Ovariectomy Increases Blood Pressure and FosB Staining in the Central Autonomic Control Regions Independent of Chronic Intermittent Hypoxia

Abstract

Chronic intermittent hypoxia (CIH) experimentally mimics the recurrent hypoxia characteristic of sleep apnea, and it induces sustained hypertension in male and ovariectomized (OVX) female rats but not intact females. While central autonomic control regions are known to mediate CIH-induced hypertension in males, their contribution to CIH hypertension in OVX females remains unclear. We tested the hypothesis that 7 days of CIH increases mean arterial pressure (MAP) and FosB staining in central autonomic regions in OVX but not intact female rats. Adult female Sprague Dawley gonadally intact (INT) or OVX rats were exposed to 7 days of CIH (10% O2 and 21% O2 cycle, every 6 mins, 8h/day) or continuous normoxia (CON). MAP was monitored by radiotelemetry. On day 8, the rats were sacrificed, and their brains were collected and processed for FosB immunohistochemistry. During the light/sleep phase, CIH increased MAP in INT females (n=7; 3.4 ± 0.4 mmHg) as compared to CON (n=6, ΔMAP 1.4 ± 0.3 mmHg; P=0.01 CON vs CIH). This difference was not observed during the dark/active phase (CON ΔMAP -1.7 ± 0.4 mmHg, CIH 0.5 ± 0.3 mmHg, P=0.07). In OVX females, CIH was not associated with significant increases in MAP during the light/sleep phase (CON (n=6) ΔMAP 0.3 ± 0.4 mmHg, CIH (n = 6) 2.1 ± 0.3 mmHg, P=0.10). During the dark phase, MAP was significantly increased in CON OVX and CIH OVX compared to their respective baselines but there were no differences between groups (CON ΔMAP 2.4 ± 0.3 mmHg, CIH 2.2 ± 0.4 mmHg, P=0.0002 vs baseline, P=0.8 CON vs CIH). OVX rats had higher baseline FosB staining in the median preoptic nucleus compared to intact female rats independent of CIH exposure (INT: CON (n = 6) 13 ± 3 cells/section, CIH (n = 6) 14 ± 2; OVX: CON (n = 6) 21 ± 3, CIH (n = 6) 23 ± 2, INT CON vs OVX CON, P < 0.05, INT CIH vs OVX CIH P < 0.05). Compared to CON, CIH significantly increased the number of FosB immunoreactive cells in the caudal nucleus of the solitary tract in INT but not OVX females (INT: CON, 7 ± 1 cells/section, CIH 11 ± 1; OVX CON 6 ± 1, CIH n=6, 9 ± 1; INT CON vs CIH, P=0.02; OVX CON vs CIH, P = 0.09). In the rostral ventrolateral medulla, there were no significant differences among any of the groups (INT: CON n=4, 19 ± 2 cells/section, CIH n=4, 20 ± 3; OVX: CON n=6, 18 ± 2, CIH n=6, 21 ± 2, all P>0.05). In OVX females, CIH tended to increase MAP during both the light and dark phases. CON OVX females showed a trend for increased MAP during the dark phase, independent of CIH. CIH was not associated with increased FosB staining in either the median preoptic nucleus or the rostral ventrolateral medulla of OVX females This suggests that changes in MAP observed in CIH OVX females may not involve the same autonomic control regions as male rats exposed to CIH. Supported by RO1 HL155977. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.