File Name: SLS1_08.DOC

EXPERIMENT SLS-1-08

STUDY OF THE DIGESTION-TRANSPORT CONVEYOR IN THE

SMALL INTESTINE

[PIs]{.underline}

[Russia:]{.underline}

K.V. Smirnov, Institute of Biomedical Problems, Moscow

[USA:]{.underline}

R. Phillips, Colorado State University, Colorado

[Co-Investigators:]{.underline}

R.A. Pechyonkina, Institute of Biomedical Problems, Moscow

N.P. Goncharova, Institute of Biomedical Problems, Moscow

[Introduction]{.underline}

A large body of factual data has been accumulated which point to
functional changes in the digestive organs of rats after space flight.
Previous experiments revealed

an increase in the acidic-peptic potential of the stomach and a decline
of the functional capability of the pancreas \[4\]. These changes may
act as limiting factors and may bring about various abnormalities in the
dependent compartments of the gastro-intestinal tract.

Due to this, the contribution that membrane digestion occurring in the
small intestine makes to the development of adaptive reactions which
compensate for changes in the gastro-duodenal compartment becomes more
important.

[Materials and Methods]{.underline}

The mucous membrane of the stomach of rats from three groups (basal
control, vivarium control and flight group) was examined. Emphasis was
given to the study of compensatory-adaptive reactions of the small
intestine based on the determination of the proximal-distal gradient of
enzymic activities, or measurement of enzyme activities in

the proximal and distal segments of the small intestine.

The intestine was cut off from the stomach and, at a distance of 10 cm,
from

the cecum, washed with saline and frozen in dry ice. After thawing a
homogenate of intestinal mucosa was prepared (500 mg of the mucous
membrane were homogenized

in 4.5 ml of Ringer\'s solution).

The function of the small intestine was measured in terms of the
following enzymes: glycyl leucine dipeptidase, saccharase, maltase,
monoglyceride lipase and alkaline phosphatase responsible for final
stages of protein, carbohydrate and fat hydrolysis.

Dipeptidase was measured using the method described in \[9\] as modified
in \[8\]. Activities of carbohydrases (saccharase and maltase) were
determined using dextrosticks and a glucometer. Monoglyceride lipase
activity was evaluated as described in \[3\]. Alkaline phosphatase was
assessed as described in \[7\]. Enzyme activities were calculated per
unit of the wet weight of the mucous membrane and not per unit protein
which is justifiable and comparable with calculations per unit protein
\[10\].

The results obtained were treated by means of variation statistics
methods. The flight data were compared with vivarium controls.
Significant differences were evaluated using the Student\'s t-test at
95%, p \< 0.05.

[Results and Discussion]{.underline}

In the flight rats, glycyl leucine dipeptidase responsible for final
stages of protein hydrolysis at enterocyte membranes remained unchanged
in the proximal segment and increased, although insignificantly, in the
distal segment. At R + 9 day, this enzyme tended to decline in the
proximal segment and increased in the distal segment thus suggesting
compensatory changes in the digestion-transport conveyor of proteins.

Analysis of changes in monoglyceride lipase involved in monoglyceride
hydrolysis to yield glycerol and free fatty acids demonstrated their
significant decline in both intestinal segments of the flight rats. At
R+9 day, monoglyceride lipase activity in the flight rats increased
slightly and reached the vivarium level. This may indicate energy
requirements during readaptation to the Earth\'s gravity.

At R+0 day, activity of alkaline phosphatase that takes part in the
final stages of lipid hydrolysis increased significantly in the proximal
segment of the small intestine.

These changes were obviously of compensatory-adaptive character.
Although pancreatic lipase and monoglyceride lipase in the small
intestine decreased at that point in time, lipid hydrolysis had the
capability to return to the optimal level. This was reflected in a
higher activity of alkaline phosphatase. Conversely, alkaline
phosphatase in the distal segment decreased substantially. It is known
that activity of alkaline phosphatase varies in response to various
abnormalities of the gastro-intestinal tract, pointing to intestinal
dysbacteriosis. The above mentioned reduction in the activity of
alkaline phosphatase in the distal segment of the small intestine can be
associated with both changes in intestinal microflora and changes in
enzyme incretion and inactivation \[1\].

Immediately after flight maltase activity in the proximal and distal
segments shifted while at R+9 day it remained unaltered. It was
previously reported \[6\] that pancreatic amylase was inhibited which
led to a compensatory-adaptive stimulation

of carbohydrases forming a maltase pool in the distal segment of the
small intestine (Table 1).

Immediately after flight saccharase activity increased significantly in
the distal segment and remained unchanged in the proximal segment. Nine
days after flight saccharase activity did not show any substantial
changes. It appears that insignificant changes in the membrane
hydrolysis of carbohydrates compensated for an enhanced activity of
pancreatic amylase seen at R+9 day. They were evidently aimed at
maintaining the hydrolytic potential required in those conditions.

Summarizing the results of the study of the small intestine after a
9-day space flight, it should be noted that the function of the
gastro-intestinal tract can be characterized by continuity of nutrient
hydrolysis \[1, 2\]. The efficacy of hydrolysis in the gastro-duodenal
compartment and dependent areas of the gastro-intestinal tract is
related to the acidity of the stomach. Enhanced pepsin excretion
produces a certain effect on the status of the pancreas and small
intestine. The compensatory-adaptive changes in the intestinal glands
help the digestive system to reach a new functional level.

[Summary]{.underline}

Study of the small intestine after a 9-day space flight revealed various
changes

in enzyme activities. With respect to protein hydrolysis in the
membrane, dipeptidase activity changed in the proximal and distal
segments in a different way suggesting compensatory nature of the
changes. Lipid changes included a lower activity of monoglyceride lipase
and a higher activity of alkaline phosphatase in the proximal segment of
the small intestine which also pointed to compensatory-adaptive changes.
Carbohydrases remained essentially unchanged.

Changes in the digestion-transport hydrolysis of proteins, fats and
carbohydrates were functional and reversible. The adaptive pattern of
changes in membrane digestion was indicated by the self-regulatory
activity of the digestive system in relation to the distribution of
enzyme activities.

[References]{.underline}

1\. P.K. Klimov. Functional Relationships in the Digestive System.
Leningrad, Nauka, 1976, 270 pp. (in Russian).

2\. G.F. Korot\'ko, Intestinal Digestion, Its Functional Organization
and Role in the Digestive Conveyor. Tashkent, Medizina, 1980 (in
Russian).

3\. I.L. Medkova, K.V. Smirnov, B.P. Surinov. Method for Measuring
Monoglyceride Lipase Activity. Lab. Delo, 1981, No. 3, pp. 64-67 (in
Russian).

4\. K.V. Smirnov. Digestion and Hypokinesia. Moscow, Nauka, 1990, 224
pp. (in Russian).

5\. K.V. Smirnov, L.G. Goland-Ruvinova, R.A. Pechyonkina et al.
Proteolytic and Carbohydrase Systems of the Gastro-Intestinal Tract Upon
Hypokinesia. In: Membrane Digestion and Absorption. Zinatne, 1986, pp.
129-131 (in Russian).

6\. K.V. Smirnov, A.M. Ugolev. Space Gastroenterology. Moscow, Nauka,
1981,

277 pp. (in Russian).

7\. A.M. Ugolev, N.N. Iezuitova. Measurement of Alkaline Phosphatase
Activity. In: Study of the Digestive Apparatus in Man (Overview of
Current Methods). Leningrad, Nauka, 1969, pp. 190-192 (in Russian).

8\. A.M. Ugolev, N.M. Timofeeva. Measurement of Peptidase Activity. In:
Study of the Digestive Apparatus in Man (Overview of Current Methods).
Leningrad, Nauka, 1969, pp. 178-181 (in Russian).

9\. B. Alexander, G. Lendwehr, A. Seligman. A Specific Micromethod for
the Colorimetric Determination of Glycine in Blood and Urine. J. Biol.
Chem., 1945, vol. 160, pp. 51-59.

10\. B. Scott, V.J. Fairman, C. Toothill, M. Losowaky. The Expression of
Enzyme Activity of Biopsy Tissue from the Small Intestine. Digestion,
1977, vol. 15, pp. 182-187.

11\. K.V. Smirnov, N.N. Lizko. The Enzymes and Microflora of the
Gastro-Intestinal Tract in Space Flight. Mikrobielle Umhelt und
Antimikrobielle Mabnahmen. B. 6. Mikroekologie des Menschen. J.
Ambrosius Verlag. Leipzig, 1982, S. 46-50.

[Table 1]{.underline}

Activity of Intestinal Enzymes in the Mucous Membrane of the Small
Intestine

(mmole/g, M [+]{.underline} m)

  ---------- ------------------------------------ -----------------------
             At R + 0 day                         At R + 9 day

  ---------- ------------------------------------ -----------------------

  ----------- ------------ ------------ ----------- ------------ -----------
              Basal        Vivarium     Flight      Vivarium     Flight

  ----------- ------------ ------------ ----------- ------------ -----------

  ----------- ------ -------- ------ -------- ------ -------- ------ -------- ------ --------
              Prox   Distal   Prox   Distal   Prox   Distal   Prox   Distal   Prox   Distal

  ----------- ------ -------- ------ -------- ------ -------- ------ -------- ------ --------

  ------------- ------ ------ ------ ------ ------ -------- ------ ------ -------- ------
  Glycyl        25.8   21.8   14.2   10.1   13.2   17.3\*   30.8   41.2   16.9\*   46.6
  leucine                                                                          
  dipeptidase                                                                      

  ------------- ------ ------ ------ ------ ------ -------- ------ ------ -------- ------

  ----------- ------ ------ ------ ------ ------ ------ ------ ------ ------ ------
              ±7.2   ±4.5   ±2.2   ±1.7   ±1.8   ±2.9   ±7.8   ±7.8   ±4.0   ±5.4

  ----------- ------ ------ ------ ------ ------ ------ ------ ------ ------ ------

  --------------- ------ ------ ------ ------ -------- -------- ------ ------ ------ ------
  Monoglyceride   3.52   3.04   6.04   4.19   2.42\*   2.18\*   4.16   1.04   3.52   1.38
  lipase                                                                             

  --------------- ------ ------ ------ ------ -------- -------- ------ ------ ------ ------

  ----------- ------- ------- ------- ------ ------- ------- ------- ------- ------ -------
              ±0.21   ±0.18   ±0.57   ±0.6   ±0.81   ±0.01   ±0.07   ±0.12   ±0.3   ±0.14

  ----------- ------- ------- ------- ------ ------- ------- ------- ------- ------ -------

  ------------- ------- ----- ------- ------ --------- ------- ------- ----- ------- -----
  Alkaline      223.0   1.7   338.0   11.3   644.0\*   2.5\*   118.5   2.8   130.0   2.3
  phosphatase                                                                        

  ------------- ------- ----- ------- ------ --------- ------- ------- ----- ------- -----

  ----------- ------- ------ ------- ------ ------ ------- ------ ------ ------- -------
              ±36.0   ±0.4   ±88.0   ±0.9   ±9.3   ±0.36   ±7.0   ±0.3   ±17.0   ±0.76

  ----------- ------- ------ ------- ------ ------ ------- ------ ------ ------- -------

  ------------ ----- ----- ------ ------ ------ -------- ------ ------ ------ ------
  Saccharase   \-    \-    1.18   0.91   1.26   1.15\*   1.07   0.81   1.12   0.83

  ------------ ----- ----- ------ ------ ------ -------- ------ ------ ------ ------

  ----------- ----- ----- ------- ------- ------- ------- ------- ------- ------- -------
                          ±0.05   ±0.02   ±0.07   ±0.05   ±0.05   ±0.01   ±0.02   ±0.02

  ----------- ----- ----- ------- ------- ------- ------- ------- ------- ------- -------

  ----------- ----- ----- ------ ------ ------ ------ ------ ------ ------ --------
  Maltase     \-    \-    9.56   9.17   8.80   9.60   7.66   4.73   7.70   3.58\*

  ----------- ----- ----- ------ ------ ------ ------ ------ ------ ------ --------

  ----------- ----- ----- ------- ------- ------- ------- ------- ------- ------- -------
                          ±0.50   ±0.31   ±0.26   ±0.22   ±0.63   ±0.24   ±0.45   ±0.42

  ----------- ----- ----- ------- ------- ------- ------- ------- ------- ------- -------

\* Significant changes