Five-week-old male spontaneously hypertensive rats (SHR) were either exposed to hypoxia or maintained in normoxia. Groups of rats were returned to normoxia after 8 or 12 weeks exposure to hypoxia while others remained in hypoxia or normoxia throughout the study. Subdivisions of the groups were sacrificed 2 or 6 weeks after return to normoxia at the same time as were rats continuously exposed to either normoxia or hypoxia. Hypoxia attenuated the development of systemic hypertension (P < 0.05); however, this protection dissipated partially when rats were returned to normoxia. Norepinephrine concentration was significantly elevated and serotonin turnover (5-hydroxyindoleacetic acid/serotonin 5HIAA/5HT) was significantly decreased in caudal brainstem of hypoxic SHR and both were gradually normalized upon return to normoxia. Similarly, left ventricular hypertrophy was attenuated and adrenal catecholamine contents were increased with hypoxic exposure. Both gradually normalized upon return to normoxia. Mechanisms associated with the development of spontaneous hypertension reemerge when adult, previously hypoxic SHR are returned to a normoxic environment. These findings implicate long-term changes in central noradrenergic and serotonergic function as components of the cardiovascular adaptation to hypoxia which includes hypoxic moderation of spontaneous hypertension. © 1992.
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