AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 2 222-R226, Copyright © 1987 by American Physiological Society
Hepatic function in rats after spaceflight: effects on lipids, glycogen, and enzymes
A. H. Merrill Jr, E. Wang, D. P. Jones and J. L. Hargrove
The inclusion of rats aboard Spacelab 3 (SL-3) allowed analyses of liver
lipids, glycogen, hepatic enzymes of cholesterol, glycerolipid and
sphingolipid biosynthesis, and other enzyme activities. Glycogen content
was markedly elevated in livers from the flight animals compared with
controls. Cholesterol was 24% (P less than 0.04) lower in livers from the
experimental groups, whereas blood cholesterol was 19% higher (P less than
0.05). The activity of 3-hydroxy-3-methylglutaryl-CoA reductase, the
rate-limiting enzyme of steroid biosynthesis, was 80% lower (P less than
0.01). Total phospholipids and sphingolipid levels did not differ
significantly. The specific activity of fatty acyl-CoA synthetase, which is
responsible for activation of fatty acids, was 37% (P less than 0.05)
higher in microsomes from the rats on SL-3; however, since these animals
had 25% less microsomal protein (P less than 0.02), there was no difference
per gram of liver. The initial enzymes of sphingolipid and glycerolipid
biosynthesis were assayed; serine palmitoyltransferase was 40% lower (P
less than 0.01), and glycerol 3-phosphate acyltransferase did not differ.
Hepatic cytochrome P-450 content decreased by 50% after spaceflight.
Enzymes that did not differ significantly between the two groups include
cytochrome b5, glutathione S-transferase, tyrosine aminotransferase,
aspartate aminotransferase, and cystathionase. These findings suggest that
spaceflight alters hepatic metabolism of several classes of compounds.
