O2 uptake by the perfused liver decreased at O2 concentrations considerably higher than levels that caused NADH reduction when the input O2 concentration was varied. The maximal rate of O2 uptake was two- to threefold higher in periportal (137 +/- 8 mumol . g-1 . h-1; O2 concentration = 478 +/- 37 microM) than pericentral regions (59 +/- 5 mumol . g-1 . h-1; O2 concentration = 263 +/- 21 microM); however, the O2 concentration required for half-maximal O2 uptake was similar (approximately 20 microM) in the two areas. The infusion of atractyloside, antimycin A, or KCN inhibited O2 uptake in both zones by 50-85%, indicating that O2 uptake in both regions was largely dependent on mitochondrial electron transport. The content of ATP and ADP and ATP:ADP were similar in microdissected samples from periportal and pericentral areas. In contrast, when livers were perfused in the retrograde direction, O2 uptake was two- to threefold greater in pericentral than in periportal regions. Maximal rates of O2 uptake correlated with the local O2 concentration irrespective of the direction of flow when the electrode was moved across the liver lobule with a micromanipulator. Lower rates of O2 uptake in pericentral areas were not altered appreciably by infusion of agents known to uncouple oxidative phosphorylation (DNP), increase ADP supply (fructose), or increase the NADH redox state (ethanol or octanoate). These data are consistent with the hypothesis that maximal rates of O2 uptake are regulated, in part, in the perfused liver by O2 concentrations far above the Km of cytochrome oxidase for O2.
1. Rates of gluconeogenesis from lactate were calculated in periportal and pericentral regions of the liver lobule in perfused rat livers from increases in O 2 uptake due to lactate. When lactate (0.1 -2.0 mM) was infused into livers from fasted rats perfused in either anterograde or the retrograde direction, a good correlation (r = 0.97) between rates of glucose production and extra O2 uptake by the liver was observed as expected.2. Rates of oxygen uptake were determined subsequently in periportal and pericentral regions of the liver lobule by placing miniature oxygen electrodes on the liver surface and measuring the local change in oxygen concentration when the flow was stopped. Basal rates of oxygen uptake of 142 & 11 and 60 f 4 pmol x g-' x h-' were calculated for periportal and pericentral regions, respectively. Infusion of 2 mM lactate increased oxygen uptake by 71 pmol x g-' x h-' in periportal regions and by 29 pmol x g-' x h -l in pericentral areas of the liver lobule. Since the stoichiometry between glucose production and extra oxygen uptake is well-established, rates of glucose production in periportal and pericentral regions of the liver lobule were calculated from local changes in rates of oxygen uptake for the first time.3. Maximal rates of glucose production from lactate (2 mM) were 60 f 7 and 25 f 4 pmol x g-' x h-l in periportal and pericentral zones of the liver lobule, respectively. The lactate concentrations required for halfmaximal glucose synthesis were similar (0.4-0.5 mM) in both regions of the liver lobule in the presence or absence of epinephrine (0.1 pM). In the presence of epinephrine, maximal rates of glucose production from lactate were 79 f 5 and 59 f 3 pmol x g-' x h-' in periportal and pericentral regions, respectively. Thus, gluconeogenesis from lactate predominantes in periportal areas of the liver lobule during perfusion in the anterograde direction ; however, the stimulation by added epinephrine was greatest in pericentral areas. Differences in local rates of glucose synthesis may be due to ATP availability, as a good correlation between basal rates of O2 uptake and rates of gluconeogenesis were observed in both regions of the liver lobule in the presence and absence of epinephrine.4. In marked contrast, when livers were perfused in the retrograde direction, glucose production was 28 f 5 pmol x g-' x h-' in periportal areas and 74 6 pmol x 8.' x h-' in pericentral regions. Epinephrine increased maximal rates of glucose production to 87 pmol x g-' x h-' and 58 pmol x g-' x h-' in pericentral and periportal regions, respectively. Thus, gluconeogenesis can be shifted rapidly from one region of the liver lobule to another in the hemoglobin-free perfused rat liver.Data has accumulated over the past decade showing that cells in various regions of the hepatic lobule contain different amounts and activities of key metabolic enzymes [I, 21. Using microdissection techniques, Guder and coworkers [3] demonstrated quantitative differences in mmy enzyme activities in tissues from periporta...
Dieulafoy's ulcer is a rare form of gastrointestinal bleeding. Although the original descriptions and early reports were of lesions in the proximal stomach, similar lesions have subsequently been reported in the esophagus, duodenum, jejunum, colon and rectum. A 55‐year‐old man was admitted to hospital for a sudden acute headache. On admission he was conscious, and had severe occipitalgia due to a subarachnoid hemorrhage demonstrated on computed tomography. On the fifteenth hospitalization day, he passed fresh blood together with stool, followed by several further episodes of massive hematochezia. Although no lesion was found by gastroduodenoscopy, colonoscopy revealed fresh blood and clots in the rectum. No obvious source of hemorrhage could be identified until careful irrigation revealed pulsatile bleeding from a protuberant vessel (2 mm in size) in the rectum 5 cm from the anal verge. The patient underwent an endoscopic hemostasis in which the pulsatile vessel was easily sutured with seven clips. The patient did not have another episode of bleeding. The finding of Dieulafoy's ulcer in the elderly‐patient group suggests that sclerotic changes to the artery may be associated with this type of rectal ulcer.
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