Adaptation of flow-induced dilation of arterioles to daily exercise

We aimed to test the hypothesis that daily exercise elicits an adaptation of blood flow/shear stress-induced dilation of arterioles. To this end we investigated the responses of isolated, pressurized arterioles of mesentery (MES) and plantaris (PL) skeletal muscle of sedentary (SED) and exercised (EX) rats to increases in perfusate flow (PF, range 0-30 microl/min). Rats were run on a treadmill, once daily for 3 to 4 weeks (with gradually increasing intensity up to 40 min at 28 m/min; a total of 15-19 sessions on the treadmill). The passive diameters of arterioles (obtained in Ca2+-free solution) were similar ( approximately 140 microm) but the pressure-induced active diameter (at 80 mmHg) of skeletal muscle arterioles was significantly smaller than that of mesenteric arterioles. The basal diameter of MES arterioles of SED and EX rats was: 83.5 +/- 3.6 and 83.9 +/- 2.9 microm, respectively; increases in PF increased the diameter of SED and EX arterioles to a similar degree by 33.2 +/- 4. 7 and 31.9 +/- 6.1 microm, respectively). The diameters of PL muscle arterioles of SED and EX rats were 62.1 +/- 6.2 and 68.0 +/- 5.5 microm. In contrast to arterioles of MES, the highest PF increased the diameters of arterioles of PL muscle from EX rats to a significantly greater extent than those from SED rats (52.4 +/- 7.8 vs 30.3 +/- 3.9 microm). Thus, there is a functional adaptation to exercise activity in arterioles of skeletal muscle but not in those of arterioles of mesentery. We speculate that the intermittent increase in blood flow/shear stress in arterioles of skeletal muscle during the periods of exercise activity may be the underlying mechanism responsible for this adaptation.