TIME-DEPENDENT CHANGES IN CATECHOLAMINE TURNOVER IN SPONTANEOUSLY HYPERTENSIVE RATS EXPOSED TO HYPOXIA

In three separate experiments, 4 to 5-week-old spontaneously hypertens ive rats (SHR) and normotensive controls (Wistar-Kyoto [WKy]) were exp osed to hypobaric hypoxia (simulated altitude = 3658 m) for 3 hr, 3 da ys, or 3 weeks. Comparable groups were maintained in ambient laborator y conditions (normoxia). Hypoxia prevented the increase in blood press ure noted in 3-week-old normoxic SHR. Right ventricular hypertrophy fi rst occurred after 3 days of hypoxia, and was found in both SHR and WK y. Catecholamine turnover was measured using the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine. In myocardium, both strains eviden ced hypoxia-induced changes in norepinephrine (NE) turnover, which was increased at 3 hr, normalized at 3 days, and increased again at 3 wee ks. Reduced basal NE concentration at 3 days indicated a temporary def icit in synthetic capacity, which would allow maintenance of a heighte ned neuronal output. Catecholamine turnover in right and left ventricl es differed little in response to hypoxia, in spite of differential he modynamic demands on SHR versus WKy or on right versus left ventricle. In contrast to findings in myocardium, significant interactive effect s between strain and altitude exposure were noted for adrenal catechol amine turnover. Specifically, hypoxia exerted a suppressive influence in SHR that was not evident in WKy, and this may represent an importan t component of hypoxia-induced protection against the development of s pontaneous hypertension.