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Biomedical subjects

N H Hunt

Publications and source records attributed to N H Hunt.

At least 109 records · Page 6Linked to original sources
PubMed1979

Cyclic nucleotide metabolism in tumours.

Many hormones act by combining with cell surface receptors and stimulating adenylate cyclase activity. The cyclic AMP generated is the mediator of a number of cellular metabolic processes. Other processes may be influenced by changes in cyclic GMP levels. Although much evidence from cultured cells suggested that low cellular levels of cyclic AMP and high levels of cyclic GMP are a feature of rapid cell growth and of malignant transformation, review of the data reveals many inconsistencies. Thus in established tumours growing in vivo, for example, cyclic AMP levels appear to be unrelated to tumour growth rates. It seems that tumour cell cyclic AMP is more likely concerned with the regulation of tumour cell function than of growth. This would have implications for therapy, in that drugs which influence cyclic nucleotide metabolism could influence tumour cell function. The control of cyclic nucleotide production in normal and tumour cells is discussed, together with the possible ways in which abnormalities of this may occur.

Adenylyl Cyclases↗
PubMed1978

Characterization of beta-adrenergic receptor linked to adenylate cyclase in a human cancer cell line (COLO 16).

1. A human cancer cell line (COLO 16) derived originally from an epidermal squamous cell carcinoma was found to possess adenylate cyclase responsiveness to beta-adrenergic agonists. 2. The adenylate cyclase response was characterized with respect to activation constants (KA) for various beta-adrenergic agonists and inhibition constants (Ki) for antagonists. 3. Intact cells responded with dose-dependent increases in production of cyclic adenosine 3':5'-monophosphate. 4. Properties of the beta-adrenergic receptor were evaluated by using the specific binding of [3H]propranolol to cell membranes. Specific binding was saturable, with KD 5.79 nmol/l and binding sites 0.68 pmol/mg of protein. 5. Competition for binding to cell membranes was shown by beta-adrenergic agonists and antagonists and was stereospecific. There was close agreement between the affinity of these various agents on adenylate cyclase and receptor binding. 6. It is likely that the beta-adrenergic receptor-linked adenylate cyclase in COLO 16 cells represents persistence in a cancer cell line of a receptor present normally in epidermal cells.

Adenylyl Cyclases↗
PubMed1978

Membranes from a transplantable osteogenic sarcoma responsive to parathyroid hormone and prostaglandins: regulation of adenylate cyclase and of hormone metabolism.

Adenylate cyclase activity in particulate fractions from a transplantable rat osteogenic sarcoma was stimulated in a dose-dependent manner by prostaglandins E1 and E2 (PGE1 and PGE2) and parathyroid hormone (PTH). Prostaglandin F2alpha was active at a high concentration (3 x 10(-4) mol/l). Pretreatment of membranes with collagenase plus hyaluronidase reduced the magnitude of the PTH effect but did not affect the size of the PGE1 effect. Guanosine 5'-triphosphate and its synthetic analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) activated adenylate cyclase in particulate preparations from the osteogenic sarcoma. The latter agent produced much larger effects, although the concentrations required for half-maximal enzyme activation were the same for both agonists (approximately 2 x 10(-6) mol/l). The effects of PTH and Gpp(NH)p were supra-additive at some concentrations of hormone. The effects of PGE1 and Gpp(NH)p were supra-additive at all hormone concentrations tested. Pre-incubation of membrane particles for 6 min with PTH produced an enzyme activation which was not reversed by dilution through washing; pre-incubation with PGE1 did not produce this effect. The response of membrane adenylate cyclase to Gpp(NH)p (10(-4) mol/l) was 75% greater in preparations pre-incubated with PTH than in membranes pre-incubated in buffer alone or in buffer containing PGE1. The basal rate of cyclic AMP production in the adenylate cyclase assay system decreased over a 35 min incubation period. This decrease was prevented by addition of PTH or PGE1. Addition of NaF or Gpp(NH)p produced a steady increase in the rate of production of cyclic AMP with time. Membrane preparations did not reduce the biological activity of PTH and did not degrade 125I-labelled PTH. The results demonstrate that the PTH- and PGE-responsive adenylate cyclases of the osteogenic sarcoma have distinctly different properties and that particulate preparations of the tumour do not metabolize PTH.

Adenylyl Cyclases↗
PubMed1977

Calcitonin-responsive adenylate cyclase in a calcitonin-producing human cancer cell line.

A calcitonin-responsive adenylate cyclase has been found in a cell line of a poorly differentiated bronchial carcinoma (BEN cells). The cells have previously been shown to secrete an immunoreactive form of calcitonin in culture. Salmon calcitonin (SCT), porcine calcitonin (PCT) and human calcitonin (CT-M) all stimulated adenylate cyclase activity in particulate preparations. CT-M sulphoxide had little effect. The concentrations of the calcitonins required for half the maximum activation of adenylate cyclase were 6-8, 18 and 90 nm respectively. SCT (30pm) and CT-M (60 pm) increased the intracellular concentration of cyclic AMP from 11-2+/-0-2 (s.e.) to 18-2+/-0-2 and 16-7+/-0-2 respectively over a 2-5-min period. SCT (labelled with 125I) bound to particulate preparations of Ben cells, and competition for binding occurred with unlabelled SCT and CT-M. The concentration of SCT required for half the maximum inhibition of [125I]SCT binding was 11 nm. CT-M sulphoxide inhibited only at high concentration (3 micron). The characteristics of the adenylate cyclase response to SCT did not change over the period between cell adhesion (after subculture) and confluence. However, pre-incubation of cells for 4 h with SCT (150 nm) abolished the subsequent adenylate cyclase response of particulate preparations to further hormone. The practical difficulties encountered in purifying and quantifying the large-mol.-wt. form of CT-M secreted by BEN cells has precluded direct investigation of the potential relationship between hormone secretion and the occurrence of the calcitonin receptor. This relationship is discussed in terms of its possible biological significance.

Adenylyl Cyclases↗
PubMed1977

Secretion of prostaglandins as bone-resorbing agents by renal cortical carcinoma in culture.

Fragments of human renal carcinoma tissue have been co-cultured with mouse calvaria. In 9/13 cases significant bone resorption occurred whilst in no case did control kidney cause significant resorption. When bone resorption did occur, it could be reduced by inclusion of indomethacin in the culture medium. In some cases when theophylline was included in culture medium to prevent cyclic AMP breakdown, there was enhancement of tumour-induced bone resorption. Control studies without tumour showed that none of the experimental treatments had a direct effect on bone. Radioimmunoassay of prostaglandin E (PGE) levels in pooled culture media showed that tumour fragments produced appreciable amounts of PGE, and that this production was lowered by indomethacin and increased by theophylline. It is concluded that the bone resorption induced by these tumours is due to a prostaglandin, and that prostaglandin production may be controlled by changes in cyclic AMP metabolism.

Animals↗
PubMed1977

Role of vasopressin in the mitotic response of rat bone marrow cells to haemorrhage.

Two days after a severe haemorrhage plasma calcium concentrations and bone marrow mitotic activity in rats were significantly increased and so remained for a further 5-6 days until the haematocrit had returned to normal. The first 48 h after bleeding were characterized by hypocalcaemia. During this phase two significant peaks in mitotic activity were observed at 4 and 18 h after haemorrhage. The mitotic surge 4 h after bleeding was still present in adrenalectomized and parathyroidectomized animals but in rats which were either hypophysectomized or had congenital diabetes insipidus this mitotic response was absent. Vasopressin was shown to stimulate bone marrow mitotic activity both in vivo and in vitro whereas angiotensin, aldosterone and erythropoietin had no rapid, direct mitogenic action on these cells. This novel hypophysial-bone marrow system suggests that vasopressin may assist in post-haemorrhagic recovery in blood cell numbers in the circulation.

Animals↗
PubMed1977

States of activation of chick kidney adenylate cyclase induced by parathyroid hormone and guanyl nucleotides.

Several aspects of the activation of adenylate cyclase by guanosine 5'-triphosphate (GTP), 5'-guanylylimidodiphosphate (Gpp(NH)p) and bovine parathyroid hormone (bPTH) have been studied in chick kidney plasma membrane preparations. GTP (10(-4) mol/l), Gpp(NH)p (10(-4) mol/l) and bPTH (10 i.u./ml) activated adenylate cyclase without any significant time lag. However a 2 min delay was observed before the activity of the enzyme increased after the addition of bPTH (-6 leads to +34) to incubations. The early (0-3 min) effects of GTP and Gpp(NH)p upon chick kidney adenylate cyclase activity were antagonized by the addition of the alternative guanyl nucleotide. After 5 min of incubation with kidney plasma membranes, Gpp(NH)p induced a stable state of activation of adenylate cyclase which was not reversible by subsequent addition of GTP. GTP did not induce an irreversible state of enzyme activation. In pre-incubation studies, GTP did not produce a persistent enzyme activation and did not modify the effect of Gpp(NH)p added subsequently at the incubation stage. Gpp(NH)p produced a stable state of activation of adenylate cyclase which was not inhibited by addition of GTP at the incubation stage. Bovine PTH (2-34) inhibited the effect of bPTH upon adenylate cyclase activity when the native hormone (10 i.u./ml) had been incubated with plasma membranes for up to 8 min before addition of the analogue (5 mug/ml). Incubation of plasma membranes with bPTH (2-34) for as little as 10 s prevented activation of adenylate cyclase by subsequent addition of bPTH. This pattern was confirmed in pre-incubation studies. After pre-incubation of kidney membranes with bPTH and bPTH (2-34), followed by washing, an acid extract of the membranes contained immunoreactive bPTH. Gpp(NH)p produced a greater increase in adenylate cyclase activity in membranes pre-incubated with bPTH or bPTH (2-34) than in membranes pre-incubated with buffer alone, suggesting that the hormone and analogue facilitated the interaction of Gpp(NH)p with adenylate cyclase.

Adenylyl Cyclases↗
PubMed1977

Radiation induced osteogenic sarcoma in the rat as a model of hormone-responsive differentiated cancer.

An osteogenic sarcoma was induced in an inbred strain of the Sprague Dawley rat using seven serial injections of 32P-orthophosphate. The tumor was maintained by transplantation over a 3-year period in the same inbred strain. During this time it retained its bone-like differentiation. Tumor membranes and freshly isolated tumor cells also retained responsiveness to parathyroid hormone and to prostaglandins of adenylate cyclase and cyclic nucleotide formation respectively. The potencies of these agents and their analogues and metabolites were found to be proportional to their efficacies as bone resorbing agents. Thus, the tumor was shown to be a model for the study of hormone-responsiveness for tumor growth and differentiation, and also of the effects of agonists which act on bone-like cells.

Adenylyl Cyclases↗
PubMed1976

Studies in vivo on the effects of parathyroid hormone upon kidney cyclic adenosine 3',5'-monophosphate content using rapid tissue fixation by microwave irradiation.

Microwave irradiation is shown to be a useful method for simultaneously killing chicks and fixing tissues. Renal adenylate cyclase and phosphodiesterase activities were rapidly abolished by microwaving. The increase in chick kidney cyclic adenosine 3',5'-monophosphate (cyclic AMP) content produced by intravenous bovine parathyroid hormone (PTH) injection was much greater in microwaved birds than in those killed by cervical dislocation with subsequent tissue fixation in liquid nitrogen. After PTH injection there was a prolonged elevation of renal cyclic AMP content. At the time of maximum response (2 minutes), log. dose-response curves were linear in the dose range 0.1-10 U. The responses to three different bovine PTH preparations were indistinguishable. Arginine vasopressin, arginine vasotocin, salmon calcitonin and prostaglandin E1 did not affect kidney cyclic AMP content within 2 minutes. Because of its specificity and precision, the method is of use for the in vivo bioassay of PTH. Injection of CaCl2 (20 mumoles) 1 minute before, or conjointly with, bovine PTH inhibited the subsequent increase in kidney cyclic AMP content. The synthetic bovine PTH peptide fragments BPTH (1-34) and BPTH (2-34) both increased chick kidney cyclic AMP content. The use of such fragments allows investigation of the structural requirements of PTH for interaction with the systems regulating cyclic AMP metabolism in the kidney in vivo.

Animals↗