Role of vasoactive substances in active hyperemia in skeletal muscle (38520).

A prolonged, 2-hr period of exercise hyperemia in the canine gracilis muscle was associated with initial increases in the arteriovenous differences for potassium, hydrogen and osmolality. However, that for hydrogen decreased and those for potassium and osmolality became negligible by the 120th min while blood flow remained elevated. Thus, potassium and osmolality do not appear to participate importantly in the maintenance of exercise hyperemia in canine gracilis muscle. A bioassay muscle did not respond with comparable dilation when submaximal, graded levels of exercise hyperemia were induced in an upstream, donor muscle but did respond more comparably in terms of magnitude and time course when the exercise was more severe. Thus, stable vasoactive substances may not entirely account for exercise hyperemia and the study fails to provide evidence that the capillary acts as a significant barrier to the vasoactive substances.