The metabolism of oleic acid by the perfused rat liver in experimental diabetes induced by antiinsulin serum

The metabolism of varying quantities of oleic acid was examined in isolated perfused livers from normal fed rats and from animals made diabetic by pretreatment with guinea pig antiinsulin serum (AIS). The data presented reemphasize the fact that the quantity of free fatty acid (FFA) coming to the liver is a necessary, but not the most important, factor affecting the subsequent metabolism of the FFA. Rates of ketogenesis and output of triglyceride and the terminal concentration of hepatic triglyceride were proportional to uptake of FFA in certain concentration ranges. For equal rates of uptake of FFA, ketogenesis was greater, and the quantity of triglyceride secreted or accumulated within the liver was less, with livers from diabetic animals than with livers from normal animals. In confirmation of previous data, the liver was observed to have a maximal capacity to secrete triglyceride. Triglyceride accumulated in livers from normal-fed and diabetic animals only when uptake of FFA was more than sufficient to saturate the secretory process. Since proportionately more FFA was catabolized by livers from AIS treated animals, greater uptake of FFA was required to produce maximal rates of output of triglyceride and accumulation in livers from diabetic than from normal animals. Rates of ketogenesis by livers from normal fed animals increased minimally with increasing uptake of FFA (up to 1.0 mM free fatty acid). Even when uptake increased considerably with FFA concentrations of approximately 2.5 mM, rates of ketogenesis by livers from normal animals were less than half those of livers from diabetic rats, and maximal rates were not achieved by the normal controls. It is evident that changes in hepatic metabolism of FFA in the intact diabetic animal result from simultaneous alterations of supply of FFA and hormonally induced metabolic changes in the liver. Moreover, although hepatic secretion and accumulation of triglyceride is greater in isolated perfused livers from normal rats than from diabetic animals when the livers are exposed to equal quantities of FFA, the diabetic livers can accumulate more triglyceride, secrete more triglyceride, and oxidize more FFA to ketone bodies than can the normal under conditions in which considerably more substrate is available to the diabetic rather than to the normal livers. These differences might also be expected to occur in the acutely insulin deficient intact animal, in which changes in hormonal status and substrate (FFA) availability occur simultaneously, and might, in part, explain the ketonemia, hypertriglyceridemia, and hepatic steatosis often observed in vivo.     

Acinar heterogeneity of fatty acid binding protein expression in the livers of male, female and clofibrate-treated rats

Liver fatty acid binding protein may play a role in the intracellular transport and compartmentation of long-chain fatty acid metabolism. The distribution of liver fatty acid binding protein in the hepatic acinus was determined by means of immunocytochemistry as well as by measurement of liver fatty acid binding protein in cellular protein selectively released from zone 1 and zone 3 cells by means of anterograde and retrograde liver perfusion with digitonin. In untreated male rats, specific immunocytochemical staining for liver fatty acid binding protein showed a declining portal-to-central hepatocellular gradient in intensity, consistent with the portal-to-central ratio of liver fatty acid binding protein abundance measured in effluents from digitonin-perfused livers of 1.6:1. Female and clofibrate-treated male rats, in both of which hepatic synthesis and abundance of liver fatty acid binding protein are greater than in untreated males, differed as well in the pattern of acinar expression of this protein. In females, periportal concentrations of liver fatty acid binding protein determined from the effluent of livers perfused anterograde with digitonin were similar to male values, whereas liver fatty acid binding protein concentration in pericentral hepatocytes determined from the effluent of retrograde perfused livers was increased, resulting in a marked attenuation of the portal-to-central gradient of this protein; this was also apparent on immunocytochemistry. Clofibrate-treated rats, in contrast, displayed a panacinar increase in liver fatty acid binding protein with maintenance of the portal-to-central ratio observed in untreated males. We conclude that there exists a declining portal-to-central gradient in liver fatty acid binding protein cellular abundance in the hepatic acinus of untreated male rats. Furthermore, the increased synthesis and abundance of liver fatty acid binding protein in female and clofibrate-treated male rats results in two different alterations in the acinar expression of this protein, i.e. a pericentral increase (female) or a panlobular increase (clofibrate). Elucidation of the relationship between the zonation of hepatic fatty acid metabolism and the acinar expression of liver fatty acid binding protein should provide a more detailed understanding of the function of this protein.     

Stimulation of in vitro triglyceride synthesis in the rat hepatocyte by growth hormone treatment in vivo

Hepatic fatty acid metabolism in the rat is sexually differentiated. Rates of esterification by the liver of fatty acid into triglyceride and other esterification products (phospholipid, diglyceride, cholesteryl esters) are higher in the female than in the male. There is evidence to suggest that GH feminizes other hepatic systems that exhibit sexual dimorphism, including hepatic steroid metabolism, PRL receptors, and estrogen binding. To investigate the role of GH in maintenance of the high rates of fatty acid esterification observed in the female, we assessed rates of [1-14C]oleic acid utilization by hepatocytes prepared from hypophysectomized (hypox) cortisol/T3-replaced female rats with an without continuous in vivo infusion of human (h) GH (5 micrograms/h). In addition, we assessed the effect of in vivo hGH treatment (5 micrograms/h) on [1-14C]oleic acid utilization in the normal male rat. Hypophysectomy was accompanied by a reduction in incorporation of [1-14C]oleic acid into products of esterification (triglyceride, phospholipid, diglyceride) and oxidation (CO2, ketone bodies). Continuous infusion of hGH (5 micrograms/h; 14 days) restored rates of fatty acid esterification in the hypox-cortisol/T3-replaced female rat, with the exception of cholesteryl esters. hGH infusion partially restored rates of fatty acid oxidation in the hypox cortisol/T3-replaced female rat. Treatment of the adult male rat with continuous infusion of hGH (5 micrograms/h; 7 days) resulted in increased rates of incorporation of [1-14C] oleic acid into triglyceride. In contrast, incorporation of oleic acid into phospholipid, diglyceride, and cholesteryl esters was unaltered. These results suggest that GH may be an important regulator of hepatic fatty acid metabolism.     

Metformin treatment of rats with diet-induced overweight and hypertriglyceridemia decreases plasma triglyceride concentrations,while decreasing triglyceride and increasing ketone body output by the isolated perfused liver

Metformin has been proposed as a potential drug treatment to reduce liver steatosis. Therefore, the study of the effects of in vivo metformin administration, on hepatic fat metabolism in the isolated perfused liver is of great interest. We have studied the effects of in vivo metformin treatment of rats with experimentally induced overweight, hyperglycemia and hypertriglyceridemia, on plasma hormone and metabolite concentrations, as well as on triglyceride and ketone body output by the isolated perfused livers. Sprague-Dawley rats were fed ad libitum with a high lipid diet for 10 weeks. Then, one rat group was treated for 7 days with 350 mug/kg of BW of metformin per day, whereas the control group received only water. Thereafter, the livers were excised and perfused in vitro under controlled conditions. The hypertriglyceridemic rats had a greater body weight, as well as greater plasma glucose, insulin and triglyceride concentrations, than the control rats fed ordinary chow. In vivo metformin treatment decreased plasma glucose, insulin and triglyceride concentrations. With respect to the overweight, hyperglycemic, hypertriglyceridemic, untreated control rats, the cumulative (i.e. over 3 h of perfusion) triglyceride output by the perfused livers was decreased by >60%, whereas total ketone body (i.e. the sum of 3-hydroxybutyrate and acetoacetate) output was increased by >100% (p < 0.01 for both). In conclusion, the in vivo treatment with metformin of rats with diet-induced overweight and hypertriglyceridemia is capable to re-address hepatic fatty acid metabolism from lipogenesis toward fat oxidation and ketone body production, either directly or through a reduction of insulin concentrations.     

Reciprocal responses to exercise in hepatic ketogenesis and lipid secretion in the rat

The effects of 4 weeks of voluntary exercise (rotating wheel) on serum and liver lipid levels were studied in 6-week-old male Wistar rats. The hypotriglyceridemic effect of exercise was not influenced by the dietary fat levels (4.5 and 14.5%), whereas the hypocholesterolemic effect was higher in a low-fat diet than in a high-fat diet. Although the serum cholesterol-lowering effect of exercise was marginal, the beneficial effect on hepatic lipids was observed only in rats fed a high-cholesterol diet. The hepatic contribution to the serum lipid-lowering action of exercise was examined in the isolated perfused livers of rats fed a low fat diet. The reduction (34%) of serum triglyceride by exercise corresponded to the decrease (32%) in the hepatic triglyceride secretion rate, indicating a significant role of the liver in the hypotriglyceridemic effect of exercise. In contrast, the decrease (31%) in serum total cholesterol was considerably greater than that (23%) in the hepatic secretion, suggesting an extra-hepatic contribution. On the other hand, the hepatic production of ketone body was increased by exercise. These results indicate that the altered hepatic partition of long-chain free fatty acids between esterification and oxidation is one of the causative factors for the serum lipid-lowering effect of exercise.     

Role of the hypophysis in estrogen-mediated induction of enzymes in the regenerating liver from castrated male rats.

Perfusions with corticosterone, of isolated regenerated livers from adult male rats, subjected to castration, partial hepatectomy and hypophysectomy with or without estradiol treatment during parenchymal regeneration, yielded very similar patterns of biliary steroid metabolites. The degree of steroid conjugation was lower than that seen in livers from normal, untreated, adult male rats. In operated animals, with or without estradiol benzoate treatment, ring A-reduced 20-keto metabolites constituted about 20%, whereas metabolites with a 20-hydroxy group made up approximately 80% of the corticosterone metabolites formed. Furthermore, no 15-hydroxylated metabolites derived from corticosterone, quantitatively the most important compounds in bile from female rats, could be detected in bile from these treated male animals. However, livers from male rats which had been castrated, hepatectomized and treated with estradiol benzoate during liver regeneration, produced 15-hydroxy-tetrahydrocorticosterone to the same extent as female rat livers, when perfused with corticosterone. The results obtained indicate that the effects of estradiol on the induction and differentiation of steroid metabolizing enzymes in the regenerating liver are pronounced and manifested only in the presence of an intact hypophysis.     

Reduced hepatic insulin clearance in rats with dietary-induced obesity

Insulin uptake in the in situ perfused liver from rats that were moderately obese after overfeeding was diminished in comparison with controls. The obese rats had higher levels of portal free fatty acids (FFA) and liver triglyceride contents but not of insulin concentration in the portal vein. There were strong negative correlations between hepatic triglyceride and insulin clearance (r approximately 0.8-0.9). The perfusions were performed with lower FFA concentrations than those in vivo in the portal vein. It is suggested that the inhibited insulin uptake in the obese rats was due to exposure of these livers in vivo to elevated FFA concentrations, and that this inhibition remained during the experiment and was associated with the triglyceride contents of the livers. It is also suggested that this mechanism was responsible for the moderate peripheral hyperinsulinemia seen in these rats. A mechanism of regulation of insulin uptake in the liver via FFA and liver triglyceride might be of importance in several conditions with hyperinsulinemia and known elevation of portal FFA, and liver triglyceride contents.     

Estrogen regulation of the nuclear 1,25-dihydroxyvitamin D3 receptor in rat liver and kidney.

We previously identified a receptor protein for 1,25-dihydroxyvitamin D3 in rat liver nuclei. The present studies were undertaken to investigate the ontogenesis of the hepatic nuclear vitamin D receptor (nVDR) and the estrogen regulation of this receptor in the liver, small intestine, and kidneys. The hepatic nVDR was significantly elevated in adult female rats compared to prepubertal female rats, while in male rats, this increase was not observed. Oophorectomized rats contained significantly less hepatic nVDR than did intact female rats. Administration of estradiol to castrated male or oophorectomized rats increased the hepatic nVDR. Further studies demonstrated that the increase in the hepatic nVDR was observed only after 2 weeks of estradiol treatment and was positively correlated with circulating estradiol concentrations. Castration of male rats did not alter the hepatic nVDR compared to intact male rats nor did testosterone administration to castrated male rats for 4 weeks change the hepatic nVDR concentration. Unlike the liver, intact female rats contained significantly less renal nVDR than did kidneys from intact male or castrated male rats. Estradiol administration to oophorectomized rats significantly decreased the renal nVDR. Renal nVDR concentrations correlated inversely with the serum concentration of estradiol. Castration of male rats had no effect on the renal nVDR. Intestinal nVDR concentrations were unaffected by castration of male rats or by treatment of castrated male rats with estrogen for up to 4 weeks. These results indicate that estradiol increases the nVDR in liver, decreases the nVDR in kidney and does not change the nVDR in the intestine. Physiological concentrations of testosterone do not regulate the nVDR in these tissues. Estradiol regulation of this receptor is organ specific and, therefore, conclusions about the regulation of the nVDR in one tissue cannot be extrapolated to other tissues.     

Carbohydrate and oxygen metabolism during hepatocellular proliferation: a study in perfused livers from mirex-treated rats

Liver regeneration after partial hepatectomy is accompanied by altered hepatic intermediary metabolism. Because the organochlorine compound mirex also causes liver cell growth, the purpose of this study was to investigate hepatic carbohydrate and oxygen metabolism in perfused livers from mirex-treated rats and to localize cell proliferation in this model. Pretreatment with mirex (100 mg/kg, intragastrically) increased liver/body weight ratios and DNA synthesis in livers of fed rats, effects that were markedly diminished in livers of fasted rats. This finding shows that liver growth caused by mirex, as is the case after partial hepatectomy, is hindered when animals are deprived of food. Furthermore, perfused livers from mirex-treated rats had depleted glycogen stores but significantly elevated oxygen uptake compared with livers from control rats. Increases in oxygen uptake and hepatocellular proliferation were observed mostly in periportal regions of the liver lobule. In regenerating livers, most DNA synthesis was reported to also occur in these regions of the liver lobule. Taken together, these data show that liver cell growth caused by mirex is accompanied by changes in hepatic intermediary metabolism and sublobular proliferation similar to those observed after partial hepatectomy.     

Liver injury and lipid metabolism: sex differences in the fatty liver induced by d-galactosamine.

The time-course of plasma lipid alterations and of triglyceride accumulation in the liver was investigated in male and female rats 12, 24 and 48 hours after treatment with 3.48 mmole/kg (0.75 g/kg) D-galactosamine (Ga1N). In the early stages of Ga1N-induced liver injury the concentrations of triglycerides, phospholipids and total cholesterol decreased, while in the later stages these values in the plasma increased above normal, especially in male animals. In contrast, glucose concentrations continually decreased, while free fatty acid (FFA) levels rose to twice those normal in female animals. Male animals had significantly lower FFA-values throughout the experiment. Consistently, the triglyceride accumulation on liver was 75 mg/g in female animals 24 hours after Ga1N administration, while male animals in the average showed only 33 mg/g triglycerides. Similar fatty infiltrations were obtained in female animals with the rather low doses of 1.16 and 2.32 mmol/kg Ga1N. It is concluded that the increase of FFA-influx after Ga1N administration is the main cause for fatty infiltration, the sex differences in the plasma FFA concentrations explaining the net differences in liver triglyceride accumulation. Additional effects in the pathogenesis of fatty liver might stem from disturbed glycosylation reactions and/or an altered secretion and metabolism of lipoproteins after Ga1N-induced liver injury.     

Aldosterone metabolism in the isolated perfused liver of female and male rats

A sex-dependent metabolism of aldosterone has been reported in intact rats. To further characterize the hepatic elimination of aldosterone and its sex dependence, the metabolism of d-[4-14C]aldosterone was studied in isolated perfused liver from male and female Wistar rats, from male rats castrated 3 weeks before experiments, and from younger male rats (same body weight as the female rats). The livers were perfused at a constant flow rate in a recirculating mode with a hemoglobin-free medium containing aldosterone at initially 1 nM. Perfusate aldosterone was measured by a specific RIA. Total 4-14C radio-activity in perfusate and bile was determined. The perfusate [4-14C]aldosterone radiometabolite concentration was calculated. The radiometabolite pattern in additional experiments was studied by HPLC. The male rats exhibited 10% higher systolic blood pressure (P less than 0.05) and 51% higher fasting values of plasma aldosterone (P less than 0.05) compared to those in the female rats. In female rats the hepatic clearance rate of aldosterone per 100 g BW was 72% higher than that in male rats (11.2 +/- 2.7 to 6.5 +/- 1.8 ml/min: P less than 0.01), and that expressed per g liver wet wt was 75% higher (3.5 +/- 1.0 to 2.0 +/- 0.7 ml/min; P less than 0.01). When female rats were compared to younger male rats with the same body weight, 33% higher hepatic aldosterone clearance rates were still found in female rats (21.0 +/- 5.4 to 15.8 +/- 3.2 ml/min; P less than 0.05), and 51% higher values when expressed per g liver wet wt (3.5 +/- 1.0 to 2.3 +/- 0.5 ml/min; P less than 0.01). No difference in the aldosterone clearance rate was observed in castrated male rats compared to that in noncastrated male rats. 4-14C-Labeled radiometabolite levels accumulated similarly in the perfusate of livers of both sexes. Perfusate 4-14C-labeled radiometabolites after 90 min of perfusion were lower in livers of castrated male rats than in noncastrated male rats (P less than 0.001). The final perfusate 14C-labeled radiometabolite concentration correlated inversely with the total 14C in bile (P less than 0.01). All 14C-labeled radiometabolites detected in perfusate and bile after 90 min were more polar than aldosterone. After enzymatic hydrolysis, some of the metabolites from the male livers cochromatographed with tetrahydro- and dihydroaldosterone, while other fractions remained more polar. Only more polar metabolites were detected in the perfusate and bile of female livers.(ABSTRACT TRUNCATED AT 400 WORDS)     

Role of carnitine in hepatic ketogenesis.

The enhancement of long-chain fatty acid oxidation and ketogenesis in the perfused rat liver, whether induced acutely by treatment of fed animals with anti-insulin serum or glucagon, or over the longer term by starvation or the induction of alloxan diabetes, was found to ba accompanied by a proportional elevation in the tissue carnitine content. Moreover, when added to the medium perfusing livers from fed rats, carnitine stimulated ketogenesis from oleic acid. The findings suggest that the increased fatty acid flux through the carnitine acyltransferase (carnitine palmitoyl-transferase; palmitoyl-CoA:L-carnitine O-palmitoyltransferase; EC 2.3.1.21) reaction brought about by glucagon excess, with or without insulin deficiency, is mediated, at least in part, by elevation in the liver carnitine concentration.     

Galactose and glucose metabolism in the isolated perfused suckling and adult rat liver

The development of the technique for the perfusion of the immature liver has enabled us to characterize metabolic differences in carbohydrate metabolism in the suckling versus adult rat livers. Livers of fasted suckling and adult rats were perfused with 4 mM galactose or 4 mM glucose. Galactose uptake was the same for both age groups during the first 35 min. The adult liver maintained the initial rate of uptake after this period while the immature liver began to take up galactose more rapidly. By the end of the experimental period, on a weight basis, uptake by the young liver was three times that of the adult. Analysis of the livers at the end of the 90 min perfusion showed hepatic galactose concentrations to be one-half of circulating media levels.Glucose output was observed in each group during perfusion with either galactose or glucose. In the immature liver, galactose perfusion stimulated more glucose output than did the glucose perfusion. In the adult, however, both sugars resulted in the same levels of glucose output. Galactose perfusion resulted in glucose levels in young liver being higher than the media; while in the adult, the level was lower than the media.Galactose perfused livers of the suckling and adult contained significantly more uridine-5′-diphosphogalactose than the glucose perfused livers of each age.     

Effects of dibutyryl adenosine 3',5'-monophosphate on hepatic metabolism of free fatty acids.

The effects of dibutyryl cyclic adenosine 3',5'-monophosphate (Bu2cAMP) on metabolism of free fatty acids by perfused livers from normal fed male rats were investigated. In one group of experiments, Bu2cAMP was added to the medium and infused at a constant rate to maintain concentrations of 0, 0.4, 1.0, 4.0, or 10. 0 X 10(-5) M nucleotide in the perfusate plasma, assuming the nucleotide was not metabolized by the liver. Oleic acid was infused as the complex with albumin at the rate of 124.3 mumoles/hr. Uptake of free fatty acid by the liver was identical in all groups. Production of ketone bodies, however, increased, and output of triglyceride decreased with increasing concentration of Bu2cAMP. The nucleotide also stimulated output of glucose. Maximal effects were observed when the concentration of Bu2cAMP was approximately 2-3 X 10(-5) M. The output of very low density lipoproteins, as judged by flotation in the zonal ultracentrifuge, was also diminshed by the nucleotide. In other experiments, 1-14C-oleate was infused (120.8 mumoles/hr) along with 2 X 10(-5) M Bu2cAMP, and the disposition of 14C into CO2, ketone bodies, and esterified lipids was evaluated. Bu2cAMP depressed the proportion of 1-14C-oleate converted to triglyceride and increased the fraction converted to ketone bodies and CO2. Not only was ketogenesis stimulated, but a larger proportion of the ketone bodies was derived from exogenous fatty acid.     

Secretion of cholesteryl ester-enriched very low density lipoproteins by the liver of cholesterol-fed rabbits

The output of lipids and lipoproteins by isolated perfused livers of normal-fed and cholesterol-fed rabbits has been examined. There was a comparable output of triglyceride by the livers of both groups, resulting in an accumulation of 40-50 mg triglyceride/liver/2 h in the perfusate in each case. The output of cholesteryl esters, however, was very much greater from the livers of cholesterol-fed (45 mg/liver/2 h) than from normal-fed (3.3 mg/liver/2 h) rabbits. The major lipoproteins in liver perfusates from both groups of animals were very low density lipoproteins (VLDL). In the perfusate of normal livers the VLDL were enriched with triglyceride and depleted of cholesteryl esters when compared with plasma VLDL from normal animals. VLDL in the perfusate of livers from cholesterol-fed rabbits, on the other hand, were markedly enriched with cholesteryl esters; cholesteryl esters accounted for 33% by mass of VLDL from cholesterol-fed livers and only 3.1% of VLDL from normal livers. The cholesteryl esters in the plasma lipoproteins of cholesterol-fed rabbits were relatively enriched with cholesteryl oleate when compared to those in normal plasma. Similarly, cholesteryl oleate predominated in the VLDL in the liver perfusate of the cholesterol-fed animals, consistent with an hepatic acyl CoA/cholesterol acyltransferase origin. Thus, cholesterol-feeding in the rabbit results in a marked increase in the hepatic secretion of cholesteryl esters as a component of VLDL.     

Ischemia-reperfusion injury in rat fatty liver: role of nutritional status

Fatty livers are more sensitive to the deleterious effects of ischemia-reperfusion than normal livers. Nutritional status greatly modulates this injury in normal livers, but its role in the specific setting of fatty liver is unknown. This study aimed to determine the effect of nutritional status on warm ischemia-reperfusion injury in rat fatty livers. Fed and fasted rats with normal or fatty liver induced by a choline deficient diet underwent 1 hour of lobar ischemia and reperfusion. Rat survival was determined for 7 days. Serum transaminases, liver histology and cell ultrastructure were assessed before and after ischemia, and at 30 minutes, 2 hours, 8 hours, and 24 hours after reperfusion. Survival was also determined in fatty fasted rats supplemented with glucose before surgery. The preischemic hepatic glycogen was measured in all groups. Whereas survival was similar in fasted and fed rats with normal liver (90% vs. 100%), fasting dramatically reduced survival in rats with fatty liver (14% vs. 64%, P <.01). Accordingly, fasting and fatty degeneration had a synergistic effect in exacerbating liver injury. Mitochondrial damage was a predominant feature of ultrastructural hepatocyte injury in fasted fatty livers. Glucose supplementation partially prevented the fasting-induced depletion of glycogen and improved the 7-day rat survival to 45%. These data indicate that rat fatty livers exposed to normothermic ischemia-reperfusion injury are much more sensitive to fasting than histologically normal livers. Because glucose supplementation improves both the hepatic glycogen stores and the rat survival, a nutritional repletion procedure may be part of a treatment strategy aimed to prevent ischemia-reperfusion injury in fatty livers.     

Effects of D-3-hydroxybutyrate and acetoacetate on lactate removal in isolated perfused livers from starved and fed rats.

We examined the influence of nutritional state on the role of the hepatic plasma membrane lactate transporter in determining overall hepatic lactate disposal. The effects of infusion of sodium D-3-hydroxybutyrate (DOHB) on lactate uptake were studied in perfused livers from fed or starved rats. In livers from starved rats, DOHB (15 to 20 mmol/L) inhibited lactate removal by approximately 45%. This effect was associated with a decrease in intracellular lactate concentration, with cell pH remaining unchanged. Inhibition was maximal when perfusate lactate was less than 1.6 mmol/L, and was undetectable at concentrations exceeding 2.5 mmol/L. A similar degree of inhibition was observed with infusion of acetoacetate. These observations add to the evidence that the inhibition of lactate removal by DOHB seen in livers from starved animals is mediated through an effect on the hepatocyte lactate transporter. At similar low levels of perfusate lactate, DOHB infusion produced a decrease in output of lactate from livers obtained from fed animals. When such livers were subjected to prolonged preperfusion, lactate removal, rather than output, was observed; in these livers DOHB stimulated lactate removal, an effect directionally opposite to that observed in livers from starved animals. These data confirm that hepatic lactate transport is a limiting factor for lactate utilization in intact livers from starved rats; in contrast, lactate utilization in livers from fed animals is limited at a step subsequent to plasma membrane transport, ie, possibly pyruvate transport into mitochondria.     

Lysosomal leakage and lack of adaptation of hepatoprotective enzyme contribute to enhanced susceptibility to ethanol-induced liver injury in female rats

BACKGROUND: Women exhibit greater liver damage than men after chronic alcohol consumption. Similar findings are reported in animal models. Here, we determined whether differential liver injury occurred in male and female rats after feeding these animals liquid diets containing either ethanol or isocaloric dextrose with fish oil as the sole source of lipid. METHODS: Control and ethanol liquid diets containing fish oil were pair-fed to male and female rats for 8 weeks. Liver damage was evaluated by triglyceride accumulation, lipid peroxide formation, serum transaminases, histological evaluation, and the activities of selected lysosomal and hepatoprotective enzymes. RESULTS: Fatty liver was detected after ethanol feeding in both genders, but in female rats, triglyceride levels were 60% higher, lipid peroxides were 2-fold higher, and inflammatory cells were more evident than in males. A 2-fold elevation of cathepsin B in hepatic cytosol fractions, indicating lysosomal leakage, was detected in ethanol-fed female rats but no such elevation was observed in males. The basal activity of the hepatoprotective enzyme, betaine-homocysteine methyltransferase was 4-fold higher in livers of control male rats than females, and the enzyme activity was further elevated in ethanol-fed male rats but not in females. CONCLUSIONS: Thus, female rats given ethanol in a diet containing fish oil exhibited more severe liver damage than males. We propose that this difference results, in part, from a greater tendency by females to accumulate hepatic fat, thereby enhancing the potential for oxidative stress, which in turn leads to hepatic inflammation. In addition, our findings indicate that female rats have a higher susceptibility to liver damage because of a reduced capacity for hepatoprotection.     

Hydrodynamic and energetic aspects of exogenous free fatty acid perfusion in the isolated rat heart during high flow anoxia and reoxygenation: a 31P magnetic resonance study.

STUDY OBJECTIVE--The aim was to show differences between the effects of various dietary long chain fatty acids (palmitic, oleic, linoleic, alpha and gamma linolenic acids) perfused in isolated rat hearts subjected to a sequence of high flow anoxia and subsequent reoxygenation. DESIGN--Isolated working rat hearts perfused with selected exogenous fatty acids were allowed an initial 30 min equilibration period followed by 60 min of high flow anoxia and 40 min of reoxygenation. Ventricular function and tissue contents of phosphorylated metabolites were monitored concomitantly using standard procedures and 31P magnetic resonance spectroscopy respectively. EXPERIMENTAL MATERIAL--Hearts were removed from male Wistar rats weighing 350-400 g. Results from eight hearts were pooled for each of the five fatty acids perfused. MEASUREMENTS AND MAIN RESULTS--High coronary flow maintained during anoxia led to an increased extracellular washout of lactate and only to mild intracellular acidosis, limiting myocardial damage by metabolites of anaerobic glycolysis. Under these conditions, marked differences between the classes of perfused fatty acids were observed. Hearts which received oleic acid showed the most depressed ventricular function and a greater depletion in high energy phosphates content. These deleterious effects were completely reversed by the separate administration of two fatty acid metabolism blocking agents, nicotinic acid and oxfenicine. Cardioprotection was enhanced by perfusion of polyunsaturated fatty acids (linoleic acid, alpha and gamma linolenic acids). Hearts perfused either with glucose or with palmitic acid behaved similarly and showed an intermediate functional and metabolic postanoxic recovery. CONCLUSION--This study documents the relation between the chemical structure of exogenous fatty acids used in heart perfusion and their ability to improve or impair postanoxic myocardial recovery. The cardioprotective effect of polyunsaturated fatty acids was documented by simultaneous evaluation of mechanical performance and metabolic response.