(1→3)-b-D-Glucan is a constituent of the cell wall or a reserved polysaccharide of algae, eumycetes, and higher plants. On the other hand, higher animals including mammal do not have any enzyme to synthesize or hydrolyze this type of glucan.1) The glucan is involved in a variety of host-defense biological responses, such as host-mediated antitumor activity in vertebrate, activation of the alternative pathway of the complement system, activation of the prophenoloxidase activating system in arthropods, and activation of the coagulation system of limulus amebocyte lysate (LAL).Measurement of (1→3)-b-D-glucan in blood by use of LAL based reagent is an aid in the diagnosis of invasive fungal diseases in humans. [2][3][4][5] As the blood (1→3)-b-D-glucan concentrations in healthy volunteers or patients with no fungal infection were almost less than the cut-off value of each reagent kit, 3,6) it is believed that the dietary glucan is not absorbed in blood stream from digestive tract. The possibility of absorption of oral administrated (1→3)-b-D-glucan into blood stream, however, has been reported in a certain clinical case with no possible fungal infection 7,8) and in the experiment where fluorescently labeled glucan was used in rat. 9) In this study, we investigated the absorptive and secretory transporting system of intact laminaran as (1→3)-b-D-glucan in rat intestine and revealed participation of its multiple transporting mechanisms.
MATERIALS AND METHODS
MaterialsLaminaria digitata laminaran, primarily poly(1→3)-b-D-glucose with some (1→6)-b-interstrand linkages and branch points with weight-average molecular weight of 7700, 10) fluorescein isothiocyanate dextran 40000 (FD-40) and 2,4-dinitrophenol was purchased from Sigma (St. Louis, U.S.A.). All other chemicals were commercial products of reagent grade.
Measurement of Intestinal Absorption by in Situ LoopMethod Intestinal absorption of laminaran was evaluated by the loop method.11,12) The ileum of male Wistar/ST rats weighing 200 to 250 g (Japan SLC, Hamamatsu, Japan) was exposed by middle line abdominal incision, and two Lshaped glass cannulas (i.d. 2 mm, o.d. 4 mm) were inserted through small slits at the proximal and distal ends (7 cm). The proximal end and distal end of the cannulas were inserted into the point of 12 cm and 5 cm above from cecum, respectively. Each cannulas was secured by ligation with a silk suture, and the intestine was returned to the abdominal cavity to maintain its integrity. A 4-cm portion of Tygon tubing (i.d. 3 mm, o.d. 5 mm) was attached to the exposed end of each cannula, and a 10-ml hypodermic syringe fitted with a connect tube and containing perfusion solution warmed at 37°C was attached to the proximal cannula. To clear the gut, saline was passed slowly through it to the distal cannula and discarded until the effluent was clear. The remaining perfusion solution was carefully expelled from the intestine by means of air pumped through the syringe, and 5 ml of laminaran solution was immediately introduced into the intestine. The di...