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1 Pediatrics, University of Louisville, Louisville, KY, USA
2 Pediatrics, University of Louisville, Louisville, KY, USA; Pharmacology and Toxicology, University of Louisville, Louisville, KY, USA
3 Pharmacology and Toxicology, University of Louisville, Louisville, KY, USA
4 Pediatrics, University of Louisville, Louisville, KY, USA; Physiology and Biophysics, University of Louisville, Louisville, KY, USA
* To whom correspondence should be addressed. E-mail: david.gozal{at}louisville.edu.
Chronic perinatal intermittent hypoxia (IH) could have long-term cardiovascular effects by altering baroreflex function. To examine this hypothesis, we exposed rats (n=6/group) for postnatal days P1-P30, or prenatal embryonic days E5- E21, to IH (8% ambient O2 for 90 s following 90 s of 21% of O2, 12 hr/day), or to normoxia (control). Baroreflex sensitivity (BRS) and cardiac chronotropic responses were examined in anesthetized animals 3.5 to 5 months later by infusing phenylephrine (PE) or sodium nitroprusside (NP) (6-12 µg/min, 1-2 min, i.v.) during normoxia and after 18 min of acute IH (IHA). In controls after IHA, baroreflex gain was 42% (P<0.05) less than during normoxia. BRS in the postnatal IH group during normoxia was approximately 50% less than in control rats and similar to controls after IHA. The heart rate (HR) response to PE in the IH group was also less than in controls (P<0.05) and was not changed by IHA. BRS and HR responses in the prenatal IH group were similar to the normoxic control group. Vagal efferent projections to atrial ganglia neurons in rats after postnatal IH (n=4) were examined by injecting tracer into the left nucleus ambiguous. After 35 days of postnatal IH, basket ending density was reduced by 17% (P<0.001) and vagal axon varicose contacts by 56% (P<0.001) compared to controls. We conclude that reduction of vagal efferent projections in cardiac ganglia could be a cause of long-term modifications in baroreflex function.
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