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Biomedical subjects

G N Kent

Publications and source records attributed to G N Kent.

51 records · Page 3Linked to original sources
PubMed1987

Fasting calcium excretion and parathyroid hormone together distinguish familial hypocalciuric hypercalcaemia from primary hyperparathyroidism.

Routine estimation of plasma calcium has made the finding of asymptomatic hypercalcaemia a frequent occurrence. A high index of suspicion for familial hypocalciuric hypercalcaemia (FHH) will lead to accurate diagnosis and avoidance of unnecessary parathyroid surgery. Four FHH kindreds with 16 hypercalcaemic members were found in an unselected referral population over 3 years. Differentiation from primary hyperparathyroidism (42 patients in the same period) was facilitated by analysis of fasting blood and urine for renal handling of calcium, phosphate and cyclic AMP. We found that a plot of serum PTH against fasting calcium excretion separated all cases of each disorder. The discriminatory power of these two variables was confirmed by multivariate discriminant function analysis. An elevated plasma chloride was found to be common to both diseases and of no value in differentiation.

Adult↗
PubMed1985

Pharmacokinetics of synthetic human parathyroid hormone 1-34 in man measured by cytochemical bioassay and radioimmunoassay.

Synthetic human parathyroid hormone (hPTH) 1-34 was given by intravenous injection to two healthy men. The time course of its appearance in and disappearance from the plasma was monitored both by cytochemical bioassay and by a specific radioimmunoassay (RIA) system. Immunoreactive N-region parathyroid hormone (iPTH) reached peak concentrations in plasma at 2 min after injection, whereas peak concentrations of biologically active parathyroid hormone (bioPTH) were delayed until 4-6 min. Bioassayable PTH-like activity then disappeared from the plasma (mean transit times 5.8 and 8.6 min), approximately twice as fast as immuno-reactivity. After separate subcutaneous administrations, a calculated 22-37% of administered hPTH 1-34 was subsequently detected in the plasma, by both assay systems. It was not possible to explain fully the non-parallel appearances of bio- and immuno-reactivities in the plasma after intravenous injection nor the non-parallel disappearances after both intravenous and subcutaneous injections on the basis of the present data. It seems likely, however, that in the process of biological degradation the immuno-reactive locus is inactivated by a different reaction from that which destroys bioactivity. To investigate these activity dissociations further will require the application of micro-fractionation procedures in conjunction with both types of assay system.

Adult↗
PubMed1985

Parathyroid hormone-like bioactivity in a patient with severe osteitis fibrosa cystica due to malignancy: renotropic actions of a tumour extract as assessed by cytochemical bioassay.

A patient is described with malignancy, hypercalcaemia and radiological evidence of severe parathyroid bone disease but undetectable concentrations of circulating immunoreactive PTH. Autopsy showed the tumour to be a metastatic bronchial carcinoid with no evidence of primary parathyroid disease. Extracts of the tumour had no PTH immunoreactivity but had high concentrations of a substance with identical activity to PTH in a cytochemical bioassay. The biological activity of the extract was not inhibited by PTH antibodies but was inhibited by an antagonist to PTH bioactivity.

Aged↗
PubMed1983

Changes in crystal size and orientation of acidic glycosaminoglycans at the fracture site in fractured necks of femur.

The aim of this study was to try to elucidate the increased susceptibility of the neck of femur to fracture. Quantitative polarised light microscopy has been applied to fresh, undecalcified sections of samples of bone taken from the site of fracture, in specimens taken at operation from patients with fractures of the femoral neck or osteoarthritic femoral heads or from the equivalent site from otherwise normal subjects at necropsy. In all 21 specimens of fractured necks of femur, but in none of the other specimens, relatively large crystals (up to 2.5 X 0.5 micrometres) were found close to the site of fracture; the properties of these crystals were compatible with their being apatite. Measurement of the natural birefringence of the collagen showed no difference in the orientation of the collagen in all three types of specimen. However, the orientation of acidic glycosaminoglycans, measured by the birefringence of alcian blue bound to these moieties, was 45 per cent lower in the specimens from fractured necks of femur than in the other specimens, even though the total content of acidic glycosaminoglycans was unchanged. Although the decreased orientation was most marked close to the site of fracture, it was still apparent 15 millimetres from that site. These changes were unlikely to be simply the sequelae of fracture since they were not found in traumatic fractures of other bones. Thus it is conceivable that changes in the orientation of the ground substance allow formation of relatively large crystals of apatite and that such crystals, in the microcrystalline mass of apatite, are the cause of the increased fragility of such bones.

Aged↗
PubMed1982

Formation of bone by isolated, cultured osteoblasts in millipore diffusion chambers.

Osteoblast-like and osteoclast-like cells freed from neonatal calvaria by sequential enzymatic digestion after 6-7 days in culture were placed in diffusion chambers and implanted in the peritoneal cavities of CD-1 mice. About half of the chambers also contained a dead calvarium to test for the need of an "inducer." After 20 days, 11 of 18 chambers containing to osteoblast-like cells formed large foci of mineralized bone that corresponded to alkaline phosphatase activity throughout the chambers. Moreover, only type I (i.e., bone) collagen was formed. Occasional deposits of bone were found in only 3 of 22 chambers containing the osteoclast-like cells. The presence of dead bone did not affect any of the results. These data confirm the osteoblast-like nature of the isolated cell populations and demonstrate that these cells retain their differentiated function in culture.

Animals↗
PubMed1981

Blood levels of calcitonin in microphthalmic (mi/mi) osteopetrotic mouse cannot account for the resistance of bone to this hormone.

Basal and calcium-stimulated levels of calcitonin were measured in blood from microphthalmic-osteopetrotic and normal mice. The basal levels in the osteopetrotic mice were not different from those in normal mice (119.8 +/- 8.1 and 93.8 +/- 8.6 pg/ml, mean +/- s.e.m., respectively). Similarly, the calcium-stimulated increase in calcitonin following injection of calcium was the same in both groups of mice. Previously it has been demonstrated that calvaria from osteopetrotic mice have a blunted response to the biochemical effects of calcitonin compared to calvaria from normal mice. The present data indicates that this decreased response to calcitonin is not due to excessive blood levels of calcitonin or to altered sensitivity of the thyroid gland to blood calcium concentration.

Animals↗
PubMed1980

Homologous and heterologous control of bone cell adenosine 3',5'-monophosphate response to hormones by parathoromone, prostaglandin E2, calcitonin, and 1,25-dihydroxycholecalciferol.

Desensitization of hormone-stimulated cAMP response to parathormone, prostaglandin E2, and calcitonin was characterized in isolated bone cells. Osteoclast- and osteoblast-like cells derived from mouse calvaria were incubated for up to 24 h with agents that cause bone resorption (parathormone, prostaglandin E2, or 1,25-dihydroxycholecalciferol) or with calcitonin, which inhibits bone resorption. The cells were then exposed to parathormone, prostaglandin E2, or calcitonin, and cAMP formation was quantified. Homologous desensitization (refractoriness to the second exposure to the same hormone) occurred for each hormone and was essentially complete after 30 min of preincubation. Heterologous desensitization to parathormone could be produced in both cell types by 1,25-dihydroxycholecalciferol and prostaglandin E2, but not by calcitonin. Heterologous desensitization was of lesser magnitude, requiring more than 8 h to reach significant proportions. In contrast, the cAMP response to calcitonin and prostaglandin E2 could not be altered by preincubation with any other hormone. Dibutyryl cAMP or 3-isobutyl-1-methylxanthine, which are bone-resorptive agents, increased cellular cAMP and caused a slowly developing refractoriness to parathormone, prostaglandin E2, and calcitonin. Calcium (5 mM), an agent which mimics the biochemical action of parathormone in the bone cells but does not affect cAMP similarly desensitized the cells to parathormone, but not to calcitonin and only slightly to prostaglandin E2. These data suggest that heterologous desensitization of bone cells to parathormone results from the initiation of resorption by any agent regardless of whether cAMP is formed during activation of the cells. According to this concept, homologous desensitization to parathormone could involve two components: a rapid phase (< 30 min) and a long term phase, possibly stemming from initiation of resorption.

Animals↗
PubMed1979

The degradation of proparathormone and parathormone by parathyroid and liver cathepsin B.

Purified cathepsin B from porcine parathyroid glands was allowed to act upon radioactive bovine parathormone and proparathormone at various ratios of enzyme to substrate and for different times. The reaction products were isolated by ion exchange chromatography and analyzed by gel electrophoresis, amino acid composition, sequence analysis, and bioassay. The enzyme cleaved parathormone between residues 36 and 37 yielding a major carboxyl and amino fragment and appeared to cleave proparathormone at the same locus. The amino fragments were degraded further by removal of small peptides (possibly, di- or tripeptides) from their COOH termini. In contrast there was little if any degradation of the carboxyl fragment (residues 37 to 84). Despite the ease with which the enzyme cleaved the arginyl bond in the synthetic substrate benzyloxycarbonyl-Val-Lys-Lys-Arg-(4-methoxy)-2-naphthylamide, it did not remove the near homologous NH2-terminal hexapeptide extension of proparathormone (Lys-Ser-Val-Lys-Lys-Arg-R)--a reaction that would lead to the formation of parathormone from proparathormone. Purified liver cathepsin B cleaved the hormonal substrates in a fashion identical with that of the parathyroid enzyme.

Amino Acid Sequence↗
PubMed1977

Anticonvulsant induced increase in 25-hydroxy-vitamin D3-1alpha-hydroxylase.

Osteomalacia has been shown to be associated with long-term anticonvulsant therapy. Anticonvulsants modify the hepatic metabolism of vitamin D3 and decrease serum 25-hydroxy-vitamin D3 (25-OH-D3) levels. We have confirmed this and have shown that diphenylhydantoin (DPH) and phenobarbitone (PB) enhance the activity of kidney 25-hydroxy-vitamin D3-1alpha-hydroxylase (1-hydroxylase) in the chicken. Thus, anticonvulsant osteomalacia may not be due to a lack of the active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 (1,25 (OH) 2D3).

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMedDate not supplied

A sensitive assay for the measurement of serum chondroitin sulfate 3B3(-) epitope levels in human rheumatic diseases.

OBJECTIVE: To develop a sensitive assay to quantitate serum 3B3(-) levels in patients with rheumatoid arthritis (RA) and osteoarthritis (OA) as well as levels in control sera. METHODS: An enzyme-linked immunosorbent assay (ELISA) was developed using the monoclonal antibody (MAb) 3B3 to detect a chondroitin sulfate (CS) epitope in the sera and synovial fluid (SF) of RA and OA patients. Keratan sulfate levels were measured in the same biological fluids using the 5D4 monoclonal antibody. RESULTS: The detection limit for our 3B3(-) assay was 2 micrograms/L. Most OA sera sample curves run on the 3B3 assay were parallel (87.5%) to the standard curve and detectable (90.0%). RA sera sample curves were 87.1% detectable and 85.2% parallel. The 3B3(-) epitope was detectable in 60% of control sera and of these 66.7% of sample curves were parallel to the standard curve. All RA and OA SF had detectable quantities of 3B3(-). For the 3B3 assay, the OA and RA sera levels were significantly higher than for control sera (P = 0.03, P = 0.04 respectively). We found a significant correlation in a subset of paired OA sera and SF 3B3(-) concentrations. No correlation was found between age, joint activity scores, HAQ and CRP in RA patients and sera 3B3(-) and 5D4 levels. CONCLUSION: We have validated this assay for the quantification of 3B3(-) epitope in RA and OA serum. Levels of this epitope are significantly higher in sera from RA and OA patients than controls. 3B3(-) levels in RA sera were found to correlate with disease duration.

Adult↗