Comparison of kinetic constants of hexose uptake in four animal species and man.

1. The rate of in vitro uptake of glucose (gl), galactose (gal), 3-O-methyl glucose (MG), and fructose (fr) was determined using jejunal discs of hamster (ham), rat, rabbit (rab) and guinea pig (gp). 2. The maximal transport rates (Jdm) of each hexose were ham greater than rab greater than gp = rat; 3. The Michaelis constants were different for the four sugars; for gl the values were gp greater than rat greater than ham greater than rab. 4. The passive permeability coefficients (Pd) were similar for each sugar, and were greatest in ham and rat, and lowest in rat and gp. 5. The effective resistance of the intestinal unstirred water layer was lowest in ham and highest in gp and rat. 6. There were differences in the kinetic constants for gl estimated using discs and biopsies of jejunum, and the greater uptake into human biopsies than in the other species was due to the higher Jdm and Pd.