Stress relaxation experiments were performed for articular cartilage (AC) specimens which were cultured in the medium (DMEM) containing collagenase and in the medium containing cellular fibronectin having an extra domain A (EDA(+)FN). For all the specimens measured, stress relaxation was divided into two processes: the process observed in the short time region (S-process) and that observed in the longer time region (L-process). Relaxation modulus of L-process was described by a simple exponential type function with single relaxation time, while the decay in S-process was more rapid than that of L-process and seemed to contain many relaxation times. In AC cultured with collagenase, S-process became dominant as compared with AC cultured in DMEM without collagenase nor EDA(+)FN (control). As type II collagen molecules in AC are destroyed by a collagenase digestion, S-process was regarded as the molecular-scale structural change in collagen fibrils. For AC cultured with EDA(+)FN, increase in modulus was observed as compared with the control system. This increase was considered as the collagen synthesis by chondrocytes activated by EDA(+)FN. A chronic existence of EDA(+)FN may break the homeostatic metabolism of AC matrix by chondrocytes, which can be a trigger of rheumatoid arthritis in AC.

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The aim of this study was to characterize the spatial distribution of microregional blood flows in the left ventricular subendocardium. The within-layer myocardial flow distributions in subendocardium (Endo) and subepicardium (Epi) of anesthetized rabbit left ventricular free walls (n=6) were measured using high-resolution digital radiography combined with the ³H-labeled desmethylimipramine deposition technique [sample size (SS) =0.1 mm]. The spatial pattern of flow distribution was quantitated by the coefficient of variation of regional flows (CV, related to global flow heterogeneity) and the correlation between adjacent regional flows (CA, related to local flow homogeneity). To evaluate the resolution-dependence of regional flows, CV and CA were also computed for several coarse-grained images reproduced from the original by increasing SS step by step from 0.1 to 1 mm. Both CV and CA were higher in Endo than in Epi at all levels of resolution (P<0.05, Wilcoxon test). Fractal nature of CV existed in both layer; however the fractal dimension was lower in Endo than in Epi (P<0.05, Wilcoxon test). In both layers, CA increased with increasing SS and reached a plateau at SS=0.4 mm. We conclude that globally, the microregional flow distribution is more heterogeneous but locally, more homogeneous in Endo than in Epi. The large global flow heterogeneity in Endo may be attributable to the high heterogeneity of coronary anatomy and myocardial stress distribution in Endo. The large local flow homogeneity and low fractal dimension in Endo may be related to the high oxygen demand in Endo. The higher oxygen demand will bring about more cooperative behavior of nearby regulatory units, the minimum size of which is estimated to be 0.4 mm.

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The nickel mesh filtration system was designed to automatically obtain the pressure -(P) vs flow rate (Q) characteristics through a personal computer (PC). Since the operating system (OS) used in the PC was MS-DOS, we updated OS using Windows 95. The disturbance of electric noise was reduced with a variable first-order lag filter. To optimize the quantification of the P-Q relationship, the P-Q relationship was numerically expressed by the polynomial fitting with the least square approximation; the polynomial order was automatically selected to the best fitting. The new system could contribute to the various related fields of erythrocyte filterability.

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