18F-fluorodeoxyglucose accumulation in the heart, brain and skeletal muscle of rats; the influence of time after injection, depressed lipid metabolism and glucose-insulin.
BACKGROUND
To study the effect of lipid depressing drugs on (18)FDG myocardial concentration. The changes of (18)FDG uptake in myocardium, brain and skeletal muscle of rats were compared as influenced by acipimox, tyloxapol and glucose with insulin.


METHODS
5.55 MBq of (18)FDG were administered to Wistar rats. Control rats were killed 15, 30, 45 and 60 minutes following intravenous injection and the radioactivity concentration (cpm/g of tissue) in relation to injected cpm was determined in a well crystal adjusted to 511 KeV in order to check the time of maximal (18)FDG tissue uptake. The radioactivity in myocardium, skeletal muscle and brain in intact animals was compared with that of rats treated with tyloxapol (tritton WR 1339, 125 mg intravenously immediately before (18)FDG injection), acipimox (nicotinic acid derivative, 25 mg by stomach cannula 15 minutes before (18)FDG), or glucose with insulin (intravenous injection of 0.04 g and 0.04 UI immediately before (18)FDG). The animals were killed 45 minutes following (18)FDG injection.


RESULTS
Tyloxapol and acipimox significantly elevated myocardial (18)FDG concentration (tyloxapol +37% and acipimox +48%), but the increase in (18)FDG concentration after glucose and insulin was slight and insignificant. The changes in skeletal muscle after lipid depressing agents were quite contrasting; the decrease in (18)FDG concentration was -74% after tyloxapol and -44% following acipimox administration. The accumulation of (18)FDG in brain was not influenced markedly by the drugs used or by glucose with insulin.


CONCLUSIONS
The highest (18)FDG uptake in myocardium could be achieved by depressing the lipid metabolism and not by administration of glucose with insulin only. A marked increase in glucose accumulation in myocardium is not possible without previous shift from the utilisation of fatty acids. This finding is fully in agreement with present knowledge about energetic metabolism of myocardium.
Department of Nuclear Medicine, Institute for Clinical and Experimental Medicine, Prague, Czech Republic. jaka@medicon.cz
J
J
Kasalický
M
M
Konopková
F
F
Melichar