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Biomedical subjects

R A Melick

Publications and source records attributed to R A Melick.

At least 19 recordsLinked to original sources
PubMed1988

The metabolic clearance rate of osteocalcin in sheep.

Plasma osteocalcin has been proposed as a useful and convenient biochemical marker of bone formation. However, the effect on plasma osteocalcin due to variations in the rate of its removal from the circulation has been little investigated. We have measured the metabolic clearance rate of plasma osteocalcin in adult oophorectomized sheep. Two methods were used: intravenous bolus injection (six animals) and 6 hour constant intravenous infusion (four animals) of 125I-ovine osteocalcin. Using the bolus injection method, the plasma clearance of osteocalcin was found to be 3.3 liters/h. With the constant infusion method, the calculated value was 2.8 liters/h; based on this value and the mean ovine plasma osteocalcin concentration of 26.9 ng/ml (N = 29), a plasma production rate of 1.8 mg/day was derived. Osteocalcin clearance was relatively constant among animals in a basal state. Hence, the present approach should permit us to evaluate the relative contributions to changes in circulating osteocalcin levels from altered osteocalcin plasma clearance and production under various physiological and pathological conditions.

Animals↗
PubMed1987

Hypokalemic periodic paralysis of thyrotoxic origin.

A 50-year-old Vietnamese man suffered recurrent episodes of hypokalemic periodic paralysis during treatment for thyrotoxicosis. Suspected precipitants of the paralysis were oral prednisolone, strenuous exertion and poor compliance with medications. Propranolol prevented the periodic paralysis. Control of the thyrotoxicosis was complicated by a florid skin reaction attributed to carbimazole, and was ultimately achieved using radioiodine.

Australia↗
PubMed1986

Metabolism of osteocalcin.

After intravenous injection, labeled bovine osteocalcin was rapidly removed from rat plasma and taken up mainly by kidney, liver, and bone. The rate of disappearance was slowed by nephrectomy but not as much by ureteric ligation, suggesting renal destruction of osteocalcin rather than renal excretion. Both liver and kidney tissue rapidly degraded osteocalcin, both in vivo and in vitro. The enzyme activity was found in microsomal, mitochondrial, and supernatant fractions. EDTA was the most potent inhibitor, suggesting that metalloenzymes are involved. Comparison of three methods of analysis--trichloroacetic acid precipitation, gel filtration on Sephadex G-50, and SDS polyacrylamide gel electrophoresis--showed that the last gave a much faster rate of degradation of osteocalcin and suggests that osteocalcin and/or fragments bind to larger proteins in the tissue homogenates.

Animals↗
PubMed1985

Plasma osteocalcin in man.

A radioimmunoassay for bovine osteocalcin has been developed. Human osteocalcin reacted identically with the bovine standard, allowing the use of this assay to measure human plasma osteocalcin. Levels were determined in 212 healthy subjects (124 men, 88 women) with an age range of 20 to 66 years. The distribution of these was skewed to the right, with the mean being 14.7 ng/ml (range 4 to 40) and the geometric mean 12.2 ng/ml. There was no alteration with age and no difference between males and females. High levels were found in chronic renal failure, Paget's disease of bone, and in primary hyperparathyroidism with severe bone disease, and there was a significant positive correlation of osteocalcin with plasma alkaline phosphatase. Low levels were found in pregnancy. Evidence is presented which suggests that the high levels measured probably reflect intact osteocalcin and not immunoreactive fragments. Our data are compared with those reported by others. Areas of disagreement are noted and discussed.

Adult↗
PubMed1984

Noncollagenous proteins in normal and pathological human bone.

The concentrations of alpha 2HS-glycoprotein, albumin, and sialic acid were measured in the bone of 28 normal individuals and 6 patients with osteogenesis imperfecta, 3 patients with Paget's disease, and 4 patients with either renal osteodystrophy, osteoporosis, osteomalacia, or osteopetrosis. The concentration of alpha 2HS-glycoprotein in neonatal bone was 3 X higher than in bone from children and 7 X higher than in adult bone. The concentrations of albumin and sialic acid in neonatal bone were 1.5 X higher that in bone from children and twice the levels in adult bone. The concentrations of alpha 2HS-glycoprotein, albumin and sialic acid were above the normal mean values in the patients with osteogenesis imperfecta, and 4 patients had significantly raised levels of one or more of these proteins. The concentrations of these noncollagenous proteins were also significantly raised in Paget's disease, and the alpha 2HS-glycoprotein was significantly raised in renal osteodystrophy. The lowest level of alpha 2HS-glycoprotein was in osteopetrotic bone and the lowest levels of albumin and sialic acid were in osteoporotic bone. The results of this study suggest that the concentrations of alpha 2HS-glycoprotein, albumin, and sialic acid in bone are related to the rate of bone turnover.

Adolescent↗
PubMed1984

Analysis of collagen from normal and abnormal human bone.

Using cyanogen bromide digestion of bone collagen, we have studied the type of collagen in normal bone, and in samples from patients with Paget's disease of bone, osteomalacia, osteoporosis and renal osteodystrophy. Despite extensive extraction with ethylene diamine tetraacetic acid and guanidine hydrochloride, not all of the glycoproteins could be removed from bone collagen. Upon electrophoresis on sodium dodecyl sulphate polyacrylamide gels, the cyanogen bromide peptides of insoluble bone collagen showed the pattern of type I collagen only in all samples, both normal and abnormal. Amino acid composition of the insoluble collagens and the ratio of hydroxylated and non-hydroxylated amino acids were similar for all adult bone samples. These results suggest that the type of collagen in bone is not altered in the bone diseases examined.

Adult↗
PubMed1983

Chemical composition of human bone.

The mineral and non-collagenous organic components of normal human femoral cortex were examined following powdering, demineralization with EDTA and digestion with bacterial collagenase. The protein, hexose, sialic acid and uronic acid contents of the matrix were determined. Neonatal bone had lower levels of mineral and calcium and higher levels of organic material and sialic acid than adult bone, suggesting increased glycoprotein content in neonatal bone. The soluble non-collagenous matrix of human femoral cortex was examined by gel filtration on Sephadex G100 and by ion-exchange chromatography on DEAE-cellulose. Four fractions were eluted off Sephadex-G100: a large molecular weight fraction, a shoulder on the descending portion of this, both of which contained sialic acid and two smaller molecular weight fractions. The material eluted off DEAE-cellulose was separated into 6 fractions which were similar to those found for beef and rabbit bone matrix. Human bone matrix appeared more resistant to collagenase digestion than beef bone, soluble collagen eluted later off DEAE-cellulose than beef bone; sialic acid gave 3 peaks: a major and two lesser ones. The sialic acid-containing material in the fifth fraction was probably bound to proteoglycan. Rabbit bone has 2 to 3 sialic acid peaks whereas beef bone has one, indicating species differences in cortical bone matrix.

Adolescent↗
PubMed1981

Effect of temperature on phospholipase C induced alterations in insulin binding.

Regulation of insulin-receptor affinity is at present poorly understood. In this study membrane structure was modified by exposing placental membranes to phospholipase C and the subsequent effect on insulin binding and dissociation was examined. As previously described, when insulin-receptor binding was performed at 4 degrees C, phospholipase C treated membranes showed an increase in the apparent number of insulin receptors. However, when binding was performed at 24 degrees C, the predominant effect of prior phospholipase C treatment was to increase the affinity of binding. At this temperature, phospholipase C pretreatment also increased membrane fluidity. Cytochalasin B, an agent which disrupts receptor aggregates, lowered average affinity at 24 degrees C. Phospholipase C treatment slowed the dissociation rate in 'infinite dilution' at 24 degrees C but the accelerating effect of 100 ng/ml insulin (negative cooperativity) was greatly enhanced. These studies suggest that in addition to its effect in unmasking receptor sites, increased membrane fluidity induced by phospholipase C may cause higher affinity binding by allowing greater receptor or receptor subunit aggregation. Receptor or subunit aggregation within a fluid membrane structure may determine in part the affinity of insulin-receptor binding and the kinetic phenomenon known as negative cooperativity.

Cytochalasin B↗
PubMed1980

The effects of trypsin and phospholipase C on insulin binding and action in the isolated adipocyte.

The effect of alterations to the insulin receptor on the insulin sensitivity of isolated adipocytes was studied. Receptor changes were induced by treatment of adipocytes with either phospholipase C or trypsin. After enzyme treatment, binding of insulin to insulin receptors and insulin-mediated glucose metabolism were examined. Exposure of adipocytes to phospholipase C (2 units/ml) significantly increased insulin binding to the cells, but destroyed the ability of the cells to oxidize glucose. After treatment with trypsin (500 micrograms/ml) for 5 min, insulin binding to the adipocytes was significantly increased. This was shown to be due to an increase in insulin-receptor affinity. Metabolic studies showed that trypsin treatment led to an increase in basal glucose transport but markedly decreased the response to insulin at all concentrations tested. Adipocytes treated with trypsin showed no significant difference in basal glucose oxidation rates when compared with controls, but were less sensitive to insulin at low insulin concentrations, and showed a decreased maximum response at high insulin concentrations. In conclusion, these findings indicate a dissociation between induced changes in binding of insulin to insulin receptors and subsequent hormone action. The importance of post-receptor events in the biological action of insulin is highlighted.

Adipose Tissue↗
PubMed1980

The demonstration of sialic acid in kidney stone matrix.

1. The organic matrices of 12 kidney stones containing calcium and two composed of uric acid were solubilized, with ethylenediaminetetra-acetate for the former and sodium hydroxide for the latter. 2. The solubilized matrices and residual fine particulate material were examined for sialic acid by the thiobarbituric acid method. 3. Sialic acid was found in every stone in either the soluble and/or insoluble material. 4. The identity of sialic acid was confirmed by the absorption spectrum of the colour produced and by its release from the protein by neuraminidase. 5. The presence of sialic acid in all stones despite widely varying composition suggests that it may be passively deposited.

Hexoses↗
PubMed1979

Hypercalcaemia in adult hospital population: comparison of inpatients of 1966 with those of 1976.

During 1976, inpatients with hypercalcaemia at The Royal Melbourne Hospital were identified from the worksheets of the Department of Biochemistry and compared with those discovered in a similar study in 1966. In 1966, the estimation of plasma calcium level had to be ordered specifically, whereas in 1976, for technical reasons, the measurement of plasma calcium level was frequently performed when not requested. Despite a six-fold increase in plasma calcium in the rate of detection of hypercalcaemia. In both studies, malignant disease was the most common casue of hypercalcaemia, but primary common cause of hypercalcaemia, but primary hyperparathyroidism was found slightly more frequently in 1976. This study suggests that screening inpatients for hypercalcaemia is of little value.

Clinical Laboratory Techniques↗
PubMed1979

Osteomalacia due to unusual causes presenting in adults.

Severe osteomalacia due to causes other than malabsorption and, where renal function was impaired, disproportionate to the degree of renal failure, is described in 15 adults. Only one was younger than 46 years, the median age being 59 years. The diagnosis was not made for months in most patients. After investigation, the patients were grouped as follows: nutritional three cases, "renal" six cases, hypophosphataemia three cases, neurofibromatosis and primary hyperparathyroidism one each. The last patient was poorly nourished and had taken anticonvulsants and analgesics. Most patients responded well to treatment with calciferol. These cases indicate the need to be aware that osteomalacia may occur in previously healthy middle-aged or elderly subjects.

Adult↗
PubMed1979

Metabolic properties of hormonally responsive osteogenic sarcoma cells.

There is sufficient impetus from the clinical nature of osteogenic sarcoma to stimulate basic studies of the effects of hormones on tumor growth and differentiation. This can probably best be done first by the use of in vitro studies to determine precisely the effects of certain hormones on tumor cell growth and biochemical function. Such investigations would hopefully indicate the direction of in vivo work. The differentiated transplantable tumor described in this paper is clearly hormone-responsive, and offers a means of investigating the effects of other hormones, including growth hormone, androgens, estrogens and glucocorticoids, on specialized function of the osteogenic sarcoma cells, and on the growth of the tumor.

Adenylyl Cyclases↗