Modulation of putrescine transport in rat intestinal brush-border membrane vesicles by fasting and refeeding

Fasting and refeeding dramatically alter small intestinal mucosal growth which is greatly dependent on polyamine biosynthesis and transport. The aim of this study was therefore to examine the uptake of the diamine putrescine by brush-border membrane vesicles from the small intestine of rats fasted for 3 days or refed a standard diet after a period of fasting. While the Michaelis-Menten constant (K-m) was essentially unaltered, the maximum velocity (V-max) for putrescine uptake was 1.85-fold higher in fasted animals than in ad libitum-fed controls. Refeeding fasted rats for 24 h caused a 31% decrease in the V-max value that, however, remained 1.27-fold higher than in control rats, while the K-m value was still unchanged. Fasting rats or refeeding rats after a period of fasting caused only a 13 or 17% increase, respectively, in the value of the constant for the nonsaturable component (P) of putrescine transport relative to the corresponding control condition. Our study also confirms that both the mucosal polyamine biosynthesis and intestinal content are altered by fasting. We suggest that an increased uptake activity may have a conservative role by preventing a substantial loss of tissue polyamines during fasting.