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Biomedical subjects

N Loveridge

Publications and source records attributed to N Loveridge.

At least 91 records · Page 5Linked to original sources
PubMed1988

The metatarsal cytochemical bioassay of parathyroid hormone: validation, specificity, and application to the study of pseudohypoparathyroidism type I.

The most sensitive method for assaying the bioactivity of PTH in unextracted plasma is the renal cytochemical bioassay. However, PTH acts on bone as well as kidney and clinical studies have suggested that the actions of circulating PTH level may be different at the two sites. We developed cytochemical bioassay for PTH based on the stimulation of glucose 6-phosphate dehydrogenase activity in the hypertrophic chondrocytes of the growth plate and the osteoblasts lining the metaphyseal trabeculae of rat metatarsal bones. The index of precision was 0.14 +/- 0.02 (SE) and the interassay variation was 31%. With this assay, plasma bioactive PTH levels in normal subjects and patients with primary hyperparathyroidism ranged from 0.5-18 ng/L and from 27-850 ng/L, respectively. Studies of patients with pseudohypoparathyroidism type I indicated that plasma PTH bioactivity in such patients is greater in the metatarsal bioassay than in the renal bioassay; no such differences were found in normal subjects or patients with primary hyperparathyroidism.

Adolescent↗
PubMed1987

PTH bioactivity in osteoporosis.

The cytochemical bioassay for parathyroid hormone was used to measure the levels of PTH bioactivity in normal elderly subjects and patients suffering from idiopathic or postmenopausal osteoporosis. In normal subjects, PTH bioactivity did not increase with age. In the osteoporotic patients levels of bioPTH discriminated between two populations, one with normal levels and the other with elevated levels. In both these groups the PTH bioactivity was neutralised by the addition of a PTH antiserum. The recovery of the bioactivity of PTH added to the plasma samples was significantly higher in the plasmas from patients with elevated levels of bioPTH. Levels of immunoreactive PTH also discriminated between the two groups of osteoporotic patient although no serum parameters indicative of increased PTH were detectable. However, patients with the high levels of bio- and immunoPTH had a lower incidence of fracture within the previous 12 months.

Adult↗
PubMed1986

Separation of inhibitory activity from biologically active parathyroid hormone in patients with pseudohypoparathyroidism type I.

Patients with pseudohypoparathyroidism type I have the symptoms of hypoparathyroidism despite elevated levels of immunoreactive parathyroid hormone (PTH). However, the circulating levels of bioactive PTH, as measured in a cytochemical bioassay, are generally within the normal range suggesting that the high levels of immunoreactive PTH are either due to the presence of biologically inactive fragments of parathyroid hormone or to the presence of an 'inhibitor' of PTH bioactivity. Gel-permeation chromatography has been used to fractionate plasma from patients with pseudohypoparathyroidism type I and revealed the presence of high levels of bioactive PTH and of an 'inhibitor'. This inhibitory activity was absent or much lower in plasma from control subjects. These results indicate, therefore, that in pseudohypoparathyroidism type I the expression of the biological activity of PTH at the level of the kidney is affected by the presence of a circulating inhibitor which can be separated from intact PTH by gel-permeation chromatography.

Adolescent↗
PubMed1986

Suppression of parathyroid hormone inhibitory activity of plasma in pseudohypoparathyroidism type I by i.v. calcium.

The biological response, as measured in the cytochemical bioassay, to the high circulating levels of immunoreactive parathyroid hormone (iPTH) in patients with pseudohypoparathyroidism type I (PSPI) is affected by the presence of an endogenous inhibitor. This is evidenced by the reduced recovery of the biological activity of PTH added to the plasma. Here we have used i.v. calcium infusion to inhibit the release of PTH and studied endogenous PTH bioactivity and immunoreactivity as well as the recovery of the bioactivity of added PTH in a normal subject and two patients with PSPI. In the control subject both bioactive PTH (bioPTH) and iPTH fell in response to the increased levels of plasma calcium and the recovery of the biological activity of PTH added to the plasma remained unchanged. In the PSPI patients, although the level of iPTH fell, the level of bioPTH remained unchanged. However, the level of inhibitory activity of the plasma, as determined by the recovery of added PTH, was transiently normalized in response to the rise in plasma calcium. Thus i.v. calcium infusions not only suppress the release of endogenous iPTH but also the inhibitory activity present in the plasma of PSPI patients.

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↗
PubMed1984

A quantitative study of peroxidase activity in unfixed tissue sections of the guinea-pig thyroid gland.

A technique for the cytochemical demonstration of peroxidase activity in unfixed guinea-pig thyroid tissue is described in this paper. The substrate 3,3'-diaminobenzidine tetrahydrochloride (DAB) is oxidized by the peroxidase to form an insoluble reaction product. Optimal results were obtained after 20 min incubation at 37 degrees C in reaction medium containing 1.4 mM DAB (in 0.1 M Tris-HCl) and 0.15 mM hydrogen peroxide at pH 8.0. Peroxidase activity was seen in the thyroid follicle cells as a diffuse brown reaction product (which was more dense and granular in erythrocytes). The enzyme activity was quantified using a scanning-integrating microdensitometer, and the effects of two specific peroxidase inhibitors were evaluated. Both 3-amino-1,2,4-triazole and methimazole inhibited peroxidase activity in the follicle cells (enzyme activity was still seen in the erythrocytes), maximal inhibition occurring at 10 mM. Stimulation of peroxidase in the thyroid was observed in vivo (1 I.U. TSH administered every 8 h for two days), with the maximal stimulation occurring after 1 day.

3,3'-Diaminobenzidine↗
PubMed1984

Biologically active parathyroid hormone in familial hypocalciuric hypercalcaemia.

Biologically active PTH (bio-PTH) has been assayed by the cytochemical bioassay in five members (three affected) of a family with typical features of familial hypocalciuric hypercalcaemia (FHH). Carboxy-terminal immunoreactive PTH was undetectable and bio-PTH was within the normal range in all the subjects regardless of whether or not they were hypercalcaemic. These results suggest that increased biological activity of circulating PTH cannot account for the hypercalcaemia of FHH.

Adolescent↗
PubMed1984

Parathyroid hormone responses to calcium stress during eggshell calcification.

PTH bioactivity during the egg-laying cycle of the chicken has been measured by the cytochemical bioassay for PTH. During the period of eggshell calcification, PTH bioactivity is elevated. After completion of the shell the plasma PTH falls to a low level but is slightly raised again 2 h after ovulation. These results indicate that changes in bioactive PTH play an important role in the calcium metabolism of the chicken during this physiological calcium stress.

Animals↗
PubMed1984

Familial hypocalciuric hypercalcaemia: evidence for continued enhanced renal tubular reabsorption of calcium following total parathyroidectomy.

A patient with familial hypocalciuric hypercalcaemia (FHH) is reported. Seven years after total parathyroidectomy he remained hypocalcaemic, with biochemical evidence of hypoparathyroidism (enhanced renal tubular reabsorption of phosphate, low nephrogenic cyclic AMP excretion, and reduced serum concentration of 1,25-dihydroxycholecalciferol in the presence of normal renal function and normal serum 25-hydroxyvitamin D levels). Iv infusions of calcium were given before and 6 years after total parathyroidectomy. The renal tubular reabsorption of calcium was compared in these two situations. No difference was found. Before and after parathyroidectomy there was enhanced renal tubular reabsorption of calcium. It is concluded that the enhanced renal tubular reabsorption of calcium in FHH is independent of parathyroid hormone. Total parathyroidectomy corrects the hypercalcaemia in FHH by a reduction in the input of calcium into the extra-cellular fluid from gut and or bone perhaps as a result of reduced renal synthesis of 1,25-dihydroxycholecalciferol.

Adolescent↗
PubMed1982

Circulating levels of biologically active parathyroid hormone in rheumatic diseases.

There has been doubt as to whether elevated levels of parathyroid hormone, reported previously by radioimmunoassay, reflect increased concentrations of the biologically active hormone. The application of a recently developed, highly sensitive bioassay has shown considerable disparity between bioactivity and immunoreactivity in 5 rheumatic conditions and in normal subjects. Six patients with chondrocalcinosis had elevated levels; 3 of these did not have hypercalcaemia or any obvious cause other than possible subclinical hyperparathyroidism. One patient, assayed during an acute episode, had an elevated concentration of the hormone which reverted to normal when she was asymptomatic. Most patients with osteoarthrosis (13 our of 15) had low normal levels; 2 showed unexplained slightly elevated concentrations. Of 6 patients with haemochromatosis 3 had elevated levels, though this may have been related to the associated presence of diabetes mellitus. A third of patients with ankylosing spondylitis (10 out of 30) showed elevated parathyroid hormone levels but without hypercalcaemia. A number of spondylitic patients also showed anomalous results in this assay, possibly due to the presence of an antagonist. This would be consistent with the absence of clinical or biochemical evidence of hyperparathyroidism.

Adult↗
PubMed1982

Inhibition of cytochemical bioactivity of parathyroid hormone by plasma in pseudohypoparathyroidism type I.

Despite the high circulating levels of immunoreactive PTH in patients with pseudohypoparathyroidism type I (PSPI) the levels of bioactive PTH (bioPTH) have been found to be close to the normal range. To elucidate this dissociation, we have studied the recovery of the biological activity of bovine PTH added to the plasma of patients with either PSPI, or with hypoparathyroidism (PTX), primary hyperparathyroidism (HPT) or of normal subjects. In PSPI (n = 10) the recovery of biological activity was 5.6% +/- 3.6 (mean +/- SEM) whereas in PTX (n = 7), in HPT (n = 4) and in normal subjects (n = 8) it was 79% +/- 5, 75% +/- 9 and 68% +/- 4, respectively. In another PSPI patient, who had undergone total parathyroidectomy, bioPTH was undetectable but the recovery from the plasma of added PTH was 84%. Thus we have found inhibition of PTH bioactivity by plasma of PSPI patients which was absent after parathyroidectomy.

Animals↗
PubMed1981

The influence on enzyme activity of storage of tissue blocks at -70 degrees C.

Blocks of tissue from various organs of the rat have been chilled by precipitate immersion in n-hexane cooled to -70 degrees C, and then stored at -70 degrees C. At various intervals (up to 14 days) after chilling, cryostat sections were prepared from these blocks and assayed for the activity of a variety of enzymes. Enzyme activity was measured by scanning and integration microdensitometry. With the exception of acid phosphatase and cytochrome oxidase, all enzymes assayed were stable for at least 7 days after storage at -70 degrees C and most were stable for 14 days, Storage of fresh-frozen sections at -30 degrees C in the cabinet of the cryostat, for up to 24 h, had little effect on enzyme activity.

Animals↗
PubMed1981

Intermediate electron-acceptors in quantitative cytochemistry. Comparison of phenazine methosulphate and Meldola Blue.

The efficacy of Meldola Blue (MB), a new intermediate electron-acceptor, has been compared with that of phenazine methosulphate (PMS) in the assay of oxidoreductase activity in cryostat sections; various tetrazolium salts have been used as the final electron-acceptors. Three enzymes: succinate dehydrogenase, glucose 6-phosphate dehydrogenase and lactate dehydrogenase were investigated, the activity in sections being quantitated by scanning and integrating microdensitometry. Phenazine methosulphate was superior to Meldola Blue in transferring reducing equivalents from reduced coenzyme to all the tetrazolium salts examined.

Animals↗
PubMed1981

Dissociation of parathyroid hormone bioactivity and immunoreactivity in pseudohypoparathyroidism type I.

Circulating levels of parathyroid hormone (PTH) in six patients with pseudohypoparathyroidism type I (PSPI) have been measured by two immunoassays and by cytochemical bioassay and compared with measurements in normal subjects and patients with clinically defined hyper- and hypoparathyroidism. In all PSPI patients, the levels of immunoreactive PTH were in the hyperparathyroid range, whereas the bioactive levels were either in the normal or close to the normal range. In one patient from whom the dihydrotachysterol therapy was withdrawn, both immunoreactive and bioactive PTH concentrations increased. The finding that the PTH measured by RIA in these PSPI patients may have reduced biological activity may explain some of the clinical findings of hypoparathyroidism in this syndrome.

Adult↗
PubMed1980

The cytochemical section-bioassay of gastrin-like activity.

A cytochemical section-bioassay of gastrin-like activity is described in which such activity in plasma is assayed by its stimulation of carbonic anhydrase activity in serial, 18 micrometers-thick, sections of suitably prepared gastric fundus of the guinea-pig. The index of precision was 0.1 +/- 0.05 (mean +/- SEM; n=8). Fiducial limits were 75-134%. Intra-assay variation was +/- 6.4% (n=4); inter-assay variation was +/- 16.3% (n=3). The mean gastrin-like activity in the plasma of 15 fasting normal subjects was 5.1 +/- 0.49 x 10(-12)M (range 1.4-18.2 x 10(-12)M).

Animals↗