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Biomedical subjects

J G Hardman

Publications and source records attributed to J G Hardman.

At least 19 recordsLinked to original sources
PubMed1998

A physiology simulator: validation of its respiratory components and its ability to predict the patient's response to changes in mechanical ventilation.

We aimed to validate the mathematical validity and accuracy of the respiratory components of the Nottingham Physiology Simulator (NPS), a computer simulation of physiological models. Subsequently, we aimed to assess the accuracy of the NPS in predicting the effects of a change in mechanical ventilation on patient arterial blood-gas tensions. The NPS was supplied with the following measured or calculated values from patients receiving intensive therapy: pulmonary shunt and physiological deadspace fractions, oxygen consumption, respiratory quotient, cardiac output, inspired oxygen fraction, expired minute volume, haemoglobin concentration, temperature and arterial base excess. Values calculated by the NPS for arterial oxygen tension and saturation (PaO2 and SaO2), mixed venous oxygen tension and saturation (PvO2 and SvO2), arterial and mixed venous carbon dioxide tension (PaCO2 and PvCO2) and arterial pH were accurate compared with measured values. Subsequently, arterial gas responses to changes in minute volume of FiO2 were measured in 31 patients and were compared with the NPS prediction for each response. The 95% limits of agreement in predicting the magnitude of change were: arterial oxygen tension -2.07 to 2.47 kPa; PaCO2 -0.33 to 0.67 kPa; and pH -0.023 to 0.033. This investigation has validated respiratory components of the NPS. We recommend the NPS as a clinical tool for predicting the effects of alterations in mechanical ventilation in stable patients in the intensive care unit.

Adult↗
PubMed1997

End-tidal carbon dioxide measurement and breathing system filters.

Breathing system filters are recommended for use during general anaesthesia. Manufacturers of gas sampling equipment recommend that gas is sampled from the 'machine side' of these filters, thereby avoiding contamination of the sampling line and waterlogging in the case of heat and moisture exchangers. The aim of this study was to investigate differences between the measured end-tidal carbon dioxide values at either side of the filter. Fifteen adults were studied during mechanical ventilation and 15 during spontaneous ventilation under general anaesthesia. End-tidal carbon dioxide values were significantly lower at the machine side of the filter in both groups (p = 0.00001). The measurement error induced by the inclusion of the breathing system filter was significantly greater in the spontaneously breathing group (p = 0.0004).

Adult↗
PubMed1986

Activation of soluble guanylate cyclase by arachidonic acid and 15-lipoxygenase products.

The activity of soluble guanylate cyclase can be increased by exposure of the enzyme to arachidonic acid or to some oxidized metabolites of the fatty acid. We have tried to determine whether activation of the enzyme by arachidonate requires that the fatty acid be converted to an oxidized metabolite, either by a possible trace contaminant of a lipoxygenase or by guanylate cyclase itself, which contains a heme moiety. Soluble guanylate cyclase purified from bovine lung was activated 4-6-fold by arachidonic acid. This activation was not dependent on the presence of oxygen in the incubation medium. No detectable metabolites of arachidonic acid were formed during incubation with soluble guanylate cyclase. Addition of soybean lipoxygenase to the incubation did not increase activation by arachidonic acid. The inhibitors of lipoxygenase activity, nordihydroguaiaretic acid and eicosatetraynoic acid, had direct effects on soluble guanylate cyclase and interfered with its activation by arachidonate, whereas another lipoxygenase inhibitor, BW 755 C, did not. The data suggest that arachidonic acid increases the activity of guanylate cyclase by direct interaction with the enzyme rather than by being converted to an active metabolite.

Animals↗
PubMed1985

Differences in the association of calmodulin with cyclic nucleotide phosphodiesterase in relaxed and contracted arterial strips.

Changes in the concentration of cytosolic Ca2+ are assumed to alter the activity of Ca2+-calmodulin-sensitive cyclic nucleotide phosphodiesterase in intact cells. However, this assumption is based on indirect evidence and by analogy from studies of enzyme activities in broken cell systems. We have developed a procedure for estimating the fraction of Ca2+-calmodulin-sensitive phosphodiesterase that is in an activated, ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) sensitive state in intact porcine coronary artery strips. The experimental approach involves homogenization of the strips and assay of cyclic guanosine monophosphate (cyclic GMP) phosphodiesterase activity under conditions that retard changes in the amount of the complex Ca2+-calmodulin-phosphodiesterase. Our findings indicate that cyclic GMP phosphodiesterase in intact coronary artery strips does associate with Ca2+-calmodulin and that interventions that change the concentration of Ca2+ in the cytosol of the intact strip change the extent of this functional association. Exposure to histamine (10 or 100 microM) or 50 mM KCl caused contraction and an increase in EGTA-sensitive cyclic GMP phosphodiesterase activity. Isoproterenol-induced relaxation of tissues that had been caused to contract with 10 microM histamine was accompanied by a reduction in EGTA-sensitive cyclic GMP phosphodiesterase activity to the same level as that present before contraction was initiated.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1984

Cyclic nucleotides and regulation of vascular smooth muscle.

Cyclic AMP probably plays an important role in blood-vessel relaxation caused by beta-adrenergic agonists and other agents, including inhibitors of cyclic nucleotide phosphodiesterases. Cyclic GMP may participate in blood-vessel relaxation caused by drugs such as nitroglycerin and nitroprusside and by agents that require the endothelium for their relaxing effects. The significance of elevated levels of cyclic GMP in response to contraction-producing agents is unknown. Cyclic nucleotides may modulate vascular smooth-muscle contraction by regulating the phosphorylation of multiple proteins involved in the action and distribution of calcium. The relative importance of different potential sites of regulation by cyclic nucleotides may vary among different blood vessels.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Calcium-induced release from platelet membranes of fatty acids that modulate soluble guanylate cyclase.

Incubation of rat or rabbit platelet membranes with Ca++ induced the release of modulators of soluble guanylate cyclase. These modulators increased basal activity and inhibited sodium nitroprusside-stimulated activity in the absence or presence of dithiothreitol. The release, but not the effects, of the modulators was inhibited by trifluoperazine and by mepacrine. Indomethacin and oxyphenbutazone did not influence the release or effects of the modulators. The factors were identified as arachidonic and linoleic acids. These fatty acids produced comparable effects on crude soluble guanylate cyclase from platelets and on the homogeneously purified enzyme from bovine lung. In the presence of MgCl2, the maximal increase in basal activity was observed at 10 to 30 microM arachidonic or linoleic acid with the crude enzyme and at 3 to 6 microM with the purified enzyme. Inhibition of basal activity was observed at higher concentrations. Half-maximal inhibition of Mg++-supported, sodium nitroprusside-augmented activity was observed at 3 to 10 microM fatty acid. The effects of arachidonic acid occurred without a lag period and were quickly reversible. These data demonstrate that unsaturated fatty acids can be released from platelet membranes by a Ca++-dependent process in amounts that are high enough to alter soluble guanylate cyclase activity. The data also indicate that unsaturated fatty acids exert their effects on soluble guanylate cyclase without having to be converted to peroxides by other enzymes.

Animals↗
PubMed1980

Cyclic nucleotide phosphodiesterase activities from pig coronary arteries. Lack of interconvertibility of major forms.

DEAE-cellulose chromatography, with or without dithiothreitol and over a pH range of 6.0 to 8.5, resolved two phosphodiesterase activities (peaks I and II) from the soluble fraction of pig coronary arteries. The activity of peak I was increased by calmodulin (3-7-fold), whereas that of peak II was not. Chromatography of peak I on Biol-Gel A-0.5 m columns resolved two peaks of phosphodiesterase activity (peaks Ia and Ib). Peak Ia was eluted in the presence or absence of 0.1 M KCl and was relatively insensitive to calmodulin. Peak Ib was eluted only in the presence of KCl and was sensitive to calmodulin. The substrate specificity and kinetic behavior were the same for peaks I, Ia, and Ib. Repeated gel chromatography of either peak Ia or Ib, under appropriate conditions, yielded a mixture of peaks Ia and Ib. Peak Ia appears to be a reversible aggregate of peak Ib. Gel chromatography of peak II resolved only one phosphodiesterase activity, which was eluted without KCl, was highly specific for cyclic AMP, was not sensitive to calmodulin and migrated differently on the gel column than either peak Ia or Ib. Sucrose density gradient centrifugation of the soluble fraction from pig coronary arteries in the presence or absence of dithiothreitol resolved two peaks of phosphodiesterase activity (6.6 S and 3.6 S) which were similar to peaks I and II separated by DEAE-cellulose chromatography with regard to their substrate specificity and their sensitivity to calmodulin. Upon recentrifugation, each of the two peaks of phosphodiesterase activity gave a single peak of activity which migrated with the same S value as did its parent. These results indicate that the two major forms of phosphodiesterase of pig coronary arteries, which are representative of those found in many tissues, are not interconvertible in cell-free systems.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

The calcium accumulation in a microsomal fraction from porcine coronary artery smooth muscle. A study of the heterogeneity of the fraction.

1. Microsomes prepared from the combined media and intima of pig coronary artery, take up Ca in an ATP-dependent way. This uptake is stimulated by oxalate. 2. Conditions have been determined to optimize the preparation of the microsomes in terms of their Ca accumulation activity. Careful homogenization of the tissue mince in 0.25 M sucrose by means of a Potter-Elvehjem homogenizer gives microsomal preparations with the highest specific activity for Ca accumulation. 3. Arguments are presented to support the hypothesis that, even in the absence of oxalate, Ca accumulation occurs into the lumen of the vesicles, and that these vesicles have a low Ca permeability. 4. Density gradient analysis shows that the microsomal fraction prepared from pig coronary artery media and intima is composed of vesicles that are heterogeneous in enzymatic composition. 5. Adenylate cyclase appears to be a predominantly plasma membrane-bound enzyme. Rotenone-insensitive NADH-cytochrome c reductase and choline phosphotransferase, two putative markers for internal membranes, give distinct banding patterns on on isopycnic centrifugation, indicating different intracellular localization. 6. There is a difference between the density gradient distribution pattern of Ca uptake measured in the presence or absence of oxalate. The latter coincides more closely with plasma membrane markers. The former resembles more the distribution of rotenone-insensitive NADH-cytochrome c reductase.

Animals↗
PubMed1978

The effect of adrenocorticotropin and nucleotides on Ca2+ uptake in adrenal cortical microsomal vesicles.

Rat and bovine adrenal cortical microsomal fractions isolated at 27,000 x g and 105,000 x g accumulated Ca2+ by a nonmitochondrial, ATP-dependent uptake system that was stimulated by ammonium oxalate. ACTH (2 mU/ml) significantly increased Ca2+ uptake in bovine adrenal cortical microsomes and in adrenal microsomes from acutely hypophysectomized rats, but only when the hormone was preincubated with intact tissue and not when it was added after homogenization. ACTH did not stimulate C2+ uptake in adrenal microsomes isolated from nonhypophysectomized, ether-stressed rats, in which basal Ca2+ uptake was higher than that observed in microsomes from hypophysectomized animals. The peptides oxytocin, insulin, and TSH did not stimulate Ca2+ uptake by adrenal cortical microsomes. ACTH preincubated with intact tissue had no effect on Ca2+ uptake in microsomes from liver, kidney, esophagus, or aorta. cAMP, 5'-AMP, and several other nucleotides, nucleosides, and related compounds stimulated adrenal cortical microsomal Ca2+ uptake by as much as 540% of control. The stimulatory effects of nucleotides, unlike those of ACTH, were apparent even when the agents were added after homogenization. However, like ACTH, the nucleotides were unable to stimulate Ca2+ uptake when they were added to isolated membrane vesicles during Ca2+ uptake measurements. It is suggested that the microsomal Ca2+ uptake system may respond to physiological stimulants and regulate Ca2+ availability in the intact cell.

Adrenal Cortex↗
PubMed1978

Characteristics of adenylate cyclase activity in pig coronary arteries.

Characteristics of adenylate cyclase activity of the intima plus media layer of pig coronary arteries have been studied. Enzyme activity in the 10,000 xg particulate fraction was linear with respect to time and protein during short incubations. Linear kinetics were observed for MgATP as a substrate and free Mg2+ as an activator. Mn2+ added in excess of ATP concentrations was only slightly stimulatory or inhibitory. Adenosine, GTP and GPP(N)P inhibited enzyme activity. Adenosine decreased the Vmax and the Ka for Mg2+ but had no effect on the Km for MgATP. The inhibition by adenosine was reversible, while that by GPP(N)P appeared to be irreversible. Although preincubation of the enzyme with GPP(N)P for short times caused irreversible inhibition, preincubation for more than 15 min caused up to 3-fold activation. Isoproterenol added to the incubation produced no or very slight stimulation with or without GPP(N)P or GTP, and preincubation with isoproterenol alone caused irreversible inhibition. However, preincubation with isoproterenol plus GPP(N)P for 30 min caused irreversible activation exceeding that observed with GPP(N)P alone. These observations suggest that vascular adenylate cyclase, like the enzyme from the other tissues, can exist in multiple states of activity and responsiveness.

Adenosine↗
PubMed1976

Implications of cross inhibitory interactions of potential mediators of hormone and neurotransmitter action.

Mediators of hormone and neurotransmitter action may exert negative control on the accumulation of one another (adenosine 3':5'-cyclic monophosphate, or conversely). A model in which one agonist stimulates the formation of two mediators which inhibit each other's accumulation has been simulated. Three types of agonist-receptor interaction, five mechanisms of inhibition, and three types of basal activity have been considered which lead to a set of 45 descriptions of the general cross inhibition model. For these submodels, pattern of the relation of agonist to mediator concentrations at steady state conditions have been defined. Some patterns are complex with mediator curves exhibiting extrema, one a maximum and the other a minimum. The complexity of the pattern depends on the submodel and on the degree of asymmetry between the parameters of each of the mediator pathways (e.g.,affinities for the agonist, strength of the inhibitions, etc.). This simple model can thus account for complex experimental results without requiring the postulation of elaborate molecular models of agonist-receptor interaction. The simulations presented emphasize the necessity of investigating a wide range of agonist concentrations.

Calcium↗