Aim: 

Extent of sympathetic activation is often inferred from the observation of different physiological variables, e.g., systemic blood pressure, heart rate, sweating. While direct recording of neural activity from presumed sympathetic fibers has been performed, the role and the importance of the hormonal component of the sympathetic system is often overlooked, being only assessable, with poor time resolution, through plasma catecholamines.

Methods: 

In the present study a method is devised to assess the extent and time course of the hormonal (HC) and neural (NC) components of sympathetic activation in conscious rabbits. Six rabbits were implanted with chronic probes allowing for continuous measurement of systemic blood pressure and blood flow, bilaterally from facial arteries. The cervical sympathetic nerve was unilaterally sectioned to remove sympathetic innervation form the vascular bed of the ipsilateral facial artery. After recovery from surgery the vascular response to different acute stressors (air-jet directed to the head, sudden noise, pin-prick, etc.) was recorded and quantified in terms of percent change of vascular conductance. The difference of the responses recorded from the two sides was used to disentangle the vasoconstrictor power of NC and HC.

Results and Conclusion: 

Preliminar results allowed to evidence the time course of the two components in response to the different stressors and revealed that NC has a major role in the first 10-20 s after which HC may prevail, in a stressor-dependent way.