Microvascular recruitment in hamster striated muscle: role for conducted vasodilation.

The influence of conducted vasodilation upon arteriolar diameter and capillary red blood cell (rbc) perfusion was investigated in the cremaster muscle of male hamsters anesthetized with pentobarbital. The muscle was surgically exposed, superfused with physiological saline solution (pH 7.4; 34 degrees C), and transilluminated for observation of microvessels using intravital video microscopy. The tip (2 microns ID) of a glass micropipette filled with acetylcholine (ACh; 1.0 M) was positioned adjacent to an arteriole. Microiontophoretic delivery of an ACh stimulus (200-1,000 nA; 200-750 ms) caused vasodilation at the pipette tip, which conducted rapidly along the arteriole and decayed with distance; this was characterized by length constants of 2.1 and 2.4 mm (P greater than 0.05) for arterioles with maximal diameters of 32 +/- 2 (means +/- SE; n = 8) and 63 +/- 2 microns (n = 5), respectively. When applied to the distal end of a terminal arteriole (TA) devoid of flow, ACh triggered a dilation that was conducted proximally (greater than 1,000 microns upstream) into the parent vessel (terminal arteriole feed, TAF) containing rbc flow, thereby inducing flow into the TA; stimulation of the TAF also induced rbc flow into TA. In capillaries fed by TA, rbc flux (rbc/s) increased from zero at rest to 23 +/- 6 during the peak of the TA dilation (n = 9); calculated tube hematocrit increased from 4 +/- 2 to 28 +/- 3%. Findings demonstrate that conduction of vasodilation can coordinate vasomotor responses between terminal and parent arterioles and promote rbc delivery to capillaries supplying striated muscle fibers.