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PubMed1997

Colon tumor promotion: is it a selective process? Effects of cholate, phytate, and food restriction in rats on proliferation and apoptosis in normal and aberrant crypts.

Promotion would suppose the selection of initiated cells. We tested the selection of aberrant crypt cells by cholic acid, a colon cancer promoter, and the effect of protectors, phytate and food restriction. After an azoxymethane injection, rats were allocated to a control diet, or to supplements of cholic acid, sodium phytate, or to a 50% food restriction. The proliferation and apoptosis of 1200 crypts were assessed, after immuno-staining for BrdU. Cholic acid increased the proliferation of aberrant crypts but not of normal crypts. Phytate and food restriction decreased the proliferation of normal crypts, but not of aberrant crypts. Apoptosis was not affected by diets. Results support the hypothesis that cholic acid can select initiated cells in the colon.

Analysis of Variance↗
PubMed1986

Characterization of high-affinity dopamine D2 receptors and modulation of affinity states by guanine nucleotides in cholate-solubilized bovine striatal preparations.

3,4-Dihydroxyphenylethylamine (dopamine) D2 receptors, solubilized from bovine striatal membranes using a cholic acid-NaCl combination, exhibited the typical pharmacological characteristics of both agonist and antagonist binding. The rank order potency of the agonists and antagonists to displace [3H]spiroperidol binding was the same as that observed with membrane-bound receptors. Computer-assisted analysis of the [3H]spiroperidol/agonist competition curves revealed the retention of high- and low-affinity states of the D2 receptor in the solubilized preparations and the proportions of receptor subpopulations in the two affinity states were similar to those reported in membrane. Guanine nucleotide almost completely converted the high-affinity sites to low-affinity sites for the agonists. The binding of the high-affinity agonist [3H]N-n-propylnorapomorphine ([3H]NPA) was clearly demonstrated in the solubilized preparations for the first time. Addition of guanylyl-imidodiphosphate completely abolished the [3H]NPA binding. When the solubilized receptors were subjected to diethylaminoethyl-Sephacel chromatography, the dopaminergic binding sites eluted in two distinct peaks, showing six- to sevenfold purification of the receptors in the major peak. Binding studies performed on both peaks indicated that the receptor subpopulation present in the first peak may have a larger proportion of high-affinity binding sites than the second peak. The solubilized preparation also showed high-affinity binding of [35S]guanosine-5'-(gamma-thio)triphosphate, a result suggesting the presence of guanine nucleotide binding sites, which may interact with the solubilized D2 receptors. These data are consistent with the retention of the D2 receptor-guanine nucleotide regulatory protein complex in the solubilized preparations and should provide a suitable model system to study the receptor-effector interactions.

Animals↗