INTRODUCTION5-Hydroxytryptamine-3 (5-HT 3 ) receptor antagonists have been found to be potent anti-emetic drugs for chemotherapy-or radiation-induced nausea and vomiting.1±4 So far, four selective 5-HT 3 receptor antagonists (ondansetron, formerly GR 38032F; tropisetron, formerly ICS 205-930; granisetron, formerly BRL 43694; and dolasetron, formerly MDL 73147EF), with comparable clinical ef®cacy, are commercially available for these indications. The mechanism of the anti-emetic effect is not fully understood. 4 It is ascribed in part to central effects on the 5-HT 3 receptors in the area postrema, where the chemoreceptor trigger zone is located, with neural connections to the vomiting centre, but also in part to the peripheral action on 5-HT 3 receptors of afferent vagal ®bres in the stomach and small bowel.4±8 It has been suggested that the anti-emetic effect of 5-HT 3 may not only be due to suppression of nausea and the vomiting re¯ex, but also to direct or indirect effects on gastric motility. Although evidence for this latter assumption has been found in several animal SUMMARY Background: In previous studies, tropisetron has been shown to accelerate gastric emptying of a solid meal. However, it is uncertain whether other speci®c 5-hydroxytryptamine-3 receptor antagonists, such as ondansetron, also have a gastroprokinetic effect in humans. Aim: To evaluate the effect of ondansetron on gastric half-emptying time (T 1/2 ) of a solid meal, gastric myoelectrical activity and hormone levels in 14 healthy volunteers. Methods: In a placebo-controlled, randomized, crossover study, we investigated the effects of ondansetron (8 mg intravenously) on the gastric emptying of solids (by scintigraphy), gastric myoelectrical activity (by

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There is considerable evidence that opioid mechanisms are involved in the mediation of pyloric motor responses that in turn regulate gastric emptying. The purpose of this randomized, placebo-controlled crossover study was to investigate the effect of naloxone on gastric emptying of a solid meal, gastric myoelectrical activity and the postprandial release of gastrointestinal peptides and neuropeptides in 20 healthy volunteers. Naloxone was administered as an intravenous bolus, followed by continuous infusion according to an intravenous dosing nomogram. Gastric emptying time was evaluated by scintigraphy and gastric myoelectrical activity was evaluated by cutaneous electrogastrography. Naloxone did not significantly alter gastric half-emptying time and postprandial dominant gastric electrical frequency compared with placebo. It also did not significantly change the plasma levels of several peptide hormones with the exception of neuropeptide Y, which was significantly increased (P = 0.001). In conclusion, in doses that influence human intestinal motility, naloxone had no effect on gastric motility and release of several peptide hormones in healthy male volunteers. The importance of the isolated increased neuropeptide Y plasma level needs further investigation.

There is a recent need to study glucose metabolism of the heart in ischemic, as well as in "hibernating or stunned" myocardium, and compare it with that in perfusion studies. In non-positron emission tomography centers, positron imaging is possible with a standard Anger-type camera if proper collimation and adequate shielding of the camera crystal can be achieved. For the study with fast-decaying isotopes, seven-pinhole tomography (7PHT), a limited-angle method designed for transaxial tomography of the left ventricle using a nonrotating camera, is well suited, because projections are acquired simultaneously. Individual adjustment (patient supine) of the camera's view axis (CAx) with the left ventricular axis (LVAx) gives excellent results: sensitivity for CHD 82%, specificity 72% in a prospective 201TI study (48 patients, x-ray coronarography as reference). Good alignment of CAx with LVAx is also achieved with the patient prone in LAO in a hammock above the camera surface. In this setting additional lead shielding of the camera is possible using a table reinforced with 5 cm of lead with a central hole for the 7PH-collimator, which has a special lead inlay. This allows utilization of the 511 KeV emitter 18F-FDG, which with a half-life of 109 minutes, can be transported a reasonable distance from the production site. System sensitivity and resolution for 18F was found comparable to 201Tl, 99mTc, and 123I using a phantom. First clinical examinations after 201Tl stress/redistribution studies showed increased 18F-FDG uptake in ischemic heart segments, as well as in "hibernating" nonperfused or "stunned" myocardium.

Gastric emptying of a test meal labelled with ⁹⁹Tc^m-sulphur colloid has been studied in 9 healthy volunteers using a gamma-camera with on-line computer. Mean transit time (MTT) was determined by fitting the time-activity histogram to a gamma-variate, and the half-time of emptying (T½) was calculated by exponential fitting of the down-slope of the time-activity curve. MTT showed a smaller coefficient of variance than T½ This result suggests that MTT may be a more suitable parameter for definition of normal values and for the separation of normal from pathological patterns of emptying.

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