Respiratory modulated sympathetic activity: a putative mechanism for developing vascular resistance?

Area of Science:

• Cardiovascular Physiology
• Neuroscience
• Hypertension Research

Background:

• Sympathetic nerve activity (SNA) shows respiratory modulation, influencing vascular tone.
• The precise impact of this modulation on vasoconstriction is not fully understood, particularly in hypertension.

Purpose of the Study:

• To investigate if respiratory modulation of SNA increases vasoconstriction more than tonic stimulation.
• To examine this effect in both normotensive and spontaneously hypertensive (SH) rats.
• To elucidate the underlying mechanisms, including noradrenaline reuptake.

Main Methods:

• Mathematical modeling of sympathetic innervation of arterioles.
• In vivo stimulation of the sympathetic chain in Wistar and SH rats.
• Measurement of vascular resistance (VR) changes in response to different SNA patterns.

Main Results:

• Respiratory modulated SNA significantly increased vasoconstriction compared to tonic stimulation in Wistar rats.
• This pattern-dependent increase in VR was quicker with modulated SNA.
• In SH rats, the difference in VR between modulated and tonic SNA was not significant.
• Mathematical modeling suggested dysfunctional noradrenaline reuptake in SH rats may explain the lack of pattern dependency.

Conclusions:

• Respiratory modulation of SNA is an effective mechanism for prompt vasoconstriction in normotensive rats.
• This pattern dependency is mediated by a noradrenergic mechanism.
• Dysfunctional noradrenaline reuptake in hypertensive rats may lead to system saturation, impairing the vasoconstrictive response.
• Respiratory modulated SNA may play a role in the development of hypertension.