To investigate the effect on the sleep EEG, a 1-mg oral dose of SR 46349B, a novel 5-HTThe pivotal role of serotonin (5-hydroxytryptamine, 5-HT) in sleep regulation has been the mainstay of the monoamine theory of sleep (Jouvet 1972). Although the views about the functions of this neurotransmitter have evolved, there is little doubt about its involvement in sleep mechanisms (McCormick 1992). Serotonergic neurons of the nucleus raphe dorsalis are most active during wakefulness and have been proposed to participate in the build-up of sleep propensity (Adrien 1995). Animal studies revealed that these neurons decrease firing upon transition from wakefulness to nonREM sleep (NREMS), and become quiescent during REM sleep (REMS). Thus, deactivation of the serotonergic system may facilitate the production of NREMS and REMS (Adrien 1995). One of the complexities in accounting for the actions of 5-HT is the large number of different receptors and receptor subtypes. 5-HT receptors are classified into four distinct classes, comprising seven fully characterized functional receptor subtypes and several recombinant receptors (Hoyer and Martin 1996). While the involvement of three main classes (i.e., 5-HT 1 , 5-HT 2 , and 5-HT 3 receptors) in the regulation of sleep and wakefulness has been studied, it is the postsynaptic 5-HT 1A receptor that seems to mediate the inhibition of REMS and the promotion of wakefulness, whereas activation of the 5-HT 2 receptor may exert a tonic inhibition of slow wave sleep (SWS) (see Adrien 1995 for review). In relation to sleep homeostasis, the latter is of particular interest because 5-HT 2 antagonists were shown to increase the amount of SWS and to enhance EEG slow-

Background: A modified 13 C-mixed triglyceride breath test ( 13 C -MTGT) detects moderate pancreatic exocrine insufficiency noninvasively and reliably, but it requires prolonged breath sampling (6 hours (hr)). Objective: We aimed to investigate whether 13 C -MTGT can be abbreviated, to optimize clinical usability. Methods: We analyzed the 13 C-MTGT of 200 consecutive patients, retrospectively. Cumulative 1-5 hr 13 C-exhalation values were compared with the standard parameter (6-hr cumulative 13 C-exhalation). We determined the sensitivity and specificity of shortened breath sampling periods, by comparison with the normal values from 10 healthy volunteers, whom also underwent a secretin test to quantitate pancreatic secretion. Moreover, we evaluated the influence of gastric emptying (GE), using a 13 C-octanoic acid breath test in a subset (N ¼ 117). Results: The 1-5 hr cumulative 13 C-exhalation tests correlated highly and significantly with the standard parameter (p < 0.0001). Sensitivity for detection of impaired lipolysis was high (!77%), but the specificity was low (!38%) for the early measurements. Both parameters were high after 4 hrs (88% and 94%, respectively) and 5 hrs (98% and 91%, respectively). Multivariate linear correlation analysis confirmed that GE strongly influenced early postprandial 13 C-exhalation during the 13 C-MTGT. Conclusion: Shortening of the 13 C -MTGT from 6 to 4 hrs of duration was associated with similar diagnostic accuracy, yet increased clinical usability. The influence of GE on early postprandial results of the 13 C-MTGT precluded further abbreviation of the test.

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