2025 年 50 巻 12 号 p. 661-675
To investigate the effects of reduced food intake on the serum and tissue levels of alkaline phosphatase (ALP) isoenzymes in rats, ALP1, ALP2, ALP3, and ALP5 were analyzed in serum, liver, bone, and small intestine of male and female Sprague-Dawley rats reared under a diet-restricted condition (fed 65% or 45% of the amount of the free-feeding group) for 4 weeks from six-week-old. In addition, to examine the effect of sex hormonal, each ALP isoenzyme level was also analyzed in free-feeding female rats with ovariectomy or testosterone administration. Food restriction was associated with the following changes: an increase of the serum ALP5 level in the females, mainly caused by an increase derived from the small intestine; increases in the liver ALP1 and small intestinal ALP5 levels in both sexes, which represented a compensatory increase of these ALP isoenzyme levels to enhance lipid absorption under the low nutritional condition; a decrease of the bone ALP3 level in females, which was considered reflective of suppressed bone formation. Regarding the sex differences, serum ALP2 and liver ALP1 levels were higher in the males than in the females; the levels in ovariectomized or testosterone-treated females shifted closer to those in the males. These results indicate that food restriction and sex hormonal intervention influenced the serum and tissue ALP isoenzyme levels in rats. These findings provide helpful information for understanding the effects of reduced food intake, often observed in toxicity studies, and sex differences in rats on ALP and help to properly evaluate the effects of test compounds.
