Absorption of Ca45 and Sr85 from Solid and Liquid Food at Various Levels of the Alimentary Tract of the Rat

Abstract

The total absorption of Ca⁴⁵ and Sr⁸⁵ from a liquid dose averaged 45 and 28%, respectively; from solid dose it averaged 19 and 13%. These differences were highly significant. It was shown that solid food left the stomach more slowly than liquid food, but that the time necessary for food to start entering the cecum was the same for both liquid and solid dose. Absorption of Ca⁴⁵ and Sr⁸⁵ occurred rapidly at first, but then tapered off and essentially ceased after about two hours for the liquid dose and 6 hours for the solid dose. The ratio of absorbed Sr⁸⁵/Ca⁴⁵ per rat, averaged over time intervals of 15 minutes to 12 hours, was 0.67 ± 0.020 for rats given labeled solid food. This ratio was not found to be a significant function of time or food consistency. The total relative per cent of Sr⁸⁵ and Ca⁴⁵ absorbed in each of the gut components was estimated after absorption had ceased. For liquid dose the values were: stomach, 0%; duodenum, 15%; jejunum, 23%; ileum, 62%. For the solid dose the corresponding values were zero, 8, 4, and 88%, respectively. The ileum was responsible for the major amount of selection against strontium in favor of calcium by the intestinal tract. Evidence indicated that the relative per cent absorption of Ca⁴⁵ and Sr⁸⁵ was the same throughout the alimentary tract. It was postulated that an absorption mechanism exists throughout the entire small intestine which is more efficient for calcium than for strontium but which handles both.