A quantitative analysis of hepatic ultrastructure in rats during enhanced bile secretion

Abstract

The ultrastructural changes in hepatocytes of rats subjected to selective biliary obstruction (SBO), wherein the biliary system draining approximately two-thirds of the liver is obstructed, were evaluated by quantitative electron microscopy or stereology. The remaining unobstructed portion of the organ compensates for this loss of bile secretion by functioning in a hypersecretory mode. This animal model permits the comparison of hepatocellular fine structure associated with the conditions of nonsecretion and hypersecretion of bile with that found in normal secreting sham-operated rats. Since recent evidence suggests the presence of lobular gradients in hepatic structure and function, both centrolobular and periportal hepatocytes were examined. The low incidence of Golgi membrane profiles in high magnification electron micrographs results in a low confidence level of sampling and, thus, necessitates the application of a novel parameter for estimating the amount of Golgi complex, i.e., the Golgi-rich area. For the most part, the lobular variation in hepatic fine structure in the sham-operated animals was similar to that described by Loud ('68). However, the periportal parenchyma contained approximately twice the volume of Golgi-rich area as the centrolobular tissue. The amount of cytoplasmic lipid increased significantly in the SBO unobstructed lobes, although there were few or no changes in the other intracellular organelles or inclusions except those related to the Golgi complex. The volume of Golgi-rich area increased significantly in the centrolobular tissue of the SBO unobstructed (hypersecretory) lobes to the extent that both intralobular zones contained similar amounts of this component. These data suggest that the Golgi complex is a dynamic unit which responds to changes in hepatocellular activity and may be involved in bile secretion.

Bile Acid-Induced Increase in Bile Acid-Independent Flow and Plasma Membrane NaK-ATPase Activity in Rat Liver

“…In support of this possibility, the recent findings of Nemchausky et al, employing scanning electron microscopy, suggest that portions of the canalicular membrane may expand after bile acid loading (41). In other studies (48), morphometric analysis ofthe liver in selectively obstructed rats failed to demonstrate a significant change in the canalicular space in the bile-secreting lobes, but the surface area of the canalicular membrane itself was not measured. Clarification of the significance of these findings will require more detailed studies of the canalicular membrane, including lipid composition and fluidity, enzyme kinetics, and morphometric analysis of membrane ultrastructure.…”

“…Isotonic saline, 3 ml/h, was administered via the duodenal catheter from 9 a.m. to 6 (7,9) and after 48 h resulted in a twofold increase in bile acid pool and secretion rate (9). After 16 h, bile acid pool and secretion rate were increased by approximately 35% (P < 0.02).1…”

Hepatic sequestration and biliary secretion of epidermal growth factor: evidence for a high-capacity uptake system.

“…Zonal differences in lobules have been well documented morphologically (40,41) and also functionally (30,(42)(43)(44). Several theories have been suggested to explain these intralobular differences, including relative differences in blood oxygen level (45), hepatocyte maturity (42,46), blood flow patterns (47), and hepatocyte receptor number or affinity for plasma-derived substances, or both (33,36).…”

“…Studies by Goresky et aL (33)(34)(35) have demonstrated that, under certain circumstances, hepatocytes remove substances from the sinusoidal blood, depending on the concentration of those substances at various locations within the hepatic lobule. Evidence has also been provided that the periportal and centrolobular hepatocytes differ in their ultrastructure (40). It is unclear whether intralobular differences in hepatocytes are solely a function of their location within the hepatic lobule or reflect a more fundamental functional difference between these cell groups.…”

Peroxisomes (Microbodies) in Human Liver: Cytochemical and Quantitative Studies of 85 Biopsies

“…The distribution of peroxisomes in the human liver lobule has not been described (13). An early finding that peroxisomes in centrolobular rat hepatocytes was nearly twice as abundant as in periportal liver cells (6) has not been reexamined in subsequent investigations (5,15,16). These morphometric studies utilized electron micrographs in which peroxisomes were identified by morphological rather than by cytochemical criteria.…”