Background: The aims of this study were to investigate the effects of melatonin and n-acetylcysteine on the baroreflex sensitivity and to verify whether those effects were correlated with their antioxidant capacity in Wistar-Kyoto and spontaneously hypertensive rats (SHR).
Methods: Rats were treated with 30 mg/kg/day of melatonin or 4 g/kg/day of n-acetylcysteine for 4 weeks. Changes in mean arterial pressure, heart rate, plasma norepinephrine, and epinephrine were measured in conscious rats after an intravenous injection of phenylephrine or sodium nitroprusside.
Results: The SHR were characterized by decreased reflex chronotropic responses to phenylephrine and sodium nitroprusside (P < .001 and P < .001), as well as by an enhanced increase in plasma catecholamine concentrations in response to sodium nitroprusside (P < .001). Melatonin and n-acetylcysteine produced a significant reduction in mean arterial pressure and heart rate in SHR (P < .001). Melatonin and n-acetylcysteine improved bradycardic (P < .001) and tachycardic (P < .001) baroreflex responses in SHR without modifying catecholamine responses. The antioxidant reserve, which was reduced in SHR as reflected by the lower glutathione peroxidase activity in plasma (P < .05), was normalized by n-acetylcysteine and melatonin (P < .05). n-acetylcysteine (P < .001) and melatonin (P < .05) increased glutathione peroxidase activity in erythrocytes from SHR.
Conclusions: The results of the present study suggest that melatonin and n-acetylcysteine improve the baroreflex response in SHR in correlation with the antioxidant effects of these substances.