W. Henley et L. Bellush, TIME-DEPENDENT CHANGES IN CATECHOLAMINE TURNOVER IN SPONTANEOUSLY HYPERTENSIVE RATS EXPOSED TO HYPOXIA, Proceedings of the Society for Experimental Biology and Medicine, 208(4), 1995, pp. 413-421
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.