Discrimination between low dietary zinc and endotoxin exposure: a model study on weaning rats

To establish a parameter for zinc status that is independent of the occurrence of infection, we studied the effects of low dietary zinc and endotoxin in weaning rats 21 d after 65Zn intubation. We monitored aspects of zinc status (tissue zinc content, 65Zn distribution, and specific 65Zn activity in tissue) and 65Zn metabolism (absorption, excretion, and biologic half-life), as well as weight gain, feed conversion, and dietary zinc use. The low zinc diet induced classical deficiency with losses of bone zinc, resulting in lower content (7.4 versus 19.6 mumol) and higher spec act (17 versus 8 kBq/mumol). Other tissue-specific and plasma-specific activities were also higher (overall, 20 versus 8 kBq/mumol; plasma, 8 versus 4 kBq/mumol). Endotoxin caused lower total-plasma zinc (0.04 versus 0.05 mumol) but did not affect spec act (4 kBq/mumol); combined endotoxin and low-zinc diet caused low total-plasma zinc (0.01 mumol) and high spec act, as did the low-zinc diet alone (12 kBq/mumol). We conclude that plasma-spec act (or stable isotope enrichment) can serve as an index for nutritional zinc status during recurrent infection.