The prostacyclin receptor (IP), a G protein-coupled receptor, mediates the actions of the prostanoid prostacyclin and its mimetics. IPs from a number of species each contain identically conserved putative isoprenylation CAAX motifs, each with the sequence CSLC. Prostacyclin (prostaglandin (PG)1 I 2 ) is a labile metabolite of arachidonic acid, which is synthesized by the sequential actions of PGH 2 endoperoxide synthases 1 and 2 and prostacyclin synthase (1). The actions of prostacyclin generally counteract those of thromboxane A 2 , and thus the relative level of these two prostanoids in the circulation are important in the local control of vascular tone and platelet aggregation (2, 3). The main physiologic roles of thromboxane A 2 and prostacyclin are their contribution to the maintenance of vascular hemostasis: thromboxane A 2 , synthesized primarily by platelets, induces platelet shape change and aggregation and constriction of bronchial and vascular smooth muscle, whereas prostacyclin, mainly synthesized by the vascular endothelium, is a potent inhibitor of platelet aggregation and induces vasodilation (4 -7). Moreover, prostacyclin has been reported to confer a cytoprotective effect against tissue injury in acute myocardial ischemia or following hypoxic exposure of vascular endothelial cells (8). Imbalances in thromboxane A 2 or prostacyclin have been reported to be a major contributing factor in the development of a number of cardiovascular disorders including thrombosis, myocardial infarction, unstable angina, stroke, and atherosclerosis (9 -13). In addition to its central role in the cardiovascular system, prostacyclin may be important in the regulation of renal blood flow (14); it also acts as a negative feedback regulator of histamine secretion from mast cells (15) and acts as a lipolytic agent, antagonizing the antilipolytic effect of PGE 2 , in adipocytes (16).The actions of prostacyclin are mediated via interaction with a specific cell surface receptor, termed the prostacyclin receptor or IP (17). The major intracellular signaling pathway used is stimulation of adenylyl cyclase leading to increases in intracellular cAMP (18,19), a pathway thought to be relevant to inhibition of platelet aggregation and vascular smooth muscle relaxation (3). However, recent evidence indicates that IP agonists may couple to multiple signaling pathways including activation and inhibition of adenylyl cyclase, via G s and G i , respectively, stimulation of phosphoinositide metabolism, and changes in [Ca 2ϩ ] i concentrations (20,21). Evidence also exists to indicate that iloprost, a stable carbacyclin analogue of prostacyclin, can stimulate opening of ATP sensitive K ϩ channels resulting in hyperpolarization and relaxation of canine carotid artery (22).Molecular cloning of the human (23, 24), mouse (25), and rat

Our objective was to determine the effects of organic acids and pH on the rate at which selected strains of Escherichia coli O157:H7 die in acid solutions representative of acidified pickle products (pH < 4.6). We used gluconic acid/sodium gluconate (pKa = 3.7) as a noninhibitory buffer to maintain pH at selected values in the absence of other organic acids. This was possible because we found that the inhibitory effects of this acid on E. coli strains at pH 3.1 were independent of acid concentration over a range of 2 to 200 mM. By this method, the lethal effects of acetic acid solutions (100 to 400 mM) at selected pH values between 3.1 and 4.1 were compared with the effects of pH alone (as determined using gluconate buffer). We found D-values were two- to fourfold lower with acetic acid compared with the effect of pH alone for simulated pickle brines in this pH range. Glutamic acid, an amino acid that is known to enhance acid resistance in E. coli and is a component of pickle brines, protected the E. coli strains from the specific effects of acetic acid.

Fractures of the tibia and femoral diaphysis are commonly repaired by intra-medullary (IM) nailing. Currently IM nails are available in either electropolished stainless steel (SS) or in Titanium-Aluminium-Niobium (TAN). After healing, removal of the nails still is common but removal of TAN IM nails often has complications whereas SS IM nails of the same design are less often associated with problems. We believe the differences in removal are due to the ability of TAN to promote strong bone on-growth. We have previously shown in vivo that polishing cortical screws reduces removal torque and the percentage of bone-implant contact. Therefore, we postulate that bony on-growth onto IM nails can be reduced by means of surface polishing, for ease of removal. Here we aim to compare the pull-out forces for removal of standard TAN (TAN-S) compared to experimental paste polished TAN (TAN-PP) IM nails from a bilateral non-fracture sheep tibia model after 12 months implantation. Histological analysis was also performed to assess tissue on-growth to the nails. We show that polishing significantly reduces (p=0.05) the extraction force required for TAN IM nail removal. This effect in part is attributable to the distinct tissue-material reaction produced. For TAN-S nails direct bone contact was observed while for TAN-PP nails a fibrous tissue interface was noted. Since TAN is preferred over SS for IM nailing due to superior biocompatibility and mechanical properties, we believe these findings could be used to recommend changes to current surface technologies of intramedullary nails to reduce complications seen with nail removal especially in rapidly growing bone in children.

The cardiotonic drug milrinone (l,6-dihydro-2-methyl-6-oxo-[3,4'-bipyridine]-5-carbonitrile) is superior to its analogue amrinone (S-amino-iS^'-bipyridinl-etlffl-one) by virtue of its greater potency and reduced side effect profile. We confirmed initial reports on the potencies of milrinone and amrinone and found that after intravenous administration to phenobarbital anesthetized dogs, the drugs had cumulative inotropic ED50's of 37 and 1891 jug/kg, respectively; relative effects on heart rate and blood pressure were comparable. There are two structural differences between amrinone and milrinone: (1) milrinone has a pyridone 2-methyl substituent and (2) the pyridone 5-amino substituent of amrinone is replaced with a nitrile in milrinone. We confirmed structure-activity studies that indicated that the 2-methyl substituent appears to be primarily responsible for the dramatic difference in the potencies of amrinone and milrinone. A plausible explanation for the effect of the methyl substituent is an altered molecular topology resulting from its steric interaction with the 3',5'-hydrogen atoms. Consequently, we probed the three-dimensional structures of these two compounds by X-ray crystallography. The dihedral angle between the planes formed by the two aromatic rings of amrinone was 1.3°. In marked contrast, the corresponding angle for milrinone was 52.2°. Moreover, 'H NMR studies revealed conformational differences in solution. Whereas the 2-methyl substituent undoubtedly produces some electronic and hydrophobic perturbations in the bipyridine cardiotonic series, the most significant effect, from a global viewpoint, is the altered molecular topology.