The effect of physical (in)activity on blood pressure and splanchnic sympathetic nerve responses to inhibition of the RVLM

Abstract

A sedentary lifestyle is a major risk factor for cardiovascular disease (CVD). CVD is often associated with enhanced activation of the sympathetic nervous system. The sympathetic nervous system is under tonic and phasic control by the rostral ventrolateral medulla (RVLM). In sedentary rats, there is enhanced sympathoexcitation in response to glutamatergic activation of the RVLM. Since the activity of RVLM is tonically restrained by γ‐amino‐butyric acid (GABA), we hypothesized that sedentary conditions may also lead to decreased responsiveness to GABA in RVLM when compared to physically active conditions. In Inactin anesthetized, sedentary (SED) or physically active (EX) rats, mean arterial pressure (MAP), heart rate (HR) and splanchnic sympathetic nerve activity (sSNA) were recorded during unilateral microinjection of GABA (30 nl, 0.3–600 mM) into the RVLM. Following GABA injections, the contralateral RVLM was inhibited with 90 nl of 2mM Muscimol and the GABA injections were repeated. There were no significant differences between SED or EX conditions for MAP, HR and sSNA responses to GABA both before and after contralateral blockade of the RVLM. Based on our results the enhanced sympathoexcitation seen in our sedentary model is not due to reduced responsiveness to GABA and may be due to enhanced responsiveness to excitatory neurotransmission. (Supported by R01‐HL096787; R01‐HL096787‐S1)