Calcium Flux During Growth in Sham-operated and Ovariectomized Rats

Abstract

It is generally accepted that sexual maturity in rats from inbred strains usually begins by age 6 to 9 weeks and is achieved by age 12 or 16 weeks. 1 It is expected that calcium retention would increase during rapid growth, and the demand for calcium would decrease until sexual maturation. In fact, intestinal calcium absorption in growing rats is significantly related to the calcium balance. 2 In addition, O'Loughlin and Morris, using 45Ca, reported a drastic reduction in both fractional true calcium absorption in the intestine and the calcium balance when rats were 6 to 15 weeks old. 3 We previously reported the details of calcium fl ux during growth in female rats. 4 Our fi ndings suggested that calcium kinetics in ovariectomized rats might also change in a time-dependent manner over a relatively short term. A two-compartment model is useful for investigating calcium flux throughout the entire body, such as intestinal apparent calcium absorption, the output of calcium into the urine and intestine, and the passage of calcium into bone or from bone. In this study, we used these methods to examine the relationship between growth and ovarian hormone deficiency on calcium fl ux in rats, under pair-fed conditions. Materials and Methods Animals and diet Female Wistar rats were obtained from Saitama Experimental Animals Supply Co., Ltd. (Saitama) at age 50 days. After 3 days of adaptation, 42 rats were equally divided into 6 groups, and housed in individual metabolic cages at 23 25°C with a 12:12 h light-dark cycle. Rats were given a purified vitamin D-deficient soft moisture diet (0.5% Ca and 0.35% Pi). Water was