EFFECT OF HYPOXIC HYPOXIA AND RITANSERIN ON CAPILLARY-FLOW AND OXYGENATION IN RABBIT SKELETAL-MUSCLE

This study examined capillary flow and oxygenation in rabbit skeletal muscle during hypoxic hypoxia (inspired oxygen fraction = 0.10) and af ter administration of ritanserin (highly selective 5-Hydroxytryptamine -2-receptor antagonist). Capillary flow (hydrogen clearance) or oxygen pressure was measured with a multiwire micro-electrode which was plac ed on the surface of the left vastus medialis muscle. For measurement of regional microcirculatory blood flow a laser-Doppler flowmeter prob e was placed on the contralateral muscle. An experimental sequence wit h normoxaemia (arterial Po-2 12.5 kPa), followed by hypoxaemia (arteri al Po-2 3.9 kPa) and thereafter sustained hypoxaemia (arterial Po-2 4. 0 kPa) during which ritanserin (0.035 mg kg(-1) i.v.) was administered , was used. During hypoxaemia a decrease was seen in mean arterial pre ssure (MAP) by 27%, capillary flow by 25%, muscle oxygen pressure by 3 2% and laser-Doppler flowmetry (LDF) flow by 24%. After the administra tion of ritanserin the mean arterial pressure was further reduced by 7 %, whereas the capillary flow increased by 59% and the muscle oxygen p ressure by 31%. The LDF flow remained unchanged. These results demonst rate that, in this animal model, a decrease in skeletal muscle capilla ry flow and oxygenation during hypoxaemia can be reversed by the admin istration of ritanserin, despite a further reduction in blood pressure .