Finally, study 5 addressed the question of whether a vasoconstrictor effect Zotarolimus(ABT-578)? of cilansetron in the colon might be provoked under conditions of mild colitis, given that IBS can be associated with low-grade inflammation in the colon (Bercik et al., 2005; Spiller, 2007; De Giorgio and Barbara, 2008). A preliminary account of some of the findings obtained in study 1 has been published in abstract form (Holzer et al., 2003b). Methods Animals All animal care and experimental procedures complied with the 1986 Directive of the European Communities Council and were approved by an ethics committee at the Federal Ministry of Science and Research of the Republic of Austria. The experiments were conducted in female Sprague Dawley rats (body weight: 180�C230 g) (Division of Laboratory Animal Science and Genetics, Department of Biomedical Research, Medical University of Vienna, Himberg, Austria).

Unless stated otherwise, the rats were deprived of food for 20 h before blood flow measurement, while tap water was available ad libitum. The animals were anaesthetised with phenobarbital (230 mg?kg?1 injected i.p.) between 7.00 and 8.00 am. After the loss of the righting reflex, they were placed on a thermostated table and, when surgical anaesthesia was achieved, fitted with a tracheal cannula to facilitate spontaneous respiration and to allow for the administration of hydrogen gas. A cannula in a jugular vein was used for continuous infusion of saline (1.5 mL?h?1) for dehydration of the animals to be avoided and for the i.v. administration of drugs.

Induction of mild colitis Dextran sulphate sodium (DSS, MP Biochemicals, Illkirch, France) was added to the drinking water at a concentration of 3% (w/v) for 7 days. The control animals received normal tap water. The DSS-containing drinking water was made fresh every day. For protocol consistency, the drinking bottles containing normal tap water were also renewed daily. Measurement of blood pressure and heart rate (HR) Arterial blood pressure was recorded from a cannula in a common carotid artery, and the blood pressure signal was sampled at a rate of 1 kHz and fed into a personal computer, which calculated mean arterial blood pressure (MAP) and HR online (Heinemann et al., 1998). Measurement of CBF with the hydrogen gas clearance technique The hydrogen clearance technique has been established to measure microcirculatory blood flow in the digestive tract and other tissues (Leung et al.

, 1984; Livingston et al., 1989; Brefeldin_A Holzer et al., 1991). Based on the washout of inhaled hydrogen, which clears essentially with a single passage of blood through the lungs, the hydrogen clearance method has the advantage of providing absolute estimates of microcirculatory blood flow at the position of a platinum electrode, which catalyses the dissociation of molecular hydrogen into protons and electrons (Guth and Leung, 1987).