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Biomedical subjects

I Clark

Publications and source records attributed to I Clark.

At least 55 records · Page 3Linked to original sources
PubMed1984

Excretion of RNA catabolites by rats with hepatoma transplants.

Rats with transplants of Morris Hepatoma 5123 excreted in their urine greater than normal amounts of modified nucleosides and bases, catabolites of RNA. Despite rapid growth of the neoplasm, the elevated levels did not appear until 22 days after inoculation with the tumor. With tumor progression, there were increased levels and number of these catabolites. This study also suggests that the source of the elevated RNA catabolites is mainly from the host RNA rather than from tumor tissue and also that mRNA and rRNA as well as tRNA may contribute to the urinary levels.

Animals↗
PubMed1984

Urinary catabolites of ribonucleic acid as cancer markers: a preliminary report of their use in patients with lung cancer.

Rats with aflatoxin-B1-induced hepatomas and dimethylnitrosamine-induced nephroblastomas excreted greater than normal amounts of urinary modified nucleosides and bases, catabolites of ribonucleic acid (RNA). Although both neoplasms caused increased excretions of the same catabolites, their quantitative profiles differed, suggesting that it may be possible to distinguish between tumors. Rats with transplanted tumors (e.g., hepatomas and osteogenic sarcomas) did not excrete elevated levels of urinary RNA catabolites until approximately 20 days after transplantation despite rapid growth of the tumor for the first 15 days. These data suggest that the source of the elevated levels of these excretory products may be the host's tissue RNA. Preliminary studies in human beings with lung cancer showed marked elevation of one or more urinary RNA catabolites. Resection of the diseased tissue in 2 patients caused a drop in levels. The measurement of urinary RNA catabolites may be useful in the diagnosis, prognosis, and evaluation of therapy in patients with lung cancer.

Aflatoxin B1↗
PubMed1983

Comparison of urinary modified nucleosides and bases in rats with hepatomas and nephroblastomas.

Hepatomas were induced in rats with aflatoxin B1, and nephroblastomas with dimethylnitrosamine. Microscopic examination of livers of aflatoxin-treated rats revealed multinodular hepatocyte hyperplasia at 8 months, and by 13 months all rats had hepatomas. Nephroblastomas were observed by 4 months and by 8 months all rats had developed them. The urinary excretion of several modified nucleosides and bases by normal rats is dependent on body weight and reflects, to a certain extent, their concentrations in tissue tRNA. Increased levels of several modified nucleosides and bases were found in all rats that had cancer. Rats with hepatomas excreted essentially the same modified nucleosides and bases as did those with nephroblastomas; the quantitative patterns of excretion were different, however, suggesting that the urinary modified nucleosides and bases may be used to differentiate between neoplasms. Although the increase in urinary modified nucleosides and bases by tumor-bearing animals results primarily from more rapid turnover of neoplastic tRNAs, the data indicate that increased turnover of mRNA and possibly rRNA may occur in neoplastic tissue. Preliminary data suggest that increases in urinary modified nucleosides and bases may occur during a precancerous stage. The urinary pattern of modified nucleosides and bases by rats with hepatomas is altered if another primary tumor is present. The results obtained from these studies support the use of modified nucleosides and bases in urine as biochemical markers of cancer.

Aflatoxin B1↗
PubMed1983

Metabolism of tRNA in rats with aflatoxin B1-induced hepatomas.

This study describes effects of aflatoxin B1-induced hepatomas on RNA metabolism in rats. At 4 and 24 hours after the administration of L-(14CH3)-methionine, tRNA was isolated from the livers and hydrolyzed enzymatically to nucleosides which were quantitatively measured by HPLC. Radioactivity of the nucleosides was also determined. The data indicate that although tRNA methylation may be more rapid in livers with hepatomas, catabolism of tRNA in tumorous tissue is slower than in control livers. The large increase in some radioactive methylated nucleosides and bases by the tumor-bearing rats during the 24-hour period following the administration of labeled methionine indicates increased turnover of mRNA and rRNA as well as tRNA. Since degradation of tumor tRNA appears to be delayed, the excessive amounts of the urinary methylated nucleosides must be derived from RNA in nonneoplastic tissue.

Aflatoxin B1↗
PubMed1981

Effects of phosphate-induced hyperparathyroidism and parathyroidectomy on rat kidney calcium in vivo.

The effects of a high-phosphate diet on the calcium metabolism of kidney cells were studied in intact and parathyroidectomized (PTX) rats. The control and the PTX rats were pair-fed a normal diet with a Ca/P of 2:1 or a high-phosphate diet with a Ca/P of 1:8 for 6 wk (chronic experiments) or 1, 3, and 6 days (acute experiments). Renal cell calcium metabolism was studied by chemical and kinetic analyses in kidney slices incubated in vitro. In the control rats the high-phosphate diet significantly increased kidney and mitochondrial calcium, the cytosolic and mitochondrial exchangeable calcium pools, and all calcium fluxes. In these controls, the plasma phosphate was not significantly elevated, but the parathyroid hormone (PTH) levels tended to be high. In PTX rats fed the same high-phosphate diet, the plasma phosphate was significantly elevated, but no change in renal calcium metabolism occurred. These results suggest that nephrocalcinosis was caused by elevated PTH levels and not by the elevated plasma phosphate and that the first step in the development of nephrocalcinosis is a stimulation of cellular calcium metabolism and transport.

Animals↗
PubMed1980

Cuckoo in the nest: some comments on the role of sociology in the undergraduate medical curriculum.

Despite the enormous strides that it has made over the past decade the position of sociology within the medical school remains precarious. Its problems are compounded by a failure to develop a coherent defence of its contribution to the education of doctors. In this paper three approaches to the teaching of sociology are identified: the human relations approach; the basic science approach; and the applied science approach. The limitations of each are discussed. It is argued that they offer a distorted version of sociology and represent competing approaches to medical education. It is further argued that sociology must curb its imperialistic tendencies, re-establish the connection between research and teaching, and through its approach both to teaching and the practice of medicine seek to provide a liberating influence in the undergraduate curriculum.

Curriculum↗
PubMed1979

Improved separation of modified nucleosides from tRNA hydrolysates: the patterns of tRNA methylation in rat tissues.

A sensitive and reproducible method for the isolation of minor nucleosides derived from tRNA is described. The nucleosides obtained from enzymatic digestion of tRNA are separated into several groups using a QAE Sephadex column and increasing concentrations of boric acid in a step-wise manner. The nucleosides in each group are separated by isocratic elution from a preparative Partisil 10-SCX column and high-performance liquid chromatography at ambient temperature. With this method we have determined the patterns of tRNA methylation in vitro with extracts from rat bone, liver, kidney and adrenal glands. Although different tissues appear to contain the same tRNA methyltransferases, the patterns of methylated nucleosides are different.

Adrenal Glands↗
PubMed1978

Mental disease.

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Humans↗