Strontium–calcium discrimination in vitro by rat tissues.

Uptake of 89Sr and 45Ca by 15 soft tissues of adult rat was studied in vitro to assess the extent of discrimination between Sr and Ca. While brain, kidney, placenta and uterus have lower uptake of.89Sr and 45 Ca that of diaphragm, lactating mammary gland, skeletal muscle, skin, spleen and testes is higher. Tissues with medium range uptake are heart, small intestine, liver, lung, non-lactating mammary gland and ovary. The 6 tissues displaying discriminating ability, as expressed by 89Sr/45Ca (tissue/medium), in the decreasing order are: small intestine, kidney, lactating mammary gland, placenta, diaphragm and heart. Non-lactating mammary gland and the other tissues did not differentiate between Sr and Ca. The efect of several enzyme inhibitors, compounds influencing Sr-Ca metabolism and other factors was studied in terms of the nature and mechanism of Sr-Ca discrimination.

Removal of radioactive strontium from the rat by feeding stable strontium.

The effect of administering the stable isotope of strontium (as phosphate) at different dietary levels to adult rats (fed on a cereal and pulse-based diet containing 0·4% Ca) on the retention of radiostrontium (89Sr) and radiocalcium (45Ca) in the femur and the whole skeleton was studied for a period up to 6 weeks after an intraperitoneal injection of the two radioisotopes. The ability of strontium to remove 89Sr under the above dietary conditions was examined. Feeding Sr at 0·5% or 1% levels for 6 weeks had no effect on the skeletal content of 89Sr or 45Ca while a dietary regimen of 2% Sr (2000 times the normal content), significantly lowered the 89Sr and 45Ca content by about 30% in the femur but not in the whole skeleton. At this Sr level, the urinary excretion of the isotopes increased with a concomitant decrease in their excretion in the faeces. This study underscores the limitations of dietary Sr to mobilise 89Sr from the bones after it is incorporated in the bone mineral.