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Biomedical subjects

M K Drezner

Publications and source records attributed to M K Drezner.

At least 91 records · Page 5Linked to original sources
PubMed1984

Impaired formation of beta-adrenergic receptor-nucleotide regulatory protein complexes in pseudohypoparathyroidism.

Decreased activity of the guanine nucleotide regulatory protein (N) of the adenylate cyclase system is present in cell membranes of some patients with pseudohypoparathyrodism (PHP-Ia) whereas others have normal activity of N (PHP-Ib). Low N activity in PHP-Ia results in a decrease in hormone (H)-stimulatable adenylate cyclase in various tissues, which might be due to decreased ability to form an agonist-specific high affinity complex composed of H, receptor (R), and N. To test this hypothesis, we compared beta-adrenergic agonist-specific binding properties in erythrocyte membranes from five patients with PHP-Ia (N = 45% of control), five patients with PHP-Ib (N = 97%), and five control subjects. Competition curves that were generated by increasing concentrations of the beta-agonist isoproterenol competing with [125I]pindolol were shallow (slope factors less than 1) and were computer fit to a two-state model with corresponding high and low affinity for the agonist. The agonist competition curves from the PHP-Ia patients were shifted significantly (P less than 0.02) to the right as a result of a significant (P less than 0.01) decrease in the percent of beta-adrenergic receptors in the high affinity state from 64 +/- 22% in PHP-Ib and 56 +/- 5% in controls to 10 +/- 8% in PHP-Ia. The agonist competition curves were computer fit to a "ternary complex" model for the two-step reaction: H + R + N in equilibrium HR + N in equilibrium HRN. The modeling was consistent with a 60% decrease in the functional concentration of N, and was in good agreement with the biochemically determined decrease in erythrocyte N protein activity. These in vitro findings in erythrocytes taken together with the recent observations that in vivo isoproterenol-stimulated adenylate cyclase activity is decreased in patients with PHP (Carlson, H. E., and A. S. Brickman, 1983, J. Clin. Endocrinol. Metab. 56:1323-1326) are consistent with the notion that N is a bifunctional protein interacting with both R and the adenylate cyclase. It may be that in patients with PHP-Ia a single molecular and genetic defect accounts for both decreased HRN formation and decreased adenylate cyclase activity, whereas in PHP-Ib the biochemical lesion(s) appear not to affect HRN complex formation.

Adenylyl Cyclases↗
PubMed1983

Measurement of 25-hydroxyvitamin D-1 alpha-hydroxylase activity in mammalian kidney.

Until recently measurement of 25-OH-D3-1 alpha-hydroxylase activity in mammalian kidney has not been possible due to the presence of a protein which inhibits the enzyme by reducing available substrate. However, utilization of sufficient unlabeled 25-OH-D3 (80 nmol/ml renal homogenate) to overcome the effect of the inhibitor while maintaining optimal concentration for 1-hydroxylation has made quantitation of enzyme activity possible. We have modified this existing technique in order to increase the sensitivity and to permit detailed study of 1 alpha-hydroxylate regulation in mouse kidney. The modifications that we have incorporated include (i) simplifying the purification scheme for obtaining measurable 1,25-(OH)2D3 by reducing to one the necessary number of high-performance liquid chromatography steps and (ii) quantifying 1,25-(OH)2D3 by radioligand assay. The sensitivity of the assay is 10 pg, which, corrected for fractionation and recovery (50-60%), allows the measurement of 0.5 fmol 1,25-(OH)2D3 produced per milligram kidney per minute. Moreover, reliability and precision of the assay have been confirmed by demonstrating that samples from carefully matched, identically treated mice have reproducible enzyme activity (interassay coefficient of variation = 9.1%, n = 5) and show appropriate dilution characteristics. We have also demonstrated appropriate modulation of enzyme activity by known effectors of 1-hydroxylation. Kidneys from D-deficient mice exhibit significantly higher enzyme activity (15.28 +/- 1.17, n = 21) than do normal mouse kidneys (5.14 +/- 0.26, n = 33). In contrast, enzyme activity is suppressed significantly in kidneys obtained from calcium-loaded (1.20 +/- 0.04, n = 5) and parathyroidectomized animals (2.94 +/- 0.29, n = 5). Our assay now permits the indepth study of 1 alpha-hydroxylase regulation in mammalian (mouse) kidneys.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1983

Deficient adenylate cyclase regulatory protein in renal membranes from a patient with pseudohypoparathyroidism.

Recent studies have established that some patients with pseudohypoparathyroidism have a deficiency of the adenylate cyclase regulatory protein (the G unit) in plasma membranes from erythrocytes, platelets, and fibroblasts. We have directly measured the activity of the G unit in renal membranes from a patient with pseudohypoparathyroidism who, in addition to parathyroid hormone resistance, has resistance to thyrotropin and gonadotropins. Erythrocyte membrane G unit activity was 57% that of control erythrocyte membranes. Lubrol PX extracts of renal membranes had only 30% of the G unit activity of control renal membrane extracts, whether assayed with sodium fluoride or guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S). In cholate extracts, the G unit activity was 37 and 48% of control with fluoride or GTP-gamma-S, respectively. Cholera toxin-dependent incorporation of [32P]ADP-ribose into the 42,000-Mr subunit of the G unit was decreased in renal membranes from the patient compared with control renal membranes. The data demonstrate that the membrane G unit deficiency in pseudohypoparathyroidism extends to the cells of a clinically relevant parathyroid hormone target tissue.

Adenylyl Cyclases↗
PubMed1983

Abnormal regulation of renal 25-hydroxyvitamin D-1 alpha-hydroxylase activity in the X-linked hypophosphatemic mouse.

Abnormal vitamin D metabolism has been suspected in patients with X-linked hypophosphatemic rickets (XLH) and X-linked hypophosphatemic mice (Hyp-mice), the murine homologue of the human disease. We compared 25(OH)D-1 alpha-hydroxylase activity in the Hyp-mouse kidney to that in normal and phosphate-depleted mouse kidney. Weanling normal and Hyp-mice were fed a 0.6% phosphorus diet; phosphate-depleted mice received a 0.02% phosphorus diet. At 8-10 wk of age the serum phosphorus values in Hyp (3.35 +/- 0.12 mg/dl) and phosphate-depleted mice (3.83 +/- 0.56) were not significantly different. Despite the similar magnitude of phosphate depletion, however, the maximum levels of 25(OH)D-1 alpha-hydroxylase activity were disparate: phosphate-depleted mouse kidney had profoundly increased activity compared to normal (17.04 +/- .104 vs. 4.96 +/- 0.23 fmol 1,25(OH)2D3 produced/mg kidney per min) while Hyp-mouse kidney had a fourfold lesser increment (8.18 +/- 0.62). These data indicate that phosphate depletion is a potent stimulus of 25(OH)D-1 alpha-hydroxylase activity in the (C57BL6J) mouse. Moreover, the results show that abnormal regulation of 25(OH)D-1 alpha-hydroxylase activity is manifest in the Hyp-mouse.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1983

Defective adenosine triphosphate synthesis. An explanation for skeletal muscle dysfunction in phosphate-deficient mice.

The basis for skeletal muscle dysfunction in phosphate-deficient patients and animals is not known, but it is hypothesized that intracellular phosphate deficiency leads to a defect in ATP synthesis. To test this hypothesis, changes in muscle function and nucleotide metabolism were studied in an animal model of hypophosphatemia. Mice were made hypophosphatemic through restriction of dietary phosphate intake. Gastrocnemius function was assessed in situ by recording isometric tension developed after stimulation of the nerve innervating this muscle. Changes in purine nucleotide, nucleoside, and base content of the muscle were quantitated at several time points during stimulation and recovery. Serum concentration and skeletal muscle content of phosphorous are reduced by 55 and 45%, respectively, in the dietary restricted animals. The gastrocnemius muscle of the phosphate-deficient mice fatigues more rapidly compared with control mice. ATP and creatine phosphate content fall to a comparable extent during fatigue in the muscle from both groups of animals; AMP, inosine, and hypoxanthine (indices of ATP catabolism) appear in higher concentration in the muscle of phosphate-deficient animals. Since total ATP use in contracting muscle is closely linked to total developed tension, we conclude that the comparable drop in ATP content in association with a more rapid loss of tension is best explained by a slower rate of ATP synthesis in the muscle of phosphate-deficient animals. During the period of recovery after muscle stimulation, ATP use for contraction is minimal, since the muscle is at rest. In the recovery period, ATP content returns to resting levels more slowly in the phosphate-deficient than in the control animals. In association with the slower rate of ATP repletion, the precursors inosine monophosphate and AMP remain elevated for a longer period of time in the muscle of phosphate-deficient animals. The slower rate of ATP repletion correlates with delayed return of normal muscle contractility in the phosphate-deficient mice. These studies suggest that the slower rate of repletion of the ATP pool may be the consequence of a slower rate of ATP synthesis and this is in part responsible for the delayed recovery of normal muscle contractility.

Adenosine Triphosphate↗
PubMed1982

Serum 1,25-dihydroxyvitamin D levels in subjects with X-linked hypophosphatemic rickets and osteomalacia.

In order to determine whether a defect in vitamin D metabolism might play a role in the pathogenesis of X-linked hypophosphatemic rickets and osteomalacia (XLH), we compared the serum 1,25-dihydroxyvitamin D [1,25(OH)2D] level in 52 normal subjects and 37 patients with XLH. In untreated patients, adults were found to have values similar to age-matched controls, while youths had values similar to growth-rate-matched controls but significantly lower than the levels of age-matched controls who were growing at a normal rate. In contrast, treated XLH patients of all ages had serum levels significantly lower than both controls and untreated XLH patients. Further, the serum levels of 1,25(OH)2D in these treated patients had a significant inverse linear correlation with serum 25-(OH)D concentrations. We propose that subjects with XLH have serum 1,25(OH)2D levels within appropriate age- and growth-rate-matched normal ranges. However, in the presence of hypophosphatemia, we would have anticipated elevated levels of 1,25(OH)2D; viewed in this light the serum 1,25(OH)2D levels are inadequate, suggesting the presence of a relative deficiency of this active vitamin D metabolite.

Adolescent↗
PubMed1982

Parathyroid hormone effects on serum 1,25-dihydroxyvitamin D levels in patients with X-linked hypophosphatemic rickets: evidence for abnormal 25-hydroxyvitamin D-1-hydroxylase activity.

Patients with X-linked hypophosphatemic rickets (XLH) have normal or marginally low serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] levels despite manifesting hypophosphatemia and phosphate depletion, which increase 1,25-(OH)2D production in many animal species. These data are consistent with the possibility that regulation of vitamin D metabolism is abnormal in XLH. However, controversy concerning the role of phosphate in the regulation of 25-hydroxyvitamin D-1-hydroxylase activity in man has raised doubt about this proposed defect. The presence of a defect in vitamin D metabolism could be established if hormonal or metabolic factors, other than hypophosphatemia, were unable to stimulate 25-hydroxyvitamin D-1-hydroxylase activity normally in patients with XLH. Thus, we compared the effects of parathyroid hormone infusion on serum 1,25-(OH)2D levels in patients with XLH and normals. In response to iv infusion of parathyroid extract (200 U at 0915 and 1700 h), the serum 1,25-(OH)2D concentration increased 218% above base line (from 34.0 +/- 3.0 to 108.8 +/- 2.5 pg/ml) in normals and only 68% (from 30.6 +/- 3.0 to 48.8 +/- 5.5 pg/ml) in patients with XLH. The disparate response occurred in spite of an equivalent increase in urinary cAMP excretion in the normals (from 3.00 +/- 0.14 to 8.70 +/- 0.25 mumol/g creatinine . 24 h) and XLH patients (from 3.10 +/- 0.39 to 8.30 +/- 1.0 mumol/g creatinine . 24 h) as well as equivalent decreases in the renal tubular maximum for the reabsorption of phosphate per liter glomerular filtrate (1.2 +/- 0.1 and 0.9 +/- 0.2 mg/dl, respectively). These observations support the possibility that regulation of vitamin D metabolism is abnormal in XLH.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1982

Osteomalacia after parathyroidectomy in patients with uremia.

Five patients on maintenance dialysis had symptoms of osteomalacia, proven by biopsy, after parathyroidectomy. In all five patients clinical and radiographic manifestations of secondary hyperparathyroidism were present before surgery, and in two patients preoperative biopsy of bone confirmed the existence of osteitis fibrosa. Like previously described patients with osteomalacia all five had multiple fractures and normal or high serum calcium concentrations that rose to abnormally high values on treatment with vitamin D or dihydrotachysterol. Quantitative histomorphometry of biopsy after parathyroidectomy showed no residual parathyroid hormone effect and nearly complete cessation of mineralization. Four patients had forearm autografts of parathyroid tissue that appeared to be functioning at very low rates according to paired venous sampling, and all five patients had relatively low circulating concentrations of parathyroid hormone. This and earlier experiences reported by others suggest that secondary hyperparathyroidism may have an important facilitative role in the mineralization of bone in uremic patients.

Adult↗
PubMed1980

Evaluation of a role for 1,25-dihydroxyvitamin D3 in the pathogenesis and treatment of X-linked hypophosphatemic rickets and osteomalacia.

Although a defect in renal transport of phosphate seems well established as the primary abnormality underlying the pathogenesis of X-linked hypophosphatemic rickets and osteomalacia, several observations indicate that renal phosphate wasting and hypophosphatemia cannot solely account for the spectrum of abnormalities characteristic of this disease. Thus, in the present study, we investigated the potential role of abnormal vitamin D metabolism in the pathogenesis of this disorder and the effect of 1,25-dihydroxyvitamin D(3) therapy on both the biochemical abnormalities characteristic of this disease and the osteomalacia. Four untreated patients, ages 14-30 yr, had normocalcemia (9.22+/-0.06 mg/dl); hypophosphatemia (2.25+/-0.11 mg/dl); a decreased renal tubular maximum for the reabsorption of phosphate per liter of glomerular filtrate (2.12+/-0.09 mg/dl); normal serum immunoreactive parathyroid hormone concentration; negative phosphate balance; and bone biopsy evidence of osteomalacia. The serum 25-hydroxyvitamin D(3) concentration was 33.9+/-7.2 ng/ml and, despite hypophosphatemia, the serum level of 1,25-dihydroxyvitamin D(3) was not increased, but was normal at 30.3+/-2.8 pg/ml. These data suggested that abnormal homeostasis of vitamin D metabolism might be a second defect central to the phenotypic expression of X-linked hypophosphatemic rickets/osteomalacia. This hypothesis was supported by evaluation of the long-term response to pharmacological amounts of 1,25-dihydroxyvitamin D(3) therapy in three subjects. The treatment regimen resulted in elevation of the serum 1,25-dihydroxyvitamin D levels to values in the supraphysiological range. Moreover, the serum phosphate and renal tubular maximum for the reabsorption of phosphate per liter of glomerular filtrate increased towards normal whereas the phosphate balance became markedly positive. Most importantly, however, repeat bone biopsies revealed that therapy had positively affected the osteomalacic component of the disease, resulting in normalization of the mineralization front activity. Indeed, a central role for 1,25-dihydroxyvitamin D(3) in the mineralization of the osteomalacic bone is suggested by the linear relationship between the serum level of this active vitamin D metabolite and the mineralization front activity. We, therefore, suggest that a relative deficiency of 1,25-dihydroxyvitamin D(3) is a factor in the pathogenesis of X-linked hypophosphatemic rickets and osteomalacia and may modulate the phenotypic expression of this disease.

Adolescent↗
PubMed1980

Hypophosphatemic osteomalacia: association with prostatic carcinoma.

Hypophosphatemic osteomalacia that remits after resection of a coexisting tumor has been described in 35 patients. Because the associated neoplasms have been of mesenchymal origin, it has been inferred that this tumor-induced osteomalacia syndrome is uniquely related to tumours of this derivation. However, in the present investigation we studied subjects with coincident hypophosphatemia and prostatic carcinoma to ascertain whether this endodermal malignancy causes the tumor-induced osteomalacia syndrome. The hypophosphatemic patients had renal phosphate wasting, gastrointestinal malabsorption of calcium and phosphate, and negative phosphate balance. Moreover, bone biopsies showed histomorphologic changes indicative of osteomalacia. Although widespread metastases precluded establishing the diagnosis of tumor-induced osteomalacia by resection of the tumor, a series of studied excluded alternate causes for the osteomalacia. Further, affected subjects had a normal serum concentration of 25-hydroxyvitamin D, 28.0 +/- 8.3 ng/mL, and serum 1,25-dihydroxyvitamin D levels were low, 15.0 +/- 1.0 pg/mL, characteristic of the tumor-induced osteomalacia syndrome. Thus, prostatic carcinoma, although an endodermal malignancy, may cause the tumor-induced osteomalacia syndrome.

Aged↗
PubMed1979

Adenosine 3',5'-monophosphate effects on cartilage ribonucleic acid synthesis.

We have previously shown that N6-monobutyryl-cAMP stimulates the incorporation of radiolabeled precursors into the macromolecules of embryonic chicken cartilage incubated in organ culture. The present study assessed the specific effects of N6-monobutyryl-cAMP on RNA synthesis in the cartilage organ culture system. The data show that treatment of cartilage with N6-monobutyryl-cAMP results in a coordinated stimulation of mRNA, rTNA, and tRNA synthesis. Incubation of cartilage with N6-monobutyryl-cAMP causes an increase of [5-3H]uridine incorporation into poly A-containing cartilage RNA and 28S, 18S, and 4S RNA as well. Increased incorporation of the radiolabeled nucleotide occurs without a measurable change in uridine triphosphate specific activity or in the rate of RNA degradation. Further, the isolated poly A-containing RNA directs protein synthesis in an in vitro cell-free system, and stimulation of cartilage mRNA by N6-monobutyryl-cAMP does not alter the size distribution of the mRNA species synthesized from that present in control tissue. These data indicate that cAMP enhances cartilage transcriptional activity. In addition, the increased synthesis of mRNA occurs antecedent to demonstrable effects on protein synthesis. Thus, the effects of cAMP on protein synthesis may be secondary to action at the nucleus.

Animals↗
PubMed1978

Primary hyperparathyroidism in paraneoplastic hypercalcaemia.

Hypercalcaemia is often associated with malignant disease. Causes of elevated serum-calcium levels in the absence of bony metastases include parathyroid-hormone production by the tumour, osteolytic factors made by the tumour, and coexistent primary hyperparathyroidism. By measuring nephrogenous cyclic-A.M.P. excretion to assess parathyroid-hormone function, we have determined the mechanism of such hypercalcaemia in 15 patients. Nephrogenous cyclic A.M.P. ranges from 0.05 to 2.40 mumol/g of creatinine in normal subjects, from 2.27 to 8.45 mumol/g in patients with primary hyperparathyroidism, and from 0.50 to 1.30 mumol/g in patients with proven non-hyperparathyroid hypercalcaemia without malignancy. 9 patients (60%) with hypercalcaemia and malignancy had normal levels of nephrogenous cyclic A.M.P. (range 0.35-2.07 mumol/g creatinine). The other 6 (40%) had elevated nephrogenous cyclic A.M.P. (range 2.70-5.55 mumol/g) consistent with increased parathyroid-hormone secretion. Surgical exploration of the neck in these patients showed that the increased parathyroid-hormone secretion was secondary to primary hyperparathyroidism, not ectopic hyperparathyroidism. Thus, the data indicate that coexistent hyperparathyroidism may be common in patients with hypercalcaemia and malignancy and that the measurement of nephrogenous cyclic A.M.P. is very useful in identifying patients at risk for hyperparathyroidism.

Adenocarcinoma↗
PubMed1978

Altered activity of the nucleotide regulatory site in the parathyroid hormone-sensitive adenylate cyclase from the renal cortex of a patient with pseudohypoparathyroidism.

A series of clinical studies suggest that the primary defect underlying pseudohypoparathyroidism is an abnormality of the parathyroid hormone-receptor-adenylate cyclase complex of the renal cortical cell plasma membrane. In the present study we compared parathyroid hormone-stimulated adenylate cyclase activity in membrane preparations from the renal cortex of three controls and a patient with pseudohypoparathyroidism. In the pseudohypoparathyroid preparation the Km for ATP was significantly greater and parathyroid hormone elicited markedly diminished adenylate cyclase activity at a subsaturating concentration of ATP. In contrast, the dose-response effect of enzyme activity to parathyroid hormone was the same in the control preparations, and that of the pseudohypoparathyroidism kidney, at a saturating concentration of ATP. The apparent alteration in enzyme kinetics, however, was normalized upon addition of guanosine 5'-triphosphate to the reaction mixtures. These results indicate that the defect in the parathyroid hormone-receptor-adenylate cyclase complex of the renal cell membranes, in our patient with pseudohypoparathyroidism, is an abnormal nucleotide receptor site of decreased activity. Such a defect may result in partial uncoupling of the parathyroid hormone receptor and adenylate cyclase, rendering the organ refractory to hormonal stimulation.

Adenylyl Cyclases↗
PubMed1978

Measurement of plasma adenosine 3',5'-monophosphate.

Currently used methods for plasma cAMP measurements are either tedious (chromatographic preparation of sample) or potentially inaccurate (direct assay of plasma samples). A rapid, simple, and accurate competitive binding assay for plasma cAMP, which does not require chromatographic preparation of the sample, has been developed. This procedure prevents destruction of plasma cAMP by utilizing both theophylline and EDTA in the collection of the blood sample. Human plasma contains variable amounts of cAMP-binding activity which interfere with the measurement of cAMP by the standard competitive binding assay. Our assay procedure removes this binding activity by precipitation of plasma proteins with perchloric acid. The normal fasting value (+/- SD) of plasma cAMP using this technique is 17.6 +/- 4.3 pmol/ml, which is identical to values obtained by methods utilizing chromatographic purification of samples (18.3 +/- 3.0). The fasting plasma cAMP of patients with hyperparathyroidism is normal (16.2 +/- 3.4), but patients with maturity-onset diabetes mellitus have fasting values significantly below normal (12.3 +/- 2.4).

Animals↗