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Biomedical subjects

K E Flaim

Publications and source records attributed to K E Flaim.

32 records · Page 2Linked to original sources
PubMed1985

Dopamine receptor agonist activity of some 5-(2-aminoethyl)carbostyril derivatives.

The potency of beta-adrenoreceptor agonists, e.g., isoproterenol, is strikingly increased by substitution of the meta catecholic hydroxyl group with the NH group of a carbostyril system. To explore the possibility that comparable potency enhancement might occur upon similar modification of the catechol ring of dopamine, a series of 5-(2-aminoethyl)carbostyril derivatives was prepared and examined for D-1 and D-2 dopamine receptor-stimulating activity. Only the parent compound, 5-(2-aminoethyl)-8-hydroxycarbostyril (2), produced measurable activation of dopamine-sensitive adenylate cyclase (29% at a concentration of 10 microM). Some of the compounds, however, did produce significant activity in tests, namely displacement of [3H]spiroperidol binding from bovine pituitary homogenate and an isolated perfused rabbit ear artery preparation, that measure interaction with D-2 receptors. Potency of the carbostyrils was enhanced by 8-hydroxylation and by appropriate substitution of the amino group of the ethylamine side chain. The most potent member of the series was 8-hydroxy-5-[2-[[2-(4-hydroxyphenyl)ethyl]-n-propylamino]ethyl] carbostyril (16b). This compound was about 3 times more effective than dopamine in the D-2 receptor tests. Clearly, the results of this study indicate that potency of dopamine receptor agonists is not increased by carbostyril replacement of the m-hydroxyl as is noted with the beta-adrenergic receptor agonists.

Adenylyl Cyclases↗
PubMed1985

Direct effect of insulin on albumin gene expression in primary cultures of rat hepatocytes.

The purpose of this study was to identify a cell culture system in which the role of insulin in regulating albumin gene expression could be investigated. The system selected was rat hepatocytes maintained in primary culture in a chemically defined, serum-free medium. Under control conditions albumin secretion was nearly the same as the rate recorded in vivo and in perfused liver and was reasonably well maintained during 8 days of culture. Deletion of insulin from the culture medium for 3-6 days resulted in 40-60% reductions in albumin secretion. Furthermore, albumin secretion relative to the rate of total protein synthesis was reduced by approximately 50% as a result of insulin deficiency. Readdition of the hormone to insulin-deficient cultures restored secretion to the control rate. A maximal effect of insulin was observed within 3 days after readdition of the hormone, and a half-maximal response was obtained with a hormone concentration of approximately 3.0 nM. The relative abundance of albumin mRNA, as measured by solution hybridization using a complementary DNA probe, responded in a parallel fashion to the changes in albumin secretion. Thus rat hepatocytes maintained under appropriate culture conditions reflect the effects of diabetes and insulin treatment on albumin gene expression observed in vivo and provide an excellent model system in which to study the mechanism(s) of insulin action.

Albumins↗
PubMed1984

Protein synthesis versus energy state in contracting muscles of perfused rat hindlimb.

The goal of these studies was to evaluate acute changes in protein metabolism in skeletal muscle in response to contractile activity. Rates of protein synthesis were measured by following L-[U-14C]phenylalanine incorporation into protein in muscles of the perfused rat hindlimb at rest, during 10 min of maximal isometric muscle contractions, and during 10 min of recovery. Synthesis measurements were carried out under conditions that ensured that the specific radioactivity of the tRNA-bound precursor amino acid was equal to that of extracellular phenylalanine. Protein degradation was estimated by measuring the release of Nt-methylhistidine. Rates of synthesis were markedly inhibited in response to muscle contractions in tibialis anterior, gastrocnemius, and plantaris but were unaffected in soleus. Rates of synthesis returned toward those observed in the resting condition during the recovery period. Rates of degradation were also markedly inhibited in response to muscle contractions. Decreased rates of synthesis correlated with reduced tissue contents of ATP and creatine phosphate, a reduced ATP/ADP, and an elevated tissue content of lactate. The results demonstrate that isometric contractions in muscles consisting of a high proportion of fast glycolytic fibers result in a marked depression in rates of protein synthesis that may be due to an altered energy state.

Amino Acids↗
PubMed1983

Insulin effects on protein synthesis are independent of glucose and energy metabolism.

Protein synthesis was accelerated in rat hearts that were provided insulin compared with provision of glucose or pyruvate alone or a mixture of glucose and pyruvate. The faster synthetic rates were accompanied by a reduction in numbers of ribosomal subunits, indicating that peptide chain initiation was accelerated relative to elongation/termination. In hearts supplied glucose, 65% of the maximal effect on protein synthesis was achieved by addition of 1.7 X 10(-10) M insulin, but significant effects on glucose uptake as well as on tissue contents of glucose 6-phosphate and creatine phosphate were obtained only with 7 X 10(-10) M insulin. Addition of glucose to perfusates containing pyruvate did not accelerate protein synthesis, although the glucose 6-phosphate content was raised. Similarly, the stimulatory effects of insulin on protein synthesis in hearts supplied pyruvate did not depend on changes in glucose 6-phosphate content, creatine phosphate/creatine, ATP/ADP, or adenylate energy charge. These studies indicate that insulin accelerated peptide-chain initiation and protein synthesis in rat heart by mechanisms independent of the hormone's effect on glucose or energy metabolism.

Adenine Nucleotides↗
PubMed1983

Effect of halothane on synthesis and secretion of liver proteins.

The effect of halothane on synthesis of retained and secreted proteins was investigated using isolated perfused rat livers. Anesthetic exposure rapidly inhibited synthesis of total liver proteins in a dose-dependent manner by a mechanism which appeared to involve reduced rates of both peptide chain initiation and elongation. While halothane concentrations comparable to the clinical dose resulted in small changes in protein metabolism, higher concentrations (4%) of the anesthetic had marked effects. At early time points, relative rates of albumin synthesis were unaffected by halothane, but, as anesthetic exposure was prolonged, production of albumin and of total secreted plasma proteins was inhibited more extensively than that of retained liver proteins. Thus, halothane appeared to exert differential inhibitory effects on synthesis of these two classes of liver proteins.

Albumins↗
PubMed1982

The role of amino acids in the regulation of protein synthesis in perfused rat liver. I. Reduction in rates of synthesis resulting from amino acid deprivation and recovery during flow-through perfusion.

The role of perfusate amino acid concentrations in regulating rates of protein synthesis was investigated using the perfused rat liver. Livers from fed rats were perfused with a nonrecirculating medium and the incorporation of [3H]leucine into albumin and total protein was determined under conditions where the leucyl-tRNALeu and perfusate leucine specific activities were equal and constant. During perfusions of less than 1 h, rates of total protein synthesis were sensitive to the concentrations of amino acids in the perfusate. When no exogenous amino acids were provided, rates of synthesis of albumin and total protein were 40% of the maximal rates which were achieved when the medium was supplemented with 5 times the normal plasma concentrations of amino acids. However, rates of synthesis in livers perfused with amino acid-deficient medium rose with extension of the duration of perfusion to 95 min. The defect induced by amino acid deficiency did not appear to result from reductions in the charging of tRNA since no change in the quantities of amino acids bound to tRNA occurred in the amino acid-deficient perfusion. The recovery of protein synthesis with time was prevented by inhibitors of proteolysis suggesting a role for protein degradation in this phenomenon.

Amino Acids↗
PubMed1982

The role of amino acids in the regulation of protein synthesis in perfused rat liver. II. Effects of amino acid deficiency on peptide chain initiation, polysomal aggregation, and distribution of albumin mRNA.

Decreased rates of protein synthesis which occurred in rat livers perfused with amino acid-deficient medium were accompanied by a loss of polysomes and a doubling of concentrations of ribosomal subunits and monomers as compared to unperfused liver or livers perfused with amino acid-supplemented medium. The loss of polysomes was not the result of mRNA degradation because this effect could be reversed by addition of amino acids to the perfusion medium. Instead, loss of polysomes indicated an impairment in peptide chain initiation. To determine whether the block of initiation could be the result of sequestration of mRNA in untranslatable pools, the content of albumin mRNA in membrane-bound and free polysomes and in the non-polysomal fraction isolated on sucrose density gradients was determined by hybridization to an albumin cDNA. In livers perfused with an amino acid-supplemented medium, 90% of the albumin mRNA was found in bound polysomes, and with amino acid-deficient medium, this value was decreased to 80%. Thus, there was no indication of a significant pool of mRNA which was not being translated. The block of initiation was, however, accompanied by a marked change in density and methionine-binding characteristics of the 40 S ribosomal subunit in livers perfused with deficient medium as compared to livers perfused with supplemented medium or to unperfused livers. There was a relative loss of 40 S subunits in a low density form, 1.41 g/cm3, an increase in the proportion in a high density form, 1.48 g/cm3, and a decrease in binding of [35S]methionine to 40 S ribosomal subunits. These changes provide evidence of reduced rates of formation of the 40 S initiation complex.

Amino Acid Sequence↗
PubMed1980

Effects of diabetes on protein synthesis in fast- and slow-twitch rat skeletal muscle.

The effects of acute (2-day) and long-term (7-day) diabetes on rates of protein synthesis, peptide-chain initiation, and levels of RNA were examined in rat skeletal muscles that are known to have differing proportions of the three fiber types: fast-twitch white, fast-twitch red, and slow-twitch red. Short-term diabetes resulted in a 15% reduction in the level of RNA in all the muscles studied and an impairment in peptide-chain initiation in muscles with mixed fast-twitch fibers. In contrast, the soleus, a skeletal muscle with high proportions of slow-twitch red fibers, showed little impairment in initiation. When the muscles were perfused as a part of the hemicorpus preparation, addition of insulin to the medium caused a rapid reversal of the block in initiation in mixed fast-twitch muscles but had no effect in the soleus. The possible role of fatty acids in accounting for these differences is discussed. Long-term diabetes caused no further reduction in RNA, but resulted in the development of an additional impairment to protein synthesis that also affected the soleus and that was not corrected by perfusion with insulin. The defect resulting from long-term diabetes may involve elongation or termination reactions.

Animals↗
PubMed1980

Diltiazem: lack of myocardial beta-adrenergic receptor-binding capacity.

It has been suggested that the mechanism of action of the calcium blocker diltiazem (DZ) is via beta-receptor blockade. In order to test this hypothesis, the effects of DZ on the competitive binding of 3H-dihydroalprenolol (3H-DHA) to myocardial beta-receptors were evaluated and compared to those of a known beta-receptor agonist. Preliminary validation studies indicate that binding sites for 3H-DHA exhibit stereospecificity for isoproterenol (IP) (l-IP>d-IP) and show greater affinity for l-epinephrine compared to l-norepinephrine. In order to test the binding capacity of DZ to beta-adrenergic receptors, binding-concentration relationships were constructed for 3H-DHA (3--60 nM) in the presence of no drugs, l-IP (10(-4) M), or DZ (2.2 x 10(-6) M). 3H-DHA binding was significantly inhibited over the entire concentration range by 1-IP but was unaffected by the other conditions. This study was repeated using two different concentrations of DZ (2.2 x 10(-5) and 2.2 x 10(-7) M) with a similar lack of inhibition of 3H-DHA binding. These data indicate that DZ does not bind to myocardial beta-receptors and, therefore, does not appear to act via a beta-receptor-blocking activity.

Animals↗
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

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

Coupling of signals to brown fat: alpha- and beta-adrenergic responses in intact rats.

The present study examines the effects of alpha- and beta-adrenergic antagonists (phentolamine and propranolol, respectively) and agonists (phenylephrine, isoproterenol) on the neurally induced temperature changes and membrane potentials of interscapular brown adipocytes. These studies, performed in vivo with anesthetized rats, indicate that both alpha- and beta-adrenergic components are associated with the biphasic temperature changes observed following sympathetic activation of the tissue. Specifically, the initial transient temperature decrease seen after brown fat stimulation appeared to reflect vasoconstriction mediated primarily via alpha-receptors, while the subsequent rise in tissue temperature was associated primarily (though perhaps not entirely) with beta-adrenergic pathways. In contrast, the redistribution of ions across the membrane of the brown adipocyte, a phenomenon manifested as a membrane depolarization, was elicited by phenylephrine (an alpha-agonist) as well as by isoproterenol (a beta-agonist), with the magnitude of the isoproterenol-induced depolarization being comparable to that of the phenylephrine-induced effect.

Adipose Tissue, Brown↗
PubMed1976

Functional and anatomical characteristics of the nerve-brown adipose interaction in the rat.

Two aspects of the coupling of neural information to brown fat thermogenesis were examined-namely, the thermal responses to increasing neural stimulation and the anatomical nature of the brown fat innervation. Upon stimulation of the nerves to the interscapular brown fat pad, there ensued a biphasic response. This response was manifested by an initial, but transient temperature decrease, followed by a rise in brown fat temperature. The magnitude of both components of this response increased with increasing stimulus strength, thereby demonstrating the ability of the tissue to respond in a graded manner a feature which may underlie the controlled thermogenic response of brown fat observed in the cold-exposed intact animal. No anatomically unique fibre types appeared to be specifically associated with innervation to the brown adipocytes or to the vessels within the fat pad. On the other hand, the nerves entering the interscapular fat pad were morphologically dissimilar, a finding consonent with their functional dissimilarity (i.e., innervation of adipocytes, innervation of blood vessels in the fat pad, and innervation of areas in the overlying skin).

Adipose Tissue, Brown↗