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Biomedical subjects

J M Dellacha

Publications and source records attributed to J M Dellacha.

At least 37 records · Page 2Linked to original sources
PubMed1983

Mouse liver specific uptake of iodinated growth hormones: evidence for the presence of somatogenic and lactogenic sites.

The distribution of human growth hormone labelled with 125I (125I-hGH) was studied in normal adult female and male mice. The radioactivity was basically concentrated by the liver and kidney reading a maximum 15 minutes after the labelled hormone injection. Only the liver showed a significant reduction of radioactivity uptake when 125I-hGH was injected together with an excess of unlabelled hormone. This reduction was dose-dependent and the amount of unlabelled hormone that prevented 50% of the liver uptake (ED50) of 125I-hGH was close to 3 micrograms for both female and male mice. Similar results were obtained in studies where bovine growth hormone labelled with 125I (125I-bGH) was injected, except that the maximum uptake value was significantly lower than that observed when 125I-hGH was used. This observation could be attributed to the difference that exists between the biological properties of both hormones since hGH has growth-promoting and lactogenic effects in rodents, whereas bGH exhibits exclusively somatotropic activity. In order to examine the nature of the radioactive material which localized in the liver soluble extracts were prepared using Triton X-100 and analyzed on Sepharose CL-6B. The majority of the radioactivity appeared as an homogeneous peak with KD = 0.31 which could be attributed to a molecular species of Stokes radius of approximately 64A. This magnitude is consistent with the effective molecular size reported for various hormone-receptor complexes.

Animals↗
PubMed1982

Structural characterization of iodinated bovine growth hormone.

Bovine growth hormone (bGH) was submitted to iodination using limited amounts of oxidizing reagent, yielding a derivative with no more than 1-g-atom of iodine per mole of hormone. Analysis of the hydrolysis products indicated that monoiodotyrosine was almost the only product of substitution. Isolation and identification of the tryptic fragments showed that half of the 125I-labeled bGH molecules were iodinated in Tyr 174, followed by Tyr 158 (16%) and Tyr 42 (14%). Frontal gel chromatography indicated that the preparation did not contain significant amounts of unreacted bGH. Circular dichroism evidenced structural similarity between the native and the iodinated bGH. The iodinated hormone, like the native protein, undergoes self-association. The dissociation constant of the iodo-labeled bGH self-association equilibrium showed a two-fold increase when compared to that corresponding to the unlabeled hormone. At pH 8.5, where the equilibrium constant was estimated, one tenth of the molecules bear a charged iodotyrosyl residue (average pKapp = 9.3), which could account for part, if not all, of the observed difference regarding self-association. By this criterion, the presence of the iodine atom does not disturb the area engaged in dimer formation.

Animals↗
PubMed1982

Biological and immunological characterization of iodinated bovine growth hormone.

Iodinated bovine growth hormone, containing no more than 1 g-atom of iodine per mole of hormone is generally used as a tracer in studies related to the action and metabolism of the hormone. This derivative was tested in different biological and immunological systems in which the hormone is known to be active. The iodinated derivative was almost indistinguishable in its properties from the native hormone when it was examined by the following criteria: body growth promoting activity, rat liver uptake in vivo, binding to rabbit liver microsomes and primary antigen-antibody interactions. Micro-complement fixation experiments suggested that the iodination produces minor alterations in the affinity of some antigenic determinants.

Animals↗
PubMed1980

Insulin binding to liver cells: a simple and useful in vivo model.

Insulin binding to rat liver cells was studied in vivo, by I. V. injection of (125I)-labelled hormone either alone or together with different amounts of unlabelled insulin. Native insulin competes with the tracer in a manner similar to the one observed in the in vitro preparation. Prolactin, bovine growth hormone or glucagon were unable to displace labelled insulin from its binding sites. The hypoglycemic effect of various amounts of native insulin was measured and correlated to the binding studies. It was found that maximal insulin-induced hypoglycemia occurs at an insulin concentration at which only about 12% of the measurable receptors are occupied.

Animals↗
PubMed1978

Specific binding of iodinated growth hormone to rat liver in vivo.

The specific uptake by rat liver of human (hGH) and bovine (bGH) GHs labeled with 125I was studied by an in vivo procedure. A significant reduction of the uptake was observed when labeled hormones were injected together with different amounts of the corresponding native GH. This reduction was dose dependent, and the concentration of native hormone that prevents 50% of the liver uptake of the labeled hormone was close to 12 microgram/100 g BW. In normal rats, only native hGH or bGH significantly decreased the liver uptake of [125I]iodo-bGH, while bovine PRL (oPRL) or heat-denatured bGH were inactive. The highest inhibition of the uptake of [125I]iodo-hGH by rat liver was obtained when this labeled hormone was injected either together with hGH or with bGH plus oPRL while partial displacement was observed with bGH or oPRL. These data suggest that hGH binds to both somatotropic and lactogenic sites in the liver of normal rats. In hypophysectomized animals, only the somatogenic binding sites could be detected.

Animals↗
PubMed1976

Specific binding of human and bovine growth hormones to hypophysectomized rat hepatocytes.

Specific binding of 125I-HGH and 125I-bGH was obtained in hypophysectomized rat liver cells. Two types of somatogenic receptors were found with apparent dissociation constants of 4.2 x 10(8) M-1 and 1.7 x 10(7) M-1. The number of sites for the higher and lower affinity receptors were: 1 x 10(4) and 6 x 10(3), respectively. Human, bovine and equine growth hormones appear to bind to liver cells with equal affinity, while ovine prolactin needs at least a two-order-magnitude greater concentration to displace 125I-bGH. A parallelism between biological activity and binding data was observed.

Animals↗