two culture chambers were designed to allow uniaxial radially unconfined compression and mechanical testing of cartilage disks: one chamber was used inside a standard incubator; the other was used with a mechanical spectrometer and allowed load and displacement to be monitored during compression. Dynamic stiffness measurements of 3-mm diameter disks identified a characteristic frequency [0.001 Hz (cycles/sec)] that separated low- and high-frequency regimes in which different flow and deformation phenomena predominated; e.g., at 0.0001-0.0001 Hz, significant fluid was exuded from cartilage disks, whereas at 0.01-1 Hz, hydrostratic pressure increased within disks. At the higher frequencies, oscillatory strains of only approximately 1-5% stimulated 3H-proline and 35S-sulfate incorporation by approximately 20-40%. In contrast, at the lower frequencies (a) compressions of less than 5% had no effect, consistent with the dosimetry of biosynthetic inhibition by static compression (approximately 25% compression caused a approximately 20% inhibition of radiolabel incorporation), and (b) higher amplitudes (cycling between disk thicknesses of 1.25 and 0.88-1.00 mm) stimulated 3S-sulfate incorporation by approximately 20-40%, consistent with the kinetics of response to a single 2-h compression and release. None of the compression protocols was associated with detectable alterations in (e.g., compression-induced depletion of) total glycosaminoglycan content. This study provides a framework for identifying both the physical and biological mechanisms by which dynamic compression can modulate chondrocyte biosynthesis. In addition, the culture and compression methodology potentially allows in vitro evaluation of clinical strategies of continuous passive motion therapy to stimulate cartilage remodeling.

Animals↗

PubMed1988

Fluorometric assay of DNA in cartilage explants using Hoechst 33258.

A simple two-step fluorometric assay of DNA in cartilage explants, utilizing the bisbenzimidazole dye Hoechst 33258, is described. Cartilage explants were prepared for assay by digestion with papain. Aliquots of the digest were mixed with dye solution, and the fluorescence emission measured. The enhancement in fluorescence of dye was specific for DNA, as demonstrated by 97% sensitivity to DNase and resistance to RNase. In addition, little or no interference was caused by non-DNA tissue components, since DNA caused an equal enhancement in fluorescence independent of the presence of papain-digested cartilage. By performing the assay on isolated chondrocytes, the cellular content of DNA was computed to be 7.7 pg per chondrocyte. The assay was stable for at least 2 h and sensitive to as little as 6 ng of DNA or equivalently less than 1000 cells. This procedure offers advantages over other established DNA assays of cartilage and may be especially useful in metabolic studies of cartilage explants.

Animals↗

PubMed1985

Pacemaker diagnostic diagrams.

Dual-chamber pacemakers interact with cardiac rhythms in complex ways. The resultant surface electrocardiograms (ECGs) are often very difficult to interpret. A simple and automatic diagnostic diagram is described that graphically illustrates pacemaker-heart interactions. Pacemaker operation is explained by a continuous series of lines and symbols that interconnect any sequence of paced and sensed events in both chambers. Fixed, programmable, and adaptive pacemaker timing intervals are all shown in a simple format. The pacemaker diagnostic diagram is plotted directly below the ECG to help users interpret the paced cardiac rhythm. The pacemaker diagnostic diagram is generated by software in a pacemaker programmer from: (1) telemetered real-time event markers; (2) fixed and programmable timing parameters (lower rate, AV interval, etc.); (3) pacemaker conditional logic. If this computer analysis of the telemetered event markers is not consistent with normal pacemaker operation, a specific error-message is printed. The pacemaker diagnostic diagram should be useful for instruction, pacemaker follow-up, and troubleshooting.

Arrhythmias, Cardiac↗

PubMed1984

Prediction of the occurrence of Marek's disease in chickens on the basis of the quantitation of cell-mediated immunity.

Cell mediated immunity was assayed in chickens on the basis of the dinitrochlorobenzene skin test, T lymphocyte numbers in peripheral blood and the graft-versus-host reaction. It was found that chickens that were to develop clinical Marek's disease following exposure to Marek's disease virus had significantly lower prechallenge levels of cell mediated immunity than those that were resistant to Marek's disease. The graft-versus-host reaction had a smaller coefficient of variation than the other two tests, and it was concluded that this test is likely to be the most reliable indicator of the outcome of infection with Marek's disease virus.

Animals↗

PubMed1974