The effects of chronic intermittent hypoxia on blood pressure and sympathetic nerve activity in rats

Abstract

To observe the changes of blood pressure and sympathetic nerve activity under different degrees of chronic intermittent hypoxia (CIH) in rats, and therefore to explore the effects of CIH on blood pressure and sympathetic nerve activity and the correlation between blood pressure and sympathetic nerve activity in the pathogenesis of CIH-induced hypertension. Male Wistar rats (n = 168) were randomly divided into untreated group (UD), severe intermittent hypoxia group (IH(1)), moderate intermittent hypoxia group (IH(2)), mild intermittent hypoxia group (IH(3)), continuous hypoxia group (CH), sham control group (SC) and were exposed to different conditions. Rats (n = 8) of the UD group were sacrificed before the experiment, while rats of the other groups were killed in weeks 2, 4, 6, and 8 of the experiment. Anticoagulated venous blood was obtained and plasma was stored at -80°C. Systolic arterial pressure (SBP) was recorded before and after the experiment, while plasma norepinephrine (NE) was measured after the experiment. Before the experiment, the SBP of rats showed no significant differences among groups (F = 0.008, P > 0.05), but the SBP of rats in the intermittent hypoxia groups increased gradually, and higher than the UD group, the SC group and the CH group from the beginning of week 4 (P < 0.05 or P < 0.01). The blood pressure was positively related with the degree of hypoxia (F = 9.844, P < 0.01), and that of the IH(1) group was significantly higher than that of the IH(3) group (P < 0.05), while no significant changes were found in the SC and the CH groups. The plasma NE level of rats in the intermittent hypoxia groups increased gradually with the experiment and significantly higher than that of the UD group, the SC group and the CH group at week 8 (P < 0.05 or P < 0.01), and the level of NE was positively related with the degree of hypoxia (F = 11.537, P < 0.01). The NE level of the IH(1) group was significantly higher than that of the IH(3) group (P < 0.05), but no significant change was found in the SC and the CH groups. The plasma NE levels were positively related with blood pressure (r = 0.530, P < 0.01). CIH can cause increased blood pressure and sympathetic activity in rats, and the effect was dependent on the degree of hypoxia and the time of exposure. The results suggested that CIH-induced higher blood pressure was associated with increased sympathetic activity.