Nitric oxide inhibition in paraventricular nucleus on cardiovascular and autonomic modulation after exercise training in unanesthetized rats

It is well known that regular physical exercise alter cardiac function and autonomic modulation of heart rate variability (HRV). The paraventricular nucleus of hypothalamus (PVN) is an important site of integration for autonomic and cardiovascular responses, where nitric oxide (NO) plays an important role. The aim of our study was to evaluate the cardiovascular parameters and autonomic modulation by means of spectral analysis after nitric oxide synthase (NOS) inhibition in the PVN in conscious sedentary (S) or swimming trained (ST) rats. After swimming training protocol, adult male Wistar rats, instrumented with guide cannulas to PVN and femoral artery and vein catheters were submitted to mean arterial pressure (MAP) and heart rate (HR) recording. At baseline, the physical training induced a resting bradycardia (S: 374 ± 5, ST: 346 ± 1 bpm) and promoted adaptations in HRV characterized by an increase in high-frequency oscillations (HF; 26.43 ± 6.91 to 88.96 ± 2.44) and a decrease in low-frequency oscillations (LF; 73.57 ± 6.91 to 11.04 ± 2.44) in normalized units. The microinjection of Nω-nitro-l-arginine methyl ester (l-NAME) in the PVN of sedentary and trained rats promoted increase in MAP and HR. l-NAME in the PVN did not significantly alter the spectral parameters of HRV of sedentary animals, however in the trained rats increased LF oscillations (11.04 ± 2.44 to 27.62 ± 6.97) and decreased HF oscillations (88.96 ± 2.44 to 72.38 ± 6.97) in normalized units compared with baseline. Our results suggest that NO in the PVN may collaborate to cardiac autonomic modulation after exercise training.

Research Highlights► NO inhibition showed tonic cardiovascular effects in sedentary and trained rats. ► NO into the PVN modulates cardiac autonomic function in exercise trained rats. ► L-NAME into the PVN increases cardiac sympathetic modulation only after exercise.