Neurogenic Hypertension and the Secret of Respiration

In spite of recent advances on the knowledgement of the neural control of cardiovascular function, the cause of sympathetic overactivity in neurogenic hypertension remains unknown. Studies from our laboratory point out that rats submitted to chronic intermittent hypoxia (CIH), an experimental model of neurogenic hypertension, present changes in the central respiratory network that impact the pattern of sympathetic discharge and the levels of arterial pressure. In addition to the fine coordination of respiratory muscle contraction and relaxation, essential for O2 and CO2 pulmonary exchanges, neurons of the respiratory network are precisely connected to the neurons controlling the sympathetic activity in the brainstem. This respiratory-sympathetic neuronal interaction provides adjustments in the sympathetic outflow to the heart and vasculature during each respiratory phase, according to the metabolic demands. Herein we report that CIH-induced sympathetic overactivity and mild hypertension are associated with increased frequency discharge of ventral medullary pre-sympathetic neurons. We also describe that their increased frequency discharge is dependent on synaptic inputs, mostly from neurons of the brainstem respiratory network, rather than to changes in their intrinsic electrophysiological properties. In perspective, we are taking into consideration the possibility that changes in the central respiratory rhythm/pattern generator contribute to increased sympathetic outflow and the development of neurogenic hypertension. Our experimental evidence provides support to the hypothesis that changes in the coupling of respiratory and sympathetic networks might be one of the unrevealed secrets of neurogenic hypertension in rats.

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