Intestinal O2 uptake during sympathetic stimulation and partial arterial occlusion

Area of Science:

• Physiology
• Gastroenterology
• Vascular Biology

Background:

• Sympathetic nerve stimulation is known to affect blood flow and oxygen delivery.
• Previous studies suggest sympathetic stimulation closes precariously sphincters, limiting oxygen diffusion.

Purpose of the Study:

• To investigate the impact of sympathetic stimulation on oxygen uptake and extraction in the canine small bowel under different perfusion conditions.
• To determine if local mechanisms can maintain oxygen uptake during reduced blood flow and if sympathetic stimulation interferes with these mechanisms.

Main Methods:

• Experiments were conducted on isolated canine small bowel loops.
• Constant blood flow and constant arterial pressure perfusion models were used.
• Sympathetic nerves were stimulated, and parameters like oxygen extraction, oxygen uptake, and blood flow were measured. 86Rb extraction was also assessed.

Main Results:

• Sympathetic stimulation at constant blood flow reduced oxygen extraction and uptake, consistent with precapillary sphincter closure.
• Under constant arterial pressure, sympathetic stimulation decreased blood flow by ~30% and reduced oxygen uptake.
• When blood flow was reduced by arterial occlusion to a similar level, oxygen extraction increased significantly, maintaining oxygen uptake, an effect blunted by sympathetic stimulation.

Conclusions:

• Sympathetic stimulation impairs oxygen uptake in the canine small bowel, primarily by reducing capillary-to-cell oxygen flux.
• Local mechanisms, involving increased oxygen extraction, can maintain oxygen uptake during reduced blood flow.
• Sympathetic stimulation interferes with these compensatory local mechanisms, highlighting its detrimental effect on gut oxygenation during hypoperfusion.