425 INTESTINAL MATURATION: CALCIUM (Ca) TRANSPORT

Abstract

Our previous study suggested that the permeability of the intestinal mucosa (PIM) to Ca was greater in suckling (S) than in adolescent (A) rats (Pediat. Res. 11:414, 1977). Definitive studies comparing PIM to Ca during development are not available. We compared transport of Ca in the proximal intestine of S (2 week old), W (3 week old) and A (6 week old) rats, using an in vivo recirculation perfusion technique. The perfusates were isotonic NaCl solution containing either 0.4, 1.6 or 3.4 mmoles of CaCl2/1 and Phenol Red 20 mg/1. Ca transport rates (mean±S.E.; μmoles/hr per g. wet wt.) from the different solutions were: 0.4 mmole/1 (S, -32.3±6.5; A, -0.1±0.2; p<.001); 1.6 mmole/l (S, -14.8±2.3; A, 1.8±0.4; p<.005); 3.4 mmole/1 (S, 27.6±6.0; A, 3.3±0.9; p<.005). Transport (T) rates in W rats were intermediate between those of S and A rats (-4.5±1.6, 5.1±1.3, 19.0±1.5 respectively, from solutions containing 0.4, 1.6 or 3.4 mmole Ca/1). The 8 fold greater net absorption (+T) rate at the high, and much greater net secretion (-T) rate at the low luminal Ca concentrations in S than A rats indicated that PIM to Ca was greater in S than A rats. The reason for the age difference is not known. However, the process of maturation appears to decrease the PIM to Ca, which continues into the post-weaning age. If the age differences in Ca transport is also present in humans, young infants, especially those with low birth weight, could be at risk of losing relatively large amounts of Ca into the intestinal lumen when dietary Ca intake stops abruptly.