Hepatology : official journal of the American Association for the Study of Liver Diseases
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We studied the pattern of intermixing of the hepatic arterial and portal venous flows in a perfused rat liver preparation under constant flow (12 ml/min) with intravital epifluorescent microscopy; changes in the steady state extraction ratio of carbon 14-labeled phenacetin and tritiated acetaminophen, probes metabolized primarily in perivenous and periportal regions of the rat liver, respectively; and the spaces accessed by noneliminated reference indicators introduced as a bolus into the hepatic artery and portal vein at different hepatic arterial/portal venous flow regimens of 0:12, 2:10 and 4:8. The sinusoidal velocities for the hepatic arterial- and portal venous (hepatic arterial/portal venous flow at 4:8)-infused fluorescein isothiocyanate-erythrocytes (100 microliters/min) were 327 +/- 78 and 301 +/- 63 microns/sec, respectively, and the velocity for the solely portal venous-perfused liver (12 ml/min) was 347 +/- 74 microns/sec; the flow-weighted sinusoidal velocity was highly correlated to the sinusoidal volume for the dually perfused rat liver. Small but significant decreases in the extraction ratio of [14C]phenacetin (from 0.989 to 0.984 and 0.980) and tritiated acetaminophen (from 0.631 to 0.607 to 0.563), delivered simultaneously into the hepatic artery and portal vein, were observed with an increment of hepatic arterial flow within the same liver preparation; oxygen consumption rate also fell slightly, in parallel fashion. ⋯ However, slightly larger total water spaces were obtained with hepatic arterial injection. This excess water space was almost completely accounted for by the "nonsinusoidal" extravascular space associated with the peribiliary capillary plexus; it averaged 0.03 ml/gm and was independent of flow. The anomaly, a reduced flow-weighted sinusoidal velocity for the dually perfused liver, an unchanged diameter of the terminal hepatic venule (32 microns) among the hepatic arterial/portal venous flow ratios and the reduction in the extraction ratio of the drug probes and oxygen consumption rates suggest that some of the arterial flow must have entered the sinusoids somewhat downstream.
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Endogenous opioids, including methionine enkephalin, have been implicated in the control of adrenocorticotrophic hormone release by acting through mu-opiate receptors in the hypothalamus. Recently, alterations in the central opioid system have been postulated to occur in cholestasis. In addition, alterations in hypothalamic corticotropin-releasing hormone content and messenger RNA levels, as well as basal release, have been described in bile duct-resected rats, and hypothalamic methionine enkephalin is colocalized with corticotropin-releasing hormone in hypothalamic neurons. ⋯ In addition, hypothalamic proenkephalin steady state messenger RNA levels were similar in the three groups of animals. mu-Opiate receptor stimulation of hypothalamic explants in vitro with the specific mu-opiate receptor agonist ligand [D-Ala2,N-Me-Phe4,Gly-ol]-Enkephalin resulted in 8.2% and 16.9% inhibition of corticotropin-releasing hormone release in sham-resected and unoperated control rats, respectively. In contrast, treatment of hypothalamic explants from bile duct-resected rats with [D-Ala2,N-Me-Phe4,Gly-ol]-Enkephalin resulted in a significant 22.5% increase in corticotropin-releasing hormone release. Systemic administration of the mu-opiate receptor agonist morphine to rats in vivo resulted in significantly higher incremental rises in plasma adrenocorticotropic hormone levels in sham-resected and unoperated control animals than in bile duct-resected rats.(ABSTRACT TRUNCATED AT 250 WORDS)