Alterations in enzymes involved in fat metabolism after acute and chronic altitude exposure

The purpose of this study was to examine the effect of acute (24 h) and chr onic (5 wk) hypobaric hypoxic exposure equivalent to a simulated altitude o f 4,300 m (446 mmHg) on the enzymes of fat metabolism. Heart, liver, and sk eletal muscle were taken from 32 male Sprague-Dawley rats. Altitude exposur e did not affect the activity of citrate synthase in any of the tissues, su ggesting that mitochondrial content was unchanged. Carnitine palmitoyltrans ferase-I (CPT-I) activity was significantly reduced in the heart by both ac ute and chronic high altitude exposure compared with controls. A similar re duction was found for CPT-I activity in extensor digitorum longus after acu te and chronic exposure compared with control animals. CPT-I activity was n ot affected by altitude exposure in the soleus muscle or the liver. 3-Hydro xyacyl-CoA dehydrogenase (beta -HAD) activity was significantly depressed i n the hearts of chronically exposed animals compared with controls. No diff erence between acute and control animals was found in the heart for beta -H AD activity. Liver beta -HAD activity was also significantly decreased in t he acclimatized as well as in the acute animals compared with the control g roup. Quadriceps beta -HAD activity was reduced for the chronic animals onl y compared with controls. These data suggest that acclimatization to high a ltitude selectively decreases key enzymes in fat utilization and oxidation in the heart, liver, and select skeletal muscles.