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Biomedical subjects

G V Segre

Publications and source records attributed to G V Segre.

At least 127 records · Page 7Linked to original sources
PubMed1983

Hypercalcemia in dogs with adenocarcinoma derived from apocrine glands of the anal sac. Biochemical and histomorphometric investigations.

Hypercalcemia, hypercalciuria, and hyperphosphaturia were present in female dogs with adenocarcinomas derived from apocrine glands of the anal sac (CA). Remission of hypercalcemia accompanied tumor excision in all six dogs undergoing surgery, whereas tumor recurrence or growth of metastases was associated with a return of hypercalcemia. Preoperatively, the plasma concentrations of immunoreactive parathyroid hormone in all dogs were undetectable or in the low normal range. Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin E2 (PGE2M) and serum 1,25-dihydroxyvitamin D were not significantly different from control dogs. Urinary cyclic AMP and hydroxyproline were increased in dogs with CA. No immunoreactive parathyroid hormone was detected in extracts from tumor tissue, and parathyroid glands from dogs with CA had ultrastructural characteristics of secretory inactivity. Lumbar vertebrae from hypercalcemic dogs had decreased trabecular bone volume and increased osteoclastic bone resorption compared with age-matched control dogs. After tumor excision, serum total calcium returned to the normal range, whereas immunoreactive parathyroid hormone increased 2- to 20-fold and 1,25-dihydroxyvitamin D decreased 2- to 8-fold. Postoperative hypocalcemia was not observed. These results indicate that CA produces a hypercalcemic factor other than immunoreactive parathyroid hormone or prostaglandin E2 that increases osteoclastic osteolysis distant from the tumor and results in hypercalcemia, hypercalciuria, and hyperphosphaturia.

Adenocarcinoma↗
PubMed1983

Hypercalcemia in dogs with lymphosarcoma. Biochemical, ultrastructural, and histomorphometric investigations.

Dogs with lymphosarcoma and hypercalcemia had decreased trabecular bone volume and increased osteoclastic osteolysis, whereas dogs with lymphosarcoma that were normocalcemic did not have increased bone resorption. Increased osteoclastic resorption was present only in bone from hypercalcemic dogs that contained neoplastic tissue but not in bone free of tumors, suggesting that the factor(s) responsible for stimulating bone resorption were elaborated locally by the tumor tissue. Hypercalcemic dogs with lymphosarcoma had decreased concentrations of plasma immunoreactive parathyroid hormone and serum 1,25-(OH)2D compared with normocalcemic dogs with lymphosarcoma and control dogs with and without other neoplasms. Immunoreactive parathyroid hormone was not detected in lymphosarcoma tissue. The plasma concentration of 13,14-dihydro-15-keto-prostaglandin E2 (PGE2M) was increased approximately 2-fold in hypercalcemic dogs with lymphosarcoma as compared with other groups. Urine excretion of calcium, phosphorus, and hydroxyproline were increased in hypercalcemic dogs with lymphosarcoma. Ultrastructurally, lymphosarcomas were composed of tumor cells with large nuclei and a paucity of cytoplasmic organelles. Light and electron microscopic examination of parathyroid glands revealed inactive or atrophic chief cells in dogs with lymphosarcoma and hypercalcemia. The increased osteoclastic bone resorption in hypercalcemic dogs with lymphosarcoma was not mediated by increased circulating levels of immunoreactive parathyroid hormone and 1,25-(OH)2D but was dependent upon infiltration of bone marrow by neoplastic cells and, presumably, the local production of a bone resorption-stimulating factor.

Animals↗
PubMed1982

Metabolism of parathyroid hormone by Kupffer cells: analysis by reverse-phase high-performance liquid chromatography.

Parathyroid hormone (PTH) undergoes rapid proteolysis in the liver, which results in the appearance of multiple COOH-terminal fragments in plasma. Using reverse-phase high-performance liquid chromatographic (HPLC) techniques, we have shown that biologically active bovine PTH (bPTH) internally labeled with [3H]tyrosine is, like 125I-labeled bPTH, rapidly metabolized by isolated rat Kupffer cells in vitro to multiple COOH-terminal fragments that are chemically identical with those previously found in plasma after metabolism in vivo. Quantitation of specific carboxyl fragments in crude mixtures is achieved rapidly by direct HPLC analysis and is as precise as that achieved by Edman degradation. In addition, several different carboxyl fragments with identical NH2 termini were resolved, revealing a complexity not apparent in previous studies employing direct Edman degradation of such mixtures. Parallel studies with [[35S]Met]bPTH show the generation, by the Kupffer cells in vitro, of several labeled NH2-terminal fragments which undergo rapid further degradation in vitro. Thus, hepatic metabolism of PTH by Kupffer cells proceeds by an initial endopeptidase cleavage within the hormonal sequence in a manner compatible with the generation of biologically active NH2 fragments.

Animals↗
PubMed1982

Calcium homeostasis in immobilization: an example of resorptive hypercalciuria.

Prolonged immobilization may result in hypercalcemia, hypercalciuria, and osteoporosis. Although bone resorption is central to this syndrome, the mechanism of resorption is uncertain. In particular, the role of systemic calcium-regulating hormones remains unclear. In 14 immobilized subjects we measured fasting calcium excretion, 24-hour urinary calcium excretion during restricted calcium intake, the renal phosphorus threshold, plasma 1,25-dihydroxyvitamin D, nephrogenous cyclic AMP, and immunoreactive parathyroid hormone. Mean serum calcium levels were normal, but fasting and 24-hour calcium excretion were markedly elevated (0.28 mg per deciliter of glomerular filtrate and 314 mg per 24 hours, respectively). The mean levels of serum phosphorus (4.8 mg per deciliter) and the renal phosphorus threshold (4.3 mg per deciliter) were elevated. Mean plasma 1,25-dihydroxyvitamin D was strikingly reduced (9.9 pg per milliliter), as were nephrogenous cyclic (0.64 nmol per deciliter of glomerular filtrate) and immunoreactive parathyroid hormone in both assays. These findings indicate that the parathyroid--1,25-dihydroxyvitamin D axis is suppressed in patients with immobilization-induced hypercalciuria, as would be predicted by a model of resorptive hypercalciuria.

25-Hydroxyvitamin D 2↗
PubMed1982

Secondary hyperparathyroidism associated with dichloromethane diphosphonate treatment of Paget's disease.

Six patients with extensive polyostotic Paget's disease were treated for 3 months with dichloromethane diphosphonate (CL2MDP; 1600 mg/day, orally). Serum alkaline phosphatase and urinary hydroxyproline excretion decreased 60-80% in each patient. Blood ionized calcium (ca++) and immunoreactive PTH (iPTH) were measured weekly during the first month of therapy and monthly thereafter. As an index of parathyroid function, PTH secretory reserve was assessed by EDTA infusions before treatment, at the end of treatment, and 3 months after Cl2 MDP therapy was stopped. Before therapy, iPTH and Ca++ were normal in all patients. During treatment, Ca++ decreased and iPTH increased in all patients; mean iPTH approximately doubled (95% confidence limits, 1.5- to 2.7-fold increase). At the end of 3 months of treatment, EDTA infusion raised iPTH in each patient to a level higher than that in the control infusion, indicating augmented PTH secretory reserve. Ca++, iPTH, and the iPTH response to EDTA-induced hypocalcemia returned toward baseline by 3 months after the end of CL2MDP treatment. The results indicate that secondary hyperparathyroidism developed as a result of Cl2MDP therapy. The cause of the parathyroid-gland adaptation is not known; the hyperparathyroidism is, however, at least partly reversible. Cl2MDP inhibits bone resorption while allowing bone mineralization to continue; this differential effect could lead to the hypocalcemia and parathyroid hyperfunction.

Aged↗
PubMed1981

Characteristics of bovine parathyroid hormone extraction by dog liver in vivo.

The metabolic fate of various 125I-labeled preparations of bovine parathyroid hormone (bPTH) during a single passage through the liver was studied in anesthetized dogs. Each 125I-bPTH preparation was injected in the portal vein with 131I-albumin and 99mTc-erythrocytes, two reference indicators. A dilution curve was obtained for each indicator by counting the radioactivity present in tubes collected by hepatic vein sampling. Hepatic blood flow (HBF) and fractional hepatic extraction (FHE) were calculated from these curves. Extraction results were further validated by comparing the gel chromotography profile of the 125I injected and of the 125I recovered. The FHE of 125I after an injection of 125I-bPTH-(1--84) was 32.75 +/- 9.39% (mean +/- SD; n = 23) for a mean HBF of 48.18 +/- 11.83 ml . kg-1 . min-1. The FHE was independent of the dose of hormone injected (0.34-812 ng) but was inversely related to the HBF (r = -0.6768, P less than 0.001). 125I was not extracted after an injection of 125I-bPTH-(1--34) ( n = 8) or of 125I-bPTH-(34/43--84) (n = 5). On the other hand, after an injection of 125I-bPTH-(28--48), 18.7 +/- 5.5% (n = 8) of the 125I was extracted for an HBF of 47.3 +/- 17.0 ml . kg-1 . min-1. Analysis of the gel chromotography profiles further disclosed that 7.6 +/- 4.2% of the 125I-bPTH-(1--84) injected was transformed into carboxyl terminal fragments; 13.1 +/- 2.6% of the 125I-bPTH-(28--48) and 20.9 +/- 4.9% of the 125I-bPTH-(1--34) injected were also cleaved into smaller molecular weight products. We conclude that the integrity of the sequence 28--48 is important for the FHE of 125I-bPTH-(1--84). Although nonsaturable, this process is inversely related to the HBF. Liver inactivation of intact PTH or of its fragments also proceeds through rapid cleavage into smaller molecular weight products.

Animals↗
PubMed1981

Effects of hepatectomy, nephrectomy, and nephrectomy/uremia on the metabolism of parathyroid hormone in the rat.

Reports from several laboratories, showing extensive hepatic extraction of circulating parathyroid hormone, led us to examine the effect of near-total hepatectomy on the metabolism of the hormone to circulating fragments, and on its clearance from plasma. The rate of disappearance of (125)I-labeled and unlabeled bovine parathyroid hormone from plasma, and the appearance, disappearance, and chemical and immunochemical characteristics of circulating fragments were examined by gel filtration and either sequence-specific radioimmunoassays or sequence analysis using the Edman reaction. Results from awake rats subjected to near-total hepatectomy were compared with those found in sham-treated, nephrectomized, and short-term uremic rats (studied 2 d after nephrectomy). When compared with the sham-treated group, all other groups clear (125)I-labeled hormone more slowly; after hepatectomy, however, the clearance rate is most strikingly decreased. After injection of intact hormone, the concentration of carboxy-terminal fragments in the circulation of hepatectomized rats is greatly reduced at all time intervals when compared with that in sham-treated rats. Sequence analysis of plasma samples, collected from rats into which (125)I-labeled hormone had been injected, shows that carboxy-terminal fragments having positions 34 and 37 of the intact hormone sequence as their amino-terminal amino acids are abundant in sham-treated, nephrectomized, and nephrectomized/uremic rats, but are undetectable in hepatectomized rats. The data suggest that inasmuch as the liver in vivo generates most of the carboxy-terminal fragments resulting from the metabolism of injected hormone, specific cell types within the liver must be the principal locus of the responsible enzyme(s); thus, studies of the enzymic properties of isolated hepatic cells in vitro most likely will yield information of physiologic relevance to the metabolism of the hormone in the intact animal.

Animals↗
PubMed1981

Metabolism of parathyroid hormone by isolated rat Kupffer cells and hepatocytes.

Data from several laboratories indicate that hepatic mechanisms may have a distinctive role in the metabolism of intact hormone after secretion, a process that accounts, at least partly, for the heterogeneity of circulating parathyroid hormone. Accordingly, we studied the proteolysis of intact hormone by isolated rat Kupffer cells and hepatocytes. Kupffer cells (10(6) cells/ml) and hepatocytes (10(7) cells/ml) were incubated with unlabeled and (125)I-labeled bovine parathyroid hormone at 37 degrees C for periods ranging up to 2 h. When incubated with Kupffer cells, intact hormone disappeared with a t((1/2)) of 12+/-4 min. Radio-immunoassays using sequence-specific antisera showed that the dominant hormonal fragments recovered in the medium have an apparent molecular weight of approximately 6,000, lack amino-terminal antigenic determinants, and react in assays that specifically recognize determinants in the carboxy-terminal portion of the intact hormone. Amino-terminal fragments also were detected in high concentrations, particularly after short incubation periods. Radioiodinated fragments resulting from incubation of (125)I-labeled bovine parathyroid hormone with Kupffer cells had the same apparent size as fragments derived from the metabolism of unlabeled, intact hormone; when analyzed by Edman degradation, positions 34 and 37 of the intact hormone sequence were the amino-terminal amino acids of these dominant carboxy-terminal fragments. Hepatocytes did not hydrolyze the hormone. Thus, metabolism of parathyroid hormone by Kupffer cells results in the appearance of fragments in the media that are immunochemically indistinguishable from, and chemically identical with, those found in plasma when intact hormone is injected intravenously. This indicates that the proteolysis observed in vitro accurately reflects the metabolism of the hormone in vivo. The detection of amino-terminal fragments in concentrations nearly equal to those of carboxy-terminal fragments indicates that cleavage of intact hormone is, initially, by an endopeptidase(s). Kupffer cells may be a source from which specific protease(s) that hydrolyze parathyroid hormone can be characterized, particularly in terms of enzymic specificity and requirements for inhibition. Detailed analysis of the cellular and molecular events during incubation of parathyroid hormone with these cells may help to clarify the biologic significance of the peripheral metabolism of the hormone.

Animals↗
PubMed1980

Parathyroid hormone and 25-hydroxyvitamin D levels in glucocorticoid-treated patients.

Abnormalities in parathyroid hormone (PTH) secretion or vitamin D action or metabolism have been suggested as pathogenetic factors in the bone disease associated with chronic glucocorticoid therapy. We have found normal plasma PTH values in forty-eight adult asthmatic patients on chronic glucocorticoid therapy, twelve asthmatics treated without glucocorticoids and ten adults on short-term, high-dose glucocorticoid therapy for non-asthmatic illnesses. The mean serum 25-OHD level in the glucocorticoid-treated asthmatics was not significantly different from a disease control group of asthmatic patients not on glucocorticoids, but nine such patients had abnormally low 25-OHD levels. Our results indicate that in asthmatic patients on chronic glucocorticoid therapy: (1) PTH and 25-OHD values are usually normal regardless of dose or duration of therapy and (2) there is a subset of patients with low 25-OHD values which may reflect unusual sensitivity to glucocorticoids.

Adult↗
PubMed1979

Analysis of parathyroid hormone and its fragments in rat tissues: chemical identification and microscopical localization.

After intravenous injection of [(125)I]-iodo-parathyroid hormone in the rat, uptake of the hormone was greatest in the liver and kidneys. Uptake was rapid, reaching a maximal concentration by 4 and 8 min, respectively. Extracts, prepared from both these organs at intervals soon after the injection of intact hormone, showed three main radioactive peaks when samples were subjected to gel filtration under protein-denaturing conditions. The first peak coeluted with intact hormone. The second eluted at a position corresponding to the carboxy-terminal fragments previously described in plasma, and the last eluted at the salt volume of the column. Microsequence analysis of the radioiodinated fragments, a method that has proved valuable for chemically defining the circulating fragments resulting from metabolism of injected hormone, showed that extracts of liver and kidney, prepared at 4 and 8 min after injection of the intact hormone, contained different fragments. The radioiodinated fragments in liver extracts were identical to those previously reported in the plasma of rats and dogs, fragments resulting principally from proteolysis between positions 33 and 34, and 36 and 37 of the intact hormone. Although the same fragments were also present in the kidneys, they constituted less than 15% of the amount present in the liver. More than 50% of the labeled renal fragments consisted of a peptide whose amino-terminal amino acid was position 39 of the intact hormone, a fragment not present in plasma. The rate of appearance of radioiodinated fragments that were chemically identical to those in plasma was more rapid in the liver than in plasma. Correlation of these chemical analyses with studies of the localization of (125)I by autoradiography showed that at the times when the intact hormone and the carboxy-terminal fragments comprised nearly all of the (125)I-labeled moieties in the tissues, the proximal convoluted tubules of the kidney and sinusoidal lining cells of the liver, which probably are Kupffer cells, contained the highest concentration of (125)I. Preferential localization of immunoreactive parathyroid hormone to these tissue sites also was shown by immunoperoxidase staining in studies with unlabeled hormone. Our results suggest that, unless multiple renal mechanisms are present for release of hormonal fragments, one of which releases the circulating fragments preferentially, the liver, rather than the kidney, is principally responsible for generating the carboxy-terminal fragments in plasma after injection of intact hormone, and the Kupffer cells may contain the enzymes that hydrolyze parathyroid hormone.

Animals↗
PubMed1979

Immunocytochemical localization of parathyroid hormone in bovine parathyroid glands and human parathyroid adenomas.

Light and electron microscopic localization of parathyroid hormone (PTH) in human and bovine parathyroid tissue has been achieved using an indirect peroxidase labeled antibody method. Granular deposition of the reaction product was found throughout the chief cell cytoplasm. There was no nuclear staining. At the ultrastructural level, parathyroid hormone localized by this method appeared to be largely confined to the secretory granules in the cytoplasm of cells. Mitochondria and nuclei were free of reaction product. Aggregated sacs of granular endoplasmic reticulum were minimally reactive, and Golgi apparatuses did not show reaction product.

Adenoma↗
PubMed1978

Human parathyroid hormone: synthesis and chemical, biological, and immunological evaluation of the carboxyl-terminal region.

The carboxyl-terminal region of human parathyroid hormone (hPTH) was synthesized by the solid phase method. The 32-amino acid fragment, hPTH-(53-84), was prepared for two reasons: 1) to produce antisera directed exclusively against the carboxyl-terminal region of hPTH, which represents the predominant form of the hormone in blood; and 2) to determine whether a portion of the hormone other than the amino-terminal region has any of the biological activity of intact hormone or can bind to PTH receptors. The synthetic fragment was evaluated for heterogeneity by amino acid composition and by several high resolution analytical systems (thin layer electrophoresis, polyacrylamide gel isoelectric focusing, and Edman sequence analysis). Synthetic hPTH-(53-84) lacked PTH-like activity in both in vitro (renal) and in vivo (bone) assays and failed to inhibit the action of native PTH in vitro, indicating lack of receptor binding by the carboxyl-terminal region of the molecule. Because the fragment lacked biological activity, nonchemical evaluation was performed to confirm that the peptide represents the carboxyl terminus of hPTH. Immunological comparison of synthetic hPTH-(53-84) to native hPTH was undertaken using an RIA that employed an antibovine PTH antiserum whose antigenic recognition was limited to the carboxyl-terminal region of the hormone. Synthetic hPTH-(53-84) was more immunoreactive than native hPTH. The immunological findings provide further evidence that the synthetic peptide accurately represents the carboxyl-terminal region of native hPTH.

Antigen-Antibody Reactions↗