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The evaluation of lower gastrointestinal bleeding (LGIB) often involves the collaborative efforts of the gastroenterologist, radiologist, and surgeon. Efforts to localize the acute LGIB have traditionally involved colonoscopy, technetium-labeled red blood cell (RBC) scintigraphy, angiography, or a combination of these modalities. The sensitivity of each method of diagnosis is limited, with the most common cause of a negative study the spontaneous cessation of hemorrhage. Other technical factors include vasospasm, lack of adequate contrast volume or exposure time, a venous bleeding source, and a large surface bleeding area. We report the use of multidetector computed tomography (MDCT), or CT-angiography (CT-A), in the initial evaluation of LGIB, and speculate on the incorporation of this technique into a diagnostic algorithm to treat LGIB. MDCT may offer a very sensitive means to evaluate the source of acute LGIB, while avoiding some of the morbidity and intense resource use of contrast angiography, and may provide unique morphologic information regarding the type of pathology. Screening with the more rapid and available MDCT, followed by either directed therapeutic angiography or surgical management, may represent a reasonable algorithm for the early evaluation and management of acute LGIB in which an active bleeding source is strongly suspected.

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Salvage surgery is an essential method in the armamentarium of the surgeon caring for the severely injured patient. The patient in unstable condition with multiple abdominal injuries is a challenge, even to the most experienced trauma surgeon. The first priority should be to control major vascular injuries and other sources of bleeding that are immediately life-threatening. Often after massive blood loss, the deadly triad of hypothermia, acidosis, and coagulopathy is present. Additional time in the operating room often worsens these physiologic parameters and patient outcome. Once surgically correctable bleeding has been addressed, such patients are best served by cessation of the operation, packing of the abdomen, and transfer to the intensive care unit. Resuscitative steps should then be taken. Once the physiologic derangement has been corrected, the patient can undergo definitive operative procedures.

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The class of diterpenoids with a 14-carbon cembrane ring, the cembranoids, includes both competitive and noncompetitive inhibitors of the nicotinic acetylcholine receptor (AChR). All 20 coelenterate-derived cembranoids studied in this report inhibited [piperidyl-3,4-3H]-phencyclidine ([3H]-PCP) binding to its high-affinity site on the electric organ AChR, with IC50s ranging from 0.9 microM for methylpseudoplexaurate to 372 microM for lophotoxin. Inhibition was complete with all cembranoids but lophotoxin and most Hill coefficients were close to 1. Methylpseudoplexaurate and [3H]-PCP binding was competitive. Methylpseudoplexaurate and the fourth most potent cembranoid, eunicin, competed with each other for [3H]-PCP displacement, indicating that there exist one or more cembranoid sites on the AChR. Cembranoid affinity for the AChR correlated with hydrophobicity, but was also dependent on other features. Methylpseudoplexaurate and n-octanol also competed with each other for [3H]-PCP displacement, indicating that the cembranoid site is linked to the n-octanol site on the AChR. Unlike lophotoxin, the five cembranoids tested did not inhibit [125I]Tyr54-alpha-bungarotoxin binding to the AChR agonist sites. All seven cembranoids tested on oocyte-expressed electric organ AChR reversibly blocked acetylcholine-induced currents, although the inhibitor concentration curves were shallow and the inhibition was incomplete.

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The two agonist-binding domains of the electric organ nicotinic acetylcholine receptor are located at the alphagamma and alphadelta subunit interfaces. alpha-Conotoxins GI and MI are competitive antagonists of this receptor and, like d-tubocurarine, bind to the alphagamma site with much higher affinity than to the alphadelta site. In the present study, alpha-conotoxin SIA also displayed strong affinity for the alphagamma site but no measurable affinity for the alphadelta site, thus showing even greater site-selectivity. In contrast, alpha-conotoxin SI does not distinguish between the two agonist sites, although its sequence differs from that of GI at only three positions: GI, ECCNPACGRHYSC; SI, ICCNPACGPKYSC. Analogues of SI and GI modified at these three positions were studied to identify the determinants of GI's alphagamma selectivity. Substituting arginine for proline at position 9 produced peptides which displayed "GI-like" selectivity for the alphagamma site. Conversely, substituting proline for arginine at position 9 resulted in "SI-like" nonselective inhibitors. An SI analogue having alanine in place of proline 9 did not distinguish between the two agonist sites and displayed about the same affinity as SI, indicating the importance of the arginyl cation. Interchanging the residues at position 1 or at position 10 influenced the affinity for the receptor but did not measurably change peptide selectivity. Therefore, of the three sequence differences in SI and GI, the variation at position 9, proline and arginine, respectively, is sufficient to account for GI's selective high-affinity binding to the alphagamma site on the electric organ acetylcholine receptor.

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