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 after 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 placed on the surface of the left vastus medialis muscle. For measurement of regional microcirculatory blood flow a laser-Doppler flowmeter probe was placed on the contralateral muscle. An experimental sequence with normoxaemia (arterial PO2 12.5 kPa), followed by hypoxaemia (arterial PO2 3.9 kPa) and thereafter sustained hypoxaemia (arterial PO2 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 pressure (MAP) by 27%, capillary flow by 25%, muscle oxygen pressure by 32% and laser-Doppler flowmetry (LDF) flow by 24%. After the administration of ritanserin the mean arterial pressure was further reduced by 7%, whereas the capillary flow increased by 59% and the muscle oxygen pressure by 31%. The LDF flow remained unchanged. These results demonstrate that, in this animal model, a decrease in skeletal muscle capillary flow and oxygenation during hypoxaemia can be reversed by the administration of ritanserin, despite a further reduction in blood pressure.