Influence of sex and level on marathon pacing strategy. Insights from the New York City race.

Different pacing profiles have been identified in the literature for endurance sporting events: the 'positive', 'negative', 'even', 'parabolic shaped' and 'variable pacing'. Most studies have focused on competitive or elite athletes (including winners) without considering more recreational runners, for many of whom the primary goal is simply to finish the event. The major city marathons provide a large heterogeneous sample to compare the pacing profiles of competitive vs. recreational runners, and thus to understand pacing more broadly. A total of 190,228 New York finishers' (69,316 women) marathon times (from 2006 to 2011) were assessed. Although all runners developed a positive pace profile, a lower variability of speed through the race was found in the top runners (coefficient of variation (CV) for speed during 5-km splits: 7.8% (men) and 6.6% (women)) compared with the less successful runners (CV ranging from 8.3 to 14.4%). Both men and women try to maintain an even pace profile along the marathon course, partly by avoiding an excessively fast start that might result in a pronounced decrease in the speed in the second half of the race.

Effects of melatonin on fuel utilization in exercised rats: role of nitric oxide and growth hormone.

We have previously reported that melatonin modifies carbohydrate and lipid utilization in exercised rats, maintaining glycemia and reducing plasma and liver lactate and plasma beta-hydroxybutyrate. This study was undertaken to determine whether effects on fuel metabolism were related to changes in nitric oxide (NO) production or growth hormone (GH) secretion. Male Wistar rats received melatonin i.p. at a dose of 0.5 mg/kg body weight 30 min before being exercised to exhaustion on a treadmill at a speed of 24 m/min and a 12% slope. Melatonin ameliorated the decrease in plasma glucose and the increase in plasma urea, free fatty acid, beta-hydroxybutyrate, and nitrite induced by exercise. Melatonin-treated exercised rats had significantly elevated liver glycogen content and hepatic tissue showed a lowered expression of both inducible and constitutive NO synthase (iNOS and cNOS). Administration of the NO inhibitor NG-nitro-L-arginine (L-NAME) to exercised rats caused a significant reduction in plasma nitrite, but liver glycogen and biochemical parameters in blood did not significantly differ from untreated exercised animals, indicating the absence of a direct association between melatonin effects on fuel metabolism and NO levels. Although results of treatment with pyridostigmine, a cholinergic agonist drug that stimulates GH release, partially differed from that of melatonin, modulation of GH secretion could play a role in the metabolic actions of the hormone because effects of melatonin on exercised rats were almost completely blocked by simultaneous administration of L-NAME.

Effect of epomediol on ethinyloestradiol-induced changes in bile acid and cholesterol metabolism in rats.

1. Epomediol is a terpenoid compound that has been reported to stimulate bile acid synthesis and to reverse 17alpha- ethinyloestradiol-induced cholestasis. The aim of the present study was to investigate the contribution of changes in bile acid and cholesterol metabolism to the protective effects of epomediol in ethinyloestradiol-treated rats. Animals received epomediol for 5 days at 100 mg/kg daily, i.p., ethinyloestradiol for 5 days at 5 mg/kg, s.c., or a combination of both drugs. 2. When compared with control animals, epomediol treatment resulted in a significant increase in bile flow (+42%) and in the secretion of bile acids (+74%) and cholesterol (+42%). Ethinyloestradiol administration caused a significant decrease in bile flow (-43%), bile acid secretion (-37%) and cholesterol secretion (-45%). Bile flow, bile acid secretion and cholesterol secretion were significantly increased in animals receiving ethinyloestradiol plus epomediol compared with ethinyloestradiol-treated rats (+13, +29 and +31%, respectively). 3. Both cholesterol 7alpha-hydroxylase and hydroxy-3- methylglutaryl coenzyme A reductase activities were significantly increased in epomediol-treated rats (+30 and +96%, respectively). Cholesterol 7alpha-hydroxylase activity was significantly reduced by ethinyloestradiol (-22%) and did not differ from control values in animals receiving epomediol plus ethinyloestradiol. Levels of cholesterol 7alpha-hydroxylase mRNA were elevated (+41%) by epomediol, but were not significantly modified by ethinyloestradiol or ethinyloestradiol plus epomediol. 4. It is concluded that epomediol enhances bile acid secretion by increasing the expression of cholesterol 7alpha-hydroxylase. Changes in bile acid metabolism contribute to the effects of epomediol in rats with ethinyloestradiol-induced cholestasis.

Factors influencing the inhibition of biliary glutathione efflux induced by biliary obstruction.

The aim of this study was to investigate mechanisms responsible for the inhibition of biliary glutathione efflux in rats with secondary biliary cirrhosis. Rats were studied after bile duct obstruction for 28 days. The biliary secretion of reduced glutathione (GSH), oxidised glutathione (GSSG) and cysteine were completely inhibited in biliary obstructed rats. Hepatic gamma glutamyltranspeptidase (gamma-GT) activity increased significantly, but following its inhibition by acivicin administration GSH, GSSG and cysteine were still absent in bile. Biliary obstruction resulted in a significant increase of the permeability of the paracellular pathway, as shown by the higher bile/plasma ratio and hepatic clearance of [14C]sucrose. GSH and GSSG were, however, significantly lower in the carotid artery and hepatic vein of obstructed animals and the arteriovenous difference across the liver was reduced. The concentration of GSH was significantly reduced and that of GSSG increased in the liver of obstructed rats. Biliary obstruction induced an increase in the hepatic concentration of cysteine and an inhibition of both gamma glutamylcysteine synthetase and methionine adenosyl transferase activities. Dichlorofluorescein (DCF) and the GSSG/GSH ratio and thiobarbituric acid reactive substances (TBARS) concentration, markers of reactive oxygen species production and lipid peroxidation, respectively, were significantly increased. Our data indicate that increased degradation or blood reflux of glutathione do not participate in the disruption of its secretion into bile and support the view that impairment of glutathione synthesis and oxidative stress could contribute to the decline in biliary glutathione output.

The flavonoid quercetin ameliorates liver damage in rats with biliary obstruction.

BACKGROUND/AIMS: Our aim was to investigate whether the antioxidant quercetin might protect against liver injury in chronically biliary obstructed rats. METHODS: Secondary biliary cirrhosis was induced by 28 days of bile duct obstruction. Animals received quercetin at 75, 150 and 300 micromol x kg body wt(-1) x day(-1) i.p. through the experimental period or at 150 micromol x kg body wt(-1) x day(-1) i.p. for the last 2 weeks. RESULTS: Bile duct obstruction resulted in a decrease in the activities of antioxidant enzymes. Liver oxidised/reduced (GSSG/GSH) glutathione ratio, hepatic and mitochondrial thiobarbituric acid reactive substances (TBARS) and collagen content were significantly increased and a marked fibrosis and bile ductular proliferation was observed. Quercetin corrected the reduction in glutathione concentration and partially prevented the increase in collagen concentration, TBARS and GSSG/GSH ratio. Treatment resulted in a significant preservation of the activities of antioxidant enzymes, a less pronounced fibrosis and a marked inhibition of bile ductular proliferation. Maximal effects were reached with the intermediate quercetin dose given for 2 or 4 weeks. CONCLUSIONS: Quercetin reduces liver oxidative damage, ductular proliferation and fibrosis in biliary-obstructed rats. These effects suggest that it might be a useful agent to preserve liver function in patients with biliary obstruction.

Enhancement of bile acid pool size, synthesis and secretion by epomediol in the rat.

Epomediol is a terpenoid compound that has been reported to reverse 17alpha-ethinylestradiol-induced cholestasis and to have a choleretic effect related to the biliary secretion of epomediol glucuronide. The aim of this study was to investigate the contribution of changes in bile acid metabolism to epomediol-induced effects on bile formation. Twenty-four-hour bile collections were performed in animals that had received intraperitoneal epomediol for five days at 100 mg/kg daily. Epomediol-treated rats had a 24% larger bile acid pool and 28% greater bile acid synthesis than controls when measured by the "washout" technique. There was no change in the fractional turnover rate and the cycling frequency of the pool. Both basal bile flow and bile acid secretion were significantly increased (+42% and +74%, respectively). Linear regression analysis between bile flow and bile acid secretion revealed that both bile acid-dependent fraction and bile acid-independent fraction were significantly increased (+40 and +27, respectively), with no change in the choleretic capacity of bile acids. Cholesterol secretion was increased by 42%, but there were no significant differences in phospholipid secretion. Cholesterol 7alpha-hydroxylase and HMG-CoA reductase activities were significantly higher in epomediol-treated rats (+39% and +97%, respectively). The activities of NADPH-cytochrome c reductase and aniline hydroxylase were also significantly elevated (+26% and +64%, respectively). It is concluded that epomediol treatment expands the bile acid pool through an enhanced bile acid synthesis. Choleresis induced by the drug is partly related to the increase in bile acid secretion.

Melatonin increases muscle and liver glycogen content in nonexercised and exercised rats.

The effects of melatonin on several parameters of carbohydrate and lipid metabolism were investigated in exercised and nonexercised rats. Animals were run to exhaustion on a rodent treadmill at 24 m/min and a 12% slope. Exercise resulted in a significant hypoglycemia and increased plasma levels of lactate and beta-hydroxybutyrate, together with a significant reduction of glycogen in muscle and liver. Muscle and liver glycogen content was elevated and plasma free fatty acid decreased in nonexercised animals receiving melatonin (0.5 or 2.0 mg/kg i.p). Melatonin at 2.0 mg/kg reduced plasma lactate and increased lactate concentration in liver. When compared to untreated exercised animals glycemia and muscle and liver glycogen content were significantly higher in melatonin-treated exercised animals, while plasma and liver lactate and plasma beta-hydroxybutyrate were significantly reduced. Our data indicate that melatonin preserves glycogen stores in exercised rats through changes in carbohydrate and lipid utilization.

Antioxidant enzyme status in biliary obstructed rats: effects of N-acetylcysteine.

BACKGROUND/AIMS: N-acetylcysteine (NAC) is a modulator of thiol levels that protects against hepatotoxic agents. The aim of this study was to investigate whether NAC might improve hepatic antioxidant defenses in chronically biliary obstructed rats. METHODS: Secondary biliary cirrhosis was induced by 28 days of bile-duct obstruction. Groups of control and cirrhotic animals received NAC (50 mumol .kg-1.d-1 i.m.) through the experimental period. RESULTS: Bile-duct obstruction resulted in decreased liver glutathione concentrations. Dichlorofluorescein (DCF) and thiobarbituric acid reactive substances (TBARS) concentrations, measured as markers of production of reactive oxygen species and lipid peroxidation, respectively, were significantly increased. Microsomal and mitochondrial membrane fluidity and the activities of catalase, cytosolic and mitochondrial superoxide dismutase (SOD), glutathione S-transferase, and cytosolic and mitochondrial Se-dependent and Se-independent glutathione peroxidase (GPx) were significantly reduced. NAC corrected the reduction in glutathione concentration and partially prevented the increases in DCF and TBARS concentrations. In addition, NAC treatment resulted in significant preservation of membrane fluidity and of the activities of catalase, mitochondrial SOD and the different forms of GPx. CONCLUSIONS: Our data indicate that NAC maintains antioxidant defenses in biliary obstructed rats. These effects of NAC suggest that it may be a useful agent to preserve liver function in patients with biliary obstruction.

Microsomal function in biliary obstructed rats: effects of S-adenosylmethionine.

BACKGROUND/AIMS: S-adenosylmethionine has been reported to have beneficial effects in the treatment of different chronic liver diseases and to protect against different hepatotoxic agents. The aim of this study was to investigate whether S-adenosylmethionine treatment might contribute to improved microsomal function in chronically biliary obstructed rats. METHODS: Secondary biliary cirrhosis was induced by 28 days of bile duct obstruction. Groups of control and cirrhotic animals received S-adenosylmethionine (10 mg/kg per day) through the experimental period. RESULTS: Bile duct obstruction resulted in a marked increase in lipid peroxidation levels and decreases in glutathione concentration, microsomal membrane fluidity, microsomal cytochrome P-450 content, NADPH-cytochrome P-450 reductase activity and the activities of the aniline hydroxylase, aminopyrine demethylase and ethoxycoumarin deethylase. Reductions in glutathione and cytochrome P-450 concentration were not corrected by S-adenosylmethionine, but lipid peroxidation, the decrease in the activities of the various microsomal monooxygenases and the reduction in microsomal membrane fluidity were partially prevented. A significant relationship was found between membrane fluidity and aniline hydroxylase, aminopyrine demethylase or ethoxycoumarin deethylase activities. CONCLUSIONS: S-adenosylmethionine administration partially preserves microsomal function. This effect could be associated to the protection of membrane function by restoring transmethylation reactions.

Impairment of bile secretion induced by exhaustive exercise in the rat. Protective effects of S-adenosyl-L-methionine.

The effects of strenuous exercise on the mechanisms of bile formation were studied in rats. Animals (n = 8) were exercised to exhaustion in a rodent treadmill at a speed of 24 m/min and a 12% slope. Hepatic glutathione concentration was significantly reduced (-40%) and liver malondialdehyde content significantly increased (+37%) when compared to sedentary controls (n = 6). Both serum alkaline phosphatase level and bile acid concentration were significantly higher in runners (+81% and +85%). Bile flow and the biliary secretion of bile acids were significantly reduced both in basal conditions and following an i.v. taurocholate infusion (0.5 mumol/min/100 g body wt). Biliary glutathione secretion was also significantly decreased following exercise. Cholestasis was caused by an impairment of both bile acid-dependent (BADF) and bile acid-independent fraction (BAIF) of bile flow (-25% and -29% respectively). Exercise caused a delay in the peak appearance time and a reduced biliary secretion of horseradish peroxidase, suggesting alterations in the functional integrity of the cytoskeleton. To test the protective effects of S-adenosyl-L-methionine (SAMe), rats received the drug for ten days at a daily dose of 8 mg/kg i.p. SAMe administration prevented hepatic glutathione depletion due to exercise, normalizing both bile flow and bile acid as well as glutathione secretion. Our results suggest that both glutathione depletion and alterations in fluidity and composition of hepatocyte membranes could contribute to the development of exercise-induced cholestasis.

The effects of total parenteral nutrition on the hepatic handling of bilirubin in the rat.

Disturbances of bilirubin metabolism such as jaundice or pigment gallstone formation occur during total parenteral nutrition (TPN). We have studied the effects of TPN on bile flow and bile acid secretion and on the hepatobiliary transport of bilirubin in rats. Animals on parenteral nutrition for 5 days received 4.8 g of amino acids and 6.9 g of glucose daily. Controls were orally fed animals. Bile flow and bile acid secretion were not significantly modified by TPN. Serum bile acid and alkaline phosphatase levels were significantly increased in TPN animals when compared with the controls (+98% and +38%, respectively), which points to a relative cholestasis in the TPN rats. The biliary excretion of bilirubin monoconjugates and bilirubin diconjugates was significantly increased (+72% and +78%, respectively). This provides evidence for enhanced production of the pigment. Serum concentration of total bilirubin was enhanced in the TPN rats (+240%). The esterified/total bilirubin ratio in serum increased, whereas the bilirubin diconjugates/bilirubin monoconjugates ratio decreased. These facts, together with the minor reduction of hepatic bilirubin UDP glucuronosyltransferase activity (-12%), suggest that hyperbilirubinemia would be a consequence of both cholestasis and increased bilirubin production. The alterations reported here could contribute to the explanation of hyperbilirubinemia and pigment gallstone formation in patients maintained on parenteral nutrition.

Changes in the biliary excretion of organic anions following exhaustive exercise in rats.

The effect of exhaustive exercise on the hepatobiliary transport of organic anions was investigated in rats. Animals were run on a rodent treadmill at 24 m/min up a 12% grade (152 +/- 15 min). Exercise resulted in significant hypoglycaemia (-46%) and increased plasma levels of lactate (+12%), together with a marked reduction of glycogen concentration in the liver (-72%). When bromosulphthalein was administered i.v., its maximal biliary excretion (Tm) was significantly reduced (-30%), and plasma and liver concentrations of the dye were increased (+31% and +56%, respectively). The decrease corresponded both to the excretion of the conjugated and unconjugated dye (-30% and -33%, respectively). Cytosolic glutathione S-transferase activity in the liver was not affected by exercise, but there was a significant reduction in the hepatic concentration of glutathione (-50%). The Tm of dibromosulphthalein was also significantly reduced (-36%) and its plasma and liver concentrations increased (+67% and +33%, respectively) in exercised rats. The results suggest that, in addition to the direct effect of liver glutathione depletion, other factors must be involved in the impairment of the biliary excretion of organic anions caused by exercise.

Sex-related differences in the hepatobiliary transport of phenolsulfonphthalein in the rat.

Sex-related differences in the hepatobiliary transport of phenolsulfonphthalein (PSP) were investigated in male and female Wistar rats. Maximal biliary excretion of unconjugated PSP was significantly higher in females while the excretion of the conjugated dye and liver UDP-glucuronosyltransferase activity toward PSP were higher in male animals. Orchidectomy decreased enzyme activity and excretion of the conjugate, whereas ovariectomy produced the opposite effect. Both in gonadectomized males and females maximal biliary excretion of the unconjugated dye was significantly reduced. Testosterone treatment increased the excretion of both conjugated and unconjugated PSP and transferase activity in orchidectomized males. Combined treatment of gonadectomized females with estradiol plus progesterone led to excretions of both conjugated and unconjugated PSP and UDP-glucoronosyltransferase activities similar to those found in control rats. These data indicate the existence of sex-related differences in the conjugation and biliary excretion of PSP in the rat and its modulation by sex hormones.

Inhibition of fibrinolysis by cellular glutathione depletion in the rabbit.

The effect of cellular glutathione depletion on fibrinolytic activity in the arterial wall and on the levels of components of the plasma fibrinolytic system was studied in rabbits. Intraperitoneal administration of buthionine sulphoximine (4.5 mmol/kg body wt), an inhibitor of gamma-glutamyl cysteine synthetase, induced a significant reduction in liver glutathione concentrations with a peak decrease of 51% at 7 hours and a progressive return to normal values. The glutathione concentration in aortic tissue was also significantly reduced 7 h after administration of the depleting agent. Fibrinolytic activity in the arterial wall was inhibited following buthionine sulphoximine administration and only reappeared at 24 hours postinjection. Diethyl maleate administration (3.2 mmol/kg body wt i.p.) also depleted liver and aortic glutathione and inhibited fibrinolysis in the arterial wall. Treatment with both glutathione-depleting agents induced a significant reduction in the functional activity of tissue plasminogen activator (t-PA) (-61% and -27% respectively for buthionine sulphoximine or diethyl maleate) and a significant increase in that of plasminogen activator-inhibitor (PAI) (+61% and +27% respectively), while alpha-2-antiplasmin activity was not modified. Our data suggest a modulatory role of glutathione in the release and/or clearance of the components of the fibrinolytic system in the rabbit.

Postnatal development of the hepatobiliary transport of phenolsulfonphthalein in rats.

1. The postnatal development of the biliary excretion of phenolsulfonphthalein (PSP) was studied in male Wistar rats. 2. Following i.v. injection of PSP at 200 mumol/kg body wt, a maximal biliary excretion of 175 +/- 10 nmol/min/100 g body wt and 32 +/- 5 nmol/min/100 g body wt was reached for unconjugated and conjugated PSP, respectively, in the adult group. 3. The maximal biliary excretion of conjugated PSP was significantly lower in the 20-, 30- and 40-day-old groups as compared to the adults. The excretion of unconjugated dye was also significantly lower in 20- and 30-day-old rats. 4. The postnatal development of PSP excretion was unrelated to changes in the activity of UDP-glucuronosyltransferase. The importance of other factors is also discussed.

Spontaneous atherosclerotic lesions and prostacyclin formation in rabbits: effects of combined dipyridamole and aspirin.

The influence of dipyridamole and lysine acetylsalicylate on the incidence of atherosclerotic lesions and on arterial prostacyclin formation was studied in rabbits. Male New Zealand rabbits received i.m. for 16 months dipyridamole (12.5 mg/kg/day) and lysine acetylsalicylate (0.5 mg/kg/day). The incidence of spontaneous atherosclerotic lesions in the aorta was reduced by 16.4% with respect to untreated animals. Administration of the drugs significantly increased prostacyclin formation with respect to the untreated rabbits both in animals developing (1124 +/- 197 pg/mg/3 min vs 316 +/- 49 pg/mg/3 min) or not developing lesions (499 +/- 40 pg/mg/3 min vs 246 +/- 19 pg/mg/3 min). The observed increase in prostacyclin formation could account for the lowered incidence of atherosclerotic lesions in rabbits receiving the combination of dipyridamole and lysine acetylsalicylate.

Influence of bile acids on the biliary transport maximum of phenolsulfonphthalein in the rat.

1. The effect of changes in bile acid secretion induced by cholestyramine treatment or taurocholate infusion on the biliary transport maximum (Tm) of phenolsulfonphthalein (PSP) was studied in Wistar rats. 2. Five hours after oral administration of cholestyramine (1.5 g/kg bodyweight) the biliary output of bile acids decreased to 51% and bile flow to 76% of control values. The percentage of conjugated and unconjugated PSP excreted into bile and the Tm of the dye were not significantly modified by cholestyramine pretreatment. 3. Administration of sodium taurocholate at increasing rates (60-480 nmol/100 g bodyweight per min) enhanced bile flow and the biliary output of bile acids in a linear dose-related fashion. The Tm of PSP increased progressively until a maximum of 29% above the control values was reached at a taurocholate dose of 240 nmol/100 g bodyweight per min). The enhancement corresponded mainly to the unconjugated dye, the excretion of conjugated PSP not being significantly modified by the infusion of the bile acid. 4. The results indicate that bile acids can influence to some extent biliary excretion of PSP in the rat, although this component is of minor importance at low bile acid secretory rates.

Impairment of sulfobromophthalein biliary excretion and inhibition of glutathione S-transferase activity induced by perhexiline maleate in rats.

The effect of the antianginal agent perhexiline maleate (160 mg/kg i.g., daily for 4 days) on the biliary excretion of sulfobromophthalein (BSP) and BSP-glutathione and the hepatic activity of glutathione S-transferases was investigated in Wistar rats. Perhexiline maleate caused a significant reduction in the maximal biliary excretion of BSP (-28%). The decrease corresponded to a lowered excretion of the conjugated dye whereas the excretion of the parent compound did not change significantly. Administration of the drug caused no effect on the maximal biliary excretion of infused BSP-glutathione. Liver glutathione concentrations were similar in control and treated rats. Perhexiline maleate significantly reduced liver glutathione S-transferase activities toward BSP (-25%), 3,4-dichloronitrobenzene (DCNB) (-21%) and 1-chloro-3,4-dinitrobenzene (DNCB) (-27%). Kinetic studies of the enzyme in liver cytosol showed that perhexiline maleate induced an uncompetitive inhibition for the BSP substrate with a reduced Vmax and Km. The results indicate that the reduction in glutathione S-transferase activity plays an important role as a factor determining the impairment in the hepatobiliary transport of BSP caused by perhexiline maleate.

Influence of acute ethanol administration on hepatic glutathione metabolism in the rat.

The effect of acute ethanol administration on the hepatic metabolism of glutathione was studied in male Wistar rats. Animals fasted for 18 hr received ethanol (5 g/kg body wt.) through a gastric tube as a 20% (w/v) solution in 0.154 NaCl. Four hours after administration of ethanol liver glutathione content was decreased by 21% when compared to saline-treated controls. A significant reduction (28%) was also found in gamma-glutamylcysteine synthetase activity and plasma glutathione levels were increased non significantly by 17% with respect to control rats. Glutathione S-transferase activity in the liver of ethanol-treated animals was decreased by 28% but no change was found in total glutathione peroxidase activity. The results indicate that the lowered glutathione synthesis could be an important factor contributing to the reduction of hepatic glutathione concentration following the acute ingestion of ethanol.