fibrous trabeculae in the liver of alligator (alligator mississippiensis)

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Fibrous trabeculae in the liver of alligator (Alligator mississippiensis) W. A. Beresford Department of Anatomy - HSN, School of Medicine, West Virginia University, Morgantown, WV 26506-9128, USA Summary. In the mature alligator, fibrous trabeculae run from the portal areas and capsule through the hepatic paren- chyma. The extent of these trabeculae becomes clear only after staining for collagen with, for example, Fast green or Picrosirius red. The trabeculae are less well developed in young caiman. The alligator's liver might use the trabeculae to withstand thrashing of the body. Key words: Liver - Trabeculae - Alligator - Picrosirius - Polarization Introduction The substantial fibrous trabeculae running through the sub- stance of the mature alligator's liver have not been reported until now. Pettit (1904), in his brief abstract on alligator liver, wrote only of masses of connective tissue enclosing the bran- ches of the portal vein and the other elements of the portal triad. Those examining the crocodilian liver microscopically have mostly been interested in particular chemical or ultra- structural features (Hack and Helmy 1964; Arvy and Bonichon 1958; Storch et al. 1989; Henninger and Beresford 1990), and have not used the collagen-selective staining that makes the trabeculae visible. Materials and methods Large pieces of Ii ver were removed immediately from eleven matu- re alligators, legally shot, and were fixed in 10% formol saline. After fixing for several weeks, smaller subcapsular and central pieces were postfixed in Bouin's solution, dehydrated through alcohols, and imbedded in paraffin for microtomy at 8 /Lm thickness. Sections were stained with Gomori's trichrome (with Fast green for collagen) or Picrosirius Red S. Sections stained with the latter technique were viewed and photographed using polarized transmitted-light micros- Ann. Anal. (1993) 175: 357-359 Gustav Fischer Verlag Jena copy (Junqueira et al. 1978) . Pieces of liver from four juvenile spec- tacled caiman (Caiman crocodilus), killed with excess pentobarbital for neuroanatomical study, were treated similarly. Results and Discussion The alligator liver is reinforced on three scales: 1. the fine perisinusoidal network staining respectively green or orange with trichrome or Picrosirius Red, accompanying the contort- ed tubules ofhepatocytes; 2. the thick connective tissue of the capsule and portal areas; 3. trabeculae of collagen, interme- diate in scale and connecting the other two categories of sup- port. Smooth muscle, visible with trichrome staining, is pre- sent as sparse fibres or bundles in the branches of the portal vein, but not in the trabeculae. The trabeculae are of various widths and have a clear iden- tity (Figs. 1 and 2), distinct from the connective tissue of small portal areas. They are crudely round or oval in cross- section and are clearly not septa - sheet-like partitions. Unli- ke some of the trabeculae of the mammalian spleen, the hepa- tic trabeculae do not form the walls of veins. They traverse the parenchyma linearly without affecting the tubular pattern, although the fine peri sinusoidal fibres sometimes connect with them, and occasionally a ductule runs alongside. In cai- man, only three of the four livers displayed trabeculae and these were thin. The hepatocytes (Fig. 1) of both species are small compared with those of chelonians, and are arranged to form branching tubules: a configuration encountered in other ectothermic vertebrates (Beresford and Henninger 1986). Are the trabeculae characteristic of crocodilians? Storch et al. (1989) mention neither trabeculae nor portal structures in their study of the liver of West African crocodile, but they concentrate on parenchymal cellular ultrastructure. That tra- beculae are inconsistently present in these caiman and may reflect the immaturity of the animals. Steiner and Ratcliffe

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Page 1: Fibrous trabeculae in the liver of alligator (Alligator mississippiensis)

ANNA~OfANATOMY===================

Fibrous trabeculae in the liver of alligator (Alligator mississippiensis)

W. A. Beresford

Department of Anatomy - HSN, School of Medicine, West Virginia University, Morgantown, WV 26506-9128, USA

Summary. In the mature alligator, fibrous trabeculae run from the portal areas and capsule through the hepatic paren­chyma. The extent of these trabeculae becomes clear only after staining for collagen with, for example, Fast green or Picrosirius red. The trabeculae are less well developed in young caiman. The alligator's liver might use the trabeculae to withstand thrashing of the body.

Key words: Liver - Trabeculae - Alligator - Picrosirius -Polarization

Introduction

The substantial fibrous trabeculae running through the sub­stance of the mature alligator's liver have not been reported until now. Pettit (1904), in his brief abstract on alligator liver, wrote only of masses of connective tissue enclosing the bran­ches of the portal vein and the other elements of the portal triad. Those examining the crocodilian liver microscopically have mostly been interested in particular chemical or ultra­structural features (Hack and Helmy 1964; Arvy and Bonichon 1958; Storch et al. 1989; Henninger and Beresford 1990), and have not used the collagen-selective staining that makes the trabeculae visible.

Materials and methods

Large pieces of Ii ver were removed immediately from eleven matu­re alligators, legally shot, and were fixed in 10% formol saline. After fixing for several weeks, smaller subcapsular and central pieces were postfixed in Bouin's solution, dehydrated through alcohols, and imbedded in paraffin for microtomy at 8 /Lm thickness. Sections were stained with Gomori's trichrome (with Fast green for collagen) or Picrosirius Red S. Sections stained with the latter technique were viewed and photographed using polarized transmitted-light micros-

Ann. Anal. (1993) 175: 357-359

Gustav Fischer Verlag Jena

copy (Junqueira et al. 1978). Pieces of liver from four juvenile spec­tacled caiman (Caiman crocodilus), killed with excess pentobarbital for neuroanatomical study, were treated similarly.

Results and Discussion

The alligator liver is reinforced on three scales: 1. the fine perisinusoidal network staining respectively green or orange with trichrome or Picrosirius Red, accompanying the contort­ed tubules ofhepatocytes; 2. the thick connective tissue of the capsule and portal areas; 3. trabeculae of collagen, interme­diate in scale and connecting the other two categories of sup­port. Smooth muscle, visible with trichrome staining, is pre­sent as sparse fibres or bundles in the branches of the portal vein, but not in the trabeculae.

The trabeculae are of various widths and have a clear iden­tity (Figs. 1 and 2), distinct from the connective tissue of small portal areas. They are crudely round or oval in cross­section and are clearly not septa - sheet-like partitions. Unli­ke some of the trabeculae of the mammalian spleen, the hepa­tic trabeculae do not form the walls of veins. They traverse the parenchyma linearly without affecting the tubular pattern, although the fine peri sinusoidal fibres sometimes connect with them, and occasionally a ductule runs alongside. In cai­man, only three of the four livers displayed trabeculae and these were thin. The hepatocytes (Fig. 1) of both species are small compared with those of chelonians, and are arranged to form branching tubules: a configuration encountered in other ectothermic vertebrates (Beresford and Henninger 1986).

Are the trabeculae characteristic of crocodilians? Storch et al. (1989) mention neither trabeculae nor portal structures in their study of the liver of West African crocodile, but they concentrate on parenchymal cellular ultrastructure. That tra­beculae are inconsistently present in these caiman and may reflect the immaturity of the animals. Steiner and Ratcliffe

Page 2: Fibrous trabeculae in the liver of alligator (Alligator mississippiensis)

(1968) found that the intra-hepatic septa of Suidae are slow to form. Studies oflivers from mature specimens of more croco­dilian species are needed, if hypotheses accounting for the presence of trabeculae are to be plausible. One such is that the thra-shing movements for subduing large prey impose excep­tional loads on the liver. However, in seeking corrobative measurements, the insertion of devices within the liver might provoke a fibrosis or otherwise disturb the architecture.

The extensive, comparative reviews of hepatic connective tissue by Castaldi (1920) and Aterman (1981) deal with the fine supporting framework of the sinusoids and the tubules or plates of hepatocytes. However, the trabeculae seen here are coarser, have an independent orientation, and possibly owe their existence to a fibroblastic population shared with the capsule and portal areas. A very few mammalian species are noted for septa partially or completely separating hepatic

lobules (Kostorz 1936; Steiner and Ratcliffe 1968; Ekataksin and Wake 1991). In kangaroo, elephant, and several species of ungulate, the interlobular connective tissue exists as strands extending from the portal areas, but the closest paral­lel to the trabeculae in alligators is the additional, intralobular, fibrous strands in elephant (Kostorz 1936) and camel (Turner 1877).

The diseased or poisoned mammalian liver lays down excess connective tissue, but usually in the form of crude par­titions or septa. Occasional reports refer to a more strand-like deposition (James et al. 1989). A clinical interest in trabecu­lae is that they should disturb blood flow less than do septa. If the cells responsible for cirrhosis (fibroblasts, fat-storing cells, or modified fat-storing cells) could be identified and targeted, they might be induced to make trabeculae rather than septa.

Fig. I. Alligator liver, trichrome­stained. Two substantial trabeculae cut partly lengthwise are accompa­nied by two others (arrows) barely visible in cross-section. The dark structures are pigment cells. Bile canaliculi run centrally in the tubu­les composed of small hepatocytes. x 190.

Fig. 2. Alligator liver, Picrosirius red-stained. The polarizing filters are not completely at 90° in order to leave the parenchyma visible. Standing out brightly are many variously sized trabeculae in longi­tudinal and cross-section. The fine lines around the tubules are the peri­sinusoidal connective tissue. x 73.

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Acknowledgements. I thank Mr. N. Kinler, Louisiana Department of Game and Wildlife, and Dr. M. Pritz, University of California, Irvine, for the livers.

References

Arvy L, Bonichon A (1958) Contribution it l'histoenzymologie de Crocodylus niloticus Laurenti. Z Zellforsch 48: 519-535

Aterman K (1981) Connective tissue: an eclectic historical review with particular reference to the liver. Histochem J 13: 341-396.

Beresford W A, Henninger JM (1986) A tabular comparative histol­ogy of the liver. Arch Histol Jap 49: 267-281

Castaldi L (1920) II connettivo nel fegato dei Vertebrati. Arch Ital AnatEmbriol17: 373-606.

Ekataksin W, Wake K (1991) Liver units in three dimensions: I. Organization of argyrophilic connective tissue skeleton in porci­ne liver with particular reference to the "compound hepatic lobu­le". AmJ Anat 191: 113-153

Hack MH, Helmy FM (1964): A comparative study of the liver of various vertebrates. Acta Histochem 19: 316-328

Henninger JM, Beresford W A (1990) Is it coincidence that iron and melanin coexist in hepatic and other melanomacrophages? Histol

Histopathol5: 457-459 James J, Lygidakis NJ, Van Eyken P, Tanka AKF, Bosch KS, Ra­

maekers FCS, Desmet V (1989) Application of keratin immuno­cytochemistry and Sirius Red staining in evaluating intrahepatic changes with acute extrahepatic cholestasis due to hepatic duct carcinoma. Hepato-gastroenterol 36: 151-155

Junqueira LCU, Cossermelli W, Brentani R (1978) Differential stai­ning of collagens type I, II and III by Sirius Red and polarization microscopy. Arch Histol Japon 41: 267-274

Kostorz R (1936) Uber die Uippchenabgrenzung in der Leber der Sliugetiere. Anat Anz 83: 121-149

Pettit A (1904) Remarques anatomiques sur Ie foie de I'Alligator lucius Cuv. Compt Rend Soc BioI 56: 298-300

Storch V, Braunbeck T, Waitkuwait WE (1989) The liver of the West African crocodile Osteolamaemus tetrapis. An ultrastructu­ral study. J Submicr Cytol Pathol21: 317-327

Steiner PE, Ratcliffe HL (1968) The hepatic lobules of Suidae, Tayassuidae, and Hippopotarnidae. Anat Rec 160: 531-538

Turner W (1877) Note on the lobules and the connective tissue ofthe camel's liver. J Anat Physioll1: 354-356

Accepted January 21, 1993

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