Effects of strontium on the absorption of calcium, magnesium and phosphateions from the ovine reticulo-rumen

The net absorption rates of strontium ions from the ovine reticulo-rumen, i solated in situ in trained conscious animals, were measured under controlle d conditions. A linear positive response was obtained from the addition of Sr2+ ions to the artificial rumen fluid. This increase in the absorption of Sr was reflected in an increase in the plasma Sr concentration. In contras t to the discrimination observed elsewhere in favour of the absorption of C a relative to Sr, the absorption rate of Sr from the reticulo-rumen was sig nificantly greater than that of Ca, from solutions containing the same mola r concentration. A graded increase in the Sr concentration in the ruminal f luid from 1 mmol/l to 4 mmol/l led to a corresponding reduction in the abso rption rate of Ca but an increase in that of phosphate. The latter result i s similar to that observed when the intra-ruminal concentration of Ca2+ ion s is increased. It is suggested that Ca and Sr share a common pathway for a bsorption from the reticulo-rumen and that this may involve coupling with t he absorption of phosphate ions.