Effect of Oleic Acid on the Oxidation and Gluconeogenesis from [1‐¹⁴C]Pyruvate in the Perfused Rat Liver

Abstract

Gluconeogenesis from [l-14C]pyruvate in the perfused liver from fasted rats was stimulated by oleic acid as indicated by an increase in medium glucose, liver glycogen and specific activity of medium [14C]glucose. A balance of carbon from pyruvate revealed that in the presence of oleic acid 2 moles of pyruvate were utilized for each mole of glucose synthesized in contrast to a ratio 4: 1 without fatty acid. From this and 14C0, data it is concluded that oleic acid inhibited pyruvate oxidation markedly. Glucagon increased glucose formation from pyruvate but not from glycerol.Tremendous interest in the factors controlling the rate of gluconeogenesis has been shown in recent years. Long-chain fatty acids have been found to stimulate gluconeogenesis in the perfused rat liver using lactate [l] or alanine as substrate [2,3], and caprylate stimulates glucose formation in liver slices [4]. Increased fatty acid oxidation and ketogenesis have also been implicated in the i n vivo stimulation of gluconeogenesis by glucagon [5,6]. This interrelationship between increased fatty acid oxidation and gluconeogenesis has pointed to an acetyl-CoA activation of pyruvic carboxylase [7] as one of the possible control points in gluconeogenesis [S]. Recently, caprylate [9] and palmitate [lo] have been observed to decrease the oxidation of pyruvate by rat liver mitochondria, which is possibly due to an inhibition of pyruvic dehydrogenase by acetylCoA [10,11].Although glucagon has been reported to stimulate glucose production from lactate [1,12,13], pyruvate [13], fructose [13], and glycerol [14], studies of hepatic intermediates [6,12] have indicated that glucagon may accelerate gluconeogenesis a t the ratelimiting level which exists between pyruvate and phosphoenolpyruvate.The present work is a continuation and extension of the studies on the control of gluconeogenesis initiated by Struck and co-workers in our laborato-' Y [151.These workers found a stimulation of gluconeogenesis from lactate by either glucagon or oleic acid. The present studies are concerned with gluconeogenesis from pyruvate and the effect of oleic acid on this rate. The effect of glucagon on gluconeogenesis from glycerol and pyruvate has also been investigated. MATERIALS AND METHODSMale albino rats (Sprague-Dawley, Gassner, Munchen), weighing between 180 and 250 g and previously fed on laboratory chow (Altromin R., Altrogge, Lage Lippe) were fasted for 18-20 h before use.All chemicals were reagent grade unless otherwise noted. L-lactic acid and DL-carnitine chloride were from Schuchardt (Munchen) and oleic acid from Riedel-DeHaen (Seelze-Hannover). The oleic acid was vacuum distilled prior to use. Glucagon was a preparation and a gift of Eli Lilly, Indianapolis, U.S.A. (Lot Nr. 258-234, B-167-1). Sodium [1-14C]-pyruvate was obtained from Radiochemical Center, Amersham, England. All substrates were prepared as neutral solutions. Glucagon was dissolved in 1/250 N HCI.The apparatus and technique of perfusion were similar to that previously described [16,17]. The perfusin...

The Role of Endogenous Lipid in Gluconeogenesis and Ketogenesis of Perfused Rat Liver

“…Confirming previous work [7], the addition of oleate together with pyruvate increases glucose formation approximately 2-fold in comparison to livers perfused with pyruvate alone ( Table 4). The efficiency of pyruvate conversion to glucose is increased by oleate as the ratio of C3 units to glucose decreases (Table 4).…”

“…The sources of animals and materials, the technique of perfusion [20], and the methods of medium analysis have been described in detail [7,20]. Samples of the liver perfusate for free fatty acid analysis were centrifuged for 2 min in a micro-centrifuge (Eppendorf Centrifuge 3200, Netheler and Hinz, Hamburg, Germany).…”

“…I n all experiments described in this paper, the effector(s) was added after 40 rnin of perfusion to give the medium concentration desired. Oleic acid emulsion was prepared and administered as described previously [7].…”

Interrelationship between Fatty Acid Oxidation and Gluconeogenesis from Pyruvate

“…Glucose formation from pyruvate (0.83 pmole x g-1 x min-1) in the present experiments was slightly lower than that reported by Ross et al [13] although considerably higher than that reported by Teufel et al [20]. A significant portion of pyruvate metabolized (approx.…”

“…Similarly t,o fatty acids, glucagon enhances glucose formation from lactate [10-18], pyruvate [12][13][14][17][18][19][20] and alanine [12,19]. The role of cyclic adenosine 3': 5'-monophosphate (Ado-3' : 5'-P) as mediator of glucagon action in liver has been extended to its enhancement of gluconeogenesis [17,18,21,22].…”