Early changes of liver phospholipase C activity in rats fed an orotic acid supplemented diet.
In this study of the effect of an orotic-acid (O.A.) diet on the activity of membrane-bound phosphoinositide-specific phospholipase C (PL-C) of rat liver, its enzymatic activity was evaluated in vitro on membranes obtained from the hepatic tissue of male Wistar rats fed a diet containing 1% O.A. for 2 and 5 days and from control rats. The rate of breakdown of labelled phosphatidylinositol-4,5-bisphosphate (Ptdins-P2) added to the isolated membranes was measured both in the absence and in the presence of guanosine-5'-O-thiotriphosphate (GTP gamma S). The enzyme stimulation by bombesin was also analysed. PL-C activity proved to be deeply and early modified by O.A. The basal activity was increased 2 days after feeding on the O.A.-supplemented diet, but the difference from control rats was no more significant after 5 days of this diet. The most interesting changes concerned the response to bombesin; the hormone failed to induce any stimulation of PL-C in O.A.-treated rats after either 2 or 5 days of diet, whereas it nearly doubled Ptdins-P2 breakdown in the liver membranes from control rats. The lack of any stimulation of the phospholipase C by bombesin in O.A.-treated rats indicates a deep impairment of this signal transmission system; its possible causes and consequences are discussed.
Rossi
M A
MA
Department of Experimental Medicine and Oncology, University of Turin, Italy.
Fidale
F
F
Dianzani
M U
MU
D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D004032:Diet; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D009963:Orotic Acid / Q000494:pharmacology*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013268:Stimulation, Chemical; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*
D019269:Phosphatidylinositol 4,5-Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009963:Orotic Acid; D010738:Type C Phospholipases; D001839:Bombesin