Developmental changes in duodenal calcium transport in female rats related to ovarian hormone status and growth rate

Abstract

Duodenal active calcium (Ca) transport is known to decrease with age in male rats. The present studies were undertaken to extend this observation to female rats, and to determine whether alterations in active Ca transport are related to sexual maturation in the female. Everted duodenal sacs from intact and ovariectomized (ovx) rats were used to measure duodenal active Ca transport. Female rats were raised from weaning, and Ca transport was measured at 2-week intervals until 12 weeks of age. Transport rates were found to be the highest from 4 to 6 weeks of age, and then to decline over the next 4–6 weeks. However, if females were ovx as weanlings, the age-related decline in Ca transport failed to occur. Ovariectomy of immature females also prevented the slowing of growth rate which normally accompanies sexual maturation in female rats. We therefore repeated the experiment, pair-feeding the ovx animal to intact controls to maintain normal growth rates. When growth was normalized in this manner, the Ca transport rate in ovx animals declined with age at the same rate as in intact animals. Since ovx of sexually mature rats has been reported to increase growth rate, we studied the relationship between duodenal Ca transport and growth rate in females ovx at 12 weeks of age and pair-fed to age-matched intact females. After 5 weeks, ovx was found to have resulted in an increase in both weight and duodenal active Ca transport relative to the intact animals. Ovariectomy did not alter circulating levels of 1,25-dihydroxyvitamin D. The results of these experiments suggest that sexual maturation may play an indirect role in modulating duodenal active Ca transport in the rat via regulation of growth. The factor related to growth which directly regulates intestinal active Ca transport remains to be determined.