Hymenolepis diminuta: Absorption of nicotinamide

Abstract

The uptake of 14C-nicotinamide was linear over the concentration range of 0.025 to 20 m M ( Y = 58.1[ x] + 0.8; r > 0.99), and the uptake of 0.05 m M 14 C-nicotinamide was not inhibited by unlabeled nicotinamide at concentrations as high as 10 m M (200:1 inhibitor/substrate ratio). Absorption appeared to occur by diffusion only. The uptake of 0.1 m M 14 C-nicotinamide was not linear with respect to time, again indicating a nonmediated mechanism of absorption. Analyses of worm extracts and incubation media after 30 min incubations demonstrated that all the radioactivity remained as labeled nicotinamide. Worms removed from rats which had received intraperitoneal injections of 14C-nicotinamide were found to contain radioactivity. On the basis of comparison of chromatograms of worm extracts with chromatograms of standard nicotinamide derivatives, this radioactivity was present as nicotinamide, nicotinic acid, and two unidentified compounds which did not correspond to nicotinuric acid, 1-methyl nicotinamide, or the reduced forms of nicotinamide adenine dinucleotide or trinucleotide.