Nonadrenergic [3H]idazoxan binding sites are physically distinct from alpha 2-adrenergic receptors

We have recently demonstrated that the alpha 2-adrenergic radioligand [3H]idazoxan also labels additional sites that do not recognize catecholamines but bind with high affinity several chemically distinct drugs previously assumed to be highly selective for alpha 2-adrenergic receptors [Mol. Pharmacol. 35:324-330 (1989)]. We now have used three approaches to distinguish the nonadrenergic [3H]idazoxan sites from alpha 2-adrenergic receptors. (a) No nonadrenergic [3H]idazoxan binding sites were found in COS-7 cells transfected with the genes for the two known alpha 2-adrenergic receptor subtypes. (b) The ratio of alpha 2-adrenergic and nonadrenergic [3H]idazoxan sites in human platelet membranes varied considerably between various donors. (c) Highly purified platelet plasma membranes were enriched for alpha 2-adrenergic receptors but did not contain any nonadrenergic [3H]idazoxan binding sites. We conclude that the nonadrenergic [3H]idazoxan binding sites are not co-expressed with alpha 2-adrenergic receptors and at least in human platelets may be located in an intracellular compartment.     

Reversal of basic fibroblast growth factor-mediated autocrine cell transformation by aromatic anionic compounds.

NIH-3T3 cells transfected with basic fibroblast growth factor (bFGF) fused to a signal peptide sequence (spbFGF cells) are transformed in vitro and tumorigenic in vivo. Treatment of spbFGF cells with low and nontoxic concentrations (0.5-2.5 micrograms/ml) of negatively charged, nonsulfated aromatic compounds (e.g., aurin tricarboxylic acid, 4-hydroxyphenoxyacetic acid) resulted in restoration of their normal proliferative rate, morphological appearance, and adhesion properties. Binding and cross-linking experiments using 125I-labeled bFGF revealed that these alterations were associated with an up-regulation of high affinity receptors bFGF receptors was induced by these compounds in spbFGF cells that were seeded on fibronectin to enforce a firm cell attachment and flattening. Thus, induction of spbFGF cell adhesion and spreading may not be related to restoration of normal bFGF-receptor interactions. Although the negatively charged aromatic compounds mimic many of the effects of heparin in other systems (e.g., release of heparin- and heparan sulfate-bound proteins, inhibition of heparanase), heparin, heparan sulfate, and dextran sulfate were not effective at the low concentrations of the anionic compounds used in the present study. Likewise, suramin, a sulfated aromatic molecule, was effective at toxic concentrations, 400-600-fold higher than the nonsulfated aromatic compounds. The development of defined, nontoxic anionic compounds may provide a new strategy to interfere with the autonomous and anchorage independent mode of cell growth involved in autocrine cell transformation and cancer.     

Successful treatment course with carbamazepine despite initial significant leukopenia: case report

A case of carbamazepine-induced leukopenia with subsequent successful carbamazepine management is presented. Despite WBC suppression to a level of 2000/cu mm on an initial trial of carbamazepine, a challenge with a much lower dose and gradual titration permitted a full treatment course with therapeutic blood levels. Although many physicians are wary of the leukopenia associated with carbamazepine, it is a distinct entity from the rare agranulocytosis and aplastic anemia that have been associated with the drug. With careful clinical management, carbamazepine can be successfully used in patients with neurologic disorders despite significant WBC suppression.     

Identification of single amino acid substitutions in the staphylococcal nuclease protein that enhance and diminish T cell clone recognition of naturally processed peptides.

It has been inferred that residue changes that affect T cell recognition of synthetic peptides will have a similar effect in the intact protein. However, since small peptides do not require antigen processing it is possible that residue changes in synthetic peptides will not have an equivalent effect in the intact protein. Mutant proteins of staphylococcal nuclease (Nase) and 15mer synthetic peptides with corresponding substitutions were compared to determine if residue changes within an immunodominant epitope have an effect on the generation of naturally processed peptides. Five different substitutions in the synthetic peptide resulted in loss of reactivity of individual Nase-specific clones. When the same single amino acid changes were made in the intact protein, the naturally-processed peptides were also unable to stimulate the Nase-specific clones. However, two other substitutions in the synthetic peptide were stimulatory for a T cell clone even though the same changes in the intact protein were non-stimulatory. These results suggest that certain residue changes affect recognition of the naturally processed peptide but not the synthetic peptide with the same amino acid change. In addition, these results demonstrate that the effects of amino acid substitutions in synthetic peptides on T cell recognition may not always reflect the effects of these substitutions in the intact protein. Substitutions located outside Nase-specific T cell epitopes were also examined. Thirty different mutant proteins were all stimulatory. Moreover, a number of these mutants proteins were 50- to 100-fold more efficient in their stimulatory capacity than the native Nase protein.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relation of growth hormone and myocardial collagen accumulation in experimental diabetes

A pathogenic role of growth hormone in the tissue complications of diabetes has been postulated. Because collagen has been found to accumulate in myocardial interstitium in diabetes, we have undertaken a study of the relationship of plasma growth hormone levels to collagen accumulation in a canine model of chronic diabetes. Sedentary normal animals and diabetic animals were compared respectively with physically conditioned animals in which the collagen increment associated with diabetes was minimized. Basal growth hormone levels as well as increments induced by hormone release after clonidine have been related to the myocardial alteration. Myocardial collagen concentration was increased to 2.94 +/- 0.11 micrograms/mg dry weight in the sedentary diabetic animals vs. 1.97 +/- 0.07 micrograms/mg dry weight in sedentary normals (P less than 0.01), but was normal in the exercised diabetic animals after 1 year. However, levels of growth hormone in the basal state were similar in all four groups. After provocative stimulation with clonidine in the normals there was a progressive rise of growth hormone levels that was similar in the sedentary and physically conditioned animals. The diabetic groups exhibited a rise of plasma growth hormone that was not significantly higher in the nonexercised animals. Moreover the peak levels of growth hormone after clonidine were comparable. The data suggest that collagen accumulation in diabetic myocardium does not appear to be dependent on increased plasma levels of growth hormone, but a role for enhanced sensitivity to hormonal action is not excluded.