MICRO-VASCULAR PRESSURES IN RAT INTESTINAL MUSCLE DURING DIRECT NERVE-STIMULATION

Microvascular pressures are assumed to be lowered by the vasoconstriction caused during increased activity of the sympathetic nervous system. This hypothesis was tested by direct simultaneous measurements of microvascular pressures and inner vessel diameters in rat intestinal muscle before and during sympathetic stimulation. Measurements of inner vessel diameter and pressure were made with a video micrometer and a servo-null pressure transducer, respectively. Direct sympathetic stimulation at 4, 8, and 16 Hz (5-7 V, 2-msec duration) was used to mimic increased sympathetic activity. Stimulation at 8 and 16 Hz caused a reduction in microvascular pressure and inner vessel diameters throughout the microcirculation. The primary site of pressure reduction was in the smallest arterioles during 8-Hz stimulation and in the largest arterioles during 16-Hz stimulation. These data are interpreted to indicate that the major site of microvascular pressure reduction shifted from the small to large arterioles as the frequency of sympathetic stimulation increased. © 1979.