Comparison of 3H-galactose and 3H-glucose as precursors of hepatic glycogen in control-fed rats.
Labeling of hepatic glycogen derived from 3H-galactose and 3H-glucose was compared shortly after intravenous injection in control-fed rats. The rats were allowed to accumulate 5-8% glycogen prior to receiving label. Fifteen minutes to 2 hours after labeling, liver was excised and processed for routine light (LM) and electron microscopic (EM) radioautography (RAG) or biochemical analysis. After injection of 3H-galactose, LM-RAGs revealed that the percentage of heavily labeled hepatocytes increased from 37% after 15 minutes to 68% after 1 hour but showed no further increase after 2 hours. alpha-Amylase treatment removed most glycogen and incorporated label; thus few silver grains were observed, indicating little incorporation of label except into glycogen. EM-RAGs demonstrated that most label occurred where glycogen was located. Biochemical analysis showed initially a high blood level of label that rapidly plateaued at a reduced level by 5 minutes. Concomitantly, glycogen labeling determined by liquid scintillation counting reflected the increases observed in the RAGs. After injection of 3H-glucose, LM-RAGs revealed that only 12% of the hepatocytes were heavily labeled at 1 hour and 20% at 2 hours. In tissue treated with alpha-amylase, glycogen was depleted and label was close to background level at each interval observed. EM-RAGs showed most grains associated with glycogen deposits. Biochemically, blood levels of label persisted at a high level for 30 minutes and tissue levels increased slowly over the 2-hour period. This study shows that incorporation from 3H-galactose was more rapid than incorporation of 3H-glucose; however, label derived from both carbohydrates appeared to be incorporated mainly into glycogen.
Michaels
J E
JE
Department of Anatomy and Cell Biology, University of Cincinnati College of Medicine, Ohio 45267-0521.
Garfield
S A
SA
Hung
J T
JT
Cardell
R R
RR
D000818:Animals; D001345:Autoradiography; D005690:Galactose / Q000378:metabolism* / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006003:Glycogen / Q000096:biosynthesis*; D007275:Injections, Intravenous; D008099:Liver / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D014316:Tritium; D000516:alpha-Amylases / Q000494:pharmacology
D014316:Tritium; D006003:Glycogen; D000516:alpha-Amylases; D005947:Glucose; D005690:Galactose