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Biomedical subjects

T Christensen

Publications and source records attributed to T Christensen.

At least 163 records · Page 9Linked to original sources
PubMed1988

Detection of proopiomelanocortin mRNA by in situ hybridization, using a biotinylated oligodeoxynucleotide probe and avidin-alkaline phosphatase histochemistry.

A synthetic 24-mer oligodeoxynucleotide complementary to the region of proopiomelanocortin (POMC) mRNA that codes for the MSH core sequence (alpha MSH/ACTH[4-11]), was synthesized and labelled in the 3'-end by use of terminal transferase. Probes tailed with either [3H]- or biotin-labelled nucleotides could be used for in situ hybridization studies. Biotinylated probes, hybridized to mouse and rat pituitary sections, were detected by avidin-alkaline phosphatase or streptavidin-alkaline phosphatase procedures and development in 5-bromo-4-chloro-3-indolyl phosphate (BCIP)-nitroblue tetrazolium (NBT). Proteinase K pretreatment of sections produced a drastic enhancement of the signal obtained, particularly in strongly fixed, paraffin-embedded material. The non-radioactive in situ hybridization technique compared favourably to radioactive in situ hybridization in terms of rapidity and precision of the localization. Controls involved deletion of the probe to prove that other components of the reaction sequence did not yield stain, digestion with RNase to prove that tissue RNA was necessary to bind the probe, prehybridization (blocking) with unlabelled probe to prove that the biotinylated probe reacted with its anti-sense region and not its tail and Northern blotting to show that the probe reacted with only one species of pituitary RNA, having the size of mouse pituitary POMC mRNA. In addition, adrenalectomy, known to increase anterior lobe POMC levels, resulted in both increased numbers and increased intensity of positive corticotroph-like cells. Synthetic oligodeoxynucleotides labelled with biotin appear to constitute attractive reagents for in situ hybridization studies when supported by appropriate control procedures.

Alkaline Phosphatase↗
PubMed1988

Characterization of extended primary and secondary cultures of hamster tracheal epithelial cells.

Studies on the regulation of differentiation in airway epithelial cells have been hampered by the lack of cell culture systems that differentiate in vitro. One such system that does exhibit differentiation is hamster tracheal epithelial cells (HTE). A major problem with this system, however, is that at the time cells differentiate, they lyze the collagen gel upon which they grow, resulting in termination of the culture. Here we report that by growing the HTE cells at 32 degrees instead of 37 degrees C we can totally prevent lysis of the collagen gel. Cells grown at this lower temperature maintain their differentiated phenotype as evidenced by abundant mucus granules and the secretion of authentic mucus glycoproteins into the culture media. We have also developed a method for subculturing the primary cells which allows growth and differentiation in secondary culture. The HTE cells were capable of being passaged at least three times and did not become transformed as judged by their inability to grow in soft agar and to produce tumors in syngeneic animals. This improved HTE cell culture system will allow detailed studies on the mechanisms which regulate growth, differentiation, and mucus secretion in surface airway epithelial cells.

Animals↗
PubMed1988

Genotoxic effects of paracetamol in V79 Chinese hamster cells.

Paracetamol was studied for possible genotoxic effects in V79 Chinese hamster cells. Paracetamol (0.5 mM for 30 min) reduced the rate of DNA synthesis in exponentially growing V79 cells to about 50% of control. A further decrease in the DNA synthesis was seen during the first 30 min after termination of paracetamol exposure. Paracetamol (3 and 10 mM for 2 h) caused a small increase in DNA single-strand breaks, as measured by the alkaline elution technique. After 16 h elution, the amount of DNA retained on the filters was 79 and 70% of controls in cells treated with 3 and 10 mM paracetamol respectively. No indication of DNA damage was seen in measuring the effect of paracetamol (0.25-10 mM for 2 h) on unscheduled DNA synthesis in growth-arrested cultures of V79 cells. At the highest concentrations (3 and 10 mM paracetamol), decreased unscheduled DNA synthesis was observed. Also UV-induced DNA-repair synthesis was inhibited by 3 and 10 mM paracetamol. DNA-repair synthesis was, however, inhibited at a much higher concentration than that inhibiting replicative DNA synthesis. The number of sister-chromatid exchanges (SCE) increased in a dose-dependent manner on 2 h exposure to paracetamol from 1 mM to 10 mM. At the highest dose tested (10 mM), the number of SCE increased to 3 times the control value. Co-culturing the V79 cells with freshly isolated mouse hepatocytes had no further effect on the paracetamol induced sister-chromatid exchanges. The present study indicates that paracetamol may cause DNA damage in V79 cells without any external metabolic activation system added.

Acetaminophen↗
PubMed1988

Low-dose dopamine infusion, renal haemodynamics and urinary albumin excretion rate in insulin-dependent diabetics and in normal man.

The effect of experimental renal vasodilatation by means of low-dose (2.0 micrograms/kg/min) intravenous dopamine infusion was investigated in 28 insulin-dependent diabetes mellitus (IDDM) patients with normal basal urinary albumin excretion rate (UAE) (less than 15 micrograms/min), 9 IDDM patients with UAE between 15-200 micrograms/min (microalbuminuria), and 7 normal subjects. Glomerular filtration rate (GFR) (thalamate clearance) showed a small increase with dopamine infusion, in the normoalbuminuric IDDM patients from 140 +/- 20 to 146 +/- 20 ml/min (2p less than 0.01), in the microalbuminuric IDDM patients from 146 to 151 ml/min (NS), and in normal subjects from 115 +/- 16 to 122 +/- 15 (2p less than 0.05). A marked increase in renal plasma flow (RPF) (hippuran clearance) was seen in all three groups--533 +/- 82 to 724 +/- 120 ml/min (2p less than 0.01), 574 +/- 69 to 777 +/- 140 ml/min (2p less than 0.01) and 523 +/- 87 to 749 +/- 145 ml/min (2p less than 0.05), respectively. Urinary albumin excretion rate (radioimmunoassay) increased from 5.3 x/divide 1.5 (tolerance factor) to 6.5 x/divide 1.8 micrograms/min (2p less than 0.05) in the normoalbuminuric IDDM patients and from 6.1 x/divide 2.1 to 7.8 x/divide 2.3 micrograms/min (2p less than 0.05) in the normal subjects, while no significant change was seen in the microalbuminuric group of diabetics. Kidney volume (ultrasonic scanning) was significantly enhanced in IDDM patients (294 +/- 73 ml vs. 196 +/- 49 ml). There was no significant correlation between kidney volume and the renal haemodynamic response to dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Gastrin and partial gastrectomy in duodenal ulcer patients 25 years postoperatively.

Serum gastrin concentrations were measured in 26 patients (Group A) who underwent partial gastrectomy for duodenal ulcer disease at least 25 years previously. The basal serum gastrin level was 31.6 +/- 1.5 pg/ml, increasing significantly after food stimulation to 36.8 +/- 2.4 pg/ml (p less than 0.05). In 16 of these patients (Group B), endoscopic biopsy specimens were taken from the minor and major curvatures of the stomach, from the jejunal part of the gastrojejunostomy, and from the duodenum. Mucosal gastrin concentrations measured were 0, 20.4 +/- 3 ng/g, and 30 +/- 7.1 ng/g, respectively. Ten of these patients (Group C) had a repeated gastroscopy with food stimulation of the duodenal pouch, using a balloon catheter in the lower duodenum. Serum gastrin concentrations after pouch stimulation did not differ significantly compared with basal values. No changes in the mucosal gastrin concentrations during pouch stimulation were seen. In conclusion, since no gastrin could be detected in the gastric mucosa and the mucosal gastrin concentration in the duodenum was 50 times lower than reported in other studies, the gastrin release measured after food stimulation could have been of extragastric or extraduodenal origin.

Aged↗
PubMed1987

Comparative genotoxic effects of IQ and MeIQ in Salmonella typhimurium and cultured mammalian cells.

The food mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) were studied for their genotoxic potential using hepatocytes isolated from untreated and Aroclor 1254 (PCB) pretreated rats as an activation system. Monolayers of hepatocytes co-incubated with Salmonella typhimurium TA98 activated IQ and MeIQ to bacterial mutagens, with MeIQ being about twice as potent as IQ. The mutagenic activities of IQ and MeIQ were increased by using hepatocytes from PCB-pretreated rats. IQ and MeIQ also caused primary DNA damage in the hepatocytes as determined by increases in the rate of alkaline elution of DNA, as well as increases in DNA-repair synthesis. Furthermore, exposure of V79 cells co-cultured with PCB-pretreated hepatocytes to IQ and MeIQ showed evidence of increased sister-chromatid exchanges and a low and variable increase in the number of 6-thioguanine-resistant mutants. The genotoxic potency of IQ and MeIQ in mammalian cells was low or virtually absent compared to their extreme potency in bacteria. This could be due to a lower capacity of mammalian cells to further metabolize the so-called directly acting bacterial mutagens, formed by a cytochrome P-450 dependent N-hydroxylation, to their ultimate reactive forms.

Animals↗
PubMed1987

Studies on the mechanism of acetamide hepatocarcinogenicity.

The hepatocarcinogen acetamide, in single doses of 100 and 400 mg/kg b.wt., was shown to act as an initiator in a dose-dependent fashion in rat liver using the Solt-Farber method. Acetamide and its putative metabolite N-hydroxy-acetamide did not cause liver necrosis in single dose experiments. Acetamide showed no evidence for genotoxicity in tests for mutations in Salmonella typhimurium, for DNA damage in rat hepatoma cells or for DNA repair in isolated rat hepatocytes. In contrast, N-hydroxy-acetamide displayed genotoxic activity in all 3 test systems. Neither acetamide nor N-hydroxy-acetamide induced transformation of primary Syrian hamster embryo cells or gave evidence of inhibition of metabolic cooperation in V79 cells. Radiolabelled acetamide and N-hydroxy-acetamide were not bound covalently to proteins in the presence of various metabolic activation systems (microsomes plus NADPH or xanthine/xanthine oxidase, cytosol or cytosol plus acetyl CoA or proline plus ATP). N-Hydroxy-acetamide was cytotoxic to monolayers of isolated hepatocytes at concentrations above 2.5 mM. This cytotoxicity was increased after diethyl maleate treatment, but N-hydroxy-acetamide did not deplete cellular glutathione. A HPLC system was developed for the separation and quantification of acetamide, N-hydroxy-acetamide and acetic acid. No significant excretion of N-hydroxy-acetamide or acetic acid in the urine could be demonstrated after treatment of rats with 100 or 1,000 mg/kg b.wt. of acetamide. The underlying mechanism for the observed initiating effect of acetamide is obscure.

Acetamides↗
PubMed1987

Isolation and characterization of an undifferentiated human colon carcinoma cell line (MIP-101).

An undifferentiated human colon carcinoma cell line was established from tumor tissue obtained from metastasis to the liver of colonic adenocarcinoma in a patient with fulminant Dukes D colorectal carcinoma. Histological analysis of the tumor biopsy from the liver confirmed the hospital pathology report of poorly differentiated colonic adenocarcinoma. Explants of this tumor tissue xenografted into a nude mouse were used to establish an epithelioid-like cell culture line, MIP-101. The cell line formed tumors in nude mice that histologically appeared undifferentiated and did not stain for carcinoembryonic antigen (CEA). No CEA was present either by radioimmunoassay (RIA) of the culture supernatant or by immunoperoxidase staining of the tumors or monolayers. MIP-101 appears to be one of the most undifferentiated human colon carcinoma cells lines available. It should prove useful in the search for markers of undifferentiated colonic cancer and in studies of colonic cancer differentiation.

Adenocarcinoma↗
PubMed1987

Fatigue and muscle amino acids during surgical convalescence.

Muscle and plasma amino acids, subjective fatigue and body weight were studied in 16 patients before and 20 days after uncomplicated elective abdominal surgery. Fatigue increased from a mean (+/- SEM) preoperative level of 2.4 +/- 0.4 arbitrary units to 4.4 +/- 0.5 on postoperative day 20, while body weight fell from 67.3 +/- 2.5 to 64.7 +/- 2.9 kg (both differences p less than 0.001). Correlation was found between increase in fatigue and fall in body weight (r = 0.56, p less than 0.05). Plasma amino acids showed little change after surgery. In muscle, the nonessential amino group taurine, asparagine, glutamate and glycine increased and histidine and arginine decreased (both p less than 0.05) postoperatively. No correlation was found between postoperative fatigue and weight loss versus changes in muscle amino acids. Some of the well-defined immediate postoperative changes in muscle amino acids thus persisted into late, otherwise uncomplicated convalescence, but postoperative fatigue was related only to weight loss--not to changes in muscle or plasma amino acids.

Adolescent↗
PubMed1986

Modulation of cytotoxic and genotoxic effects of 2-acetylaminofluorene in rat and hamster hepatocytes by 3-methylcholanthrene pre-treatment.

It is well known that 2-acetylaminofluorene (AAF)-induced liver cancer is reduced by simultaneous administration of 3-methylcholanthrene (MC) in the rat, but not in the hamster. The present report examines the effects of MC pre-treatment on the metabolism and toxicity of AAF in monolayer cultures of hepatocytes. Hepatocytes isolated from pre-treated animals of both species metabolized AAF and 2-aminofluorene (AF) to metabolites mutagenic to Salmonella typhimurium more efficiently than hepatocytes from control animals. MC-pre-treated rat hepatocytes showed increased responses to AAF- and AF-induced unscheduled DNA synthesis, while MC-pre-treated hamster hepatocytes were less responsive than the untreated hepatocytes. Increased cytotoxic effects of AAF were observed in MC-pre-treated rat hepatocytes, whereas AAF was not cytotoxic in hamster hepatocytes from either pre-treated or control animals. MC pre-treatment caused increased rates of formation of C-hydroxylated, N-hydroxylated, water-soluble and covalently macromolecular bound AAF metabolites in both species. No significant effect of MC pre-treatment was seen on the formation of AF from AAF. A large decrease in the ratio between covalently macromolecular bound (activated) metabolites and the sum of C-hydroxylated and water-soluble (detoxified) AAF metabolites, was seen after MC pre-treatment of rat hepatocytes, whereas no or only a minor decrease was observed in hamster hepatocytes. This ratio correlated much better with the in vivo carcinogenicity data than the other parameters such as mutagenicity, DNA repair or covalent macromolecular binding. Thus, the hypothesis that AAF-induced liver cancer depends less on the rate at which AAF is activated, but more on the relative proportion of the dose which is activated, is supported by the present data.

2-Acetylaminofluorene↗
PubMed1986

The effect of six months continuous subcutaneous insulin infusion on kidney function and size in insulin-dependent diabetics.

Glomerular filtration rate (GFR), renal plasma flow (RPF), kidney volume, and urinary albumin excretion rate were measured in 24 insulin-dependent diabetics, aged 29 +/- 7 years (mean +/- S.D.) of 8 +/- 4 years duration, randomly allocated to either continuous subcutaneous insulin infusion (CSII) (n = 12) or unchanged conventional insulin treatment (CIT) (n = 12). Glomerular filtration rate, renal plasma flow, and kidney volume were identical in the two groups at the start of the study, although significantly increased above normal values. During the 6 months CSII treatment a reduction of the GFR from 145 +/- 21 to 132 +/- 14 ml/min (2p = 2.4%) was seen, no change was observed in the CIT group while in both groups RPF and kidney volume remained unchanged. Urinary albumin excretion rate was normal or near normal in both groups and remained unchanged. Thus improved glycaemic control in insulin-dependent diabetics studied before the onset of microalbuminuria is associated with improved (reduced) GFR. Nephromegaly does not improve with 6 months CSII treatment. Whether it would improve with more prolonged treatment is uncertain.

Adult↗