Effects of vasodilators and perfusion pressure on coronary flow and simultaneous release of nitric oxide from guinea pig isolated hearts

OBJECTIVE: The aims were to validate the use of a direct reading NO electrode, to compare the effects of diverse acting drugs on altering coronary flow (CF) and NO release, and to examine the effects of altered perfusion pressure on flow-induced changes in NO concentration [NO] in the hemoglobin free effluent of guinea pig isolated hearts. METHODS: Hearts were isolated and perfused initially at a constant perfusion pressure (55 mmHg) with a modified Krebs-Ringer's solution equilibrated with 97% O2 and 3% CO2 at 37 degrees C. Heart rate, left ventricular pressure, CF, and effluent pH, pCO2, pO2, and NO generated current were monitored continuously on-line. Effluent was sampled for L-citrulline. Percent O2 extraction and O2 consumption were calculated. [NO] was quantitated with a sensitive amperometric sensor (sensitivity > or = 1 nmol/l approximately 3 pA) and a selective gas permeable membrane. RESULTS: The electrode was not sensitive to changes in solution pO2, flow, or pressure. The electrode was sensitive to pCO2 (-0.50 nmol/l/mmHg) and temperature (+24.5 nmol/l/degree C), so coronary effluent pCO2 was measured to compensate for a small decrease in pCO2 that occurred with an increase in coronary flow, and effluent temperature was rigidly controlled. Serotonin, bradykinin, and nitroprusside increased NO release along with CF, whereas nifedipine, butanedione monoxime, zaprinast, and bimakalim comparably increased CF but did not increase [NO] or NO release. Increases in CF (ml/g/min) and NO release (pmol/g/min), respectively, were 5.0 +/- 1 and 100 +/- 17 for 1 mumol/l serotonin, 7.5 +/- 1 and 148 +/- 18 for 100 nmol/l bradykinin, and 7.8 +/- 1 and 173 +/- 28 for 100 mumol/l nitroprusside. The increases in effluent NO by bradykinin were proportional to the increases in L-citrulline. Tetraethylammonium decreased CF, but did not change NO release, indomethacin changed neither CF nor NO release, and NG-nitro-L-arginine methyl ester (L-NAME) reduced CF by 2.6 +/- 1 ml/g/min and NO release by 25 +/- 8 pmol/g/min. An increase of CF of 8.0 +/- 0.3 ml/g/min, produced by increasing perfusion pressure from 25 to 90 mmHg, increased [NO] by 30 +/- 4 nmol/l; L-NAME but did not reduce the pressure-induced increase in CF, but reduced the increase in [NO] to 10 +/- 5 nmol/l. CONCLUSIONS: This study demonstrates in intact hearts real-time release of NO by several vasodilator drugs and by pressure-induced increases in flow (shear stress) and attenuation of these effects by L-NAME.     

Missed opportunities for immunisation at hospitals in the western Cape--a reappraisal

Immunisation practices were examined at 6 hospitals in the western Cape during the latter half of 1992 to determine whether these practices had improved subsequent to the February 1991 resolution of the Health Matters Committee (HMC) on immunisation in hospitals, and since a similar study was undertaken in 1990. Exit interviews were conducted with the escorts of all children aged 3-59 months who attended the study hospitals on the days designated for the study. In the second study, 88 of the 311 children studied (28.3%) were in need of immunisation on arrival, but only 12 of the 88 (13.6%) were immunised during the hospital visit. There was no evidence of an increase in requests to see children's Road-to-Health cards (37.1% compared with 35.2% previously). The incidence of missed opportunities for measles immunisation in children aged 6-59 months remained unacceptably high (51.4% compared with 63.7% previously, when a strict definition was used; and 15.7% compared with 18.1% previously, when a lenient definition was used). Health authorities at all levels need to take urgent action to address the problem of missed opportunities for immunisation at hospitals.     

Purification and cloning of PZR, a binding protein and putative physiological substrate of tyrosine phosphatase SHP-2

Overexpression of a catalytically inactive mutant of tyrosine phosphatase SHP-2 in 293 cells resulted in hyperphosphorylation of a glycoprotein specifically associated with the enzyme. The protein has been purified to near homogeneity. Based on the amino acid sequences of peptides obtained from the protein, a full-length cDNA was isolated. The cDNA encodes a protein with a single transmembrane segment and a signal sequence. The extracellular portion of the protein contains a single immunoglobulin-like domain displaying 46% sequence identity to that of myelin P0, a major structural protein of peripheral myelin. The intracellular segment of the protein shows no significant sequence identity to any known protein except for two immunoreceptor tyrosine-based inhibitory motifs. We name the protein PZR for protein zero related. Transfection of the PZR cDNA in Jurkat cells gave rise to a protein of expected molecular size. Stimulation of cells with pervanadate resulted in tyrosine phosphorylation of PZR and a near-stoichiometric association of PZR with SHP-2. Northern blotting analyses revealed that PZR is widely expressed in human tissues and is particularly abundant in heart, placenta, kidney, and pancreas. As a binding protein and a putative substrate of SHP-2, PZR protein may have an important role in cell signaling.     

Thio-sugars. IV: Design and synthesis of S-linked fucoside analogs as a new class of alpha-L-fucosidase inhibitors

alpha-1-Thio-L-fucose derivative 4 and 5 as new alpha-fucosidase inhibitors (K1 = 4.6, and 5.9 microM) have been synthesized in three steps by base catalyzed coupling with bromonitromethane followed by reduction of the nitro group with sodium borohydride/cobalt chloride complex and acetylation.     

Data-driven parameterization of polymer electrolyte membrane fuel cell models via simultaneous local linear structured state space identification

In order to mitigate the degradation and prolong the lifetime of polymer electrolyte membrane fuel cells, advanced, model-based control strategies are becoming indispensable. Thereby, the availability of accurate yet computationally efficient fuel cell models is of crucial importance. Associated with this is the need to efficiently parameterize a given model to a concise and cost-effective experimental data set. A challenging task due to the large number of unknown parameters and the resulting complex optimization problem. In this work, a parameterization scheme based on the simultaneous estimation of multiple structured state space models, obtained by analytic linearization of a candidate fuel cell stack model, is proposed. These local linear models have the advantage of high computational efficiency, regaining the desired flexibility required for the typically iterative task of model parameterization. Due to the analytic derivation of the local linear models, the relation to the original parameters of the non-linear model is retained. Furthermore, the local linear models enable a straight-forward parameter significance and identifiability analysis with respect to experimental data. The proposed method is demonstrated using experimental data from a 30 kW commercial polymer electrolyte membrane fuel cell stack.     

PID controller design for nonlinear systems represented by discrete-time local model networks

This paper deals with proportional–integral–derivative (PID) controller design for nonlinear systems represented by local model networks. The proposed method is based on the concept of parallel distributed compensators where the scheduling of the local model network is adopted for the PID parameters. The proposed design method for nonlinear PID controllers considers closed-loop stability by means of a Lyapunov stability criterion as well as closed-loop performance. All PID parameters are determined by a multi-objective genetic algorithm (multiGA), which handles the trade-off between stability and performance. A simulation example demonstrates the effectiveness of the proposed method.     

Biochemical and molecular changes at the cellular level in response to exposure to environmental estrogen-like chemicals

The pharmacokinetic and pharmacodynamic properties of nonpeptide angiotensin antagonists in humans are reviewed in this paper. Representatives of this new therapeutic class share common features: lipophilia, intermediate bioavailability, high affinity for plasma proteins and liver metabolism; some have active metabolites. Angiotensin II antagonists block the blood pressure response to exogenous angiotensin II in healthy volunteers, decrease baseline blood pressure in both normal and hypertensive patients, produce a marked rise in plasma renin activity and endogenous angiotensin II and increase renal blood flow without altering glomerular filtration rate. These effects are dose-dependent, but their time course varies between the drugs owing to pharmacokinetic and pharmacodynamic differences. Additionally, the extent of blood pressure reduction is dependent on physiological factors such as sodium and water balance. The characterisation of their pharmacokinetic-pharmacodynamic relationships deserves further refinement for designing optimal therapeutic regimens and proposing dosage adaptations in specific conditions.     

Modulation of cardiac sodium current by alpha1-stimulation and volatile anesthetics

BACKGROUND: Alpha1-adrenoceptor stimulation is known to produce electrophysiologic changes in cardiac tissues, which may involve modulations of the fast inward Na+ current (I(Na)). A direct prodysrhythmic alpha1-mediated interaction between catecholamines and halothane has been demonstrated, supporting the hypothesis that generation of halothane-epinephrine dysrhythmias may involve slowed conduction, leading to reentry. In this study, we examined the effects of a selective alpha1-adrenergic receptor agonist, methoxamine, on cardiac I(Na) in the absence and presence of equianesthetic concentrations of halothane and isoflurane in single ventricular myocytes from adult guinea pig hearts. METHODS: I(Na) was recorded using the standard whole-cell configuration of the patch-clamp technique. Voltage clamp protocols initiated from two different holding potentials (V(H)) were applied to examine state-dependent effects of methoxamine in the presence of anesthetics. Steady state activation and inactivation and recovery from inactivation were characterized using standard protocols. RESULTS: Methoxamine decreased I(Na) in a concentration- and voltage-dependent manner, being more potent at the depolarized V(H). Halothane and isoflurane interacted synergistically with methoxamine to suppress I(Na) near the physiologic cardiac resting potential of -80 mV. The effect of methoxamine with anesthetics appeared to be additive when using a V(H) of -110 mV, a potential where no Na+ channels are in the inactivated state. Methoxamine in the absence and presence of anesthetics significantly shifted the half maximal inactivation voltage in the hyperpolarizing direction but had no effect on steady-state activation. CONCLUSION: The present results show that methoxamine (alpha1-adrenergic stimulation) decreases cardiac Na+ current in a concentration- and voltage-dependent manner. Further, a form of synergistic interaction between methoxamine and inhalational anesthetics, halothane and isoflurane, was observed. This interaction appears to depend on the fraction of Na+ channels in the inactivated state. (Key words: Anesthetics, volatile: halothane; isoflurane; methoxamine. Patch clamp: whole-cell configuration; sodium current; ventricular guinea pig myocytes.)