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Biomedical subjects

T Fletcher

Publications and source records attributed to T Fletcher.

At least 37 records · Page 2Linked to original sources
PubMed1995

Nonpeptide endothelin receptor antagonists. V: Prevention and reversal of acute renal failure in the rat by SB 209670.

The ability of the mixed endothelin (ETA/ETB) receptor antagonist (+/-)-SB 209670 to prevent and reverse ischemia-induced acute renal failure (ARF) was studied in rats with moderate and severe ARF. Uninephrectomized, chronically instrumented Sprague-Dawley rats were used. Moderate and severe ARF was induced by occlusion of the renal artery for 30 and 45 min, respectively. During the 24 hr after 30-min ischemia (moderate ARF), glomerular filtration rate (GFR) decreased by 95%, and fractional excretion of sodium increased from 0.6% to 10%. Infusion of (+/-)-SB 209670 at 10, 30 and 100 micrograms/kg.min for 30 min before, during and 60 min after renal ischemia had a moderate effect on renal function. Thus, with the highest dose, the ischemia-induced reduction in GFR was 70%. This dose, however, had no effect in rats when given before, during and after 45 min of renal ischemia (severe ARF). In contrast, when infused at 30 micrograms/kg.min for 3 hr on the day after ischemia, (+/-)-SB 209670 markedly increased survival rate (75%) in rats with severe ARF by significantly increasing tubular reabsorption of Na+, followed by a slow and gradual increase in GFR and reversal of the increase in plasma K+ concentration. Data from acute renal clearance studies in rats with moderate ARF showed that when infused 24 hr after ischemia, (+/-)-SB 209670 acutely reversed the impairment in sodium reabsorption without increasing GFR or renal blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1995

Autosomal dominant zonular cataract with sutural opacities localized to chromosome 17q11-12.

Congenital cataracts constitute a morphologically and genetically heterogeneous group of diseases that are a major cause of childhood blindness. Different loci for hereditary congenital cataracts have been mapped to chromosomes 1, 2, 16, and 17q24. We report linkage of a gene causing a unique form of autosomal dominant zonular cataracts with Y-sutural opacities to chromosome 17q11-12 in a three-generation family exhibiting a maximum lod score of 3.9 at D17S805. Multipoint analysis gave a 1-lod confidence interval of 17 cM. This interval is bounded by the markers D17S799 and D17S798, a region that would encompass a number of candidate genes including that coding for beta A3/A1-crystallin.

Adolescent↗
PubMed1994

Reversal of postischemic acute renal failure with a selective endothelinA receptor antagonist in the rat.

Studies were designed to examine the effect of a selective endothelinA (ETA) receptor antagonist, BQ123, on severe postischemic acute renal failure (ARF) in Sprague-Dawley rats. Severe ARF was induced in uninephectomized, chronically instrumented rats by 45-min renal artery occlusion. BQ123 (0.1 mg/kg.min) or vehicle was infused intravenously for 3 h on the day after ischemia. Measurements before infusion (24 h control) showed a 98% decrease in glomerular filtration rate (GFR), increase in fractional excretion of sodium from 0.6 to 39%, and in plasma K+ from 4.3 to 6.5 mEq/liter. All vehicle-treated rats died in 4 d because of continuous deterioration of renal function, resulting in an increase of plasma K+ to fatal levels (> 8 mEq/liter). Infusion of BQ123 significantly improved survival rate (75%) by markedly improving tubular reabsorption of Na+ and moderately increasing GFR and K+ excretion. Plasma K+ returned to basal levels by the 5th d after ischemia. Improved tubular function was followed by gradual recovery in GFR and urinary concentrating mechanism. Additional data from renal clearance studies in rats with moderate ARF (30-min ischemia) and in normal rats with intact kidneys showed that ETA receptor blockade increases Na+ reabsorption and has no effect on renal hemodynamics. These results indicate that in the rat, the ETA receptor subtype mediates tubular epithelial function, and it plays a significant role in the pathogenesis of ischemia-induced ARF. Treatment with the selective ETA receptor antagonist reverses deteriorating tubular function in established ARF, an effect of possible therapeutic significance.

Acute Kidney Injury↗
PubMed1993

Investigation of parameters influencing intraocular pressure increases during sleep.

In previous studies, we have observed that young normal subjects show an increase in intraocular pressure (IOP) after sleep. Here we describe three experiments which investigated: (i) the effects of sleep in five groups of subjects: glaucoma, suspect glaucoma, young high-normal IOP, old high-normal IOP groups and an elderly control group, (ii) the effect of exposure to bright light (2500 lux) during sleep on associated IOP changes, and (iii) the relationship between changes in IOP and plasma melatonin during sleep. For all experiments IOP was measured before and after sleep. We found that IOP increased significantly after sleep. There was also a significant difference between the five groups with the old high-normal group showing the greatest increase, and the young high-normal group showing the lowest increase in IOP. The increase in IOP after sleep was reduced when the same subjects slept in bright light compared to that recorded when subjects slept in the dark. Plasma melatonin levels, as well as IOP, increased after sleep in the dark although there was no correlation between these changes for individual subjects.

Adult↗
PubMed1988

Relative effectiveness of alternative androgen withdrawal therapies in initiating regression of rat prostate.

From a large number of potentially effective androgen withdrawal regimens including bilateral orchiectomy, estrogens, antiandrogens and LHRH agonists alone or in combinations, we compared the ability of 12 different treatment options to mimic the acute results of surgical castration on the rat prostate. Agents were administered s.c. in clinical doses to groups of male rats daily for three days. On day 4 the prostatic tissue was removed and analyzed by conventional methods for whole-tissue and nuclear concentrations of dihydrotestosterone, nuclear androgen receptor and cytoplasmic androgen receptor. Castration-like changes were most pronounced with the synergistic combinations of cyproterone acetate + low-dose diethylstilbestrol, and megestrol acetate + low-dose diethylstilbestrol. Comparing the effectiveness of single agents, low-dose diethylstilbestrol was superior to cyproterone acetate, megestrol acetate, flutamide, leuprolide and RU23908. Leuprolide combined with flutamide was superior to leuprolide + cyproterone acetate, leuprolide + cyproterone acetate + low-dose diethylstilbestrol or leuprolide + RU23908 after three days of administration; however, this advantage disappeared when the treatments were extended to seven days. The observations indicate that the most potent androgen withdrawal therapies such as cyproterone acetate + low-dose diethylstilbestrol and megestrol acetate + low-dose diethylstilbestrol at best approximate but do not surpass the early effects of surgical castration. During the same time course, other regimens are characterized by a slower onset of action and a lesser degree of suppression of androgenic mechanisms within the cell.

Anilides↗
PubMed1988

Kinetic parameters of 5 alpha-reductase activity in stroma and epithelium of normal, hyperplastic, and carcinomatous human prostates.

To study the influence of 5 alpha-reductase on the concentration of dihydrotestosterone in prostatic tissue, we measured the activity of this enzyme in stroma and epithelium from 15 normal, 50 hyperplastic, and 20 carcinomatous prostates. Maximum velocity (Vmax) and Km parameters based on the Lineweaver-Burk and Eadie-Hofstee transformations of the Michaelis-Menten equation were related to the stromal and epithelial concentrations of dihydrotestosterone. On the basis of relative Vmax values, there was 6-15 times more 5 alpha-reductase activity in stroma than in epithelium regardless of the histology of the prostate. Stromal enzyme activity also was unique in having a 2- to 5-fold larger mean Km value and greater resistance to competitive and noncompetitive inhibition. Despite the enrichment of 5 alpha-reductase activity in stroma, the dihydrotestosterone concentrations in the stromal and epithelial fractions were very similar. In addition, similar concentrations were found in the stromal fractions of hyperplastic and carcinomatous tissues, notwithstanding a 4-fold difference in the mean Vmax values. This anomaly occurred in association with a large disparity in mean Km values, i.e. 68.3 +/- 1.6 (+/- SE) nmol/L in hyperplasia vs. 23.0 +/- 2.9 nmol/L in carcinoma. The dissociation between parameters of 5 alpha-reductase activity and tissue dihydrotestosterone concentrations was apparent to some extent in benign prostatic hyperplasia, in which the lowest stromal androgen concentrations were found in prostates with the largest Vmax and Km values; also, a rise in stromal Km was almost invariably associated with a proportional increase in Vmax (correlation coefficient = 0.95). These data strongly suggest that the stromal and epithelial forms of 5 alpha-reductase are separate isoenzymes, and that the excess of 5 alpha-reductase in stroma does not promote accumulation of an abnormal amount of dihydrotestosterone. They also imply that both the augmentation of 5 alpha-reductase activity in hyperplastic stroma and the condition of benign hyperplasia of the prostate are mutual consequences of a primary increase in Km.

Aged↗
PubMed1985

Redesigning trypsin: alteration of substrate specificity.

A general method for modifying eukaryotic genes by site-specific mutagenesis and subsequent expression in mammalian cells was developed to study the relation between structure and function of the proteolytic enzyme trypsin. Glycine residues at positions 216 and 226 in the binding cavity of trypsin were replaced by alanine residues, resulting in three trypsin mutants. Computer graphic analysis suggested that these substitutions would differentially affect arginine and lysine substrate binding of the enzyme. Although the mutant enzymes were reduced in catalytic rate, they showed enhanced substrate specificity relative to the native enzyme. This increased specificity was achieved by the unexpected differential effects on the catalytic activity toward arginine and lysine substrates. Mutants containing alanine at position 226 exhibited an altered conformation that may be converted to a trypsin-like structure upon binding of a substrate analog.

Amino Acid Sequence↗
PubMed1985

Diacylglycerol lipase and kinase activities in rat brain microvessels.

Diacylglycerols can accumulate transiently in intact cells as a consequence of the degradation of phosphatidylinositol by phospholipase C, but little information is available concerning their metabolic fate in the vascular endothelium. Diacylglycerol lipase and kinase activities were measured in rat brain microvessel preparations. Lipase activity, measured by the release of free fatty acids, was much greater at pH 4.5 than at pH 7. The acid lipase was predominantly particulate and likely originated in lysosomes, whereas the neutral lipase was mainly soluble. The fatty acid at the sn-1 position of the diacylglycerol substrate was hydrolyzed faster than that at the sn-2 position at both pH 4.5 and 7. The 2-monoacylglycerol accumulated at pH 4.5 but not at 7 due to the presence of a monoacylglycerol lipase activity with a neutral pH optimum. The formation of phosphatidic acid (kinase activity) was also measured in microvessels. When lipase and kinase activities were measured simultaneously, the formation of phosphatidic acid from a 1-palmitoyl-2-[1-14C]oleoyl-sn-glycerol substrate was 4-fold greater than the release of fatty acid (oleate) from the sn-2 position. Introduction of arachidonic acid to the sn-2 position of the diacylglycerol substrate increased kinase activity but reduced lipase activity. The release of fatty acids from the sn-2 position of phosphatidic acid could not be detected.

Animals↗
PubMed1985

Regulation of lysophosphatidylcholine-metabolizing enzymes in isolated myocardial cells from rat heart.

Enzymatic pathways involved in the metabolism of lysophosphatidylcholine were investigated in rat heart myocardial cells. Acyl CoA-dependent acyltransferase activity was localized in microsomes, and was much greater than lysophospholipase activity in either cytosolic or microsomal fractions. The cytosolic lysophospholipase was more sensitive to inhibition by palmitylcarnitine in comparison to free fatty acids. In contrast, free fatty acids (oleate and palmitate) produced a greater inhibition of the microsomal acyltransferase and lysophospholipase than did palmitylcarnitine. A reduction in the assay pH to 6.5 resulted in an increase in microsomal acyltransferase and cytosolic lysophospholipase activities, but brought about a marked reduction in the microsomal lysophospholipase activity. At pH 6.5, the percentage inhibition of the microsomal acyltransferase by palmitylcarnitine was reduced, whereas the inhibition by palmitic acid was enhanced. The inhibition of the microsomal lysophospholipase by both palmitylcarnitine and palmitic acid was reduced at pH 6.5. With respect to myocardial ischemia, the inhibition of microsomal acyltransferase by free fatty acids and the reduction in microsomal lysophospholipase activity due to acidosis may contribute to the elevation of cellular lysophosphoglycerides which are arrhythmogenic.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1984

Hormonal regulation of acid cholesterol ester hydrolase activity: effects of triiodothyronine and 17 alpha-ethynylestradiol.

Cholesterol ester hydrolase activity was measured in isolated rat hepatocytes and adipocytes. Administration of triiodothyronine to rats resulted in a specific and selective increase in lysosomal acid (pH 4.5) cholesterol ester hydrolase activity in hepatocytes. Since the majority of lipoprotein degradation occurs in liver parenchymal cells (hepatocytes), the stimulation of liver (hepatocyte) acid cholesterol ester hydrolase activity by triiodothyronine could contribute to the hypocholesterolemic action of thyroid hormones. Treatment of rats with 17 alpha-ethynylestradiol to increase the hepatic degradation of lipoprotein did not change acid cholesterol ester hydrolase activity in liver, indicating that the thyroid hormone induced stimulation of acid cholesterol ester hydrolase activity in hepatocytes is not a secondary effect owing to the increased hepatic catabolism of low density lipoproteins (LDL). In contrast to the results with hepatocytes, hyperthyroidism did not increase acid cholesterol ester hydrolase activity in rat adipocytes.

Acetylglucosaminidase↗
PubMed1982

Effect of hyperinsulinemia on acid cholesterol ester hydrolase activity in liver, heart and epididymal fat pad preparations from rats and mice.

The effect of insulin on lysosomal acid cholesterol ester hydrolase activity was studied in liver, heart and fat pad preparations from rats and mice. Hyperinsulinemia was induced for a period of 6 days in rats by the subcutaneous administration of exogenous insulin by an osmotic minipump. The effect of more chronic endogenous hyperinsulinemia was studied using genetic strains of diabetic (db/db) mice at 12 weeks of age. Mouse liver and heart preparations were characterized as having an acid pH optimum of 4.5-5 for cholesterol ester hydrolase activity; a smaller but distinct pH optimum could also be observed at pH 7. In contrast, hydrolase activity in mouse fat pad preparations had only one distinct pH optimum of 6.5. Hyperinsulinemia in rats and mice resulted in a significant decrease in acid cholesterol ester hydrolase activity in heart preparations, but had no consistent effect on acid hydrolase activity observed in liver and fat pad preparations. This decrease in lysosomal acid cholesterol ester hydrolase activity in cardiac tissue due to hyperinsulinemia cannot be related to any changes in lipoprotein turnover caused by insulin or diabetes.

Adipose Tissue↗
PubMed1982

Properties of acid and neutral cholesterol ester hydrolases in rat and pigeon aortas.

The activity of cholesterol ester hydrolase was measured in subcellular fractions from rat and pigeon aortas using a glycerol-dispersed cholesterol oleate substrate preparation. The specific activity of acid cholesterol ester hydrolase (assayed at pH 5) in adventitia tissue fractions was 40-50 fold greater than in media-intima fractions from rat aorta. Soluble and particulate subcellular fractions from rat aorta (media-intima) were observed to have cholesterol ester hydrolase activity with both an acid (pH 4.5-5) and a neutral (pH 7.5) pH optimum. A comparison of the subcellular distribution of acid cholesterol ester hydrolase with the lysosomal marker enzyme, N-acetylglucosaminidase, suggests that the acid hydrolase activity originated in aortic lysosomes; the neutral cholesterol ester hydrolase was predominantly soluble. Acid and neutral cholesterol ester hydrolases could also be distinguished on the basic of the effects of Mg Cl2 and NaCl on hydrolase activity and on rates of thermal denaturation. Both acid an neutral hydrolases from rat aorta (media-intima) were inhibited by chloroquine (half-maximal at 2-4 mM), and both hydrolases were characterized as having the same apparent affinity for the glycerol-dispersed cholesterol oleate substrate. Acid and neutral cholesterol ester hydrolases were also observed in preparations from pigeon aortas. The specific activity for both acid and neutral hydrolases was higher in atherosclerosis-susceptible White Carneau pigeon aortas in comparison to Show Racer pigeon aortas.

Animals↗
PubMed1982

Tolerant Staphylococcus aureus causing vertebral osteomyelitis.

Vertebral osteomyelitis due to Staphylococcus aureus was suppressed by not cured by optimal therapy with nafcillin sodium; cure eventually was achieved by treatment with cefazolin sodium and gentamicin sulfate. This is vivo result correlated with in vitro observations that showed that the infecting organism was inhibited but not killed by prolonged incubation with nafcillin or cefazolin; killing was readily achieved in vitro by adding subinhibitory concentrations of gentamicin. Bacterial tolerance in this case appeared to be responsible for the failure of vertebral osteomyelitis to be cured by accepted therapy with beta-lactam antibiotics.

Aged↗
PubMed1981

Studies on the activity of acyl-CoA:cholesterol O-acyltransferase and acid cholesterol ester synthetase in rat aortas.

Acyl-CoA: cholesterol O-acyltransferase (ACAT) activity was measured in microsomal preparations from rat aorta (intima-media) with [14C]oleoyl CoA and endogenous cholesterol as substrates. The specific activity of ACAT in liver and adrenal microsomal preparations was 10--20-times greater than ACAT activity in aortic microsomes; no ACAT activity could be detected in fat pad microsomes. ACAT activity in liver and adrenal microsomes was enhanced by the addition of exogenous cholesterol. In contrast, exogenous cholesterol did not increase ACAT activity in rat aortic microsomes. Levels of endogenous cholesterol and ACAT activity in microsomal preparations from rat aorta were not reduced when circulating plasma cholesterol levels were decreased by the administration of 4-aminopyrazolopyrimidine to rats. Acid cholesterol ester synthetase activity was not detectable in high-speed supernatant fractions from rat aorta; low levels of activity could be measured in rat aorta microsomal preparations but this was less than 10% of ACAT activity. Thus, ACAT would seem to be the principal enzymatic route for the synthesis of cholesterol esters in aorta.

Acyltransferases↗
PubMed1981

Effect of thyroid hormones on acid cholesterol ester hydrolase activity in rat liver, heart and epididymal fat pads.

The regulation of acid cholesterol ester hydrolase activity by thyroid hormones was studied in subcellular fractions from rat liver, heart, and epididymal fat pads; hydrolase activity was determined at pH 5 with a glycerol-dispersed cholesterol oleate substrate preparation. Acid cholesterol ester hydrolase activity was decreased in liver preparations from thyroidectomized rats relative to activity in livers from euthyroid control rats. Administration of triiodothyronine to either euthyroid or hypothyroid (thyroidectomized) rats resulted in an increase in acid cholesterol ester hydrolase activity in liver preparations. Similar effects of thyroidectomy and the administration of triiodothyronine on acid cholesterol ester hydrolase activity were observed with fat pad preparations. In contrast, no effect of thyroid hormones was observed on acid cholesterol ester hydrolase activity in heart. These results suggest that thyroid hormones may regulate the catabolism of serum lipoproteins, in part, by alterations in lysosomal acid cholesterol ester hydrolase activity in liver and epididymal fat pads.

Acetylglucosaminidase↗