Growth hormone regulation of the growth hormone receptor mRNA in cultured rat epiphyseal chondrocytes.

This study was designed to investigate whether growth hormone (GH) influences the expression of its own receptor in chondrocytes. To investigate this possibility GH-receptor mRNA was measured in cultured rat epiphyseal chondrocytes in the absence or presence of GH under various experimental conditions. Chondrocytes were isolated enzymatically from epiphyseal growth plates of the proximal tibia of 20-day-old male rats and cultured in monolayer in Ham's F-12 medium supplemented with 10% calf serum and 1% of a serum substitute.

Regulation of insulin-like growth factor-I and growth hormone receptor gene expression by diabetes and nutritional state in rat tissues.

Insulin-like growth factor-I (IGF-I) mRNA and GH receptor mRNA levels were analysed in different tissues from rats made diabetic with streptozotocin, fasted rats and rats fed with a protein-reduced diet. Diabetes decreased IGF-I mRNA levels in liver, heart, diaphragm, kidney and aorta, but not in brain. GH receptor mRNA levels were decreased in heart and diaphragm, but not in liver and kidney.

Regulation of rat growth hormone receptor gene expression.

A cDNA encoding the growth hormone (GH) receptor was cloned from rat liver. Both the nucleotide and translated amino acid sequence share greater than 70% similarity with the GH receptors from rabbit and human. An RNA probe was generated from this sequence for use in a solution hybridization assay to quantitate GH receptor mRNA expression in rat tissues.

Histopathology associated with elevated levels of growth hormone and insulin-like growth factor I in transgenic mice.

Serum levels of GH and insulin-like growth factor I (IGF-I) were genetically increased to investigate the physiological activities of these proteins. Lines of mice expressing chimeric genes composed of bovine GH, human GRF, or human IGF-I coding sequences fused to the mouse metallothionein I promoter were examined for consequences of chronic exposure to high levels of these peptides. Animals with elevated serum levels of GH (either bovine GH or mouse GH) have selective splanchnomegaly coupled with glomerular sclerosis and hepatocellularmegaly.

Growth enhancement of transgenic mice expressing human insulin-like growth factor I.

A line of transgenic mice carrying a chimeric gene composed of human insulin-like growth factor I (IGF-I) coding sequences fused to the mouse metallothionein I promoter was generated to study the effects of chronically elevated exposure to IGF-I. Mice in this line overexpress IGF-I in most tissues studied and have circulating IGF-I levels 1.5 times the normal value.

Effects of folate deficiency on the metastatic potential of murine melanoma cells.

Experiments were designed to measure the effect of folic acid deficiency on a major determinant of cancer lethality, the propensity to form metastases. Murine B16 melanoma cells (F10 strain) were grown in folate-deficient and -supplemented media. After 3 days, cells in the deficient medium had restricted proliferative capacity, low folate levels by bioassay, increased cell volume, abnormal deoxyuridine suppression tests, accumulation of cells in S phase by flow cytometry, and increased numbers of DNA strand breaks.

Expression of insulin-like growth factor I in transgenic mice with elevated levels of growth hormone is correlated with growth.

To study the role of insulin-like growth factor I (IGF-I) in mediating the growth-promoting function of GH, IGF-I expression was assayed in transgenic mice carrying either GH or GRF fusion genes. These mice exhibit enhanced growth as a result of high level ectopic expression of GH and have 2-fold elevation of both hepatic IGF-I mRNA levels and circulating IGF-I levels. Hepatic IGF-I mRNA levels are low at birth regardless of GH levels; they increase approximately 10-fold during postnatal development and become GH inducible 2 weeks after birth.

Regulation of insulin-like growth factor messenger ribonucleic acid in rat growth plate by growth hormone.

The mechanism of action for the stimulatory effect of GH on longitudinal bone growth is not yet clarified. Several recent reports indicate that GH has a direct effect at the site of the epiphyseal growth plate, as opposed to the somatomedin hypothesis which holds that the effect of GH is mediated by circulating insulin-like growth factors (IGFs). Using a RNA probe in a solution hybridization assay we investigated the presence of IGF-I mRNA in rat rib growth plate.

Dwarf mice produced by genetic ablation of growth hormone-expressing cells.

Fusion of the 310 bp located 5' of the rat growth hormone (GH) gene to the human GH structural gene resulted in somatotrope-specific expression in transgenic mice. Human GH transcripts were detected only in pituitaries of these mice, and immunocytochemical analyses revealed that this expression was limited to GH-expressing cell types. The rat GH 5' sequences were then used to direct the expression of diphtheria toxin to the GH-expressing cells of transgenic mice.

Regulation of insulin-like growth factor I gene expression by growth hormone.

Recombinant clones containing exon 3 of the insulin-like growth factor I (IGF-I) gene were isolated from a mouse genomic library. These sequences were used to generate an RNA probe, which was used in a solution hybridization assay to quantitate IGF-I mRNA in various murine tissues as a function of growth hormone status. The liver is the major site of IGF-I synthesis and the level of IGF-I mRNA is regulated about 10-fold by growth hormone in the growth hormone-deficient lit/lit mouse.

Metabolic epidemiology of colon cancer: fecal mutagens in healthy subjects from rural Kuopio and urban Helsinki, Finland.

Fecal mutagenic activity and dietary pattern of rural and urban Finnish population groups with distinct risk for the development of colon cancer were studied in a low-risk population in rural Kuopio and an intermediate-risk population in urban Helsinki. The average daily intake of protein and fat was the same in the two groups but the frequency of consumption of whole-grain cereals and whole-grain bread, as well as the amount of fiber from the bread were higher in Kuopio as compared to Helsinki. Fecal samples collected for 2 days were incubated under anaerobic conditions at 37 degrees C for 96 h, extracted with hexane: peroxide-free diethyl ether, partially purified on a silica Sep-Pak cartridge, and assayed for mutagenic activity using the Salmonella typhimurium/mammalian microsome system.

Effect of Japanese seaweed (Laminaria angustata) extracts on the mutagenicity of 7,12-dimethylbenz[a]anthracene, a breast carcinogen, and of 3,2'-dimethyl-4-aminobiphenyl, a colon and breast carcinogen.

Animal model studies suggest that diets containing Laminaria angustata, a brown seaweed commonly eaten in Japan, inhibit breast carcinogenesis. In order to identify the compound(s) in the seaweed responsible for tumor-inhibiting activity, we used Ames/mammalian microsome assay system to determine the antimutagenic (or anticarcinogenic) effect of various solvents and water extracts of Laminaria angustata. The antimutagenic effects of acetone, ether, chloroform, chloroform + methanol, hot water and cold water extracts on the mutagenicity induced by 7,12-dimethylbenz[a]anthracene (DMBA), a breast carcinogen, and 3,2'-dimethyl-4-aminobiphenyl (DMAB), a colon and breast carcinogen, was studied using the Salmonella typhimurium strains TA98 and TA100.

Fecal mutagens from subjects consuming a mixed-western diet.

Because of potential significance of fecal mutagens (presumptive carcinogens) in the pathogenesis of colon cancer, feces from 99 healthy subjects from the New York metropolitan area were studied. The diet histories indicate that all participants were consuming a mixed-western diet which is high in total fat and low in fiber. Fecal samples that were incubated under anaerobic conditions at 37 degrees C for 96 h or frozen without incubation, were extracted with hexane: peroxide-free diethyl ether (1:1), partially purified on a silica Sep-pak cartridge and assayed for mutagenicity using the Salmonella typhimurium/mammalian microsome system.

Effect of micronutrients, antioxidants and related compounds on the mutagenicity of 3,2'-dimethyl-4-aminobiphenyl, a colon and breast carcinogen.

The possible antimutagenic effects of butylated hydroxytoluene (BHT), ethoxyquin, disulfiram, indole-3-carbinol, indole-3-acetonitrile, sodium selenite and alpha-tocopherol on 3,2'-dimethyl-4-aminobiphenyl-induced mutagenicity were studied using the Ames Salmonella/mammalian microsome assay system with strains TA98 and TA100. All seven compounds were nonmutagenic in both bacterial tester strains. The addition of or 50-250 micrograms of sodium selenite, 5-50 mg of alpha-tocopherol or 50-250 microgram of BHT per plate inhibited DMAB-induced mutagenicity in TA98 and/or TA100.

Effect of butylated hydroxytoluene and butylated hydroxyanisole on the mutagenicity of 3,2'-dimethyl-4-aminobiphenyl.

This study was undertaken to investigate the possible antimutagenic effects of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced mutagenicity, using the Ames Salmonella/mammalian microsome system. The addition of 100-250 micrograms of BHT or 25-500 micrograms of BHA/plate was found to inhibit DMAB-induced mutagenicity in Salmonella strains TA 98 and TA 100. In TA 100, the mutagenicity was further inhibited with the addition of S9 prepared from the livers of rats fed a 0.

Fecal sterols and bacterial beta-glucuronidase activity: a preliminary metabolic epidemiology study of healthy volunteers from Umea, Sweden, and metropolitan New York.

The dietary pattern, fecal bile acid and neutral sterol concentrations, and the bacterial beta-glucuronidase activity of 2 population groups with a varied risk for colon cancer development (i.e., a high-risk population in the metropolitan New York area and an intermediate-risk population in Umea, Sweden) were investigated.

Effect of high-fat, high-beef diet and of mode of cooking of beef in the diet on fecal bacterial enzymes and fecal bile acids and neutral sterols.

The effect of a high-fat, high-beef diet and of method of preparation of beef in the diet on the fecal bile acids and neutral sterols and on the activities of fecal bacterial beta-glucuronidase, cholesterol dehydrogenase and 7 alpha-dehydroxylase was studied in healthy men and women, 24-41 years old, who were consuming a customary mixed-western diet. The experimental diets were high in fat and beef, which was cooked rare, medium or well-done. The sequence of dietary regimen was selected at random and each diet phase lasted for 4 weeks.