Regulation of Zn2+ Uptake from the Gastrointestinal Tract of a Marine Teleost, the Winter Flounder (Pseudopleuronectes americanus)

Abstract

The gastrointestinal uptake of Zn2+ was studied in winter flounder (Pseudopleuronectes americanus) using an in situ technique. The entire digestive tract was capable of absorbing Zn2+, with the uppermost portion of the intestine having the highest and the stomach the lowest capacity. A seasonal study revealed that the capacity of the digestive tract to absorb Zn2+ was greatest during the summer months. At least two steps appeared to be involved in the absorption process, the first a rapid accumulation of Zn2+ by the tissue, and the second a slower transfer into the body. The amount of Zn2+ absorbed increased with increasing loads of Zn2+ in the lumen; the transfer mechanism(s) was not saturated at the highest Zn2+ loads tested. Zn2+ uptake was inhibited in the presence of Cu2+, Cd2+, Co2+, Cr2+, Ni2+, Fe3+, Mn2+, and Hg2+. The capacity of the digestive tract to absorb Zn2+ was not affected by feeding the flounder a high-Zn2+ diet or by increasing body Zn2+ loads by intravenous injections. It is suggested that elimination mechanisms may play a greater role in maintaining Zn2+ homeostasis than controlling gastrointestinal uptake.