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© 2004 The American Society for Nutritional Sciences J. Nutr. 134:1929-1934, August 2004

Nutrient Metabolism

Estrogen Prevents the Reduction in Fractional Calcium Absorption Due to Energy Restriction in Mature Rats1

Mariana Cifuentes2, Juan P. Advis* and Sue A. Shapses3

Department of Nutritional Sciences and * Department of Animal Sciences, Rutgers University, New Brunswick, NJ

3To whom correspondence should be addressed. E-mail: Shapses{at}aesop.rutgers.edu.

Weight reduction is a risk factor for bone loss. We previously showed that energy restriction is associated with a decrease in calcium (Ca) absorption and decreased estrogenic activity (EA). We hypothesized that this hypoestrogenic status may be the cause of the decrease in Ca absorption and that estrogen replacement during energy restriction would prevent it. Six-month-old rats were ovariectomized and implanted subcutaneously with 17ß-estradiol (E2) pellets to maintain levels within the physiological range. After 3 wk, rats ate ad libitum [control (CTL) group, n = 12] or were 40% energy restricted (EnR group, n = 12) for 10 wk. At the end of this study, rats were divided into 2 groups according to their uterine weight: those with higher EA and those with lower EA. Whereas CTL rats gained ~46% weight from baseline, EnR rats maintained their weight throughout the study. Energy restriction was associated with lower Ca absorption (5-d measurement, 45Ca radioisotope) and Ca balance in lower EA but not higher EA rats. Similarly, Ca absorption was correlated with both serum E2 (r = 0.68, P < 0.05) and body weight (r = 0.72, P < 0.05) in rats with lower EA but not in those with higher EA. Finally, 24-h corticosterone excretion was higher in EnR than in CTL rats, a response that was blunted in the higher EA rats. Our findings suggest that decreases in estrogen and hyperadrenocorticism with energy restriction play an important role in the regulation of Ca absorption and balance.

KEY WORDS: • absorption • calcium • estrogen • corticosterone • weight loss






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