. 1987; Knospe and Plendl, 1997 . After incubation, the tissue sections were coverslipped
with mounting medium and examined under a light microscope. Enzyme activities were evaluated as strong, weak or absent depending on the staining intensity of the azo dye in
Ž .
the tissue Hirji and Courtney, 1982; Gawlicka et al., 1995 . Intestinal sections incubated without substrate were used as controls.
3. Results
Intestinal enzymes demonstrated a marked difference in regional distribution and Ž
. localization along the intestinal length Table 2 . Activities of various enzymes were
detected at characteristic sites along the first four intestinal segments. Most of these activities were localized along the brush border, but non-specific esterases were also
present in the cytoplasm of the enterocytes, and DAP IV was also detected in the basal lamina of all segments.
Ž Maltase activity was found in the brush border of the columnar epithelial cells Fig.
. 2A in the first four intestinal segments, with the most intense staining observed in the
third segment. Leucine aminopeptidase and DAP IV were detected in the microvilli of Ž
. the enterocytes Fig. 2B and C, respectively in the first four intestinal segments. Both
peptidases demonstrated stronger activities in the first three intestinal segments than in Ž
. the fourth. Weak DAP IV staining was also observed in the basal lamina Fig. 2C of all
Ž .
intestinal segments. Lipase activity was detected in the brush border Fig. 2D of the first three parts of the intestine, with the most intense enzyme reaction observed in the
first two regions. Uniform non-specific esterase activity was found in the first four intestinal regions. The esterase reactions were present in the microvilli, and also in
Ž .
cytoplasm of the enterocytes Fig. 3A . Intestinal alkaline phosphatase activity was detected in the first four intestinal regions. The strongest reaction was observed in the
first three intestinal segments, with a rapid decrease in intensity taking place at the
Table 2 Distribution and localization of the enzymes along the intestinal tract of the Nile tilapia
Ž .
Ž .
Ž .
Level of the staining intensity: qq strong , q weak , y absent . Intestinal segment
Hepatic loop First major coil
Gastric loop Distal major coil
Terminal part Brush border enzymes:
Malt q
q qq
q y
LAP qq
qq qq
q y
DAP IV qq
qq qq
q y
Lip qq
qq q
y y
NSE qq
qq qq
qq y
IAP qq
qq qq
q y
Cytoplasmic enzyme: NSE
qq qq
qq qq
y
a
Basal enzyme: DAP IV
q q
q q
q
a
In the basal lamina.
Ž . Ž .
Fig. 2. Intestinal sections showing enzyme staining arrows . A Maltase in the microvilli of the first major Ž
. Ž . Ž
. Ž . coil 66= . B Leucine aminopeptidase in the brush border of the second major coil 50= . C Dipeptidyl
Ž . Ž .
aminopeptidase IV with strong reaction s in the microvilli in comparison to the weaker intensity w in the Ž
. Ž . basal lamina. Counterstained with hematoxylin 40= . D Lipase in the brush border of the first major coil
Ž .
40= .
transition from the third to the fourth segment. The enzyme reaction was localized in the Ž
. brush border of the columnar epithelial cells Fig. 3B,C . Higher magnification also
Ž demonstrated this enzyme activity in the supranuclear cytoplasm of the enterocytes Fig.
. 3C .
Ž . Ž .
Fig. 3. Intestinal sections showing enzyme staining arrows . A Non-specific esterases in the brush border Ž
. Ž . and cytoplasm of the columnar epithelial cells of the gastric loop 100= . B Alkaline phosphatase in the
Ž . Ž .
Ž .
microvilli of the gastric loop 40= . C Alkaline phosphatase in the brush border in white and supranuclear Ž
. Ž
. cytoplasm in black of the enterocytes of the gastric loop. Counterstained with hematoxylin 330= .
4. Discussion
