Search PubMed⌕ Search

Biomedical subjects

L S Jefferson

Publications and source records attributed to L S Jefferson.

At least 19 recordsLinked to original sources
PubMed1992

Age-dependent decrease in the amount of eukaryotic initiation factor 2 in various rat tissues.

Recent studies have suggested that the decline in protein synthesis that occurs in rat liver and brain during development and aging is associated with a decrease in the activity of eukaryotic initiation factor 2 (eIF-2). One way in which eIF-2 activity could be decreased in tissue extracts would be through a decrease in the activity of the GDP exchange factor, eIF-2B. In the present study, the activity of eIF-2B was measured in tissue extracts and was found to be less in older than in younger rats. Thus a decrease in eIF-2B activity could account for part of the decrease in protein synthesis that occurs during aging. Another way in which eIF-2 activity could be decreased would be through a decrease in amount of the protein. Therefore the amount of eIF-2 in various tissues was quantified by protein immunoblot analysis. We found that the amount of eIF-2 relative to total protein tended to fall with increasing age. Furthermore, eIF-2 content was directly proportional to the rate of protein synthesis in the tissues examined. Finally, slot-blot analysis of polyadenylated RNA revealed no significant change in the relative abundance of eIF-2 alpha mRNA with age. The last-mentioned experiments suggest that the synthesis of eIF-2 may be regulated through changes in the deficiency of translation of eIF-2 alpha mRNA rather than through changes in gene transcription.

Aging↗
PubMed1992

Severe laryngotracheobronchitis complicating measles.

OBJECTIVE: To determine the incidence of severe measles-related laryngotracheobronchitis in patients hospitalized during a recent measles epidemic and to evaluate factors associated with severity of airway injury and its management. DESIGN: Clinical description of patient series. SETTING: Children's hospital and county general hospital, Houston, Tex. PATIENTS: One hundred twenty-four children (aged 1 month to 19 years) admitted with a diagnosis of measles. INTERVENTIONS: None. MEASUREMENTS/RESULTS: Twenty-seven patients had significant laryngotracheobronchitis, including 10 who had not received appropriate immunization. Six patients required endotracheal intubation for relief of upper airway obstruction. The median age of patients requiring intubation was 12 months (range, 4 to 24 months). Two patients died of complications of superinfection. Two patients survived but required prolonged intubation. Two patients underwent early diagnostic laryngoscopy and bronchoscopy and required shorter artificial airway maintenance. CONCLUSIONS: Severe laryngotracheobronchitis frequently occurs in patients younger than 2 years hospitalized with measles and may be related to bacterial or viral super-infection. Early diagnostic laryngoscopy and bronchoscopy for injury assessment and possible endotracheal tube exchange are recommended and, in some severe cases, tracheostomy should be considered to shorten artificial airway maintenance and decrease the incidence of airway complications.

Adolescent↗
PubMed1992

Regulation of protein synthesis by modulation of intracellular calcium in rat liver.

The rate of protein synthesis can be modulated in intact cells by varying the concentration and subcellular distribution of intracellular calcium. Because the biochemical reactions required for the pathway of protein synthesis occur in the cytosol of the cell, it might be expected that protein synthesis would be controlled by free cytosolic calcium rather than the sequestered cation. However, a recent report proposed that maintenance of optimal rates of protein synthesis depends on the amount of calcium sequestered in the endoplasmic reticulum rather than free cytosolic calcium (C.O. Brostrom and M. A. Brostrom, Annu. Rev. Physiol. 52: 577-590, 1990). In the present study, rat livers were perfused with buffer containing various compounds previously shown to alter intracellular calcium concentration and distribution in isolated cells. It was found that conditions designed to cause a rise in free cytosolic calcium had no effect on protein synthesis. In contrast, conditions designed to cause depletion of sequestered calcium resulted in an inhibition of protein synthesis characterized by a reduction in peptide-chain initiation relative to elongation. The inhibition of protein synthesis was further localized to a decrease in the activity of eukaryotic initiation factor (eIF) 2B as measured in extracts from perfused livers. The inhibition of eIF-2B activity was associated with a 2.4-fold increase in the proportion of the alpha-subunit of eIF-2 in the phosphorylated form. In summary, the results of the present study support a model whereby mobilization of calcium sequestered in the endoplasmic reticulum results in an inhibition of protein synthesis in rat liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of insulin on total RNA, poly(A)+ RNA, and mRNA in primary cultures of rat hepatocytes.

The purpose of this study was to examine mechanisms involved in the regulation of protein synthesis in primary cultures of rat hepatocytes. Hepatocytes were maintained in a chemically defined serum-free medium in the presence or absence of insulin. The rate of protein synthesis in hepatocytes deprived of insulin between days 2 and 5 of culture was reduced to 67% of the rate observed in insulin-maintained controls. The decrease in protein synthetic rate was accompanied by a proportional fall in the content of both total RNA and poly(A)+RNA, suggesting that the capacity for protein synthesis was reduced in the absence of insulin. Both total RNA and poly(A)+ RNA contents and the protein synthetic rate were returned to control values after 3 days of insulin resupplementation. In addition, the effect of insulin on the expression of specific mRNAs was assessed by in vitro translation of total RNA followed by two-dimensional gel analysis of radiolabeled translation products. Only 13 of the greater than 150 spots discernible on the two-dimensional gels were altered in response to insulin. The mRNAs that were altered include examples of repression and stimulation of expression in response to insulin deprivation. Thus, in isolated rat hepatocytes, insulin regulates the capacity of both overall protein synthesis as well as the capacity for the synthesis of specific proteins.

Animals↗
PubMed1978

Correlation of albumin production rates and albumin mRNA levels in livers of normal, diabetic, and insulin-treated diabetic rats.

We have studied the effects of alloxan-induced diabetes and subsequent insulin replacement on albumin and total hepatic protein synthesis. Diabetes resulted in a reduction to approximately 20% of normal in albumin synthesis relative to the rate of total protein synthesis in vivo and a reduction to 10% in the absolute rate of albumin secretion by perfused livers. In contrast, the synthesis of total secretory protein and retained hepatic protein was affected to a lesser extent by diabetes. Treatment of diabetic rats with insulin restored rates of albumin and total hepatic protein synthesis to normal levels. The molecular basis of these alterations in albumin synthesis was investigated by examining albumin mRNA levels in livers of normal, diabetic, and insulin-treated diabetic animals. The level of albumin mRNA, whether assayed by cell-free translation or by hybridization to a specific complementary DNA probe, was markedly decreased in livers of diabetic animals and was restored to normal by insulin treatment. These changes occurred in parallel with changes in the rates of albumin secretion observed in perfused liver, suggesting that albumin mRNA content is the primary factor responsible for altering rates of albumin synthesis under these conditions.

Albumins↗
PubMed1978

Protein turnover in rat skeletal muscle: effects of hypophysectomy and growth hormone.

The role of growth hormone in regulating protein turnover was examined in a perfused preparation of rat skeletal muscle. The perfused muscle maintained in vivo levels of ATP and creatine phosphate and exhibited constant rates of oxygen consumption and protein synthesis. Hypophysectomy reduced the rate of protein synthesis, the concentration of RNA, and the efficiency of protein synthesis in gastrocnemius muscle to 30, 46, and 66 percent of normal, respectively. In vivo treatment of hypophysectomized (hypox) rats with bovine growth hormone (250 microgram/day for 5 days) resulted in small increases in protein synthesis and RNA, whereas synthesis/RNA was returned to near normal. Elevation of ribosomal subunits in psoas muscle indicated an inhibition of peptide-chain initiation in hypox rats that was reversed by in vivo growth hormone treatment. Thus, hypox rats exhibited both a decreased capacity and a decreased efficiency of protein synthesis. Growth hormone replacement primarily increased efficiency of protein synthesis. The rate of protein degradation and the activity of cathepsin D in gastrocnemius muscle were decreased by hypophysectomy. Growth hormone treatment had no significant effect on degradation.

Animals↗
PubMed1978

Effect of starvation on initiation of protein synthesis in skeletal muscle and heart.

Psoas muscle of rats starved for 2 or 4 days contained increased levels of ribosomal subunits and exhibited reduced rates of protein synthesis in vitro, demonstrating a starvation-induced inhibition of peptide-chain initiation. The activity of an eIF-2-like initiation factor, assayed in postribosomal supernatants, decreased in psoas during starvation, parallel to a 25% reduction in the RNA level. Reduced eIF-2 activity did not result from nucleotide depletion or increased deacylation of initiator tRNA, nor was it abolished by extensive dialysis. Perfusion of psoas muscle in the presence of insulin reversed the starvation-induced block in peptide-chain initiation, but did not alter the activity of eIF-2 or level of RNA. Furthermore, heart muscle did not manifest a starvation-induced block in peptide-chain initiation even though the activity of eIF-2 and the level of RNA decreased as a result of food deprivation. Thus loss of eIF 2 activity in psoas and heart did not parallel changes in peptide-chain initiation but was associated with a reduction in tissue RNA. These results indicate that the level of eIF-2 is not rate-limiting for peptide-chain initiation under the conditions tested in this study.

Amino Acids↗
PubMed1978

Effects of thyroxine on protein turnover in rat skeletal muscle.

The effects of thyroxine (T4) on protein turnover in skeletal muscle were studied using normal, thyroidectomized (thyrex), and hypophysectomized (hypox) rats. Thyrex rats had a depressed growth rate that was accompanied by 50% reductions in the level of RNA and the rate of protein synthesis in gastrocnemius muscle, as determined in the perfused hemicorpus. Protein synthetic efficiency (protein synthesis per unit RNA) was decreased by 18%. Daily treatment of thyrex rats with T4 at different dose levels for up to 16 days led to improved growth rates, elevated RNA concentrations, and increased protein synthesis rates. The primary effect of T4 was to increase the protein synthetic capacity of muscle. Protein degradation, determined in the perfused hemicorpus, and activity of a lysosomal protease, determined in unperfused muscle, were reduced in the thyrex condition. Treatment of thyrex rats with T4 increased protein degradative rates, but not protease activity. Hypox rats, which also exhibited depressed skeletal muscle protein synthesis, responded to T4 and combined T4 and growth hormone with marked improvements in protein synthesis.

Animals↗
PubMed1977

Synthesis and secretion of rat albumin in vivo, in perfused liver, and in isolated hepatocytes. Effects of hypophysectomy and growth hormone treatment.

The effects of hypophysectomy on albumin and total protein synthesis in rat liver were investigated in vivo, in perfused liver, and in isolated hepatocytes. In all systems, hypophysectomy resulted in about a 50% decrease in the rate of total protein synthesis and a 30 to 50% decrease in the relative rate of albumin synthesis. Albumin synthesis accounted for 11 to 13% of total protein synthesis in all normal systems, but represented only 5 to 8% of the total in all systems derived from hypophysectomized rats. Growth hormone, administered subcutaneously to hypophysectomized rats for 5 days, restored the relative rate of albumin synthesis to normal in vivo; however, only partial restoration was demonstrated in the in vitro systems. Perfused livers and isolated hepatocytes exhibited linear rates of total protein and albumin secretion for 3 h. The rate of albumin secretion by normal perfused livers was 3 times that of perfused livers from hypophysectomized animals, being 0.54 and 0.17 mg/g of liver/h, respectively. Isolated hepatocytes synthesized total protein and albumin at nearly the same rate as perfused livers. The amount of albumin secreted by cells derived from normal and hypophysectomized rats was 0.38 and 0.10 mg/ml of packed cells/h, respectively. Ribosome half-transit times for albumin and total liver protein were 1.6 to 1.7 min in isolated liver cells derived from both normal and hypophysectomized rats. Analysis by polyacrylamide gel electrophoresis showed no difference in the qualitative distribution of the proteins secreted by perfused livers and isolated hepatocytes.

Albumins↗
PubMed1977

Regulation by insulin of amino acid release and protein turnover in the perfused rat hemicorpus.

Net changes in the concentrations of 18 amino acids in perfusate and skeletal muscle were followed during perfusion of hemicorpus preparations from fed rat. Perfusate levels of 16 amino acids showed little change from their initial concentrations during the 1st h, but increased dramatically during the 2nd and 3rd h. Aspartate and glutamate levels decreased continuously throughout the perfusion. Release of alanine and glutamine accounted for approximately 50% of the total change in perfusate amino acids. The increase in perfusate amino acids was derived from net breakdown of muscle proteins and not from leakage from the intracellular pool as evidenced by elevated concentrations of intracellular amino acids in perfused muscle. Addition of insulin to the perfusate did not change the pattern of amino acid release during the 1st h of perfusion. However, during the 2nd and 3rd h the hormone completely prevented the net release of most amino acids and maintained intracellular concentrations of most amino acids at levels found in upperfused tissue. Effects of time of perfusion and insulin on amino acid release were accounted for by changes in the rate of protein turnover. Protein synthesis in gastrocemius and psoas muscles in control perfusions decreased after 1 h to approximately 50% of the initial rate. This decrease was accompanied by a 2-fold increase in the level of ribosomal subunits, indicating development of a block in peptide chain initiation. Addition of insulin maintained the initial rate of synthesis and the in vivo level of ribosomal subunits, demonstrating that the hormone prevented the block in peptide chain initiation from forming. Addition of insulin after 2 h reversed the perfusion-induced block in initiation. Synthesis of the specific muscle protein myosin was increased 45% over the control rate in the presence of insulin. Insulin also produced a 50% decrease in the rate of protein degradation during the 2nd and 3rd h of perfusion. A similar effect was noted when protein synthesis was inhibited by addition of cycloheximide. Higher concentrations of insulin were required to maximally inhibit protein degradation than to increase protein synthesis. Involvement of lysosomal proteases in the effect of insulin on protein degradation was evaluated by measuring cathepsin D activity in psoas muscle homogenates. "Free" enzyme activity increased as a result of perfusion while addition of insulin maintained this activity at the unperfused level. Neither perfusion nor insulin had any effect on total cathepsin D activity. Alterations in protein degradation and lysosomal enzyme activity were not due to changes in levels of adenine nucleotides, GTP, or creatine phosphate.

Adenosine Diphosphate↗
PubMed1977

Effect of isoproterenol on amino acid levels and protein turnover in skeletal muscle.

The effect of isoproterenol on amino acid concentrations in perfusate and skeletal muscle was studied during a 3-h perfusion of the isolated rat hemicorpus. The beta-adrenergic agonist inhibited the accumulation of alanine, threonine, phenylalanine, tyrosine, lysine, arginine, leucine, and valine and increased the loss of glutamate, aspartate, serine, and isoleucine from the pool of free amino acids in perfusate and muscle. The loss of glutamate was accompanied by a greater accumulation of glutamine. Changes in alanine levels showed the greatest response with a net accumulation of 98 mumol in the controls becoming a net loss of 54 mumol in the experimentals. These changes in amino acid levels were accounted for in part by a 20% decrease in protein degradation. Protein synthesis was not affected by isoproterenol. In addition to an effect on degradation, it appeared that isoproterenol affected amino acid levels by increasing alanine utilization and causing formation of glutamine instead of alanine. Other effects of the drug included increased rates of lactate production, muscle glycogen breakdown, and oxygen consumption, whereas no effects were observed on ATP and creatine phosphate levels. Pyruvate content of muscle was maintained at a higher level in the presence of the drug than in control perfusions.

Alanine↗
PubMed1977

Perfusion of rat testes and accessory sex organs: a new method.

Rat testes and accessory sex organs were perfused in situ by recirculating an artificial medium through the hemicorpus preparation previously developed for studies of skeletal muscle. The advantages and limitations of this system for studying the male productive tract were examined. The electrolyte and gas composition of the perfusate remained constant and glucose levels did not fall below normal during 3 h of perfusion. Testicular water content, temperature, and ATP and GTP levels were normal at 90 min. The mean arterial pressure was 40 mm Hg and the flow rates, measured with microspheres, were normal to high to the caput epididymides, ventral prostate and seminal vesicles and approximately half normal to the testes in preparations from 90 day old rats perfused at 35 ml/min. Administration of vasodilators indicated the absence of significant vasoconstriction in the hemicorpus. There was appreciable testosterone metabolism by the preparation and in addition, there was absorption of testosterone by the plastic tubing of the perfusion apparatus. Testosterone levels in the perfusate rose for 90 min in response to hCG. There was a dose-response relationship between hCG (20-1000 mIU/ml of medium) and testosterone levels at 90 min. FSH, prolactin, insulin and vitamins had no significant effect on hCG-stimulated testosterone levels. This perfusion system should prove useful for studies of hormone action.

Animals↗
PubMed1977

Nuclear accumulation of androgens in perfused rat accessory sex organs and testes.

The uptake of androgens into the nuclei of caput epididymis, ventral prostate, seminal vesicle and testis was studied by recirculating physiological and pharmacological concentrations of [3H]testosterone in an artificial medium through the lower half (hemicorpus) of castrated or hypophysectomized rats. The accumulation of dihydrotestosterone in accessory sex organ nuclei was saturable, inhibited by perfusion of excess testosterone or cyproterone acetate, and associated with binding to 3S salt-extractable molecules. In castrated preparations the mean saturation levels (pmol/mg DNA) were different in the three organs: seminal vesicle, 2.8; ventral prostate, 1.8; caput epididymis, 0.9. The saturation level was significantly lower in ventral prostate of hypophysectomized rats (1.2) treated with testosterone to regenerate the accessory sex organs. Testosterone was the major nuclear androgen in the testes of mature hypophysectomized preparations perfused with testosterone. Although there was a large amount of nonspecific accumulation, testosterone binding to 3S molecules was shown by sucrose gradient centrifugation. Binding of dihydrotestosterone to 3S molecules in testicular nuclei was also demonstrated. The ratio of dihydrotestosterone to testosterone was different in immature and mature testicular nuclei and was altered by treatments known to affect testicular 5 alpha-reductase activity. The results suggest that in rat accessory sex organs and immature testis the major active androgen is dihydrotestosterone, whereas in mature testis it is testosterone. The shift in the predominant nuclear androgen in the testis from dihydrotestosterone to testosterone is most simply explained by the maturational change in 5 alpha-reductase activity.

Androgens↗