Elevated ambient oxygen does not affect autoregulation in cat mesentery.

The purpose of this study was to determine whether oxygen plays a role in the autoregulation of blood flow in the isolated mesentery of the cat. Arteriolar diameter and red cell velocity were measured at normal arterial pressure and during 2 min of pressure reduction to 80 and 40 mmHg under ambient levels of 0, 10, and 20% oxygen in nitrogen. Autoregulatory responses during pressure reductions to 80 and 40 mmHg were not significantly different under 0% oxygen compared with those under 10 or 20% oxygen. Also, no significant difference was found in the control state between the mean diameters, linear velocities, or volume flows under 10 and 20% oxygen compared with 0% oxygen. We also determined oxygen levels just under the mesentery with different ambient oxygen levels. These values were the same as in the ambient gas mixture, suggesting that tissue oxygen levels in mesentery are determined by those in the external environment. Oxygen levels in the abdominal cavity averaged 67 mmHg, indicating that mesentery is normally exposed to a high-oxygen environment. We conclude that a change in tissue oxygen tension is not an essential factor in the mechanism of blood flow autoregulation in cat mesentery.