[Carotid body inflammation and carotid sinus nerve afferent activity after intermittent hypoxia exposure of various frequencies in rabbits].
OBJECTIVE
To explore the inflammatory reactions, endothelin level and carotid sinus nerve (CSN) afferent activity of carotid body (CB) after intermittent hypoxia/reoxygenation (IH/ROX) exposure of various frequencies in rabbits.


METHODS
Forty-nine male adult New Zealand white rabbits (2.5-3.0 kg) were separated into 7 groups (n = 7 each). After anesthetization, the right carotid artery and CSN were cleared of surrounding tissues without touching the right CB and the left carotid region. The CSN was unenveloped to partially expose the myelin sheath, and electrodes were placed to the "single" chemoreceptor bundle of the CSN, with CSN afferent activity carefully monitored and recorded. Then the right common carotid artery was exposed, cannulated to distal part and its proximal part was ligated. Preparations were challenged by changing the PO2 of the gas mixture equilibrating the perfusate. Alternatively perfusion (2 ml/min) of equilibrated perfusate bubbled with normoxia or hypoxia gas mixtures formed IH/ROX cycles in right carotid common artery, simulating the pattern of hypoxic episodes seen in obstructive sleep apnea, or with continuously perfusing hypoxia perfusate to form continuous hypoxia (CH) modes. Groups were defined with different frequencies, and groups were: intermittent normoxia group (IN group) (21% O2, 15 s; 21% O2, 1 min 45 s), 10/hr group (5% O2, 15 s; 21% O2, 5 min 45 s), 30/hr group (5% O2, 15 s; 21% O2, 1 min 45 s), 50/hr group (5% O2, 15 s; 21% O2, 57 s), 60/hr group (5% O2, 15 s; 21% O2, 45 s) and 90/hr group (5% O2, 15 s; 21% O2, 25 s). All the above groups were exposed to 60 treatment cycles; continuous hypoxia group (CH group), IN for 1 h 45 min and then 5% O2 for 15 min. After exposure and 30 min of static placing, CSN afferent frequencies (Charge F) were recorded from chemoreceptor bundles, and the right CB was cleared of surrounding tissues and harvested. Interleukin-6 (IL-6), endothelin-1 (ET-1), hypoxia-inducible factor-1 (HIF-1), and vascular endothelial growth factor (VEGF) concentrations of the CB lysate were measured with enzyme linked immuno sorbent assay (ELISA) kits and standardized. Data were analyzed with SPSS 12.0 software package; and after one way analysis of variance (ANOVA) for whole difference, Tamhane's T2 was used for post hoc analysis.


RESULTS
IL-6, ET-1 and Charge F increased but then decreased with increasing IH frequencies (F = 25,601.39, 2390.48, 6945.84, all P values < 0.01). IL-6, ET-1 and Charge F levels in 50/hr group were the highest among groups. Charge F levels correlated significantly with IL-6 or ET-1 (with IL-6: r = 0.736, P < 0.01; with ET-1: r = 0.757, P < 0.01, respectively). IL-6, ET-1 and Charge F levels between IN group and CH group were not statistically different (all P values > 0.05). HIF-1 levels elevated gradually (F = 5241.10, P < 0.01) with increasing exposure frequencies, and the CH group had the highest value (all P values < 0.01). VEGF level in CH group was the highest in all groups (all P values < 0.01).


CONCLUSIONS
After IH/ROX exposure, afferent activity of CB CSN increases, which significantly correlates with inflammation and vasomotor mechanism of CB. CB inflammation comes not from IH phases but from ROX phases. Increased CB CSN activity results in elevated SNA tension, which plays a key role in the pathogenesis of systemic hypertension. This procedure influenced by IH/ROX frequencies. CH for 15 min causes no definitely damages. However, HIF-1 and VEGF can be considered as members of adaptive pathway during IH/ROX exposure.
Feng
Jing
J
Respiratory Department of Tianjin Medical University General Hospital, Tianjin 300052, China.
Chen
Bao-yuan
BY
Cui
Lin-yang
LY
Wang
Bao-li
BL
Liu
Chun-xia
CX
Chen
Pan-feng
PF
Guo
Mei-nan
MN
Dong
Li-xia
LX
Li
Shuo
S
D000344:Afferent Pathways / Q000378:metabolism*; D000818:Animals; D002344:Carotid Body / Q000473:pathology*; D002346:Carotid Sinus / Q000294:innervation; D000860:Hypoxia / Q000378:metabolism* / Q000473:pathology*; D007249:Inflammation; D008297:Male; D011817:Rabbits