ADAPTATION OF FLOW-INDUCED DILATION OF ARTERIOLES TO DAILY EXERCISE

We aimed to test the hypothesis that daily exercise elicits an adaptat ion 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 (S ED) and exercised (EX) rats to increases in perfusate flow (PF, range 0-30 mu l/min). Rats were run on a treadmill, once daily for 3 to 4 we eks (with gradually increasing intensity up to 40 min at 28 m/min; a t otal of 15-19 sessions on the treadmill). The passive diameters of art erioles (obtained in Ca2+-free solution) were similar (similar to 140 mu m) but the pressure-induced active diameter (at 80 mmHg) of skeleta l muscle arterioles was significantly smaller than that of mesenteric arterioles. The basal diameter of MES arterioles of SED and EX rats,va s: 83.5 +/- 3.6 and 83.9 +/- 2.9 mu m, respectively; increases in RE i ncreased the diameter of SED and EX arterioles to a similar degree by 33.2 +/- 4.7 and 31.9 +/- 6.1 mu m, respectively). The diameters of PL muscle arterioles of SED and EX rats were 62.1 +/- 6.2 and 68.0 +/- 5 .5 mu m. In contrast to arterioles of MES, the highest PF increased th e diameters of arterioles of pi. muscle from EX rats to a significantl y greater extent than those from SED rats (52.4 +/- 7.8 vs 30.3 +/- 3. 9 mu m). Thus, there is a functional adaptation to exercise activity i n arterioles of skeletal muscle but not in those of arterioles of mese ntery. We speculate that the intermittent increase in blood flow/shear stress in arterioles of skeletal muscle during the periods of exercis e activity may be the underlying mechanism responsible for this adapta tion. (C) 1998 Academic Press.