Effect of zinc status on salivary zinc concentrations in the rat

Three experiments were done to determine whether salivary zinc concentration is a more sensitive indicator of zinc status than plasma zinc. Weanling male rats fed a low zinc (less than 1 ppm) diet for 5 weeks with or without zinc (100 ppm) in the drinking water had salivary zinc concentration of 0.19, 0.16, and 0.20 microgram/ml for the zinc-deficient, zinc-supplemented restricted-intake, and zinc-supplemented ad libitum-fed groups, respectively. Combined values for male and female rats after 4 weeks of the same treatments in experiment 2 were 0.60, 1.2 and 0.44 microgram/ml. Saliva collected on day 22 of pregnancy contained 0.30 and 0.24 microgram/ml from zinc-supplemented and zinc-deficient rats, respectively. Salivary zinc concentrations in the deficient rats did not differ from those of the zinc-supplemented ad libitum-fed controls in any of the experiments. Salivary zinc concentration in the zinc-supplemented restricted-intake group in experiment 2 was significantly higher than that in the other two groups. Decreases in serum, bone, and fetal zinc concentrations indicated that the rats were definitely zinc-deficient. Since zinc concentration of mixed saliva in the rat was not decreased by even a severe zinc deficiency, salivary zinc does not appear to be as good an indicator of zinc status as plasma zinc.