MODULATION OF PUTRESCINE TRANSPORT IN RAT INTESTINAL BRUSH-BORDER MEMBRANE-VESICLES BY FASTING AND REFEEDING

Fasting and refeeding dramatically alter small intestinal mucosal grow th which is greatly dependent on polyamine biosynthesis and transport. The aim of this study was therefore to examine the uptake of the diam ine putrescine by brush-border membrane vesicles from the small intest ine 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. Refeed ing 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 p eriod of fasting caused only a 13 or 17% increase, respectively, in th e value of the constant for the nonsaturable component (P) of putresci ne transport relative to the corresponding control condition. Our stud y also confirms that both the mucosal polyamine biosynthesis and intes tinal content are altered by fasting. We suggest that an increased upt ake activity may have a conservative role by preventing a substantial loss of tissue polyamines during fasting.