This fractional concentration of oxygen was maintained at this level for 60 seconds before an electric fan located at one side of the cage allowed a gradual return over 60 seconds to 20%-21% of oxygen for 60 seconds (Fig. 1). Regular checks of chamber oxygen concentrations during the experiment were made using an oxygen sensor (VMX300, Viamed, UK) PS-341 cost and were registered through an amplifier and recorded on a computer data acquisition system (ADInstruments, Mountain View, LA). For sham exposure (handled controls [HC]), rats were kept in an identical plastic cage placed side by side. The inflow gas was always room air, but the

solenoid switches, fan, and inlets reproduced the noise and airflow disturbances of the CIH protocol. Rats in both groups were housed

six per cage in accordance with space recommendations in the National Institutes of Health Guide for the Care and Use of Laboratory Animals (NIH Pub. No. 85-23, Revised 1985). The temperature and the relative humidity of the chambers were maintained at 21%-24°C and between 30% and 70%, respectively. At the end of the 12-hour treatment period, animals were transferred to their standard cages in a separate area and housed under MK-1775 concentration room air conditions for the remainder of the day in an animal care facility at the University of La Laguna. All protocols were approved by the Animal Care and Use Committee. Hematocrit was evaluated in control (n = 46) and CCl4-induced advanced cirrhotic rats (n = 14) to confirm the effect of CIH. The blood samples (1-2 mL) were withdrawn from the tail, placed in microcapillary tubes, and spun in a microcentrifuge (MPW-250e, Med. Instruments, Warsaw, Poland) for hematocrit measurement. At the end of the intermittent hypoxia exposure protocol, rats were anesthetized as mentioned previously. First, a catheter was inserted

in the carotid artery to monitor blood pressure (mean arterial pressure [MAP]; mm Hg) and heart rate (beats per minute, bpm), and into the portal vein through an ileocolic vein to measure portal pressure (mm Hg). The catheter was connected to a Power Lab (4SP) linked to a computer using Chart version 5.5.6 for Windows software (ADInstruments) and, after a period of 10 minutes Quisqualic acid of stabilization, recordings were performed with pressure transducers. In a supplementary group of cirrhotic rats, after baseline measurements following the stabilization period, HC and CIH rats underwent volume expansion with incremental doses (1-8 mL/kg, every 2 minutes) of hydroxyethyl starch 6% (Voluven 6% 130/0.4, Fresenius Kabi, Barcelona, Spain)16 via a femoral vein catheter. A flow-controlled perfusion system was used in this study. The system has been described elsewhere17 (see Supporting Information for details).