Homeostatic response of Zn metabolism to dietary Zn supplements from sulfate, gluconate, orotate, aspartate or histidine in ⁶⁵Zn labeled non-growing rats as a model to adult individuals

The objective of the study was the long-term reaction of Zn homeostasis on dietary Zn supplies from gluconate, orotate, aspartate and histidine under condition of a sufficient Zn supply. Method: Thirty female rats were homogenously labeled with 65Zn according to the alimentary technique with a semisynthetic diet containing Na phytate (8 g/kg) and 50 ppm Zn from ZnSO₄. At a mean body weight of 224 g the animals were allotted to 6 groups (n = 5) and were fed restrictively (7.9 g/d) for 14 days 6 diets with either unchanged composition (control) or with an extra addition of 50 ppm Zn from sulfate, gluconate, orotate, aspartate or histidine. Results: The extra additions of dietary Zn were completely compensated by increased fecal Zn excretions irrespective of the Zn source, while urinary Zn and retention of Zn remained constant among all animal groups. Absorption of dietary Zn and fecal excretion of endogenous Zn was increased in all extra Zn groups without being altered by the type of Zn source. Concentrations and amounts of Zn in various organs, tissues and whole body were affected neither by quantity nor by type of dietary Zn. The rate of Zn exchange in tissues and whole body increased due to extra Zn additions irrespective of the type of Zn source. Conclusions: Dietary Zn from sulfate, gluconate, orotate, aspartate and histidine is physiologically equivalent as soon as the metabolic requirement of Zn is met. Possible differences in bioavailability are covered completely by counter regulation of Zn homeostasis.