Hypotension produced by vagal block in primates

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation

Background:

• The vagus nerve contains afferents that inhibit sympathetic tone in many species.
• Vagal block (VB) is known to increase blood pressure in dogs.

Purpose of the Study:

• To investigate the effects of vagal block on blood pressure and sympathetic tone in intact and sinoaortic-denervated (SAD) monkeys.
• To determine the location of peripheral receptors that influence sympathetic tone.

Main Methods:

• Vagal block was induced in intact and SAD monkeys using local anesthetic infiltration.
• Cardiovascular parameters including heart rate (HR), blood pressure (BP), and left atrial pressure (LAP) were monitored.
• Experiments included blood volume expansion and head-out water immersion.

Main Results:

• Vagal block significantly decreased blood pressure in both intact and SAD monkeys.
• Volume expansion affected blood pressure differently in intact versus SAD monkeys.
• Water immersion in vagal block SAD monkeys increased blood pressure more than volume expansion, indicating venous pooling.

Conclusions:

• Vagal block in monkeys removes inhibitory input from peripheral receptors, which normally maintain sympathetic tone.
• The observed hypotension suggests these receptors are located in the venous system, likely within the chest or abdomen.
• Cardiopulmonary receptors may play a role in regulating sympathetic tone via the venous system.