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Biomedical subjects

N H Bell

Publications and source records attributed to N H Bell.

At least 127 records · Page 7Linked to original sources
PubMed1978

Vitamin-D-dependent rickets type II. Resistance of target organs to 1,25-dihydroxyvitamin D.

Studies were done to determine the cause for hypocalcemia, secondary hyperparathyroidism, osteomalacia and osteitis fibrosa cystica in a 22-year-old black woman. The patient had normal serum 25-hydroxyvitamin D (14 ng per milliliter) and markedly elevated serum 1,25-dihydroxyvitamin D (137 pg per milliliter). Vitamin D3, 4000 units per day for four weeks, increased the serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D to as high as 29 and 297 pg per milliliter, respectively, and corrected the hypocalcemia and secondary hyperparathyroidism. The results suggest that the disorder results from impaired end-organ response to 1,25-dihydroxyvitamin D. We propose that the entity be called vitamin-D-dependent rickets Type II.

Adult↗
PubMed1978

A bioassay capable of measuring 1 picogram of 1,25-dihydroxyvitamin D3.

Fetal rat bones in organ culture constitute a sensitive system for assay of the vitamin D metabolite, 1 alpha,25-dihydroxyvitamin D3. Significant bone resorption is obtained with as little as 2 pg 1,25-dihydroxyvitamin D3 after 48 h of culture and with 1 pg after 64 h of culture. In the current study, organ cultures of fetal rat bone are used as a bioassay for 1,25-dihydroxyvitamin D i normal human plasma, which was prepared for assay by extraction with dichloromethane, chromatography on Sephadex LH-20, and purification on silicic acid by high pressure liquid chromatography. The concentration of 1 alpha,25-dihydroxyvitamin D3 in normal adult human plasma was 24.8 +/- 2.0 pg/ml (n = 19) by this assay.

Animals↗
PubMed1976

On the lipolytic action of parathyroid hormone in man.

An investigation was carried out to determine whether bovine PTH stimulates lipolysis in human fat tissue, whether this action is mediated by cyclic adenosine 3', 5'-monophosphate and whether the N-terminal 1-34 peptide of bovine PTH is responsible for the lipolytic effect. Studies were also performed to determine if parathyroid extract (PTE) produces lipolysis in normal subjects and in patients with pseudohypoparathyroidism in whom there is a defect in the adenylate system in response to PTH in the renal cortex and presumably in the skeletal system as well. It was found that highly purified bovine PTH in the concentration range between 10(-9) M and 10(-5) M stimulated lipolysis in vitro by human fat in a dose-dependent manner. Significant increases in glycerol production were observed at concentrations of PTH as low as 10(-9) M and maximal increases were seen at 10(-6) M. The hormone significantly increased the concentration of cyclic adenosine 3' ,5'-monophosphate in fat tissue. The synthetic N-terminal 1-34 peptide of bovine PTH was as effective as the native hormone in stimulating glycerol production at a concentration of 10(-9) M-10(-6) M. PTE, 100 mU per kg per min for 30 min given intravenously, produced transient increases in the concentration of plasma free fatty acid in each of eight normal subjects, three patients with hypoparathyroidism and eight patients with pseudohypoparathyroidism. Purified bovine PTH also increased plasma free fatty acid in each of two normal subjects. It is concluded that PTH stimulates lipolysis in human subcutaneous fat, that this action of the hormone is mediated through cyclic adenosine 3', 5'-monophosphate and that the N-terminal 1-34 peptide portion of the hormone is responsible for this lipolytic action. Further, PTE stimulates lipolysis in vivo in man. There appears to be no defect in the adenylate cyclase system in the fat cell in response to PTH in patients with pseudohypoparathyroidism.

Adipose Tissue↗
PubMed1976

Demonstration that cyclic adenosine 3',5'-monophosphate mediates the lipolytic action of parathyroid hormone.

Studies were carried out with rat epididymal fat pads first to compare the effects of the synthetic N-terminal 1-34 peptide of bovine parathyroid hormone and of the native hormone to determine whether this portion of the molecule is responsible for the lipolytic action of the hormone and second to determine whether this biologic action of parathyroid hormone is mediated by cyclic adenosine 3',5'-monophosphate. The N-terminal polypeptide was as effective as the native hormone in stimulating lipolysis in the concentration range between 10(-8) M and 10(-6) M. Parathyroid hormone stimulated lipolysis by isolated fat cells. The concentration of cyclic adenosine 3',5'-monophosphate in the fat pads was significantly increased by the hormone (10(-6)M). Lipolytic stimulation by parathyroid hormone (10(-6)M) was diminished by insulin (100 muU/ml) and prostaglandin E1 (1 mug/ml), both of which are known inhibitors of lipolysis. The findings indicate that the amino-terminal 1-34 peptide portion of parathyroid hormone is responsible for the lipolytic action and that this effect is mediated through cyclic adenosine 3',5'-monophosphate.

Adipose Tissue↗
PubMed1976

Acquired resistance to parathyroid hormone.

Studies are presented in a patient with pseudohypoparathyroidism who showed a partial response to parathyroid extract. Resistance to the extract was observed after its short-term administration for the gourth time. Serum from the patient contained antibodies of the gamma G globulin class which bound 125I-labelled bovine parathyroid hormone. Prior incubation of parathyroid hormone with the serum prevented the activation in vitro of adenylate cyclase from pork renal cortex. The antibodies were directed primarily toward the C-terminal portion of the molecule. Thus, clinical resistance to parathyroid hormone is attributed to specific antibodies.

Adenylyl Cyclases↗
PubMed1976

A radioimmunoassay for serum calcitonin in the rat.

A radioimmunoassay for serum calcitonin in the rat is described. Materials for assay of human calcitonin are employed. The sensitivity of the assay is 3 pg and corresponds to a lower limit of detection of 60 pg/ml for peripheral serum. The normal range is up to 650 pg/ml in rats weighing between 125 and 200 g. Serum calcitonin is not detectable in thyroparathyroidectomized animals. It increases and varies directly with the serum calcium after intraperitoneal administration of the ion. Values for serum calcitonin in male and female rats are comparable under basal conditions and after calcium. The radioimmunoassay should allow the further characterization of calcitonin secretion in response to physiologic and pathophysiologic stimuli in this species.

Animals↗
PubMed1976

Technique of handling neonatal blood samples for zinc analysis.

Short segments of Chemfluor flexible Teflon tubing (2.38 mm ID) previously coated with sodium heparin (1,000 units/ml) serve as ideal containers in which blood from neonates can be collected for zinc analysis. The ends of the tube are plugged with Teflon TFE round beading so that the sample comes in contact only with Teflon and the risk of contamination is minimized. The heparin coating facilitates easy collection of the sample and separation of plasma by centrifugation. It does not contribute zinc to the specimen.

Blood Specimen Collection↗
PubMed1975

Solubilization of calcitonin-responsive renal cortical adenylate cyclase.

Purification of pork renal cortex membranes yielded a particulate adenylate cyclase retaining good sensitivity to stimulation by parathyroid hormone and glucagon and a modest but significant response to porcine calcitonin. Treatment of this partially purified membrane fraction with 0.5% Lubrol PX and 5 mM NaF released adenylate cyclase activity into a fraction which was not sedimented by centrifugation for 20 min at 37,000 X g or for 2 hours at 100,000 X g and passed through a Millipore filter (0.22 mum pore). This solubilized adenylate cyclase was stimulated by porcine calcitonin and NaF but not by parathyroid hormone or glucagon. On gel filtration (Sephadex G-200) in the presence of 1mM dithiothreitol and 5mM NaF, the major portion of the adenylate cyclase activity eluted with the void volume of the column and showed 2.0-fold stimulation with 10 muM calcitonin. Binding of 125I-labeled porcine calcitonin was demonstrated in the 37,000 X g and the 100,000 X g supernatants. From 74 to 86% of the observed binding could be blocked by the addition of unlabeled porcine calcitonin to the reaction mixture. Addition of salmon calcitonin, parathyroid hormone, or glucagon blocked only 12 to 18% of the binding. The dose-response curves for inhibition of binding of iodinated calcitonin by unlabeled calcitonin and the activation of adenylate cyclase by the hormone each showed 50% maximal effect at a concentration between 4.5 and 8 muM porcine calcitonin and maximal effect at a concentration between 33 and 66 muM porcine calcitonin.

Adenylyl Cyclases↗
PubMed1975

Calcitonin: a general survey.

Since the initial discovery of calcitonin, a considerable amount of information has been obtained concerning structure, function, secretion, and effects of the hormone from a number of species. The purpose of the present report is to review the studies of structure and function, the factors that influence secretion and synthesis, and the effects and mechanism of action of calcitonin. The clinical uses of the hormone and syndromes of calcitonin excess are discu,sed.

Amino Acid Sequence↗
PubMed1975

Demonstration of a diurnal variation in serum parathyroid hormone in primary and secondary hyperparathyroidism.

It had been reported previously that there is a diurnal variation in serum parathyroid hormone (PTH) in normal subjects but not in patients with primary hyperparathyroidism. Studies were performed to determine whether there is a diurnal variation in serum PTH in primary or secondary hyperparathyroidism and whether the nocturnal increase in serum PTH, if present, could be prevented by induced hypercalcemia. Serum PTH and calcium were measured in five normal subjects, two patients with pseudohypoparathyroidism, and fourteen patients with primary hyperparathyroidism, twelve of whom were subsequently found to have parathyroid adenomas. In the normals, there was a mean decline in serum PTH of 0.07 ng/ml before noon and a mean increase of 0.04 ng/ml after 8 PM. In primary hyperparathyroidism there was a mean decline in serum PTH before noon of 0.11 ng/ml and a mean increase of 0.11 ng/ml after 8 PM. In both groups, the lowest mean serum calcium values were noted between midnight and 6:00 AM. Patients with pseudohypoparathyroidism showed a nocturnal increase in serum PTH. In each of two normal subjects, two patients with primary hyperparathyroidism, and two patients with pseudohypoparathyroidism, calcium, 4 mg/kg body weight per hour for 4 hours (8:00 PM to 12 midnight), produced hypercalcemia and prevented the nocturnal increase in serum PTH. We have concluded that a diurnal variation in serum PTH often occurs in both normal subjects and in patients with primary or secondary hyperparathyroidism and that nocturnal increases in serum PTH can be prevented by induced hypercalcemia.

Adult↗