Local application of adenosine induces an increase of capillary diameter in skeletal muscle of anesthetized rabbits

The effects of locally applied adenosine (ADO) and/or femoral artery pressure reduction (induced by complete aorta occlusion) on capillary diameter were investigated in the tenuissimus muscle of anesthetized rabbits. Capillaries were visualized by means of intravital video microscopy. Diameters were measured using an image shearing device. During control femoral artery pressure (median: 83 mm Hg) and without ADO, median capillary diameter was 4.3 mu m (range: 3.2-5.3 mu m; 27 capillaries in 7 animals). Complete aorta occlusion (median femoral artery pressure: 18 mm Hg) resulted in a reduction of capillary diameter to 3.9 mu m (2.7-4.7 mu m; p < 0.0001). Subsequent reactive hyperemia resulted in an increase in diameter to 5.2 mu m (3.7-6.0 mu m; p < 0.0001). Locally applied ADO (10(-4) M) probably led to complete vasodilation of the arterioles, because their diameters did not further increase during reactive hyperemia after complete occlusion. ADO (10(-4) M) induced an increase of control capillary diameter to 5.5 mu m (4.1-6.4 mu m; median relative increase: 27%; p < 0.0001), resulting in a decrease of capillary resistance by 61%. In the presence of ADO, aorta occlusion resulted in a capillary diameter decrease to 4.7 mu m (3.4-6.1 mu m; p < 0.0001). Subsequent reactive hyperemia resulted in an increase to maximally 5.6 mu m (4.3-6.4 mu m; p < 0.0001). This diameter was approximately the same as the control diameter during ADO. During occlusion in the presence of ADO, capillary diameter was significantly larger (11%; p < 0.0001) than during control without ADO. The capillary diameter changes induced by the various interventions were mainly passive, i.e., proportional to capillary transmural pressure changes. However, capillary diameter was larger during aorta occlusion in the presence of ADO than during control femoral artery pressures without ADO, even though capillary pressure was probably higher in the latter case. It is proposed that the prolonged increase in transmural capillary pressure due to ADO may induce changes in capillary wall configuration, leading to larger diameters.