Effect of Neonatal MSG Treatment on Day-Night Alkaline Phosphatase Activity
in the Rat Duodenum
A. MARTINKOVÁ, Ľ. LENHARDT1, Š. MOZEŠ
Institute of Animal Physiology, Slovak Academy of Sciences and 1Department
of Pathology, University of Veterinary Medicine, Košice, Slovakia
Received June 10, 1999
Accepted January 12, 2000
Summary
The day-night variation of food intake and alkaline phosphatase (AP) activity was studied in the duodenum of rats neonatally treated
with monosodium glutamate (MSG) and saline-treated (control) rats. The animals
were kept under light-dark conditions (light phase from 09:00 h to 21:00 h) with
free access to food. AP activity was cytophotometrically analyzed in the
brush-border of enterocytes separated from the tip, middle and cryptal part of
the villi every 6 h over a 24-hour period. In comparison with the controls,
MSG-treated rats consumed about 40 % less food during the dark period and their
24-hour food intake was thus significantly lowered (P<0.001). On the other
hand, the nocturnal feeding habit showed a similar pattern: food consumption was
high during the night (65 % vs. 75 %) and the lowest consumption was found
during the light phase (35 % vs. 25 %) in MSG-treated and control rats,
respectively. In agreement with the rhythm of food intake, the highest AP
activity was observed during the dark phase and was lowest during the light
phase in both groups of animals. These significant day-night variations showed
nearly the same pattern in the enterocytes of all observed parts along the villus axis. In comparison with the controls, a permanent increase of AP
activity was observed in neonatal MSG-treated rats. This increase was more
expressive during the dark phase of the day in the cryptal (P<0.001) and
middle part of the villus (P<0.01). From the viewpoint of feeding, this
enzyme in MSG-treated rats was enhanced in an inverse relation to the amount of
food eaten i.e. despite sustained hypophagia the mean AP activity in the enterocytes along the villus axis was higher than in the control animals during
all investigated periods. The present results suggest that the increased AP
activity in MSG-treated rats is probably not a consequence of actual day-night
eating perturbations but could be a component of a more general effect of MSG.
This information contributes to better understanding of the function of
intestinal AP and its relation to day-night feeding changes especially in
connection with the MSG syndrome.
Key words
Light-dark rhythm · Alkaline phosphatase · Duodenal enterocytes ·
Neonatal MSG treatment
Reprint requests
A. Martinková, Institute of Animal Physiology, Slovak
Academy of Sciences, Šoltesovej 4, 040 01 Košice, Slovak Republic, e-mail: martink@mail2.saske.sk,
mozes@saske.sk
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