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M L Reeves

Publications and source records attributed to M L Reeves.

17 recordsLinked to original sources
PubMed1992

Characterization of the cyclic nucleotide phosphodiesterase isoenzymes present in rat epididymal fat cells.

Soluble and particulate fractions from extracts of rat epididymal fat cells were shown to exhibit a number of different phosphodiesterase activities, as determined by substrate specificity and sensitivity to activators and inhibitors. These activities were then further characterized following separation by MonoQ fast protein liquid chromatography (FPLC). A cyclic AMP-specific activity, unaffected by the presence of calcium and calmodulin and inhibited by rolipram, was the major soluble phosphodiesterase. This fraction also contained distinct calcium and calmodulin- and cyclic-GMP-stimulated activities. Over 80% of the phosphodiesterase activity in the particulate fraction could be accounted for by an insulin-activated cyclic AMP and cyclic GMP-hydrolysing enzyme, which was sensitive to inhibition by cyclic GMP, SKF 94120, SKF 95654 and cilostamide, and eluted as a single peak during MonoQ chromatography. At 1 microM cyclic AMP, the phosphodiesterase activity in the soluble fraction was about eight times greater than in the particulate fraction. Specific inhibitors to the particulate phosphodiesterase (cilostamide and SKF 95654) were added to incubations of isolated fat cells, and were able to potentiate sub-maximal concentrations of isoproterenol in the stimulation of lipolysis. These inhibitors were also able to reverse the antilipolytic effect of insulin, demonstrating the importance of the particulate phosphodiesterase in insulin action, despite the fact that its activity represents only a small proportion of the total phosphodiesterase activity in fat cells. Inhibitors of the major soluble phosphodiesterase had no effect on lipolysis.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Potential use of selective phosphodiesterase inhibitors in the treatment of asthma.

Selective inhibitors of the cyclic nucleotide phosphodiesterase (PDE) isoenzymes have been studied to assess the potential for such agents in the treatment of asthma. A novel selective PDE V inhibitor, SK&F 96231, reversed the bronchoconstriction induced in anaesthetised guinea pigs by histamine, a thromboxane-mimetic or by ovalbumin challenge. There was no effect of SK&F 96231 on heart rate or blood pressure in conscious dogs. Siguazodan (SK&F 94836, a selective PDE III inhibitor) caused bronchodilation but also had cardiovascular effects in conscious dogs. Studies on the PDE profile of various inflammatory cells have indicated that inhibition of PDE IV would be beneficial in the treatment of the inflammatory aspects of asthma and this is briefly reviewed.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1990

Use of a synthetic dodecapeptide (malantide) to measure the cyclic AMP-dependent protein kinase activity ratio in a variety of tissues.

1. The cyclic AMP-dependent protein kinase activity-ratio assay was investigated by comparing histone and a synthetic peptide, malantide [Malencik & Anderson (1983) Anal. Biochem. 132, 32-40], as substrates. 2. In several tissues the activity ratio was higher when assayed with histone as the substrate; this result was obtained in control tissues and also in those incubated with agents known to increase cyclic AMP. The effect of these agents to increase the activity ratio was more clearly demonstrated with malantide. 3. The higher activity ratios observed with histone are due to: (a) measurement of phosphorylation not catalysed by cyclic AMP-dependent protein kinase; (b) activation of cyclic AMP-dependent protein kinase by histone during the assay. 4. When tissues were homogenized in buffers without NACl, lower activity ratios were found, owing to the catalytic subunit being artifactually removed from the supernatant. 5. We conclude that the measured activity ratio more faithfully reflects that in the tissue when NaCl is included in the homogenization buffer and malantide is used in the assay. This was confirmed in experiments where cyclic AMP-dependent protein kinase was added to the tissue before homogenization, and no dissociation of the exogenous enzyme was observed.

Amino Acid Sequence↗
PubMed1990

1,4-bis(3-oxo-2,3-dihydropyridazin-6-yl)benzene analogues: potent phosphodiesterase inhibitors and inodilators.

1,4-Bis(3-oxo-2,3-dihydropyridazin-6-yl)benzene and a series of related bis(azinone) compounds were synthesized. These novel compounds were evaluated for inhibition of the low Km, cAMP-selective, cGMP-inhibited phosphodiesterase (PDE III) derived from cat heart and hemodynamic activity in the ganglion- and beta-blocked anesthetized cat. The most potent PDE III inhibitor of the series was 6-[4-(5-methyl-3-oxo-2,3,4,5-tetrahydropyridazin-6-yl)-phenyl]p yridazin- 3(2H)-one (IC50 = 0.07 microM), which also retained the greatest inotrope and vasodilator (inodilator) potency (ED50 for first derivative of left ventricular pressure (dLVP/dt(max)) = 0.02 mumol/kg, ED15 for 15% fall in perfusion pressure = 0.01 mumol/kg). The structure-activity relationships observed within the bis(azinone) series were consistent with those reported for formally analogous 6-(4-substituted-phenyl)pyridazin-3(2H)-one-based PDE III-inhibiting inodilators with less-extended phenyl substituents (see e.g. Sircar et al. J. Med. Chem. 1987, 30, 1955, Moos et al. J. Med. Chem. 1987, 30, 1963). PDE III inhibitory potency is associated with overall planar topology of the phenylpyridazinone moiety and the presence of two critically separated electronegative centers. A methyl group at the 5-position of a dihydropyridazinone ring leads to enhanced potency. However, the generally higher levels of PDE III inhibitory potency shown by compounds in the bis(azinone) series relative to earlier 6-(4-substituted-phenyl)pyridazin-3(2H)-one derivatives appears to derive from a closer to optimal separation of two interacting points in the inhibitor molecule achieved through the more extended bis(azinone) structure. Correlation between the pharmacological and PDE III inhibitory activities of compounds in the bis(azinone) series provides additional evidence for PDE III being an important mediator of inodilator action.

Animals↗
PubMed1990

The effects of siguazodan, a selective phosphodiesterase inhibitor, on human platelet function.

1. The effects of siguazodan (SK&F 94836) a selective phosphodiesterase (PDE) inhibitor with inotropic and vasodilator activity, were studied on human platelets. 2. Siguazodan selectively inhibited the major cyclic AMP-hydrolysing PDE in human platelet supernatants. The inhibited enzyme has been variously termed cyclic GMP-inhibited PDE or PDE-III. 3. In platelet-rich plasma (PRP), siguazodan inhibited U46619-induced aggregation more potently than that induced by ADP and collagen. Treatment of the PRP with aspirin had no effect on the potency of siguazodan. 4. In washed platelets, siguazodan increased cyclic AMP levels and reduced cytoplasmic free calcium [( Ca2+]i). ADP decreased the ability of siguazodan to raise cyclic AMP and this may explain its lower potency in inhibiting responses to ADP. 5. Siguazodan has anti-platelet actions over the same concentration range that it is an inotrope and vasodilator.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1989

Protein phosphorylation and compartments of cyclic AMP in the control of cardiac contraction.

The roles of cyclic AMP, cyclic AMP-dependent protein kinase and the phosphorylation of specific proteins in the regulation of cardiac contractility are briefly reviewed. Criteria for determining whether changes in cyclic AMP and protein phosphorylation are involved in a physiological response are discussed. Although cyclic AMP-dependent phosphorylation of the voltage-operated Ca2+ channel, phospholamban, troponin-I and C-protein have all been implicated in the response of the heart to inotropic agents which elevate cyclic AMP, none of these phosphorylations satisfy all of the criteria completely. Evidence is presented that there are compartments of cyclic AMP in heart which are coupled to different functional responses.

Animals↗
PubMed1988

Effects of SK&F 94120, an inhibitor of cyclic nucleotide phosphodiesterase type III, on human platelets.

Elevation of cyclic AMP concentrations in platelets inhibits agonist-induced responses. Pharmacological interventions which could increase the levels of platelet cyclic AMP include activation of the synthesis of cyclic AMP or inhibition of its breakdown. In this study we have investigated the effects of SK&F 94120 on human platelet phosphodiesterase (PDE) activities separated by ion-exchange chromatography, and studied the effects of this agent on platelet responses caused by the agonists collagen, U44069 and ADP. Four PDE activities were identified from human platelet preparations. The PDE activities found comprised a cyclic GMP selective PDE, a Ca2+/calmodulin stimulated PDE, a cyclic GMP stimulated PDE and a "low Km" PDE activity called PDE III by analogy with activities described in other tissues. SK&F 94120 was found selectively to inhibit the "low Km" PDE III activity with an IC50 of 10.8 microM, which is consistent with the effects of this compound on cardiac ventricle PDE activities. Exposure of human platelets to SK&F 94120 produced concentration dependent increases in cyclic AMP, showing that inhibition of PDE III activity alone can cause an increase in the level of platelet cyclic AMP. SK&F 94120 also caused an inhibition of platelet responses to collagen, U44069 and ADP. However, SK&F 94120 was much less effective as an inhibitor of aggregation induced by ADP (IC50 greater than 100 microM) than by collagen (IC50 = 24.1 microM) or by U44069 (IC50 = 1.7 microM). Isobutylmethylxanthine (IBMX), a non-selective PDE inhibitor, was less effective than SK&F 94120 as an inhibitor of platelet responses for the same measured increase in cyclic AMP levels. M&B 22948 and rolipram, inhibitors of PDE I and PDE IV respectively, had no significant effect on platelet responses. These data suggest that selective inhibition of PDE III is the primary mechanism of action of SK&F 94120 as an inhibitor of agonist-induced platelet responses, and that increased cyclic AMP in the pool controlled by PDE III has important consequences on platelet responses. Moreover, these data suggest that some form of compartmentalization of cyclic AMP and/or PDE activity exists in human platelets.

1-Methyl-3-isobutylxanthine↗
PubMed1987

The identification of a new cyclic nucleotide phosphodiesterase activity in human and guinea-pig cardiac ventricle. Implications for the mechanism of action of selective phosphodiesterase inhibitors.

Four cyclic nucleotide phosphodiesterase (PDE) activities were separated from low-speed supernatants of homogenates of human cardiac ventricle by DEAE-Sepharose chromatography, and designated PDE I-PDE IV in order of elution with an increasing salt gradient. PDE I was a Ca2+/calmodulin-stimulated activity, and PDE II was an activity with a high Km for cyclic AMP which was stimulated by low concentrations of cyclic GMP. Human ventricle PDE III had Km values of 0.14 microM (cyclic AMP) and 4 microM (cyclic GMP), and showed simple Michaelis-Menten kinetics with both substrates. PDE IV is a previously unrecognized activity in cardiac muscle, the human enzyme having Km values of 2 microM (cyclic AMP) and 50 microM (cyclic GMP). PDE III and PDE IV were not activated by cyclic nucleotides or calmodulin. Four PDE activities were also isolated from guinea-pig ventricle, and had very similar kinetic properties. By gel filtration, the Mr of PDE III was 60,000, and that of PDE IV 45,000. The drug SK&F 94120 selectively and competitively inhibited PDE III with a Ki value of 0.8 microM (human), showing simple hyperbolic inhibition kinetics. Rolipram (Schering ZK 62711) and Ro 20-1724 (Roche), which have previously been reported to inhibit PDE III-like activities strongly, were shown to be weak inhibitors of human and guinea-pig PDE III enzymes (Ki values greater than 25 microM), but potent inhibitors of PDE IV [Ki values 2.4 microM (Rolipram) and 3.1 microM (Ro 20-1724) with human PDE IV]. The inhibition in all cases demonstrated simple hyperbolic competition. These observations suggest that the previously reported complex inhibition of PDE III-type activities from cardiac muscle was caused by incomplete separation of the PDE III from other enzymes, particularly PDE IV.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1984

Medial plantar sensory response. Sensitive indicator of peripheral nerve dysfunction in patients with diabetes mellitus.

The effects of near-normal glucose control on nerve conduction results were studied in 10 patients with insulin-dependent diabetes mellitus who underwent a six-month program of intensification of therapy. The most striking electrophysiologic abnormality was the medial plantar sensory nerve conduction response. A sensory nerve action potential could not be elicited in seven of the 10 patients at the baseline evaluation. Over the six-month period of near-normal glucose control, there was a return of sensory nerve action potential in all 10 patients. Medial plantar sensory nerve conduction responses appear to be a sensitive and early electrophysiologic indicator of peripheral nerve dysfunction in patients with diabetes mellitus. Near-normalization of plasma glucose levels by intensification of diabetes management may be accompanied by correction of this early abnormality.

Adult↗
PubMed1982

Glycemic control in insulin-dependent diabetes mellitus. Comparison of outpatient intensified conventional therapy with continuous subcutaneous insulin infusion.

We compared glycemic control achieved on an outpatient basic with three insulin regimens in 10 patients with insulin-dependent diabetes mellitus. The regimens studied included: (1) intensified conventional therapy with twice-daily regular and lente insulin; (2) intensified conventional therapy with long-acting ultralente insulin plus multiple preprandial injections of regular insulin; (3) continuous subcutaneous insulin infusion. Each treatment period was two months long. At the beginning of the study and the close of each study period, patients were hospitalized for a 48-hour evaluation of glycemic control. Each new insulin regimen was begun after discharge, with the dosage adjusted using preplanned algorithms, patient self-monitoring of blood glucose and defined blood glucose targets. Glycemic control markedly improved on all three treatment regimens, to a comparable degree, as assessed by mean plasma glucose level, mean amplitude of glycemic excursions, M value (an index of glycemic lability), urinary glucose excretion and glycosylated hemoglobin level.

Adolescent↗
PubMedDate not supplied

Lack of a persistent reduction in serum lipid and apoprotein levels in insulin-dependent diabetic patients receiving intensified insulin treatment.

Type I insulin-dependent diabetic patients have an increased risk of atherosclerotic vascular disease that may be determined in part by their tendency to develop circulating lipid and lipoprotein abnormalities. The occurrence of such findings in asymptomatic ambulant Type I patients with mild or moderate hyperglycemia might suggest that conventional methods of insulin treatment are as inefficient at normalizing lipid abnormalities as they are in achieving euglycemia. It would then be important to ascertain whether intensive methods of insulin treatment effectively normalized lipid levels. Ten insulin-dependent young adult diabetic patients were studied on a conventional insulin treatment regimen and then at two-monthly intervals for a six-month period during which they were managed by three different intensified insulin treatment regimens. Plasma glucose levels improved substantially (p less than 0.001) after two months of intensified therapy (106 +/- 4 mg/dl) and did not change significantly thereafter for the remaining four months of intensified insulin treatment. Apart from a short-lived decrease in total-, LDL- and HDL-cholesterol after two months of intensified treatment (baseline total triglyceride 116 +/- 13 mg/dl, total cholesterol 174 +/- 16 mg/dl, HDL-cholesterol 46 +/- 3 mg/dl). There were no persistent changes in serum lipids, lipoprotein cholesterol or in levels of their major apoproteins A-I, A-II and B. These findings support the contention that, despite moderate hyperglycemia, conventional insulin treatment may be adequate to maintain normal lipid levels. In such circumstances achievement of euglycemia by intensified insulin therapy leads to little change in circulating lipid and lipoprotein values.

Adolescent↗
PubMedDate not supplied

Optimizing pumped insulin delivery.

The use of portable devices for the subcutaneous infusion of insulin may facilitate the attainment of improved glycemic control in selected patients with insulin-dependent diabetes mellitus. Successful use of a program of continuous subcutaneous insulin infusion requires patient cooperation and motivation, routine monitoring of glycemia, and attention to food intake and activity. This article describes an approach by which patients may optimize glycemic control utilizing a set of algorithms based on patient-determined blood glucose measurements. The algorithms permit programming the insulin infusion device to achieve the desired control.

Diabetes Mellitus, Type 1↗
PubMedDate not supplied

Lack of effect of improved glycemic control on C-peptide secretion in patients without residual B-cell function.

Ten patients with insulin-dependent diabetes mellitus underwent a program of intensification of therapy that resulted in marked improvement in glycemic control. C-peptide secretion in response to a test meal and to an intravenous glucagon challenge was used to assess pancreatic B-cell function in terms of residual endogenous insulin secretion. Patients, who had diabetes for a mean (+/- SEM) of 8.4 +/- 1.9 yr, had minimal or no C-peptide response at baseline evaluation. C-peptide responses remained unchanged when reassessed after 2, 4, and 6 mo of improved glycemic control.

Blood Glucose↗
PubMedDate not supplied

A comparison of insulin regimens in insulin-dependent diabetes mellitus.

Glycemic control in 10 ambulatory patients with insulin-dependent diabetes mellitus was compared on three intensive treatment regimens: (1) twice-daily regular and lente insulin; (2) multiple preprandial injections of regular insulin accompanied by long-acting ultralente insulin; and (3) continuous subcutaneous insulin infusion with a portable infusion pump. All regimens included (1) careful attention to diet, exercise, and insulin; (2) patient self-monitoring of blood glucose; and (3) the use of algorithms for the attainment of improved control. Treatment periods were 2 mo in duration. All parameters of glycemic control evaluated (including inpatient mean plasma glucose, mean amplitude of glycemic excursions, M-value, urinary glucose excretion; glycosylated hemoglobin; and outpatient blood glucose values) showed marked improvement from baseline, yet no difference when the intensive regimens were compared with each other. All elements of the treatment system appeared to be important in achieving improved glycemic control.

Adolescent↗
PubMedDate not supplied

Psychological effects of intensification of diabetic control.

We studied the psychological effects of a program of intensification of glycemic control, using three different insulin regimens: (1) twice-daily regular and lente insulin; (2) multiple preprandial doses of regular insulin coupled with long-acting ultralente insulin; and (3) continuous subcutaneous insulin infusion (CSII). Ten patients used each of the regimens for periods of 2 mo. Patients monitored blood glucose 4-7 times daily. Using the Hopkins Symptom Checklist, there were significant reductions in depression, interpersonal sensitivity, and anxiety during all three treatment programs. Self-concept scores were more positive following CSII therapy. Positive self-concept ratings were correlated with positive attitudes about diabetes, medical care, persons with diabetes, and current diabetes regimens. After all subjects had experienced CSII, self-concept was positively related to attitudes regarding the insulin pump. Patients reporting more positive attitudes toward their current diabetes regimens had lower glycosylated hemoglobin levels. Thus, there were no adverse psychological effects of blood glucose monitoring, intensification of therapy, or use of infusion pumps by the parameters measured.

Adult↗