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Biomedical subjects

R F Peters

Publications and source records attributed to R F Peters.

At least 19 recordsLinked to original sources
PubMed1994

The amine-donor substrate specificity of tissue-type transglutaminase. Influence of amino acid residues flanking the amine-donor lysine residue.

The amine-donor substrate specificity of tissue-type transglutaminase has been studied in a series of recombinant alpha A-crystallin mutants. These mutant proteins have been provided with a potential substrate lysine residue, flanked by different amino acid residues, in the C-terminal extended arm of alpha A-crystallin. A biotinylated amine-acceptor hexapeptide was used as a probe for labelling the amine-donor sites. Wild-type bovine alpha A-crystallin does not function as an amine-donor substrate for tissue-type transglutaminase. Yet, upon introduction of a lysine residue at the C-terminal or penultimate position, all mutant alpha A-crystallins act as amine-donor substrates, although to different extents. This shows that accessibility is the primary requirement for a lysine residue to function as an amine-donor substrate for transglutaminase and that the enzyme has a broad tolerance towards the neighbouring residues. However, the nature of the flanking amino acid residues does clearly affect the reactivity of the substrate lysine residue. Notably, we found that a proline or glycine residue in front of the substrate lysine has a strong adverse effect on the substrate reactivity as compared to a preceding leucine, serine, alanine or arginine residue.

Amino Acid Sequence↗
PubMed1991

The characterisation of thrombus development in an improved model of arterio-venous shunt thrombosis in the rat and the effects of recombinant desulphatohirudin (CGP 39393), heparin, and iloprost.

An existing arterio-venous shunt thrombosis model in the rat has been modified to increase its usefulness for the testing of anti-thrombotic agents and characterised using morphological and radiometric techniques. The thrombus formed on the cotton thread held in the shunt was found to be composed of platelet aggregates surrounded by red thrombus. After 30 min of blood flow there was a 15-fold increase in the platelet content of the thrombus and a 4-fold increase in the fibrin(ogen) content compared with an equivalent weight of whole blood. Use of the anticoagulants recombinant desulphatohirudin (CGP 39393, 4 mg/kg, s.c.) and unfractionated heparin (800 IU/kg, s.c.) showed that approx. 90% inhibition of thrombus weight and approx. 80% inhibition of fibrin(ogen) content could be achieved without significant effect on the platelet content. Conversely, using the platelet inhibitor Iloprost (1 microgram kg-1 min-1), a reduction in thrombus weight of 50% was associated with 75% inhibition of platelet content and only 20% inhibition of fibrin(ogen). These observations suggest that the growth of this type of thrombus is largely the result of continued fibrin formation rather than continued platelet recruitment and activation.

Animals↗
PubMed1991

The effects of recombinant desulphatohirudin on arterial thrombosis in rats.

The role of thrombin in the formation of arterial thrombi is poorly understood. With the new availability of the specific thrombin inhibitor, recombinant desulphatohirudin, in large quantities this is now under investigation. A new model of arterial thrombosis in rats is described where a thrombus is formed on a mechanically injured vessel in vivo. Both platelet and fibrin deposition is inhibited by a recombinant hirudin (CGP 39393) at doses which prolong the activated partial thromboplastin time (APTT) to no more than 3-4 times the control level. In contrast, both unfractionated heparin and Fragmin only inhibit thrombosis when the APTT is excessively prolonged (i.e. to greater than 15 times the control value). It is concluded that CGP 39393 is an effective antithrombotic in arterial thrombosis at lower levels of anticoagulation than either heparin or Fragmin.

Animals↗
PubMed1989

Recombinant desulphatohirudin (CGP 39393) anticoagulant and antithrombotic properties in vivo.

The effects of the newly available biotechnology product, recombinant desulphatohirudin (CGP 39393) have been investigated in rats. This highly potent and selective thrombin inhibitor exhibited marked anticoagulant properties with controllable titration of anticoagulant effect, as measured by activated partial thromboplastin time (APTT), up to nearly four times control values. Furthermore, CGP 39393 exhibited impressive antithrombotic activity in vivo. In an arteriovenous shunt model of thrombus formation on a cotton-thread, the compound was capable of complete inhibition of thrombus development (ED50 = 0.3 mg/kg i.v. and 1.0 mg/kg s.c.). Venous stasis thrombosis was also highly susceptible to inhibition by CGP 39393 (ED50 = 0.01 mg/kg i.v. and 0.45 mg/kg s.c.). Comparison of the anticoagulant and antithrombotic activities of the compound shows that potent antithrombotic effects (83-97% inhibition in the rat shunt model) are achieved within the generally acceptable range of anticoagulation. These results suggest a clear potential for this new agent in the clinical treatment of thrombotic disease.

Animals↗
PubMed1978

The relationship between cyclic adenosine 3', 5' - monophosphate and biochemical events in rat skin after the induction of epidermal hyperplasia using hexadecane.

Sequential changes in skin metabolism have been studied in a model system of epidermal hyperplasia and hyperkeratinization induced by the application of n-hexadecane to shaved rat skin. The epidermal accumulation of glycogen typical of the hyperplastic response has been correlated with an increase in glycogenesis and a decrease in glycogenolysis. DNA synthesis was increased by 6 h after the start of hexadecane treatment and reached a maximum after one day. The concentration of skin cyclic AMP fell immediately after hexadecane application and subsequently rose to give a prolonged increase. Use of the combined topical application of hexadecane and the anti-inflammatory drugs triamcinolone acetonide, hydrocortisone and indomethacin showed that the hexadecane-induced changes in DNA synthesis and glycogen metabolism were linked to the initial fall in cyclic AMP concentration. The significance of the biphasic change in cyclic AMP levels is discussed as a possible system of control for the development and maintenance of hyperplasia.

Administration, Topical↗
PubMed1976

The existence of a glyconeogenic pathway in rat skin.

The existence of a glyconeogenic pathway in rat skin has been demonstrated by measurement of three of the key glyconeogenic enzymes, fructose 1,6-bisphosphatase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase, and by studies on the incorporation in vitro of carbon from pyruvate and alanine into skin glycogen.

Alanine↗
PubMed1972

Relative changes in the function of muscle ribosomes and mitochondria during the early phase of steroid-induced catabolism.

1. Five glucocorticoids, when administered daily to rats for 5-7 days at a dosage of 5mg/kg, were in the following order of effectiveness with respect to their ability to decrease the weight gain of whole animals and the vastus lateralis, vastus medialis and gluteus medius muscles: corticosterone<prednisolone<triamcinolone <betamethasone<dexamethasone<triamcinolone acetonide. 2. The low catabolic potencies of corticosterone and prednisolone were reflected in the high doses (20mg/kg) required to decrease significantly the incorporating activity in vitro of ribosomes isolated from the muscles 6h later. However, triamcinolone was as effective as triamcinolone acetonide in causing a significant effect at 0.05mg/kg, although it had a far lower catabolic potency than the acetonide. 3. The relationship between decrease in ribosomal activity in vitro and weight loss was better understood by considering the duration of the effect after single doses of steroids. Ribosomes returned to normal function between 6 and 12h after the administration of corticosterone (20mg/kg), but still had decreased activity 12h after a similar dose of prednisolone. Normal ribosomal function was renewed between 12 and 18h after the administration of triamcinolone and betamethasone at 5mg/kg, but decreased activity persisted for more than 48h after similar doses of dexamethasone or triamcinolone acetonide. 4. There was no difference in the rate of incorporation of amino acids into nascent protein on polyribosomes from muscle of control animals and animals treated 6h previously with triamcinolone acetonide or dexamethasone. 5. The rate of weight gain of the heart was not affected by any of the steroids tested and heart ribosomes maintained normal activity although concentrations of steroids in this organ 5min after administration were 2-3 times that in skeletal muscle. 6. Mitochondria, isolated from the muscle of animals that had received triamcinolone acetonide (20mg/kg) 12h previously, were shown, by using a Coulter counter, to be enlarged. Nevertheless oxidation was only slightly uncoupled 12h after drug administration and they had normal function 6h later. Similar results with respect to mitochondrial function were obtained after the administration of dexamethasone (20mg/kg) and betamethasone (20mg/kg). 7. From these results it is concluded that the mitochondria are not functionally involved in the early phase of steroid-induced muscle catabolism. The observed decrease in the incorporating ability of muscle ribosomes in vitro appears to be much more closely linked to the initial catabolic event.

Amino Acids↗
PubMed1970

Some biochemical effects of triamcinolone acetonide on rat liver and muscle.

1. The powerful anti-inflammatory glucocorticoid triamcinolone acetonide, administered to rats at 20 and 2.5mg/kg, leads to a decrease in the incorporation in vivo of [(3)H]uridine and [(32)P]orthophosphate into hind-limb skeletal muscle. 2. At the higher dose, this decrease in the rate of incorporation of precursors into RNA precedes a decrease in the incorporating ability of muscle ribosomes, which commences about 4-5h after drug administration, but is unaccompanied by any changes in the concentration of tissue ATP or free amino acids. 3. The ribosomal dysfunction extends to polyribosomes, which can only be successfully isolated from the muscle of triamcinolone-treated animals after the addition of alpha-amylase to the tissue homogenate to remove glycogen. 4. The specific radioactivity of muscle protein labelled in vivo with (14)C-labelled amino acids does not decrease progressively after triamcinolone administration. After 2h there is an apparent stimulation of incorporation which leads to an overall discrepancy between measurements of protein-synthetic activity made in vivo and in vitro. 5. There is a significant increase in muscle-glycogen concentration between 8 and 12h after the administration of triamcinolone acetonide (20mg/kg), although a significant decrease occurs after 4h. The fall in glycogen concentration may be due to a decrease in the rate of synthesis of protein essential for glucose uptake into the tissues. 6. As judged by (a) incorporation of (14)C-labelled amino acids into protein, (b) [(3)H]uridine and [(32)P]-orthophosphate incorporation into RNA, (c) the rate of induction of tryptophan pyrrolase and (d) changes in the pool sizes of taurine and tryptophan, the responses in liver followed the same time-course as those in muscle after administration of the drug.

Adenosine Triphosphate↗