Apyrase administration prolongs discordant xenograft survival.

Platelet thrombi and vascular inflammation are prominent features of discordant xenograft rejection. The purinergic nucleotides ATP and ADP, which are secreted from platelets and released by injured endothelial cells (EC), are important mediators of these reactions. Quiescent EC express the ectoenzyme ATP-diphosphohydrolase (ATPDase; an apyrase), which exerts an important thromboregulatory function by hydrolyzing both ATP and ADP. We have shown that ATPDase activity is rapidly lost from the surface of the EC following ischemia-reperfusion injury and during xenograft rejection. The aim of this study was to supplement ATPDase activity within xenografts by infusion of soluble apyrases, and thereby validate the importance of local ATPDase activity in the modulation of xenograft rejection. Lewis rats underwent heterotopic cardiac xenografting from guinea pigs and apyrase was administered intravenously (200 U/kg) as a single dose to evaluate effects on hyperacute rejection (HAR). This initial dose was followed by a continuous apyrase infusion (8.0 U/kg/hr) directly into the graft aorta in combination with systemic cobra venom factor (CVF) administration to deplete complement when delayed xenograft rejection (DXR) was studied. Functional apyrase levels in vivo were assessed by the capacity of blood samples taken at the time of surgery and rejection to inhibit platelet aggregation in vitro. Apyrase administration significantly prolonged graft survival in HAR and DXR. Functional assays showed inhibition of platelet aggregation suggesting effective systemic antiaggregatory effects of the administered apyrases. Histologic studies showed that apyrase administration abrogated local platelet aggregation and activation in HAR and DXR. Our data demonstrate that local administration of apyrase prolonged discordant xenograft survival. These observations emphasize the potential importance of purinergic mediators in platelet activation during xenograft rejection.

Phorbol-12,13-dibutyrate and pinacidil cardioplegia. Novel forms of myoprotection.

BACKGROUND: Activation of either protein kinase C or the ATP-sensitive potassium channel has been shown to induce the preconditioning response. METHODS AND RESULTS: To investigate whether preconditioning activation adjuvant to hypothermic blood cardioplegia enhances postischemic contractile recovery, 23 adult (0.5 to 1.0 year old) sheep were randomized to receive cardioplegia based on the hyperpolarizing ATP-sensitive potassium channel opener pinacidil, the protein kinase C activator 4 beta-phorbol-12, 13-dibutyrate (PDBu), or standard potassium-magnesium (K1/Mg2+). All groups underwent 60 minutes of 10 degrees C antegrade intermittent blood cardioplegia and 30 minutes of reperfusion. Mechanics were assessed on modified right heart bypass by the preload recruitable stroke work relation and the end-systolic pressure-volume relation. Diastolic function was modeled by the exponential time constant of isovolumic left ventricular pressure decay (Tau) and the "stiffness" coefficient (beta) of the end-diastolic pressure volume relation. Recovery rhythm was defined by the first electrical activity seen during reperfusion. Cardioplegic arrest and preconditioning induced by pinacidil provided superior recovery of contractile function compared with PDBu (100% versus 57% recovery, P < .05) or K+/Mg+ (100% versus 56% recovery, P < .05). Active (Tau) and passive (beta) diastolic function was preserved by all three arrest modalities. Hearts treated with pinacidil demonstrated a rapid recovery of a coordinated contraction pattern, which was offset by a reperfusion tachycardia, whereas PDBu arrest was associated with ventricular fibrillation on reperfusion. CONCLUSIONS: Preconditioning during cardioplegic arrest is agent specific, feasible at cold temperatures, and may be superior to the use of standard K+/Mg2+ cardioplegia.

31P-NMR studies on an animal model of human defective muscle glycolysis.

Sequential metabolic changes in leg muscles of a model of defective muscle glycolysis that was produced by intraaortic injection of sodium iodoacetate were observed by in vivo 31P-NMR spectroscopy with a surface coil. Spectra obtained from iodoacetate-treated muscles presenting exercise-induced cramp showed decreased levels of phosphocreatinine (PCr) and adenosine triphosphate (ATP) and an accumulation of sugar phosphate. The chemical shift of inorganic phosphate (Pi) resonance, which reflects the intracellular pH of the contracted muscles, showed a milder shift to the acidic condition than those of controls. In vivo 31P-NMR study showed dynamic information on the muscle energetics under defective glycolytic conditions.

Topographical distribution of gamma-aminobutyric acid within the cat thalamus in relation to the basal ganglia, as determined by mass fragmentometry.

Chemical ionization mass spectrometry was introduced for the assay of GABA in the cat brain. The method is quite simple, sensitive, and specific for quantitative analysis. Study of the regional distribution of the GABA content within the thalamus disclosed that the ventromedial nucleus (VM) of the thalamus had a high concentration of GABA. The VM receives the afferent projection from the zona reticulata of the substantia nigra. The result, together with the results obtained by physiological as well as pharmacological studies, supports the hypothesis that the transmitter substance of the nigrothalamic pathway is GABA.