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Biomedical subjects

J Chayen

Publications and source records attributed to J Chayen.

At least 55 records · Page 3Linked to original sources
PubMed1985

Increased myosin orientation during muscle contraction: a measure of cardiac contractility.

Myosin form birefringence has been studied in cryostat sections of left ventricular myocardium from the dog and human. The muscle in such sections has been shown to demonstrate the sliding filament phenomenon. The sarcomere length of canine myocardium agreed with that found in comparable electron micrographs. Unexpectedly, it was found that glycerol, normally used as an inert and optically ideal mountant, caused profound change in myosin birefringence. This apparently invalidates results obtained with this mountant. The absolute birefringence found in these sections, whether mounted in glycerol or in an ATP-calcium buffer, corresponded to values found by other workers with skeletal muscle and isolated myosin. However, the birefringent properties (optical path difference: o.p.d.) of well functioning muscle was found to be low, the o.p.d. increasing when exposed to ATP and calcium. Poorly functioning muscle could be distinguished from well functioning muscle on the basis of its higher 'in air' o.p.d. This difference correlated well with physiological assessments of myocardial function or with clinical assessments of cardiac failure. Evidence is presented indicating that changes in apparent birefringence, caused by ATP-calcium or by anoxia, are due to altered orientation of the myosin micelles and can be inhibited by agents that inhibit myosin ATPase activity.

Adenosine Triphosphate↗
PubMed1985

Altered orientation of glycosaminoglycans and cellular changes in the tibial cartilage in the first two weeks of experimental canine osteoarthritis.

Changes in the cellularity and in the nature of the matrix were studied in the cartilages of the tibial plateau in experimentally induced arthritis in the dog, 7 and 14 days after section of the anterior cruciate ligament. Samples from the different regions of these cartilages were chilled and sectioned in a cryostat, with a variable microtome chuck to allow precise orientation of the specimens. The samples were examined by normal light microscopy, by microscopic interferometry, and by quantitative polarized light microscopy. The orientation of the glycosaminoglycans was assessed by the new "induced birefringence" method. The results indicated that only the region of the medial tibial cartilage that was unprotected by the meniscus was affected, showing increased water content, loss of superficial cells, and a decrease in orientation of the glycosaminoglycans. Whereas the birefringence of the collagen was unaffected, the superficial area that lacked oriented glycosaminoglycans was markedly increased; this may be a useful indicator of early osteoarthritic changes.

Alcian Blue↗
PubMed1985

Electrochemical detection of depressed circulating levels of vitamin K1 in osteoporosis.

If gamma-carboxylation, by the vitamin K1 - cycle, of glutamate residues of bone-matrix peptides is essential for the formation of bone, the circulating levels of this vitamin might indicate the potential efficiency of this process. Methods involving HPLC with electrochemical detection have very recently been developed for assaying the low levels of vitamin K1 that occur in normal plasma. Using such methods, we found that the circulating levels of vitamin K1 in osteoporotic patients (who had sustained either spinal crush-fractures or fractures of the neck of the femur) were significantly lower than those of age-matched control subjects.

Aged↗
PubMed1984

Use of microscopic interferometry for measuring changes in water content of small samples of tissue.

Oedema following periods of ischaemic arrest and subsequent reperfusion has been shown experimentally and clinically to affect the functional state of the heart. Tissue water content has been measured in myocardial sections by microscopic interferometry and densitometry, and the results correlated with those obtained by wet and dry weight analysis (r = 0.87; p less than 0.001). Microscopic interferometry also revealed the distribution of the water in the tissue. Experimentally induced ischaemic arrest in isolated rat hearts resulted in predominantly intra-fibrillar oedema, whilst subsequent reperfusion resulted in interfibrillar oedema. Microscopic interferometry facilitates accurate measurement of water content in tissue samples as small as 2 mg wet weight and shows (as conventional wet/dry weight analysis cannot) the distribution of the water in the tissue.

Animals↗
PubMed1984

Possible mechanism for target cell lysis by cytotoxic T-cells.

The mechanism of the lysis of target cells by cytotoxic T-cells (Tc) is still obscure; there is no evidence for transfer of material from the Tc and prior to lysis, despite intimate contact, the plasma membranes of both types of cell appear to remain intact. The effects on the target cell lysosomes of brief contact between anti-viral Tc and targets bearing both the appropriate histocompatibility and viral antigens, have been examined cytochemically. Both the distribution of acid phosphatase activity and the percentage bound lysosomal naphthylamidase activity indicated that, in virus-infected target cells exposed to Tc, the lysosomal membranes became totally labilized. Thus the contact between Tc and targets appears to cause sufficient perturbation of the target plasma membrane as to cause the intracellular release of some agent that activates 'suicide capsule' lysosomes.

Acid Phosphatase↗
PubMed1984

Effects on fracture healing of an antagonist of the vitamin K cycle.

The anticoagulant, dicumarol, inhibits the vitamin K cycle by blocking the conversion of the vitamin K epoxide. The effects of dicumarol on ossification have been tested by feeding it to rats in which a closed fracture of the metatarsals had been induced; the effects were studied up to 12 days postfracture. At 12 days, treatment with dicumarol caused a highly significant decrease in the amount of bone produced, without affecting the total size of the callus. Quantitative cytochemistry of unfixed, undemineralized sections showed that dicumarol also markedly affected the periosteal activities of glucose 6-phosphate dehydrogenase and of alkaline phosphatase in the first 2 mm from the fracture measured at 3 and 5 days postfracture when normally, new bone is first formed. In contrast, dicumarol had little effect on these activities in the fully formed callus.

Alkaline Phosphatase↗
PubMed1984

An investigation of the biological activity of parathyroid hormone in pseudohypoparathyroidism: comparison with vitamin D deficiency.

Circulating parathyroid hormone was studied in patients with pseudohypoparathyroidism and compared with that in normal subjects and patients with hypocalcaemia due to postsurgical or idiopathic hypoparathyroidism or vitamin D deficiency. The cytochemical bioassay was used to measure bioactivity and an amino-terminal specific immunoradiometric assay was used to measure immunoreactivity. In normal subjects (n = 12) the concentration of bioactive parathyroid hormone was 1.1-5.9 pg/ml. It was higher in patients with newly diagnosed, untreated pseudohypoparathyroidism (n = 4, range 20-53 pg/ml) and similarly raised in patients with untreated vitamin D deficiency (n = 9, range 23-74 pg/ml). The degree of hypocalcaemia was similar in these two groups of patients. By contrast, the concentration of bioactive parathyroid hormone was low (less than 0.6 pg/ml) in four patients with untreated postsurgical or idiopathic hypoparathyroidism. Restoration of normocalcaemia reduced the concentrations of bioactive PTH in both pseudohypoparathyroidism and vitamin D deficiency. Thus, in this respect the parathyroid glands in both conditions appeared to respond to the circulating calcium concentration. Immunoreactive PTH was also raised in patients with untreated pseudo-hypoparathyroidism and vitamin D deficiency, but restoration of normocalcaemia did not always reduce immunoreactive PTH to normal in these patients. Thus, there can be dissociation between bioactivity and immunoreactivity even when the PTH is measured in an amino-terminal specific assay.

Adolescent↗
PubMed1983

Aerobic glycolysis of bone and cartilage: the possible involvement of fatty acid oxidation.

The apparent paradox of aerobic glycolysis has been investigated in bone and in cartilage. A new cytochemical procedure for hydroxyacyl dehydrogenase (HOAD) activity showed that the maximal activity of this enzyme in both tissues was equivalent to the maximal activity of glyceraldehyde 3-phosphate dehydrogenase (GAPD). The sum of these activities gave a measure of the maximum amount of acetyl-coenzyme A that could be produced. In these tissues, but not in liver which does not exhibit aerobic glycolysis, this summed value exceeded the maximal activity of succinate dehydrogenase (SDH). Consequently, it suggested that where fatty acid oxidation is sufficient to supply all the acetyl-coenzyme A required for the Krebs' cycle, that derived from fatty acid oxidation may inhibit pyruvate dehydrogenase causing accumulation of pyruvate which must be converted to lactate if pentose-shunt activity is to be maintained.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1983

Biopsy assessment of preservation during open-heart surgery with cold cardioplegic arrest.

The efficacy of cold cardioplegic arrest as a method of myocardial preservation has been evaluated by cytochemical and biophysical assessments made on needle biopsies taken from 150 patients undergoing open-heart surgery (e.g., aortic valve replacement, aortic and mitral valve replacement, mitral valve replacement, coronary artery bypass graft, repair of atrial or ventricular septal defects). Comparison of endo- and epicardial preservation showed improved endocardial preservation with cardioplegia compared with that achieved with the previous method used--continuous coronary perfusion at 32 degrees C; however, care had to be taken to ensure adequate cooling of the epicardium. Biopsies also showed the need for repeated infusions of cardioplegic solution if the aorta was occluded for more than 70 min. Preservation of right and left ventricle has also been compared.

Biopsy↗
PubMed1983

Metabolic changes in the cells of the callus during fracture healing in the rat.

Unfixed, undecalcified sections from closed fractures of rat metatarsals have been studied by quantitative cytochemistry from the first week after fracture to late in the fracture-healing process. Alkaline phosphatase activity appeared to be related to calcification. Glucose 6-phosphate dehydrogenase activity was associated with proliferation and with calcification. Studies made with the critical electrolyte Alcian blue technique suggested that whether the ossification process is of the endochondral or membranous type might be predetermined in the relatively undifferentiated callus.

Alkaline Phosphatase↗
PubMed1983

The effect of ionized calcium, pH, and temperature on bioactive parathyroid hormone during and after open-heart operations.

Normal myocardial function is dependent on the metabolic balance of a number of electrolytes and hormones. The calcium ion plays a major role in muscle contraction and is rigorously controlled within narrow limits. Open-heart surgery imposes metabolic disturbances on both electrolytes and hormones, especially ionized calcium. Normally, ionized calcium levels are controlled by parathyroid hormone with a negative feedback from the ionized calcium controlling the system, but the results from this study suggest that during open-heart procedures, ionized calcium does not impose its normal negative feedback on bioactive parathyroid hormone secretion. The low blood pH levels that occurred during the operative conditions of the patients studied and the level of hypothermia imposed on the circulating blood during cardiopulmonary bypass appeared to influence the control of parathyroid hormone secretion, causing high levels of hormone to be secreted during this period.

Adult↗
PubMed1983

The cytochemical bioassay of parathyroid hormone: further experience.

The procedure for the cytochemical bioassay of parathyroid hormone has been examined to improve the reliability and robustness of the assay. It has been shown that the control of the pH, at all stages of the assay, is essential. The use of the assay confirmed that the circulating level of the biologically active form of this hormone is less than one tenth of the values found by the more recent immunoassays, and is in good agreement with previously calculated values. The assay clearly distinguished between normal, hypoparathyroid and hyperparathyroid levels and allowed relative potencies to be ascribed to preparations of the hormone obtained from human, bovine and porcine sources.

Animals↗
PubMed1983

An effect of parathyroid hormone on the epiphyseal plate and osteoblasts: studies towards a cytochemical bioassay.

There are reports of an apparent dissociation between the responses of kidney and bone to parathyroid hormone (PTH): certain fragments or analogues have been shown to have differential activity in these two tissues. Consequently, cytochemical bioassay techniques have been applied to the development of an assay for PTH using the epiphyseal plate of the rat metatarsal as the target organ. Glucose 6-phosphate dehydrogenase activity in the zone of hypertrophic cartilage is stimulated in a log-linear fashion with increasing concentrations of parathyroid hormone over the range 0.001 - 1.0 pg/ml. A parallel response was found in the osteoblasts of the metaphysis. Measurements of a normal and a hyperparathyroid plasma sample showed good parallelism to the standard graph and good discrimination. Addition of a PTH - specific antibody inhibited both the effect of the standard preparation of the hormone, and the response induced by dilutions of a normal plasma.

Animals↗