We recently demonstrated that the ratio between colonic K+ absorptive and K+ secretive pathways was higher in infant than in adult rats. To test the hypothesis that hormones selectively affect these pathways during ontogeny we examined the effect of adrenergic agonists on cellular K+ uptake in distal colon from infant (10-day-old) and adult (50-day-old) rats. Here we describe that adrenaline (10−5 M) increased total and ouabain-insensitive 86Rb uptake in both age groups, but it did not affect ouabain-sensitive 86Rb uptake. This stimulation was more pronounced in adult than in infant rats. The effect of adrenaline was mediated via β-adrenergic receptors. Incubation in vitro with β-agonist, isoproterenol, stimulated SCH-28080-sensitive, i.e. H+, K+-ATPase-dependent, 86Rb uptake in adult but not in infant rats. The threshold dose of β-agonist was at 10−7 M, and the maximal activation was observed at 10−5 M. In vivo inhibition of β-adrenergic system with propranolol caused a significant decrease in H+, K+-ATPase-dependent 86Rb uptake in infant but not in adult colon. In conclusion, this study suggests that the higher colonic K+ absorption in infant rats may be as a result of a selective β-adrenergic up-regulation leading to stimulation of the apical H+, K+-ATPase.