Biomedical subjects

T J Martin

Publications and source records attributed to T J Martin.

At least 343 records · Page 19Linked to original sources

PubMed1986

Calcitonin gene-related peptide (CGRP) acts independently of calcitonin on cyclic AMP formation in clonal osteogenic sarcoma cells (UMR 106-01).

In several human cancer cell lines and in a subclone of rat osteogenic sarcoma cells (UMR 106-06) possessing calcitonin receptors and a calcitonin-responsive adenylate cyclase, calcitonin gene-related peptide (CGRP) behaved as a weak calcitonin agonist. In another subclone of the same osteogenic sarcoma (UMR 106-01) with no measurable calcitonin receptors or response, both rat and human CGRP were found to increase cyclic AMP formation in a dose-dependent manner. The data indicate that CGRP is capable of a weak calcitonin-like action in cells with calcitonin receptors, but also that in some cells CGRP activates adenylate cyclase itself, independently of calcitonin receptors.

Animals↗

PubMed1986

Localization of binding sites for calcitonin gene-related peptide in rat brain by in vitro autoradiography.

The distribution of binding sites for calcitonin gene-related peptide (CGRP) in rat brain were studied using in vitro autoradiography. In a radioreceptor assay using [125I]human calcitonin gene-related peptide as the radioligand, with cerebellar cortical membranes, rat calcitonin gene-related peptide had a binding affinity constant of 1.16 +/- 0.23 X 10(10) M-1 and a site concentration of 43.4 +/- 3.4 fmol/mg protein. In this system, human calcitonin gene-related peptide had a binding affinity constant of 3.9 +/- 0.7 X 10(9) M-1 whereas salmon calcitonin was very weak with a binding affinity constant of only 6.8 +/- 4.0 X 10(5) M-1. CGRP binding localized by in vitro autoradiography, using [125I]rat calcitonin gene-related peptide, had a characteristic distinct distribution in the rat brain. There were high concentrations of binding found over the accumbens nucleus, the organum vasculosum of the lamina terminalis, ventral caudate putamen, median eminence, the arcuate nucleus, lateral amygdaloid nucleus and lateral mammillary nucleus, the superior and inferior colliculi, pontine nuclei, molecular and Purkinje cell layers of the cerebellar cortex, the nucleus of the solitary tract, the inferior olivary nuclei, hypoglossal complex and the vestibular and cochlear nuclei. The distribution of these binding sites suggests multiple roles for CGRP in the central nervous system including auditory, visual, gustatory and somatosensory processing, and in neuroendocrine control.

Animals↗

PubMed1986

Basal and stimulated release of calcitonin gene-related peptide (CGRP) in patients with medullary thyroid carcinoma.

Calcitonin gene-related peptide (CGRP) is a recently discovered peptide whose existence was first predicted following sequence analysis of the rat calcitonin gene. In the present study, plasma levels of CGRP were measured in patients with medullary thyroid carcinoma, both basally and following calcium or pentagastrin stimulation. Using a sensitive radioimmunoassay for CGRP, 19 of 21 patients with medullary thyroid carcinoma had elevated plasma levels of immunoreactive CGRP (median value 114 pmol/l) while 23 normal subjects had plasma CGRP levels below the detection limit of the assay (less than 10 pmol/l). Calcium or pentagastrin infusion in medullary thyroid carcinoma patients were potent stimuli to CGRP release, increasing plasma levels two- to five-fold. Chromatographic characterization using high pressure liquid chromatography of the CGRP immunoreactivity in plasma from two patients with medullary carcinoma of the thyroid demonstrated the presence of two molecular forms, neither of which co-eluted with synthetic human CGRP. The role of CGRP in the pathophysiology of medullary thyroid carcinoma is not clear but it may contribute to some of the clinical features associated with the disease. Furthermore, measurement of CGRP in conjunction with calcitonin could help in determining the prognosis of these patients.

Calcitonin↗

PubMed1986

Abundant calcitonin receptors in isolated rat osteoclasts. Biochemical and autoradiographic characterization.

Calcitonin receptors have been characterized for the first time in isolated osteoclasts. These receptors have been demonstrated by autoradiographic and biochemical methods, and the cells have also been shown to respond to calcitonin with a dose-dependent increase in cyclic AMP. The receptors in rat osteoclasts are specific and of high affinity (dissociation constant, Kd, 1 to 6 X 10(-10) M), and are present in greater numbers than in any cell previously studied (greater than 10(6) per cell). Chemical cross-linking of 125I-labeled salmon calcitonin to osteoclasts using disuccinimidyl suberate resulted in identification of a receptor component with a relative molecular weight of 80,000-90,000. By counting grains in autoradiographic experiments, we found that greater than 80% of specifically bound radioactivity was associated with multinucleate osteoclasts and the remainder was associated with mononuclear cells that are not osteoblasts, but that may be osteoclast precursors.

Animals↗

PubMed1986

Glucocorticoid treatment facilitates cyclic adenosine 3',5'-monophosphate-dependent protein kinase response in parathyroid hormone-responsive osteogenic sarcoma cells.

Late passage cultures of a clonal osteogenic sarcoma line (ROS 17/2.8) failed to respond to PTH with activation of cAMP-dependent protein kinase isoenzymes despite showing a sensitive and dose-dependent increase in cAMP after treatment with the hormone. When cells were treated with hydrocortisone or dexamethasone, protein kinase responsiveness to PTH was readily demonstrated; such treatment also resulted in enhanced cAMP production. Forskolin preincubation resulted in a cAMP response to PTH of similar magnitude to that seen with hydrocortisone but no activation of cAMP-dependent protein kinase occurred. Thus, the effect of glucocorticoid cannot be explained merely by the increased amplitude and sensitivity of the cAMP response which developed with glucocorticoid treatment in these cells. The data indicate that cellular activation of cAMP-dependent protein kinase does not automatically follow cAMP generation and that information transfer can be restored by pharmacological means.

Adenylyl Cyclases↗

PubMed1986

Identification of calcitonin and calcitonin gene-related peptide messenger ribonucleic acid in medullary thyroid carcinomas by hybridization histochemistry.

Synthesis and secretion of calcitonin and calcitonin gene-related peptide (CGRP) were studied in medullary thyroid carcinomas (MTC) by hybridization histochemistry on tissue sections and by Northern gel analysis of mRNA. Five patients with MTC and elevated serum levels of calcitonin and CGRP were studied. Surgically obtained tumor samples (four primary and three lymph node metastases) were extracted after freezing, and the RNA was fractionated on Northern gels. Hybridization was carried out with 32P-labeled synthetic oligodeoxyribonucleotides coding specifically for calcitonin and CGRP. Calcitonin- and CGRP-specific mRNAs approximately 1000 nucleotides in length were demonstrated in all 7 tumor samples. However, neither calcitonin nor CGRP mRNA was detected in a pheochromocytoma from 1 of the patients who had multiple endocrine neoplasia type II. A series of unselected lung carcinomas yielded the same result. Hybridization histochemistry was carried out on sections from the same tumors using the same probes. The mRNAs for calcitonin and CGRP were located in all cells of neoplastic MTC appearance, with CGRP mRNA at significantly lower levels. This demonstrated that both calcitonin and CGRP mRNA were present within the same tumor cells. The lung tumors and pheochromocytoma were negative with both probes. Hybridization histochemistry is likely to be of use in diagnosis of medullary thyroid cancer and in studying the calcitonin-CGRP mRNA processing mechanism in whole cells.

Calcitonin↗

PubMed1986

Efficacy and specificity of human parathyroid hormone analogues as antagonists in intact clonal osteogenic sarcoma cells.

Five synthetic analogues of human parathyroid hormone (hPTH), (Tyr34)hPTH(3-34) amide, (5-34) amide, (7-34) amide, (8-34) amide and (9-34) amide, were tested for their ability to antagonize hPTH action specifically in intact cultured cells. Clonal rat osteogenic sarcoma cells were used (UMR 106-06 line) which respond to PTH with an increase in cyclic AMP (cAMP) formation. The most potent antagonists were (Tyr34)hPTH(3-34) amide and (5-34) amide, which inhibited the effect of hPTH(2.4 nmol/l) with half maximally effective concentrations of 0.1 mumol/l. When conditioned medium was used from a human lung cancer cell line producing osteoblast adenylate cyclase-stimulating activity, these two analogues were capable of inhibiting the increase in cAMP production. The specificity of the antagonism was indicated by the inability of the analogues to influence the effects of prostaglandin E2 or of calcitonin, which are alternative stimulators of cAMP production in the osteogenic sarcoma cells. Only (Tyr34)hPTH(3-34) amide showed some PTH-like agonist activity at high concentrations. These analogues should prove valuable in the investigation of PTH actions on target cells and of tumour products which appear to act through the PTH receptor.

Animals↗

PubMed1986

Testing models of insulin binding in rat adipocytes using network thermodynamic computer simulations.

Many different models have been proposed to explain the complex binding behavior of insulin to its receptor, but a systematic comparison of models with experimental results is lacking. We have used network thermodynamic computer simulations to compare models of insulin binding against the results of several experimental tests designed to differentiate between the models. Six models of insulin binding were tested (simple, diffusion-reaction, conversion, dissociation, heterogeneous site, and two-step intramembrane) against results reported in the literature for isolated rat adipocytes. Although still a matter of experimental controversy, the criteria selected for modeling were curvilinear Scatchard plots, bi-or multi-exponential dissociation, insulin-accelerated dissociation, lack of dependence of the overall dissociation constant on receptor number, and receptor reserve. Using a given set of parameter values most appropriate for each model, none was able to account for all of the observed experimental results. This indicates both the complexity of the binding reaction and the need for further model development. The approach of using computer simulations to systematically test models against experimental results affords not only insight into the critical features of a model enabling it to pass a test, but also indicates potential experiments which might differentiate between models.

Adipose Tissue↗

PubMed1986

Significance of 1,25-dihydroxyvitamin D3 receptor in primary breast cancers.

Specific high affinity receptors for 1,25-dihydroxyvitamin D3 are present in several human breast cancer cell lines, and this hormone can regulate the replication of these cells. These receptors are also present in primary breast carcinomas. The present study has resulted from the follow-up for up to 68 mo of 263 women, who had had 1,25-dihydroxyvitamin D receptor (1,25-DR) levels measured in their primary tumors. Survival data on 191 women were correlated with the levels of 1,25-DR and other steroid hormone receptors, menopausal status, and age by life table analysis. Survival was not affected by 1,25-DR level in either absolute terms or relative levels. However, the late development of lymph node metastases in eight of 47 individuals was correlated with the 1,25-DR level (P = 0.05). There was no correlation between 1,25-DR or other hormone receptor levels and the development of hypercalcemia or bone metastases in the small number of individuals so affected. As we had observed previously, there was no correlation between the level of 1,25-DR and that of the other steroid hormones. These data show that the presence of 1,25-DR in primary breast cancers is independent of other prognostic indicators and, inasmuch as it correlated with late lymph node metastasis, may be an adverse prognostic indicator.

Aged↗

PubMed1986

Osteolytic Paget's disease. Recognition and risks of biopsy.

The cases of five patients with the predominantly osteolytic form of Paget's disease affecting weight-bearing long bones are described. The diagnosis was not recognized initially in three. In two of them a biopsy was performed, and one subsequently had a fracture through the biopsy site more than a year later. In all five, calcitonin treatment was effective in restoring the bone architecture toward normal as determined radiographically. Relapse occurred in two patients shortly after the cessation of calcitonin treatment and in a third despite continued treatment. The flame-shaped resorption from of the osteolytic component of Paget's disease has a pathognomonic appearance radiographically. Radionuclide bone-scanning can help in establishing the diagnosis. Diagnostic biopsy of such an area, particularly in a weight-bearing long bone, is unnecessary and should be avoided because of the increased risk of fracture.

Aged↗

PubMed1985

Calcitonin gene-related peptide stimulates cyclic AMP formation in rat aortic smooth muscle cells.

In rat aortic smooth muscle cells in culture, calcitonin gene-related peptide stimulated cAMP formation in a dose-dependent manner, half-maximally effective at 0.5 to 1 nM. There was no effect on formation of cGMP, which was increased 300-fold in the same experiments by atriopeptin or sodium nitroprusside. The vasodilator effect of CGRP in rat aorta requires an intact endothelium, indicating that increase in vascular smooth muscle cAMP is not in itself sufficient to bring about relaxation. cAMP is probably a mediator of CGRP action in vascular smooth muscle.

Animals↗

PubMed1985

Effect of 1,25-dihydroxyvitamin D3 on cyclic AMP responses to hormones in clonal osteogenic sarcoma cells.

The effect of 1,25-dihydroxyvitamin D3 on adenylate cyclase responsiveness was studied in the clonal osteogenic sarcoma cell line, UMR 106-06, which responds to several bone active hormones. 1,25-dihydroxyvitamin D3 treatment had no consistent effect on basal formation of cyclic AMP in intact cells, but the responses to parathyroid hormone, isoproterenol, prostaglandin E2, salmon calcitonin and the plant diterpene, forskolin, were all attenuated, by up to 90%. The effect of 1,25-dihydroxyvitamin D3 was dose-dependent, with half-maximal effectiveness at 0.1 nM, and required 48 h treatment of cells before it became apparent. The relative potencies of other vitamin D3 compounds correlated closely with their relative affinities for the 1,25-dihydroxyvitamin D3 receptor and their biological activities in other systems. 1,25-dihydroxyvitamin D3 treatment had no effect on the kinetics of labelled calcitonin binding to UMR 106-06 cells. Furthermore, the fact that such a range of hormones was affected made a receptor mediated mechanism unlikely. Nucleotide stimulatory (Ns) unit activity was assayed after 1,25-dihydroxyvitamin D3 treatment and found to be unchanged. Islet activating protein, an inhibitor of nucleotide inhibitory unit (Ni) activity, failed to modify the 1,25-dihydroxyvitamin D3 effect. Thus the effect of 1,25-dihydroxyvitamin D3 appeared to be exerted beyond hormone receptor and nucleotide regulatory components of the adenylate cyclase complex. It is concluded that 1,25-dihydroxyvitamin D3 attenuates adenylate cyclase response to hormones by a direct or indirect action on the catalytic component of adenylate cyclase.

Adenylate Cyclase Toxin↗

PubMed1985

Embryo research.

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Beginning of Human Life↗

PubMed1985

Characterization of an osteoblast-like clonal cell line which responds to both parathyroid hormone and calcitonin.

The clonal cell line UMR 106, which was originally derived from a rat transplantable osteogenic sarcoma with an osteoblastic phenotype, was subcloned after the emergence of a calcitonin-responsive adenylate cyclase was noted in late passages. Detailed studies on the stimulation of adenylate cyclase and activation profile of the cyclic AMP-dependent protein kinase isoenzymes in response to parathyroid hormone (PTH) and salmon calcitonin (SCT) were conducted on two subclones (UMR 106-01 and UMR 106-06). Both subclones responded in an identical manner to PTH, which stimulated adenylate cyclase and activated both isoenzyme I and isoenzyme II of cyclic AMP-dependent protein kinase. In contrast, only UMR 106-06 cells responded to calcitonin. At 3 X 10(-8)M SCT, there was a sevenfold stimulation of adenylate cyclase, 84% activation of isoenzyme I, and 44% activation of isoenzyme II. The activation profiles of the isoenzymes to PTH and SCT in UMR 106-06 were similar. Furthermore, their response to SCT correlates with the presence of specific, saturable binding of 125I-labeled SCT. Binding parameters indicate apparent Kd = 0.8 nM and 6,000 receptors/cell. These data point to a significant phenotypic change having taken place in this clonal cell line with prolonged maintenance in culture, with the emergence of a calcitonin receptor linked to adenylate cyclase and protein kinase activation.

Acid Phosphatase↗

PubMed1985

Inhibitory effects of parathyroid hormone on growth of osteogenic sarcoma cells.

The effects of the bone resorbing hormone, parathyroid hormone (PTH), on the growth of malignant osteoblastic cells have been examined. The malignant osteoblastic cells were a clonal line (UMR 106) derived from a transplantable rat osteogenic sarcoma. The predominant effect of PTH at doses above 10(-10) M was an inhibition of replication and DNA synthesis. Replication was decreased by PTH in both the presence or absence of serum and at various cell seeding densities. Both bovine PTH (1-84) and the synthetic hormone, human PTH (1-34), inhibited replication, but with bovine hormone being an order of magnitude more potent. The effects could be observed in as short a time as 6 hours with DNA synthesis and 24 hours with replication.

Animals↗

PubMed1985

Regulation of prostaglandin production by osteoblast-rich calvarial cells.

The effect of various factors upon prostaglandin (PG) production by the osteoblast was examined using osteoblast-rich populations of cells prepared from newborn rat calvaria. Bradykinin and serum, and to a lesser extent, thrombin, were all shown to stimulate PGE2 and 6-keto-PGF1 alpha (the hydration product of PGI2) secretion by the osteoblastic cells. Several inhibitors of prostanoid synthesis, dexamethasone, indomethacin, dazoxiben and nafazatrom, were tested for their effects on the calvarial cells. All inhibited PGE2 and PGI2 (the major arachidonic acid metabolites of these cells) production with half-maximal inhibition by all four substances occurring at approximately 10(-7) M. For dazoxiben and nafazatrom, this was in contrast to published results from experiments in vivo which have indicated that the compounds stimulated PGI2 production. Finally, since the osteoblast is responsive to bone-resorbing hormones, these were tested. Only epidermal growth factor (EGF) was shown to modify PG production. At early times EGF stimulated PGE2 release, however, the predominant effect of the growth factor was an inhibition of both PGE2 and PGI2 production by the osteoblastic cells. The present results suggest that the bone-resorbing hormones do not act to cause an increase in PG by the osteoblast and that any increase in PG production by these cells may be in response to vascular agents.

6-Ketoprostaglandin F1 alpha↗

PubMed1985

Hormone-dependent transformation and nuclear localisation of 1,25-dihydroxyvitamin D3 receptors from human breast cancer cell lines and chick duodenum.

Recent studies on the 1,25-dihydroxyvitamin D3 (calcitriol) receptor have shown association of unoccupied receptor with isolated nuclei, thus suggesting that hormone is not required for transformation and nuclear localisation of this receptor. In the present work calcitriol receptors from cultured breast cancer cells were studied for evidence of hormone-dependent activation and compared to those from chick duodenum. Unlike other steroid receptors changes in receptor mobility on ion exchange and gel filtration were not found for occupied and unoccupied receptors. Furthermore no changes in affinity were observed on DNA-cellulose with both hormone-bound and unoccupied receptor having equally high affinity, eluting at 0.25 M KCI. However, a substantial hormone-dependent increase in receptor affinity for nuclei was seen. Thus calcitriol receptors do appear to undergo hormone-dependent transformation which is detected by their increased affinity for nuclei, without any accompanying gross changes in charge density, size or affinity for DNA-cellulose. Previously, we have reported that fractionation of T-47D cells in a low salt buffer resulted in recovery of unoccupied receptors in the cytosol, whereas occupied receptors were associated with purified nuclei. The data presented in this paper and our previous work suggest that calcitriol receptors do undergo a hormone-dependent increase in their affinity for nuclei. Furthermore in all this work calcitriol receptors from cultured human breast cancer cells displayed identical physicochemical characteristics to those of chick duodenal receptors.

Animals↗

PubMed1985

Pharmacologic modification of blood flow in the rabbit microvasculature with prostacyclin and related drugs.

The rabbit epigastric free flap was used to investigate the effect of prostacyclin and drugs modifying its synthesis in vivo on microvascular blood flow. Prostacyclin and its analogue carbacyclin caused an increase in flow with a maximal twofold increase at approximately 6.5 and 250 ng/ml, respectively, in the flap. Thromboxane synthetase inhibitors such as dazoxiben hydrochloride, UK-38,485, 7-IHA, and imidazole (up to 7 X 10(-4) M in the flap) as well as the prostaglandins 6-oxo-PGF1 alpha and PGE2 (up to 3.7 and 9.2 ng/ml, respectively, in the flap) all failed to modify the control flow rate in the cutaneous microcirculation. It is concluded that the vasodilatory properties of prostacyclin and carbacyclin, together with their known platelet antiaggregatory properties, warrant further study in problem areas of microsurgery such as flap ischemia. The use of thromboxane synthetase inhibitors had no demonstrable effect on the normal flap, and their effect on the ischemic flap remains to be investigated.

6-Ketoprostaglandin F1 alpha↗