Abstract-Intermittent hypoxia is used to mimic the arterial hypoxemia that occurs during sleep apnea. The present study examined the blood pressure and heart rate responses to exposure to intermittent hypoxia in male rats and in female rats before and after ovariectomy. Rats were instrumented with telemetry transmitters and blood pressure, heart rate, and activity measured during 7 days of exposure to intermittent hypoxia (3 minutes of normoxia [21% oxygen] alternating with 3 minutes 10% oxygen between 8 AM and 4 PM, remainder of day at normoxia). Blood pressure increased in males, females, and ovariectomized females in response to 7 days of intermittent hypoxia during the hours of exposure to hypoxia. Blood pressure increased less in intact females (average change in blood pressure 1.6Ϯ0.6 mm Hg, nϭ11) than in females studied after ovariectomy (5.1Ϯ1.1 mm Hg, nϭ6) or males (5.4Ϯ1.0 mm Hg, nϭ10). This elevated blood pressure persisted throughout the remainder of the day when the animals were not exposed to intermittent hypoxia and remained significantly attenuated in female rats. Ovariectomy abolished the protection against the elevated blood pressure response to intermittent hypoxia in females. Heart rate increased only in males, and only during the period of the day associated with intermittent hypoxia. Female rats were protected against this tachycardia independent of the ovarian hormones. These results indicate that females are protected from the hypertensive and tachycardia effects of intermittent hypoxia. Key Words: blood pressure Ⅲ heart rate Ⅲ sleep apnea syndromes S leep apnea is a significant health problem in the US. Whether of central or peripheral (obstructive) origin, periodic cessation of ventilation during sleep is associated with increased arterial pressure 1 and elevated sympathetic nerve discharge 2 during waking hours. There is also gender specificity in the incidence of sleep apnea. Premenopausal women have a lower occurrence of sleep apnea, whereas in postmenopausal women the incidence is the same as in males. [3][4][5] Even though premenopausal women have a lower incidence of sleep apnea, they do experience sleep apnea; however, whether blood pressure increases in young women with sleep apnea is unknown.Intermittent hypoxia (IH) is used to model the arterial hypoxemia that occurs during sleep apnea. In both animals and humans, repetitive exposures to hypoxia increase blood pressure 6 -9 and sympathetic nerve discharge. 10,11 However, all of these studies have been performed in males. In light of the evidence that premenopausal women and ovary-intact female animals exhibit reduced responses to a variety of sympatho-excitatory stimuli, we hypothesized that female rats exposed to episodes of intermittent hypoxia will be protected against the associated hypertension, and this protection will be dependent on circulating female sex hormones. The goal of the present study was to compare the cardiovascular responses to intermittent exposure in male, female, and ovariectomized female rats.
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