Analysis of vasodilator responses to peroxynitrite in the hindlimb vascular bed of the cat

The free radical peroxynitrite (ONOO-) is formed in biological systems from the reaction of nitric oxide (NO) with superoxide (O2-) and can react with protein and nonprotein thiol groups to produce tissue injury. However, these pathologic actions of (ONOO-) may have been overemphasized, in that (ONOO-) has vasorelaxant properties through activation of soluble guanylate cyclase; inhibits leukocyte-endothelial cell interactions; and reduces ischemia-reperfusion injury in the heart, lung, and liver. It has been reported that tolerance develops to the vasodilator actions of (ONOO-) and that (ONOO-) impairs vascular function. However, little, if anything, is known about responses to (ONOO-) in the hindlimb circulation of the cat. To better understand the effects of (ONOO-) on responses to vasoactive agonists and the mechanism by which (ONOO-) induces vasodilation, the effects of short-term exposure to (ONOO-) were investigated under constant-flow conditions in the hindlimb vascular bed of the cat.In these studies, direct intraarterial injections of (ONOO-) produced dose-dependent decreases in hindquarters perfusion pressure. The vasodilator responses to (ONOO-) were rapid in onset, were short in duration, and could be repeated without exhibiting tachyphylaxis. Vasodilator responses to (ONOO-) were not changed in the presence of inhibitors of nitric-oxide synthase, cyclooxygenase, or K+-ATP (adenosine triphosphate-sensitive potassium) channels. Furthermore, responses to (ONOO-) were enhanced in duration by the type 5-cGMP (cyclic guanosine monophosphate) phosphodiesterase inhibitor zaprinast, whereas rolipram, a type 4-cGMP phosphodiesterase inhibitor, was without effect. Repeated administration of (ONOO-) had no significant effect on responses to vasoconstrictor or to vasodilator agents including acetylcholine. These results show that (ONOO-) has significant vasodilator activity in the hindlimb vascular bed of the cat and suggest that the response is mediated by a cGMP- dependent mechanism.The results of experiments with repeated injections of (ONOO-) indicate that (ONOO-) does not impair vasoconstrictor and endothelium-dependent or endothelium-independent vasodilator responses. Furthermore, tolerance did not develop with repeated short-term exposure to (ONOO-). Moreover, the results of experiments with inhibitors suggest that responses to (ONOO-) are not dependent on K-ATP (adenosine triphosphate-sensitive potassium) channel activation, increased NOS activity, or the formation of products in the cyclooxygenase pathway. The results of these studies are consistent with the hypothesis that (ONOO-) is rapidly converted in the hindlimb circulation to a substance that has the properties of an NO donor. These studies suggest that under physiologic conditions, the cytotoxic effects of (ONOO-) on a short-term basis may have been overemphasized.     

Visual identification of bacterially contaminated red cells

There have been increasing numbers of reports of transfusion-acquired Yersinia enterocolitica bacteremia (including several fatal cases). Fifteen units of whole blood were inoculated with various concentrations of Y. enterocolitica serotype 0:3 and processed into AS-3 preserved red cells (RBCs). Consistent growth of the organism was found at inoculum concentrations greater than or equal to 10 colony-forming units per mL. In all 13 units of RBCs that supported the growth of Y. enterocolitica, a darkening in color (due to hemolysis and a decrease in pO2) was observed in the bag. The attached sample segments, which were sealed from the main unit, remained sterile and did not darken. This color change was apparent in all the contaminated units by Day 35, which was 1.5 to 2 weeks after the bacteria were first detected in cultures of the blood. Hence, by comparison of the color of the segment tubing with that of the unit itself, units grossly contaminated with Y. enterocolitica can be identified prior to transfusion. Moreover, review of photographs on file at the Centers for Disease Control revealed this dramatic color change in 2 units of blood that caused transfusion-transmitted sepsis (Enterobacter agglomerans and an unidentified gram-negative bacillus, not Yersinia sp.), which demonstrated that the color change was not limited to Y. enterocolitica. This method of visual identification of contaminated units of blood could decrease the incidence of posttransfusion bacterial sepsis.     

Effects of cholinergic modulation on responses of neocortical neurons to fluctuating input

Neocortical neurons in vivo are spontaneously active and intracellular recordings have revealed strongly fluctuating membrane potentials arising from the irregular arrival of excitatory and inhibitory synaptic potentials. In addition to these rapid fluctuations, more slowly varying influences from diffuse activation of neuromodulatory systems alter the excitability of cortical neurons by modulating a variety of potassium conductances. In particular, acetylcholine, which effects learning and memory, reduces the slow alterhyperpolarization, which contributes to spike frequency adaptation. We used whole-cell patch-clamp recordings of pyramidal neurons in neocortical slices and computational simulations to show, first, that when fluctuating inputs were added to a constant current pulse, spike frequency adaptation was reduced as the amplitude of the fluctuations was increased. High- frequency, high-amplitude fluctuating inputs that resembled in vivo conditions exhibited only weak spike frequency adaptation. Second, bath application of carbachol, a cholinergic agonist, significantly increased the firing rate in response to a fluctuating input but minimally displaced the spike times by < 3 ms, comparable to the spike jitter observed when a visual stimulus is repeated under in vivo conditions. These results suggest that cholinergic modulation may preserve information encoded in precise spike timing, but not in interspike intervals, and that cholinergic mechanisms other than those involving adaptation may contribute significantly to cholinergic modulation of learning and memory.      

Detection and viability of tumor cells in peripheral blood stem cell collections from breast cancer patients using immunocytochemical and clonogenic assay techniques [see comments]

Although peripheral blood stem cell collections (PBSC) are thought to have less tumor involvement than bone marrow (BM), the incidence of circulating tumor cells in patients with breast cancer has not been widely investigated. We prospectively investigated the incidence and viability of tumor cell involvement in PBSC and BM collections from breast cancer patients undergoing high-dose chemotherapy/hematopoietic stem cell transplantation. Paired samples of PBSC and BM from 48 patients were analyzed using an immunocytochemical technique that detects one epithelial-derived tumor cell per 5 x 10(5) mononuclear cells. Immunostained tumor cells were detected in 9.8% (13/133) PBSC specimens from 9/48 (18.7%) patients and in 62.3% (38/61) BM specimens from 32/48 (66.7%) patients, a significantly higher rate than in PBSC (P < .005). The geometric mean concentration of tumor cells in contaminated PBSC specimens was 0.8/10(5) mononuclear cells (range 0.33 to 2.0/10(5)) compared with 22.9/10(5) mononuclear cells in BM (range 1 to 3,000/10(5), P < .0001). In culture experiments, clonogenic tumor colonies grew in 21/26 immunocytochemically positive specimens. No tumor colony growth was detected in 30/32 immunocytochemically negative specimens. Immunocytochemical detection of tumor involvement in BM and PBSC correlated significantly with in vitro clonogenic growth (P < .0001). We conclude that PBSC contain fewer tumor cells than paired BM specimens from patients with advanced breast cancer and that these tumor cells appear to be capable of clonogenic growth in vitro.     

Invasion of erythrocytes by Plasmodium falciparum malaria parasites: evidence for receptor heterogeneity and two receptors

Plasmodium falciparum malaria parasites with different capabilities of invading sialic acid-deficient erythrocytes were identified. Thai-2 parasites cultured in Tn erythrocytes invaded neuraminidase-treated and Tn erythrocytes twice as efficiently as Thai-2 parasites cultured in normal erythrocytes and seven to ten times more efficiently than a cloned line of Camp parasites cultured in normal erythrocytes. All three parasite lines required sialic acid for optimal invasion, but Thai-2 parasites cultured in Tn erythrocytes invaded neuraminidase- treated erythrocytes with 45% efficiency whereas Camp parasites invaded neuraminidase-treated erythrocytes with less than 10% efficiency. P falciparum malaria parasites probably possess two receptors: one that binds to a sialic acid-dependent ligand and another that binds to a sialic acid-independent ligand. Parasites may differ in the quantity or affinity of their receptors for the sialic acid-independent ligand.     

Increased expression of nestin in the major pelvic ganglion following cavernous nerve injury

In an effort to identify neuronal repair mechanisms of the major pelvic ganglion (MPG), we evaluated changes in the expression of nestin, an intermediate filament protein and neural stem cell marker following cavernous nerve crush injury (CNI). We utilized two groups of Sprague Dawley rats: (i) sham and (ii) bilateral CNI. Erectile responses to cavernous nerve stimulation (CNS) were determined at 48?h in a subset of rats. The MPG was isolated and removed at 48?h after CNI, and nestin immunolocalization, protein levels and RNA expression were evaluated. At 48?h, erectile responses to CNS in CNI rats were substantially reduced (P<0.05; ～70% decrease in intracavernous pressure/mean arterial pressure) compared with sham surgery controls. This coincided with a dramatic 10-fold increase (P<0.05) in nestin messenger RNA expression and protein levels in the MPG of rats with CNI. Immunoflourescence microscopy demonstrated that nestin upregulation after CNI occurred within the ganglion cell bodies and nerve fibers of the MPG. In conclusion, CNI induces nestin in the MPG. These data suggest that nestin may be involved in the regenerative process of the cavernous nerve following crush injury.     

Medical management of ischemic stuttering priapism: a contemporary review of the literature

Priapism is defined as a prolonged and persistent erection of the penis without sexual stimulation. This is a poorly understood disease process with little information on the pathophysiology of this erectile disorder. Complications from this disorder are devastating due to the irreversible erectile damage and resultant erectile dysfunction (ED). Stuttering priapism, though relatively rare, affects a high prevalence of men with sickle-cell disease (SCD) and presents a challenging problem with guidelines for treatment lacking or resulting in permanent ED. The mechanisms involved in the development of priapism in this cohort are poorly characterized; therefore, medical management of priapism represents a therapeutic challenge to urologists. Additional research is warranted, so we can effectively target treatments for these patients with prevention as the goal. This review gives an introduction to stuttering priapism and its clinical significance, specifically with regards to the patient with SCD. Additionally, the proposed mechanisms behind its pathophysiology and a summary of the current and future targets for medical management are discussed.