Idiorrhythmic zinc dose-rate induction of intestinal metallothionein in rats depends upon their nutritional zinc status

The idiorrhythmic dose-rate feeding experimental model was used to study th e induction of intestinal metallothionein (iMT) by zinc (Zn) in the gastroi ntestinal (GIT) mucosa of young growing male rats relative to their nutriti onal Zn status. The idiorrhythmic approach requires that the average dietar y Zn concentration, referred to as module (M), is kept constant across diff erent groups over the whole experimental epoch (E). This is done by adjusti ng the Zn concentration of the supplemented diet to compensate for the redu ction in the number of days on which this diet is fed, the latter being spr ead evenly over the whole experiment. Idiorrhythms (I) involve offering the diet with n times the overall Zn concentration (M) only every nth day with a Zn-deficient diet offered on other days. We studied three modules (low-Z n, M3; adequate-Zn, M12; and high-Zn, M48), each M having 8 analogous idior rhythms (I = Mx/1 to 8Mx/8); every I was fed over a 48-d idiorrhythmic E. O ver the wide range of peak doses of dietary Zn (3-384 mg Zn/kg diet), the h igher the modulo, the greater the capacity for iMT to be induced (M3 < M12 < M48; P < 0.05). Also, the ability of Zn to induce iMT increased proportio nally with the progression of the idiorrhythms from I = Mx/1 to 8Mx/8 (P < 0.001). When rats were fed M3, less Zn was required to induce iMT than when they were fed M12 or M48. Thus, within the M and E limits of this study, t he better the nutritional Zn status of the animal, the more Zn is required to induce iMT and vice versa. The fact that iMT was increased means that th e amount of available Zn was not proportional with the actual steady state of its metabolism. This indicates that for any Zn supplementation program t o be effective, it should progress gradually from a lower to a higher Zn do se relative to the given nutritional Zn status. (C) 2001 Elsevier Science I nc. All rights reserved.