Augmented sympatho‐excitatory reflexes in rats exposed to chronic intermittent hypoxia

Abstract

Chronic intermittent hypoxia (CIH) yields persistent elevations in sympathetic nerve activity (SNA) and arterial pressure (AP). In addition, acute hypoxia evokes a larger rise in SNA in rats after CIH due to enhanced sensory and central mechanisms. We examined the hypothesis that other sympatho‐excitatory reflexes are also augmented after CIH. Male Sprague‐Dawley rats (4 wks old) were exposed to CIH (6% O2 for 40s, every 9 min, 8h/day, 3 wks). Isoflurane‐anesthetized, ventilated, paralyzed rats were prepared for recording AP, splanchnic SNA, phrenic nerve discharge and then switched urethane anesthesia (1.5 g/kg, iv). To activate the somatic pressor reflex a sciatic nerve was stimulated (5 sec, 100 μA, 33 Hz). To activate the diving reflex, water (2 ml) was passed through the nose via a tracheal catheter. Compared to control rats (n=17), rats with CIH (n=13) had elevated mean AP (134±5 vs.115±3 mmHg, P<0.05), SNA (63±7 vs. 38±6 mV, P<0.05) and hematocrit (45.1±0.5 vs. 42.4±0.6%, P<0.05). Stimulation of the sciatic nerve evoked a greater increase in SNA in CIH rats (67%±16 vs. 15±8%, P<0.05). Likewise, stimulation of the diving reflex induced an exaggerated rise in SNA in rats with CIH compared to control rats (n=6/group; 674±236% vs. 123±41%, P<0.05). These data suggest that exposure to CIH leads to adaptations that facilitate activation of the sympathetic nervous system. Support: AHA0755292B, NIH‐HL075174.