Fission products and the dairy cow. 2. Some aspects of the metabolism of the alkaline-earth elements calcium, strontium and barium

Abstract

The isotopes Ca45 and Sr89, and Ba140, or Ca45 and Ba140 were administered simultaneously, first orally and, later, intravenously, to pairs of lactating cows. The mean recoveries of Ca45, Sr89 and Ba140, in the 8 days after oral administration, were (respectively): from feces, 71, 89 and 98%; from urine, 0.4, 1.3 and 1.1%; from milk, 16, 1.9 and 0.6% of the dose; and, in the 8 days after intravenous administration: from feces, 16, 18 and 36%; from urine, 1. 2, 21 and 34%; from milk, 32, 16 and 10% of the dose. Calculation of individual discrimination factors, by formula indicates that absorptive discrimination was a major factor in overall discrimi-nationbetween Ca, Sr and Ba during their passage from diet to milk. Mammary secretion also played a considerable part with Sr; but, with Ba, the effects of renal excretion, endogenous secretion into the gut and mammary secretion were approximately equal. The comparative behavior of Ca45, Sr89 and Ba140 in the whole body treated as a calcified tissue was examined. The rate of removal of Ca45 and Sr89 from plasma by exchange reactions was approximately the same; the rate of removal of Ba140 by this process was 80% of that of Ca45. The rates of incorporation of Sr89 and Ba140 into the non-exchangeable fraction of the whole skeleton were 91 and 61% respectively of that of Ca45. Ba140 was released from the skeleton more quickly and extensively than Ca45 or Sr39.