COMPARATIVE ABSORPTION OF GLUCOSE (G) AND LACTOSE(L) IN PREMATURES ASSESSED WITH ¹³C-SUBSTRATES

Abstract

Postmortem intestinal lactase assay & postnatal breath H₂ studies suggest suboptimal lactose absorption until 38+ wks postconception. G and L absorption were compared directly using ¹³C substrates. 18 paired studies were done in 6 infants (gest age 28-34wk, age 11-60d, wt 770-2050g, intake 94-161 kcal/kg/d.) Breath ¹³CO₂ above baseline by interval samples during 8 hr after ¹³C-1-L or ¹³C-I-G had been added to 8 am feeding was determined by isotope ratio MS, as was ¹³C(non- and dialyzable)in 24hr stool collections. ¹³C was recovered in breath by 0.5hr in only 18% of studies with G, 21% with L. Peak respiratory ¹³CO₂ excretion occurred at 2-4 hr with both G&L. Cummulative %dose ¹³C(Cum%d) was unexpectedly greater with L than G at 5,6,7,8 hrs pc,the opposite of that found with full terms. (P<0.05-0.001, x̄8hr Cum%d; G=41±14% L=51±10%, assuming CO₂ production rate 300mM/M²/hr). Despite this, L was excreted in stool more frequently than G (89%vs56% of studies, X²=4.98) & in greater amount (x̄:G 3.3% of dose, L 6.1%). The apparent % dose oxidized per % dose absorbed was 22% greater after L than G. In 3 studies multiple breath ¹³CO₂ peaks followed breath H₂ peaks. The small premature assimilates L more rapidly than G. Paradox of increased ¹³C in breath and stool and altered apparent oxidation of L suggest different routes of absorption of G and L and implicate colonic bacteria in L assimilation. NIH HD 10111, HD 18188, AM 28129, USDA/ARS.

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